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Research Papers

Sub-100μm SnAg Solder Bumping Technology and the Bump Reliability

[+] Author and Article Information
Xiaoqin Lin

Graduate School, Chinese Academy of Sciences, Beijing, 100049, P.R.C.; Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865 Changning Road, Shanghai, 200050, P.R.C.

Le Luo

 Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, No. 865 Changning Road, Shanghai, 200050, P.R.C.leluo@mail.sim.ac.cn

J. Electron. Packag 131(1), 011014 (Feb 18, 2009) (6 pages) doi:10.1115/1.2957333 History: Received April 29, 2007; Revised February 19, 2008; Published February 18, 2009

Lead-free solder bumping and its related interconnection and reliability are becoming one of the important issues in today’s electronic packaging industry. In this paper, alloy electroplating was used as SnAg solder bumping process. Multiple reflow was preformed on as-plated solder bumps. Scanning electron microscopy and energy dispersive X-ray analysis were used to investigate the intermetallic compound and microvoids of cross-sectioned solder bump. Shear test was used to evaluate the reliabilities of the SnAg bumps. The 13×13 area-array Sn/3.0Ag solder bumps of 70μm in height and 90μm in diameter were fabricated with a smooth and shiny surface and with a uniform distribution of Ag. During multireflow, the scalloped Cu6Sn5 phase grows by a ripening process. Volume shrinkage was the main reason for the formation of microvoids during multireflow. The average shear strength of solder bumps on TiW/Cu under bump metallurgy (UBM) increased with reflow times. The electroplating process is suitable for mass production of well-controlled geometry and uniformity of SnAg solder bumps. Microvoids have trivial negative impacts on the solder bonds. The combination of TiW/Cu UBM and SnAg solder is reliable.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 9

Cross section of the solder joint after thermal cycling

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Figure 8

Shear plane of SnAg solder bumps: (a) 1 time reflow and (b) 13 times reflow

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Figure 7

Shear strength distribution of the solder bumps with different reflow times: (a) 1 time reflow, (b) 3 times reflow, (c) 6 times reflow, and (d) 13 times reflow

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Figure 6

Line scan map of electroprobe crossing IMC layer after 13 times reflow

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Figure 5

Micrographs of cross sections through the SnAg solder/Cu interface after 13 times reflow

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Figure 4

Metallographic images of cross sections of Sn/3.0Ag solder bumps with different reflow times: (a) 1 time reflow, (b) 6 times reflow, and (c) 13 times reflow

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Figure 3

SEM and EDAX images of cross section of solder bumps: (a) SEM image of solder bumps and (b) EDAX mapping of Ag

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Figure 2

EDAX of cross-sectional surface of the solder bump

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Figure 1

SEM images of electroplated SnAg solder bumps: (a) 13×13 area-array and (b) a magnification of (a)

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