[sdiy] Do LDRs and/or LEDs age?

[Ken Stone]

Considering that many displays, such as used in calculators, 7 segments,
games, vu meters, etc simply mount the bare silicon LED straight on the PCB,
I doubt moisture is too much of an issue. Basically I think it comes down to
poor quality control. Take this for example - on one of the first mass
produced transistors, every set baked for qc test came though with 100
percent of devices accounted for, yet when they dismantled the oven years
later, they found thousands of transistors kicking around in the bottom of
it. Simply put, some one though it easier to just tick the box than actually
do what was required.

Ken

>>Looking at Paul's awesome Buchla pictures got me to wondering about the 
>>lifetime and ageing of LDR/diode control devices - Varactrols, CLM6000, 
>>home-brew, and otherwise.
>
>I have some CLM6000 that I bought from a surplus guy, old stock from when 
>they first came out.
>About 20% seemed to be 'out of spec', as though not enough output from
>the led (and I can't imagine any kind of amorphous semi going high in
>resistance with age).
>I vaguely remember reading once that early leds sometimes had 
>bodies that allowed warer vapor to diffuse in slowly, with resulting 
>decreasing light output.
>No idea whether this is true or not, but it seems a plausible mechanism..
>what do the semi fabrication experts here think?
>
>paul perry melb australia
>
>
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Ken Stone   sasami at hotkey.net.au  
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