U.S. patent application number 10/055580 was filed with the patent office on 2003-07-10 for cylindrical bonding structure and method of manufacture.
Invention is credited to Chou, Chien-Kang, Kuo, Hsi-Shan, Lee, Jin-Yuan, Lin, Shih-Hsiung.
Application Number | 20030127734 10/055580 |
Document ID | / |
Family ID | 21688166 |
Filed Date | 2003-07-10 |
United States Patent
Application |
20030127734 |
Kind Code |
A1 |
Lee, Jin-Yuan ; et
al. |
July 10, 2003 |
Cylindrical bonding structure and method of manufacture
Abstract
A cylindrical bonding structure and its method of manufacture.
The cylindrical bonding structure is formed over the bonding pad of
a silicon chip and the chip is flipped over to connect with a
substrate board in the process of forming a flip-chip package. The
cylindrical bonding structure mainly includes a conductive cylinder
and a solder block. The conductive cylinder is formed over the
bonding pad of the silicon chip and the solder block is attached to
the upper end of the conductive cylinder. The solder block has a
melting point lower than the conductive cylinder. The solder block
can be configured into a cylindrical, spherical or hemispherical
shape. To fabricate the cylindrical bonding structure, a patterned
mask layer having a plurality of openings that correspond in
position to the bonding pads on the wafer is formed over a silicon
wafer. Conductive material is deposited into the openings to form
conductive cylinders and finally a solder block is attached to the
end of each conductive cylinder.
Inventors: |
Lee, Jin-Yuan; (Hsinchu,
TW) ; Chou, Chien-Kang; (Tainan Hsien, TW) ;
Lin, Shih-Hsiung; (Hsinchu, TW) ; Kuo, Hsi-Shan;
(Neihu Chu, TW) |
Correspondence
Address: |
J.C. Patents, Inc.
Suite 250
4 Venture
Irvine
CA
92618
US
|
Family ID: |
21688166 |
Appl. No.: |
10/055580 |
Filed: |
January 22, 2002 |
Current U.S.
Class: |
257/737 ;
257/738; 257/778; 257/E21.508; 257/E23.021; 438/108; 438/613;
438/614; 438/615 |
Current CPC
Class: |
H01L 2224/13147
20130101; H01L 2924/01033 20130101; H01L 24/03 20130101; H01L
2224/13083 20130101; H01L 2224/16145 20130101; H01L 2924/01046
20130101; H01L 2224/05684 20130101; H01L 2924/0002 20130101; H01L
24/05 20130101; H01L 24/13 20130101; H01L 2224/05611 20130101; H01L
2224/1308 20130101; H01L 2224/13116 20130101; H01L 2224/13139
20130101; H01L 2924/01029 20130101; H01L 2924/01082 20130101; H01L
24/11 20130101; H01L 2224/11462 20130101; H01L 2224/11474 20130101;
H01L 2224/05664 20130101; H01L 2224/05666 20130101; H01L 2224/13118
20130101; H01L 2924/01051 20130101; H01L 2924/04953 20130101; H01L
2224/05644 20130101; H01L 2924/014 20130101; H01L 2224/13111
20130101; H01L 2924/01023 20130101; H01L 2224/05657 20130101; H01L
2224/13609 20130101; H01L 2224/16237 20130101; H01L 2924/01012
20130101; H01L 2924/00013 20130101; H01L 2924/01074 20130101; H01L
2924/01005 20130101; H01L 2224/13113 20130101; H01L 2224/05671
20130101; H01L 2224/13109 20130101; H01L 2224/13099 20130101; H01L
2924/01047 20130101; H01L 2924/01078 20130101; H01L 2224/05647
20130101; H01L 2224/1147 20130101; H01L 2225/06513 20130101; H01L
2924/0103 20130101; H01L 2224/05572 20130101; H01L 2224/05639
20130101; H01L 2224/05655 20130101; H01L 2924/01024 20130101; H01L
2924/01022 20130101; H01L 2924/01079 20130101; H01L 2224/13022
20130101; H01L 2224/11849 20130101; H01L 2224/13155 20130101; H01L
2924/01027 20130101; H01L 2924/01073 20130101; H01L 2224/0401
20130101; H01L 2224/11906 20130101; H01L 2924/01049 20130101; H01L
25/0657 20130101; H01L 2224/13017 20130101; H01L 2924/10253
20130101; H01L 2224/1312 20130101; H01L 2924/14 20130101; H01L
2224/13123 20130101; H01L 25/50 20130101; H01L 2224/81191 20130101;
H01L 2224/13144 20130101; H01L 2924/01006 20130101; H01L 2224/05672
20130101; H01L 2224/13144 20130101; H01L 2924/00014 20130101; H01L
2224/13147 20130101; H01L 2924/00014 20130101; H01L 2224/13139
20130101; H01L 2924/00014 20130101; H01L 2224/13111 20130101; H01L
2924/00014 20130101; H01L 2224/13155 20130101; H01L 2924/00014
20130101; H01L 2224/1312 20130101; H01L 2924/00014 20130101; H01L
2224/13116 20130101; H01L 2924/00014 20130101; H01L 2224/13109
20130101; H01L 2924/00014 20130101; H01L 2224/13113 20130101; H01L
2924/00014 20130101; H01L 2224/13118 20130101; H01L 2924/00014
20130101; H01L 2224/13123 20130101; H01L 2924/00014 20130101; H01L
2224/1308 20130101; H01L 2224/13144 20130101; H01L 2224/1308
20130101; H01L 2224/13147 20130101; H01L 2224/1308 20130101; H01L
2224/13139 20130101; H01L 2224/1308 20130101; H01L 2224/1312
20130101; H01L 2224/1308 20130101; H01L 2224/13111 20130101; H01L
2224/1308 20130101; H01L 2224/13116 20130101; H01L 2224/1308
20130101; H01L 2224/13118 20130101; H01L 2224/1308 20130101; H01L
2224/13109 20130101; H01L 2224/1308 20130101; H01L 2224/13113
20130101; H01L 2224/1308 20130101; H01L 2224/13123 20130101; H01L
2924/00013 20130101; H01L 2224/13099 20130101; H01L 2224/05572
20130101; H01L 2924/00014 20130101; H01L 2924/00013 20130101; H01L
2224/29099 20130101; H01L 2924/10253 20130101; H01L 2924/00
20130101; H01L 2924/0002 20130101; H01L 2224/05552 20130101; H01L
2224/05611 20130101; H01L 2924/00014 20130101; H01L 2224/05639
20130101; H01L 2924/00014 20130101; H01L 2224/05644 20130101; H01L
2924/00014 20130101; H01L 2224/05647 20130101; H01L 2924/00014
20130101; H01L 2224/05655 20130101; H01L 2924/00014 20130101; H01L
2224/05664 20130101; H01L 2924/00014 20130101; H01L 2224/05666
20130101; H01L 2924/00014 20130101; H01L 2224/05671 20130101; H01L
2924/00014 20130101; H01L 2224/05684 20130101; H01L 2924/00014
20130101; H01L 2224/05666 20130101; H01L 2924/013 20130101; H01L
2224/05684 20130101; H01L 2924/013 20130101; H01L 2224/05671
20130101; H01L 2924/013 20130101; H01L 2224/05647 20130101; H01L
2924/013 20130101; H01L 2224/05655 20130101; H01L 2924/013
20130101; H01L 2224/05657 20130101; H01L 2924/013 20130101; H01L
2224/05639 20130101; H01L 2924/013 20130101; H01L 2224/05644
20130101; H01L 2924/013 20130101; H01L 2224/05611 20130101; H01L
