Predicting the effect of high speed laser trimming on resistor stability

A study of the relationships between laser trim parameters and the post-trim stability of resistors is discussed. A materials system designed for high-speed processing and a high-powered laser trimming system were selected for this investigation. The experimental data points were chosen using a three-factorial face-centered-cube statistical design. Each trim parameter was represented by one of the dimensions of the cube. The post-trim environmental stability data was analyzed using response surface modeling techniques. The model was used to predict the combination of trim parameters required to produce the optimum resistor stability for trimming speeds of 100 mm/s (4 in/s). The experimental results are presented and discussed. The results indicate that: (1) fast laser trimming is feasible; (2) the correlation between predicted and actual stability is good; (3) process sensitivity can be predicted; and (4) 15-20 kHz appears to be practical limit for the pulse frequency on a 10-W laser in routine applications.<>