Trimming Potentiometers
Often designers use potentiometers, which are adjusted during end testing until the desired function of the circuit is reached. In many applications, the end user of the product would prefer not to have potentiometers, as they can drift, be mis-adjusted or develop noise. Therefore manufacturers determine the needed resistance or capacitance values by measurement and calculation methods and afterwards solder the suitable component into the final PCB; this approach is called "Select on Test" (SOT) and is quite labor-intensive.
It is simpler to substitute the potentiometer or the SOT part with a trimmable chip resistor or chip capacitor, and the potentiometer adjusting screwdriver is replaced by the laser trimming. The achieved accuracy can be higher, the procedure can be automated and the long term stability is better than with potentiometers and at least as good as with SOT components. Often the laser for active trimming can be integrated in existing measurement systems by the manufacturer.
Read more about this topic: Laser Trimming