U.S. patent application number 13/743213 was filed with the patent office on 2014-07-17 for substrate with bond fingers.
This patent application is currently assigned to Texas Instruments Incorporated. The applicant listed for this patent is TEXAS INSTRUMENTS INCORPORATED. Invention is credited to James Raymond Baello, Jesus Bajo Bautista, JR., Raymond Maldan Partosa, Roxanna Bauzon Samson.
Application Number | 20140197534 13/743213 |
Document ID | / |
Family ID | 50982065 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140197534 |
Kind Code |
A1 |
Partosa; Raymond Maldan ; et
al. |
July 17, 2014 |
SUBSTRATE WITH BOND FINGERS
Abstract
A flip chip mounting board includes a substrate having a top
surface and a plurality of generally parallel, longitudinally
extending, laterally spaced apart bond fingers are formed on the
top surface. Each of the plurality of bond fingers has a first
longitudinal end portion and a second longitudinal end portion. A
first strip of laterally extending solder resist material overlies
the first longitudinal end portions of the bond fingers. The first
strip has an edge wall with a plurality of longitudinally
projecting tooth portions separated by gaps with a longitudinally
extending tooth portion being aligned with every other one of the
bond fingers. Adjacent bond fingers have first end portions covered
by different longitudinal lengths of solder resist material.
Inventors: |
Partosa; Raymond Maldan;
(Baguio City, PH) ; Bautista, JR.; Jesus Bajo;
(Baguio City, PH) ; Baello; James Raymond; (Baguio
City, PH) ; Samson; Roxanna Bauzon; (Benguet,
PH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TEXAS INSTRUMENTS INCORPORATED |
Dallas |
TX |
US |
|
|
Assignee: |
Texas Instruments
Incorporated
Dallas
TX
|
Family ID: |
50982065 |
Appl. No.: |
13/743213 |
Filed: |
January 16, 2013 |
Current U.S.
Class: |
257/737 ;
174/261; 438/108 |
Current CPC
Class: |
H01L 2224/73203
20130101; H01L 23/49811 20130101; H01L 2224/16225 20130101; H01L
2224/83862 20130101; H01L 2224/13147 20130101; H01L 2224/83385
20130101; H01L 24/92 20130101; H01L 2224/2919 20130101; H01L
23/49894 20130101; H01L 2224/2919 20130101; H01L 2224/81815
20130101; H01L 24/30 20130101; H01L 2224/3015 20130101; H01L
2224/9211 20130101; H01L 24/73 20130101; H01L 2224/83862 20130101;
H01L 2224/13147 20130101; H01L 24/13 20130101; H01L 23/49838
20130101; H01L 2224/131 20130101; H01L 2224/131 20130101; H01L
2224/83192 20130101; H01L 2924/00014 20130101; H01L 2924/00014
20130101; H01L 2224/81 20130101; H01L 2924/014 20130101; H01L
2224/81815 20130101; H01L 2224/83 20130101; H01L 2924/00012
20130101; H01L 2924/00014 20130101; H01L 2924/00014 20130101; H01L
24/29 20130101; H01L 2224/16237 20130101; H01L 2224/81191 20130101;
H01L 24/83 20130101; H01L 2224/13023 20130101; H01L 2224/73203
20130101; H01L 2224/81385 20130101; H01L 2224/9211 20130101; H01L
24/81 20130101 |
Class at
Publication: |
257/737 ;
438/108; 174/261 |
International
Class: |
H01L 23/498 20060101
H01L023/498; H01L 23/00 20060101 H01L023/00 |
Claims
1. A flip chip mounting board comprising: a substrate having a top
surface; a plurality of generally parallel, longitudinally
extending, laterally spaced apart bond fingers formed on said top
surface, each of said plurality of bond fingers having a first
longitudinal end portion and a second longitudinal end portion; and
a first strip of laterally extending solder resist material
overlying said first longitudinal end portions of said bond
fingers, said first strip comprising an edge wall having a
plurality of longitudinally projecting tooth portions separated by
gaps with a longitudinally extending tooth portion being aligned
with every other one of said bond fingers whereby adjacent ones of
said bond fingers have first end portions covered by different
longitudinal lengths of solder resist material.
