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August 2017 • The PCB Magazine 53 50 μm glass with a top diameter of 40 μm and an exit diameter of 16 μm using the company system (not shown). Applying the laser-based glass etching and copper seeding methods outlined above, a two- sided PCB pattern measuring 20 x 35 mm was prepared (Figure 5). The pattern is an actual cir- cuit design, albeit scaled down to ~25% of the original size so that it can fit on a 22 x 50 mm borosilicate glass coverslip 150 μm thick. The smallest features in this design are ~ 35 μm wide. The pads, wires and alignment points of the de- sign were machined using a single set of laser parameters, utilizing a 7 μm crosshatch pattern within the individual polygons. Next, the vias were drilled using a different set of parameters. The piece was flipped over and aligned using the alignment marks made on the top of the glass piece, and the wires, pads and addition- al text on the bottom were machined. After the forward transfer process, both the top and bot- tom were gently polished to remove excess cop- per from the surface, leaving only copper seeds in the laser machined areas. Plating was carried out in an electroless plating bath. To illustrate the capabilities and gain insight as to whether the adhesion of copper to a glass substrate holds up to direct heat from a solder- Figure 5: Images of a two-sided demo pattern on a 150 μm glass cover slip. The total pattern is approximately 20 x 35 mm and the glass is ablated using a 7 μm crosshatch pattern within the individual polygons. Left: Photo of the plated design imposed against a grayscale image. Right: Composite optical microscope image detailing a portion of the pattern. LASER PATTERNING AND METALLIZATION TO REDUCE PROCESS STEPS FOR PCB MANUFACTURING