FEM Analysis on Warpage and Stress at the Micro Joint of Multiple Chip Stacking

Abstract

Flip chip plastic ball grid array (FCPBGA) utilizing an interposer for multiple chip stacks, so called 2.5D or 3D package, is gaining prominence in order to achieve the next generation high performance computing. The multi-tier stacking of Si chip, Si interposer and organic substrate induces complicated warpage behavior and stress at the micro joints during the joining process. The authors studied warpage behavior and thermo-mechanical stress of multiple chip stacks on Si interposer package with different thickness of top chip, different thickness of Si interposer, different middle chip stacks and different metallurgy of micro joints after joining of stacked chips on the interposer using finite element method (FEM). Thicker stacked Si chips and thicker Si interposer showed higher von Mises stress at chip-to-interposer joint. Comparing SnAg joint and CuSn joint, CuSn joint always shows higher stress than SnAg joint because of its higher elastic modulus.