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July 2005

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Subject:
From:
Graham Naisbitt <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Graham Naisbitt <[log in to unmask]>
Date:
Fri, 1 Jul 2005 17:56:22 +0100
Content-Type:
text/plain
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text/plain (103 lines)
Carl
In answer to your questions:

1   Yes.
2   Yes.
3   Definitely maybe.

Was the board conformally coated?
Have you investigated the resistivity or conductivity of the water? Have you
analysed the water to determine what impurities are present?

If you can answer these it will make the solution easier to fathom......ooh
sorry about the puns, they will make Dewey's day!
--
Regards Graham Naisbitt

[log in to unmask]          [log in to unmask]

Golf Quote of the week: I don't play golf to feel bad. I play bad golf and
still feel good.

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On 1/7/05 15:43, "Carl VanWormer" <[log in to unmask]> wrote:

> Background:
> I am trying to fix a circuit board that has been running in an underwater
> environment.  The water was not a planned condition.  The board was in a
> waterproof box with waterproof grommets for the cables that came into the
> box.  Unfortunately, the CAT-5 cable that went up the antenna tower had
> water leaking into the other end of the cable, which was 100 feet higher, so
> the water made its way into the enclosure.  Since the enclosure was "water
> proof", no water leaked out of the box.  The board ran in this condition for
> a while.  I cleaned and dried the board, then added a jumper to replace the
> 24V power lead terminal on the switching regulator, which had been etched
> away.
>
> As I slowly increased the input power to the system, I saw the regulator
> start working, but the output voltage didn't rise.  I measured the
> resistance from VCC to ground at under 1 Ohm.  I fired up my favorite short
> circuit location tool (SS-2) and observed the following:
> 1.  several short circuits under the BGA chip
> 2.  several short circuits on areas of board without traces showing on the
> top and bottom sides.
>
> Question to the group:
> 1.  Can running a board under water cause short circuits to form under a BGA
> chip?
> 2.  Can letting a multi-layer circuit board soak in water (with or without
> bias) cause shorts to appear on inner layers?
> 3.  Is there anything that can be done to reverse the action that caused
> these shorts?
>
>
>
> Thanks,
> Carl
>
>
> Carl Van Wormer
> [log in to unmask]
>
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