U.S. patent application number 09/911797 was filed with the patent office on 2001-11-22 for wire bonding method and apparatus, and semiconductor device.
Invention is credited to Shigemura, Tatsuya, Suzuki, Osamu, Taneda, Yukinori, Yamamoto, Noriaki, Yamamura, Hirohisa, Yasukawa, Akio.
Application Number | 20010042925 09/911797 |
Document ID | / |
Family ID | 14988424 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010042925 |
Kind Code |
A1 |
Yamamoto, Noriaki ; et
al. |
November 22, 2001 |
Wire bonding method and apparatus, and semiconductor device
Abstract
A wire bonding method and apparatus implement the flatly thinner
plastic deformation for the joint section of a wire, which has a
diameter ranging 100-600 .mu.m, on its feed side, feed out and
position the flatly deformed wire joint section to a target joint
surface, and join the wire to it by pressing the positioned wire
joint section, with vibration being applied, onto the joint surface
with a ultrasonic wire bonder. A high-power semiconductor device
fabricated based on this scheme has a long life of wire joints.
Inventors: |
Yamamoto, Noriaki;
(Fujisawa-shi, JP) ; Taneda, Yukinori;
(Yokohama-shi, JP) ; Yamamura, Hirohisa;
(Hitachioota-shi, JP) ; Yasukawa, Akio;
(Kashiwa-shi, JP) ; Suzuki, Osamu; (Niihari-gun,
JP) ; Shigemura, Tatsuya; (Hitachinaka-shi,
JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
14988424 |
Appl. No.: |
09/911797 |
Filed: |
July 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09911797 |
Jul 25, 2001 |
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09305448 |
May 6, 1999 |
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6271601 |
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Current U.S.
Class: |
257/784 ;
257/E21.518 |
Current CPC
Class: |
H01L 2224/49111
20130101; H01L 2924/01029 20130101; H01L 2924/2076 20130101; H01L
2924/00014 20130101; H01L 2224/45124 20130101; H01L 2224/48455
20130101; H01L 2224/48472 20130101; H01L 2224/49111 20130101; H01L
24/45 20130101; H01L 2224/85181 20130101; H01L 2224/45015 20130101;
H01L 2924/01006 20130101; H01L 2224/85205 20130101; H01L 2924/01047
20130101; H01L 2924/01079 20130101; H01L 2224/85205 20130101; H01L
2224/48472 20130101; H05K 13/06 20130101; H01L 24/49 20130101; H01L
2224/78313 20130101; H01L 2924/13055 20130101; H01L 2224/49111
20130101; H01L 2224/48472 20130101; H01L 2224/48599 20130101; H01L
2224/45015 20130101; H01L 2224/73265 20130101; H01L 2224/85181
20130101; H01L 2924/01074 20130101; H01L 2224/45124 20130101; H01L
2224/32225 20130101; H01L 2924/1305 20130101; H01L 2224/45124
20130101; H01L 2224/45124 20130101; H01L 2224/45139 20130101; H01L
2224/49175 20130101; H01L 2224/786 20130101; H01L 2924/00014
20130101; H01L 2924/01023 20130101; H01L 2224/851 20130101; H01L
2224/73265 20130101; H01L 2224/49175 20130101; H01L 2224/48227
20130101; H01L 2224/48227 20130101; H01L 2924/00 20130101; H01L
2924/2076 20130101; H01L 2924/00014 20130101; H01L 2924/00
20130101; H01L 2924/2076 20130101; H01L 2924/00 20130101; H01L
2924/2076 20130101; H01L 2224/48227 20130101; H01L 2224/48227
20130101; H01L 2224/45144 20130101; H01L 2924/00015 20130101; H01L
2224/45139 20130101; H01L 2924/00014 20130101; H01L 2924/00
20130101; H01L 2924/00015 20130101; H01L 2224/45124 20130101; H01L
2224/48472 20130101; H01L 2224/48472 20130101; H01L 2924/00
20130101; H01L 2224/32225 20130101; H01L 2924/00 20130101; H01L
2224/48472 20130101; H01L 2924/00012 20130101; H01L 2924/00014
20130101; H01L 2924/00 20130101; H01L 2924/01028 20130101; H01L
2924/00 20130101; H01L 2224/48227 20130101; H01L 2924/00 20130101;
H01L 2924/01014 20130101; H01L 2924/00014 20130101; H01L 2924/00
20130101; H01L 2224/05599 20130101; H01L 2224/48091 20130101; H01L
2924/00 20130101; H01L 2224/85399 20130101; H01L 2924/00 20130101;
H01L 2924/00 20130101; H01L 2224/45124 20130101; H01L 2924/00014
20130101; H01L 2224/85205 20130101; H01L 24/85 20130101; H01L
2224/45015 20130101; H01L 2924/1305 20130101; H01L 2224/48091
20130101; H01L 2224/45015 20130101; H01L 2924/19043 20130101; H01L
2224/49175 20130101; H01L 2224/85951 20130101; H01L 2924/01014
20130101; H01L 2924/01028 20130101; H01L 2224/45144 20130101; H01L
2224/45144 20130101; H01L 2224/48091 20130101; H01L 2224/49111
20130101; H01L 2224/85205 20130101; H01L 2924/01013 20130101; H01L
24/78 20130101; H01L 2224/45144 20130101; H01L 2224/48699 20130101;
H01L 2224/48227 20130101; H01L 24/48 20130101; H01L 2924/014
20130101; H01L 2224/45139 20130101; H01L 2924/01005 20130101; H01L
2924/00014 20130101 |
Class at
Publication: |
257/784 |
International
Class: |
H01L 029/40; H01L
023/52; H01L 023/48 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 1998 |
JP |
10-128586 |
Claims
What is claimed is:
1. A wire bonding method comprising the steps of: implementing the
flatly thinner plastic deformation for the joint section of a wire
on the feed side thereof; and joining the wire to a target joint
surface by feeding out and positioning the flatly deformed wire
joint section processed by said wire deforming step to the target
joint surface, and pressing the positioned wire joint section, with
vibration being applied, onto the target joint surface with a
ultrasonic wire bonder.
2. A wire bonding method according to claim 1, wherein the wire has
a diameter ranging from 100 to 600 .mu.m.
3. A wire bonding method according to claim 1, wherein the wire is
made of aluminum or aluminum alloy.
4. A wire bonding method according to claim 1, wherein said wire
deforming step implements the flatly thinner plastic deformation
for the joint section of the wire at a degree of 2 or more in terms
of deformation factor W/D, where W is the width of deformed wire at
the joint section and D is the original wire diameter.
