Thick-Film Resistor

Thick-film is the manufacturing technology behind essentially every modern SMD chip resistor (0201, 0402, 0603, 1206, 2512), most current-sense shunts under 5 W, and a large class of HV cylindrical and chip resistors. A resistive paste — primarily ruthenium dioxide grains in a glass matrix, sometimes bismuth or iridium oxides — is screen-printed onto an alumina substrate, fired to fuse the glass and form a continuous resistive layer 10 – 50 μm thick, then laser-trimmed to value and overcoated with protective glass.

The technology offers very high volume manufacturing economy, excellent dimensional control, automatic pick-and-place compatibility and pulse-energy handling that competes with wirewound at small sizes. Thick-film parts span resistance from 1 mΩ (current shunts) to 100 GΩ (HV dividers), and power ratings from 1/32 W chips to 35 W heatsink-mountable bricks.

The downsides are higher TCR (typically 100 – 400 ppm/K, premium 50 ppm/K), higher noise index than wirewound, and a voltage coefficient that becomes significant at high voltage. Specialty HV thick films overcome the VCR issue with proprietary paste formulations. For SMD resistors below 1206 size, parasitic inductance is < 10 nH — far better than wirewound — making thick-film the standard for switching power supplies and digital circuits.