The fluxless soldering process without intermetallic compounds

Basic soldering is a chemical reaction between the solder element such as tin (Sn) and the base metal such as copper (Cu) or nickel (Ni), producing intermetallic compound (IMC) such as Cu₆Sn₅ or Ni₃Sn₄. It is the IMC that connects the solder to the metal. The IMC layer grows with time during usage, resulting in potential reliability issues. In this research, we looked into and developed soldering processes that do not produce IMC. The fundamental concept is to choose barrier metal that does not form IMC with the solder. An example is chromium (Cr). Several bonding experiments have been performed. Preliminary results seem to show that high quality Sn solder joints could be made without IMC and without the use of flux.