5. A wire bonding method according to claim 1, wherein said wire
joining step joins the joint section of the wire to the target
joint surface at a deformation factor W/D of 2 or more, where W is
the width of deformed wire at the joint section and D is the
original wire diameter.
6. A wire bonding method according to claim 1, wherein said wire
deforming step implements the flatly thinner plastic deformation
for the joint section of the wire at a degree in the range from 4
to 6 in terms of deformation factor W/D, where W is the width of
deformed wire at the joint section and D is the original wire
diameter.
7. A wire bonding method according to claim 1, wherein said wire
joining step joins the joint section of the wire to the target
joint surface at a deformation factor W/D in the range from 4 to 6,
where W is the width of deformed wire at the joint section and D is
the original wire diameter.
8. A wire bonding method comprising the steps of: implementing the
flatly thinner plastic deformation for the joint section of a wire
on the feed side thereof to match with an intended length of wire
loop; and joining the wire to a target joint surface by feeding out
and positioning the flatly deformed wire joint section processed by
said wire deforming step to the target joint surface, and pressing
the positioned wire joint section, with vibration being applied,
onto the target joint surface with a ultrasonic wire bonder.
9. A wire bonding method according to claim 8, wherein the wire has
a diameter ranging from 100 to 600 .mu.m.
10. A wire bonding method according to claim 8, wherein the wire is
made of aluminum or aluminum alloy.
11. A wire bonding method according to claim 8, wherein said wire
deforming step implements the flatly thinner plastic deformation
for the joint section of the wire at a degree of 2 or more in terms
of deformation factor W/D, where W is the width of deformed wire at
the joint section and D is the original wire diameter.
12. A wire bonding method according to claim 8, wherein said wire
joining step joins the joint section of the wire to the target
joint surface at a deformation factor W/D of 2 or more, where W is
the width of deformed wire at the joint section and D is the
original wire diameter.
13. A wire bonding method according to claim 8, wherein said wire
deforming step implements the flatly thinner plastic deformation
for the joint section of the wire at a degree in the range from 4
to 6 in terms of deformation factor W/D, where W is the width of
deformed wire at the joint section and D is the original wire
diameter.
14. A wire bonding method according to claim 8, wherein said wire
joining step joins the joint section of the wire to the target
joint surface at a deformation factor W/D in the range from 4 to 6,
where W is the width of deformed wire at the joint section and D is
the original wire diameter.
15. A wire bonding method comprising the steps of: implementing the
flatly thinner plastic deformation for a wire; feeding out and
positioning the flatly deformed wire joint section processed by
said wire deforming step to a target joint surface, and holding the
wire; and joining the wire to the target joint surface by releasing
the hold of the wire and pressing the positioned wire joint
section, with vibration being applied, onto the target joint
surface with a ultrasonic wire bonder.
16. A wire bonding apparatus comprising: means of implementing the
flatly thinner plastic deformation for the joint section of a wire
on the feed side thereof; and means of joining the wire to a target
joint surface by feeding out and positioning the flatly deformed
wire joint section processed by said wire deforming means to the
target joint surface, and pressing the positioned wire joint
section, with vibration being applied, onto the target joint
surface with a ultrasonic wire bonder.
17. A wire bonding apparatus according to claim 16, wherein said
wire deforming means includes an upper mold and a lower mold, with
one mold being moved to another mold by means of a driving device
so that the wire is deformed.
18. A wire bonding apparatus according to claim 17, wherein said
one mold has the formation of a V-shaped groove and has slope
sections at the wire inlet and outlet thereof.
19. A wire bonding apparatus according to claim 17, wherein said
one mold has the formation of a flat groove and has slope sections
at the wire inlet and outlet thereof.
20. A wire bonding apparatus according to claim 16, wherein said
joining means includes a wire press section having a V-shaped
groove.
21. A wire bonding apparatus according to claim 16, wherein said
joining means includes a wire press section having a flat
groove.
22. A wire bonding apparatus according to claim 16, wherein the
wire has a diameter ranging from 100 to 600 .mu.m.
23. A wire bonding apparatus according to claim 16, wherein said
wire deforming means implements the flatly thinner plastic
deformation for the joint section of the wire at a degree of 2 or
more in terms of deformation factor W/D, where W is the width of
deformed wire at the joint section and D is the original wire
diameter.
24. A wire bonding apparatus according to claim 16, wherein said
wire deforming means implements the flatly thinner plastic
deformation for the joint section of the wire at a degree in the
range from 4 to 6 in terms of deformation factor W/D, where W is
the width of deformed wire at the joint section and D is the
original wire diameter.
25. A semiconductor device having a wire joint surface of
semiconductor chip, to which is joined a wire by ultrasonic wire
bonding with the prior rendition of flatly thinner plastic
deformation for the joint section of the wire at a degree of 2 or
more in terms of deformation factor W/D, where W is the width of
deformed wire at the joint section and D is the original wire
diameter.
26. A semiconductor device having a wire joint surface of
semiconductor chip, to which is joined a wire by ultrasonic wire
bonding with the prior rendition of flatly thinner plastic
deformation for the joint section of the wire at a degree in the
range from 4 to 6 in terms of deformation factor W/D, where W is
the width of deformed wire at the joint section and D is the
original wire diameter.
27. A semiconductor device according to claim 25, wherein said wire
diameter D ranges from 100 to 600 .mu.m.
28. A semiconductor device according to claim 26, wherein said wire
diameter D ranges from 100 to 600 .mu.m.
29. A semiconductor device according to claim 25, wherein the wire
is made of aluminum or aluminum alloy.
30. A semiconductor device according to claim 26, wherein the wire
is made of aluminum or aluminum alloy.
31. A semiconductor device comprising a high-power semiconductor
device which includes: a positive terminal and an output terminal
which are fixed on an insulation substrate; a first power element
and a second diode which are joined to said positive terminal, and
a second power element and a first diode which are joined to said
output terminal; and a negative terminal which is fitted on said
insulation substrate through an insulator, said first power element
having its emitter electrode connected to said output terminal by
wire bonding, said second diode having its cathode electrode
connected to said output terminal by wire bonding, said second
power element having its emitter electrode connected to said
negative terminal by wire bonding, and said first diode having its
anode electrode connected to said negative terminal by wire
bonding, wherein wires to be joined by ultrasonic wire bonding to
the joint surfaces of said first and second power elements and said
first and second diodes are rendered at the joint sections thereof
the flatly thinner plastic deformation at a degree of 2 or more in
terms of deformation factor W/D, where W is the width of deformed
wire at the joint section and D is the original wire diameter.
