DocumentCode :
844953
Title :
A reliability comparison of electroplated and stencil printed flip-chip solder bumps based on UBM related intermetallic compound growth properties
Author :
Jing-Feng Gong ; Chan, P.C.H. ; Guo-Wei Xiao ; Lee, R.S.W. ; Yuen, M.M.F.
Author_Institution :
Dept. of Electr. & Electron. Eng., Hong Kong Univ. of Sci. & Technol., China
Volume :
29
Issue :
1
fYear :
2006
fDate :
3/1/2006 12:00:00 AM
Firstpage :
164
Lastpage :
172
Abstract :
The effects of under bump metallurgy (UBM) microstructures on the intermetallic compound (IMC) growth of electroplated and stencil printed eutectic Sn-Pb solder bumps were investigated. The process parameters and their effects on UBM surface morphology and UBM shear strength were studied. For the electroplating process, the plating current density was the dominant factor to control the Cu UBM microstructure. For the stencil printing process, the zincation process has the most significant effect on the Ni UBM surface roughness and Ni grain sizes. In both processes, the good adhesion of UBM to aluminum can be obtained under suitable UBM processing conditions. Samples with different UBM microstructures were prepared using the two processes. The resulting samples were thermal aged at 85/spl deg/C, 120/spl deg/C, and 150/spl deg/C. It was observed that the Cu UBM surface roughness had larger effect on the IMC growth and solder ball shear strength than the Ni UBM surface roughness. The thickness of Cu/sub 3/Sn and Cu/sub 6/Sn/sub 5/ IMC depended strongly on the UBM microstructure. However, for Ni/Au UBM, no significant dependence was observed. More likely, the thickness of Au-Ni-Sn IMC near the IMC/solder interface was controlled by the amount of gold and the gold diffusion rate in the solder. Shear tests were performed after thermal aging tests and thermal/humidity tests. Different failure modes of different sample groups were analyzed. Electroless Ni UBM has been developed because it is a mask-less, low-cost process compared to electroplated Cu UBM. This study demonstrated that the process control was much easier for Ni UBM due to its lower reactivity with Sn material. These properties made Ni UBM a promising candidate for the lead-free solder applications.
Keywords :
ageing; copper alloys; current density; electroplating; eutectic alloys; failure analysis; flip-chip devices; gold alloys; grain size; lead alloys; metallisation; metallurgy; nickel alloys; process control; reliability; shear strength; solders; surface morphology; surface roughness; tin alloys; 120 C; 150 C; 85 C; Au-Ni-Sn; Cu/sub 3/Sn; Cu/sub 6/Sn/sub 5/; SnPb; UBM shear strength; UBM surface morphology; UBM surface roughness; electroless UBM; electroplating process; eutectic solder bumps; flip-chip solder bumps; gold diffusion rate; intermetallic compound growth; process control; shear tests; stencil printing process; thermal aging tests; thermal-humidity tests; under bump metallurgy microstructures; zincation process; Aging; Current density; Gold; Intermetallic; Microstructure; Rough surfaces; Surface morphology; Surface roughness; Testing; Tin; Copper; electroless Ni; electroplating; flip-chip; intermetallic compound (IMC); reliability; stencil printing; zincation;
fLanguage :
English
Journal_Title :
Components and Packaging Technologies, IEEE Transactions on
Publisher :
ieee
ISSN :
1521-3331
Type :
jour
DOI :
10.1109/TCAPT.2005.853178
Filename :
1599506
Link To Document :
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