Fluxless Sn-3.5 mass% Ag solder bump flip chip bonding by ultrasonic wave

Abstract

The ultrasonic solder bump flip chip bonding was investigated as a method of fluxless bonding. The 100 μm-diameter Sn-3.5 mass%Ag solder bumps were formed at 12 positions on a test Si-die by laser ball bonding process. The test flip chip dies were bonded to a TSM-coated glass substrate on a hotplate at different bonding loads and ultrasonic power condition. The die shear strength was evaluated and fracture surfaces were examined with SEM. The Sn-Ag solder flip chip bonding was possible at lower temperature than the melting point of Sn-3.5Ag solder. The die shear strength increased with increasing bonding temperature, bonding load, and ultrasonic power. However, at excessive bonding load condition over 0.8 N/bump, the die shear strength decreased. The bump height decreased with increasing bonding load.