2924/013 20130101; H01L 2224/05672 20130101; H01L 2924/013
20130101; H01L 2224/05664 20130101; H01L 2924/013 20130101 |
Class at
Publication: |
257/737 ;
257/738; 257/778; 438/108; 438/613; 438/614; 438/615 |
International
Class: |
H01L 023/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2002 |
TW |
91100092 |
Claims
What is claimed is:
1. A cylindrical bonding structure on a chip having one or more
bonding pads thereon, comprising: a conductive cylinder on the
bonding pad of the chip; and a solder block on the conductive
cylinder, wherein the solder block is made from a material having a
melting point lower than the conductive cylinder.
2. The structure of claim 1, wherein the bonding pad is the
original bonding pad on the chip.
3. The structure of claim 1, wherein the chip further includes a
redistribution circuit layer and the bonding pad is a pad on the
redistribution circuit layer.
4. The structure of claim 1, wherein the solder block is a solder
ball.
5. The structure of claim 1, wherein the solder block is a
cylindrical solder cap.
6. The structure of claim 5, wherein the cylindrical solder cap has
an outer diameter smaller than the conductive cylinder.
7. The structure of claim 1, wherein material forming the
conductive cylinder is selected from a group consisting of tin,
lead, copper, gold, silver, zinc, bismuth, magnesium, antimony,
indium and an alloy of the aforementioned metals.
8. The structure of claim 1, wherein material forming the solder
block is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
9. The structure of claim 1, wherein the structure further includes
a ball contact metallic layer between the conductive cylinder and
the bonding pad.
10. The structure of claim 1, wherein the structure further
includes a transition layer between the conductive cylinder and the
solder block.
11. The structure of claim 10, wherein the transition layer has at
least one conductive layer.
12. A method of forming one or more cylindrical bonding structures
over a silicon wafer having an active surface and at least one
bonding pad on the active surface, comprising the steps of: forming
a ball contact metallic layer over the entire active surface of the
silicon wafer, including the bonding pads; forming a patterned mask
layer over the ball contact metallic layer, wherein the first mask
layer has at least one opening that corresponds in position to the
bonding pad and exposes a portion of the ball contact metallic
layer; depositing conductive material into the opening to form a
conductive cylinder over the ball contact metallic layer, wherein
the conductive material only partially fills the opening;
depositing solder material into the remaining space of the opening
to form at least one cylindrical solder cap on the upper surface of
the conductive cylinder, wherein the solder material has a melting
point lower than the conductive cylinder material; and removing the
mask layer and the ball contact metallic layer outside the
conductive cylinder such that the remaining ball contact metallic
layer, the conductive cylinder and the cylindrical solder cap
together form the cylindrical bonding structure.
13. The method of claim 12, wherein the bonding pad is an original
bonding pad on the wafer.
14. The method of claim 12, wherein the wafer further includes a
redistribution circuit layer and the bonding pad is a pad on the
redistribution circuit layer.
15. The method of claim 12, wherein after removing the mask layer
and a portion of the ball contact metallic layer, further includes
conducting a reflow operation to transform the cylindrical solder
cap into a solder block.
16. The method of claim 12, wherein the step of depositing
conductive material into the opening includes conducting an
electroplating operation.
17. The method of claim 12, wherein the step of depositing solder
material into the opening includes conducting an electroplating or
a printing operation.
18. The method of claim 12, wherein after forming the conductive
cylinder but before forming the cylindrical solder cap, further
includes forming a transition layer over the upper surface of the
conductive cylinder so that the cylindrical solder cap is formed
over the transition layer.
19. The method of claim 18, wherein the transition layer has at
least one conductive layer.
20. The method of claim 12, wherein material forming the conductive
cylinder is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
21. The method of claim 12, wherein material forming the solder
block is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
22. The method of claim 12, wherein material forming the mask layer
includes photoresist.
23. The method of claim 12, wherein the step of forming the
patterned mask layer includes forming a photoresist layer over the
ball contact metallic layer and patterning the photoresist
layer.
24. The method of claim 23, wherein the step of patterning the
photoresist layer includes conducting a photo-exposure and
developing the exposed photoresist layer.
25. A method of forming one or more cylindrical bonding structures
over a silicon wafer having an active surface and at least one
bonding pad on the active surface, comprising the steps of: forming
a ball contact metallic layer over the entire active surface of the
silicon wafer, including the bonding pads; forming a patterned mask
layer over the ball contact metallic layer, wherein the mask layer
has at least one opening that corresponds in position to the
bonding pad and exposes a portion of the ball contact metallic
layer; depositing conductive material into the opening to form a
conductive cylinder over the ball contact metallic layer, wherein
the conductive material only partially fills the opening; removing
the mask layer and the ball contact metallic layer outside the
conductive cylinder; and attaching a solder ball onto the upper
surface of the conductive cylinder such that the remaining ball
contact metallic layer, the conductive cylinder and the solder ball
together form the cylindrical bonding structure.