2. The flip chip mounting board of claim 1 wherein said
longitudinally projecting tooth portions have generally straight
edged rectangular tooth shapes.
3. The flip chip mounting board of claim 1 wherein said
longitudinally projecting tooth portions have generally rounded
edged rectangular tooth shapes.
4. The flip chip mounting board of claim 1 wherein said
longitudinally projecting tooth portions have generally straight
edged triangular tooth shapes.
5. The flip chip mounting board of claim 1, further comprising a
second strip of laterally extending solder resist material
overlying said second longitudinal end portions of said bond
fingers, said second strip comprising an edge wall having a
plurality of longitudinally projecting tooth portions separated by
gaps that overlies said second end portions of said plurality of
bond fingers with a longitudinally extending tooth portion being
aligned with every other one of said bond fingers, whereby adjacent
ones of said bond fingers have second end portions covered by
different longitudinal lengths of solder resist material.
6. The flip chip mounting board of claim 5 wherein tooth portions
of said first solder resist strip are aligned with gaps in said
edge wall of said second solder resist strip.
7. The flip chip mounting board of claim 7 wherein tooth portions
of said first solder resist strip overlap with tooth portions of
said second solder resist strip.
8. The flip chip mounting board of claim 1 each longitudinally
extending tooth portion of said edge wall having a proximal end,
and further comprising a layer of nonconductive paste (NCP)
overlying said first strip of solder resist material except for
said longitudinally projecting tooth portions thereof whereby
overrun from said NCP layer onto said plurality of bond fingers is
substantially confined to portions of said bond fingers located in
said gaps between said tooth portions.
9. A flip chip assembly comprising: a flip chip mounting board
comprising: a substrate having a top surface; a plurality of
generally parallel, longitudinally extending, laterally spaced
apart bond fingers formed on said top surface, each of said
plurality of bond finger having a first longitudinal end portion
and a second longitudinal end portion; a first strip of laterally
extending solder resist material overlying said first longitudinal
end portions of said bond fingers, said first strip comprising an
edge wall having a plurality of longitudinally projecting tooth
portions separated by gaps, with a longitudinally extending tooth
portion being aligned with every other one of said bond fingers,
whereby adjacent ones of said bond fingers have first end portions
covered by different longitudinal lengths of solder resist
material; and a flip chip die having a plurality of solder tipped
copper pillar conductors mounted on said flip chip mounting board
with said plurality of solder tipped copper pillar conductors
bonded to said bond fingers on said flip chip mounting board.
10. The flip chip assembly of claim 9 wherein said flip chip
mounting board comprises one of an interposer and a chip
carrier.
11. The flip chip assembly of claim 9 wherein said flip chip
mounting board comprises a printed circuit board.
12. A method of making a flip chip assembly comprising: forming a
plurality of laterally spaced apart, longitudinally extending bond
fingers on a surface of an organic substrate; and applying a
transversely extending solder resist strip over first end portions
of the plurality of bond fingers, the solder resist strip having an
edge wall comprising a plurality of tooth portions separated by
gaps, with each tooth portion and each gap aligned with a different
one of the bond fingers in each adjacent pair of bond fingers.
13. The method of claim 12 further comprising: connecting a
plurality of solder tipped copper pillar connectors on a flip chip
die with the plurality of longitudinally extending bond fingers on
the surface of the substrate.
