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What is a resistor?

Laser trimming

The need for a laser trimming process

Screen printing is used to form each layer of a thick-film chip resistor, and involves placing paste on the alumina substrate. Hundreds of chips are processed at the same time, inevitably leading to slight variations in printing conditions (i.e. paste thickness).
This results in varying resistance values, making it impossible to ensure optimum resistances. Therefore, an additional process is required to adjust the resistance values to within specified tolerances.

Laser trimming Resistance Value Distribution Graph
The laser trimming process

A laser cuts the resistive element while the resistance is measured in order to achieve target resistance values with minimal variation. Laser trimming narrows the current pathway, which increases resistance. Once the target resistance has been met the laser is stopped to reduce variations between chips.

Resistance Increase Resistance Value Distribution (Before Trimming/ After Trimming)