On Dec 15, 12:28, Matthew Sell wrote:
> Typically, the time spent "in the water" isn't long enough to damage.
Even
> items made of steel and iron won't rust if the water is removed after the
> cycle is complete. If they sit overnight, well, that's a different story.
>
> The only production problem I saw with untreated water was with an
> electronic test instrument that had a lot of high-impedance signal
> interconnects throughout. Many signal lines ran for long distances next
to
> each other. While the design of this piece of test equipment was
> questionable, it was our duty to get it to work.
>
> The two biggest problems were contaminants from the water supply used in
> the washing process (city water - switched to using a commercial
filtration
> system), and humidity (had to paint a sealant on all of the boards).
That's a well-known problem. Some of the residues from a domestic water
supply -- especially in hard water areas -- are mildly hygroscopic, and as
a result, the boards would acquire very small amounts of moisture on the
surface, especially when exposed to a humid atmosphere. In combination
with the salts in the residue, this makes for leakage across the board,
which could easily upset very high impedance circuits.
I heard of someone who had the opposite problem. He designed a CMOS
circuit which worked fine when forst contructed, but stopped when given
anti-environment protection or was potted. He'd inadvertantly relied on
the normal leakage across a PCB to hold the unused inputs of a CMOS gate at
a particular level. Remove the leakage current and the gate stops working
properly. Solution: add the pullup resistor that should have been there in
the first place.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Sat Dec 15 2001 - 14:50:31 GMT