Reliability Study of Copper Pillar Bump Interconnects for Acoustic Wave - Wafer Level Package

Abstract

Replacing solder ball interconnects through copper pillar bump (CPB) interconnects on acoustic wave components (AWC) like SAW (surface acoustic wave) filters saves valuable chip space and facilitates chip miniaturization. In this contribution, we present our very first assembly and reliability results for CPBs on lithium niobate chips with TFAP(tm) (Thin Film Acoustic Package) for SAW filters. The CPBs consist of a Cu/Ni/SnAg layer stack and are soldered on a test board with Cu/Ni/Au finish. Leaving aside premature failures due to poor soldering, CPBs withstand 770 cycles of RCoT (Rapid Change of Temperatur, −40°C / + 125°C) reliability testing. The solder joints were investigated via cross section micrographs. Additionally, uHAST (Accelerated Moisture Resistance - unbiased HAST), DH (Dry Heat) and DHSS (Damp Heat Steady State) reliability tests were performed.