Gregorio Murtagian

Fundamentals based approach to predict socket stack performance

The field performance of a separable socket/connector is governed by its ability to maintain the target contact resistance throughout its life. Contact resistance stability and protection against field degradation mechanisms is achieved by maintaining a critical normal force on the contact. With growing socket contact pin counts and package complexities there are challenges with achieving and maintaining this critical contact normal force across the array of contacts in the socket. In this effort, the authors characterized the key mechanical and resistance relationship (Force-Deflection-Resistance)through single contact resistance measurements. An analytical model of a socket stack was developed to better capture the contact normal force distribution across the contact array. The contact forces extracted from the analytical model were then converted to contact resistances through the Force-Deflection-Resistance relationship obtained from single contact resistance measurements. Force-Resistance variation from contact to contact was comprehended through a Bootstrapping technique. This fundamental based approach of using finite element, single contact data and statistics was then validated against fully enabled socket measurements using electrically daisy chained test vehicles.

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.