32. A semiconductor device comprising a high-power semiconductor
device which includes: a positive terminal and an output terminal
which are fixed on an insulation substrate; a first power element
and a second diode which are joined to said positive terminal, and
a second power element and a first diode which are joined to said
output terminal; and a negative terminal which is fitted on said
insulation substrate through an insulator, said first power element
having its emitter electrode connected to said output terminal by
wire bonding, said second diode having its cathode electrode
connected to said output terminal by wire bonding, said second
power element having its emitter electrode connected to said
negative terminal by wire bonding, and said first diode having its
anode electrode connected to said negative terminal by wire
bonding, wherein wires to be joined by ultrasonic wire bonding to
the joint surfaces of said first and second power elements and said
first and second diodes are rendered at the joint sections thereof
the flatly thinner plastic deformation at a degree in the range
from 4 to 6 in terms of deformation factor W/D, where W is the
width of deformed wire at the joint section and D is the original
wire diameter.
33. A semiconductor device according to claim 31, wherein said wire
diameter D ranges from 100 to 600 .mu.m.
34. A semiconductor device according to claim 32, wherein said wire
diameter D ranges from 100 to 600 .mu.m.
35. A semiconductor device according to claim 31, wherein the wire
is made of aluminum or aluminum alloy.
36. A semiconductor device according to claim 32, wherein the wire
is made of aluminum or aluminum alloy.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a wire bonding method and
apparatus for interconnecting electronic parts by using
electrically conductive wires, and to a semiconductor device.
Particularly, the inventive method and apparatus are applied
suitably to semiconductor devices which are intended for high-speed
switching of large currents in automobile equipment controllers,
electric-car drive controllers and other vehicle-installed motor
controllers.
[0003] 2. Description of the Prior Art
[0004] In the manufacturing process of semiconductor devices which
include multiple semiconductor chips and electronic parts, a scheme
of wire bonding is used for the electrical connection between the
electrodes of semiconductor chips and electronic parts and between
the terminals of electronic parts.
[0005] A typical conventional wire bonding apparatus will be
explained first with reference to FIG. 14. FIG. 14 is a side view
of the conventional wire bonding apparatus. This wire bonding
apparatus is designed to feed a wire 101, which is supplied from a
bobbin (not shown), to the groove of wire press section 112 of a
bonding tool 111 by way of a through-hole 115 formed in a horn 110
and a gap of clamp section of a wire clamp mechanism 120.
[0006] With ultrasonic vibration being applied to the bonding tool
111 which is fixed to the tip section of the horn 110, the wire 101
is pressed onto the electrode of a semiconductor chip 102 as one
part of connection so that the wire 101 is joined to it, and next
the wire 101 is fed and brought by the bonding tool 111 to the
terminal 104 of another electronic part, e.g., a resistor, as
another part of connection and joined to it in the same manner.
[0007] The wire clamp mechanism 120 is located between the wire
press section 112 of the bonding tool 111 and the through-hole 115
of the horn 110, and it serves to hold and guide the wire 101 when
it is fed out. The bonding tool 111 and horn 110 are supported on a
vertical moving mechanism and horizontal moving table so that they
can move vertically and horizontally relative to the semiconductor
chip 102 and electronic part.
[0008] Automobile equipment controllers and electric-car drive
controllers are required to be made much smaller in size and
weight. The drive controller incorporates semiconductor devices
which implements high-speed switching of large currents for
producing a.c. power for driving motors by being supplied with
power from such a d.c. power source as battery.
[0009] Electronic components have their operating currents
increasing to match with the trend of higher-power drive
controllers, and therefore wires of large diameters are used for
the electrical connection between semiconductor chips and between
semiconductor chips and electronic parts of semiconductor devices.
For wires of large diameters, aluminum wires which are inexpensive
and light are used, instead of wires having higher electrical
conductivity that mainly consist of expensive gold. Aluminum wires
are thicker due to the lower electrical conductivity than gold
wires, and aluminum wires with diameters of 100-600 .mu.m are
necessary for high-power semiconductor devices.
[0010] Semiconductor devices used in automobile equipment
controllers and electric-car drive controllers are required to be
durable against severe heat cycles and power cycles thereby to last
long, in addition to the demand of compactness and light weight. In
order to meet these requirements, it is necessary to improve the
strength of wire joints.
[0011] There is a limit in widening the joint area based merely on
pressing the wire 101 having a circular cross section onto the
planar target joint surface, and there is also a limit in improving
the strength and life of joints based merely on the application of
ultrasonic vibration to the limited joint area. Specifically, the
conventional wire bonding scheme works for joining by pressing the
wire 101 having a circular cross section onto a planar target joint
surface so that the wire is deformed, and the pressing force needs
to be increased progressively to overcome the increasing resistance
of deformation.
[0012] Accordingly, in order for the conventional wire bonding
scheme to improve the strength and life of wire joints by raising
the degree of deformation of the wire 101 while retaining the
mechanical strength of the deformed section of the wire 101, it is
necessary to increase the ultrasonic output for the metallic joint
process thereby to increase the pressing force of the wire 101.
However, an excessive pressing force by the increased ultrasonic
output can result in the breakage of the electronic part or
semiconductor chip 102 having the target joint surface.
[0013] On this account, conventionally, there is a limit in
widening the joint area, and thus there is a limit in improving the
strength and life of wire joints.
SUMMARY OF THE INVENTION
[0014] The present invention is intended to overcome the foregoing
prior art deficiency, and its prime object is to provide a wire
bonding method and apparatus capable of accomplishing wire joints
which are durable against severe heat cycles and power cycles
thereby to have a long life, and are useful for semiconductor
devices which implement high-speed switching of large currents.
[0015] Another object of the present invention is to provide a
high-power semiconductor device which is smaller in size and weight
and durable against severe heat cycles and power cycles thereby to
have a long life based on the enhanced strength of wire joints.
[0016] In order to achieve the above objective, the inventive wire
bonding method comprises a step of implementing the flatly thinner
plastic deformation for the joint section of a wire on the feed
side thereof, and a step of joining the wire to a target joint
surface by feeding out and positioning the flatly deformed wire
joint section processed by the wire deforming step to the target
joint surface, and pressing the positioned wire joint section, with
vibration being applied, onto the target joint surface with a
ultrasonic wire bonder. Preferred wire diameters range from 100 to
600 .mu.m.
[0017] Alternatively, the inventive wire bonding method comprises a
step of implementing the flatly thinner plastic deformation for the
joint section of a wire on the feed side thereof to match with the
intended length of wire loop, and a step of joining the wire to a
target joint surface by feeding out and positioning the flatly
deformed wire joint section processed by the wire deforming step to
the target joint surface, and pressing the positioned wire joint
section, with vibration being applied, onto the target joint
surface with a ultrasonic wire bonder. Preferred wire diameters
range from 100 to 600 .mu.m.