14. The method of claim 12 further comprising: applying a layer of
nonconductive paste to an area of the solder resist layer that
excludes the tooth portions thereof; positioning a plurality of
solder tipped copper pillar connectors on a flip chip die over the
plurality of longitudinally extending bond fingers on the surface
of the substrate; moving the flip chip die into contact with the
layer of nonconductive paste; and using thermal compressive bonding
to attach the solder tipped copper pillar connectors to the bond
fingers.
15. The method of claim 12 wherein said applying a transversely
extending solder resist layer comprises making the width of each
generally tooth shaped portion at its proximal end approximately
the same as the width of an aligned bond finger added to the width
of the gap between adjacent bond fingers.
16. The method of claim 12 wherein said applying a transversely
extending solder resist layer over first end portions of the
plurality of bond fingers, the solder resist layer having an edge
wall comprising a plurality of generally rectangular tooth shaped
portions separated by rectangular voids, with each tooth shaped
portion and each void aligned with a different one of each adjacent
pair of said plurality of bond fingers.
17. The method of claim 16 wherein said applying a transversely
extending solder resist layer comprises providing a solder resist
layer having an edge wall comprising a plurality of generally
rectangular tooth shaped portions having linear sides and right
angle corners.
18. The method of claim 16 wherein said applying a transversely
extending solder resist layer comprises providing a solder resist
layer having an edge wall comprising a plurality of generally
rectangular tooth shaped portions having curved sides and rounded
corners.
19. The method of claim 12 wherein said applying a transversely
extending solder resist layer over first end portions of the
plurality of bond fingers comprises applying a solder resist layer
having an edge wall comprising a plurality of generally triangular
tooth shaped portions separated by triangular voids.
20. The method of claim 12 further comprising applying a second
transversely extending solder resist strip over second end portions
of the plurality of bond fingers, the second solder resist strip
having an edge wall comprising a plurality of tooth portions
separated by gaps, with the tooth portion in the second solder
resist strip aligned with gaps in the first solder resist strip.
Description
BACKGROUND
[0001] During the past decade flip chip technology has emerged as a
popular alternative to wire bonding for interconnecting
semiconductor devices such as integrated circuit (IC) dies to
substrates such as printed circuit boards, carrier substrates,
interposers and other dies.
[0002] "Flip chip," is also known as "controlled collapse chip
connection" or its acronym, "C4." With flip chip technology, solder
balls/bumps are attached to electrical contact pads on one face of
a die/chip. The flip chip dies are usually processed at the wafer
level, i.e., while multiple identical dies are still part of a
large "wafer." Solder balls are deposited on chip pads on the top
side of the wafer. The wafer is sometimes "singulated" or "diced"
(cut up into separate dies) at this point to provide a number of
separate flip chip dies each having solder balls on the top face
surface. The chips may then be "flipped" over to connect the solder
balls to matching contact pads on the top surface of a substrate
such as a printed circuit board or carrier substrate on which the
flip chip is mounted. Solder ball attachment is usually provided by
reflow heating.
[0003] As IC dies have become more complex, the number of solder
bumps/balls on flip chips have increased dramatically. Whereas in
the past the solder balls were usually provided by relatively large
round solder balls attached to the chip contact pads, more recently
copper pillars ("CuP's") have been used in place of the solder
balls. A CuP is an elongated copper post member that is attached at
one end to a contact pad on the flip chip die. The CuP extends
outwardly from the die in a direction perpendicular to the face of
the die. Each CuP has a generally bullet or hemisphere shaped
solder piece attached to its distal end. The CuP's are bonded by
this solder piece to corresponding contact pads on a substrate as
by reflow heating. CuP's are capable of being positioned much more
densely, i.e., at a "higher pitch," than conventional solder
balls/bumps. One manner of facilitating connection of a substrate
to a die having such high CuP density is to provide bond fingers,
rather than conventional contact pads, on the substrate to which
the flip chip is to be mounted. The bond fingers are elongated
contact pads that may be positioned in close parallel relationship
without any insulating material between them.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a top isometric view of a conventional flip chip
die with copper post connectors.
