Room temperature soldering of connectors to PCB using reactive multilayer foils

This paper describes a process which uses a multilayered reactive foil to solder gold coated stainless steel connectors to Rogers PCB at room temperature. The technology is based on a reactive foil comprised of thousands of nanoscale layers that alternate between Al and Ni. After being initiated with a small electrical or thermal stimulus, the reactive foil acts as a local heat source, melting solder on either side of the foil and bonding the two components without exposing them to high temperatures. The use of reactive joining allows for the bonding of the connector at any point during the population of the board at room temperature and without flux. The reactive foil also allows for the replacement of Pb-Sn solder, used previously, with Au-Sn solder. This enables the joint to undergo subsequent reflow steps without any degradation in bond strength. We optimized the reactive bond with regards to reactive foil properties and joining pressure. Numerical simulations were used to estimate the thermal exposure of the components during bonding and melting duration of the solder. Results of mechanical and environmental testing of these components are also presented.