Evaluation of Irregular Inter-Metallic Compound Growth in Gold Wire Bonds Encapsulated with Reliable, Green Epoxy Molding Compound

摘要

The thermal stability of selected additives used in epoxy mold compound is evaluated using thermo-gravimetric analysis. Certain additives degrade at lead-free reflow temperature as well as high temperature storage exposure at 175 deg C. The influence of such additives used in epoxy mold compound on gold-aluminum inter-metallic compound formation has been studied. Plastic ball grid array test package encapsulated with thermally unstable additives show trace elements from the degraded additive when analyzed by scanning electron microscopy and energy dispersive x-ray analysis. The element ingress and reside on the non-bonded regions of the ball bonds with increasing high temperature exposure. As the bonded regions remain free of the degraded elements,regular growth of inter-metallic compound progress while inter-metallic compound formation is retarded at non-bonded regions contaminated with trace elements. The resulting morphology after extended high temperature storage exposure shows voids that coalescence into a series of micro cracks. Thermally stable additives are found to be critical in ensuring green,reliable epoxy mold compound fulfilling the qualification requirements of ultra fine pitch integrate circuit package. Evidence of this being further validated with Quad Flat No-Lead package.