Impact of press-fit connector pin microstructure elastic response to PCB through-hole Cu wall interface long-term contact reliability

Press-fit compliant pin connection is used widely to provide electrical and mechanical connections from a printed circuit board (PCB) to an electrical connector, which then providing board to board electrical and mechanical connection. Since these pin connections carry both electrical and mechanical load, the compliant pin and PCB through-hole (PTH) interferences are critical to the long-term reliability and integrity of the connection. Yet comparing with the ball grid array (BGA) connection, there are still a quite few unknowns regarding degradation mechanisms about the press-fit compliant pin connection. This study compares complaint pins with similar chemical composition but different initial microstructures and identifies the regions of severe plastic deformation. The bonding strength, microstructural evolution and effect of thermo-mechanical cycling were observed using micro-mechanical tester, and electron backscatter diffraction (EBSD) for further measurements and analysis. The results revealed that initial microstructure played a major role in the strain development, deformation percentage, grain spread, local mis-orientation, hardness and the bonding strength of the connectors. The extended test with thermal cycling with -40°C to 125°C cycles was performed to identify any potential thermo-mechanically induced degradation.