Study on the performance of Cu foam with different porosity on SAC305 solder joints under ultrasonic-assisted soldering

Cu foams with 75% and 98% porosity were employed as reinforcing structures to enhance the performance of the Sn3.0Ag0.5Cu(SAC305)/Cu solder joints. The effects of Cu foam porosity and ultrasonic power on the microstructure and shear properties of solder joints were investigated. The results suggested that the Cu substrate produced excellent metallurgical reactions with both composite solder foils, but more Cu6Sn5 was generated in 75% porosity Cu foam/SAC305 solder joints. The increase of ultrasonic power would accelerate the dissolution of Cu skeleton and effectively refine and homogenize the intermetallic compound grains. Higher power ultrasonic vibration optimized the microstructure of the solder joint, so the shear strength of the joint was increased, but excessive ultrasonic power would cause microcracks at the interface of the solder joint in turn reducing the shear strength.