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I am trying to build some thermal models for leaded and surface-mount diodes and transistors.

Below is a picture of the TO-220 outline I got from the internet. What kind of material is the black part that mates with the copper padding and encapsulates the silicon chip inside? Is it just plastic or some sort of epoxy?

enter image description here

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  • \$\begingroup\$ Epoxy as discussed in this article. \$\endgroup\$
    – qrk
    Commented Jan 10, 2023 at 1:57

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It is an epoxy resin (epoxy molding compound), with added hardener and other additives (silica often being one if them). The exact composition varies and is usually proprietary, but the properties can be found on manufacturer's websites, like this one (no affiliation).

Other materials have been, and are being, used for encapsulating semiconductor dies, like ceramics and plastics, but, especially for TO220s, epoxy resin is the most common.

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  • \$\begingroup\$ thanks for your response. Would you say the same for TO-247? Do they also usually use epoxy resin? \$\endgroup\$
    – FlakR
    Commented Jan 10, 2023 at 3:18
  • \$\begingroup\$ @HYQ: Not sure, but I think so. If you google "to-247 resin" you'll find some manufacturers' package data sheets with the composition. \$\endgroup\$
    – ocrdu
    Commented Jan 10, 2023 at 3:27

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