26. The method of claim 25, wherein the bonding pad is the original
bonding pad on the wafer.
27. The method of claim 25, wherein the wafer further has a
redistribution circuit layer and the bonding pads are pads on the
redistribution circuit layer.
28. The method of claim 25, wherein the step of depositing
conductive material into the opening includes conducting an
electroplating operation.
29. The method of claim 25, wherein after forming the conductive
cylinder but before attaching the solder ball, further includes
forming a transition layer on the upper surface of the conductive
cylinder so that the solder ball is attached to the transition
layer.
30. The method of claim 29, wherein the transition layer has at
least one conductive layer.
31. The method of claim 25, wherein material forming the conductive
cylinder is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
32. The method of claim 25, wherein material forming the solder
ball is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
33. The method of claim 25, wherein material forming the mask layer
includes photoresist.
34. The method of claim 25, wherein the step of forming the
patterned mask layer includes forming a photoresist layer over the
ball contact metallic layer and patterning the photoresist
layer.
35. The method of claim 34, wherein the step of patterning the
photoresist layer includes conducting a photo-exposure and
developing the exposed photoresist layer.
36. A cylindrical bonding structure on a silicon chip such that the
structure may flip over and connect with a substrate, wherein the
chip has at least one bonding pad and the substrate has a substrate
surface having a patterned solder mask and at least one junction
pad thereon, and the solder mask layer has at least an opening that
exposes the junction pad, the cylindrical bonding structure
comprising: a conductive cylinder on the bonding pad of the chip;
and a cylindrical solder cap on the conductive cylinder, wherein
the cylindrical solder cap has an outer diameter smaller than the
diameter of the opening in the solder mask and a length greater
than the depth of the opening, and the solder material has a
melting point lower than the conductive cylinder material.
37. The structure of claim 36, wherein the bonding pad is the
original bonding pad on the chip.
38. The structure of claim 36, wherein the chip further includes a
redistribution circuit layer and the bonding pad is a pad on the
redistribution circuit layer.
39. The structure of claim 36, wherein material forming the
conductive cylinder is selected from a group consisting of tin,
lead, copper, gold, silver, zinc, bismuth, magnesium, antimony,
indium and an alloy of the aforementioned metals.
40. The structure of claim 36, wherein material forming the
cylindrical solder cap is selected from a group consisting of tin,
lead, copper, gold, silver, zinc, bismuth, magnesium, antimony,
indium and an alloy of the aforementioned metals.
41. The structure of claim 36, wherein the structure further
includes a ball contact metallic layer between the conductive
cylinder and the bonding pad.
42. The structure of claim 36, wherein the structure further
includes a transition layer between the conductive cylinder and the
cylindrical solder cap.
43. The structure of claim 42, wherein the transition layer has at
least one conductive layer.
44. A method of forming one or more cylindrical bonding structures
over a silicon wafer having an active surface and at least one
bonding pad on the active surface, comprising the steps of: forming
a ball contact metallic layer over the entire active surface of the
silicon wafer, including the bonding pads; forming a patterned
first mask layer over the ball contact metallic layer, wherein the
first mask layer has at least one opening that corresponds in
position to the bonding pad and exposes a portion of the ball
contact metallic layer; depositing conductive material into the
opening to form a conductive cylinder over the ball contact
metallic layer; forming a patterned second mask layer over the
first mask layer, wherein the second mask layer has at least one
opening than exposes a portion of the conductive cylinder;
depositing solder material into the opening to form a cylindrical
solder cap over the conductive cylinder, wherein the solder
material has a melting point lower than the conductive cylinder
material; and removing the first mask layer, the second mask layer
and the ball contact metallic layer outside the conductive cylinder
such that the remaining ball contact metallic layer, the conductive
cylinder and the cylindrical solder cap together form the
cylindrical bonding structure.
45. The method of claim 44, wherein the bonding pad is the original
bonding pad on the wafer.
46. The method of claim 44, wherein the wafer further has a
redistribution circuit layer and the bonding pads are pads on the
redistribution circuit layer.
47. The method of claim 44, wherein the step of depositing
conductive material into the first mask layer opening includes
conducting an electroplating operation.
48. The method of claim 44, wherein the step of depositing solder
material into the second mask layer opening includes conducting an
electroplating operation.
49. The method of claim 44, wherein after forming the conductive
cylinder but before the cylindrical solder cap, further includes
forming a transition layer on the upper surface of the conductive
cylinder so that the cylindrical solder cap is formed over the
transition layer.
50. The method of claim 49, wherein the transition layer has at
least one conductive layer.
51. The method of claim 44, wherein material forming the conductive
cylinder is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
52. The method of claim 44, wherein material forming the solder
material is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
53. The method of claim 44, wherein material forming the first mask
layer includes photoresist.
54. The method of claim 44, wherein the step of forming the
patterned first mask layer includes forming a photoresist layer
over the ball contact metallic layer and patterning the photoresist
layer.
55. The method of claim 54, wherein the step of patterning the
photoresist layer includes conducting a photo-exposure and
developing the exposed photoresist layer.
56. The method of claim 44, wherein material forming the second
mask layer includes photoresist.
57. The method of claim 44, wherein the step of forming the
patterned second mask layer includes forming a photoresist layer
over the first mask layer and patterning the photoresist layer.
58. The method of claim 57, wherein the step of patterning the
photoresist layer includes conducting a photo-exposure and
developing the exposed photoresist layer.
59. A method of connecting a chip to a substrate to form a
flip-chip package, wherein the chip has an active surface having at
least a bonding pad thereon, the substrate has a substrate surface
having a patterned solder mask and at least one junction pad
thereon, and the solder mask has at least one opening that exposes
the junction pad, the method comprising the steps of: forming a
cylindrical bonding structure on the bonding pad of the chip,
wherein the cylindrical bonding structure comprises a conductive
cylinder and a solder block, the bottom surface of the conductive
cylinder is on top of the bonding pad and the bottom surface of the
solder block is on the upper surface of the conductive cylinder,
and the solder block has a melting point lower than the conductive
cylinder; flipping over the active surface of the chip to face the
substrate surface of the substrate such that the upper surface of
the solder block contacts the junction pad; and conducting a reflow
process to melt the solder block material so that the conductive
cylinder and the junction pad are joined together.
