Hi Phil -
There are a great many devices with internal cavities: variable resistors;
connectors; switches; hybrids; speakers; ad infinitum. Their ability to
withstand fluid immersion is dependent on how well the device is sealed, by
design and manufacture. Obviously the solid state and hermetic devices
aren't a problem. So far as the others go, it has to be determined on a
device by device basis.
Case in point: We had our process set up to wave solder and clean a group of
about eight very pricey MIL grade filter pin connectors on a flight
motherboard. Connectors supplied to SCD by "Manufacturer A" passed thru
this process with flying colors, producing no failures in acceptance test or
field usage, over the span of several thousand units. "Manufacturer A"
discontinued filter pin connector production, so we brought "Manufacturer B"
on line to the same SCD. Leakage into the innards of "Manufacturer B's"
filter pin connectors brought the program to a grinding halt until we forced
them to redesign their connector sealing provisions. (We also learned that
the connectors, even though they met the MIL spec provisions for leakage
were inadequate to go thru the Qual rain test.)
I ran into similar problems with MIL-SPEC trim pots, where the seals were
quite adequate on two of the three manufacturers parts.
Another item learned: If a part which is susceptible to leakage is quite
warm, the air in its internal cavity will have expanded and partially
expelled itself. Cooling the part rapidly will cause the internal cavity to
reach a pressure less than atmospheric pressure, allowing it to inhale fluid
if it is immersed.
Regards - Kelly
-----Original Message-----
From: Phil Nutting <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Friday, February 16, 2001 9:50 PM
Subject: [TN] components prohibited from aqueous wash
>Hi all,
>
>I don't remember if I posted this question in the past months, but I'll
>repost to get a fresh answer.
>
>Are there any components (pth) that can't be washed in an aqueous system?
>Over the years we've had problems with electrolytics, polystyrene bodied
>caps and small board mount relays.
>
>Does anyone have experience with thermal compound or other thermal
>management materials in aqueous clean?
>
>Oh ya, the system I just installed is a closed loop DI water wash with no
>chemicals.
>
>Phil Nutting
>Manufacturing Engineer
>Kaiser Systems, Inc.
>High Voltage Power Supplies That Work(tm)
>126 Sohier Road
>Beverly, MA 01915
>ph: 978-922-9300
>fx: 978-922-8374
>[log in to unmask]
>
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