Experimental And Simulation Board Level Reliability Assessment Of Wafer Level Chip Scale Packages (WCSPs) Under Thermal Cycling

Abstract

Various studies have been conducted to study the effect of varying board thickness on thermo-mechanical reliability of BGA packages. Wafer level chip scale packages (WLCSP) have also been studied in this regard to determine the effect of PCB build-up thickness on the solder joint reliability. The studies clearly demonstrate that the thinner Printed Circuit Boards (PCBs) result in longer thermo-mechanical fatigue life of solder joints. Due to an extensive research, literature and past trends to support the theory that thinner PCBs perform better than thicker ones, Texas Instruments (TI) opted to move forward by decreasing the thickness of their PCBs by 30% to improve the reliability of their packages. The thickness was reduced by decreasing the thicknesses of individual layers and keeping the total number of layers constant. When subjected to thermal cycling, it was observed that the thinner board was failing earlier than the thicker board. Since this behavior of a WCSP is in contrast to the past trends, it required extensive study to determine and understand the pre-mature physics of failure/causality of failure in the thinner board.