The Basic Research Of Rapidly-solidified Lead-free Solders

In recent years, with the rapid development of the electronic packaging industry and the higher requirements of the people for the environment and health, developing the lead-free solders which can replace the traditional Sn-Pb solder has become a hot research in the field of electronic packaging. So far, without any kind of the lead-free solder which performance can exceed the position of Sn-Pb solder in the microelectronic packaging. There is still a large difference between the lead-free solders and Sn-Pb solders on the soldering properties and solder joint reliability. So, the development of new lead-free solder to improve the performance of the solder as well as welding performance, so as to improve the reliability of solder joints is a very important issue.In this study, the rapidly-solidified Sn-0.7Cu and Sn-3.5Ag lead-free solders which prepared by the single roller quenching techniques were selected to react with polycrystalline Cu substrate at250℃, systematic studied the physical properties such as wettability, the melting temperature range and the microstructure as well as the growth behavior of the intermetallic compounds(IMCs) with different soldering time, different soldering holding time and different cooling ways of the rapidly-solidified lead-free solders through carrying out the comparative experiments with the as-cast Sn-0.7Cu and Sn-3.5Ag lead-free solders, further studied the rapidly-solidified lead-free solders and obtained a series of research results, which were expected to provide valuable reference for developing the rapidly-solidified lead-free solders which is new and can be applied in the electronic packaging industry.The main conclusions were summarized as follows:(1) Comparing with the as-cast lead-free solders, the microstructure of rapidly-solidified Sn-0.7Cu and Sn-3.5Ag solders was more uniform and the content of β-Sn in matrix increased than that of the as-cast ones.(2) Comparing with the as-cast lead-free solders, the wettability improved, the melting interval reduced and the melting rate was faster of the rapidly-solidified solders than that of the as-cast ones, the rapidly-solidified solders had the instant melting characteristic. So, they were suitable for the short-term soldering.(3) When the short soldering time was3s,5s,10s and15s, the Cu6Sn5grains formed on the rapidly-solidified Sn-0.7Cu composite solder/Cu changed from a facet-type to a scallop-type morphology with increasing soldering time while the Cu6Sn5grains formed on the as-cast Sn-0.7Cu composite solder/Cu were common scallop-type morphology with the same soldering progress at250℃with air cooling.(4) The IMCs formed on the rapidly-solidified Sn-0.7Cu solders and Cu substrate were much thicker than the as-cast ones at250℃with different reflow holding time(20s,60s,300s) and different cooling ways(furnace cooling, air cooling, water cooling) in the reflow soldering. So, regardless of which type of the cooling ways used, the rapidly-solidified Sn-0.7Cu solders were not suitable for the long time reflow soldering.(5) When the short soldering time was3s,5s,10s and15s, the IMCs formed on the rapidly-solidified Sn-3.5Ag solders and Cu substrate were much thicker than the as-cast ones because of the characteristic of instant melting of the rapidly-solidified Sn-3.5Ag solders at250℃with air cooling.(6) The amount of the nano-Ag3Sn particles adsorbed on the surface of the Cu6Sn5IMCs of the rapidly-solidified Sn-3.5Ag solders was more than the as-cast ones and the distribution location was wide at250℃for3s with furnace cooling, air cooling and water cooling. And the IMCs growth was inhibited much stronger during the aging.