Experiments were carried out to investigate the effect of reversing the heat flux direction during cooling on the formation of voids during the reflow process. Under different upward and downward solidification conditions, 480 high-lead solder joints of flip-chip assemblies were processed. The solder samples were then microsectioned to determine the size and location of voids. The results show that reversing the flow direction during cooling has a significant effect on the final void formation. For the case of the melting direction from top (flip-chip side) to bottom (test board side), reversing the heat flux direction results in solidification direction from top to bottom. The percentage of defective bumps was found to be 28% and the volume of voids per defective bump was 1.5%. This is the best reflow methodology to minimize voids. Without reversing the heat flux the defective bumps were 80% with 4.0% void volume. In the case of solidification direction/melting direction from bottom to top, the percentage of defective bumps increases from 40% to 51%, accompanying a rise of the volume of voids from 3.0% to 3.7%.
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e-mail: rpanton@mail.utexas.edu
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December 2005
Research Papers
Effect of Reversing Heat Flux Direction During Reflow on Void Formation in High-Lead Solder Bumps
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. Dec 2005, 127(4): 440-445 (6 pages)
Published Online: January 4, 2005
Article history
Received:
June 29, 2004
Revised:
January 4, 2005
Citation
Wang, D., and Panton, R. L. (January 4, 2005). "Effect of Reversing Heat Flux Direction During Reflow on Void Formation in High-Lead Solder Bumps." ASME. J. Electron. Packag. December 2005; 127(4): 440–445. https://doi.org/10.1115/1.2070047
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