EEVblog #730 – Thin Film Resistor Networks

How ceramic backed precision thin film resistor networks are constructed and laser trimmed.
Examples come from the resistor networks in the 7.5 digit Keithley DMM7510 Multimeter, manufactured by Fluke.
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  1. Let me take a stab at it. The resistors are trimmed by focusing the lasers under the glass and done in circuit while energized. As they cut measurements are taken and as they get close to the value, cooling time is allowed, then if necessary, lasing begins again and is pulsed until the exact, precise, value is presented to the measuring circuit. As these are under glass, they are most certainly the most high precision of the laser trimmed resistors.

    • It seems they may be trimmed under the glass, that may be why there is the dark residue. And perhaps in combination with some pre-glass trimming as well. Whether or not it’s done once soldered in the final product we don’t know.

      • Hi Dave,
        I worked at the Visteon factory for close to 13 years. We trimmed in circuit, live, and used pulsed lasers, cutting until close, the using short bursts while moving the beam with galvomirrors, until the exact measurement was made. Very cool toys.

  2. Does the area of the square correspond to the amount of power that the square can dissipate?

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