There is a need for a new Acceleration Factor (AF) that can relate Accelerated Thermal Cycle (ATC) fatigue life to Power Cycle (PC) fatigue life quickly and accurately in order to avoid over designing electronic packages for benign environments. An AF, such as the Norris-Landzberg AF, is only applicable when using it to predict fatigue life within the same environment, i.e. ATC to ATC or PC to PC. This work proposes an AF that takes into account the differences between ATC tests and PC tests for ceramic ball grid array (CBGA) packages by considering relevant design and environmental parameters.
The new AF is based on relevant design parameters such as substrate size, substrate thermal conductivity, substrate thickness, coefficient of thermal (CTE) mismatch between the substrate and printed wiring board (PWB), PWB thickness, and environmental parameters such as temperature range (ΔT), frequency of cycles (f), and peak/junction temperature (Tj). Finite Element Models (FEM), experimental data, laser moiré interferometry, Design of Simulation (DOS), ANOVA, and regression analysis are used to develop the new AF. The new AF can be used to more accurately assess PC fatigue life from ATC tests so that expensive over-designing of electronic packages can be avoided for desktop/server/laptop applications.