60. The method of claim 59, wherein the bonding pad is the original
bonding pad on the chip.
61. The method of claim 59, wherein the wafer further has a
redistribution circuit layer and the bonding pads are pads on the
redistribution circuit layer.
62. The method of claim 59, wherein material forming the conductive
cylinder is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
63. The method of claim 59, wherein material forming the solder
block is selected from a group consisting of tin, lead, copper,
gold, silver, zinc, bismuth, magnesium, antimony, indium and an
alloy of the aforementioned metals.
64. The method of claim 59, wherein the solder block is a
cylindrical solder cap.
65. The method of claim 64, wherein the cylindrical solder cap has
an outer diameter smaller than the opening diameter on the solder
mask.
66. The method of claim 65, wherein the cylindrical solder cap has
a length greater than the depth of the opening on the solder
mask.
67. The method of claim 59, wherein the cylindrical bonding
structure further includes a ball contact metallic layer between
the conductive cylinder and the bonding pad on the chip.
68. The method of claim 59, wherein the cylindrical bonding
structure further includes a transition layer between the
conductive cylinder and the solder block.
69. The method of claim 68, wherein the transition layer has at
least a conductive layer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Taiwan
application serial no. 91100092, filed Jan. 7, 2002.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to a cylindrical bonding
structure and its method of manufacture. More particularly, the
present invention relates to a cylindrical bonding structure for a
flip chip package and a method of fabricating the cylindrical
bonding structure.
[0004] 2. Description of Related Art
[0005] In this information-saturated society, working with
electronic products has become an integral part of our daily life.
Currently, integrated circuit products are used for doing business,
educating our children or providing us with games for recreation.
As a result of rapid progress in electronic technologies, devices
having powerfill functions and personalized designs have been
developed. Moreover, most electronic products have light and
compact design. Nowadays, high-density integrated circuits are
frequently housed with in compact semiconductor packages such as a
flip-chip package and a ball grid array (BGA) package.
[0006] In the flip-chip technique, bumps are formed on the bonding
pads of a chip so that the bumps may be attached to corresponding
contact points on a substrate after flip over. Compared with
conventional wire bonding and tape automatic bonding (TAB)
packaging techniques, a flip-chip package has the shortest signal
transmission path between the chip and the substrate and hence has
superior electrical properties. In addition, a flip-chip package
may be designed to have its back exposed so as to increase heat
dissipation rate. Due to the above reasons, flip-chip packaging
techniques are widely adopted in the semiconductor fabrication
industry.
[0007] FIG. 1A is a partially magnified view showing a connection
configuration between a bump on a chip and a contact point on a
substrate in a conventional flip-chip package. A chip 110 normally
has a plurality of bonding pads 112 (only one is shown in FIG. 1A).
Each bonding pad 112 has a bump 114. In general, the bump 114 is a
solder bump so that the flip-over chip 110 may directly connect
with one of the bonding pads 122 (only one is shown in FIG. 1A) on
the substrate 120. Since the chip 110 and the substrate 120 each
has a different coefficient of thermal expansion (CTE), a standoff
distance must be provided between the chip 110 and the substrate
120 so that differential thermal expansion will not accumulate too
much shear stress to break the bumps 114 prematurely.
[0008] Thus, to prevent shear stress from damaging the bumps 114,
bumps 114 having a great height are often attached to the bonding
pads 112 of the chip 110 so as to increase the distance of
separation between the chip 110 and the substrate 120 as much as
possible. However, increasing the overall height of the bumps 114
must be accompanied by a corresponding increase in outer diameter
and volume of the bumps. Moreover, to prevent short-circuiting,
pitch between neighboring bumps 114 must be increased. Ultimaately,
distance between neighboring bonding pads 112 on the chip 110 is
hard to reduce.
[0009] In addition, pre-solder material is often applied on the
junction pads 122 of the substrate 120 before the lower end of the
bumps 114 are put against the pads 122. In a reflow operation, the
low melting point pre-solder melts and joins the bumps 114 and the
junction pads 122 together. Because an additional step of applying
low melting point solder over the junction pads 122 of the
substrate 120 has to be conducted, cost of fabricating the
substrate 120 is increased Furthermore, to increase the distance of
separation between the chip 110 and the substrate 120, high lead
solder is a principle ingredient of the bumps 114. Since a high
temperature treatment of the bump material to form a spherical
shape bump often produces oxide material near the surface, the
bumps 114 and the junction pads 122 often have poor adhesion after
the solder reflow process. Poor adhesion often leads to bad
electrical connections between the chip and the substrate and a low
overall yield of the flip chip package.
[0010] FIG. 1B is a partially magnified view showing an alternative
connective configuration between a bump on a chip and a contact
point on a substrate in a conventional flip-chip package. A solder
mask 124 is formed over the substrate 120 to pattern out contact
area around the junction pads 122. In fact, there are two major
patterning techniques that employ the solder mask 124. The first
one is called a `solder mask define` (SMD) and the other one is
called a `no solder mask define` (NSMD). In FIG. 1A, a `solder mask
define` (SMD) technique is used. An opening 126 in the solder mask
124 exposes a portion of the junction pad 122 so that a bump on the
chip 110 is in a corresponding position over the junction pad 122
on the substrate 120. In FIG. 1B, a `no solder mask define` (NSMD)
technique is used. An opening 126 in the solder mask 124 completely
exposes a junction pad 122 so that a bump is completely connected
to the junction pad 122. The most commonly used material for
forming the solder mask 124 is, for example, green lacquer.
