Resistance microwelding of crossed fine nickel wires was investigated by means of detailed mechanical testing and metallurgical examinations. Welding current and force had the greatest effects on joint microstructure evolution and hence joint strength, compared to weld time. Increasing welding current increased joint breaking force but too high a current caused lower breaking force because of recrystallization softening in the HAZ. An optimum welding force was seen, with low welding force resulting in low joint breaking force because of low bonded area and excessive welding force reducing the breaking force because of low interfacial strength.

It is proposed that resistance microwelding of crossed fine nickel wires includes the following stages: 1. cold wire collapse; 2. surface melting; 3. liquid phase squeeze out; and 4. solid-state bonding. It is believed that sufficient surface melting and subsequent squeezing out of the liquid phase is needed to produce fresh metal surfaces for strong solid-state bonding. Sufficient local heat generation is the key to high quality welds, first to generate enough transient surface melting, second to facilitate plastic deformation in order to squeeze out liquid and expand the bonded area. This requires a proper balance of high initial contact resistance and sufficiently high welding force, which could be easily realized by setting a low firing force compared to the nominal welding force.