Reliability Study of Low Normal Force LGA Sockets

Finer pitch, lower height, increased working range, and lower cost are clear roadmap trends for many connector systems. The reduction of contact normal force is a key enabler, if not necessity, to keep pace with these trends. Stable gold to gold milliohm level electrical contact can be made at 0.05N normal force and with wipe at the contact interface, the contact resistance can be further reduced. To characterize the effect of reduced normal force in a product, an industry standard LGA (land grid array) socket was used as a test platform. Contacts were modified to incorporate a longer unsupported length, narrower beam section and lower elastic modulus material to provide a nominal beginning of life normal force of 0.05N. This low force socket was subjected to EIA standard qualification test sequences. It was determined that for the system evaluated, the lower contact force demonstrated a larger standard deviation of values as compared to the standard higher force socket, however the standard deviation remained constant through environmental exposure. From a failure mechanism perspective, increased susceptibility to corrosion and contamination failure mechanisms was found while mechanical and thermally driven mechanisms were less impacted.