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For years the most common material had been the BAKELITE ..
And that "stuff" was alwys as black as the inside of your a ..
**broken link removed**
Why some transistors are green - nowadays you can find white bakelite, gray bakelite, red bakelite .. and green bakelite .. someone just likes that colour ..
In my opinion, simply it is black just due to the tradition, as everybody does the same, and everybody gets used to that color.
The same question you may ask why PC/monitor/keyboard/mouse/other PC-related stuff have the ivory color, while laptops are black or darkgrey.
Recently, manufacturers seem to change color/geometery of some devices for easy regconization: optocoupler are ivory, some Japanese manufacturers make their TO-220 packages dark-green, the same with some European manufacturers make their TO-220 chambered.
Nobody uses bakellite for things like that its too hard too make.
The die is connected using silver filled modified epoxies (Cyanate Ester Blends) that is if they are not made fully of metal and just connected with an AuAl bond. The packaging can be made of different things: Standard its usually epoxy cresol novolac(ECN) or angular (and sometimes round) fused silica. Biphenyl epoxy is used for low moisture absorption systems.
Why is it black?- It radiates heat the best. Believe me there is a substantial difference between it being black or even gray and some of those ic even have internal heat exchange plates just beneath the upper side. Its probably easier to see the markings as well.
if u see the long history of valve bases, they were in black. Black is good for heat dissipation. But in those days the valve base were made of bakelite material which was very brittle. As the other engineering semicondutors & materials developed, also available many colours. Mainly the material used for ic encapsulation, is made by few companies. universally it was black colour preferred due to heat dissipation properties.
This is not fashion show but a technical product. some ceramic encapsulated transistors & ic's r available in white.
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