U.S. patent application number 09/791245 was filed with the patent office on 2001-07-12 for microelectronic mounting with multiple lead deformation using restraining straps.
Invention is credited to Distefano, Thomas H..
Application Number | 20010007370 09/791245 |
Document ID | / |
Family ID | 27364298 |
Filed Date | 2001-07-12 |
United States Patent
Application |
20010007370 |
Kind Code |
A1 |
Distefano, Thomas H. |
July 12, 2001 |
Microelectronic mounting with multiple lead deformation using
restraining straps
Abstract
A microelectronic assembly includes a first microelectronic
element including contacts on a contact-bearing face and a second
microelectronic element confronting the first microelectronic
element. The assembly also has a plurality of vertically extended
signal leads electrically interconnecting the first and second
microelectronic elements, and a plurality of vertically extended
straps attached to the first and second microelectronic elements,
whereby the straps are shorter than the signal leads for limiting
vertical movement of the first and second microelectronic elements
away from one another.
Inventors: |
Distefano, Thomas H.; (Monte
Sereno, CA) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,
KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Family ID: |
27364298 |
Appl. No.: |
09/791245 |
Filed: |
February 22, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09791245 |
Feb 22, 2001 |
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09385320 |
Aug 30, 1999 |
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6208024 |
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09385320 |
Aug 30, 1999 |
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08989582 |
Dec 12, 1997 |
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5976913 |
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60045690 |
May 6, 1997 |
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60033066 |
Dec 12, 1996 |
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Current U.S.
Class: |
257/696 ;
257/E23.065; 257/E23.07; 257/E23.078 |
Current CPC
Class: |
H01L 24/72 20130101;
H01L 2924/01023 20130101; H01L 2924/01006 20130101; H01L 23/4985
20130101; H01L 2924/19042 20130101; H01L 2924/01074 20130101; H01L
2924/01078 20130101; H01L 2924/01005 20130101; H01L 2924/01033
20130101; H01L 2924/19041 20130101; H01L 2924/01082 20130101; H01L
23/49838 20130101; H01L 2924/01029 20130101; H01L 2924/19043
20130101 |
Class at
Publication: |
257/696 |
International
Class: |
H01L 023/48 |
Claims
1. A microelectronic assembly comprising: a first microelectronic
element including contacts on a contact-bearing face; a second
microelectronic element confronting said first microelectronic
element; a plurality of vertically extended signal leads
electrically interconnecting said first and second microelectronic
elements; a plurality of vertically extended straps attached to
said first and second microelectronic elements, wherein said straps
are shorter than said signal leads for limiting vertical movement
of said first and second microelectronic elements away from one
another.
2. The microelectronic assembly as claimed in claim 1, wherein said
signal leads are longer than said straps so that said signal leads
do not constrain vertical movement of said first and second
microelectronic elements away from one another.
3. The microelectronic assembly as claimed in claim 1, wherein said
signal leads are partially curved.
4. The microelectronic assembly as claimed in claim 1, wherein said
straps are substantially straight and fully extended for arresting
vertical movement of said first and second elements away from one
another.
5. The microelectronic assembly as claimed in claim 1, wherein said
straps are stronger than said signal leads.
6. The microelectronic assembly as claimed in claim 1, wherein said
straps are thicker than said signal leads.
7. The microelectronic assembly as claimed in claim 1, wherein said
straps are less numerous than said signal leads.
8. The microelectronic assembly as claimed in claim 1, wherein said
signal leads have fixed ends permanently attached to said second
microelectronic element and free ends bonded to the contacts of
said first microelectronic element.
9. The microelectronic assembly as claimed in claim 8, wherein the
fixed ends of said signal leads are electrically interconnected
with terminals accessible at a surface of said second
microelectronic element.
10. The microelectronic assembly as claimed in claim 1, wherein
said straps have fixed ends permanently attached to said second
microelectronic element and free ends bonded to said first
microelectronic element.
11. The microelectronic assembly as claimed in claim 10, wherein
the free ends of said straps are bonded to the contact-bearing face
of said first microelectronic element.
12. The microelectronic assembly as claimed in claim 10, wherein
the free ends of said straps are bonded to one or more of the
contacts of said first microelectronic element.
13. The microelectronic assembly as claimed in claim 1, wherein
said first and second microelectronic elements include
constant-potential connections and wherein at least one of said
straps electrically interconnects the constant-potential
connections of said first and second microelectronic elements.
14. The microelectronic assembly as claimed in claim 1, wherein
some of said straps are connected to a first potential plane
serving as a power plane and other said straps are connected to a
second potential plane serving as a ground reference plane.
15. The microelectronic assembly as claimed in claim 1, wherein
said straps have larger cross-sectional areas than said signal
leads.
16. The microelectronic assembly as claimed in claim 1, wherein one
of said first and second microelectronic elements includes a wafer
having a plurality of semiconductor chips and the other said
microelectronic element includes one or more connection
components.
