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I want to measure heatsink temperature using LM35 TO-92 package. heatsink is a flat surface of aluminum.

What is the proper way of mounting a TO-92 temperature sensor on a heatsink so that can measure the temperature of the surface of heatsink and also not fall off easily?

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    \$\begingroup\$ check this link: tech.mattmillman.com/…, i think this is exactly what you need. \$\endgroup\$
    – Cheche Romo
    Commented Feb 19, 2020 at 17:45
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    \$\begingroup\$ @ChecheRomo using an extra clip may bring additional Rth which may lead to incorrect measurements because there's no guarantee of perfect thermal coupling between the two metals. Instead, "fastening" (e.g. via a glue-like material like epoxy) the chip directly onto the heatsink will bring the best result. \$\endgroup\$
    – Rohat Kılıç
    Commented Feb 19, 2020 at 18:36

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Heatsinks do exist for TO-92 packages. Use the parametric search at your favorite components supplier and look for Thermal Management > Heat Sinks > Designed for or Package Cooled and select TO-92.

Here are some examples:

  • Aavid Thermalloy MAX12NG (rail mounted clip for TO-92 sensors)
  • Aavid Thermalloy 575200B00000G (slide-on heatsink)

(The second link is less a datasheet and more a catalog.)

However, I think your question title is somewhat misleading. You're not trying to cool the TO-92 device (the LM35), but rather sense the temperature of some other heatsink with it.

The TI LM35 datasheet under Layout Guidelines states:

The LM35 is easily applied in the same way as other integrated-circuit temperature sensors. Glue or cement the device to a surface and the temperature should be within about 0.01°C of the surface temperature.

Given that information, you might also want to look for thermal epoxy and adhere the device to the surface you intend to measure. MG Chemicals, 3M, Wakefield-Vette, and many others make such epoxies. With this in mind, you should be able to find application information and datasheets to accomplish your goal.

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Among other packages, LM35 comes in TO-220. This package is a better option for measuring temperature of a heatsink. It has a metal tab with good thermal conductivity, and it has a mounting hole. Depending which net your heat sink is connected to, you may need a heatsink mounting kit.

If you have a choice, use LM35 in a TO-220 package for measuring temperature of a heatsink.

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