[0011] To shorten pitch between neighboring junction pads 122, SMD
technique such as the one shown in FIG. 1A is often employed. Only
a portion of the junction pad 122 is exposed through the solder
mask 124 for contact with the lower edge of a bump 114 (shown in
profile by dash lines 114a). However, because actual dimension of a
bump 114 may vary from the standard dimension by .+-.10%, variation
in positional accuracy between the bump 114 and the junction pad
122 of up to 10 .mu.m is possible. Furthermore, the opening 126 in
the solder mask layer 124 may have an intrinsic diametrical
variation of about 15 .mu.m. Hence, when the bump 114 and the
junction pad 122 are laid on top of each other, the lower edge of
the bump 114 may not come into direct contact with the surface of
the junction pad 122. In extreme cases, part of the outer edge of
the bump 114 may lean upon the upper ccorner of the opening 126 of
the solder mask layer 124 shown by the dash line 114b in FIG. 1A.
Hence, after a solder reflow operation, the bump 114 may not be
properly bonded with the junction pad 122 to form a good electrical
connection. To ensure proper bonding between the lower edge of the
bump 114 with the junction pad 122, diameter of the opening 126 of
a conventional solder mask 124 is generally larger than the
external diameter of the bump 114. Since distance between
neighboring junction pads 122 must be increased to accommodate the
extension, ultimate level of integration is greatly reduced.
SUMMARY OF THE INVENTION
[0012] Accordingly, one object of the present invention is to
provide a cylindrical bonding structure and its method of
manufacture capable of reducing the separation between neighboring
bonding pads on a chip while increasing distance of separation
between the chip and a substrate. Ultimately, reliability of the
junctions connecting the chip and the substrate is improved and
post-packaging life of the chip is extended.
[0013] A second object of this invention is to provide a
cylindrical bonding structure and its method of manufacture capable
of reducing the diameter of openings on a solder mask for exposing
a junction pad so that distance of separation between neighboring
junction pads on the substrate is reduced. Consequently, the
distance of separation between neighboring bonding pads (bumps) on
the chip is also reduced.
[0014] A third object of this invention is to provide a cylindrical
bonding structure and its method of manufacture that requires no
application of low melting point solder material on the junction
pads of a substrate or the surface of bumps before conducting a
reflow process. Thus, production cost of a flip-chip package is
reduced.
[0015] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a cylindrical bonding structure and
its method of manufacture. A ball contact metallic layer is formed
over the entire surface of a silicon wafer. A patterned mask layer
is formed over the ball contact metallic layer. The mask layer has
openings that correspond in position to bonding pads on the wafer
and expose a portion of the underlying ball contact metallic layer.
By conducting an electroplating process, for example, conductive
material is deposited into the openings of the mask layer to form
conductive cylinders. Through electroplating or printing, solder
material is deposited into the openings of the mask layer to form a
cylindrical solder cap on the upper surface of the conductive
cylinders. The mask layer and the ball contact metallic layer
outside the conductive cylinder are removed. The residual ball
contact metallic layer, the conductive cylinder and the solder cap
together form a cylindrical bonding structure. In addition, the
cylindrical solder cap may undergo a reflow treatment to transform
the cylindrical solder cap into a solder block attached to the
upper surface of the conductive cylinder. Alternatively, the
deposition of solder material into the openings may be deleted.
After the formation of the conductive cylinders, the mask layer and
the ball contact metallic layer outside the conductive cylinders
are removed. Thereafter, a ball implant process is conducted to
attach a solder ball directly onto the exposed surface of each
conductive cylinder. The residual ball contact metallic contact,
the conductive cylinder and the solder ball together form a
cylinder bonding structure.
[0016] This invention also provides an alternative cylindrical
bonding structure and its method of manufacture. A ball contact
metallic layer is formed over the entire surface of a silicon
wafer. A patterned first mask layer is formed over the ball contact
metallic layer. The first mask layer has openings that correspond
in position to bonding pads on the wafer and expose a portion of
the underlying ball contact metallic layer. By conducting an
electroplating process, for example, a conductive material is
deposited into the openings of the mask layer to form a conductive
cylinder. A patterned second mask layer is formed over the first
mask layer. The second mask layer has openings that expose the
upper surface of the conductive cylinders. Similarly, by conducting
another electroplating operation, solder material is deposited into
the openings of the mask layer to form cylindrical solder caps on
the upper surface of all conductive cylinders. The first mask
layer, the second mask layer, and the ball contact metallic layer
outside the conductive cylinder are removed. The residual ball
contact metallic layer, the conductive cylinder and the cylindrical
solder cap together form a cylindrical bonding structure. In
addition, the cylindrical solder cap may be designed to have an
outer diameter smaller than the diameter of the opening in the
solder mask. Hence, the cylindrical solder cap may pass through the
solder mask opening to contact the junction pad on the substrate
when the chip is flipped over the substrate.
[0017] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0019] FIG. 1A is a partially magnified view showing a connection
configuration between a bump on a chip and a contact point on a
substrate in a conventional flip-chip package;
[0020] FIG. 1B is a partially magnified view showing an alternative
connective configuration between a bump on a chip and a contact
point on a substrate in a conventional flip-chip package;
[0021] FIGS. 2A.about.2F are schematic cross-sectional views
showing the progression of steps for producing a cylindrical
bonding structure according to a first embodiment of this
invention;
[0022] FIGS. 3A.about.3E are schematic cross-sectional views
showing the progression of steps for producing a cylindrical
bonding structure according to a second embodiment of this
invention;
[0023] FIGS. 4A.about.4F are schematic cross-sectional views
showing the progression of steps for producing a cylindrical
bonding structure according to a third embodiment of this
invention;
[0024] FIGS. 5A.about.5C are schematic cross-sectional views
showing an application of the third cylindrical bonding structure
according to this invention to the fabrication of a flip-chip
package; and
[0025] FIGS. 6A.about.6E are cross-sectional views showing
cylindrical bonding structures fabricated according to this
invention with each cylindrical bonding structure having an
addition transition layer between the conductive cylinder and the
solder cap.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0027] FIGS. 2A.about.2F are schematic cross-sectional views
showing the progression of steps for producing a cylindrical
bonding structure according to a first embodiment of this
invention. As shown in FIG. 2A, a silicon wafer 210 is provided.
Since each chip (not shown) is formed by cutting up the wafer 210
and any redistribution layer or bumps are formed before cutting,
the wafer 210 actually represents a congregation of uncut chips.