17. The microelectronic assembly as claimed in claim 16, wherein
said wafer is severable for forming individual units each including
one or more semiconductor chips and a part of said one or more
connection components connected to the chips in such unit.
18. The microelectronic assembly as claimed in claim 1, wherein
said first and second microelectronic elements include opposing,
horizontally-extending surfaces that confront one another, wherein
said signal leads and said straps are disposed between said opposed
surfaces.
19. The microelectronic element as claimed in claim 10, wherein the
fixed ends of said straps and the free ends of said straps are
offset from one another in a first horizontal direction, wherein
said straps constrain movement of said first and second
microelectronic elements away from one another in said first
horizontal direction.
20. The microelectronic assembly as claimed in claim 1, further
comprising a compliant layer extending between said first and
second microelectronic elements.
21. The microelectronic assembly as claimed in claim 20, wherein
said compliant layer covers at least some of said signal leads and
straps.
22. The microelectronic assembly as claimed in claim 1, wherein
said straps and said signal leads are made of a common electrically
conductive material.
23. The microelectronic assembly as claimed in claim 1, wherein at
least some of said straps are made of nonconductive materials.
24. The microelectronic assembly as claimed in claim 23, wherein
one of said first and second microelectronic elements includes a
conductive metallic sheet.
25. The microelectronic assembly as claimed in claim 1, wherein
said first microelectronic element includes a semiconductor chip
having rows of contacts along its edges and said second
microelectronic element includes a connection component having a
dielectric structural element with terminals thereon, and wherein
said signal leads extend beyond peripheral edges of said dielectric
element.
26. The microelectronic assembly as claimed in claim 25, wherein
said signal leads have inner ends electrically connected to said
terminals on said dielectric structure and outer ends connected to
one of said chip contacts.
27. The microelectronic assembly as claimed in claim 26, wherein
said straps have fixed ends permanently secured to said dielectric
element and free ends bonded to said chip.
28. The microelectronic assembly as claimed in claim 25, wherein
said straps are interspersed in the rows of said signal leads.
29. A microelectronic assembly comprising: a first microelectronic
element including contacts on a contact-bearing face; a second
microelectronic element juxtaposed with said first microelectronic
element; a plurality of vertically extended signal leads
electrically interconnecting said first and second microelectronic
elements; a plurality of vertically extended straps attached to
said first and second microelectronic elements, wherein said straps
are shorter and stronger than said signal leads for limiting
vertical movement of said first and second microelectronic elements
away from one another.
30. The microelectronic assembly as claimed in claim 29, wherein
said signal leads are longer than said straps so that said signal
leads do not constrain vertical movement of said first and second
microelectronic elements away from one another.
31. The microelectronic assembly as claimed in claim 30, wherein
said signal leads are partially curved.
32. The microelectronic assembly as claimed in claim 29, wherein
said first microelectronic element includes a semiconductor chip
and said second microelectronic element includes a dielectric
substrate.
33. The microelectronic assembly as claimed in claim 29, wherein
one of said first and second microelectronic elements includes a
wafer having a plurality of semiconductor chips and the other of
said microelectronic elements includes one or more connection
components.
34. The microelectronic element as claimed in claim 33, wherein
said wafer is severable for forming individual units each including
one or more semiconductor chips and a part of said one or more
connection components connected to the chips in such unit.
35. The microelectronic assembly as claimed in claim 29, wherein
said first and second microelectronic elements include opposing,
horizontally-extending surfaces that confront one another, wherein
said signal leads and said straps are disposed between said opposed
surfaces.
36. The microelectronic assembly as claimed in claim 29, wherein
said straps are substantially straight and fully extended for
arresting vertical movement of said first and second elements away
from one another.
37. A microelectronic assembly comprising: a first microelectronic
element having rows of contacts along one or more edges thereof; a
second microelectronic element juxtaposed with said first
microelectronic element, said second microelectronic element having
conductive terminals; a plurality of signal leads electrically
interconnecting said first and second microelectronic elements,
wherein each said signal lead has an inner end electrically
connected with one of said terminals and an outer end electrically
connected with one of said contacts; a plurality of restraining
straps having fixed ends permanently fastened to said second
microelectronic element and free ends connected to said first
microelectronic element, wherein said restraining straps are
shorter than said signal leads for limiting vertical movement of
said first and second microelectronic elements away from one
another.
38. The microelectronic assembly as claimed in claim 37, wherein
said signal leads are longer than said straps sp that said signal
leads do not constrain movement of said first and second
microelectronic elements relative to one another.
39. The microelectronic assembly as claimed in claim 37, wherein
said signal leads are partially curved.
40. The microelectronic assembly as claimed in claim 37, wherein
said straps are substantially straight and fully extend for
arresting vertical movement of said first and second
microelectronic elements away from one another.
