Abstract
Accelerated thermal cycling (ATC) test is a widely used test methodology in the semiconductor industry to assess reliability performance of packaging solder joint. A typical type of packaging solder joint failure is the propagation of fatigue cracks due to the coefficient of thermal expansion (CTE) mismatch in the interface between materials. However, ATC test is very time consuming and the test time can take more than several months. In light of it, the efficiency of ATC test has become an important topic. The parameters of ATC test, such as temperature dwell time and ramp rate, significantly influence fatigue failure in solder joints. The testing time can be reduced by fast temperature cycle, but the effects of ramp rate will cause some variations in solder joints’ material properties and mechanics behavior due to strain rate and stress changes. This study assesses solder joint reliability under different thermal cycling ramp rates based on the creep properties of lead-free material. This study uses finite element (FE) analysis with a temperature-dependent Young’s modulus and well known Garofalo–Arrhenius creep equation to assess the solder deformation behavior. An energy density-based empirical equation is used, along with the optimal mesh size for finite element simulation to determine how to accommodate the strain rate effect in solder joints caused by various thermal cycling ramp rates. A remarkable agreement in the correlation between the finite element analysis and experimental results is observed. Two major contributions emerge from this study. The first is a simplified energy density-based lifetime equation to effectively assess solder joint reliability. The equation is validated for different solder joint geometries and packaging types with lifetimes ranging from a few hundred to thousands of cycles, including plastic BGA, flip-chip, and wafer-level chip-scale packaging. In addition, an optimal mesh size is recommended for finite element simulation analysis and validated for different solder joint geometries. The second contribution is the development of a novel dimensionless acceleration-factor (AF) equation to characterize the effects of ramp rate and dwell time under varying thermal cycle loading conditions. The proposed AF equation shows high correlation with the simulation and test results for various thermal cycle loadings. In addition, the proposed AF equation is validated by confirming the consistency of its prediction results with test data on a range of packages and thermal cycling profiles reported in the literature. The research results not only reveal the strain rate effect on packaging solder joints at varying ramp rates, but also provide a quick reliability assessment methodology to accommodate this effect. The reliability of package solder joints can be analyzed using the lifetime and AF equations developed in this study, which effectively reduce reliability testing time and the fabrication costs of test runs.