U.S. patent number 3,737,986 [Application Number 05/202,348] was granted by the patent office on 1973-06-12 for explosive bonding of workpieces.
This patent grant is currently assigned to Western Electric Company, Incorporated. Invention is credited to Benjamin Howell Cranston.
United States Patent |
3,737,986 |
Cranston |
June 12, 1973 |
EXPLOSIVE BONDING OF WORKPIECES
Abstract
First workpieces, for example, beam-leaded integrated circuits,
and the like, are bonded to second workpieces, for example,
metallized ceramic substrates by first depositing a quantity of
primary explosive, such as lead azide, onto each beam lead and then
detonating the explosive to explosively bond the integrated
circuits to the substrate. In another embodiment of the invention,
the explosive bonding force is applied through a buffer sheet of
plastic or metallic material which protects the surface of the
substrate from contamination and which, in addition, dampens the
shock of the explosion. In yet another embodiment of the invention,
metal conductive paths are explosively bonded directly to a ceramic
or glass substrate to form a "printed circuit pattern." The same
techniques are used to manufacture resistors, capacitors,
inductors, etc.
Inventors: |
Cranston; Benjamin Howell
(Trenton, NJ) |
Assignee: |
Western Electric Company,
Incorporated (New York, NY)
|
Family
ID: |
22749507 |
Appl.
No.: |
05/202,348 |
Filed: |
November 26, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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68431 |
Aug 31, 1970 |
|
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|
|
6829 |
Jan 29, 1970 |
|
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Current U.S.
Class: |
228/106;
219/121.14; 438/125; 219/121.64; 29/840; 29/827; 228/107; 257/735;
228/180.21 |
Current CPC
Class: |
B23K
20/08 (20130101); H05K 3/328 (20130101); H01L
24/80 (20130101); H05K 3/38 (20130101); H01L
21/67144 (20130101); H01L 2924/00 (20130101); H01L
2924/00 (20130101); H01L 2924/00 (20130101); H01L
2224/48 (20130101); H01L 2924/00 (20130101); H01L
2924/00 (20130101); H01L 2224/45124 (20130101); H01L
2924/351 (20130101); H05K 3/202 (20130101); H01L
2924/01047 (20130101); H01L 2924/19043 (20130101); H05K
2203/0271 (20130101); H01L 2924/19041 (20130101); H01L
2924/12042 (20130101); H01L 2224/45144 (20130101); H01L
2924/01033 (20130101); H01L 2924/01006 (20130101); H01L
2924/12042 (20130101); H01L 2924/19042 (20130101); H05K
1/0306 (20130101); Y10T 29/49144 (20150115); H05K
2201/10628 (20130101); H01L 2224/45144 (20130101); H01L
2924/01032 (20130101); H01L 2924/14 (20130101); H01L
2924/15787 (20130101); H01L 2924/01014 (20130101); H01L
2924/01056 (20130101); H01L 2924/01079 (20130101); H01L
2924/15787 (20130101); H01L 2224/45124 (20130101); H01L
2924/00014 (20130101); H01L 2924/00014 (20130101); H01L
2924/09701 (20130101); Y10T 29/49121 (20150115); H01L
2924/01082 (20130101); H01L 2924/01075 (20130101); H01L
2924/01013 (20130101); H01L 2924/01078 (20130101); H01L
2924/01012 (20130101); H01L 2924/01029 (20130101); H01L
2924/351 (20130101); H01L 2924/01005 (20130101) |
Current International
Class: |
H01L
21/00 (20060101); H01L 21/607 (20060101); H01L
21/02 (20060101); B23K 20/08 (20060101); B23K
20/06 (20060101); H05K 3/32 (20060101); H05K
3/38 (20060101); H05K 3/20 (20060101); H05K
1/03 (20060101); B01j 017/00 (); H01l 007/02 ();
H01l 007/16 () |
Field of
Search: |
;29/421E,470.1,471.1,486,497.5,589,628 ;117/201,212
;102/70.2,28 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Overholser; J. Spencer
Assistant Examiner: Shore; Ronald J.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a division, of application Ser. No. 68,431 filed Aug. 31,
1970, which is a continuation-in-part of my application, Ser. No.
6829, filed Jan. 29, 1970 which is related to the EXPLOSIVE BONDING
OF BEAM LEAD-LIKE DEVICES.
Claims
What is claimed is:
1. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a frangible workpiece,
comprising the steps of:
placing a charge of primary explosive material proximate each of
the microleads to be bonded, in a position to accelerate the
microlead towards the corresponding region of said workpiece;
and
detonating said primary explosive material to explosively bond said
microleads to the corresponding regions of said workpiece, the
magnitude of each charge of said primary explosive material being
sufficiently large to form said explosive bond but not so great as
to cause deleterious damage to said workpiece or said device.
2. The method according to claim 1 wherein said detonating step
comprises:
raising the temperature of said explosive material above the
critical detonation temperature thereof.
3. The method according to claim 1 wherein said explosive material
is photosensitive and said detonating step comprises:
applying a beam of light to said photosensitive material of a
wavelength and an intensity sufficient to induce explosion
thereof.
4. The method according to claim 1 wherein said detonating step
comprises:
applying a beam of .alpha. particles to said explosive material of
an intensity sufficient to induce explosion thereof.
5. The method according to claim 1 wherein said detonating step
comprises:
passing an electrical discharge through said explosive material of
an intensity sufficient to induce explosion thereof.
6. The method according to claim 1 wherein said detonating step
comprises:
directing an electron beam onto said explosive material of an
intensity sufficient to induce explosion thereof.
7. The method according to claim 1 wherein said detonating step
comprises:
applying a beam of collimated, coherent radiation from an optical
maser to said explosive material, said radiation being of a
wavelength and an intensity sufficient to induce explosion
thereof.
8. The method according to claim 1 wherein said detonating step
comprises:
applying a mechanical force to said explosive material of an
intensity sufficient to induce explosion thereof.
9. The method according to claim 1 wherein said detonating step
comprises:
applying a shock wave to said explosive material of an intensity
sufficient to induce explosion thereof.
10. The method according to claim 1 wherein said detonating step
comprises:
applying a beam of acoustical energy to said explosive material of
a wavelength and an intensity sufficient to induce explosion
thereof.
11. The method according to claim 1 wherein said detonating step
comprises:
applying an alternating magnetic field to said explosive material
of a frequency and an intensity sufficient to induce explosion
thereof.
12. The method according to claim 1 wherein said detonating step
comprises:
applying an alternating electric field to said explosive material
of a frequency and an intensity sufficient to induce explosion
thereof.
13. The method according to claim 1 wherein said detonating step
comprises:
introducing a chemical atmosphere to react with said explosive
material and initiate explosion thereof.
14. The method according to claim 1 wherein an inhibitory chemical
atmosphere is maintained about said beam lead-like device and said
detonating step comprises:
removing said inhibitory chemical atmosphere to initiate explosion
of said explosive material.
15. The method according to claim 1 wherein said explosive material
is a primary explosive and said placing step comprises:
applying to at least one surface of each of the micro-leads to be
bonded a mass of primary explosive which exceeds the critical mass
of said primary explosive.
16. The method according to claim 1 comprising the further step
of:
maintaining a partial vacuum about said beam lead-like device and
said workpiece, prior to the detonation of said explosive
material.
17. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, said
microleads each having a quantity of primary explosive material
deposited thereon sufficient to create an explosive bond between
each of said microleads and its respective predetermined region but
insufficient to deleteriously damage said beam lead-like device or
said workpiece, comprising the steps of:
orienting said beam lead-like device with respect to said
workpiece, thereby to place said microleads adjacent their
respective predetermined regions on the workpiece; and
detonating said explosive material to explosively bond said
microleads to said respective predetermined regions on the
workpiece.
18. The method according to claim 17 wherein said detonating step
comprises:
raising the temperature of said explosive material above the
critical detonation temperature thereof.
19. The method according to claim 17 wherein said explosive
material is photosensitive and said detonating step comprises:
applying a beam of light to said photosensitive material of a
wavelength and an intensity sufficient to induce explosion
thereof.
20. The method according to claim 17 wherein said detonating step
comprises:
applying a beam of .alpha. particles to said explosive material of
an intensity sufficient to induce explosion thereof.
21. The method according to claim 17 wherein said detonating step
comprises:
passing an electrical discharge through said explosive material of
an intensity sufficient to induce explos1on thereof.
22. The method according to claim 17 wherein said detonating step
comprises:
directing an electron beam onto said explosive material of an
intensity sufficient to induce explosion thereof.
23. The method according to claim 17 wherein said detonating step
comprises:
applying a beam of collimated, coherent radiation from an optical
maser to said explosive material, said radiation being of a
wavelength and an intensity sufficient to induce explosion
thereof.
24. The method according to claim 17 wherein said detonating step
comprises:
applying a mechanical force to said explosive material of an
intensity sufficient to induce explosion thereof.
25. The method according to claim 17 wherein said detonating step
comprises:
applying a shock wave to said explosive material of an intensity
sufficient to induce explosion thereof.
26. The method according to claim 17 wherein said detonating step
comprises:
applying a beam of acoustical energy to said explosive material of
a wavelength and an intensity sufficient to induce explosion
thereof.
27. The method according to claim 17 wherein said detonating step
comprises:
applying an alternating magnetic field to said explosive material
of a frequency and an intensity sufficient to induce explosion
thereof.
28. The method according to claim 17 wherein said detonating step
comprises:
applying an alternating electric field to said explosive material
of a frequency and an intensity sufficient to induce explosion
thereof.
29. The method according to claim 17 wherein said detonating step
comprises:
introducing a chemical atmosphere to react with said explosive
material and initiate explosion thereof.
30. The method according to claim 17 wherein an inhibitory chemical
atmosphere is maintained about said beam lead-like device and said
detonating step comprises:
removing said inhibitory chemical atmosphere to initiate explosion
of said explosive material.
31. The method according to claim 17 comprising the further step
of:
maintaining a partial vacuum about said at least one beam lead-like
device and said workpiece prior to detonation of said explosive
material.
32. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said at least one beam lead-like device with respect to
said substrate;
applying an apertured buffer member over said aligned beam
lead-like device, said buffer member having a plurality of
explosive charges deposited on the upper surface thereof
corresponding in location to the microleads of said beam lead-like
device;
registering said buffer member with respect to said beam lead-like
device so that said plurality of explosive charges are positioned
over said microleads; and
detonating said explosive charges to apply an explosive bonding
force through the buffer member to said microleads to bond said
microleads to the corresponding regions of said workpiece.
33. The method according to claim 32 wherein said buffer member is
transparent and said registering step comprises:
optically aligning said explosive charges with respect to said
microleads through the transparent buffer member.
34. The method according to claim 32 wherein said detonating step
comprises:
raising the temperature of said explosive material above the
critical detonation temperature thereof.
35. The method according to claim 32 wherein said explosive
material is photosensitive and said detonating step comprises:
applying a beam of light to said photosensitive material of a
wavelength and an intensity sufficient to induce explosion
thereof.
36. The method according to claim 32 wherein said detonating step
comprises:
applying a beam of .alpha. particles to said explosive material of
an intensity sufficient to induce explosion thereof.
37. The method according to claim 32 wherein said detonating step
comprises:
passing an electrical discharge through said explosive material of
an intensity sufficient to induce explosion thereof.
38. The method according to claim 32 wherein said detonating step
comprises:
directing an electron beam onto said explosive material of an
intensity sufficient to induce explosion thereof.
39. The method according to claim 32 wherein said detonating step
comprises:
applying a beam of collimated, coherent radiation from an optical
maser to said explosive material, said radiation being of a
wavelength and an intensity sufficient to induce explosion
thereof.
40. The method according to claim 32 wherein said detonating step
comprises:
applying a mechanical force to said explosive material of an
intensity sufficient to induce explosion thereof.