41. The microelectronic assembly as claimed in claim 37, wherein
said straps are stronger than said signal leads.
42. The microelectronic assembly as claimed in claim 37, wherein
said straps are thicker than said signal leads.
43. The microelectronic assembly as claimed in claim 37, wherein
said straps are less numerous than said signal lead.
44. The microelectronic assembly as claimed in claim 37, further
comprising a compliant layer extending between said first and
second microelectronic elements.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 09/385,320, filed Aug. 30, 1999, which is a
divisional of U.S. patent application Ser. No. 08/989,582, filed
Dec. 12, 1997, which in turn claims benefit of United States
Provisional Application Serial Nos. 60/045,690, filed May 6, 1997
and 60/033,066, filed Dec. 12, 1996. The disclosures of the
above-mentioned applications are hereby incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to methods and components for
making microelectronic assemblies. Complex microelectronic devices
such as modern semiconductor chips require numerous connections to
other electronic components. For example, a complex microprocessor
chip may require many hundreds of connections to external
devices.
[0003] As disclosed in U.S. Pat. No. 5,518,964, the disclosure of
which is also incorporated by reference herein, flexible
connections can be provided between microelectronic elements using
a process in which the leads are connected between the elements and
the elements are then moved through a predetermined displacement
relative to one another so as to deform the leads. For example, a
first element may be a microelectronic connection component which
includes a dielectric element such as a flexible sheet having a
bottom surface. A plurality of leads are also provided. Each lead
has a terminal end permanently attached to the dielectric element
and a tip end remote from the terminal end. Each lead initially
extends in a horizontal plane, generally parallel to the bottom
surface of the dielectric sheet. Desirably, the tip ends of the
leads are releasably connected to the dielectric element. While the
leads are in this condition, the tip ends are attached to a second
element, such as a further dielectric sheet, a semiconductor chip,
a semiconductor wafer or other microelectronic element. After the
tip ends of the leads have been attached to the second element, the
first and second elements are moved away from one another, so that
the tip ends of the leads are pulled away from the first element
and bent to a vertically extensive configuration. In this
condition, the leads are flexible and allow movement of the first
and second elements relative to one another. Preferably, a curable
liquid material is introduced between the elements to form a
compliant layer therebetween. Thus, in the completed assembly the
first and second elements are movable relative to one another.
[0004] As further described in the '964 patent, these arrangements
offer numerous advantages. The resulting assembly provides
mechanical decoupling between the elements, and thus provides
compensation for thermal expansion and warpage of the elements. The
preferred processes according to the '964 patent can make a large
number of connections in a single operation. For example, where a
wafer incorporating numerous chips is used as one element in the
connection process, all of the leads to all of the chips can be
connected in a single set of operations. The resulting wafer-scale
assembly can be severed to provide numerous individual units, each
including one or more chips. Further variations, improvements and
adjuncts to the processes and components taught in the '964 patent
are also disclosed in U.S. Pat. No. 5,688,716, and in copending,
commonly assigned U.S. patent application Nos. 08/532,528 Filed
Sep. 22, 1995; 08/678,808 Filed Jul. 12, 1996; and 08/690,532 Filed
Jul. 31, 1996, the disclosures of which are also incorporated by
reference herein.
[0005] Despite the advances in the art discussed above, still
further improvements would be useful.
SUMMARY OF THE INVENTION
[0006] One aspect of the present invention provides methods of
making a microelectronic assemblies. A method in accordance with
this aspect of the invention desirably includes the steps of
providing a pair of elements having a plurality of signal leads
attached to said elements and electrically interconnecting said
elements, and also having a plurality of straps attached to said
elements, said signal leads and said straps extending generally in
a horizontal direction. The method further includes the step of
moving the elements vertically away from one another so that said
straps and said signal leads are bent to a vertically extensive
disposition. In the moving step, the straps at least partially
constrain movement of the elements relative to one another.
However, the signal leads most preferably do not constrain this
movement. Stated another way, the straps control the relative
movement so that the signal leads are not pulled taut and placed
under tension between the elements. Accordingly, little stress is
applied to the relatively delicate signal leads and their
connections to the microelectronic elements. The straps may be
considerably stronger than said signal leads. The straps may also
be shorter than the signal leads so that as the elements move away
from one another, the straps will be pulled taut before the signal
leads. Typically, the straps are less numerous than the signal
leads.
[0007] The straps may also be electrically connected to the
microelectronic elements so that the straps further electrically
interconnect the elements. In a particularly preferred arrangement,
the elements include constant-potential connections such as power
or ground connections and some or all of the straps are
electrically connected between constant-potential connections on
both of said elements. Thus, the straps may serve as power leads,
ground leads or both in the finished assembly.
