A PTH Reliability Model Considering Barrel Stress Distributions and Multiple PTHs in a PWB

Plated through hole (PTH) failure due to CTE-mismatch-induced fatigue is a major interconnection failure in electronic products. The IPC methodology that is widely used in industry for PTH reliability assessment assumes a uniform thermal stress distribution in PTH barrels and considers no effect of peripheral PTHs on the one under investigation. As a result, IPC-methodology-based PTH reliability assessment becomes insensitive to the factors, such as board thickness and PTH separations, which, however, are considered having considerable influence on PTH fatigue life. It also leads to deviation of prediction results from experimental ones. In this study, an improved analytical model that considers barrel stress distributions and the effect of multiple PTHs in a PWB is developed to address the issues. Comparisons between the analytical and FEM results indicate significantly improved correlation. This model verifies the maximum stress location at PTH barrels´ middle section. This result agrees with FEM results as well as failure observations on PTH barrel cracking in experiments and field. The model also provides a quantitative explanation on the strain distribution factor that is used to adjust assessment results for correlating with experiment in the existing IPC methodology