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68 DESIGN007 MAGAZINE I APRIL 2021 commercial sources for printable or deposited thick-film resistive materials and the base value range that they offer are furnished in Table 2. When the application requires a value modi- fication or a tolerance that is better than that noted in Table 2, laser trimming systems can be employed to make the necessary adjust- ments. e examples shown in Figure 2 illus- trate thick film resistors that have been modi- fied using laser technology to achieve a specific value or tolerance target. Laser trimming systems developed for high volume PCB fabrication are equipped with multiple flying probe contactors that are pre- programmed to reach any component location, size, orientation and layout within the board or multi-unit panel. e probe contactors sweep across the board's surface contacting the embedded component lands or dedicated test point locations to measure and transmit the resistor value and tolerance as printed to direct the laser in making the required cut (Figure 3). Automated calibration routines ensure cut placement accuracy within 15 microns. Cut widths are typically in the 10–50-micron range. ose considering thick-film resistor tech- nology must understand that the process requires precise imaging and consistent mate- Table 2: Thick film material selection guide. Note: The resistor value tolerance shown in column five represents the resistive material as printed and cured. Figure 2: Laser trim variations for thick film resistor elements. (Trim examples courtesy of PPI Systems)