Evaluation of Press-Fit Zone Performance Across PCB Surface Finishes like ENIG, Immersion Tin, Immersion Silver, and OSP
Press-fit zones, originally designed as simple square solid cross-sections for the telecommunications industry, have now become integral to a wide range of applications, from automotive to consumer electronics. Over time, these square pins have been adapted into different shapes and sizes to meet diverse application needs and environmental conditions. Typically, a press-fit zone is inserted into a printed circuit board (PCB) hole, forming a stable, gas-tight connection with the plated through-hole. The overall performance of press-fit zones is largely influenced by both the design of the press-fit and the surface finish of the PCB. The PCB itself has undergone significant advancements, especially in surface finishes. Traditionally, hot air solder leveling was commonly used, but with the introduction of lead-free regulations, alternative finishes have emerged. Among the most commonly used finishes for press-fit applications are immersion tin (ImSn), favored in Europe for its cost-effectiveness, electroless nickel immersion gold (ENIG) and immersion silver (ImAg) for their superior electrical properties, and organic solderability preservatives (OSP), which are increasingly popular in Asia due to their affordability. While extensive research has been conducted on PCB surface finishes alone and their individual benefits and drawbacks, the interaction between press-fit zones and these finishes is still underexplored. This paper examines the interconnection performance of commonly used press-fit zone designs - such as spring shape and eye of needle with PCB finishes including ENIG, ImSn, ImAg, and OSP. Through extensive testing, we analyze insertion and retention forces, contact resistance, and long-term stability to determine the impact of these surface finishes on press-fit performance. The findings provide valuable insights for optimizing press-fit technology in various applications, enhancing the reliability and efficiency of electronic assemblies.