[0005] FIG. 2 is a detailed cross sectional view of a portion of
the flip chip die of FIG. 1.
[0006] FIG. 3 is a top plan view of a portion of a conventional
substrate to which the flip chip die of FIG. 1 may be
connected.
[0007] FIGS. 4a-4d are schematic representations of various stages
in the process of connecting a flip chip die such as shown in FIGS.
1 and 2 to a substrate such as shown in FIG. 3.
[0008] FIG. 5 is a top isometric view of a conventional bond finger
array of a substrate.
[0009] FIG. 5a is a detailed top isometric view of a portion of the
bond finger array of FIG. 5 showing a nonconductive paste (NCP)
void bridging two bond fingers.
[0010] FIG. 6 is a top isometric view of one alternative to the
conventional bond finger array of FIG. 5.
[0011] FIG. 6a is a detailed top isometric view of a portion of the
bond finger array of FIG. 6 illustrating the occurrence of an NCP
void in this array.
[0012] FIG. 7 is a top isometric view of another alternative to the
conventional bond finger array of FIG. 5.
[0013] FIG. 8 is a top isometric view of yet another alternative to
the conventional bond finger array of FIG. 5.
[0014] FIG. 9 is a top view of still another alternative to the
conventional bond dinger array of FIG. 5.
[0015] FIG. 10 is a side elevation view of a flip chip assembly
having a flip chip mounted on a substrate with a bond finger
configuration of the type illustrated in FIG. 6, 7, 8 or 9.
[0016] FIG. 11 is a flow chart illustrating one method of making a
flip chip assembly.
DETAILED DESCRIPTION
[0017] This specification, in general, discloses a flip chip
mounting board that comprises a substrate 120 with a top surface
121, FIGS. 6 and 6A. A plurality of generally parallel,
longitudinally extending, laterally spaced apart bond fingers 122,
124, etc., are formed on the top surface 121. Each of the plurality
of bond fingers 122, 124, etc., has a first longitudinal end
portion 132 and a second longitudinal end portion 134. A first
strip of laterally extending solder resist material 142 overlies
the first longitudinal end portions 132 of the bond fingers 122,
124, etc. The first strip of solder resist material 142 comprises
an edge wall 146 that overlies the first end portions 132 of the
plurality of bond fingers 122, 124, etc. The edge wall 146 has a
plurality of longitudinally projecting tooth portions 152 separated
by gaps 153. One of the longitudinally extending tooth portions 152
is aligned with every other bond finger 122, 128, etc. Thus,
adjacent bond fingers, e.g., 122, 124, have first end portions 132
covered by different longitudinal lengths of solder resist material
142 depending upon whether they are aligned with a tooth portion
152 or a gap 153. This solder resist strip configuration solves a
problem in the prior art involving nonconductive paste (NCP)
bridging and solder bridging between adjacent bond fingers.
[0018] This specification also discloses a method of making a flip
chip assembly. This method, in general, includes forming a
plurality of laterally spaced apart, longitudinally extending bond
fingers 122, 124, etc., on a surface 121 of a substrate 120. The
method also includes applying a transversely extending solder
resist layer or strip 142 over first end portions 132 of the
plurality of bond fingers 122, 124, etc. The solder resist strip
142 if formed with an edge wall 146 including a plurality of
longitudinally extending tooth portions 152 separated by gaps 153,
with each tooth portion 152 and each gap 153 aligned with a
different one of the bond fingers 122, 124, etc. in each adjacent
pair of bond fingers, e.g. 122, 124. Having thus generally
described an embodiment of a flip chip mounting board and an
embodiment of a method of making a flip chip assembly, these and
other embodiments will now be described in detail.
[0019] As illustrated by FIG. 1, a conventional flip chip die 10
comprises a semiconductor substrate 12 that contains internal
circuitry. The substrate has a first or active face 14 and a second
or inactive face 15 opposite the first phase. An array of copper
post connectors 18 project from the active face surface 14 of the
die 10. The copper post array 16 includes a number of individual
copper post connectors 18 which may be arranged in any desired
configuration on the first face 14.
