Characterization and Reliability Performance of the Immersion Gold Plated Module Fingers

Abstract

Memory modules are inserted into a socket in a typical PC set up. In order to maintain the conductivity and rigidity, the edge connect fingers are made of copper plated with thin gold layer, which is chosen for its tarnish resistance and good electrical conductivity. Traditionally, about 1 micron hard gold is used together with nickel under plate. The hard gold contributes a significant cost to the module. Immersion gold layer as a surface finish is targeted as a means to improve cost effectiveness. However, there is increasing evidence indicating that immersion gold may be detrimental in applications calling for long-term reliability.

A brief introduction into the gold plating technology, PCB surface finish and contact resistance theory is given in this thesis. Subsequently a study of the reliability of immersion gold connectors is carried out using hard gold connectors as a reference. This is done by examining the effects of aging on their contact resistance. Surface analysis, insertion, hardness and thickness tests are also performed on selected samples to further characterize the gold connectors.

Preliminary findings indicate that there are not much significant differences between the reliability of immersion gold connectors and electrolytic gold connectors. However there is still a possibility that its reliability performance will degrade after longer usage. Further work need to be done before conclusive results can be established.