[0018] Wires used for the inventive wire bonding method are
preferably made of aluminum or aluminum alloy.
[0019] Preferably, the wire deforming step of the inventive wire
bonding method implements the flatly thinner plastic deformation
for the joint section of the wire at a degree of 2 or more in terms
of deformation factor W/D, where W is the width of deformed wire at
the joint section and D is the original wire diameter.
[0020] Preferably, the wire joining step of the inventive wire
bonding method joins the joint section of the wire to the target
joint surface at a deformation factor W/D of 2 or more, where W is
the width of deformed wire at the joint section and D is the
original wire diameter.
[0021] More preferably, the wire joining step of the inventive wire
bonding method joins the joint section of the wire to the target
joint surface at a deformation factor W/D in the range from 4 to 6,
where W is the width of deformed wire at the joint section and D is
the original wire diameter.
[0022] In order to achieve the above objective, the inventive wire
bonding apparatus comprises means of implementing the flatly
thinner plastic deformation for the joint section of a wire on the
feed side thereof, and means of joining the wire to a target joint
surface by feeding out and positioning the flatly deformed wire
joint section processed by the wire deforming means to the target
joint surface, and pressing the positioned wire joint section, with
vibration being applied, onto the target joint surface with a
ultrasonic wire bonder.
[0023] The wire deforming means of the inventive wire bonding
apparatus includes an upper mold and a lower mold, with one mold
being moved to another mold by means of a driving device so that
the wire is deformed. Preferably, the one mold has the formation of
a V-shaped groove and has slope sections at its wire inlet and
outlet. Preferably, the one mold has the formation of a flat groove
and has slope sections at its wire inlet and outlet. Preferably,
the joining means includes a wire press section having a V-shaped
groove or a flat groove.
[0024] The inventive wire bonding apparatus comprises means of
implementing the flatly thinner plastic deformation for the joint
section of a wire, which has a diameter in the range from 100 to
600 .mu.m, on the feed side thereof, and means of joining the wire
to a target joint surface by feeding out and positioning the flatly
deformed wire joint section processed by the wire deforming means
to the target joint surface, and pressing the positioned wire joint
section, with vibration being applied, onto the target joint
surface with a ultrasonic wire bonder.
[0025] In order to achieve the above objective, the inventive
semiconductor device has a wire joint surface of semiconductor
chip, to which is joined a wire by ultrasonic wire bonding with the
rendition of flatly thinner plastic deformation for the joint
section of the wire at a degree of 2 or more in terms of
deformation factor W/D, where W is the width of deformed wire at
the joint section and D is the original wire diameter.
[0026] Alternatively, the inventive semiconductor device has a wire
joint surface of semiconductor chip, to which is joined a wire by
ultrasonic wire bonding with the rendition of flatly thinner
plastic deformation for the joint section of the wire at a degree
in the range from 4 to 6 in terms of deformation factor W/D, where
W is the width of deformed wire at the joint section and D is the
original wire diameter.
[0027] Preferred wire diameters D for these semiconductor devices
range from 100 to 600 .mu.m. Wires used for these semiconductor
devices are preferably made of aluminum or aluminum alloy.
[0028] The inventive semiconductor device comprises a high-power
semiconductor device, which includes a positive terminal and an
output terminal which are fixed on an insulation substrate, a first
power element and a second diode which are joined to the positive
terminal, and a second power element and a first diode which are
joined to the output terminal, and a negative terminal which is
fitted on the insulation substrate through an insulator, with the
first power element having its emitter electrode connected to the
output terminal by wire bonding, the second diode having its
cathode electrode connected to the output terminal by wire bonding,
the second power element having its emitter electrode connected to
the negative terminal by wire bonding, and the first diode having
its anode electrode connected to the negative terminal by wire
bonding, wherein wires to be joined by ultrasonic wire bonding to
the joint surfaces of the first and second power elements and the
first and second diodes are rendered at the joint sections thereof
the flatly thinner plastic deformation at a degree of 2 or more in
terms of deformation factor W/D, where W is the width of deformed
wire at the joint section and D is the original wire diameter.
[0029] Alternatively, the inventive semiconductor device comprises
a high-power semiconductor device, which includes a positive
terminal and an output terminal which are fixed on an insulation
substrate, a first power element and a second diode which are
joined to the positive terminal, and a second power element and a
first diode which are joined to the output terminal, and a negative
terminal which is fitted on the insulation substrate through an
insulator, with the first power element having its emitter
electrode connected to the output terminal by wire bonding, the
second diode having its cathode electrode connected to the output
terminal by wire bonding, the second power element having its
emitter electrode connected to the negative terminal by wire
bonding, and the first diode having its anode electrode connected
to the negative terminal by wire bonding, wherein wires to be
joined by ultrasonic wire bonding to the joint surfaces of the
first and second power elements and the first and second diodes are
rendered at the joint sections thereof the flatly thinner plastic
deformation at a degree in the range from 4 to 6 in terms of
deformation factor W/D, where W is the width of deformed wire at
the joint section and D is the original wire diameter.
[0030] Preferred wire diameters D for these high-power
semiconductor devices range from 100 to 600 .mu.m. Wires used for
these high-power semiconductor devices are preferably made of
aluminum or aluminum alloy.
[0031] According to the inventive wire bonding method and
apparatus, it becomes possible to increase the joint area between
the wire and the target joint surface without imposing an excessive
ultrasonic output, pressing force and their application time length
at the wire joining process, whereby it is possible to manufacture
electronic components and semiconductor devices which are enhanced
in the strength of wire joints and durable against severe heat
cycles and power cycles thereby to have a long life.
[0032] The inventive wire bonding method and apparatus implement
the prior wire deformation, so that the ultrasonic output, pressing
force and their application time length can be reduced at the wire
joining process, whereby it becomes possible to prevent the
breakage of electronic parts including semiconductor chips and
eventually manufacture reliable electronic components and
semiconductor devices.
