Understanding the formation of voids in solder joints is important for predicting the long-term reliability of solder interconnects. This paper reports experimental research on the formation of void bubbles within molten solder bumps in flip-chip connections. For flip-chip-soldered electronic components, which have small solder volume, voids can be more detrimental to reliability. A previous theory based on thermocapillary flow reveals that the direction of heating influences void formation. Using different heating profiles, 480 solder joints of flip-chip assemblies were processed. A high-lead solder was employed in the experiments. The solder samples were microsectioned to determine the actual size or diameter of the voids. A database on sizes and locations of voids was then constructed. More defective bumps, 80%, and higher void volume were found when the solder was melted from top (flip-chip side) to bottom (test board side). The observation on cases with melting direction from bottom to top had 40% defective bumps. The results show that a single big void is near the solder bump center with a few small voids near the edge. This supports the numerical study based on the thermocapillary theory. When the melting direction was reversed, many small voids appear near the edge. Big and middle-size voids tend to stay in the middle and outer regions from top towards middle layer of the bump. This experimental finding does not completely agree with the interpretation on the formation of voids by thermocapillary theory, however, the results do show that heat flux direction plays significant role in the formation and distribution of void bubbles in molten solder.
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e-mail: rpanton@mail.utexas.edu
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June 2005
Research Papers
Experimental Study of Void Formation in High-Lead Solder Joints of Flip-Chip Assemblies
Daijiao Wang,
Daijiao Wang
Mechanical Engineering Department,
The University of Texas at Austin
, 1 University Station C2200, ETC 5.160, Austin, TX 78712
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Ronald L. Panton
Ronald L. Panton
Fellow ASME
Mechanical Engineering Department,
e-mail: rpanton@mail.utexas.edu
The University of Texas at Austin
, 1 University Station C2200, ETC 5.160, Austin, TX 78712
Search for other works by this author on:
Daijiao Wang
Mechanical Engineering Department,
The University of Texas at Austin
, 1 University Station C2200, ETC 5.160, Austin, TX 78712
Ronald L. Panton
Fellow ASME
Mechanical Engineering Department,
The University of Texas at Austin
, 1 University Station C2200, ETC 5.160, Austin, TX 78712e-mail: rpanton@mail.utexas.edu
J. Electron. Packag. Jun 2005, 127(2): 120-126 (7 pages)
Published Online: May 18, 2004
Article history
Received:
January 12, 2004
Revised:
May 18, 2004
Citation
Wang, D., and Panton, R. L. (May 18, 2004). "Experimental Study of Void Formation in High-Lead Solder Joints of Flip-Chip Assemblies." ASME. J. Electron. Packag. June 2005; 127(2): 120–126. https://doi.org/10.1115/1.1876472
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