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Older wire-based interconnection technology has a way of finding new applications. In many cases traditional wire provides a means for overcoming the shortfalls of the latest and most sophisticated micro flex circuit techniques. Use of wire seems somewhat antiquated. However small gauge coated wire, such as 38-gauge (0.004” diameter) stainless steel, offers benefits when applied to newer medical and automotive sensor applications where coiling or excessive vibration requires a wire connection with greater flexibility. Years ago, wire conductors of this size were used in precision applications such as read/write heads for disk drives, only to be replaced by more efficient assembly methods that leveraged the use of micro flex circuits. Even with these changes in the marketplace, newer applications emerge that benefit from such small wire, coated with a dielectric such as Teflon or polyimide. This trend has led to a resurgence for precision wire stripping or precision laser micromachining technology. UV laser micromachining, utilizing imaging of a laser beam, such as an Excimer or UV DPSS laser, provides a minimally thermal ablative process for the removal of dielectric coatings while minimizing the heat affected zone on the underlying exposed wire. These laser beams are first shaped to illuminate an aperture that is then imaged to perform a high finesse ablation process to remove away the coating in precise locations along the wire. This paper outlines several laser beam shaping techniques used to ablate such micro-sized wires and wire harnesses with an emphasis on laser beam shaping methods that are commonly used as well as techniques that allow for maximum throughput. Techniques are explored such as using single sided and retroreflective optics in conjunction with the laser imaging and beam shaping system. Evaluation of a retroreflective wire stripping technique with performance results showing the sophistication of such simple optical designs are presented.
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