Resistor Trimming

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After processing, thick and thin-film resistors will always have some statistical variation from their intended value. In the case of separate chip resistors, parts can be measured, then binned into 10%, 5% or even 1% tolerances (standard RETMA values). In larger format thick-film or thin-film networks where the resistors are just one small detail in complex artwork, often the final part will not work if the resistor value deviates too much, and out-of-spec resistors means scrapped parts. The alternative is to trim the resistors into the correct value. In laser trimming, a YAG laser is used to ablate the resistor material from the substrate, raising its resistor value.

Rule of thumb: Note that you can only trim a resistor up in value, not down.

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There are three ways to laser-trim resistors, shown below. Plunge-cut gives the "fastest" resistor change, but from a reliability point-of-view, it may , may , L-cut, edge trim, etc.

In a "poor-man's version" of laser trimming that is sometimes used in prototype shops, you can abrade a resistor with emery paper to raise its value. Here you are actually decreasing the effective thickness of the resistor, rather than altering the number of squares. Thin-film resistors will have to be re-stabilized after this step, since you would be removing the oxide layer.

With laser trimmed resistors ATP can achieve tolerance of ±0.5% depending on design and material. Polished material is recommended when tighter tolerances are needed. Most laser trim types can achieve the ±1.0% without difficulty as long as the TaN area is large enough. See Recommended Minimum Trimmable TaN Area chart.

Below are listed all the different types of resistors that can achieve these types of tolerances.

For more laser resistor trimming machineinformation, please contact us. We will provide professional answers.