Analysis of microstructure and interface morphology of Sn- based solder / Cu during pulsed hot - pressing welding

Sn-3.0Ag-0.5Cu lead-free solder, PCB copper clad laminate and copper thin film substrate were used as experimental materials and the Cu/SAC305/Cu interconnection plate-level structure micro-solder joint was prepared by pulsed hot-pressing welding test. The author aimed at investigating the pulse welding time, pulse welding temperature and welding pressure which influence on the microstructure of solder joint and the pattern of the interface and obtained the optimum range of welding parameter, as well as analyzed the difference of the microstructure and interface pattern between the two methods of pulse hot-pressing welding and reflow welding under the same welding temperature. The results show: When the welding temperature and welding pressure were the same and the thickness of Cu/SAC305/Cu solder joint IMC layer increased with the welding time, the size of the primary crystal phase of the β-Sn in the brazing filler metal increased with the extension of the welding time at the same time. When the welding time and welding pressure were the same, the thickness of Cu/SAC305/Cu solder joint IMC layer increased with the welding temperature increased. When the welding temperature and welding time were the same, the pressure was not applied and pulse heat welding could not form effective solder joint. When the pressure was 20N ~40N, the solder joint IMC layer was continuous and almost uniform. When the pressure reached 60N, the pattern of IMC solder joint distribution was not smooth. Under the condition of same temperature, the thickness of the solder joint IMC of the pulsed hot-pressing welding was thinner than that of the reflow soldering point. At a temperature of 260 °C, the thickness of the solder joint IMC of pulse hot-pressing welding was only 40% of the reflow soldering joint and at the same time reflow soldering reaction could not occur wetting reaction to form effective solder joints at 240°C, but pulse hot-pressing welding could form valid solder joint.