Furthermore, the active surface 212 of the wafer 210 has a
passivation layer 214 and a plurality of bonding pads 216 (only one
bonding pad is shown in FIG. 2A). The active surface 212 of the
wafer 210 refers to the side of the wafer 210 where active devices
are formed. The patterned passivation layer 214 exposes the bonding
pads 216. Note that bonding pads 216 includes those original pads
on the chips or the bonding pads of any redistribution circuit
layer on the chips. The purpose of having a redistribution layer is
to relocate the original bonding pads on the chip to some other
places on the chip.
[0028] As shown in FIG. 2A, a ball contact metallic layer 220 is
formed over the entire active surface 212 (that is, the passivation
layer 214) of the wafer 210 by conducting, for example, an
electroplating operation, an evaporation plating operation or
sputtering. The ball contact metallic layer 220 covers the bonding
pads 216 and serves as an interface between a subsequently formed
conductive cylinder 240 (as shown in FIG. 2C) and the bonding pad
216. Hence, the ball contact metallic layer must be a material that
produces as little stress as possible, has a high adhesive
strength, resists corrosion and sticks to surface quite easily. In
general, the ball contact metallic layer is a composite layer
comprising two or more metallic layers, for example, including an
adhesive layer and a wetting layer. Common metallic material for
fabricating the ball contact metallic layer includes titanium (Ti),
tungsten (W), chromium (Cr), copper (Cu), nickel (Ni), cobalt (Co),
silver (Ag), gold (Au), tin (Sn), vanadium (V), palladium (Pd) or
an alloy of some of the aforementioned metals.
[0029] As shown in FIG. 2B, a patterned mask layer 230 is formed
over the ball contact metallic layer 220. The mask layer 230 has a
plurality of openings 232 (only one is shown in FIG. 2B) that
corresponds in position to the bonding pads 216 and exposes a
portion of the ball contact metallic layer 220. The patterned mask
layer 230 is formed, for example, by forming a photoresist layer
over the ball contact metallic layer 220, conducting a photographic
exposure and developing the photoresist layer. Aside from
depositing photoresist and conducting photographic procedures, the
mask layer 230 with openings 232 thereon may also be formed by a
corresponding method using some other materials.
[0030] As shown in FIG. 2C, an electroplating operation is
conducted to deposit conductive material into the opening 232 using
the ball contact metallic layer 220 as a seed layer. The opening
232 is partially filled to form a conductive cylinder 240 over the
ball contact metallic layer 220. The conductive material deposited
into the opening 232 is a high melting point metal or alloy such as
tin (Sn), lead (Pb), copper (Cu), gold (Au), silver (Ag), zinc
(Zn), bismuth (Bi), magnesium (Mg), antimony (Sb), indium (In) or
an alloy containing various combination of the aforementioned
metals.
[0031] As shown in FIG. 2D, an electroplating operation or a
printing operation is conducted to fill the remaining space of the
opening 232 with solder material using the conductive cylinder 240
as a seed layer. The solder material forms a cylindrical solder cap
250 over upper surface of the conductive cylinder 240. Note that
the solder material is a metal or alloy having a melting point
lower than that of the conductive cylinder. Suitable solder
material includes tin (Sn), lead (Pb), copper (Cu) gold (Au), zinc
(Zn), bismuth (Bi), magnesium (Mg), antimony (Sb), indium (In) or
an alloy containing various combinations of the aforementioned
metals.
[0032] As shown in FIG. 2E, the mask layer 230 and the ball contact
metallic layer 230 outside the conductive cylinder 240 are removed.
The reserved ball contact metallic layer 220, the conductive
cylinder 240 and the cylindrical solder cap together constitute a
cylindrical bonding structure 260. As an example, the conductive
cylinder 240 may contain tin and lead in the ratio 5:95 (5Sn/95Pb)
or 10:90 (10Sn/90Pb) and the cylindrical solder cap 250 may contain
tin and lead in the ratio 63:37 (63Sn/37Pb) or 60:40 (60Sn/40Pb).
The conductive cylinder 240 can also be a copper rod while the
cylindrical solder cap 250 can be a tin cap. Alternatively, the
conductive cylinder 240 can be a rod made from a high melting point
lead-free alloy such as a tin-silver-copper (Sn/Ag/Cu) alloy and
the cylindrical solder cap 250 can be a cap made from a low melting
point lead-free alloy such as tin-bismuth (Sn/Bi) alloy.
[0033] As shown in FIG. 2F, a reflow treatment is conducted after
the cylindrical bonding structure 260 is exposed. In the reflow
process, the cylindrical solder cap 250 is partially melted to form
a solder block 250a having a hemispherical profile over the upper
surface of the conductive cylinder 240.
[0034] As shown in FIGS. 2E and 2F, the cylindrical bonding
structure 260 of the first embodiment mainly comprises the
conductive cylinder 240 and the solder block 250a. The solder block
may have a cylindrical shape (the cylindrical solder cap 250 shown
in FIG. 2E) or a hemispherical shape (shown in FIG. 2F). The
cylindrical bonding structure 260 serves a similar function as the
bump 114 in FIGS. 1A and 1B. When the solder block 250a melts, the
conductive cylinder 240 and the junction pad 122 are joined
together. Hence, the cylindrical bonding structure 260 not only
serves as a medium for connecting the chip 110 and the substrate
120 together electrically, the conductive cylinder 240 also serves
as an cushioning pad from the chip 110 that pushes the solder block
further towards the substrate 120. Note that outer diameter of the
conductive cylinder 240 is fixed even when height of the conductive
cylinder 240 is increased. Hence, distance of separation between
neighboring cylindrical bonding structures 260 and hence
neighboring bonding pads 114 (or bonding pads 216) on the chip 110
is shortened.