[0008] The elements may include opposed, horizontally-extending
surfaces of said elements confronting one another and the signal
leads and said straps may be disposed between these opposed
surfaces. For example, one of the elements may be a connection
component including a structure such as a dielectric sheet having a
bottom surface, whereas the second element may include one or more
semiconductor chips having top surfaces with contacts thereon. The
leads and straps may be provided on the bottom surface of the
connection component, so that the leads and straps extend along the
bottom surface of the connection component, and the connection
component may be positioned with the bottom surface facing the top
surfaces of the chips. The leads and straps may be connected
between the elements by bonding ends of the leads and straps to the
top surfaces of the chips.
[0009] Each strap may have a first end connected to a first one of
the elements and a second end connected to a second one of the
elements. Before the moving step, the second end of each strap may
be offset from the first end of that strap in a first horizontal
direction. In this arrangement, the straps will constrain the first
element to move relative to the second element in the first
horizontal direction during the moving step. Each signal lead may
also have first and second ends connected to the first and second
elements, respectively. Prior to the moving step, the second end of
each lead may be offset from the first end of the lead in the first
horizontal direction. Thus, the movement of the first element with
a component of motion in the first horizontal direction will cause
the ends of each said signal lead to move horizontally towards one
another while the lead ends move vertically away from one another
as the elements move away from one another. Where the signal leads
are initially straight, this compound movement can bend the leads
into a generally S-shaped configuration.
[0010] The step of moving the elements vertically away from one
another may include the step of applying a fluid under pressure
between opposed surfaces of the elements so that the fluid forces
the elements away from one another. Because the movement of the
elements relative to one another is constrained by the straps,
there is no need to use external mechanical elements to control the
movement.
[0011] A further aspect of the present invention provides
connection components for making microelectronic assemblies. A
connection component according to this aspect of the invention
desirably includes a structural element, and a plurality of
flexible signal leads, each such lead having a fixed end
permanently attached to the structural element and a free end
detachably secured to the structural element. The component also
includes a plurality of flexible straps. Each strap has a fixed end
permanently attached to the structural element and a free end
detachably secured to the structural element. Most preferably, the
straps are shorter and stronger than the leads, and the straps are
disposed adjacent the leads. The structural element may have a
surface with the straps and the leads extending along the surface.
The straps and the leads desirably are disposed in an array on the
bottom surface and the leads are interspersed with the straps in
the array. The structural element may be a dielectric element such
as a flexible dielectric sheet or may be a semiconductor chip or
wafer.
[0012] As discussed above in connection with the method, the free
end of each the lead may be offset from the fixed end of that lead
in a first horizontal direction along the bottom surface, and the
free end of each the strap may be offset from the fixed end of that
strap in the same first horizontal direction. Components in
accordance with this aspect of the invention may be used in methods
as discussed above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a fragmentary diagrammatic bottom view, taken
along lines 1-1 in FIG. 2, depicting the first element used in the
structure of FIG. 2.
[0014] FIG. 2 is a fragmentary, diagrammatic sectional elevational
view depicting first and second elements in accordance with one
embodiment of the invention after connection of the leads between
these elements, but prior to relative movement of these
elements.
[0015] FIG. 3 is a view similar to FIG. 1 but depicting the
structure in a later stage of the process, during relative movement
of the elements.
[0016] FIGS. 4, 5 and 6 are views similar to FIGS. 1, 2 and 3
respectively, but depicting elements in accordance with a further
embodiment of the invention, FIG. 5 being taken along line 5-5 in
FIG. 4.
[0017] FIG. 7 is a diagrammatic top plan view of an assembly during
a process in accordance with a further embodiment of the
invention.
[0018] FIG. 8 is a diagrammatic sectional view taken along line 8-8
in FIG. 7.
[0019] FIG. 9 is a view similar to FIG. 8 but depicting the
assembly in a later stage of the process.
[0020] FIG. 10 is a diagrammatic sectional view of an assembly
during a process according to a further embodiment of the
invention.
[0021] FIG. 11 is a perspective view of a wafer in accordance with
a further embodiment of the invention.
[0022] FIG. 12 is a fragmentary, diagrammatic view of a portion of
the wafer depicted in FIG. 11.
DETAILED DESCRIPTION
[0023] An assembly in accordance with one embodiment of the
invention includes a first element or connection component 10. The
connection component includes a flexible sheet dielectric structure
11 having a bottom surface 12, a top surface 14, and a set of
conductive power and ground planes extending parallel to these
surfaces. One such conductive plane 16 is visible in the drawing
figures; the others (not shown) extend inside the dielectric
structure or on its surfaces. The dielectric structure 11 of the
connection component may include one or more sheets of a flexible
but substantially inextensible dielectric material such a polyimide
or other or other known dimensionally stable polymeric films used
in the semiconductor industry. The dielectric sheet desirably is
about 25-35 microns thick. The conductive planes may be formed as
thin, flexible metal layers such as copper layers formed by
conventional additive or subtractive plating and etching
processes.
