Carl,
More than likely there are dendrites along with the CAF.
I seriously doubt this board is repairable. The reason is that the
enclosure is not hermetically sealed.
The existing conditions will reoccur very rapidly (dendrites) if the
humidity in the enclosure rises above 50%.
The CAF can only vaporize inside the lamination. This results in a
hole/delamination coated with metal ions and carbon. A very nasty
combination!
David A. Douthit
Manager
LoCan LLC
Carl VanWormer 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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