Reliability Assessment of Land Grid Array Sockets Subjected to Mixed Flowing Gas Environment

摘要

Land grid array (LGA) sockets are used as separable interconnects between printed circuit boards, and high I/O integrated circuit components. Because the socket contacts with the component and the circuit board on both sides, low and stable contact resistances among these interfaces are desirable for the reliable electrical connection of the LGA package. This paper compares the contact resistance degradation of two LGA socket designs, silver particles in an elastomer column, and silver-plated-nickel in an elastomer film, subjected to accelerated corrosion environment, or so-called mixed flowing gases (MFG). Increased contact resistance was observed in the sockets due to corrosion products over the contact surface after metal corrosion. Corrosion products were analysed using environmental scanning electron microscopy (E-SEM), energy dispersive spectroscopy (EDS), and x-ray photoelectron spectroscopy (XPS). AgCl, ${rm Ag}_{2}{rm O}$, and ${rm Ag}_{2}{rm SO}_{4}$ were identified after silver corrosion; ${rm NiCl}_{2}$, ${rm Ni}_{2}{rm SO}_{4}$ , and NiS were found after Ni corrosion. The nickel corrosion product bridged the adjacent contacts as whiskers with time. The lifetime can be estimated by an acceleration factor: two day MFG Battelle Class II exposure equals one year of field service. The shelf life of conductive elastomer LGA sockets is expected to be longer than five years.