Proportional Hazard Model of doped low creep lead free solder paste under vibration

Abstract

In this experiment, the vibrational performance of various lead-free doped (micro-alloyed) solder paste alloys on 15mm BGA packages were investigated. The Primary Goal of this test is to find a manufactureable solder paste that will mitigate the effects of aging on lead free solder joints. The results discuss the effects of different paste materials, the effects of doping level, and reflow profile on the resulting reliability of a variety of surface mount components. The test vehicle consists of 15 mm (CABGA 208) ball grid array packages with 0.8mm pitch, a leadless 5mm QFN package (MLF 20) with 0.65mm pitch and 2512 SMRs in order to understand the effect of doped solder paste on conventional packages. The test boards are built with three different reflow profiles and two different stencil thicknesses 8 mil (6 mil with overprint) and 4 mil to study the differences in doping effect of the new doped alloys. The test boards were built to withstand JEDEC JESD22-B103B standards of high stress test in vibrational shaker table to assess the solder joint performance. The test vehicle was subjected to accelerated life test of severe random vibration per board. The reliability of the component is determined by the ability of the components to withstand vibration as a result of motion produced by field operations. The deleterious effect of the mechanical loading of BGA's on the characteristic fatigue lifetime is reported. The time to failure were right censored after 20 hours. The experimental variables include paste materials, solder paste manufacturer, reflow profile, stencil thickness and component solder sphere. The response variable used in this test is Time to Failure (hours). The effect of experimental variables on Time to Failure were assessed at 5% level of significance using Cox Proportional Hazard Model. It is found that all the experimental variables have significant impact on the Time to Failure.