Abstract
Trimming plays an essential role in the manufacture of thick-film resistor networks. The process used to define circuit elements on a substrate, based on silk-screening techniques, is fast and inexpensive and has greatly increased the volume of manufactured devices. However, the same factors that contribute to making the screening process economical in terms of time and simplicity also present difficulties in creating consistently accurate devices. Because of inaccuracies and variations in the screening process, manufacturers cannot guarartee resistors to better than ±10 to 20% of the desired value. Trimming each resistor enables them to overcome the inherent limitations of the screening process and increase their yields of accurate and reliable devices. The laser has become an effective tool for trimming resistors because it is fast as well as accurate and can be controlled in order to produce consistent results. The following article discusses the objectives and principles behind laser trimming, the variables that affect the ability to produce an accurate trim, and different trimming techniques. It also offers recommendations for achieving optimum trimming speed and precision.