[SI-LIST] Re: IC package

I want to add another reason: the encapsulation is black, because the epoxy 
is filled with silica fillers (to match the thermal expansion of the 
encapsulant with the CMOS chip, to avoid delamination) and filled with 
other stuff to improve the heat conduction (pure epoxy has a very large CTE 
and bad thermal conductivity). And the fillers are selected to be black, so 
that there is no need to coat the package afterwards for light shielding.

LEDs and detectors have indeed a transparant encapsulation, I can assure 
that it is not simple to select a good and transparant encapsulation. In 
case of LEDs, this is not a big problem because LED chips are typically 
small (and mechanical stresses due to thermal mismatch are proportional to 
the third power of the length). And detectors are typically cool (no such 
internal heating as with LEDs and active electronics). There is great 
interest in silicone-like transparant encapsulants for opto-electronics.

Ronny
----
Visit http://www.intec.ugent.be/IO


At 10:19 17/08/2004 -0700, Wyland wrote:
>The packages are black partly to avoid sensitivity to light.
>This was a problem in the early days.
>
>The transistors in ICs are photoelectric.
>The transistors are composed of PN junctions, the same kind of junctions
>in solar cells.
>Light shining on a PN junction creates photocurrent in the junction.
>Solid black absorbs the most light.
>Light sensitive devices such as photocells and photo transistors
>use clear plastic packages. See TI, etc.
>
>In the early days, some tried different colored packages for marketing.
>Fairchild had some red plastic packages for a while.
>However since black worked well and was cheap, it became the default.
>
>Black is a better radiator of heat than other colors,
>but the effect is very small at normal IC temperatures.
>Remember that the heat flow goes up (and down) proportional
>to the fourth power of the temperature. Wearing black clothes
>in the sun draws heat because the sun is at 10K degrees.
>IC case temperatures seldom achieve 70 degrees C.
>
>
>s.raja wrote:
>
> >why all IC packages are Black in colour?.
> >Regards
> >Raja
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=====
Ronny Bockstaele
   Independent Consultant Photonics
   bvba PHOCON, Bergbosstraat 224
   B-9820 Merelbeke, Belgium
   tel+fax: 32-9-362.1995, GSM: 32-473-645879
   mail:ronny@xxxxxxxxx, web: http://www.phocon.be

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