Microstructure and Properties of Ultrasonic Assisted Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joint S Under Thermal Cycling

Abstract

Through ultrasonic wave assisted Sn2.5Ag0.7Cu0.1RExNi/Cu(x=0, 0.05, 0.1) soldering test and -40~125℃ thermal shock test, the microstructure and mechanical properties of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints under thermal cycling were studied by the SEM, EDS andXRD. The results show that the Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints with high quality and high reliability can be obtained by ultrasonic assistance. During the thermal cycling process, the shear strength of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had a linear relationship with the thickness of interfacial intermetallic compound (IMC). The addition of an appropriate amount of Ni could inhibit the excessive growth of IMC, improve the shear strength of solder joints and improve the reliability of solder joints. Under the condition of 1000 cycles of thermal cycling, the thickness and roughness of IMC of the solder joints with 0.05 wt.% Ni were the smallest, and the shear strength of the solder joints was 19.8 MPa, which was 28.6% higher than that of the solder joints without Ni.The interfacial IMC layer of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints consisted of (Cu,Ni) 6Sn5 and Cu3Sn. In the thermal cycling, the thickness of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints was linearly related to the square root of equivalent time. The growth of interfacial IMC of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints had an incubation period, and the growth of IMC was slow within 300 cycles. And after 300 cycles, the IMC grew rapidly, the granular IMC began to merge, the thickness and roughness of IMC increased obviously, the defects such as microcracks and microvoids began to appear, and the shear strength of the solder joints decreased rapidly.The fracture mechanism of ultrasonic-assisted Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints changed from the ductile-brittle mixed fracture in the solder/IMC transition zone to the brittle fracture in the interfacial IMC.