Welding of plated, dissimilar metals for RF/EMI shielding

Improvements in the resistance welding process used in attaching plated beryllium-copper shield clips in cellular portable telephones to the plated steel core of the circuit board are discussed. The production welding process in a narrow, space-limited area closely adjacent to conductor traces is characterized by widely varying weld strengths, the need for multiple welds to achieve weld strength, ejection of metal during welding, frequent electrode dressing, and frequent electrode replacement. It is determined that the process could be improved by the use of projections; the use of larger, harder electrodes; slightly softened shield clips; and an angled electrode to aid the operator. An analysis of the improved weld was done using cross sections, optical and scanning electron microscopy, and energy dispersive X-ray spectroscopy.<
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