Impact of Thermal Cycling on Cu Press-Fit Connector Pin Interconnect Mechanical Stability

Abstract

Press-fit technology provides an electrical and mechanical connection by inserting a press-fit pin into a through-hole of a printed circuit board (PCB). Recently, there has been a wide interest in the long-term reliability of the press-fit pin interconnect of electric systems under various thermo-mechanical conditions due to the integration and minimization of electric devices. Compared to a ball grid array (BGA) interconnection, press-fit pin connector interconnects are expected to have a different degradation mechanism. In this study, the impact factors affecting reliability and degradation mechanism of press-fit connector pins were investigated. The bonding strength of inserted pins was measured before and after thermal cycling at room temperature and elevated temperature conditions. It is observed that the bonding strength of the press-fit pins to the PCB Cu wall increased after thermal cycling. The development of an intermetallic compound between the Cu pin and the Cu wall is observed. The microstructure of the press-fit connector pin and the Cu wall and localized stress and strain levels were analyzed by electron backscattered diffraction including inverse pole figure maps, grain reference orientation deviation maps, and strain contouring maps. Along with the increase of pull strength after thermal cycling, an increase in residual stresses was observed while strain contouring maps exhibited a decrease in localized strains at the interface between a press-fit pin and copper wall of a PCB.