41. The method according to claim 32 wherein said detonating step
comprises:
applying a shock wave to said explosive material of an intensity
sufficient to induce explosion thereof.
42. The method according to claim 32 wherein said detonating step
comprises:
applying a beam of acoustical energy to said explosive material of
a wavelength and an intensity sufficient to induce explosion
thereof.
43. The method according to claim 32 wherein said detonating step
comprises:
applying an alternating magnetic field to said explosive material
of a frequency and an intensity sufficient to induce explosion
thereof.
44. The method according to claim 32 wherein said detonating step
comprises:
applying an alternating electric field to said explosive material
of a frequency and an intensity sufficient to induce explosion
thereof.
45. The method according to claim 32 wherein said detonating step
comprises:
introducing a chemical atmosphere to react with said explosive
material and initiate explosion thereof.
46. The method according to claim 32 wherein an inhibitory chemical
atmosphere is maintained about said beam lead-like device and said
detonating step comprises:
removing said inhibitory chemical atmosphere to initiate explosion
of said explosive material.
47. The method according to claim 32 comprising the further step
of:
maintaining a partial vacuum about said at least one beam lead-like
device and said workpiece, prior to the detonation of said
explosive charges.
48. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, said
microleads each having a quantity of photosensitive primary
explosive material deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
placing said workpiece with the oriented beam lead-like device
thereon within a chamber having at least one transparent
portion,
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion, and
applying light energy from at least one light source to said
microleads through said at least one transparent portion of the
chamber to detonate said photosensitive primary explosive material
and bond said microleads to said respective predetermined
regions.
49. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, said
microleads each having a quantity of photosensitive primary
explosive material deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
positioning said workpiece with said oriented device thereon
proximate the exit port of an optical maser,
energizing said optical maser to produce a beam of light, and
passing said beam of light through a beam expander so that it
impinges upon said microleads and detonates said photosensitive
primary explosive material to explosively bond said microleads to
the respective predetermined regions of said workpiece.
50. The method according to claim 49 comprising the further steps
of, prior to said energizing step:
placing said workpiece with said oriented device thereon within a
chamber having at least one transparent portion,
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion, and then
directing said expanded beam of light through said transparent
portion of the chamber to impinge upon said microleads.
51. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said workpieces having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
positioning said workpiece with said oriented device thereon
proximate the focus of at least one focused radiant energy lamp,
and
energizing said lamp to apply focused radiant energy to said
microleads to detonate said primary explosive material and
explosively bond said microleads to the respective predetermined
regions of said workpiece.
52. The method according to claim 51 comprising the further steps
of, prior to said energizing step:
placing said workpiece with said oriented device thereon within a
chamber having at least one transparent portion,
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion, and
directing the focused radiant energy from said at least one lamp
through said transparent portion of the chamber to impinge upon
said microleads.
53. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
placing said workpiece with the oriented device thereon upon a
thermally conducting susceptor, and
heating said susceptor to raise the temperature of said primary
explosive material above the critical detonation temperature
thereof to explosively bond said microleads to the respective
predetermined regions of said workpiece.
54. The method according to claim 53 comprising the further steps
of, prior to said heating step:
positioning said susceptor with the workpiece and oriented device
thereon within a chamber, and
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion.
55. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads thereof are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
placing said workpiece with said oriented device thereon within the
coils of a radio frequency induction heater, and
passing a radio frequency current through said coils to raise the
temperature of said explosive material above the critical
detonation temperature thereof to explosively bond said microleads
to the respective predetermined regions of said workpiece.
56. The method according to claim 55 comprising the further step
of, prior to said passing step:
creating a partial vacuum about said workpiece and said oriented
device to exhaust unwanted by-products of the explosion.
57. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
placing said workpiece with said oriented device thereon between
the plates of a radio frequency dielectric heater, and
applying a radio frequency potential to the plates of said
dielectric heater to raise the temperature of said explosive
material above the critical detonation temperature thereof to
explosively bond said microleads to the respective predetermined
regions of said workpiece.
58. The method according to claim 57 comprising the further step
of, prior to said applying step: creating a partial vacuum about
said workpiece and said oriented device to exhaust unwanted
by-products of the explosion.
59. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said beam lead-like device with respect to said workpiece
so that said microleads are positioned over the respective
predetermined regions of the workpiece to which they are to be
bonded,
positioning said workpiece and the oriented device thereon
proximate the exit port of an ultrasonic horn, and
applying ultrasonic energy to the input port of said horn to apply
ultrasonic energy to said microleads to detonate said explosive
material and explosively bond said microleads to the respective
predetermined regions of said workpiece.
60. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said device with respect to said workpiece so that said
microleads are positioned over the respective predetermined regions
of the workpiece to which they are to be bonded,
positioning a compliant member over said workpiece and said
oriented device, and
applying mechanical force through said compliant member to said
microleads to detonate said explosive material and explosively bond
said microleads to the respective predetermined regions of said
workpiece.
61. The method according to claim 60 comprising the further step
of, prior to said applying step:
creating a partial vacuum about said workpiece and said oriented
device to exhaust unwanted by-products of said explosion.
62. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said device with respect to said workpiece so that said
microleads are positioned over the respective predetermined regions
of the workpiece to which they are to be bonded,
contacting at least one land area of said workpiece with a first
electrical contact,
contacting the explosive material on at least one microlead of said
device with a second electrical contact, and
applying an electrical potential to said first and second
electrical contacts to create an electrical discharge through said
explosive material to detonate said explosive material and
explosively bond said at least one microlead to the respective
predetermined region of said workpiece.
63. The method according to claim 62 comprising the further step
of, prior to said applying step:
creating a partial vacuum about said workpiece and said oriented
device to exhaust unwanted by-products of the explosion.
64. A method of bonding microleads of a beam lead-like device to
respective predetermined regions of a frangible workpiece, each of
said microleads having a quantity of primary explosive material
deposited thereon, comprising the steps of:
orienting said device with respect to said workpiece so that said
microleads are positioned over the respective predetermined regions
of the workpiece to which they are to be bonded,
placing said workpiece and said oriented device within the vacuum
chamber of an electron beam machine,
exhausting said vacuum chamber,
energizing the gun of said electron beam machine to produce a beam
of electrons, and
deflecting said electron beam to impinge upon all of said
microleads to detonate the explosive material thereon and
explosively bond said microleads to the respective predetermined
regions of said workpiece.
65. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
placing said buffer medium, workpiece, and aligned device within a
chamber having at least one transparent portion;
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion; and
applying light energy from at least one light source to the upper
surface of said buffer medium through said at least one transparent
portion of the chamber to detonate said photosensitive explosive
material and bond said microleads to said corresponding
regions.
66. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
positioning said workpiece with said aligned device and said buffer
medium thereon proximate the exit port of an optical maser;
energizing said optical maser to produce a beam of light; and
passing said beam of light through a beam expander so that it
impinges upon the upper surface of said buffer medium and detonates
said photosensitive explosive charges to explosively bond said
microleads to the corresponding regions of said workpiece.
67. The method according to claim 66, comprising the further steps
of, prior to said energizing step:
placing said workpiece with said aligned device and said buffer
medium thereon within a chamber having at least one transparent
portion,
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion, and then
directing said expanded beam of light through said transparent
portion of the chamber to impinge upon said buffer medium.
68. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
positioning said workpiece with said aligned device and said buffer
medium thereon proximate the focus of at least one focused radiant
energy lamp; and
energizing said lamp to apply focused radiant energy to said buffer
medium to detonate said explosive charges and explosively bond said
microleads to the corresponding regions of said workpiece.
69. The method according to claim 68, comprising the further steps
of, prior to said energizing step:
placing said workpiece with said aligned device and said buffer
medium thereon within a chamber having at least one transparent
portion,
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion, and
directing the focused radiant energy from said at least one lamp
through said transparent portion of the chamber to impinge upon
said buffer medium.
70. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
placing said workpiece with the aligned device and said buffer
medium thereon upon a thermally conducting susceptor; and
heating said susceptor to raise the temperature of said explosive
charges above the critical detonation temperature thereof to
explosively bond said microleads to the corresponding regions of
said workpiece.
71. The method according to claim 70, comprising the further steps
of, prior to said heating step:
positioning said susceptor with the workpiece, aligned device, and
buffer medium thereon within a chamber; and
creating a partial vacuum within said chamber to exhaust unwanted
by-products of the explosion.
72. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
placing said workpiece with said aligned device and said buffer
medium thereon within the coils of a radio frequency induction
heater; and
passing a radio frequency current through said coils to raise the
temperature of said explosive charges above the critical detonation
temperature thereof to explosively bond said microleads to the
corresponding regions of said workpiece.
73. The method according to claim 72, comprising the further step
of, prior to said passing step:
creating a partial vacuum about said workpiece, said aligned
device, and said buffer medium to exhaust unwanted by-products of
the explosion.
74. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
placing said workpiece with said aligned device and said buffer
medium thereon between the plates of a radio frequency dielectric
heater; and
applying a radio frequency potential to the plates of said
dielectric heater to raise the temperature of said explosive
charges above the critical detonation temperature thereof to
explosively bond said microleads to the corresponding regions of
said workpiece.
75. The method according to claim 74, comprising the further step
of, prior to said applying step:
creating a partial vacuum about said workpiece, said aligned
device, and said buffer medium to exhaust unwanted by-products of
the explosion.
76. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
positioning said workpiece with said aligned device and buffer
medium thereon proximate the exit port of an ultrasonic horn;
and
applying ultrasonic energy to the input port of said horn to apply
ultrasonic energy to said buffer medium to detonate said explosive
charges and explosively bond said microleads to the corresponding
regions of said workpiece.
77. A method of bonding the microleads of at least one beam
lead-like device to corresponding regions of a workpiece,
comprising the steps of:
aligning said device with respect to said workpiece so that the
microleads thereof are positioned over the corresponding regions of
the workpiece to which they are to be bonded;
placing a buffer medium over said aligned device and said
workpiece, said buffer medium having a plurality of photosensitive
explosive charges deposited on the upper surface thereof;
aligning said buffer medium with respect to said at least one
device so that said plurality of explosive charges substantially
overlay said microleads;
placing said workpiece, said aligned device, and said buffer medium
within the vacuum chamber of an electron beam machine;
exhausting said vacuum chamber;
energizing the gun of said electron beam machine to produce a beam
of electrons; and
deflecting said electron beam to impinge upon said buffer medium to
detonate said explosive charges and explosively bond said
microleads to the correspondng regions of said workpiece.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Broadly speaking, this invention relates to explosive bonding. More
particularly, in a preferred embodiment, this invention relates to
a method of explosively bonding a first workpiece to a second
workpiece.
2. Description of the Prior Art
In the manufacture of electronic circuitry, the use of discrete
electrical components, such as resistors, capacitors, and
transistors, is rapidly becoming obsolete. These discrete
components are largely being supplanted by the integrated circuit,
a small chip of silicon which, by a series of selected masking,
etching, and processing steps, can be made to perform all of the
functions which may be performed by discrete components when these
discrete components are suitably interconnected by conventional or
printed wiring to form an operating circuit.
Integrated circuit devices are very small, the dimensions of a
typical device being approximately 0.035 inch .times. 0.035 inch.
While these microscopic dimensions permit a heretofore undreamed of
degree of miniaturization, there are other reasons why these
devices are made as small as they are, one reason being that the
microscopic dimensions significantly improve the operating
characteristics of circuits which are fabricated on IC devices. For
example, the switching speed of gating circuits and the bandwidth
of I.F. amplifiers, are significantly improved by this
miniaturization.
Of course, an integrated circuit cannot operate in vacuo, and must
be interconnected to other integrated circuits and to the outside
world, for example, to power supplies, input/output devices, and
the like. Here, however, the microscopic dimensions are a distinct
disadvantage.
