Pulsed Nd:YAG laser fine spot welding for attachment of refractory mini-pins

Molybdenum (Mo) feedthrough pins (with a diameter of smaller than half of a millimeter) are commonly used for rechargeable batteries because of their inert nature and close CTE match with glass. Pure Mo has a very high melting temperature, and is not conducive to soldering. Due to the small geometry, the attachment of electrical conducting wire/ribbon to the pin is very challenging if conventional attachment methods were possible. Solid-state bonding by resistance welding is marginally feasible, but often results in moderate bond strength. In this work, fine spot welding using a pulsed Nd:YAG laser for the attachment of a conductive ribbon to a Mo pin is reported. The effect of the conductive ribbon materials was investigated. The weld condition was studied with the aim of determine the best set of laser processing parameters, including the angle of laser beam incidence, the laser power and the pulse duration. Weld strength testing on ribbon-pin weld structures was conducted. The laser fine spot welding resulted in a three times higher bond strength than resistance welding.