Intermetallic Compound Thickness of Ball Grid Array Solder Joints Under Thermal Cycling Test Using ANOVA

Abstract

Thermal cycling testing is an accelerated reliability test that provides confidence that the design and the ball grid array (BGA) components assembly processes are complying with the intended goals of product performance. Nevertheless, the fatigue life models for solder joints can be determined by observing the thickness of intermetallic compound (IMC) layer development on BGA solder joints when subjected to multiple thermal cycling loadings. This paper studies the IMC layer growth variances on BGA components subjected to multiple thermal cycling loadings using ANOVA analysis. The IMC layer thickness data were measured after the cross-sectioning process. Three variables were observed; sample a: BGA balls without thermal cycling loadings, samples b and c: the BGA balls were exposed to 500 and 1000 thermal cycling loadings respectively. Samples b and c were placed in the testing chamber under the temperature of 0°C- 100°C by the ramp rate of 10°C per minute with hot and cold soak duration of 10 minutes per cycle. The studies revealed the comparison of the IMC layer growth variances between the thermal cycling loadings samples via ANOVA can determine the differences among the means and estimate whether the variance was practically significant. Each confidence interval has a confidence level of 98.08%. This result indicated that we can be 98.08% confident that each interval contains the true difference between a specific pair of group means. The individual confidence level for each comparison produces a 95% simultaneous confidence level for all three comparisons. IMC formation and growth were characterized during thermal cycle loading conditions and its effect on reliability was determined by observing the solder joints quality to permit the analytical prediction of reliability based on the ANOVA analysis data and technical understanding.