Because of improved manufacturing techinques and increased yield,
the cost of integrated circuits has dropped drastically in the last
decade and now, in many instances, the cost of interconnecting an
integrated circuit to another integrated circuit or to the outside
world exceeds the cost of the device itself, a most undesirable
situation.
In one prior art method of interconnecting integrated circuit
devices, each device is bonded to the header of a multiterminal,
transistor-like base. Fine gold wires are then hand bonded, one at
a time, from the terminal portions of the integrated circuit to
corresponding terminal pins on the transistor-like base, which
pins, of course, extend up through the header for this purpose, in
a well-known manner. Interconnection of the device to other devices
or to the outside world is then made by plugging the base, with the
integrated circuit device attached thereto, into a conventional
transistor-like socket which is wired to other similar sockets, or
to discrete components, by conventional wiring or by printed
circuitry.
Because of the extremely small size of IC devices, and the
attendant alignment problems, attempts to automate this
uneconomical hand-bonding process have not proved to be successful.
Further, apart from the economics, the use of plug-in integrated
circuit devices vitiates many of the highly desirable properties
possessed by such devices, for example, the compactness which may
be realized and the improved circuit performance which they are
capable of yielding.
For these reasons, circuit designers generally prefer to connect
integrated circuits directly to an insulating substrate, such as
glass or ceramic, upon which a suitable pattern of metallic, for
example, aluminum or gold, conductor paths has been laid down.
Unfortunately, most existing techniques for laying down metallic
conductor paths on glass or ceramic are expensive and time
consuming. Examples of these existing techniques include sputtering
or vacuum depositing a thin metallic film on the substrate followed
by the application of a photoresist over the metallic film so
deposited. Next, the photoresist is exposed, through an appropriate
mark, and developed and the metal film selectively etched away to
leave the desired metallic pattern on the substrate. Finally, the
metallic pattern is built up to the desired thickness by the
electrolytic or electroless deposition technique in which
additional metal is deposited onto the existing metallic pattern.
An alternate technique, known in the art, for depositing conductive
metallic paths on a substrate involves screening a granular
suspension of metal particles in a suitable vehicle, such as ethyl
cellulose, onto the substrate, in the desired pattern, and then
firing the substrate to bind and diffuse the metal granules in the
surface of the substrate to thereby create the desired pattern of
conductive paths on the substrate. Because of the large number of
steps involved, it will be self evident that these prior art
techniques are expensive and time consuming.
Returning now to the problems of bonding the devices themselves,
the above-described hand-bonding technique for integrated circuit
devices may, of course, be used to connect an integrated circuit
device to the terminal land areas of a printed conductor pattern.
However, techniques which more readily lend themselves to
automation have also been developed.
U.S. Pat. No. 3,425,252, for example, which, issued to M. J.
Lepselter on Feb. 4, 1969, describes a semiconductor device
including a plurality of beam-lead conductors cantilevered outward
from the device. To bond such a beam-leaded device to a substrate,
the device is first aligned with respect to the terminal land areas
of the substrate and then heat and pressure are applied to each of
the beam leads, by means of a suitably shaped bonding tool, to
simultaneously and automatically bond the beam leads to the
substrate.
Another bonding technique which may be used with beam-lead devices
is the compliant bonding technique described in U.S. Pat.
application, Ser. No. 651,411 of A. Coucoulas which was filed on
July 6, 1967, now U.S. Pat. No. 3,533,155. This application
describes a bonding technique wherein heat and pressure are applied
by a bonding tool to the beam leads through a compliant medium,
such as a sheet of 2024 aluminum. The heat and pressure which is
applied causes the aluminum sheet to flow plastically and to
transmit the bonding pressure to the beam leads, thereby bonding
the beam leads to the substrate.
The above-described techniques successfully permit the simultaneous
bonding of all the beam leads of a single device, and, of course,
are equally well suited for large area bonding, that is to say, the
case where it is desired to simultaneously bond a plurality of
beam-leaded devices to a single substrate. However, it is somewhat
difficult to align a massive, multi-apertured bonding tool (or a
plurality of closely spaced, individual bonding tools) with respect
to the integrated circuit devices to be bonded. Yet another problem
in large area bonding is that, while it is possible to closely
control the dimensions of a given IC device and its alignment with
respect to a given set of land areas on a substrate, it is very
difficult to control the spacing between this set of land areas and
another set of land areas at, say, the other end of the substrate.
Since there is thus some uncertainty as to the exact location where
each integrated circuit device will be found on the substrate, the
use of a massive multi-apertured bonding tool (or a plurality of
individual bonding tools) becomes difficult because of the
variation in device-to-device spacing from one substrate to
another.
Another reason why alternative techniques are desirable for use in
large area bonding applications is the fact that it is not possible
to manufacture large substrates which are substantially flat over
the entire surface area of the substrate. There thus exists a
substantial degree of nonparallelism between the substrate (and
hence the IC devices to be bonded) and the bonding tool (or tools).
This lack of parallelism may result in bonding pressures being
applied to some IC devices which are far in excess of the maximum
permitted pressure, resulting in damage to, or the complete
destruction of, the affected devices. Similarly, the lack of
parallelism may cause bonding pressures to be applied to other IC
devices which are far below the minimum pressures required for
satisfactory bonding, resulting in weak or non-existent bonds
between the devices and the substrate.
Broadly speaking then, the problem is to find an improved method of
bonding a first workpiece to a second workpiece. In particular, an
important aspect of this problem is to find a method of
simultaneously bonding the microleads of a plurality of integrated
circuit devices to the corresponding land areas of a substrate,
after the devices have been aligned with respect to the substrate,
without using a bonding tool which must itself be aligned with
respect to the devices and/or the substrate or which must be
provided with a complicated compensating mechanism to compensate
for lack of parallelism between the substrate and the bonding
tool.
A second important aspect of this problem is to find a method of
forming metallic conductive paths or regions on an insulating
substrate, particularly a large area substrate, without subjecting
the substrate to numerous expensive and time-consuming processing
steps.
I have discovered that explosive bonding provides a highly
satisfactory solution to the above-described problems. The use of
high explosives for metal-working purposes dates, of course, from
the turn of the century; however, serious research into this
subject matter was not begun until the late forties and early
fifties. Initially, research was concentrated on the use of high
explosives to shape massive workpieces which could not be
conveniently or economically worked by any other technique. More
recently, however, research has been concentrated on explosive
welding; the aircraft and aerospace industries, in particular,
being extremely active in this area, as explosive welding is highly
attractive to these industries because of the exotic nature of the
metals and alloys employed therein.
Explosive metal cladding has also proved extremely successful and
is used, for example, to produce the blank cupro-nickel/copper
stock used by the Government to mint U.S. currency.
When compared to the dimensions of typical substrates and
electronic components, the workpieces which are welded or clad by
prior art explosive techniques are truly massive. For example, a
typical prior art application might be to explosively clad a layer
of 14 guage titanium to the surface of a cylindrical pressure
vessel, 15 feet in diameter by 30 feet long, and which is
fabricated from 4 inch thick steel. As another example of the
massive workpieces handled by the prior art, in the previously
discussed explosive cladding of cupro-nickel/copper stock, a 10
foot by 20 foot sheet of cupro-nickel, 9/10ths of an inch thick, is
explosively clad to a correspondingly dimensioned sheet of copper,
33/4 inches thick, which in turn is explosively clad to a second
9/10ths inch thick sheet of cupro-nickel, to form the finished
product.
By way of contrast, the miniature workpieces which are explosively
bonded according to the methods of my invention are several
magnitudes of order smaller. For example, a typical integrated
circuit device may measure only 0.035 inch by 0.035 inch and the 16
or more beam leads to be bonded to the substrate are cantilevered
outward from the device and may each measure only 0.0005 inch thick
by 0.002 inch wide by 0.006 inch long. Further, typical ceramic or
glass substrates may measure only 4 inches .times. 2 inches .times.
20 mils thick.
In prior art explosive bonding techniques, such as above described,
the workpieces to be bonded are placed in proximity to each other
and a sheet charge of high explosive, such as RDX
(cyclotrimethylene trinitramine) is overlaid on the upper surface
of one of the workpieces to be bonded. A commercial detonator is
then implanted at one end of the sheet explosive, and ignited from
a safe distance by means of an electrical spark. The detonator then
explodes, setting off in turn an explosion in the sheet charge of
RDX. The force created by this latter explosion accelerates the
first workpiece towards the second workpiece to firmly bond them
one to the other.
Because of the massive size of the workpieces used in the prior
art, unwanted by-products of the explosion are not of particular
concern; neither is contamination of the workpieces or damage to
the workpiece surfaces. If a "clean" surface is required, the
workpieces can easily be machined, sanded or buffed to the desired
finish. Again by way of contrast, the miniature workpieces to be
bonded by the methods of my invention, particularly electronic
components such as integrated circuits, are extremely sensitive to
contamination. Further, because of their extremely small size,
buffing, sanding or polishing of these workpieces to smooth the
surfaces thereof and remove impurities therefrom is impractical, if
not impossible. In addition, substrates such as glass and ceramic
are extremely brittle and tend to craze or crack when subjected to
sudden concentrated stresses.
The use of a buffer layer which is positioned intermediate the
sheet charge of explosive and the upper surface of one of the
workpieces is known in the prior art. However, in the prior art
this buffer layer is not provided for the purpose of (and indeed
would be inoperative for) protecting the surfaces of the workpieces
from chemical contamination or reducing stress concentrations in
the workpieces. Rather, in the prior art, these buffer layers are
provided to modify the characteristics of the secondary explosive
material and, in particular, to reduce the velocity of
detonation.
In the case of massive workpieces of the type bonded by prior art
explosive bonding techniques, as much as several hundred pounds of
explosive may be required. Obviously, the explosion must be
performed out of doors, under the most carefully controlled safety
conditions.
While the exact mechanism by which explosive bonds are formed with
workpieces and explosive charges of this size is not fully known,
through trial and error, certain formulae have been developed
relating the quantity of explosive required to produce a
satisfactory bond under given conditions and workpiece dimensions.
These formulae are, for the most part empirically derived, and,
therefore, do not yield satisfactory results when applied to
workpieces which are several orders of magnitude smaller.
An explosive may be defined as a chemical substance which undergoes
a rapid chemical reaction, during which large quantities of gaseous
by-products and much heat are generated. There are many such
chemical compounds and, for convenience, They are divided into two
main groups: low explosives, such as gun powder; and high
explosives. The latter category may be further subdivided into
initiating (or primary) explosives and secondary explosives.
Primary explosives are highly sensitive chemical compounds which
may easily be detonated by the application of heat, light,
pressure, etc. thereto. Examples of primary explosives are the
azides and the fulminates. Secondary explosives, on the other hand,
generate more energy than primary explosives, when detonated, but
are quite stable and relatively insensitive to heat, light, or
pressure. In the prior art, primary explosives are used exclusively
to initiate detonation in the higher energy, secondary
explosives.
Strictly speaking, the difference between a low explosive, such as
gun powder, and a high explosive, such as TNT, is in the manner in
which the chemical reaction occurs. The fundamental difference is
between burning (or deflagration) and detonation, not between the
explosive substances themselves. It is quite common to find that an
explosive can either deflagrate or detonate according to the method
of initiation or the quantity of explosive involved. If the mass of
explosive matter is small, thermal ignition thereof, as by an open
flame, usually, if not always, leads to deflagration; but if the
mass exceeds a certain critical value, it is possible for the
burning to become so rapid that it sets up a shock-wave front in
the explosive material and detonation ensues. The critical mass
varies from explosive to explosive, thus, for the primary explosive
lead azide, the critical mass is too small to measure, whereas for
TNT it is in the order of 2000 pounds. Thus, the application of an
open flame to a mass of TNT of, say, 1800 pounds would not produce
detonation but only deflagration. The application of the same open
flame to 2200 pounds of TNT, however, would produce an immediate
detonation. Quantities of secondary explosive, therefore, which are
smaller than the critical mass must be detonated by an intense
shock, e.g., from the detonation of a primary explosive such as
lead azide and are thus of no value for the bonding of miniature
workpieces.
