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Why are ICs/Semis black?
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ataradov:
Soviet KT315/KT361 transistors came in orange, red, green, brown and other colors. I don't think color meant anything about the device itself, it may have coded the factory.

There is probably no specific reason why everything is black. It is just  easier to carry and characterize only one pigment.

A video from just today on that topic:

JohnnyMalaria:
1. Opacity
2. Quicker thermal equilibrium
3. Cheap. It's easy to maintain the color consistency when all you have is a single black pigment dispersed in a polymer matrix. Other colors would require multiple pigments and other additives which just adds to the complexity and cost of ensuring uniform encapsulation material.
Benta:

--- Quote from: srb1954 on May 03, 2021, 01:13:14 pm ---Some opto-coupler devices are encapsulated in white plastic. Can anyone explain the reasoning behind that.

--- End quote ---

The original reason for that was to simplify the lead frame of the optocoupler (cost factor). The idea came from either Sharp or Toshiba, I believe.

A classic optocoupler has the LED and detector placed one above the other in a sort of Z/inverse-Z shape lead frame (seen from the side).
Using white epoxy, it's possible to place LED and detector side by side in a planar lead frame. The LED radiates vertically and the light is reflected to the detector by the white epoxy.
Much easier and cheaper.

Concerning other colours: many reasons for those. I remember repairing Salora TVs back in the 80s that had two fast SCRs (RCA types) in the horizontal output stage. They were identical, but paired, and one had to be a teeny weeny bit faster than the other for the circuit to work. One was green and the other was gray to ensure correct replacement.

magic:
No idea why black other than same reasons that applied to Ford T.

As for green, I have one such PNP made in commie Poland.
retiredfeline:
Probably because it's cheapest, does the job, and people generally don't care about the look inside equipment. I have a few gray TTL chips from the 70s, a few red NPN and green PNP GE power transistors, and white optocouplers but the rest are boring black.
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