Assessment of Press-Fit Zones with Diverse Platings to Study Their Respective Strengths

Solderless press-fit zones have become prevalent interconnections, originating in the telecommunications sector but now also widely adopted in an automotive industry as a key enabler for the trend to switch from large hand-wired discrete power electronics to more economic printed circuit boards (PCB). Typically, these press-fit zones are produced by stamping base material, primarily copper sheet metal, and are layered with galvanic platings. In the past, plating involved tin with lead, effectively preventing tin whisker growth. However, with the omission of lead, there's now a shift toward press-fit zones with diverse platings emerging in the market. Extensive research and experimentation have been done on tin with lead plating to mitigate whisker formation with specific press-fit zones such as eye of needle and cracking zone. The influence of comparatively pure tin, silver, and indium platings on insertion force, retention force, and contact resistance for special press-fit zones has not been sufficiently examined, primarily owing to the novelty of some press-fit zones, e.g., flexx and spring shape. Therefore, this paper specifically delves into press-fit zones such as the eye of the needle, spring shape, and flexx as all of them are substantially different in geometry, all stamped out of same material. The platings under scrutiny consist of tin as it is widely used, silver suitable for high current applications, and indium, due to its popularity now in the Asian market. Although previous research indicates a similar impact on press-in force between tin and silver plating, the field lacks a more comprehensive understanding of contact performance under harsh environment and load conditions. We therefore tested the mechanical as well as electrical strength of press-fits and thermally shocked them, providing a more nuanced perspective on the platings' effectiveness.