Prior to my invention, then, primary explosives were used
exclusively for initiating detonation in secondary explosives such
as TNT, dynamite and the like. Because the critical mass of such
primary explosives is so small as to be unmeasurable, the empirical
equations developed for the use of subcritical masses of secondary
explosives are inapplicable. This is primarily due to the
difference in the parameters, such as the detonation velocity, of
the highly sensitive primary explosives, and the relatively
insensitive secondary explosives. The detonation velocity of the
primary explosive mercury fulminate, for example, is approximately
2000 meters per second, whereas the detonation velocities of the
secondary explosives TNT and nitroglycerin are approximately 6000
meters per second and 8000 meters per second, respectively. A more
detailed discussion of the thermochemistry of explosives may be
found in the publications entitled, "Detonation in Condensed
Explosives," by J. Taylor, published by Oxford University Press,
London, 1952 and "Explosive Working of Metals," by J. S. Rinehart
and J. Pearson, published by Macmillan, New York, 1963.
SUMMARY OF THE INVENTION
Briefly, my invention comprises, in a first preferred embodiment, a
method of bonding a first workpiece to a second workpiece. The
method comprises the steps of: placing said first and second
workpieces in juxtaposition to each other; and detonating a primary
explosive in the region of the desired bond, the force created by
the detonation of said primary explosive accelerating at least one
of said workpieces towards the other, to thereby form an explosive
bond between said workpieces.
Detonation of the explosive material is accomplished, in one
embodiment of the invention, by applying heat to the workpiece. In
other embodiments of the invention, detonation is accomplished by
the application of light, laser, or acoustic energy to the
explosive material. In still further embodiments of the invention,
detonation is accomplished by means of alpha particles, shock
waves, mechanical pressure, an electron beam, alternating magnetic
or electric fields, an electric discharge or the provision (or
removal) of a chemical atmosphere. In some embodiments of the
invention, the bonding force is applied directly to the
microcircuits to be bonded; in other embodiments, the bonding force
is applied through a protective bonding medium.
Another embodiment of my invention comprises a method of bonding
the microleads of at least one beam leadlike device to
corresponding regions of a workpiece. The method comprises the
steps of placing a charge of explosive material proximate each of
the microleads to be bonded in a position to accelerate the
microleads towards the workpiece and detonating the explosive
material to explosively bond the microleads to corresponding
regions of the workpiece. As before, the explosive material may be
detonated by heat, light, sound, pressure, etc. and may be applied
directly to the workpiece or through a protective buffer medium,
such as stainless steel or a polyimide, such as KAPTON.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of an apparatus which may be utilized
to deposit explosive material on the microleads of a beam lead-like
device;
FIG. 2 is a partial top view of a plurality of beam-lead devices,
prior to separation, and shows in greater detail the manner in
which the explosive material is deposited thereon;
FIG. 3 is an isometric view of a single beam-lead device and shows
the location of the explosive material on the microleads thereof in
greater detail;
FIG. 4 is a partial, cross-sectional view of a beam-lead device
prior to the explosive bonding thereof to the land areas of a
substrate;
FIG. 5 is a partial, cross-sectional view of the beam-lead device
shown in FIG. 4 after it has been explosively bonded to the
substrate;
FIG. 6 is a partial, cross-sectional view of the beam-lead device
shown in FIG. 4 illustrating the use of a buffer member positioned
intermediate the explosive material and the beam-lead device;
FIG. 7 is a plan view of the buffer member shown in FIG. 6
depicting the location of the explosive charges thereon in greater
detail;
FIG. 8 is a partial, cross-sectional view of the beam-lead device
shown in FIG. 6 after explosive bonding to the substrate has
occurred;
FIG. 9 is an isometric view of an apparatus for explosively bonding
a plurality of beam-lead devices to a substrate by the application
of light thereto;
FIG. 10 is a partially illustrative, partially schematic diagram
depicting the use of light from an optical maser to detonate the
explosive material;
FIG. 11 is an isometric view of an apparatus for explosively
bonding a plurality of beam-lead devices to a substrate by the use
of focused light from an incandescent lamp;
FIG. 12 is an isometric view of an apparatus which may be used to
explosively bond a plurality of beam-lead devices to the land areas
of a substrate by the application of heat thereto;
FIG. 13 is a side view of an apparatus which may be used to bond a
plurality of beam-lead devices to the land areas of a substrate by
the use of radio frequency induction heating;
FIG. 14 is a side view of an apparatus which may be used to bond a
plurality of beam-lead devices to the land areas of a substrate by
the use of radio frequency dielectric heating;
FIG. 15 is an isometric view of an apparatus which may be used to
bond a plurality of beam-lead devices to the land areas of a
substrate by the use of acoustical energy;
FIG. 16 is a side view of an apparatus which may be used to bond a
plurality of beam-lead devices to the land areas of a substrate by
the use of simple mechanical pressure applied through a compliant
medium;
FIG. 17 is a side view of an apparatus which may be used to bond a
plurality of beam-lead devices to the land areas of a substrate by
means of an electrical discharge passing through the explosive
material on the beam leads;
FIG. 18 is an isometric view of an apparatus which may be used to
bond a plurality of beam-lead devices to the land areas of a
substrate by means of a beam of electrons;
FIG. 19A is a cross-sectional view of a beam-lead device
illustrating the manner in which the upper surface of the beam
leads may be rendered undulating to improve the quality of the
bond; and
FIG. 19B is a similar cross-sectional view illustrating the manner
in which the upper surface of the beam leads may be castellated to
improve the quality of the bond;
FIG. 20 is a partial, cross-sectional view illustrating the manner
in which the contact pads of a "flip chip" IC device may be
explosively bonded to the land areas of a substrate;
FIG. 21 illustrates an alternative embodiment of the invention
which may advantageously be used to deposit conductive metal paths
on an insulating substrate;
FIG. 22 illustrates the finished appearance of the apparatus shown
in FIG. 21;
FIG. 23 is a side view of another embodiment of the invention in
which spacing elements are provided intermediate the workpieces to
be bonded to ensure the creation of a strong bond;
FIG. 24 is a side view of the elements depicted in FIG. 23 after an
explosive bond has been formed;
FIG. 25 is a side view of a buffer medium having a patterned
workpiece fabricated on one side thereof and a correspondingly
patterned explosive charge on the other surface thereof;
FIG. 26 is an isometric view of the buffer medium shown in FIG. 28
positioned over a substrate to which the metallic pattern is to be
bonded;
FIG. 27 is an isometric view of the apparatus shown in FIG. 26
after the explosive bond has been formed;
FIG. 28 illustrates yet another embodiment of the invention which
may be used to manufacture thin or thick film capacitors by
explosive bonding techniques;
FIG. 29 illustrates the embodiment shown in FIG. 28 after the
electrode of a capacitor has been explosively bonded to a
substrate;
FIG. 30 is another view of the capacitor shown in FIG. 29
illustrating the manner in which a counter-electrode may be
explosively bonded thereto; and
FIG. 31 is an isometric view of the capacitor shown in FIG. 30
after the counter-electrode has been explosively bonded
thereto.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 depicts an apparatus which may be used to deposit a small
quantity of explosive material on the microleads of a beam-leaded
IC device, or the like. As shown, a conventional wax-coated
semiconductor carrier plate 30, having a plurality of beam-leaded
IC devices 31, temporarily secured thereto, is placed on the bottom
surface 32 of a hollow, rectangular container 33. Carrier plate 30
is restrained from movement, and aligned, by means of a plurality
of first registration pins 34 which mate with a corresponding
plurality of notches 35 in carrier plate 30. A second plurality of
registration pins 38 are provided at the four corners of container
33. A rectangular stencil plate 40, having a plurality of
orthogonally oriented slot apertures 41 therein, is adapted to fit
down inside container 33 so that registration pins 34 and 38 mate
with a corresponding plurality of apertures 39 in the stencil
plate. When so mated, the slot apertures 41 align with the beam
leads of the IC devices 31.
Referring now to FIG. 2, as is well known, each of the beam-leaded
IC devices 31 is provided with a plurality of gold beam leads 42
cantilevered outward therefrom. In accordance with standard
manufacturing techniques for these devices, prior to separation,
the beam leads of each device are interdigitated with the beam
leads of its immediate neighbors. Registration pins 34 and 38, FIG.
1, align stencil plate 40 so that the slot apertures 41 therein are
positioned intermediate each pair of beam-lead devices and cross
the interdigitated beam leads 42, FIG. 2, in the region of
overlap.
Returning to FIG. 1, a squeegee 43 having a rubber roller 47 is
sldeably mounted in a frame (not shown) which in turn is attached
to the walls of container 33. The rubber roller 47 is adapted to
fit within container 33 and to engage the upper surface of stencil
plate 40 when the plate is mated with registration pins 34 and 38
and positioned over IC carrier plate 30.
In operation, the carrier plate, bearing the IC devices whose beam
leads are to be coated with explosive material, is placed on the
bottom surface 32 of container 33 and aligned therewith by means of
registration pins 34. Next, stencil plate 40 is fitted over the
aligned carrier plate 30 and a metered quantity of explosive
material deposited from a suitable container onto the stencil
plate. Squeegee 43 is then lowered into engagement with the stencil
plate and rolled back and forth to force the explosive material
down into slotted apertures 41 and, hence, onto the beam leads of
each IC device. When the metered quantity of explosive material has
been consumed, the stencil plate and the carrier are removed from
container 33 and the explosive material permitted to dry. The
individual IC devices are then separated from the carrier by any of
several conventional techniques.
It is, of course, necessary to select an explosive which is not so
sensitive that the squeegee operation will cause premature
detonation thereof. Typically, the explosive material is dissolved
in some suitable chemical solution which facilitates the stenciling
of the explosive onto the IC device. In addition, the solvent may
inhibit premature detonation, at least until the solution has
evaporated and the explosive material is dry.
It will be appreciated that a suitably patterned silk-screen (or
other equivalent screening device) could be substituted for stencil
plate 40. Other analogous printing techniques may, of course, also
be used to apply the explosive to the workpiece. It will further be
appreciated that this technique for depositing a patterned charge
of explosive material onto a workpiece to be explosively bonded is
not necessarily restricted to miniature workpieces, such as IC
devices or to substrates. The technique may be used, for example,
on much larger workpieces. Indeed, a patterned charge of a
conventional, secondary explosive may also be deposited on a
workpiece by this technique, provided that the secondary explosive
is dissolved in some suitable vehicle to render it sufficiently
mobile to pass through the apertures of a stencil or a screen. In
this latter event, the stencil plate or silk-screen could be
re-used to screen-on the necessary charge of primary explosive
required to detonate the secondary explosive.
FIG. 3 illustrates the appearance of a beam-lead device after it
has been coated with explosive material and separated from its
neighboring devices. As can be seen, a small quantity of explosive
material 48 has been deposited on each beam lead 42. It will be
apparent that the quantity of explosive deposited, and hence the
bonding force produced when the explosive is detonated, may be
controlled by varying the width of the apertures in the stencil
plate and/or by altering the thickness of the stencil plate,
thereby affecting the amount (i.e., width and height) of explosive
material deposited on the beam leads.
For some special applications, it may be desirable to deposit
unequal amounts of explosive material on each beam lead. The
above-described apparatus can easily accommodate this requirement
by a combination of the above-described changes to the apertures of
the stencil plate. Further, the apparatus may easily be adapted to
handle different IC circuit configurations, or different substrate
arrangements, by merely substituting an appropriately configured
stencil plate. The apparatus can also handle an individual IC
device, if so desired, by the use of a suitably dimensioned holder
for the individual device. Advantageously, apertures 41 in stencil
40 are arranged to deposit explosive material onto each beam lead
no closer to the main part of the device than 1/3 of the length of
the beam lead and no further from the device than 2/3 of the length
of the beam lead. Advantageously, the average distance used in
practice is approximately 1/2 of the length of a beam lead.
