Investigation of Fretting Corrosion at Dissimilar Metal Interfaces in Socketed IC Device Applications

Gold has traditionally been the material of choice for separable connector contact surfaces in high reliability applications. With the rising cost of gold, major efforts have been focused on finding ways of reducing or altogether eliminating its use while still maintaining low and stable values of contact resistance. Currently in commercial semiconductor devices, gold-plated device leads are often not available. Tin and solder finishes are common. Recently early intermittent contact resistance failures were found when dissimilar metal (Au/Sn and Au/solder) interfaces were used in conjunction with socketed integrated circuit (IC) devices. Analysis of these failures indicated that fretting corrosion of tin had occurred. To better understand the phenomena of fretting corrosion in such applications, a laboratory study was conducted on a variety of dissimilar metal (socketed device) interfaces under conditions of mild vibration. The static resistance behavior of the samples was studied for a ten month period. The samples were then disassembled and the contact surfaces were examined using scanning electron microscope (SEM) and scanning Auger microprobe (SAM) techniques. The resistance data obtained indicated that, without lubrication, all metal interfaces except Au/ Au failed repeatedly. Subsequent SEM and SAM investigations showed that all interfaces of Sn and SnPb (solder) mated to themselves or to Au failed by tin fretting corrosion, resulting in high contact resistances (>100
\Omega
.