Path: utzoo!attcan!uunet!lll-winken!lll-ncis!helios.ee.lbl.gov!nosc!ucsd!rutgers!rochester!kodak!ornitz
From: ornitz@kodak.UUCP (barry ornitz)
Newsgroups: sci.electronics
Subject: Re: Bright LEDs, visible infrared? Colored Chips?
Summary: Been done
Keywords: Colour, Chips, Larry Lippman, Cats
Message-ID: <1590@kodak.UUCP>
Date: 6 Jan 89 02:39:08 GMT
References: <743@optilink.UUCP> <888@ubu.warwick.UUCP>
Reply-To: ornitz@kodak.UUCP (barry ornitz)
Followup-To: sci.electronics
Organization: Eastman Kodak Co, Rochester, NY
Lines: 45

In article <888@ubu.warwick.UUCP> haldane@uk.ac.warwick.cs (Steve Sykes) writes:
>The light detection devices they use are ordinary 8 pin dil packages
>that are made from transparant plastic - so why, I think to myself, could one
>not package other chips in the same way?  It looks really neat.  Ok,
>maybe light would affect them, but you could do different colours - blue
>for ttl, red for cmos etc - why not even colour code chips in stripes in
>the same way resistors are?
>
>Thinking it over, it ocurred to me that someone must have already thought of
>doing it, and so there must be a good physical reason for not doing it.
>But I'm not really sure what this might be - surely not just the price of
>the dye?

Light does affect many chips creating surface charge carriers.  I have even
seen circuits where the leakage current caused by light in glass encased small
signal diodes (1N914, 1N4148) caused erratic behavior.  I even saw a RAM chip
used as the basis for a video camera - someone had cut the top off the ceramic
package and discovered the effect by accident.  The results were crude with
essentially infinite contrast (black or white, no gray) and poor light sensi-
tivity but it did work.

I have some vintage Westinghouse chips someplace in the junque bin that are 
blue and some beautiful pink ceramic chips from TI in a DIP package with
gold-plated, brazed-on leads.  Heck, I still have a pile of germanium parts!

The chip packages are colored with a pigment rather than a dye.  It takes very
little carbon black to get a black or dark gray epoxy; it takes a lot more of
any other color pigment, usually with titanium dioxide.  If you sell a part
for ten cents, you don't want to spend another half cent on color - carbon
black is _very_ cheap and much of the plastic is filler anyway.

Color coding for numbering chips is also expensive - lots of numbers and how
do you have room for the date code, lot number, the manufacturers logo and the
made in Malaysia disclaimer?  ;-)
                                          73, Barry  WA4VZQ
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|  ___  ________  |
| |  / /        | |  Dr. Barry L. Ornitz  UUCP:..rutgers!rochester!kodak!ornitz
| | / /         | |  Eastman Kodak Company
| |< < K O D A K| |  Eastman Chemicals Division Research Laboratories
| | \ \         | |  P. O. Box 1972
| |__\ \________| |  Kingsport, TN  37662       615/229-4904
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And I did hug my cats today - all 10; but I only shake hands with the 5 dogs.