[0035] According to the first embodiment, the steps involved in
fabricating the cylindrical bonding structure include forming a
ball contact metallic layer globally over a wafer and then forming
a patterned mask layer over the ball contact metallic layer. The
mask layer has an opening that surrounds a bonding pad and exposes
a portion of the ball contact metallic layer. An electroplating
operation is conducted to partially fill the mask opening with
conductive material, thereby forming a conductive cylinder. Another
electroplating operation or printing operation is conducted to fill
up the remaining space of the opening, thereby forming a
cylindrical solder cap on the upper surface of the conductive
cylinder. Finally, the mask layer and the ball contact metallic
layer outside the conductive cylinder are removed to form the
cylindrical bonding structure. Furthermore, a reflow operation may
also be conducted to transform the cylindrical solder cap into a
solder block having a hemispherical shape attached to the upper
surface of the conductive cylinder.
[0036] In summary, the method of fabricating the cylindrical
bonding structure according to the first embodiment of this
invention mainly involves forming a conductive cylinder over the
bonding pad of a chip. The conductive cylinder serves as a
conductive medium as well as a pad for cushioning up the distance
between the chip and the substrate. In addition, by attaching a
solder block on the upper end of the conductive cylinder, the
conductive cylinder and the junction pad on the substrate are
bonded together after the solder block material is partially melted
in a reflow operation. Hence, at the same height level, the
conductive cylinder can be designed to have an outer diameter
smaller than the outer diameter of a spherical bump in a
conventional design. Ultimately, the distance of separation between
neighboring cylindrical bonding structures and hence the
corresponding distance of separation between neighboring bonding
pads on the chip can be reduced.
[0037] FIGS. 3A.about.3E are schematic cross-sectional views
showing the progression of steps for producing a cylindrical
bonding structure according to a second embodiment of this
invention. The second embodiment differs from the first embodiment
in that a solder ball is planted onto the upper surface of the
conductive cylinder instead of forming the solder block (or the
cylindrical solder cap). Since the initial steps as shown in FIGS.
3A.about.3C for forming the cylindrical bonding structure are
identical to the ones shown in FIGS. 2A.about.2C, detailed
description is omitted.
[0038] As shown in FIG. 3D, the mask layer 330 and the ball contact
metallic layer 320 outside the conductive cylinder 340 are removed
to expose the conductive cylinder 340. As shown in FIG. 3E, a ball
placement operation is conducted to attach a solder ball 350 on the
upper surface of the conductive cylinder 340. The solder ball 350
serves an identical function as the solder block 250a (or
cylindrical solder cap 250) in the first embodiment. Hence, a
cylindrical bonding structure 360 is formed on the bonding pad 314
of the chip 316.
[0039] In summary, one major aspect of both the first and the
second embodiment of this invention is to form a block of solder
material on top of a conductive cylinder for joining the conductive
cylinder with junction pad on the substrate. The block of solder
material may be shaped into a variety of forms including
cylindrical, spherical or hemispherical The solder block is formed
over the conductive cylinder by depositing solder material into the
same opening for forming the conductive cylinder through conducting
an electroplating operation or printing operation as in the first
embodiment. Alternatively, a solder ball is planted on top of the
conductive cylinder as in the second embodiment.
[0040] FIGS. 4A.about.4F are schematic cross-sectional views
showing the progression of steps for producing a cylindrical
bonding structure according to a third embodiment of this
invention. One major aspect in the third embodiment that differs
from the first and the second embodiment of this invention is the
control of outer diameter and length of the solder block (or
cylindrical solder cap) so that pitch between neighboring bonding
pads on a chip can be further reduced.
[0041] As shown in FIG. 4A, a wafer 410 having an active surface
412 is provided. The active surface 412 has a plurality of bonding
pads 416 thereon. A passivation layer covers the active surface 412
but exposes the bonding pads 416. A ball contact metallic layer 420
is formed over the entire active surface 412 (the passivation layer
414) of the wafer 410 including the bonding pads 416 by conducting
an electroplating operation, evaporation plating operation or
sputtering, for example.
[0042] As shown in FIG. 4B, a first patterned mask layer 430 is
formed over the ball contact metallic layer 420. The first mask
layer 430 has a plurality of openings 432 that corresponds in
position to the bonding pads 416 and exposes a portion of the ball
contact metallic layer 420. Since the patterned first mask layer
430 is formed in a manner similar to the mask layer 230 in the
first embodiment, description is not repeated here.
[0043] As shown in FIG. 4C, an electroplating operation is
conducted to deposit conductive material into the openings 432
using the ball contact metallic layer 420 as a seed layer. Hence,
conductive cylinders 440 are formed over the ball contact metallic
layer 420. Note that the conductive material is a high melting
point metal or alloy.
[0044] As shown in FIG. 4D, a second patterned mask layer 434 is
formed over the first mask layer 430. The second mask layer 434 has
a plurality of openings 436 and exposes the central region of the
conductive cylinder 440. Since the patterned second mask layer 434
is formed in a manner similar to the mask layer 230 in the first
embodiment, description is not repeated here.
[0045] As shown in FIG. 4E, another electroplating operation is
conducted to deposit conductive material into the openings 436
using the conductive cylinder 440 as a seeding layer. Hence, a
cylindrical solder cap 450 is formed on the upper surface of each
conductive cylinder 440. Note that the conductive material
deposited into the openings 436 is a low melting point metal or
alloy so that the cylindrical solder cap 450 has a melting point
lower than the conductive cylinder 440.
[0046] As shown in FIG. 4F, the first mask layer 430, the second
mask layer 434 and the ball contact metallic layer 420 outside the
conductive cylinder 440 are removed. The remaining ball contact
metallic layer, the conductive cylinder 440 and the cylindrical
solder cap 450 together form a cylindrical bonding structure
460.
[0047] FIGS. 5A.about.5C are schematic cross-sectional views
showing an application of the third cylindrical bonding structure
according to this invention to the fabrication of a flip-chip
package. As shown in FIG. 5A, a cylindrical bonding structure 514
according to the third embodiment of this invention is formed on
the bonding pad 512 of a chip 510. The cylindrical bonding
structure 514 comprises a ball contact metallic layer 514a, a
conductive cylinder 514b and a cylindrical solder cap 514c. In
addition, a substrate 520 having a solder mask layer 524 and a
junction pad 522 thereon is also provided. The solder mask 524 has
a plurality of openings 526 that exposes the junction pads 522.
