Laser trim pattern modelling and optimisation for CuAlMo thin film resistors

The influence of varying laser trim patterns on the electrical performance of a novel CuAlMo thin film resistor material were investigated. The benefits and limitations of various trim geometries were considered before two patterns, the ‘L’ cut and serpentine cut, were selected to laser trim resistor samples to target values of 1 to 10 Ω, using previously optimized laser conditions. The effect of increasing trim gain and varying trim pattern on the stability and standard deviation of the films were then systematically investigated. A two stage trimming process was utilized to reduce resistance drift figures to <0.1% following storage for 168 hours at 125 °C in air and also allowed much tighter resistance tolerances of <±0.1% to be achieved.