Various factors affecting precision of trim and resistor stability are considered. The influence of machine operating parameters (beam power, pulse frequency and trim speed) on resistor performance are examined and quantified through statistically designed experiments for aQ-switched YAG laser system. Laser kerf quality is examined by scanning electron microscopy and related to kerf isolation resistance measurements. A relatively simple, production oriented, quality control test is proposed for rapid determination of kerf electrical stability. In addition, the effect of cut design and extent of trim on precision and stability are discussed.
Many recommendations have been made on the proper operating conditions for the laser trimming process. In general these recommendations have centered on accuracy, precision or throughput. In some instances, these have appeared to be mutually exclusive. If one wanted accuracy and precision, one had to sacrifice trimming speed and, therefore, throughput.It has been reported that 40% of the processing cost of a thick film resistor network is due to laser trimming. To continue to make these networks commercially attractive, the manufacturers of laser trimming systems have addressed themselves to the problem of providing suitable cuts at higher and higher trimming speeds.It is important for the user of such a system to understand the basics of the trimming process and to have an appreciation for the new factors which will affect the performance characteristics of laser trimmed thick film resistors. This paper summarizes the previous work as it relates to present technology. It then attempts to develop new guidelines for high speed laser trimming.
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