FeNi alloy is considered a possible substitute for Cu as under bump metallization (UBM) in wafer level package (WLP) since it forms very thin intermetallic compound (IMC) layer with Pb-free solder in the reflow process. In this paper, WLPs with FeNi and Cu UBM were fabricated and their board level reliabilities were studied comparatively. The WLP samples assembled on the printed circuit board (PCB) were subjected to temperature cycling and drop tests according to JEDEC standards. The results showed that the reliability of WLP with FeNi UBM was a little lower than that with Cu UBM. The main failure modes for both FeNi and Cu UBM samples in temperature cycling test were the crack in IMC or solder ball on PCB side. And detachments between UBM and the redistribution layer (RDL) were also observed in Cu UBM WLPs. In drop test, the crack of RDL was found in all failed FeNi UBM samples and part of Cu UBM ones, and the primary failure mode in Cu UBM samples was the crack of IMC on PCB side. In addition, the finite element analysis (FEA) was carried out to further understand the difference of the failure modes between the FeNi UBM samples and the Cu UBM samples. The high stress was observed around the UBM and the pad on PCB in the temperature cycling model. And the maximum stress appeared on the RDL in the drop simulation, which was obviously larger than that on the pad. The FEA results showed that the introduction of FeNi UBM increased the stress levels both in temperature cycling and drop tests. Thus, the FeNi alloy cannot simply replace Cu as UBM in WLP without further package structural optimization.

References

References
1.
Liu
,
P. S.
,
Wang
,
J. L.
,
Tong
,
L. Y.
, and
Tao
,
Y. J.
,
2014
, “
Advances in the Fabrication Processes and Applications of Wafer Level Packaging
,”
ASME J. Electron. Packag.
,
136
(
2
), p.
024002
.
2.
Crosbie
,
P.
, and
Lee
,
Y. J.
,
2010
, “
Multiple Impact Characterization of Wafer Level Packaging (WLP)
,”
Microelectron. Reliab.
,
50
(
4
), pp.
577
582
.
3.
Fan
,
X. J.
,
Varia
,
B.
, and
Han
,
Q.
,
2010
, “
Design and Optimization of Thermo-Mechanical Reliability in Wafer Level Packaging
,”
Microelectron. Reliab.
,
50
(
4
), pp.
536
546
.
4.
Xu
,
S.
,
Keser
,
B.
,
Hau-Riege
,
C.
,
Bezuk
,
S.
, and
Yau
,
Y. W.
,
2013
, “
A Study of Wafer Level Package Board Level Reliability
,”
IEEE 63rd Electronic Components and Technology Conference
(
ECTC
),
Las Vegas, NV
, May 28–31, pp.
1204
1209
.
5.
An
,
T.
,
Qin
,
F.
, and
Xia
,
G. F.
,
2013
, “
Analytical Solutions and a Numerical Approach for Diffusion-Induced Stresses in Intermetallic Compound Layers of Solder Joints
,”
ASME J. Electron. Packag.
,
136
(
1
), p.
011001
.
6.
Ladani
,
L.
, and
Abdelhadi
,
O.
,
2014
, “
Structural Size Effect on Mechanical Behavior of Intermetallic Material in Solder Joints: Experimental Investigation
,”
ASME J. Electron. Packag.
,
137
(
1
), p.
014501
.
7.
Zeng
,
K.
, and
Tu
,
K. N.
,
2002
, “
Six Cases of Reliability Study of Pb-Free Solder Joints in Electronic Packaging Technology
,”
Mater. Sci. Eng., R
,
38
(
2
), pp.
55
105
.
8.
He
,
M.
,
Lau
,
W. H.
, and
Qi
,
G. J.
,
2003
, “
Intermetallic Compound Formation Between Sn-3.5Ag Solder and Ni-Based Metallization During Liquid State Reaction
,”
Thin Solid Films
,
462
, pp.
376
383
.
9.