[0024] A large number of electrically conductive signal leads 18
are provided on bottom surface 12. Each signal lead has a terminal
end 20 and a tip end 22. The terminal end of each lead is
permanently secured to the dielectric structure of first element
10. In the particular structure illustrated, the terminal end of
each lead is secured to the dielectric structure by a metallic via
structure 24 extending through the first element and a terminal 26
integral with the structure 24 overlying top surface 14. Because
the terminal ends of the leads are permanently attached to the
dielectric structure, the terminal ends are also referred to herein
as the fixed ends of the leads. The via structures 24 associated
with the signal leads extend through holes 30 in conductive planes
16, so that the via structures 24 and the signal leads are
insulated from the conductive planes 16. Optionally, some of the
signal leads 18 may be connected to the conductive planes by the
via structures 24 or by other interconnecting elements (not
shown).
[0025] The tip end 22 of each lead is provided with a mass of
bonding material 28. The tip end of each signal lead 18 is
releasably secured to bottom surface 12 of the dielectric sheet 11.
As described in greater detail in the aforementioned '964 patent,
the tip ends of the leads may be releasably attached to the bottom
surface itself by adhesion between the lead material and the bottom
surface of the dielectric layer, within a relatively small region
disposed between the lead tip end and the bottom surface of the
dielectric layer. Alternatively or additionally, the tip ends of
the leads may be secured to the bottom surface by frangible
elements or may be bonded to the bottom surface of dielectric sheet
by a bonding process which provides a relatively low peel strength.
Low peel strength connections are described in further detail in
copending, commonly-assigned U.S. patent application Ser. No.
08/547,170, filed Oct. 24, 1995, the disclosure of which is
incorporated by reference herein. Because the tip ends of the leads
can be freed from their attachment to the bottom structure or
dielectric sheet, the tip ends are also referred to herein as free
ends.
[0026] In the condition illustrated in FIGS. 1 and 2, each lead 18
is curved and extends in a horizontal plane substantially parallel
to the bottom surface of the dielectric layer. As used in this
disclosure with reference to a structure of microelectronic on or
associated with a surface of the component, the term "horizontal"
refers to the direction parallel to the component surface. As used
with reference to a pair of components having opposed, confronting
surfaces, the term "horizontal" refers to the directions along the
confronting surfaces. The term "vertical" refers to the direction
transverse to the horizontal directions. Thus, in the case of
components having confronting surfaces, the vertical directions are
the directions from one component toward the other component.
[0027] Each signal lead 18 desirably is thin and flexible. The
leads may be formed from metallic or other conductive material,
alone or in conjunction with a dielectric material such as a
polymeric material. The dimensions of the signal leads may be as
described in the '964 patent. For example, where the connection
component is intended to connect with a microelectronic component
having contacts in a rectilinear grid with row and column spacings
of about 1000 microns, the leads may be on the order of 35 microns
wide, and the distance D.sub.1 between the center of the fixed or
terminal end 20 and the center of the free or tip end 22 of each
lead may be on the order of 500-1000 microns. However, because
leads 18 are curved, the length of each lead is considerably longer
than the straight-line distance D.sub.1. As used in this disclosure
with reference to a curved lead or strap, the term "length" should
be understood as referring to the shortest distance between the
fixed end and the free end, measured along the lead itself. Where
the lead is curved, the shortest distance along the lead itself
normally will not be a straight line.
[0028] A plurality of restraining straps 32 are also provided on
the bottom surface 12 of the dielectric sheet or first element 10.
As shown in FIG. 2, restraining straps 32 are interspersed in the
array of signal leads 18. Thus, the restraining straps are provided
at intervals over the area encompassed by the array of restraining
straps. The structure of the restraining straps 32 is generally
similar to the structure of signal leads 18. Thus, each restraining
strap 32 has a fixed or terminal end 34 permanently fastened to the
dielectric structure 11 of connection component 10 by a via
structure 36 extending through the dielectric sheet and a terminal
38 on the top surface 14. Each restraining strap 32 further has a
tip end or free end 40 releasably connected to the bottom surface
12 of the dielectric sheet, each such tip end being provided with a
bonding material 42. Most or all of the restraining straps 32 are
connected to the potential planes 16, as by interconnection between
via structures 36 and one or more of the potential planes, or by
other connecting elements (not shown). Different ones of the
restraining straps 32 may be connected to different potential
planes. For example, some of the restraining straps may be
connected to a first potential plane which serves as a power plane
whereas other restraining straps 32 may be connected to a second
potential plane serving as a ground reference plane. The
restraining straps 32 are shorter than signal leads 18. That is,
the length of each restraining strap 32, measured along the strap
itself, in the manner discussed above, is less than the length of
each signal lead 18. Also, restraining straps 32 have larger
cross-sectional areas than signal leads 18. For example, the
restraining straps may have cross-sectional areas about 1.5 times
the cross-sectional areas of the signal leads or more. The masses
of conductive bonding material 42 on the tip ends of the
restraining straps may cover larger areas than the corresponding
masses 28 on the tip ends of the signal leads. In short, the
restraining straps are of stronger, more robust construction than
the signal leads. Typically, the assembly will include a relatively
small number of restraining straps 32 and a relatively large number
of signal leads 18. Therefore, any additional area consumed by
providing relatively large, robust restraining straps will be
minimal.
