Melting Characteristic, Wettability, Interfacial Reaction, and Shear Property of Ball Grid Array Structure Cu/Sn0.3Ag0.7Cu/Cu Solder Joints With Ni-Modified Carbon Nanotubes

In this study, Sn0.3Ag0.7Cu solder paste reinforced with different mass fractions (0, 0.02, 0.05, 0.1, 0.3, and 0.5 wt%) of Ni-modified carbon nanotubes (CNTs) was fabricated by mechanical mixing method to improve the properties of Sn0.3Ag0.7Cu low-Ag solder alloys. The effects of CNTs on the melting characteristics, wettability, interfacial reaction, and shear property of ball grid array (BGA) structure Cu/Sn0.3Ag0.7 Cu- $x$ CNTs/Cu solder joints were comprehensively investigated. Results show that adding CNTs does not change the melting temperature of the composite solder. The melting temperature of all samples is 217.1 °C–217.5 °C. With the addition of CNTs, the undercooling increases significantly, and the wettability of the composite solder first increases and subsequently decreases. When the CNTs content is 0.02 wt%, the wetting angle is lowest (23.3°). In addition, CNTs addition could decrease the thickness and grain diameter of interfacial intermetallic compounds (IMCs) in composite solder joints. When the CNTs content reaches 0.05 wt% or higher, the surface of interfacial Cu6Sn5 grains of Sn0.3Ag0.7Cu- $x$ CNTs/Cu solder joints becomes very rough after four reflow times due to the good bonding between CNTs and interfacial Cu6Sn5 grains. Besides, it is also found that the shear strength of the Cu/Sn0.3Ag0.7Cu- $x$ CNTs/Cu solder joints increases and then decreases with the increase of CNTs content. When CNTs content reaches 0.1 wt%, the shear strength of joint is highest. Moreover, the shear fracture of the Cu/Sn0.3Ag0.7Cu- $x$ CNTs/Cu solder joints mainly occurs near the twice reflow interface between the solder and the Cu substrate. In general, adding a proper amount of CNTs is conducive to the improvement of reliability of low-Ag solder joints.