[0048] As shown in FIG. 5B, the cylindrical solder cap 514c has an
outer diameter smaller than the diameter of the opening 526 on the
solder mask 524. Hence, tolerance between the cylindrical solder
cap 514c on the cylindrical bonding structure 514 and the junction
pad 522 on the substrate 520 is greatly increased. Furthermore, if
the conductive cylinder 514b has an outer diameter greater than the
diameter of the opening 526, the cylindrical solder cap 514c must
be designed to have a length greater than the depth of the opening
526. Hence, when the cylindrical solder cap 514c is lowered into
the opening 526, the upper end of the cylindrical solder cap 514c
is able to contact the junction pad 522.
[0049] As shown in FIG. 5C, a reflow process may be conducted after
the upper surface of the cylindrical solder cap 514c is positioned
to contact the junction pad 522. In the reflow process, the
cylindrical solder cap 514c partially melts and joins together the
conductive cylinder 514b and the junction pad 522. Moreover, an
under fill material may be injected into the space between the chip
510 and the substrate 520 to protect the cylindrical bonding
structure 514 and serve as a vibration damper.
[0050] The method of fabricating the cylindrical bonding structure
according to the third embodiment includes forming a ball contact
metallic layer over the surface of a wafer surface and forming a
patterned first mask layer over the ball contact metallic layer.
The first mask layer has openings that correspond in position to
various bonding pads on the wafer and exposes a portion of the ball
contact metallic layer An electroplating operation is conducted to
deposit conductive material into the openings of the first mask
layer to form conductive cylinders. A patterned second mask layer
is formed over the first mask layer. The second mask layer has
openings that expose a portion of the upper surface of the
conductive cylinders. Similarly, solder material is deposited into
the openings of the second mask by conducting an electroplating
operation to form cylindrical solder caps over the conductive
cylinders. The first mask layer, the second mask layer and the ball
contact metallic layer outside the conductive cylinder are removed
so that the remaining ball contact metallic layer, the conductive
cylinder and the cylindrical solder cap together form a cylindrical
bonding structure on the chip.
[0051] One major difference between the cylindrical bonding
structure according to the third embodiment and the first two
embodiments is that the cylindrical solder cap is designed to have
an outer diameter smaller than opening diameter on the solder mask.
Hence, the cylindrical solder cap may easily lower into the opening
to contact the junction pad on the substrate. This increases the
yield of fabricating a flip-chip package and reduces the diameter
of the opening. Ultimately, distance of separation between
neighboring junction pads on a substrate and distance of separation
between neighboring bonding pads on a chip may both be reduced.
[0052] FIGS. 6A.about.6E are cross-sectional views showing
cylindrical bonding structures fabricated according to this
invention with each cylindrical bonding structure having an
additional transition layer between the conductive cylinder and the
solder cap. As shown in FIGS. 6A.about.6E, a transition layer 670
is inserted between the conductive cylinder 640 and the solder
block 650 in each case. The transition layer 670 may provide
different functions according to the constituent materials.
Furthermore, the transition layer 670 can be a single layer or a
multiple of layers. In FIG. 6A, the transition layer 670 provides a
function very similar to the ball contact metallic layer 620
between the bonding pad 616 and the conductive cylinder 640. The
transition layer 670 may contain one or a more layers. The
transition layer mainly boosts the connectivity between the
conductive cylinder 640 and the solder block 650 or prevents the
collapse of solder block 650 material onto the peripheral section
of the conductive cylinder 640 after conducting a reflow operation
leading to a short-circuit between neighboring conductive
cylinders.
[0053] The transition layer 670 is fabricated after forming the
conductive cylinder 640. The transition layer 670 is formed over
the upper surface of the conductive cylinder 640. Thereafter, a
cylindrical solder cap 650 is formed over the transition layer 670
in FIG. 6A, while a solder block having a hemispherical shape is
formed over the transition layer 670 in FIG. 6B. In FIG. 6C, the
transition layer 670 is also fabricated on the upper surface of the
conductive cylinder 640 after forming the conductive cylinder 640.
However, a solder ball 650 is attached to the transition layer 670
instead of a solder cap. Similarly, in FIGS. 6D and 6E, the
transition layer 670 is fabricated on the upper surface of the
conductive cylinder before forming a solder cap over the transition
layer 670. One major difference is that the transition layer 670 in
FIG. 6D is formed inside the opening of the patterned first mask
layer 430 (in FIG. 4C) while the transition layer 670 in FIG. 6E is
formed inside the opening of the patterned second mask layer 434
(in FIG. 4D).
[0054] In conclusion, the cylindrical bonding structure according
to this invention is formed by constructing a conductive cylinder
over the bonding pad of a chip and using the conductive cylinder to
cushion up the distance of separation between the chip and a
substrate. The solder block on the tip of the conductive cylinder
is also used to join the conductive cylinder to a junction pad on
the substrate. Compared with a conventional design using spherical
bumps, the cylindrical bonding structure can provide a smaller
contact separation. In addition, the solder block may have a
variety of profiles including cylindrical, spherical or
hemispherical shape. Note that when the solder block has a
cylindrical shape, the length and outer diameter of the cylinder
may be adjusted to fit into the opening leading to the junction
pad. Consequently, outer diameter of the opening may be reduced and
separation between neighboring junction pads may be reduced. In
other words, separation of neighboring bonding pads on a chip may
be reduced.
[0055] Because the conductive cylinder and the junction pad are
connected by partially melting the solder block in a reflow
process, the step of applying a low melting point solder material
on the junction pads of the substrate or the surface of bumps in a
conventional design can be eliminated. Hence, production cost of
the flip-chip package is reduced.
[0056] Furthermore, the conventional high-temperature reflow
process for shaping the bumps into a spherical shape may result in
the formation of excessive oxide material on bump surface and may
lead to poor bonding between the bump and the junction pad. In this
invention, however, the solder block is formed on the upper surface
of the conductive cylinder. A high-temperature reflow process for
shaping the solder block into a spherical form is not absolutely
required. Even if a spherical shape is demanded, the solder block
is shaped using a low-temperature reflow process. Hence, not much
oxidation occurs at the surface of the solder block material.
Ultimately, a better junction structure is formed linking up the
conductive cylinder and the junction pad.
[0057] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *