Open Access

ARTICLE

Evaluations of the BGA Solder Ball Shape by Using Energy Method

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1 Corresponding author. E-mail: hclinh@gmail.com, Tel: +886-6-2426135. 2 Department of Engineering Science, National Cheng Kung University. 3 Department of Computer Application Engineering, Far East University.

Computers, Materials & Continua 2007, 6(1), 43-50. https://doi.org/10.3970/cmc.2007.006.043

Abstract

Presented herein are the evaluation results of the BGA solder ball shape using energy method, two types of solder, viz. Sn37Pb and Sn80Pb, are selected .The geometry of the solder bump is firstly estimated using free computer software, the Surface Evolver, an interactive program which is an energy-based approach for the study of liquid droplet surfaces shaped by surface tension and other energies. The solder bump is then numerically constructed in a finite element model that simulates a BGA package. The influences of both upper and bottom solder pad radii, the surface tension on the balls, and the external load axially applied to the reflow solders on the stand-off height and the contact angle for both solder materials are investigated. The results show that for both solder materials, the stand-off height remains at a height under some pad radius. The height decreases as both upper and bottom pad radii increase. On the other hand, the contact angle presents a nearly inverse trend with respect to the pad radii. The study of the effect of surface tension reveals that at a constant pad radius, the solder ball stand-off height increases with surface tension; however, the trend becomes saturated eventually. The contact angle decreases as the surface tension becomes large. The trend also tends to be saturated. The results of the effects of axially applied load on the stand-off height and the contact angle show that as the applied load is increased so is the contact angle; nevertheless, the stand-off height becomes shorter.

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