Balancing temperature and time in reflow soldering for improving Sn-3.0Ag-0.5Cu solder joint strength

The transceiver module serves as the core components of active phased array radar systems. During reflow soldering using Sn-3.0Ag-0.5Cu solder, the frequent failure of solder joints significantly restricts the yield rate of the transceiver module production. The solder joint is between the housing module and the AuPtPd pad predeposited on the low-temperature co-fired ceramic substrate. This study aims to investigate the influences of the reflow soldering process on the microstructure and shear strength of the solder joints. Solder joints were prepared under soldering temperatures ranging from 230 °C to 270 °C and soldering times ranging from 0 to 240 s. Research findings indicate that at temperatures below 250 °C or soldering time less than 120 s, a thin layer of Au–Sn intermetallic compounds (IMC) film can be formed in the solder joint with minimal consumption of the AuPtPd pad. With increasing temperature or soldering time, shear strength exhibits gradual increases and minimal variability. Conversely, when the temperature exceeds 250 °C or the soldering time surpasses 120 s, more IMC is formed with the greater consumption of the AuPtPd pad, resulting in the formation of a thicker, discontinuous, and uneven IMC layer, leading to a rapid decrease in the shear strength of the solder joint. Considering the overall joint strength, soldering at 250 °C for 120 s is identified as the optimal process, achieving a shear strength of 61.48 MPa.