As previously discussed, in the bonding of miniature workpieces,
the conventional use of a secondary high explosive, which is
detonated by means of a detonator, is impossible. I have
discovered, however, that primary explosives may be used to bond
such miniature workpieces. Of the many known primary explosives,
the azides and the fulminates are probably the most widely
understood, although many other chemical compounds exhibit similar
characteristics and may also be used for the explosive bonding of
miniature workpieces. The choice of the particular primary
explosive to be used in any given bonding application is a function
of the amount of explosive force required and/or the manner in
which it is desired to initiate detonation. Advantageously, the
detonation of the primary explosive, in accordance with my
invention, may be accomplished by the application of heat, light,
sound, pressure, shock waves and the introduction (or removal) of a
suitable chemical atmosphere. For example, if light is employed as
the detonating mechanism, then silver nitride (Ag.sub.3 N) or
cuprous azide (Cu(N.sub.3).sub.2) may be used as the primary
explosive. Alternatively, if detonation is accomplished by means of
mechanical force and pressure, mercury fulminate (C.sub.2 N.sub.2
O.sub.2 Hg) or lead azide (Pb(N.sub.3).sub.2) may be used as the
primary explosive.
Table A, below, lists some of the more common azide compounds,
together with their critical detonation temperatures.
TABLE A
THE MORE COMMON AZIDE EXPLOSIVES
Critical Compound Formula Detonation Temp. .degree.C Lead Azide
Pb(N.sub.3).sub.2 350 Silver Azide Ag(N.sub.3).sub.2 300 Titanium
Azide Ti N.sub.3 350 Boron Azide B(N.sub.3).sub.2 Silicon Azide
Si(N.sub.3).sub.4 Mercuric Azide Hg(N.sub.3).sub.2 460 Copper Azide
Cu(N.sub.3).sub.2 215 Cadmium Azide Cd(N.sub.3).sub.2 144 Ammonium
Azide NH.sub.4 (N.sub.3) 170 Mercurous Azide Hg.sub.2
(N.sub.3).sub.2 210 2
table B, below, lists some of the more common fulminate compounds,
together with their critical detonation temperatures.
TABLE B
THE MORE COMMON FULMINATE EXPLOSIVES
Critical Compound Formula Detonation Temp. .degree.C Mercury
Fulminate Hg(ONC).sub.2 190 Silver Fulminate Ag(ONC).sub.2 170
Copper Fulminate Cu(ONC).sub.2
table C, below, lists some additional primary explosive compounds,
together with their critical detonation temperatures.
TABLE C
MISCELLANEOUS PRIMARY EXPLOSIVES
Critical Compound Formula Detonation Temp. .degree.C Mercuric
Acetylidette HgC.sub.2 260 Mercurous Acetylide Hg.sub.2 C.sub.2 280
Copper Acetylide CuC.sub.2 280 Silver Acetylide Ag.sub.2 C.sub.2
200 Lead Styphnate C.sub.6 H.sub.3 N.sub.3 O.sub.9 Pb 295 Barium
Styphnate C.sub.6 H.sub.3 N.sub.3 O.sub.9 Ba 285 Silver Nitride
Ag.sub.3 N 155 Tetrazene 200 Diazodinitrophenol HOC.sub.6 H.sub.3
(NO.sub.2).sub.2 N(:N) 180 (DDNP)
the above three tables are by no means all inclusive. There are
many other unstable chemical compounds which may be classified as
primary explosives and which, under appropriate conditions of
temperature and pressure, might conceivably be utilized for the
explosive bonding of miniature workpieces. However, the explosives
listed in the above tables are of primary interest in this
regard.
Turning now to FIG. 4, there is shown a cross-sectional view of
integrated circuit device 31 prior to its being bonded to the
terminal land areas 50 of a ceramic substrate 52. A thin film 51 of
grease, dirt, metal oxide, or other contaminants is shown on the
upper surface of land areas 50. A similar film will generally also
be present on the surface of beam leads 42 but, for the sake of
clarity, this film has been omitted from the drawing.
It will be noted that each beam lead is bent upward away from the
substrate to form a small angle .alpha. with the plane of the
substrate. In order for a bond to form between a beam lead and the
corresponding land area of the substrate, the explosive charge 48,
when detonated, must accelerate the beam lead downward towards the
land area with a sufficiently high impact velocity that the
resultant impact pressure is of sufficient magnitude to cause
substantial plastic flow of the workpieces to be joined. Thus, the
yield points of the materials from which the workpieces are
fabricated must be considerably exceeded by the impact
pressure.
An important aspect of explosive bonding is the phenomenon known as
"jetting," that is, the process of material flow which occurs when
two metal workpieces strike each other at sufficiently high impact
velocity to cause plastic flow of the workpiece metals and the
formation of a re-entrant "jet" of material between the workpieces,
as shown by the arrows 49 in FIG. 4. The formation of this "jet" of
molten material is important to the establishment of a strong bond,
as it removes any impurities and oxides which may be present on the
surfaces of the workpieces to be bonded and brings freshly exposed,
virgin metal surfaces into intimate contact in the high-pressure
collision. Notwithstanding the above, some workpiece materials, for
example, gold, may be satisfactorily bonded even without the
presence of "jetting." This is due to the inherently oxide-free
surfaces of these materials. In that event, the angle which is
formed between the beam lead and the substrate becomes less
critical and in some instances even unimportant.
The impact pressure required to bond a beam lead to the
corresponding substrate land area may be calculated from the shock
Hugoniot data for the workpiece materials. Once the impact pressure
required for bonding is known, the impact velocity may be
calculated. This in turn yields the necessary ratio of accelerating
explosive charge to metal mass (C/M), hence, the quantity of
explosive material required for a given bonding operation.
The desirable jetting phenomenon, however, only occurs if the angle
of impact, .beta., at the collision point exceeds a certain
critical value. Further, there can exist either a stable jetting
condition or an unstable jetting condition, the latter being
undesirable as it results in a bond of poor quality.
Stable jetting will occur if the collision point at which the two
surfaces first meet, travels along the interface with a velocity
equal to or greater than the highest signal velocity in either of
the two workpiece materials. Table D, below, lists the velocity of
sound in several typical metals and, for comparison, Table E, lists
the detonation velocity of several typical primary explosives.
TABLE D
Velocity of Sound in Several Typical Metals
Metal Velocity (m/sec) Gold 2030 Silver 2680 Aluminum 5000 Platinum
2800
TABLE E
Detonation Velocity of Typical Primary
Explosives Explosive Detonation Velocity (m/sec) Lead Azide 4000
Lead Styphnate 5000 Mercury Fulminate 5050 DDNP 6800
if the two workpieces to be bonded are positioned parallel to one
another, the collision point velocity equals the detonation
velocity of the accelerating explosive charge. It will thus be seen
that for the types of metals commonly used for microleads and land
areas in the electronics industry, by the choice of an appropriate
explosive material, the collision point velocity will always exceed
the bulk sonic velocity in the workpiece metals.
Actually, if the collision point velocity substantially exceeds the
bulk sonic velocity in the workpiece materials, another undesirable
effect is noted. That is, the generation of expansion waves in the
workpieces which tend to separate the inner surfaces thereof and
destroy or weaken the bond immediately after its formation. The
ideal situation is when the collision point velocity slightly
exceeds the bulk sonic velocity so that stable jetting occurs, yet
undesirable expansion waves do not occur. For parallel geometry,
this condition can be achieved by slowing down the detonation
velocity of the explosive material, for example, by the addition of
inert materials such as liquid paraffin or French Chalk thereto, or
by reducing the density of the explosive. For example, the addition
of 30 percent liquid paraffin to lead azide will reduce the
velocity of detonation from 4000 m/sec to 500 m/sec, but the mixing
process is difficult to control and the results are often
unpredictable. For these reasons, other means must be employed to
reduce the collision point velocity.
If the workpieces to be bonded are not held parallel, but rather
are aligned so that they make a small angle .alpha. to one another,
the collision point velocity is no longer the same as the
detonation velocity of the explosive material, but falls to some
fraction thereof. Thus, by varying the geometry of the bonding
configuration, the collision point velocity may be adjusted so that
it is only slightly more than the bulk sonic velocity in the
workpiece materials, which is the optimum condition.
As previously discussed, there is a critical angle of contact
.beta. for the collision below which jetting and satisfactory
bonding usually will not occur. For parallel geometry, .beta. can
be increased by increasing the ratio of explosive charge to mass
(C/M). However, if this is attempted in nonparallel geometry, such
as shown in FIG. 4, it is found that the collision point velocity
also increases. There is thus an interaction between changing the
impact angle .beta. so that it exceeds the critical angle below
which jetting does not occur, and lowering the collision point
velocity to approximately the bulk sonic velocity in the workpiece
materials. Nevertheless, despite this interaction, for workpieces
of the type shown in FIG. 4, and primary explosives of the types
listed in Tables A, B, and C, there exists a broad range of
orientations, charge densities, and explosive compounds which will
simultaneously satisfy all these criteria and produce strong, sound
bonds. As an example of a specific bond, which I have produced,
according to the methods of this invention, a gold wire measuring
0.002 inch by 0.0005 inch was bonded to a gold-plated ceramic
substrate by means of from 25 to 40 .mu. grams of lead azide.
Detonation was accomplished by an electrical discharge from a 3
volt D.C. source. The wire made an angle of less than 5.degree. to
the plane of the substrate. I further discovered that bonding was
facilitated if the temperature of the substrate was raised to
175.degree.C prior to passing the electrical discharge through the
substrate.
FIG. 5 depicts the beam-leaded device shown in FIG. 4 after it has
been explosively bonded to the substrate. The beam leads 43 are
now, of course, flattened and substantially parallel to the
substrate. A small area of discoloration or pitting 53 will be
noted on each beam lead in the region priorly occupied by explosive
material 48. This discoloration and pitting, however, does not
affect the mechanical strength or electrical characteristics of the
beam leads to any detectable degree.
In the explosive bonding of massive workpieces, the explosive is
laid down upon the upper surface of the upper workpiece as a sheet
charge. In the methods of my invention, however, the explosive
material is not laid down as a sheet charge, but rather as a point
charge. Thus, the region 54 in which bonding actually occurs does
not extend over the entire area of the beam lead. This is of no
great import, however, as it approximates the geometry which occurs
in other satisfactory bonding techniques, such as thermocompression
or ultrasonic bonding.
As previously mentioned, because of the size of the workpieces and
the extremely large quantities of explosive materials employed,
conventional explosive bonding is usually performed out of doors.
Thus, the unwanted by-products of the explosion are quickly
discharged into the atmosphere. Further, in the prior art, the
massive workpieces employed are not particularly sensitive to
contamination by these by-products. This is not necessarily true,
however, of the miniature workpieces contemplated by this
invention, particularly integrated circuits and the like. Here, the
by-products of the explosion, both gaseous and particulate, pose a
very real threat of contamination to the silicon or germanium
material from which the active devices in the integrated circuits
are fabricated. This contamination may, under certain
circumstances, alter the operating characteristics of the devices
or, worse, render them totally inoperative. The same is true, to a
lesser extent, of thin-film capacitors and resistors which may also
be fabricated upon the same substrate. Fortunately, I have
discovered that this contamination can, in part, be prevented by
conducting the explosive bonding in a partial vacuum, for example,
by the use of a conventional bell-shaped vacuum jar. In addition,
by removing the air which is normally present between the
workpieces, the partial vacuum tends to increase the workpiece
acceleration, thereby improving the quality of the bond. As an
alternative to the use of a partial vacuum, the explosive bonding
may be effected through an intermediate buffer, such as a layer of
plastic, for example the polyimide sold under the registered
trademark "KAPTON," of the E. I. DuPont de Nemorus Co. Metallic
material, for example, stainless steel, or the like, may also be
used for the buffer medium.
