A NOVEL METHOD OF COMPARING LASER TRIM PATTERN GEOMETRIES OF THIN FILM RESISTORS

摘要

This paper studies the effects of varying laser trimming geometries on key performance parameters of bar-shaped thin film resistors. Several popular trim patterns including the plunge cut, L-cut and serpentine cut were modelled and their effect on heat-affected zone (HAZ) sensitivity and temperature coefficient of resistance (TCR) were investigated. It is found that variation in resistor dimensions and trim length in the trimming algorithm can give significant increases in the TCR of the thin films with results of 220-250 ppm/C for the serpentine cut, 220-320 ppm/C for the plunge cut and 250-290 ppm/07°C for the L-cut. It is also shown that the serpentine cut is the most sensitive to variation in the dimensions of the HAZ with a sensitivity value of 12% when compared to the L-cut and plunge cut which produced values of 10% and 11% respectively. In addition to results for the TCR and HAZ, a novel method of predicting the optimum trim pattern to minimize the final resistance value tolerance of the thin film is proposed.