[0029] In an assembly method according to an embodiment of the
invention, first element or connection component 10, with the leads
thereon, is connected to a second element such as a semiconductor
wafer 50. Wafer 50 has signal contacts 52 and ground and power
reference contacts 54 distributed over its top surface 56. The tip
ends 22 of signal leads 18 are connected to the signal contacts 52
whereas the tip ends 40 of the restraining straps 32 are connected
to the reference contacts 54. Depending upon the design of the
particular chip or wafer, reference contacts 54 may be larger and
more robust than the signal contacts 52. The bottom surface 12 of
the first element or connection component, with the leads and
straps thereon, is juxtaposed with the top surface 56 of the second
element or wafer. The elements are aligned with one another so as
to align the tip or free end of each lead and each strap with a
contact on the wafer. The bonding materials on the tip ends of the
leads are activated to bond the free or tip ends of the leads and
straps to the contacts. For example, where the bonding materials 28
and 42 on the leads and straps include a heat-activatable bonding
material, heat may be applied while pressing the dielectric element
11 of the connection component toward the wafer. The alignment and
bonding steps may be performed as described in the '964 patent. As
further set forth in that patent, the dielectric element may be
held taut in a rigid frame, and may be reinforced by a reinforcing
element (not shown) on the top surface 14 to facilitate accurate
alignment over the entire area of the dielectric element.
[0030] After the free or tip ends of the leads and straps have been
bonded to the contacts, first element 10 and second element 50 are
moved with a component of motion in a vertical direction V away
from one another. This may be accomplished by injecting a fluid
material such as gas or, preferably, a curable liquid 60, under
pressure between the first and second elements. Movement of the
first and second elements relative to one another brings the
assembly to the condition illustrated in FIG. 3. In this movement,
the leads 18 and straps 34 are bent vertically away from the bottom
surface of the first element. Thus, the tip end 22 of each lead is
moved vertically away from the terminal end 20 of the same lead.
This movement is accommodated by the initial curvature of each
signal lead, which is partially straightened. Similarly, the tip
ends 40 of the restraining straps move vertically away from the
terminal ends 34 of the restraining straps. Here again, the
vertical movement of the tip ends straightens the initial curvature
of the lead. Restraining straps 32 reach a substantially straight,
fully extended condition as illustrated in FIG. 3. In this
condition, the restraining straps 32 arrest further vertical
movement of first element 10 relative to second element 50. Because
restraining straps 32 are shorter than signal leads 18, restraining
straps 18 will reach this condition while signal leads 18 are still
slack and still partially curved. Thus, the restraining straps
constrain the movement of the first and second elements away from
one another, and assure that such movement ceases before the signal
leads are pulled taut.
[0031] After the moving step is complete, the curable liquid
material is cured to form a compliant layer such as a gel or
elastomer between the two elements. The resulting assembly is then
severed, as by sawing the assembly to sever the dielectric element,
compliant layer and wafer and form individual units. Each unit
includes one or more of the semiconductor chips included in the
wafer or second element 50, together with the overlying portions of
the connection component or first element 10. Each unit provides a
packaged semiconductor chip or assembly of chips, which may be
mounted to a circuit board or other substrate, as by solder-bonding
the terminals 26 and 38 to the substrate. The leads and restraining
straps provide electrical interconnection to the substrate, but
allow relative movement of the semiconductor chip and the
substrate. The curing and severing steps can be performed as
described in greater detail in the '964 patent.
[0032] As also discussed in the '964 patent, the leads may be
provided on the surface of either element as, for example, on the
chip or wafer rather than on a dielectric sheet. The same
considerations apply to the restraining straps. Also, as described
in the '964 patent, the signal leads may be initially straight and
the movement of the first and second elements relative to one
another may include both a vertical component of motion and a
horizontal component of motion. In this embodiment as well,
restraining straps in accordance with the present invention may be
provided. Here again, the restraining straps will be shorter than
the signal leads.
[0033] Thus, as shown in FIGS. 4 and 5, straight restraining straps
132 and straight signal leads 118 may be provided. The first
element 110 and second element 150 are connected by bonding the
free or tip ends 122 of the signal leads to signal contacts on the
second element or semiconductor device 150 and by bonding the free
or tip ends 140 of restraining straps 132 to contacts such as power
or ground contacts on the second element 150 As shown in FIGS. 4
and 5, all of the leads are initially straight. The free or tip end
122 of each lead is offset from the terminal end 120 of the same
lead in a first horizontal direction H. The free end 140 of each
restraining strap is also offset in first horizontal direction H
from the fixed end 134 of the same strap. However, the restraining
straps 132 are shorter than the signal leads 118.
