A novel double layer NCF for highly reliable micro-bump interconnection

40 μm pitch Cu-pillar/Sn-Ag bump to Ni pad thermo-compression bonding was performed using non-conductive films (NCFs) with different curing agents. The joint morphology of Cu-pillar/Sn-Ag bump/Ni pad was dependent on the viscosity and curing speed of NCFs. Imidazole NCF with high viscosity and fast curing speed showed no solder wetting on both Cu-pillar and Ni pad. However, anhydride NCF with low viscosity and slow curing speed showed both solder wetting on Cu-pillar and Ni pad. Double layer NCF consisting of imidazole NCF as top layer and anhydride NCF as bottom layer was designed and optimized to eliminate solder wetting on Cu-pillar. Joints bonded using double layer NCF showed ideal joint shape with no solder wetting on Cu pillar and good wetting on pad. Thermal aging at 150 C was performed and IMC growth rate of Cu₆Sn₅ and Cu₃Sn was slower for double layer NCF compared to single layer NCF due to reduced reacting area for Cu and Sn.