Chip Scale Package (CSP) solder joint reliabiltiy and modeling

摘要

A viscoplastic constitutive model was used ot analyze the thermally induced plastic and creep deformation and low cycle fatigue behavior fo the solder joints in Chip Scale Packages (CSP) mounted on Printed Circuit Boards (PCB). The time-dependent and time-independent viscoplastic strain rate and plastic hardenign work factors of solder material were used in 2-D plane strain finite element models. The viscoplastic strain rate data was fitted to the viscoplastic flow equation. The plastic hardening factors were considered in the evolution equation. A viscoelastic constitutive modle was used for molding compound. Finite element models, incorporating the viscoplastic flow and evolution equations ofr solder and the viscoelastic equations for molding compound, were verified by temperaute cycling tests on assembled CSPs. The effect of the cyclic frequrncy, dewell time, and temperautre cycling tests on assembled CSPs. The effect of the cyclic frequency, dwell time, and temperature ramp rate on the response of the viscoplastic deformation was studied or a tapeless lead-on-Chip (LOC) CSP sn a flexible substrate CSP. The ramp rate significantly affects the equivalent stress range in solder siginificantly affects the equivalent stress range in solder joints while a dwell time in excess of 10min per half cycel does not result in icreased strain range. The failure data from the experiments was fitted to the Weibull failure distribution and the Weibull parameters were extracted. After satisfactory correlation between teh experiment and the model was observed, the effect of material proper