[0034] As shown in FIG. 6, when the first element 110 and second
element 150 are moved in a vertical direction V away from one
another, restraining straps 132 remain taut. The first element 110
thus moves in an arc generally as indicated by the arcuate arrow A
relative to the second element. Stated another way, the restraining
straps 132 constrain the movement of the first element relative to
the second element and constrain first element 110 to move in first
horizontal direction H relative to the second element as the first
element moves vertically away from the second element. The combined
vertical and horizontal motion deforms each of signal leads 118
into a bent, generally S-shaped configuration as shown in FIG. 6.
Such horizontal motion will occur without the use of mechanical
devices to move the two elements horizontally relative to one
another. For example, a fluid such as a gas or, preferably, a
curable liquid encapsulant such as an elastomer 151 may be injected
under pressure between the first and second elements. This pressure
will force the elements away from one another in the vertical
direction. The restraining straps will constrain the first element
to move horizontally relative to the second element during this
process.
[0035] Although it is advantageous to use the restraining straps as
power or ground connections in the manner discussed above, the same
is not essential. For example, the restraining straps may be
connected to "dummy" contacts on the chip or wafer, and may serve
no electrical function whatsoever. Alternatively or additionally,
the restraining straps can be used to provide additional signal
connections. In the preferred embodiment, the restraining straps
are formed from the same materials as the signal leads and hence
the restraining straps act as electrically conductive leads.
However, in the broad compass of the invention, it is possible to
form the restraining straps from nonconductive materials such as
polymers. The number of restraining straps or restraining straps
and the placement of these elements on the surfaces of the elements
can be varied. Preferably, where one or both of the elements
includes a flexible sheet, restraining straps are dispersed at
spaced apart locations over substantially the entire extent of the
sheets, so that restraining straps limit vertical movement of each
area of the flexible sheet. As disclosed in copending, commonly
assigned U.S. Provisional Patent Application No. 60/032,828 filed
Dec. 13, 1996, and in the commonly assigned United States Patent
Application entitled Microelectronic Assembly Fabrication With
Terminal Formation From A Conductive Layer, filed of even date
herewith, claiming benefit of said '828 provisional application and
naming John W. Smith and Joseph Fjelstad as inventors, the
disclosures of which are incorporated by reference herein, a
flexible sheet-like element may be provided with a rigid
reinforcing element such as a conductive metallic sheet. After
movement of the elements to deform the leads, and after formation
of a compliant layer between the elements, the rigid reinforcing
element can be etched or otherwise treated to remove metal from it
and convert the reinforcing element to electrically conductive
parts of the assembly such as terminals. This restores flexibility
of the flexible element, and allows the terminals to move relative
to one another and relative to the opposite element such as the
chip or wafer. These techniques can be used in the present
invention. When such a rigid reinforcement is provided, the
flexible sheet-like element will not tend to bulge out of plane.
Therefore, greater spacings can be provided between the restraining
straps. Likewise, when both elements are rigid and do not tend to
bulge or bend, large spacings can be provided between restraining
straps.
[0036] An assembly according to a further embodiment of the
invention includes a semiconductor chip 250 having rows of contacts
252 along its edges. The assembly further includes a connection
component 210 having a dielectric structural element 211 with
terminals 226 thereon. In the condition illustrated in FIGS. 7 and
8, signal leads 218 extend horizontally outwardly, beyond edges 213
of the dielectric element. An inner end 220 of each signal lead is
fixed to the dielectric structure and electrically connected to a
terminal 226 on the dielectric element, whereas the outer or free
end 222 of each lead is connected to one of the chip contacts 252.
The assembly further includes restraining straps 232, each having a
fixed end 234 permanently fastened to the dielectric element and a
free end 240 bonded to the chip. The restraining straps are
interspersed in the rows of leads. Here again, the restraining
straps are shorter and stronger than the leads. The leads are
curved. As best seen in FIG. 8, in the initial, unmoved condition
of the assembly, leads 218 are curved in both the vertical and
horizontal directions, and extend both vertically and horizontally.
Leads 218 may be provided as a part of the connection component, or
may be formed in place by a process such as wire bonding while the
connection component is in place on the chip. Restraining straps
232 are curved, but are shorter than signal leads 218. The
restraining straps also may be provided as part of the connection
component or may be formed in place, as by wire bonding using a
relatively heavy-gauge wire. The assembly further includes a
foamable layer 270 disposed between the dielectric element and the
chip. The foamable layer may include a thermoplastic or other
polymeric material in conjunction with a blowing agent adapted to
form a gas upon exposure to heat. As described in greater detail in
commonly assigned U.S. Provisional Patent Application 60/032,870,
the disclosure of which is hereby incorporated by reference herein,
such a foamable material will generate a gas under pressure and
hence will introduce the gas under pressure between the opposed
surfaces of the elements. For example, the blowing agent in the
foamable material may be a heat-activated agent.
