Fluid Abrasive Trimming of Thin-Film Resistors

Thin-film nickel-chromium resistors have been trimmed using the fluid jet from an air brush. Micrometersized distilled water droplets impinge on the resistor surface at high velocity, eroding away resistor material, thereby increasing resistance. The need for top hats is eliminated. Substrate damage and the hot spots which result from trim-line cuts are avoided. Trimming up to 230 percent has been achieved on narrow (0.0012-in) resistors. Test results at power densities up to 6000 W/in²indicate that power density ratings as high as 2400 W/in²are feasible.