Rapid Solder Interconnect Fatigue Life Test Methodology for Predicting Thermomechanical Reliability

A rapid reliability test methodology was devised for simulating mechanical stresses induced from thermal expansion induced shear in temperature cycling of flip-chip devices in order to de-convolute shear stress from thermal effects in typical environmental tests. Using controlled force application according to spring deflection, a test stand was created to mechanically apply shear stress to solder interconnects in flip chip devices at isothermal conditions. The shear stress was applied cyclically using a tribometer to simulate the mechanical stresses induced in the interconnects of a device during a thermal cycle while in operation or accelerated testing. In the mechanical application of shear, the control of loading and cyclic rate can be precisely controlled while monitoring key factors for observing crack propagation and damage. In doing so, this novel approach introduces the ability to directly correlate shear stress and plastic work accumulation (damage) to fatigue life in a generic device, utilizing help from finite element models alongside data acquisition. Using the obtained correlations, lifetime predictions through early stage design analysis are possible, paving the way for a-priori optimized design for thermomechanical reliability in flip-chip devices. The methodology presented herein creates the opportunity to eliminate costly lifetime testing on multiple electronic device designs/configurations, while also expediting any data collection needed for new materials or process related impacts to reliability.