Feasibility study of laser microwelding of high density cable assemblies with applications to portable electronics

Continued trends in miniaturization of electronic components place ever increasing demands for development of high density interconnections and cable assemblies, especially as they apply to portable electronics. This paper evaluates feasibility of one of such developments based on a laser microwelding of small diameter wires to contacts in cable assemblies for portable electronics. More specifically, the paper addresses characterization of laser spot welded 32 AWG solid copper/silver plated wires to contacts on 0.050 in. centers. The copper alloy contacts were provided on strips in two lots, one unplated, and the other with 75 /spl mu/in. of plated nickel. To simulate manufacturing environment, an industrial type IR, Nd:YAG, pulsed laser was used to produce welds. Quality of the welds was evaluated by metallurgical analysis, tensile testing, SEM, and nanoindentation characterization. These methods have been also used in setting up the welding process parameters. Tensile test results obtained, during this study, on the laser welded interconnections are presented in a statistical format. They indicate that the tensile strength of the laser welded wire, relative to a bare (unwelded) wire, was 95.47% for joints on unplated contacts, and 98.25% for nickel plated contacts. Microscope examination of the samples, after pull test, shows that all wires broke behind the weld area. These results are encouraging because they have significantly exceeded the required minimum tensile strength of a welded joint, i.e., 60% of the tensile strength of the bare wire. They also indicate that laser microwelding of small diameter wires to high density contacts can be considered as a valuable process alternative in manufacturing of cable assemblies for portable electronics.