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54 The PCB Magazine • August 2017 ing iron, a two-layer circuit board was designed and built. This circuit, known as a "Joule Thief," operates in a similar way to a boost converter, in that it takes a smaller DC voltage and uses in- ductive spiking to generate a larger voltage via a transistor used for switching and a transform- er. The design has three parallel circuits, which control an individual color of a common cath- ode RGB LED, and a resistive touch pad acti- vates each circuit. A 1.5-volt button cell battery was used to power the circuit, and the switch- ing frequency was measured to be approximate- ly 400 kHz. Although the circuit itself has a rel- atively low parts count and does not require a two-layer PCB design, a two-layer board was de- signed to demonstrate the capabilities of creat- ing plated through-holes. Trace widths on the board range from 100 μm to 400 μm (4 mils to 16 mils), which were created without issue us- ing the methods described above. During the assembly of the circuit board, the quality of the adhesion of copper to the glass substrate was observed to be similar to that of copper on FR-4. There were no traces or pads Figure 6: Resistive touchpad RGB LED demonstrator, plated on 1 mm borosilicate glass. In the upper left picture, the red features are on the front side of the board, the green circles are through-holes, and the blue features are on the back side of the board. The series of photographs shows that each touch pad activates a single LED. LASER PATTERNING AND METALLIZATION TO REDUCE PROCESS STEPS FOR PCB MANUFACTURING