Thin-film microcircuits on flexible substrates

The feasibility of fabricating flexible thin-film circuits while planar, and then folding or rolling the circuits to conform to packaging constraints was investigated. This approach would significantly increase microcircuit packing density and offer a new dimension to the thin-film circuit engineer. The flexible substrate used was the polyimide film, Kapton; identical circuits were also fabricated on borosilicate glass substrates for comparison. The conductor-resistor arrays used a new material system (copper/Kanthal) offering low cost, low temperature coefficient resistors, and a simple fabrication process. The flexible thin-film resistors were found to show very small resistor value changes when flexed (average about 0.2% for 1-cm radius of curvature), and resistor temperature coefficients comparable to those on glass substrates. This work suggests that flexible thin-film substrates may help solve complex thin-film microcircuit packaging problems.