FIGS. 6 and 7 illustrate the use of such a buffer layer in an
explosive bonding operation. As shown therein, a film of plastic
(e.g., a KAPTON film 3 mils thick) or metallic material (e.g., 303
type stainless steel 2 mils thick) 60 having a plurality of
apertures 61 therein is positioned over the top surface of
beam-lead device 31. The explosive material 48, which priorly was
deposited directly onto the beam leads 42, is now deposited on the
upper surface of the film 60. Additionally, if film 60 is plastic
and, in addition, transparent, alignment of the explosive charges,
with respect to the beam leads of the integrated circuit devices,
may be facilitated, for example, by use of the alignment technique
disclosed in U.S. Pat. application, Ser. No. 820,179 of F. J.
Jannett, filed on Apr. 29, 1969.
The explosive charges which are deposited onto the buffer film may
be placed there by means of the apparatus illustrated in FIG. 1, or
by the use of a patterned silk-screen or printed onto the film,
intaglio fashion, by means of a suitable rubber or metallic roller
having a raised surface thereon which corresponds to the desired
locations of the explosive charges.
FIG. 8 depicts the beam-lead device shown in FIG. 6 after the
explosive material 48 has been detonated. As was the case
illustrated in FIG. 5, the beam leads 42 are now substantially
parallel to substrate 52 and bonded to the land areas 50 of the
substrate at locations 54. The buffer film 60 is forced down about
device 31 by the explosion, but is not ruptured. As a result,
unwanted by-products of the explosion are prevented from reaching
the sensitive portions of the substrate, and damage thereto is
completely avoided. Although in FIG. 6 buffer sheet 60 is depicted
as being apertured so that it may be fitted over the beam-lead
devices, it will be appreciated that sheet 60 could be contoured,
rather than apertured, and in that event would also serve to
protect the IC device from contamination as well as the substrate.
After the bonding operation has been satisfactorily performed,
buffer film 60 may be peeled off the substrate. If the sheet is
fabricated from plastic material, however, no deleterious effects
will occur if it is permitted to remain in place.
As previously mentioned, the detonation of the primary explosive,
in accordance with my invention, may advantageously be accomplished
by exposure to light.
Table F, below, lists some of the primary explosive compounds
exhibiting this property, together with the minimum light intensity
required to initiate detonation thereof.
TABLE F
PHOTOSENSITIVE EXPLOSIVE COMPOUNDS
Compound Formula Light Intensity in Joules Centimeter.sup.2 Silver
Azide AgN.sub.3 2.6 Silver Nitride Ag.sub.3 N 0.2 Silver Acetylide
Ag.sub.2 C.sub.2 0.8 Silver Fulminate AgONC 2.1 Lead Azide
Pb(N.sub.3).sub.2 2.0
the mechanism which renders these and other similar primary
compounds sensitive to detonation by light is not fully understood.
One theory is that the light is absorbed in a thin surface layer of
the explosive material and within 50 .mu. seconds is degraded into
heat; the explosion is then believed to occur by a normal thermal
mechanism. Another theory is that the explosion occurs as a result
of a direct photochemical decomposition of the explosive matter.
Regardless of the theory, however, these compounds may be detonated
by the application of light thereto and are useful for the
explosive bonding of miniature workpieces.
FIG. 9 illustrates an apparatus which may be used to explosively
bond the beam leads of an IC device using light as the detonating
mechanism. It will be appreciated that this apparatus may also be
used to bond other types of workpieces, for example, to explosively
bond conductive metal paths onto a ceramic or glass substrate or to
explosively bond the elements of capacitors, resistors, etc. to a
substrate. The same is also true for the other apparatus discussed
below with reference to FIGS. 10-18. The illustrative example of
bonding the leads of an IC device to corresponding land areas on a
substrate is not intended to be limiting and is only exemplary. The
beam leads of the devices 62 to be bonded are coated with a
quantity of light-sensitive primary explosive, for example, silver
azide, and the devices then aligned with respect to the land areas
of the substrate 63 in a conventional manner. If desired, the
devices may be temporarily tacked to the substrate by means of a
drop of alcohol, or the like. Substrate 63 is then placed within a
glass vacuum jar 64, which is exhausted by means of an exhaust pipe
65 and a pump 66. One or more photo flash lamps 67, for example,
krypton-filled quartz flash lamps are positioned outside the vacuum
jar so that the light which is generated by the tubes will fall
upon the photosensitive material on the beam leads. Clearly, vacuum
jar 64 must be "transparent" to the light energy from lamp 67. The
vacuum jar may thus be entirely fabricated from glass or quartz or
have one or more glass or quartz windows set in the walls thereof.
Photo flash lamps 67 are connected via a pair of conductors 68 to a
switch 69, thence to a suitable source of energizing potential
70.
In operation, switch 69 is closed to complete a circuit from source
70 to photo flash lamps 67. In a well-known manner, the lamps fire
and generate an intense burst of light which passes through the
walls or windows in vacuum jar 64, and strikes the silver azide on
each beam lead, detonating it and explosively bonding each of the
IC devices 62 to substrate 63.
Silver azide is primarily responsive to light in the ultraviolet
range (.lambda. = 3500 A units) and krypton-filled photo flash
lamps of the type shown in FIG. 9 produce more than enough energy
in this ultraviolet range to detonate photosensitive silver azide.
The typical duration of the flash from photo flash lamps 67 is
approximately 60.mu.s and explosion of the silver azide usually
occurs within 20.mu.s thereafter. From Table F the critical light
intensity required to detonate silver azide is 2.6 joules/cm.sup.2
which corresponds to 8 .times. 10.sup..sup.-4 calories/mm.sup.2.
This critical light intensity is independent of the mass of
explosive material used, at least in the range of from 200 to 1500
micrograms. Unwanted by-products of the explosion are, as
previously discussed, vented from vacuum jar 64 by pump 66.
However, in applications where these by-products are not
troublesome, the bonding process can, of course, be conducted in a
normal atmosphere. The use of a transparent plastic film positioned
over the IC devices for alignment purposes is, of course, possible,
provided that the intensity of the photo flash is sufficient to
compensate for any light energy lost in passing through the
transparent film. Further, this method of detonation may also be
used with an explosively coated transparent buffer member
positioned over the IC device and the substrate.
If the intensity of light from photo flash lamps 67 is not
sufficient, additional lamps may be provided or a simple lens
system (not shown) may be placed in front of each lamp to focus the
light energy therefrom and thereby increase the light intensity
above that critical value needed to detonate the explosive.
I have also discovered that a laser beam may be used to detonate
the light-sensitive explosive, rather than the photo flash lamp
illustrated in FIG. 9. As shown in FIG. 10, light from a pulsed or
Q-switched laser 71 is expanded by a pinhole beam expander 72 and
collimated by a lens 73. The collimated beam of laser energy is
then directed upon the IC devices 62 on substrate 63 detonating the
silver azide, or other photosensitive primary explosive, deposited
on the beam leads thereof. Again, the substrate and IC devices
could be positioned within a transparent vacuum jar, if desired,
and the laser energy applied through the walls of the jar to
detonate the photosensitive explosive material.
Contrary to what might be expected, the amount of light energy
required to initiate detonation of a photosensitive explosive
varies inversely with the duration of the flash. Thus, a longer
flash, as might be obtained, for example, from a magnesium-filled
flash bulb, would have to be several times as intense to produce
detonation of the same explosive material. Further, due to thermal
lag, if the duration of the flash is too great, the explosive
material will deflagrate rather than detonate, regardless of the
intensity. Thus, the use of pulsed light sources is, generally
speaking, preferable to the use of a continuous light source.
FIG. 11 illustrates the use of a conventional light source to
explosively bond a plurality of beam devices to a substrate. As
shown, a quartz incandescent lamp 74 is positioned at the focus of
an ellipsoidal reflector 75. The filament of lamp 74 is connected
by a circuit 76 and a switch 77 to a suitable source of energizing
potential 78. When switch 77 is closed and lamp 74 energized, the
focused light therefrom impinges upon the surface of substrate 63
and detonates the photosensitive explosive deposited on the beam
leads of the integrated circuits to be bonded.
Actually, because of the intense heat which is generated by quartz
incandescent lamps of this type, which, may be rated at as much as
5 kilowatts, it is difficult to say whether it is the light energy
or the thermal energy from the lamp which initiates the explosion.
As with the previous examples, the substrate and the IC devices may
be placed within a glass or quartz vacuum jar and the light from
the incandescent lamp focused through the transparent walls of the
vacuum jar. This, of course, provides protection from contamination
by unwanted by-products of the explosion.
I have discovered that in the explosive bonding methods according
to this invention the threshold sensitivity of certain
photosensitive explosives may be lowered by the addition of other
elements thereto. For example, by mixing approximately 28 percent
by weight gold powder with the silver azide powder, the minimum
light energy required to induce detonation of the mixture is
significantly reduced.
In any application employing photosensitive explosives, it is
necessary to apply the explosive to the beam leads of the devices
to be bonded in total darkness, or at least at levels of
illumination which are sufficiently low that there is no danger of
premature detonation of the explosive.
Advantageously, the detonation of the primary explosive, in
accordance with my invention, may be accomplished chemically. Thus,
if the substrate and the beam-lead devices which are to be bonded
thereto are placed within a container, for example, a vacuum jar,
and a suitable chemical atmosphere allowed to flow over the
substrate, the reaction which occurs between the primary explosive
and the chemical atmosphere will initiate detonation of the
explosive and bonding will occur.
Other primary explosives are inhibited from explosion by the
presence of an appropriate chemical atmosphere. For example, the
detonation of nitrogen iodide (Ni.sub.3.NH.sub.3) is inhibited by
the presence of ammonia (NH.sub.3) or water vapor. Thus, if the
primary explosive is applied to the beam leads of an IC device in
the presence of such an inhibitory atmosphere, detonation and
bonding may be accomplished, after the device has been properly
positioned over the land areas of a substrate, by exhausting the
inhibitory atmosphere. In either of the above cases, care must be
taken that the chemical atmosphere does not deleteriously affect
the IC devices or the substrates.
I have also discovered that the explosive bonding of miniature
workpieces may be effected by the use of primary explosives which
are detonated by other means. FIG. 12, for example, illustrates a
method of explosively bonding a plurality of IC devices to a
substrate by the application of heat to the bottom surface of the
substrate. As shown, substrate 63, with a plurality of IC devices
62 temporarily tacked thereto, is placed upon the surface of a flat
metal susceptor 79. A plurality of cartridge-type heaters 80 are
mounted within the body of susceptor 79 and connected via a circuit
81 and a switch 82 to a suitable source of potential 83. When
switch 82 is closed, the cartridge heaters rapidly increase the
temperature of the susceptor, and hence the substrate, so that when
the critical detonation temperature of the explosive material
deposited on the beam leads is reached, the explosive detonates to
explosively bond the IC devices to the substrate. Again, to prevent
deflagration of the explosive material, the thermal inertia of the
system must be kept as low as possible.
As can be seen from Tables A, B, and C, above, the critical
detonation temperature of primary explosives of the type
contemplated for use with my invention ranges from about
150.degree.C to over 400.degree.C, with most compounds detonating
in the range of from 280.degree.C to 300.degree.C. The maximum
temperature to which an integrated circuit device may be safely
raised is in the order of 350.degree.C, although this may be
exceeded for short time intervals, without damage to the device. It
will be evident that since the critical detonation temperature of
most primary explosives is well below the maximum safe temperature
for the IC device, detonation of the explosive material by the
direct application of heat to the substrate poses no real danger to
the characteristics and operability of the IC devices fabricated
thereon. The heat required to initiate detonation may be applied to
the substrate by means other than thermal induction from a heated
susceptor. Referring back to FIG. 11, if quartz lamp 74 is replaced
by an infrared source, the focused radiant energy therefrom will
rapidly raise the temperature of the substrate above the critical
detonation temperature and explosive bonding will again occur. As
previously, the radiant energy from lamp 74 may be applied through
the walls of a glass vacuum jar, if it is desired to conduct the
explosive bonding in a partial vacuum.
