Hi Carl
From your description and taking Werners observation, I think that scrapping
the assemblies is your best option.
As for trying to minimise the risk of this happening again, I think you
should remove the CAT-5 cable. That should do the trick but if you still
need it for some reason, then I would first look for a better insulated
cable and gland.
I might suggest putting a small drain hole in the box and coating the
assembly. You could also mount the board in the vertical axis to help ensure
that the water drains off the surface - unless this does literally have to
life under-water?
I hope this helps
--
Regards Graham Naisbitt
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Golf Quote of the week: I find it more satisfying to be a bad player at
golf. The worse you play, the better you remember the occasional good shot.
CONCOAT SYSTEMS LIMITED
Unit B2, Armstrong Mall
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Farnborough GU14 0NR
Phone: +44 (0)12 5252 1500
Fax: +44 (0)12 5252 1112
CONCOAT - Engineering Reliability in Electronics
CONCOAT SYSTEMS - Measuring Reliability in Electronics
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On 1/7/05 20:57, "Carl VanWormer" <[log in to unmask]> wrote:
> Hi Graham, thanks for the reply.
>
> The board was not coated. Who needs to coat it if it's in a waterproof
> enclosure - hahahahahah! The water was dumped and the board with all the
> white fuzzy stuff on it was given to me. I ran it through a couple of
> cleaning cycles (solvent, dishwasher, etc.) and took most all of the
> corrosion products off of it. The water in the enclosure must have been
> quite conductive, maybe because of residual contamination on the board. The
> evident corrosion appeared to be caused by electrical bias action. There
> was some discoloration of the board, particularly around vias, where it
> looked like water had seeped into the solder mask or into the laminate.
> Would pictures be in order?
>
>
> Carl Van Wormer
> [log in to unmask]
>
>
>
> -----Original Message-----
> From: Graham Naisbitt [mailto:[log in to unmask]]
> Sent: Friday, July 01, 2005 9:56 AM
> To: [log in to unmask]; IPC TechNet
> Subject: Re: [TN] Water damage question
>
>
> 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.
>
> CONCOAT SYSTEMS LIMITED
> Unit B2, Armstrong Mall
> Southwood Business Park
> Farnborough GU14 0NR
>
> Phone: +44 (0)12 5252 1500
> Fax: +44 (0)12 5252 1112
>
> CONCOAT - Engineering Reliability in Electronics
> CONCOAT SYSTEMS - Measuring Reliability in Electronics
> A British Manufacturer
>
> www.concoat.co.uk & www.concoatsystems.com
>
> Cell: 079 6858 2121
>
>
>
> 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
>>
>>
>
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