[0033] These and other features and advantages of the present
invention will become more apparent from the following description
of preferred embodiments taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a plan view showing an embodiment of high-power
semiconductor device to which the inventive wire bonding method is
applied suitably;
[0035] FIG. 2 is a cross-sectional view taken along the line X-X of
FIG. 1;
[0036] FIG. 3 is a schematic diagram showing the principal portion
of the high-power semiconductor device shown in FIG. 1;
[0037] FIGS. 4A, 4B and 4C are diagrams used to explain the
improved strength and life of wire joints of the inventive
semiconductor device, of which FIG. 4A is a plan view of a wire,
FIG. 4B is a side view of the wire and electrode, and FIG. 4C is a
cross-sectional view taken along the line A-A of FIG. 4B;
[0038] FIG. 5 is a brief side view of a wire bonding apparatus
based on a first embodiment of this invention;
[0039] FIG. 6A is a cross-sectional view of the apparatus used to
explain the wire pre-forming mechanism shown in FIG. 5, and FIG. 6B
is a cross-sectional view taken along the line C-C and seen along
the direction D of FIG. 6A;
[0040] FIG. 7 is a brief perspective view of a wire bonding
apparatus based on a second embodiment of this invention;
[0041] FIGS. 8A and 8C are cross-sectional views of the apparatus
used to explain the wire pre-forming mechanisms, and FIGS. 8B and
8D are side views of the wire press section at the tip of the
respective wire bonding tools;
[0042] FIGS. 9A, 9B and 9C are partially cross-sectional side views
of the inventive wire bonding apparatus used to explain the first
operation;
[0043] FIGS. 10A and 10B are side views of the inventive wire
bonding apparatus used to explain the second operation;
[0044] FIG. 11A is a partially cross-sectional perspective view
showing the joint of the wire joint section and target joint
surface based on this invention, and FIG. 11B is a cross-sectional
view taken along the line B-B of FIG. 11A;
[0045] FIG. 12 is a characteristic graph showing the relation
between the forming pressure exerted on a wire and the resulting
deformation factor;
[0046] FIG. 13 is a characteristic graph showing the joint life of
aluminum wire attributable to power cycles and the forming pressure
plotted against the ratio of the inventive wire thickness to the
conventional wire thickness; and
[0047] FIG. 14 is a side view of the conventional wire bonding
apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0048] Embodiments of the inventive wire bonding method and
apparatus and semiconductor device will be explained with reference
to the drawings.
[0049] FIG. 1 is a plan view of a high-power semiconductor device
based on an embodiment of this invention, FIG. 2 is a
cross-sectional view taken along the line X-X of FIG. 1, and FIG. 3
is a schematic diagram showing the principal portion of this
semiconductor device.
[0050] This semiconductor device is intended for high-speed
switching of large currents for producing a.c. power for driving a
motor by being supplied with power from such a d.c. power source as
battery, as disclosed in Japanese Published Unexamined Patent
Application No. Hei 9-102578.
[0051] In FIG. 1 through FIG. 3, a frame-shaped case 12 is fixed to
an insulation substrate 10 which is made of aluminum nitride or the
like. The insulation substrate 10 has on its rear side the
attachment of a heat sink plate 90.
[0052] A positive terminal (connecting conductor) 20, output
terminal 22 and negative terminal 24 are made of a material having
a high electrical conductivity, such as copper or aluminum, and
dimensioned so as to conduct a certain value of current at a low
power loss. The positive terminal 20 and output terminal 22 are
fixed to the insulation substrate 10 of aluminum nitride or the
like by means of soldering of good heat dissipation or silver
brazing.
[0053] First power switching elements 30A and 30B such as IGBT
(Insulated Gate Bipolar Transistor) chips and second diodes 42A and
42B are soldered to the positive terminal 20, and second power
switching elements 32A and 32B such as IGBT chips and first diodes
40A and 40B are soldered to the output terminal 22. The first power
switching elements 30A and 30B have their emitter electrodes bonded
to the output terminal 22 through wires 50A1 and 50A2, and the
second diodes 42A and 42B have their cathode electrodes bonded to
the output terminal 22 through wires 50A3 and 50A4.
[0054] A negative terminal 24 is fixed on column-shaped insulators
60A-60F over the first power switching elements 30A and 30B and
second diodes 42A and 42B in parallel to the positive terminal 20.
The second power switching elements 32A and 32B have their
collector electrodes bonded to the negative terminal 24 through
wires 50B1 and 50B2, and the first diodes 40A and 40B have their
cathode electrodes bonded to the negative terminal 24 through wires
50B3 and 50B4.
[0055] On the insulation substrate 10, there is attached a terminal
pad 70, on which gate resistors 74A and 74B are fixed. The gate
resistors 74A and 74B are bonded to the base electrodes (formed of
a material such as silicon) of the first power switching elements
30A and 30B of IGBTs or the like through wires 78A1 and 78B1,
respectively. Further attached on the insulation substrate 10 is
another terminal pad 72, on which gate resistors 76A and 76B are
fixed. The gate resistors 76A and 76B are bonded to the base
electrodes of the second power switching elements 32A and 32B of
IGBTS or the like through wires 78A2 and 78B2, respectively.
[0056] In FIG. 2, indicated by 80 and 82 are solder for connecting
the first power switching element 30A to the positive terminal 20
and connecting the second power switching element 32A to the output
terminal 22, respectively.
[0057] The semiconductor device shown in FIG. 1 and FIG. 2 has a
circuit arrangement as shown in FIG. 3. Common reference numerals
are used throughout these figures. Specifically, the second diode
42A is connected between the positive terminal 20 and the output
terminal 22 by the wire 50A3, and further connected between these
terminals are the first power switching elements 30A and 30B by the
wires 50A1 and 50A2, respectively, and the second diode 42B by the
wire 50A4. The first diode 40A is connected between the output
terminal 22 and the negative terminal 24 by the wire 50B3, and
further connected between these terminals are the second power
switching elements 32A and 32B by the wires 50B1 and 50B2,
respectively, and the first diode 40B by the wire 50B4.
[0058] The circuit receives d.c. power on the positive terminal 20
and negative terminal 24, and produces a.c. power on the output
terminal 22.
[0059] The wires 50A1-50A4, 50B1-50B4, etc. are connected by wire
bonding. Because of the limited current capacity of a single wire
for the connection between a power switching element or diode and
other electronic part, multiple wires are generally used in
parallel depending on the value of current flowing out of the power
switching element or diode.
[0060] The foregoing circuit arrangement constitutes a
semiconductor device which implements high-speed switching of large
currents for driving a motor or the like by being supplied with
power from a d.c. power source.
[0061] The wires 50A1-50A4, 50B1-50B4, 78A1, 78A2, 78B1 and 78B2
which conduct large currents are made of aluminum or aluminum alloy
which includes silicon, nickel, etc. In case the electrical
conductivity is major concern, wires of gold, silver or their
alloys may be used.
[0062] In semiconductor devices in which electrodes of
semiconductor chips and electronic parts are connected by wire
bonding, the current flowing through each wire brings about the
peel-off of joint between the wire and electrode, resulting in the
heat concentration. The concentrated heat aggravates the peel-off
of the joint. Therefore, it is required to prolong the device life
attributable to power cycles which is dependent on the peel-off
life of wire joints.