[0020] FIG. 2 illustrates the typical structure of a pair of
conventional copper post connectors 18 projecting from the first
face 14 of the die 10. Each of the individual copper post
connectors 18 may comprise a generally bullet or hemisphere shaped
solder tip portion 20 mounted on a generally cylindrical copper
post portion 22. Each copper post portion 22 is mounted on a
contact pad 24 that is formed at the top surface of the silicon
substrate 12. The contact pad 24 is connected to internal circuitry
(not shown) in the silicon substrate 12. The copper post portion 22
may be conventionally physically and electrically connected to the
contact pad 24 as by under bump metal layer 26 in a manner well
known in the art. Thus, each copper post connector 18 is
electrically connected to internal circuitry in the semiconductor
substrate 12 through the contact pad 24 and under bump metal layer
26. A passivation layer 17 on the top surface 14 of the die 10
encompasses each copper post connector 18.
[0021] FIG. 3 is a top plan view of a portion of a substrate 30
which is adapted to be connected to some of the copper post
connectors ("CuP's") 18 of the flip chip die 10. The substrate 30
may be an organic substrate such as a printed circuit board, IC
package carrier board, interposer, or other type of electrical
connection substrate. The substrate 30 has a top surface 32 upon
which a plurality of generally parallel bond fingers 34, 36, 38, 40
are provided as by conventional metal plating or other methods. The
bond fingers 34, 36, 38, 40 may be made of copper or another
conductive metal. The bond fingers 34, 36, 38, 40 are separated by
spaces 44, 46, 48 which may all be of the same width. The bond
fingers 34, 36, 38, 40 may also be of the same width. A typical
width range for the bond fingers 34, etc., is 16 .mu.m to 20 .mu.m.
The spaces 44, 46, 48 between bond fingers may have a typical width
range of 40 .mu.m to 80 .mu.m. The ratio of the width of a bond
finger to the width of the space between them is typically about
2.5 to 4. The positions at which the solder tip portions 20 of
associated copper post connectors 18 are connected to individual
bond fingers 34, 36, 38, 40 are illustrated by dash circles and
cross hairs at 52, 54, 56, 58. Opposite longitudinal ends of the
bond fingers 34, 36, etc., are covered, respectively, with strips
62, 64 of solder resist. Solder resist is a nonconductive material
used to shield conductive pads and traces from solder or other
conductive material. Solder resist is sometimes referred to in the
art as "solder mask." A typical width (a direction parallel to the
direction in which the bond fingers extend) range of a solder
resist strip provided over an end portion of a bond finger is 70
.mu.m to 170 .mu.m.