[0037] After the signal conductors and restraining straps are
connected between the two elements, foamable layer 270 is
activated. The blowing agent introduces a gas under pressure
between chip 250 and connection component 210, thus forcing the two
elements vertically away from one another and deforming leads 218
to a more vertically-extensive disposition. Here again, the
restraining straps arrest the vertical movement of the elements
away from one another before the signal leads are pulled taut.
[0038] Numerous variations and combinations of the features
discussed above can be employed. Thus, structural arrangements
other than the via and terminal structures discussed above with
reference to FIGS. 1-3 can be used to permanently secure the fixed
or terminal ends of the leads and straps to the dielectric
structure. For example, the fixed ends of the leads and straps may
be securely bonded to the dielectric structure itself. Also, the
leads and straps may be electrically connected to traces or to
other parts of the connection component which do not mechanically
secure the fixed ends. The straps may be formed integrally with
potential reference planes such as ground or power planes in
connection component. Also, the methods and components according to
the FIGS. 1-6 can be used with single chips, rather than with a
wafer. Both elements may includes chips or wafers. For example, the
present invention can be applied to connect two chips to one
another. Further, the methods and components discussed above can be
used with assemblies of plural chips, which may remain united in
the finished device to form a multichip module. In this case, the
connection component and leads may serve to interconnect the chips
in the module. Also, the elements may include microelectronic
elements other than chips or wafers.
[0039] For example, in the assembly depicted in FIG. 10, one
element 310 is itself an assemblage including a package element 312
in the form of a metallic can having a flange 314 at its periphery,
and further including a semiconductor chip 316 and additional
electrical elements 318 such as capacitors, inductors, resistors or
additional semiconductor chips. The chip and other electrical
elements have front surfaces 322 substantially coplanar with the
front surface 324 of flange 314. The front surfaces of the flange,
together with the front surfaces of the chip and of the other
electrical elements cooperatively define the front surface of
element 310. The other element 350 is a connection component
including a flexible dielectric sheet 352 and one or more metallic
potential planes 354. Only one such potential plane is partially
shown in FIG. 10. Connection component 350 further includes
interconnect leads 356 extending along one or both surfaces of the
dielectric sheet, or disposed within the sheet, and also includes
terminals 358. Although only a few such leads and terminals are
depicted in FIG. 10, numerous leads would be provided in actual
practice. Flexible signal leads 360 are connected between
connection component 350 and the chip 316 and other electrical
components 318 of assemblage 310. The restraining straps 362 are
provided only adjacent the periphery of the connection component,
and are connected between a potential plane 354 of the connection
component and the flange 314 of the package. As described in
further detail in the aforementioned U.S. patent application Ser.
No. 08/690,532, the terminals and leads may be arranged to provide
a "fan-out" arrangement, wherein the terminals 358 are disposed
over a surface area larger than the area of chip 316. The
interconnect leads 356 and signal leads 360 may be arranged to
connect the various electrical components to one another and to the
appropriate terminals 358.
[0040] During the process used to make this assembly, the terminals
358 of the connection component are disposed in engagement with a
flat surface such as a support 370. Package 312 is urged toward the
support by a weight 372 or other device for applying a force in the
vertical direction without impeding horizontal movement of the
package. A fluid such as a liquid encapsulant or foam is provided
under pressure between assembly 310 and connection component 350,
causing these elements to move vertically away from one another.
Here again, the restraining straps 362 constrain the relative
motion of the elements. Thus, the restraining straps limit vertical
movement of the elements, and cause horizontal movement of the
elements relative to one another. Support 370 maintains coplanarity
of the terminals 358, and limits bulging of the flexible dielectric
member 352.
[0041] In a further variant, the structural element which bears the
leads and straps prior to assembly may be a semiconductor chip,
wafer or other assemblage of plural chips. A unitary semiconductor
wafer 401 (FIG. 11) includes a plurality of chips 403. Each chip
has numerous signal leads 405 (FIG. 12) and restraining straps 407
disposed on the top, contact-bearing surface of the chip. The
signal leads and straps have fixed ends connected to the structural
element or wafer 401. The signal leads are connected to signal
contacts of each chip, and hence are connected to internal signal
connections 411 within the chip. The restraining straps 407 are
connected to constant-potential connections or reference contacts
409 such as power or ground connections. As in the embodiments
discussed above, the free ends of the leads and straps are
releasably secured to the structural element. For example, the
wafer may have a layer of a polymer such as polyimide on its top
surfaces, and the leads and straps may be connected to the wafer in
the same manner as discussed above with reference to leads
connected to a dielectric film.
[0042] Although the invention herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *