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microprocessor covered with black coating?

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I opened my calculator to check it from inside, just a matter of curiosity, :-D
and I found out that the microprocessor is covered with a black layer:shock:... is it for protection or other purposes? Please can you explain to me why covering the microprocessor with the black material? and what is it made of? Look at the attached photo.
Thank you.

Novice :)

 

It is probably not a microprocessor, but a custom IC. It is "chip on board" i.e. the silicon is put directly onto the PCB and globbed with some epoxy to protect it and the bond wires.

Keith.
 
Thank you Keith :)

what is the benefit of mounting the silicon die on the board directly?? is is a matter of cost? speed? performance?

Nonice
 

If you bond the die right to the board, you don't have to pay for packaging the die, which is a significant part of the total cost.
 
So far as the issue of black (that too opaque) goes, a bare chip exposed to radiations of all sorts is never advisable and is never seen except for EPROM's where it is intentionally left a transparent quartz window for erasing. The effect of radiation under different conditions is known.
 

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