Alam
,
M. O.
,
Chan
,
Y. C.
, and
Tu
,
K. N.
,
2003
, “
Effect of Reaction Time and P Content on Mechanical Strength of the Interface Formed Between Eutectic Sn-Ag Solder and Au/Electroless Ni(P)/Cu Bond Pad
,”
J. Appl. Phys.
,
94
(
6
), pp.
4108
4115
.
10.
Alam
,
M. O.
,
Chan
,
Y. C.
, and
Hung
,
K. C.
,
2002
, “
Reliability Study of the Electroless Ni-P Layer Against Solder Alloy
,”
Microelectron. Reliab.
,
42
(
7
), pp.
1065
1073
.
11.
Chonan
,
Y.
,
Komiyama
,
T.
,
Onuki
,
J.
,
Urao
,
R.
,
Kimura
,
T.
, and
Nagano
,
T.
,
2002
, “
Influence of Phosphorus Concentration in Electroless Plated Ni-P Alloy Film on Interfacial Structures and Strength Between Sn-Ag-(-Cu) Solder and Plated Ni-P Alloy Film
,”
Mater. Trans.
,
43
(
8
), pp.
1840
1846
.
12.
Hwang
,
C. W.
,
Suganuma
,
K.
,
Lee
,
J. G.
, and
Mori
,
H.
,
2003
, “
Interface Microstructure Between Fe-42Ni Alloy and Pure Sn
,”
J. Mater. Res.
,
18
(
5
), pp.
1202
1210
.
13.
Dariavach
,
N.
,
Callahan
,
P.
, and
Liang
,
J.
,
2006
, “
Intermetallic Growth Kinetics for Sn-Ag, Sn-Cu, and Sn-Ag-Cu Lead-Free Solders on Cu, Ni, and Fe-42Ni Substrates
,”
J. Electron. Mater.
,
35
(
7
), pp.
1581
1592
.
14.
Guo
,
J. J.
,
Zhang
,
L.
, and
Xian
,
A. P.
,
2007
, “
Solderability of Electrodeposited Fe-Ni Alloys With Eutectic SnAgCu Solder
,”
J. Mater. Sci. Technol.
,
23
(
6
), pp.
811
816
.
15.
Zhu
,
Q. S.
,
Guo
,
J. J.
, and
Wang
,
Z. G.
,
2008
, “
Shear of Sn-3.8Ag-0.7Cu Solder Balls on Electrodeposited FeNi Layer
,”
International Conference on Electronic Packaging Technology and High Density Packaging
(
ICEPT-HDP 2008
),
Shanghai
, July 28–31, pp. 848–851.
16.
Zhang
,
H.
,
Wu
,
D.
,
Zhang
,
L.
,
Duan
,
Z. Z.
,
Lai
,
C. M.
, and
Liu
,
Z. Q.
,
2012
, “
Wafer Level Electrodeposition of Fe-Ni Novel UBM Films
,”
Acta Metall. Sin.
,
48
(
10
), pp.
1273
1280
(in Chinese).
17.
JEDEC
,
2005
, “
Temperature Cycling
,”
JEDEC Solid State Technology Association
,
Arlington, VA
.
18.
IPC
,
2002
, “
Performance Test Methods and Qualification Requirements for Surface Mount Solder Attachments
,”
IPC–Association Connecting Electronics Industries
,
Bannockburn, IL
.
19.
JEDEC
,
2003
, “
Board Level Drop Test Method of Components for Handheld Electronic Products
,”
JEDEC Solid State Technology Association
,
Arlington, VA
.
20.
Zhang
,
H.
,
Zhu
,
Q. S.
,
Liu
,
Z. Q.
,
Zhang
,
L.
,
Guo
,
H. Y.
, and
Lai
,
C. M.
,
2014
, “
Effect of Fe Content on the Interfacial Reliability of SnAgCu/FeeNi Solder Joints
,”
J. Mater. Sci. Technol.
,
30
(
9
), pp.
928
933
.
You do not currently have access to this content.