FIG. 13 illustrates another technique which I have discovered may
be used to raise the temperature of a device to initiate detonation
of the explosive material deposited on the beam leads thereof. As
shown, substrate 63 with beam-lead devices 62 temporarily tacked
thereto is placed upon a suitable, non-metallic support member 84.
An induction coil 85 surrounds support member 84 and is connected
via a pair of conductors 86 to a source of radio frequency energy
87. When source 87 is energized, a radio frequency current flows
through the windings of coil 85 and eddy currents are induced in
all of the metallic portions of the substrate and the IC devices.
These eddy currents rapidly raise the temperature of the beam leads
above the critical detonation temperature of the explosive compound
deposited thereon, so that the explosive compound detonates,
bonding the devices to the substrate.
FIG. 14 illustrates the analogous use of dielectric heating, rather
than induction heating, to raise the temperature of the substrate.
As shown, substrate 63, with the IC devices 62 to be bonded
thereto, is placed between the capacitor plates 88 of a dielectric
oven 89. A sheet of plastic material 90 may be placed between the
substrate 63 and each plate 88 to prevent physical damage to the IC
devices, and the substrate, during the bonding process. Plates 88
are connected via circuit 91 to a radio frequency source 92 which,
when energized, supplies a high-frequency alternating current to
capacitor plates 88. The rapidly alternating electric field which
is generated between plates 88 will induce hysteresis excursions in
the nonconducting ceramic substrate, which excursions will rapidly
raise the temperature of the substrate, and hence the beam leads,
above the critical detonation temperature of the explosive material
on the beam leads. It is not entirely clear if the explosive
compound is heated directly by the hysteresis losses or by thermal
conduction from the heated substrate, but in any event, the net
effect is to detonate the explosive and bond each of the beam leads
to the substrate.
Advantageously, the detonation of the primary explosive, in
accordance with my invention, may be accomplished by the
application of mechanical shock or vibration to the explosive. For
example, acoustic energy may be employed to detonate the explosive
material. Referring to FIG. 15, the substrate, and IC devices to be
bonded, are positioned beneath the outlet end of an acoustical horn
93 which is coupled to an ultrasonic oscillator 94. When energized,
ultrasonic oscillator 94 generates ultrasonic waves which are
propagated by horn 93 into the atmosphere. The acoustic waves from
horn 93 strike the surface of the substrate, as well as the
explosive material present on the beam leads of the IC devices to
be bonded thereto, and, if the energy level of ultrasonic
oscillator 94 is sufficiently high, shock waves are induced in the
explosive material which are of sufficient magnitude to detonate
the explosive material and bond the devices to the substrate. In
this instance, it is not possible to conduct the bonding operation
in a vacuum, as sound waves are not propagated in a vacuum.
However, essentially the same degree of protection from unwanted
by-products of the explosion may be obtained by flowing an inert
gas, such as helium, through the vacuum jar during the bonding
process so that unwanted by-products of the explosion are vented by
the flow of inert gas. Subsonic and sonic waves may also be
utilized to detonate the explosive material, although the use of
ultrasonic energy is preferred as it requires less energy from the
transducer and is easier to direct onto the substrate.
FIG. 16 illustrates yet another method which I have discovered may
be used to mechanically detonate the primary explosive on the beam
leads of each device. As shown, a substrate 63, to which a
plurality of IC devices 62 are to be bonded, is placed upon a
support bed 95 and a sheet of compliant material 96, for example,
KAPTON or 2024 aluminum overlaid thereon. A contoured bonding tool
97 (or a flat bonding tool with a fluid pressure transmitting
medium attached thereto) is then forced down into engagement with
the compliant sheet to deform the sheet about the IC devices. As
the sheet deforms about the IC devices, it contacts the beam leads
thereof, detonating the explosive material 48 which is deposited
thereon, thereby bonding the IC devices to the substrate.
In addition to transmitting mechanical pressure from the bonding
tool to each of the beam leads, the compliant sheet also acts to
constrain the upward forces of the explosions thereby increasing
the bonding pressure which is applied to the beam leads. To a
certain extent, the compliant member also inhibits contamination of
the IC devices and the substrates, but not, of course, to the same
extent as would be the case illustrated in FIG. 6, where the
explosive material is applied to the upper surface of the buffer
member rather than to the beam leads themselves.
The apparatus shown in FIG. 16 must be distinguished from the
apparatus disclosed in the above-identified U.S. Pat. application
of A. Coucoulas, Ser. No. 651,411, now U.S. Pat. No. 3,533,155. As
disclosed in that application, the force which is applied to the
compliant member actually creates the bonds between the beam leads
and substrate; and this force, therefore, must be considerably
greater than the force which is applied by the apparatus shown in
FIG. 16, which need only be sufficient to detonate the primary
explosive.
I have also discovered that explosive bonding of miniature
workpieces can be accomplished by the use of primary explosives,
for example, copper acetylide, lead styphnate, lead azide, mercury
fulminate and tetrazine, which are detonated by an electrical
discharge. The minimum spark energy necessary for detonation of
these explosives varies from a low of 20 ergs for copper acetylide
to more than 100,000 ergs for mercury fulminate. The minimum energy
required is also a function of impurities present in the explosive
material.
FIG. 17 illustrates a method in which an electrical discharge is
utilized to initiate detonation of the primary explosive. As shown,
an IC device 62, which is to be bonded to a substrate 63, is
aligned over the land areas 50 of the substrate and temporarily
tacked thereto in a conventional manner. A plurality of spring leaf
contacts 98 are pressed into engagement with the terminal land
areas 50, or other contact points, of the substrate. Contacts 98
are connected via a lead 99 and a switch 100 to one terminal of a
high-voltage source 101. The other terminal of source 101 is
connected via a lead 102 to a metallic plate 103 to which a
plurality of second spring leaf contacts 104 are riveted. Contacts
104 are positioned on plate 103 so that when plate 103 is lowered,
by means of an insulated handle 105, into engagement with device
62, each one of the plurality of contacts 104 engages the explosive
material 48, which is deposited on the corresponding one of the
plurality of beam leads 42.
Since device 62 is not yet permanently bonded to substrate 63,
there will be an imperfect electric contact between each beam lead
42 and the corresponding land area 50 of the substrate. For
example, dirt, grease, metal oxide and other contaminants may be
present on the surfaces of the connection, so that the unbonded
resistance of the connection is typically several hundred ohms, or
greater. However, if the potential of source 101 is made
sufficiently high, the electric field developed across the
interface of the connection will break down at least a portion of
the nonconducting film, and cause a momentary spark. This momentary
spark, however, is more than adequate to detonate the primary
explosive 48 on each beam lead thereby forming a permanent bond
between each beam lead and the corresponding land area of the
substrate.
I have also discovered that explosive bonding of miniature
workpieces may be accomplished by the use of primary explosives
which are detonated by radiant energy. Lead and silver azide, for
example, may be detonated by the use of an electron beam and
nitrogen iodide may be detonated by means of gamma rays and neutron
bombardment.
FIG. 18 illustrates an apparatus which may be utilized to
explosively bond a plurality of beam-lead integrated circuits by
the use of an electron beam. As shown, the integrated circuit
devices 62 to be bonded are aligned with respect to a substrate 63
and temporarily secured thereto. The substrate is then placed upon
the objective stage 106 of an electron beam machine 107. The vacuum
chamber of the electron beam machine is then evacuated by means of
a pump 108 and the electron beam gun activated. A control circuit
109, which may be connected, for example, to a suitably programmed
general purpose digital computer (not shown), successively deflects
the electron beam to the approximate location of each beam lead on
the substrate. As the electron beam strikes each charge of
explosive material it detonates it, thereby explosively bonding the
device to the substrate. Since the electron beam is not used to
create the bond, per se, but only to detonate the explosive charge
on the beam leads, it need not be of a particularly high intensity,
and thus the electron beam can be defocused into a relatively broad
beam. This eliminates most of the registration problems inherent
with the use of an apparatus of this type.
I have discovered that in some instances a combination of more than
one of the above-described detonation techniques facilitates the
bonding operation. For example, where the primary explosive is to
be detonated by the passage of an electric current therethrough, I
have found that raising the temperature of the substrate prior to
detonation reduces the amount of current required to produce
detonation and results in a more reliable bond. Similarly, where
the explosive mechanism is optical or acoustical, the application
of heat to the substrate will also improve the quality of the
bond.
The above-described methods of detonation assumed that the
explosive material was deposited directly onto the beam leads of
the device. However, one skilled in the art will appreciate that
these methods are equally applicable to the situation where the
explosive material is deposited onto the upper surface of a buffer
member, such as a sheet of stainless steel, with the explosive
bonding force being applied through the buffer sheet to the beam
leads.
It must again be emphasized that all of the above-described
detonation techniques may be used with workpieces other than IC
devices. They may be used, for example, to explosively bond the
electrode and counter electrode of a thick- or thin-film capacitor
to a ceramic substrate. The same detonation techniques may also be
used with more conventional metal cladding and metal working
processes utilizing secondary explosives provided, of course, that
an appropriate primary explosive is present to detonate the
secondary explosive (the above-described detonation techniques, of
course, do not have sufficient energy to directly detonate the
secondary explosive).
Returning momentarily to FIG. 4, it will be recalled that each of
the beam leads 42 of IC device 31 were bent upwards to form a small
angle .alpha. with the plane of the substrate. This bending may be
accomplished by any of several simple mechanical devices, as the
beam leads are extremely thin and easily bent. FIGS. 19A and 19B,
however, illustrate two alternate arrangements for the beam leads
of IC device 31. In FIG. 19A, the beam leads are fabricated so that
they have an undulating upper surface. In FIG. 19B, the beam leads
are fabricated so that they have a castellated upper surface. The
undulations and castellations may be effected, during fabrication
of the beam leads, by the use of an appropriately exposed photo
mask. In both instances, when the IC device is inverted over the
land areas of the substrate to which it is to be bonded, and an
explosive charge detonated proximate what is now the upper surface
of the beam leads, there will be a plurality of air gaps separating
the beam leads from the land areas of the substrate. Thus, portions
of the beam leads are capable of being accelerated downward towards
the substrate, as is required for explosive bonding to occur. If
the beam leads are so patterned, it is not necessary to bend the
beam leads upwards to form an angle .alpha. with respect of the
plane of the substrate. This, of course, eliminates the slight risk
of damage to the integrated circuit device which exists when the
beam leads are so bent.
I have also discovered that, in some instances, neither beam lead
bending nor castellation of the beam leads is necessary to obtain a
good metal-to-metallized substrate bond. While this phenomenon is
not fully understood, it is believed that the "hills" and "valleys"
in substrate surfaces provide sufficient space through which the
leads can accelerate to provide a high quality bond. This effect is
more noticeable on ceramic substrates than glass substrates and is
even more noticeable when an explosive bond is made directly
between metal and bare ceramic, rather than between metal and
metallized ceramic.
Not all integrated circuits are provided with beam leads. FIG. 20
illustrates the so-called "flip chip," another widely used
configuration. Here the integrated circuit 121 is provided with a
plurality of contact pads 122 and, in the prior art, connection of
the "flip chip" device to the outside world is accomplished by
applying heat and pressure directly to the upper surface of the
device by means of a suitably shaped bonding tool. The heat and
pressure is transmitted through the device to the contact pads to
bond the pads to the land areas 123 of the substrate.
It will be apparent that the methods and apparatus of my invention
are adaptable for use with the "flip chip" as well as with many
other integrated circuit configurations. One skilled in the art
could readily adapt the teachings of this invention to handle the
different bonding geometries which result when different IC device
configurations are employed. In FIG. 20, for example, the explosive
charges 124 are applied to the upper surface of "flip chip" device
121 so that they are located directly above the contact pads 122 on
the bottom surface thereof. Thus, when detonated, the explosive
charges 124 apply pressure, through the substrate, to the contact
pads 122, bonding them to the land areas of the substrate.
A metallic (e.g., stainless steel) or plastic (e.g., KAPTON) buffer
layer may also be used intermediate the explosive charge and the
substrate. As in the example discussed with reference to FIG. 6,
the buffer layer acts to cushion the force of the explosion and, in
addition, inhibits contamination of the workpiece surfaces.
FIG. 21 illustrates yet another embodiment of my invention which
may advantageously be used to fabricate "printed circuit"
substrates, that is to say, substrates having a patterned
arrangement of conductive metal paths arranged thereon in the
well-known fashion. As shown in FIG. 21, a plurality of metallic
elements (e.g., aluminum film) 131, are to be bonded to an
insulating substrate 132 of aluminia or glass. Elements 131 may be
shaped to the desired pattern by any of several known techniques,
for example, by stamping the pattern from a continuous roll of
metallic tape by means of a cutting die, or the like. A plurality
of apertures 133 are provided in substrate 132 and align with a
corresponding plurality of apertures 134 in elements 131. These
apertures are provided to receive the leads of electronic
components when the finished substrate is utilized in a
manufacturing process. Alternatively, apertures 133 may be drilled
through the substrate after the elements 131 have been bonded
thereto, in the well-known manner. A buffer medium of metallic or
plastic material (e.g., KAPTON) 136, having a shaped charge of
explosive material 137 deposited on the upper surface thereof, is
positioned over the elements 131 and substrate 132.
In operation, the explosive charge 137 is detonated by any of the
previously discussed detonation techniques and the explosive force
which results forces the patterned metallic elements 131 down onto
the substrate, thereby forming an explosive bond between each of
the metallic elements 131 of the substrate. (For the sake of
clarity, the various layers depicted in FIG. 21 are separated; in
actual practice, however, the metallic elements, buffer medium, and
substrate are placed in close proximity to each other, prior to
detonation of the explosive material.) As previously stated, in
most instances, it has not been found necessary to provide a gap
between each metallic element 131 and the substrate 132, through
which gap each element is accelerated to form the explosive bond.
It is believed that the "hills" and "valleys" in the surface of the
substrate provide sufficient space for the required acceleration to
occur and it is for this reason that, in most cases, it has not
been found necessary to provide spacing elements.
Buffer medium 136, in addition to providing a support mechanism for
the shaped pattern of explosive charge 137, also acts to inhibit
contamination of substrate 132 by by-products of the explosion. In
addition, buffer medium 136 cushions the effect of the detonation
and tends to reduce the creation of concentrated mechanical and
thermal stresses in the workpiece, which, of course, is an
important consideration in the case of fragile substrates, such as
glass or ceramic.
FIG. 22 illustrates the appearance of the substrate after metallic
elements 131 have been explosively bonded thereto. It will be noted
that the substrate is indistinguishable from a substrate product by
one of the more conventional techniques (e.g., by metal deposition
followed by a selective etch procedure), except that the insulation
resistance of the substrate produced by my explosive bonding
technique is somewhat superior, due to the absence of chemical
residues of the etching solutions, photoresist, developers,
etc.
FIG. 23 illustrates yet another embodiment of my invention which
may advantageously be employed if the surface of the substrate is
highly polished so that the "hills" and "valleys" required for
satisfactory bonding are not present. As shown, a pair of spacing
elements, for example, 0.004 inch diameter, gold or aluminum wire,
are positioned intermediate substrate 132 and metallic element 131.
Buffer sheet 136, with explosive charge 137 overlaid thereon, is
then positioned adjacent metallic element 131 and the explosive
charge detonated, as in the previous example. Spacing elements 141
ensure that a sufficient gap exists between substrate 132 and
metallic element 131 so that an acceleration of element 131 towards
substrate 132 occurs and a sound metal-to-ceramic bond is formed
between the element and the substrate.
FIG. 24 illustrates the appearance of the completed bond. Spacing
elements 141, slightly flattened by the force of the explosion, may
be removed from the bond area. Alternatively, the spacing elements
may simply be left in place as, in general, they do not affect the
operation of the completed circuit.
The techniques described with reference to FIGS. 21-24 may not be
practical for all types of metallic film patterns. For example,
some patterns of conductive metal film may be so complicated and
intricate that they are not self-supporting or pose difficult
alignment or orientation problems. Accordingly, FIGS. 25-27
illustrate yet another embodiment of my invention which overcomes
this difficulty. The specific example is directed towards a thin-
or thick-film resistor, but one skilled in the art will appreciate
that this embodiment of the invention is not so limited and has
general application to any explosive bonding process where at least
one of the workpieces to be bonded is not self-supporting or needs
careful alignment, e.g., the explosive bonding of indicia to the
crown of a wrist watch. As shown in FIG. 25, a castellated pattern
of conductive (actually resistive) metallic film 151 is to be
explosively bonded to an insulating substrate 152. The metallic
film 151 which is to be bonded to the substrate has priorly been
fabricated, in a reverse image, on the bottom surface of buffer
medium 153. Advantageously, buffer medium 153 comprises a polyimide
film, such as KAPTON, and, in that event, the patterned layer of
metallic film may be deposited thereon by the process disclosed in
U.S. Pat. application, Ser. No. 719,976, filed Apr. 9, 1968 in the
names of M. A. DeAngelo and D. J. Sharp, now U.S. Pat. No.
3,562,005, and which is assigned to the assignees of the instant
invention. Other techniques for depositing the metallic film on the
bottom surface of buffer member 153 may, of course, also be
employed.
After metallic film 151 has been deposited on buffer medium 153, a
correspondingly patterned charge of explosive material is
stenciled, screened, or otherwise deposited on the upper surface of
buffer medium 153. As shown in FIG. 26, the combined structure is
then positioned over substrate 152 and the explosive material
detonated, by any of the previously discussed tehcniques, to
explosively bond the intricately patterned conductive metal film
151 (which is now "right side up") onto the substrate. After
detonation, the buffer medium is stripped away, leaving the
finished product, as shown in FIG. 27. (The polyimide KAPTON is
particularly good in this respect and is thus preferred for this
embodiment.) As in the case discussed with reference to FIG. 24,
spacing elements may be interposed between metallic film 151 and
substrate 152, if necessary. Alternatively, as film 151 is
deposited onto the bottom surface of buffer medium 153, portions of
the film may be deliberately made thicker than others to provide
the necessary gap required for a good metal-to-ceramic bond.
In the embodiments of my invention illustrated in FIGS. 21-27, the
explosive charge is depicted to be patterned to approximate the
size and shape of the workpiece to be bonded. Strictly speaking,
however, this is not an absolute requirement and the charge may
assume a pattern somewhat smaller or somewhat larger than the
actual outline of the workpiece. Indeed, the charge need not be
patterned at all. All that is required is that a sufficiently large
bonding force be created to accelerate the workpiece down onto the
substrate.
FIGS. 28 through 31 illustrate yet another embodiment of my
invention which may advantageously be used to manufacture thin- or
thick-film capacitors on an insulating substrate, such as glass or
ceramic. As is well known, in the prior art, such capacitors may be
fabricated by sputtering, or vacuum depositing, an electrode onto
the insulating substrate, either directly or through a selective
masking and etching process, then oxidizing the upper surface of
the electrode to form a nonconductive dielectric layer and finally
depositing, or sputtering, a counter-electrode on top of the
dielectric layer. According to my invention, any one, or all of the
above steps may be performed by an explosive bonding technique.
As shown in FIG. 28, electrode 161 is bonded to ceramic substrate
162 by positioning the electrode over the substrate and then
applying a buffer medium 163 over the electrode 161 and substrate
62. Buffer medium 163 may comprise a sheet of stainless steel of
from two to three mils thickness or a sheet of polyimide plastic,
such as KAPTON, of approximately the same thickness. A patterned
charge of explosive material 164 is deposited on the upper surface
of buffer medium 163 and, when detonated by any of the detonation
techniques previously discussed, accelerates the electrode 161 down
into the "hills" and "valleys" of the ceramic substrate 162,
forming an explosive bond therebetween.
As with regard to the example illustrated in FIG. 23, spacing
elements (not shown) may be interposed between electrode 161 and
substrate 162, if the surface characteristics of the substrate are
such that a good explosive bond cannot be formed without the use of
such spacing elements. After the detonation has occurred, the
buffer medium 163 may be stripped away, leaving electrode 161
firmly bonded to the substrate. As previously discussed, electrode
161 may be fabricated on the lower surface of buffer medium 163 by
the technique taught in the above-referenced patent application of
M. A. DeAngelo- D. J. Sharp, Ser. No. 719,976, now U.S. Pat. No.
3,562,005.
As shown in FIG. 29, the upper surface of electrode 161 may now be
oxidized by any of several well-known techniques to form an
insulating dielectric layer thereon. Alternatively, the previously
discussed technique illustrated in FIG. 28 may be repeated to
explosively bond an insulating dielectric layer to the electrode
161. Indeed, the buffer medium itself may be left in place for this
purpose; however, the buffer medium may be too thick for most
practical applications and, in that event, a thinner dielectric
layer may be created on the lower surface of the buffer medium,
explosively bonded to the electrode and the buffer medium stripped
away, as previously discussed.
As shown in FIG. 30, the technique used to bond the electrode may
be reiterated to explosively bond a counter electrode to electrode
161 and dielectric layer 166. To that end, a counter electrode 167,
which may be either self-supporting or formed on the lower surface
of a second buffer medium 168, is positioned over, and aligned with
respect to, electrode 161 and dielectric layer 166. The upper
surface of buffer medium 168 is provided with a patterned explosive
charge 169 and, when this charge is detonated, counter electrode
167 is accelerated towards electrode 161 and dielectric layer 166,
forming an explosive bond therebetween.
FIG. 31 illustrates the appearance of the finished product. It is,
of course, feasible to fabricate the counter electrode by means
other than explosive bonding, for example, by conventional
sputtering or deposition procedures. Further, although FIGS. 28 and
30 indicate that the explosive charges 164 and 169 are patterned to
correspond to the underlying electrode 161 and counter electrode
169, respectively, it will be appreciated that the explosive
charges may have a shape which does not exactly correspond to the
underlying electrode and counter electrode. The creation of a
capacitor, or other electronic components, such as inductors,
resistors, etc., by explosive bonding techniques may, of course, be
coupled with the simultaneous deposition of conductive metallic
paths on the same substrate. That is to say, a single large area,
explosive bonding process may be used to simultaneously lay down
thin-film resistors, the electrodes of thin-film capacitors, and
the necessary conductive circuitry to interconnect these devices.
One or two additional explosive bonding steps will bond the
additional circuit elements required so that an entire operating
package, including explosively bonded semiconductor devices may be
manufactured in only two or three processing steps, which contrasts
to the dozens of steps which would be required to manufacture an
equivalent package by conventional techniques.
While my invention has been disclosed in the context of the bonding
of electronic components, such as integrated circuit devices, the
methods and apparatus disclosed herein may be employed to bond
other miniature workpieces, for example, those used in the watch
making, camera, aerospace and scientific industries. More
specifically, my invention is of use in any application where it is
desired to bond a first miniature workpiece to a second workpiece.
One skilled in the art will appreciate that certain aspects of my
invention are also of use in more conventional explosive bonding
and metal working techniques which utilize both primary and
secondary explosives.
It will also be apparent that one skilled in the art may make
various changes and modifications to the methods and apparatus
disclosed herein without departing from the spirit and scope of
this invention.
* * * * *