Research on the Effect of Ultrasonic on the Interfacial Reliability of Micro Copper Pillar Solder Joints

As electronic products continue to develop in the direction of high density and small size, the size of interconnect solder joints continues to decrease. Under normal service conditions, micro solder joints will simultaneously be subjected to thermal, electrical, and mechanical loads, leading to many reliability issues in packaging structures. Ultrasound is generally used to alter the properties of materials and is repeatedly applied in industries to optimize process performance. This article primarily studies the impact of various ultrasonic parameters on the reliability of micro copper pillar solder joints and analyzes the corresponding failure modes and mechanisms. First, high-strength Ni/Sn/Ni structure micro copper pillar solder joints were obtained by adjusting the thermocompression bonding parameters, and then ultrasonic regulation experiments were performed on the micro copper pillar solder joints. The results show that under the conditions of a bonding temperature of 360 °C, a bonding pressure of 45 MPa, and a holding time of 10 s, the push shear strength of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40 \; \mu $ </tex-math></inline-formula>m micro copper pillar solder joints can reach 37 MPa, with an intermetallic compound (IMC) thickness of less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \; \mu $ </tex-math></inline-formula>m. The optimal ultrasonic regulation parameter was found to be 35 W of ultrasound applied during the mid-stage of the holding period for 6 s.