[0022] A conventional process by which a flip chip die 10 with
copper post connectors 18 is mounted on a substrate 30 is
illustrated in FIGS. 4A-4D. Initially, FIG. 4A, a layer of
nonconductive paste ("NCP") 68 is deposited on the upper surface of
solder resist layers or strips 62, 64 as with a conventional,
laterally displaceable NCP dispenser 66. Next, as illustrated in
FIG. 4B, a flip chip die 10 with the active face 14 thereof facing
downwardly is carried by a die placement and bonding head 70 to a
position directly over the substrate 30. The copper post connectors
18 on the die 10 are positioned directly above the target areas 52,
54, 56, 58, FIG. 3, where the copper post connectors 18 are to be
attached to the bond fingers 34, 36, 38, 40. Next, FIG. 4C, the
placement and bonding head 70 is lowered to position the die 10 in
near contact with the top surface of the solder resist strips 62,
64, thereby spreading the nonconductive paste (NCP) 68 across the
top surface of the solder resist strips 62, 64. At the same time,
the solder tip 20 of each copper post connector 18 comes into
contact with the target area, e.g., 52, on an associated bond
finger, e.g., 34. The die 10 and substrate 30 are maintained in
this position under heat and pressure which causes the individual
copper post connectors 18 to bond with the associated bond fingers
34, 36, 38, etc., on the substrate 30. As a final step, the die
placement and bonding head 70 is removed leaving a flip chip and
substrate assembly 72 that comprises the flip chip die 10 and
substrate 30 attached to one another by the solder bonds between
the copper post connectors 18 and bond fingers 34, etc. The flip
chip die 10 and substrate 30 are also physically bonded by the thin
NCP layer between them. This assembly 72 may be a printed circuit
(PC) board having a die mounted thereon or an integrated circuit
package comprising a flip chip die and substrate assembly, which in
some embodiments further comprise a lid over the flip chip die and
in some embodiments includes encapsulant covering the flip chip die
and substrate. The substrate 30 may also include connectors such as
a ball grid array for attaching and electrically connecting the
package to other circuitry. Other flip chip and substrate
assemblies 72 may include a flip chip and interposer or a flip chip
and another type of electrical substrate.
[0023] FIGS. 5 and 5A illustrate a portion 80 of a substrate having
a plurality of bond fingers 82, 84, 86, etc. Each bond finger has a
first end 91 and an opposite second end 92. The first ends 91 of
the bond fingers 82, 84, etc. are covered with a first solder
resist layer or strip 94 that has a straight inside edge face 96. A
second solder resist layer 97 covers the second ends 92 of the bond
fingers 82, 84, etc. This second solder resist layer 97 also has a
straight edge face 98. As heat and pressure are applied to the die
and substrate in the process step shown in FIG. 4(C), the
nonconductive paste 68 spreads generally evenly across each solder
resist layer 94, 97. However, in some cases, the nonconductive
paste may bubble over the edge face 96 of the solder resist layer
94. This bubble or so called "NCP void" 110 may bridge two of the
bond fingers, e.g., 84, 86 as illustrated in FIG. 5A. Subsequently,
as the solder tip portion 20 of a copper post connector 18
liquefies, it may splatter or otherwise spread to this NCP void
110, which tends to channel the molten solder. The molten solder
may thus form a solder bridge 112 which may have generally the same
shape as the NCP void 110. Such a solder bridge 112 will cause a
short circuit between the adjacent bond fingers 84, 86. As a
result, a flip chip assembly 72 that includes the substrate 30 with
the short circuit will fail.
[0024] FIGS. 6 and 6A illustrate an alternative to the conventional
design of FIG. 5 that eliminates or substantially reduces the
occurrence of short circuits caused by solder bridging. As
illustrated by FIG. 6, a substrate 120 having a plurality of bond
fingers 122, 124, 126, 128, 130, with first end portions 132 and
opposite second end portions 134, has a plurality of generally
evenly spaced gaps 123, 125, 127, 129, etc., between bond fingers.
A first solder resist layer or strip 142 is positioned over the
first end portions 132 and a second solder resist layer or strip
144 is positioned over the second end portions 134. The edge walls
146, 148 of the solder resist strips 142, 144 are defined by
alternating, generally rectangular, longitudinally extending tooth
shaped portions 152 (hereinafter, "tooth portions" 152) and
generally rectangular gaps 153, which may have the same size and
shape of the tooth portions 152. A tooth portion 152 in one
nonlimiting embodiment may have a longitudinal dimension of about
40 .mu.m and a width of about 40 .mu.m. As a result of these
alternating tooth-shaped portions 152 and gaps 153, any NCP
material 114 (sometimes referred to in the art as an NCP "void"),
FIG. 6A, that bubbles over the edge wall, e.g., 146, will in most
cases end up in a gap 153 and therefore comes into contact with
only one bond finger, e.g., 130. Thus, any solder which may follow
the NCP material 114 will not result in a short because the solder
immediately comes into contact with the solder resist edge wall,
e.g., 146 rather than the adjacent bond finger, e.g., 128.
