Study of polyimide coated chip and mold compound adhesion

Abstract

This study investigates the adhesion strength between polyi-mide coated chip and epoxy mold compound (EMC). Polyi-mide is an important material to reduce chip stress and pro­tect the mobility ions from EMC to the chip circuitry that can lead to an electrical failure. However, there was a delamination issue between encapsulation material and polyimide during reliability test. Two samples were prepared named as EMC A (sample without adhesion promoter) and EMC B (sample with adhesion promoter). Prior to curing process, wafers were coated with 7±1 μm thickness of polyimide us­ing spin coating process. Then, samples were cured at 175 °C for 5 hours in oven after molding process. Samples were then soaked in the Autoclave test chamber (ACLV) at 121°C with 100% relative humidity (RH) for 0.5 hour, 1 hour, 1.5 hours and 2 hours to test the sample reliability. Adhesion strength was measured at room temperature and 260 °C. In addition, water absorption with varies moisture sensitivity level (MSL) was carried out. The MSL test was set for three level which were 85 °C / 85% RH, 85 °C / 60% RH and 30 °C / 60% RH for level 1, 2 and 3, respectively. There was a significant different on moisture absorption but less significant in delamination response. Based on the strength test, EMC B showed a gap between polyimide and mold compound after 0.5 hour of ACLV test while no gap was observed for EMC A even after 2 hours of ACLV test. It could be concluded that EMC that formulated with adhesion promoter provided significant factor to the delamination issue compared with EMC without adhesion promoter.