A land-grid array connector, electrically connecting an array of plated contact pads on a ceramic substrate chip carrier to plated contact pads on a printed circuit board (PCB), failed in a year after assembly due to time-delayed fracture of multiple C-shaped spring connectors. The land-grid-array connectors analyzed had arrays of connectors consisting of gold on nickel plated Be-Cu C-shaped springs in compression that made electrical connections between the pads on the ceramic substrates and the PCBs. Metallography, fractography and surface analyses revealed the root cause of the C-spring connector fracture to be plating solutions trapped in deep grain boundary grooves etched into the C-spring connectors during the pre-plating cleaning operation. The stress necessary for the stress corrosion cracking mechanism was provided by the C-spring connectors, in the land-grid array, being compressed between the ceramic substrate and the printed circuit board.

Contrary to known art, we have discovered that lubricated tin-silver connectors have better electrical performance and are more reliable than lubricated silver-silver connectors under high-current and high-vibration conditions. The antifretting lubricant, that enhances the performance and reliability of the tin-silver connectors, is a grease consisting of a hydrocarbon oil in a nano-sized silica-particle base. Focused ion beam and scanning electron microscopy were used to understand the contact degradation mechanism. The superior electrical performance and reliability of the lubricated tin-silver connectors is due to a mechanism that replaces the tin plating from the contact surface with a coating of silver. The removal of the tin plating may be due to wear and the replacement by the silver coating may be due to an electrochemical displacement reaction.