Therefore, the solder resist configuration illustrated in FIGS. 6
and 6A prevents or substantially reduces the risk of short circuits
caused by bubbles of NCP flowing over the edge walls 146, 148 of
the solder resist strips 142, 144. In the embodiment of FIGS. 6 and
6A, each of the tooth portions 152 and gaps 153 defining the edge
walls 146, 148 have generally linear edge wall portions 160, 162,
164, 166 that meet at right angle corners, as best shown if FIG.
6A. The more outwardly positioned wall portion 166 is generally
where the NCP bubble over occurs because it is nearest to the NCP
leading edge 159. This leading edge 159 generally does not extend
onto tooth portions 152 because, when the NCP is applied, none is
applied on the tooth portions 152.
[0025] In the embodiment illustrated in FIG. 7, the tooth portions
170 and gaps 172, have curved edge wall portions 182, 184, 186,
etc. that meet at rounded corners.
[0026] In another embodiment illustrated in FIG. 8, rather than
square teeth, the tooth portions 192 and gaps 194 in the solder
resist edge walls 196, 198 are triangular-shaped providing a
generally saw tooth shaped edge wall 196, 198. Further resist edge
walls with many other geometric shapes could also be provided. Each
embodiment that has such an edge wall configuration forms "traps"
for any over flowing NCP and following solder that isolates it to a
single bond finger, e.g. 128, FIG. 6.
[0027] FIG. 9 illustrates and embodiment in which each tooth
portion 181 of a first solder resist strip 183 has a tip portion
185 that overlaps, i.e. is coextensive with the tip portion 195 of
adjacent tooth portions 191 in a second solder resist strip 193. In
this embodiment each gap 187 associated with the first strip 183 is
"capped" by the tip portion 195 of a tooth portion 191 of the
second strip 193, and vice verse. In one embodiment the overlap
distance A may be at least about 20 .mu.m. Thus, each gap 187 on
the first strip 183 and each gap 197 on the second strip 193,
except for the gaps at the lateral ends of the strips, is a
rectangular enclosure. The portion of each bond finger 189, 199
within each such rectangular enclosure or partial enclosure, e.g.,
gaps 187, 197, is totally isolated from the adjacent bond
fingers.
[0028] Solder resist strip edge walls having the various shapes
described herein and other shapes may be formed by screen printing
the solder resist strips in such shapes. Solder resist screen
printing is known in the art.
[0029] FIG. 10 illustrates a flip chip assembly 200 comprising a
flip chip 202 attached to a substrate 204. The flip chip 202 may be
a conventional flip chip such as illustrated in FIGS. 1 and 2. The
substrate 204 may have bond finger arrays and solder resist layers
configured as illustrated in FIG. 6. Alternatively the bond fingers
arrays and solder resist layers may be configured as illustrated in
FIG. 7 or FIG. 8 or FIG. 9.
[0030] FIG. 11 illustrates a method 220 of making a flip chip
assembly. The method as indicated at 222 includes forming a
plurality of laterally spaced apart, longitudinally extending bond
fingers on a surface of an organic substrate. The method also
includes applying a transversely extending solder resist layer over
first end portions of the plurality of bond fingers, the solder
resist layer having an edge wall comprising a plurality of
generally tooth shaped portions separated by gaps, with a tooth
shaped portion or a gap aligned with a different one of the bond
fingers in each adjacent pair of bond fingers.
[0031] Although certain specific embodiments of a flip chip
mounting board and a flip chip assembly and a method of making a
flip chip assembly have been described in detail herein, various
modification of such apparatus and method will be obvious to
persons skilled in the art after reading this disclosure. It is
intended that the appended claims be broadly construed so as to
encompass such alternative embodiments, except to the extent
limited by the prior art.
* * * * *