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Subject: Re: Temperature cycling of wirebonds.
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Mon, 30 Sep 2002 05:08:16 GMT
NNTP-Posting-Date: Mon, 30 Sep 2002 07:08:16 MET DST
> > Ian Stirling wrote:
> >>I know this is a "how long is a bit of string question".
> >>I'm wondering about cooled camera chips in vacuum.
> >>Specifically orbiting ones, thermoelectrically cooled.
> >>These might see a temperature range of -100C - 50C or so, and
> >>perhaps over 10K cycles.
> >>Do many sorts of wirebond fail at this sort of cycling?
> > In space cooling is not a real problem. In some cases satellites need
> > heaters to keep certain areas warm. The temperature in space is around
> > 4 Kelvin. The only 'problem' is to transport heat to the dark side of
> > a satellite. This is usually done by heatpipes and radiators (plain
> > old heatsink). Passive cooling is also an option. A relative of mine
> I know.
> Camera chips are often cooled actively, in order to reduce noise.
> In low earth orbit, you'r in shadow for 1/2 the time, and may have
> providing power in the dark (batteries have limited cycle life).
> In low earth orbit, it's hard to get much below 0C, unless you try
> hard, as the hot earth fills one side of the sky.
There are a few hybrids in space I designed, mostly on 2"x2" substrate. Most
active parts are wirebonded with tiny gold wires. We never had a failure on
Worse is heat. One hybrid for "communications" was specified to work up to
150°C and you have to take this brittle GaAs. Cracks already when you come
close with the bonder.
It turned out it was mounted right on top of the bomber sheds portals to
sharpen the nasty atomic weapons, when the President had given his OK.
The afterburner would make it that hot even with another ceramic protection
in front and cooling behind. These things work only very short range for
evident reason. I quit that job when I came to know. :-)
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