Formation of pure silver (Ag) flip-chip interconnect of silicon (Si) chips on copper (Cu) substrates is reported. Arrays of Ag columns, each 36 μm in height and 40 μm in diameter, are fabricated on 2-in. Si wafers which are first coated with chromium (Cr)/gold (Au) dual layers. The Si wafers are diced into 6 mm × 6 mm chips, each having 50 × 50 Ag columns. The Si chip with Ag columns is directly bonded to Cu substrate at 260 °C in 80 mTorr vacuum to inhibit oxidation. The static bonding pressure is as low as 680 psi (4.69 MPa), corresponding to a load of 0.021 oz (0.60 g) per column. During bonding, the Ag columns deform and conform to the Cu substrate. They are well bonded to the Cu. No molten phase is involved in the bonding process. The joints consist of pure Ag only. The ductile Ag joints are able to accommodate the thermal expansion mismatch between Si and Cu. It is well known that in nearly all soldering processes used in electronic industries, intermetallic compound (IMC) formation is essential to make a solder joint. In the pure Ag interconnect, no IMCs exist. Thus, reliability issues associated with IMCs are eliminated. Compared to tin-based lead-free solders, pure Ag joints have superior electrical and thermal properties.

References

References
1.
Tummala
,
R. R.
,
Rymaszewski
,
E. J.
, and
Klopfenstein
,
A. G.
, 1997,
Microelectronics Packaging Handbook-Semiconductor Packaging
,
2nd ed.
,
Chapman and Hall
,
London
.
2.
Li
,
M.
,
Lee
,
K. Y.
,
Olsen
,
D. R.
,
Chen
,
W. T.
,
Tan
,
B. T. C.
, and
Mhaisalkar
,
S.
, 2002, “
Microstructure, Joint Strength and Failure Mechanisms of SnPb and Pb-Free Solders in BGA Packages
,”
IEEE Trans. Electron. Packag.
,
25
(
3
), pp.
185
192
.
3.
Frear
,
D. R.
,
Jang
,
J. W.
,
Lin
,
J. K.
, and
Zhang
,
C.
, 2001, “
Pb-Free Solders for Flip-Chip Interconnects
,”
JOM
,
53
(
6
), pp.
28
33
.
4.
International Technology Roadmap for Semiconductors
,
2005 ed.
, Assembly and Packaging, 2005.
5.
Wang
,
P. J.
and
Lee
,
C. C.
, 2010, “
Silver Flip-Chip Technology by Solid-State Bonding
,”
J. Electron. Packag.
,
132
(
3
), p.
035001
.
6.
Lee
,
C. C.
,
Wang
,
P. J.
, and
Kim
,
J. S.
, 2007, “
Are Intermetallics in Solder Joints Really Brittle?
Proceedings of the IEEE Electronic Components and Technology Conference
, pp.
648
652
.
7.
Jang
,
J. W.
,
De Silva
,
A. P.
,
Drye
,
J. E.
,
Post
,
S. L.
,
Owens
,
N. L.
,
Lin
,
J. K.
, and
Frear
,
D. R.
, 2007, “
Failure Morphology After Drop Impact Test of Ball Grid Array (BGA) Package With Lead-Free Sn-3.8Ag-0.7Cu and Eutectic SnPb Solders
,”
IEEE Trans. Electron. Packag. Manuf.
,
30
(
1
), pp.
49
53
.
8.
Qu
,
S.
,
Xu
,
Y.
,
Tu
,
K. N.
,
Alam
,
M. O.
, and
Chan
,
Y. C.
, 2005, “
Micro-Impact Test on Lead-Free BGA Balls on Au/Electrolytic Ni/Cu Bond Pad
,”
Proceedings of the IEEE Electronic Components and Technology Conference
, pp.
467
471
.
9.
Lee
,
C. C.
,
Wang
,
D. T.
, and
Choi
,
W. S.
, 2006, “
Design and Construction of a Compact Vacuum Furnace for Scientific Research
,”
Rev. Sci. Instrum.
,
77
(
12
), p.
125104
.
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