[0063] Next, the breakage of wire joint caused by power cycles will
be explained with reference to FIGS. 4A-4C. FIG. 4A is a plan view
of a wire, FIG. 4B is a side view of the wire and electrode, and
FIG. 4C is a cross-sectional view taken along the line A-A of FIG.
4B.
[0064] The wire 101 is rendered the flatly thinner plastic
deformation in its portion to be joined to the electrode 102A so
that it has an increased joint area, as shown in FIGS. 4A and 4B.
With a ultrasonic vibration being applied, for example, the
deformed joint section of the wire 101 is joined by wire bonding to
the electrode 102A of a semiconductor chip or electronic part.
[0065] When a large current flows through the joint repeatedly,
there emerges a crack 103 around the joint 100 between the wire 101
(50A1-50A4, 50B1-50B4, 78A1, 78A2, 78B1 and 78B2) and the electrode
102A as shown in FIG. 4B. The crack 103 progresses to reduce the
connection area, resulting in an increased resistance of the joint
100 and eventually in the defective connection. Provided that the
speed of progress of crack (the amount of progress of crack in a
power cycle: da/dn) is virtually constant throughout the life, the
life N of the joint 100 is formulated as follows.
N=(bo-bf)/(da/dn)/2 (1)
[0066] where bo and bf are the original and final widths of the
joint 100 as shown in FIG. 4C, and da/dn is the rate of progress of
the amount of crack a with respect to the number of times of
current conduction n.
[0067] In the context of fracture mechanics, the term da/dn is
dependent on the fracture mechanics parameter .DELTA.J as
follows.
da/dn=C.sub.1.multidot.(.DELTA.J.sup.m) (2)
[0068] where C.sub.1 and m are constants.
[0069] When the wire 101 in its portion of the joint 100 is modeled
to be a film, the .DELTA.J is proportional to the wire thickness H
(shown in FIG. 4C) at the joint 100 as follows.
.DELTA.J=(.alpha..multidot..DELTA.T).sup.2.multidot.E.multidot.H/(2-2.upsi-
lon.) (3)
[0070] where .DELTA..alpha. is the difference of linear expansion
coefficients between the wire 101 and the power switching element
102 (30A, 30B, 32A, 32B, 40A, 40B, 42A and 42B), .DELTA.T is the
width of temperature variation, E is the Young's modulus of the
wire 101, and .upsilon. is the Poisson's ratio of the wire 101.
[0071] Based on the formulas (1) and (3), the influence of H on N
is assessed by the following formula.
N=C.sub.2/H.sup.m (4)
[0072] where C.sub.2 is a constant.
[0073] In the case of the wire 101 of pure aluminum, m takes a
value of around 1.4.
[0074] Accordingly, in order to enhance the strength and life of
the joint 100, it is suggested to reduce the wire thickness H, or,
in other words, increase the deformation factor W/D, where W is the
width of deformed wire and D is the original wire diameter which is
determined from the current capacity. The wire 101 of pure
aluminum, which is inferior to gold in electrical conductivity,
needs to be thicker than a gold wire, and its diameter D ranges
from 100 to 600 .mu.m for the foregoing high-power semiconductor
device, for example.
[0075] Next, embodiments of the inventive wire bonding method and
apparatus will be explained with reference to FIG. 5 through FIG.
7. FIG. 5 is a brief side view of the wire bonding apparatus based
on the first embodiment of this invention.
[0076] This wire bonding apparatus includes a horn 110, on which is
attached a bonding tool 111 having a wire press section 112 and
functioning to press a wire 101 with a diameter of the 100-600
.mu.m range, with vibration being applied, onto a target joint
surface, e.g., the electrode 102A of semiconductor device, a wire
pre-forming mechanism 140 which is located between the wire press
section 112 of the bonding tool 111 and the through-hole 115 formed
in the horn 110 and adapted to act the flatly thinner deformation
on the wire 101 which is supplied from a supply reel (not shown)
and fed through the through-hole 115 of the horn 110, a wire clamp
mechanism 120 which clamps the wire 101, and a stage 160 which
mounts an object of bonding 105, i.e., the semiconductor
device.
[0077] On the figure of bonding object 105, indicated by 102 is a
semiconductor chip which represents the power switching elements
30A, 30B, 32A, 32B, 40A, 40B, 42A and 42B, and 104 is a terminal
which represents the output terminal 22 and negative terminal
24.
[0078] This wire bonding apparatus is characterized in the
disposition, on the wire feed-through path, of the wire pre-forming
mechanism 140 which deforms in advance the wire 101 of aluminum or
aluminum alloy which includes silicon, nickel, etc. and with a
diameter of the 100-600 .mu.m range at a degree of deformation
factor W/D of around 2.0 or more (preferably 2.5 or more, or more
preferably in the range from 4 to 6).
[0079] FIG. 6A is a cross-sectional view of the apparatus used to
explain the wire pre-forming mechanism 140 shown in FIG. 5, and
FIG. 6B is a cross-sectional view taken along the line C-C and seen
along the direction D of FIG. 6A.
[0080] This wire pre-forming mechanism 140 includes molds 141 and
142 located below and above the wire 101, as shown in FIGS. 6A and
6B. The lower mold 141 and upper mold 142 are supported at the
positions on both sides of the horn 110 so that they can move
independently of the horn 110, as shown in FIG. 7 of another wire
pre-forming mechanism 140A which will be explained later.
[0081] A cam 145, which is movable to the right and left on the
drawing by a formation driving device 144, is disposed in contact
with the upper mold 142 as shown in FIG. 6A. The driving device 144
moves the cam 145 to the left on the drawing so that the upper mold
142 is pushed down toward the fixed lower mold 141, thereby
pressing the wire 101, which is then deformed in its cross section
in accordance with the shape of the mold. The wire 101 is deformed
to meet a deformation factor W/D of around 2.0 or more, or
preferably 2.5 or more, or more preferably in the range from 4 to
6.
[0082] In this embodiment, the lower mold 141 has a planar wire
contact surface and the upper mold 142 has its wire contact surface
formed to include a V-shaped profile, so that an excessive tensile
stress which can break the wire 101 does not emerge in the wire
center. This V-shaped profile of the upper mold 142 also serves to
guide the wire 101 in its longitudinal and lateral directions. In
addition, the upper mold 142 has its wire inlet and outlet formed
to have rounded slope sections 149, so that the shearing stress
acting on the ends of deformation section of the wire 101 is
alleviated.
[0083] A variety of variant versions of the wire pre-forming
mechanism 140 are conceivable to carry out the flatly thinner
deformation of the wire 101 while avoiding a concentrated stress.
Shown in FIG. 7 is a variant mechanism as an example.
[0084] Using the wire pre-forming mechanism 140, when the wire 101
having a diameter of 300 .mu.m, for example, is deformed at a
deformation factor W/D of 2.0, it will become to have a thickness H
of around 120 .mu.m. The wire pre-forming mechanism 140 of this
embodiment can be adjusted independently of the horn 110, so that
the deformation factor W/D can be set arbitrarily. Specifically,
when the wire 101 having a diameter of 300 .mu.m, the thickness H
will be around 100 .mu.m by the process at W/D=2.5, it will be
around 80 .mu.m by the process at W/D=3.0, it will be around 70
.mu.m by the process at W/D=3.5, it will be around 60 .mu.m by the
process at W/D=4.0, it will be around 50 .mu.m by the process at
W/D=5.0, and it will be around 40 .mu.m at W/D=6.0.
[0085] For a wire diameter of 300 .mu.m, when the deformation
factor W/D is set in the range from 4 to 6 so that the resulting
thickness H will be around 40 to 60 .mu.m, the above formula (4)
suggests the significant improvement of the strength and life of
the joint 100.
[0086] Although the wire pre-forming mechanism 140 of the foregoing
embodiment uses the cam 145 to move the upper mold 142, variant
versions include a swing motion mechanism as shown in FIG. 7 and an
up/down motion mechanism.
[0087] FIG. 7 is a brief perspective view of the wire bonding
apparatus based on the second embodiment of this invention. The
wire pre-forming mechanism 140A of this embodiment includes a lower
mold 141A which is fixed obliquely to a side frame 161, an upper
mold 142A which is fixed on a shaft 162 pivoted on the side frame
161 so that the upper mold 142A can have a swing motion, and a
swing drive device 144A including a servo motor for driving the
upper mold 142A to swing about the shaft 162.
[0088] The lower mold 141A and upper mold 142A have the same
formation on their wire contact surfaces as those of the lower mold
141 and upper mold 142 of the previous embodiment shown in FIGS. 6A
and 6B.
[0089] In operation, in contrast to the embodiment shown in FIG. 6A
in which the driving device 144 moves the cam 145 straight so that
the upper mold 142 is pushed down thereby to press the wire 101 to
deform, the embodiment shown in FIG. 7 is designed such that the
swing drive device 144A directly drives the upper mold 142A to
swing thereby to press the wire 101 to deform.
[0090] According to the foregoing embodiments, in which the wire
pre-forming mechanisms 140 and 140A are employed for implementing
the flatly thinner deformation of the wire 101, it is possible to
shape the wire press section 112 of the bonding tool 111 to the
upper molds 142 and 142A, so that the joint area becomes wide
enough for stable wire bonding to take place.
[0091] FIGS. 8A and 8C are cross-sectional views of two embodiments
of wire pre-forming mechanism, and FIGS. 8B and 8D are side views
of the wire press section located at the tip of the wire bonding
tool. Specifically, FIGS. 8A and 8C show a V-shaped groove 142a and
flat groove 142b formed on the upper mold 142 (142A) of the
pre-forming mechanism 140 (140A), and FIGS. 8B and 8D show a
V-shaped groove 112a and flat groove 112b formed on the wire press
section 112 of the bonding tool 111. Namely, the bonding tool 111
which presses the wire 101 (not shown) has its wire press section
112 at the tip rendered the virtually same formation of the
V-shaped groove 112a or flat groove 112b as the groove 142a or 142b
of the upper mold 142 (142A) of the pre-forming mechanism 140
(140A), so that the joint area becomes wide enough for stable wire
bonding to take place.
[0092] Next, the operation of the inventive wire bonding apparatus
equipped with the wire pre-forming mechanism 140 (140A) will be
explained with reference to FIGS. 9A-9C and FIGS. 10A and 10B.
[0093] FIGS. 9A-9C are partially cross-sectional side views of the
inventive wire bonding apparatus used to explain the first
operation. The wire clamp mechanism 120 is adapted to hold the wire
101 and allow it to run in its longitudinal direction. The wire
pre-forming mechanism 140 (140A) is located on the wire feed path
by being aligned to the wire clamp mechanism 120.
[0094] First, the operation of wire bonding apparatus for joining
the wire 101 to the first target joint surface based on the
inventive wire bonding method will be explained with reference to
FIGS. 9A-9C.
[0095] The wire 101 which has been deformed by the pre-forming
mechanism 140 (140A) and fed out is positioned at its deformed
section to the wire press section 112 of the bonding tool 111, and
the wire clamp mechanism 120 is operated to hold the wire 101 so
that the wire movement relative to the bonding tool 111 stops, as
shown in FIG. 9A. In this state, the pre-forming pressure P1
exerted by the pre-forming mechanism 140 (140A) on the wire 101 is
zero, while the wire clamp mechanism 120 exerts a wire clamping
pressure P2=P2c on the wire 101 to hold it.
[0096] Subsequently, the bonding tool 111 and the target joint
surface of the wire bonding object 105, i.e., the electrode 102A of
the semiconductor chip 102, are moved relatively in the vertical
and horizontal directions, so that deformed section of the wire 101
is positioned to the target joint surface.
[0097] Subsequently, the wire press section 112 at the tip of the
bonding tool 111 presses the deformed wire 101 onto the target
joint surface, i.e., the electrode 102A of the semiconductor chip
102, with vibration being applied, so that both members undergo
ultrasonic bonding as shown in FIG. 9B. In this state, the wire 101
is free from the clamping force of the wire clamp mechanism 120 of
the pre-forming mechanism 140 (140A), i.e., the pressures P1 and P2
are both zero.
[0098] Subsequently, the pre-forming mechanism 140 (140A) is moved
along the wire feed path 116 to the position which matches with the
prescribed wire length Lp along the finished wire loop measured
from the wire joint, as shown in FIG. 9C. The driving device 144
(144A) shown in FIG. 6 (FIG. 7) is activated to exert a pressure
P2=Pf on the wire 101 between the lower mold 141 (141A) and upper
mold 142 (142A) shown in FIG. 8A (FIG. 8C), thereby deforming the
wire 101 in its cross section. At this time, the wire clamp
mechanism 120 in not holding the wire 101.
[0099] In this case, the pre-forming mechanism 140 (140A) deforms
the wire 101 for the amount of two joint sections at once, since
both ends of each piece of wire are always bonded. A groove may be
formed at the end or middle of the deformed section of the wire 101
so that it can be cut easily.
[0100] Next, the operation of wire bonding apparatus for joining
the wire 101 to the second target joint surface based on the
inventive wire bonding method will be explained with reference to
FIGS. 10A and 10B. FIGS. 10A and 10B are side views of the wire
bonding apparatus used to explain the second operation of the
apparatus based on this invention.
[0101] Shown in FIG. 10A is the state of the apparatus after the
wire 101 has been joined to the first target joint surface 102A.
The wire 101 is released from the molds 141 and 142 of the
pre-forming mechanism 140 (140A), and the bonding tool 111 is moved
to the next target joint surface of the electrode 104 along the
predetermined wire loop, and, as a result, the wire 101 is
positioned at its deformed section to the wire press section
112.
[0102] The wire clamp mechanism 120 exerts a pressure P2=P2c on the
wire 101 to hold it thereby to stop its movement relative to the
bonding tool 111. In this state, the wire press section 112 presses
the deformed wire 101 onto the electrode 104, with vibration being
applied, as shown in FIG. 10B, so that ultrasonic wire bonding
takes place in the same manner as the previous bonding process.
With the wire 101 being clamped, the wire clamp mechanism 120 is
moved together with the bonding tool 111 to retreat from the joint
surface, and the wire 101 is cut off.
[0103] Based on the deformation of both ends of the wire 101 to
match with the wire loop by the pre-forming mechanism 140 (140A)
prior to the joining process, it becomes possible to accomplish the
wire bonding of enhanced joint strength and life N resulting from
the wider joint area.
[0104] Although in the foregoing embodiments, the wire preforming
mechanisms 140 and 140A are equipped independently of the wire
clamp mechanism 120, an alternative design is to eliminate the wire
clamp mechanism 120 and use the wire pre-forming mechanism 140
(140A) to clamp and deform the wire 101. Although in the foregoing
embodiments, the wire preforming mechanisms 140 and 140A are
movable relative to the wire clamp mechanism 120, both devices may
be moved as a unitary member.
[0105] Next, the joint surface of the electrode 102A and wire 101
will be explained with reference to FIGS. 11A and 11B. FIG. 11A is
a partially cross-sectional perspective view showing the joint of
the wire joint section and target joint surface based on this
invention, and FIG. 11B is a cross-sectional view taken along the
line B-B of FIG. 11A.
[0106] For a high-power semiconductor device, the wire 101 of
aluminum or aluminum alloy which includes silicon, nickel, etc. and
with a diameter D of the 100-600 .mu.m range, as shown in FIG. 11B,
is used. The wire 101 is deformed in advance by the wire
pre-forming mechanism 140 (140A) at a degree of deformation factor
W/D of around 2.0 or more, or preferably 2.5 or more, or more
preferably in the range from 4 to 6. The deformed wire 101 is
brought in contact with the electrode 102A and joined to it by
ultrasonic wire bonding with no risk of damage to the semiconductor
chip 102.
[0107] As compared with the conventional wire bonding, in which the
bonding conditions including the ultrasonic output, pressing force
and their application time length are optimized to such an extent
that the semiconductor chip 102 is not damaged and a wire thickness
H of 200 .mu.m is achieved for a wire diameter D of 300 .mu.m at a
deformation factor W/D of about 1.3, the inventive wire bonding
method and apparatus are capable of reducing drastically the
deformed wire thickness in terms of H1/H2, where H1 and H2 are the
inventive and conventional thickness, to around 0.6 or less, or
hopefully around 0.5 or less, or more hopefully in the range from
0.3 to 0.2. Consequently, based on the formula (4), the inventive
wire bonding method and apparatus are capable of enhancing the
strength and life of wire joint attributable to power cycles by
2-fold or more, or hopefully 2.5-fold or more, or more hopefully in
the range from 5 to 9-fold.
[0108] FIG. 12 is a characteristic graph showing the relation
between the forming pressure P1 (kg f/mm.sup.2) exerted on an
aluminum wire having a diameter D of 300 .mu.m plotted along the
vertical axis and the deformation factor W/D after deforming
process plotted along the horizontal axis. The graph suggests that
achieving W/D=3 requires a forming pressure of about 50-100 kg
f/mm.sup.2, and exerting such a large pressure during the wire
joining process will damage a semiconductor chip or electronic
part. Whereas, the inventive wire bonding method and apparatus can
exert the large forming pressure on the wire 101 by means of the
pre-forming mechanisms 140 and 140A.
[0109] A consequent large wire deformation factor W/D based on the
inventive wire bonding method and apparatus reduces the wire
thickness to 0.6 or less in terms of H1/H2, where H1 and H2 are the
inventive and conventional thickness, as mentioned previously. The
smaller wire thickness ratio H1/H2 signifies the extension of joint
life attributable to power cycles as shown in FIG. 13.
[0110] FIG. 13 is a characteristic graph showing the joint life of
aluminum wire attributable to power cycles and the forming pressure
plotted against the ratio of the inventive wire thickness to the
conventional wire thickness. On this graph, the ratio of the
inventive and conventional wire thickness H1/H2 is plotted along
the horizontal axis, the ratio of the inventive and conventional
joint life (RLF) resulting from cyclic power applications to the
wire is plotted along the first vertical axis to draw a curve 201,
and the forming pressure P2 exerted on the aluminum wire is plotted
along the second vertical axis to draw a curve 202.
[0111] The graph reveals that the smaller the wire thickness ratio
H1/H2, the more extended is the joint life, and also suggests that
an increased forming pressure is required to make the wire 101
thinner.
[0112] The inventive wire bonding method and apparatus are capable
of reducing the wire thickness by the provision of the wire
pre-forming mechanism, and thus extending the wire joint life
attributable to power cycles, and the inventive high-power
semiconductor device is durable against severe heat cycles and
power cycles thereby to last long, while yet being compact and
light-weight.
[0113] Although the present invention has been explained
specifically for the case of wire-bonding a high-power
semiconductor device, it is also applicable to wire-bonding of
other semiconductor devices and electronic components.
[0114] The inventive wire bonding method and apparatus are capable
of increasing the joint area between the wire and target joint
surface without the burden of an excessive ultrasonic output,
forming pressure and their application time length at the wire
joining process. Consequently, it becomes possible to enhance the
wire joint strength, and accomplish semiconductor devices and
electronic components having improved life against severe heat
cycles and power cycles.
[0115] Particularly, the inventive wire bonding method and
apparatus are designed to deform the wire in advance, so that
ultrasonic output, forming pressure and their application time
length can be reduce at the wire joining process, whereby it
becomes possible to prevent the breakage of semiconductor chips and
other electronic parts and accomplish reliable semiconductor
devices and electronic components.
[0116] The invention may be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The present embodiment is therefore to be considered in
all respects as illustrative and not restrictive, the scope of the
invention being indicated by the appended claims rather than by the
foregoing description and all changes which come within the meaning
and range of equivalency of the claims are therefore intended to be
embraced therein
* * * * *