Optimizing gold thickness of land grid array pads for cost, performance and reliability of connectors

Gold plated socket contact tips and substrate lands are commonly used in the electronics industry for optimum electrical properties. Increasing the gold thickness improves corrosion resistance and provides stable contact resistance at lower mechanical forces. However, with the ever increasing cost of gold it is critical to optimize the socket stack for cost, performance and reliability. To demonstrate this balance, a study on the stability of socket contact resistance was conducted at various gold thicknesses of substrate lands ranging from 60 to 400 nm using a single contact test setup. Contact forces were measured with a tri-axial force sensor that provided a means for extracting the coefficient of friction between the contact interface and substrate lands. An empirical model that relates the contact resistance to mechanical force and plating thickness was derived from the Force-Deflection-Resistance trends observed across various gold thicknesses. In this study, some of the plating options considered included a layer of Palladium (Pd) between the Nickel (Ni) and Gold (Au) layers to improve the corrosion resistance. The corrosion resistance was quantified by exposing the substrates to temperature, humidity and mixed flowing gas (MFG) chambers. The experimental findings could be used for optimization of the Gold plating thickness for cost, performance and reliability.