Doug,
The traces were bordering the edges on the surface, maybe 5mm or so in from the edge, one could see where the edges were abraded from going in and out of the card guides, so I suspect that was a contributing factor. I don't think any of the boards that had moisture issues were multilayer, the ones we have in service made by Intel seem to be very forgiving except when techs try to remove components incorrectly, such as not clipping the leads on dips and trying to unsolder the whole chip and lift it at once. That was about 6 hours repair time. We would periodically pull the drawers and hose them off the surfaces of the board would have sand and salt imbedded in them, however we replaced some of the management and they felt that level of maintenance was no longer cost effective, they found out differently. Fortunately the system was supplemental and deemed not required, but others found differently.
Actually I am getting ready to pull the plug so to speak, the big "R" is beckoning. I will unsubscribe tech-net the end of this week but will re-subscribe from my home email in the future. Hopefully the company will keep me registered on IPC since I will be doing contract work for them in the near future.
Pat
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Monday, May 20, 2013 9:39 AM
To: Goodyear, Patrick
Cc: [log in to unmask]
Subject: RE: [TN] Conformal Coating Question
Thank you Pat.
I would guess the material was Cyanate Ester Modified (CEM) if it is beige or light brown. When you talk about the trace edges corroding, were those traces on the surface of the assembly, but near the edge, or exposed circuitry on the side (end face) of the board?
Hope you had a good time off.
Doug Pauls
From: "Goodyear, Patrick" <[log in to unmask]<mailto:[log in to unmask]>>
To: "[log in to unmask]<mailto:[log in to unmask]>" <[log in to unmask]<mailto:[log in to unmask]>>, "[log in to unmask]" <[log in to unmask]<mailto:[log in to unmask]>>
Date: 05/20/2013 11:26 AM
Subject: RE: [TN] Conformal Coating Question
________________________________
Doug,
Don't have a clue as to the type of resin or glass the boards are made from. This is technology that existed in the late '60s early '70s time frame. Most of the boards we have had a major issue with are light brown to a translucent tan in color, the edges tend to wick moisture and on one system we have since scrapped the trace edges started eroding away. They were exposed to direct salt air for about 20 years before we noticed issues, and when they started failing it was the whole system in about 6months. We had to replace it because the parts and technology used were obsolete and no longer available anywhere.
Sorry this didn't get back until today but I was off Thursday and Friday.
Pat
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Thursday, May 16, 2013 7:36 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Conformal Coating Question
That's taking it to the ragged edge Dewey.
Doug Pauls
From: "Whittaker, Dewey (EHCOE)" <[log in to unmask]<mailto:[log in to unmask]>>
To: TechNet E-Mail Forum <[log in to unmask]<mailto:[log in to unmask]>>,
"[log in to unmask]<mailto:[log in to unmask]>" <[log in to unmask]<mailto:[log in to unmask]>>
Date: 05/16/2013 09:33 AM
Subject: RE: [TN] Conformal Coating Question
There's no coating it: this gives a whole new meaning to punch-drunk.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Thursday, May 16, 2013 7:28 AM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Conformal Coating Question
Pat,
For the boards you talk about delaminating from moisture, are the boards made of a good FR4 and are the edges routed or punched? If FR-4, low Tg or high Tg?
In my experience, routing the board edges tends to seal the face of the board side. Punching the board means the fibers are unsealed and so moisture absorption can be greater?
Doug Pauls
From: "Goodyear, Patrick" <[log in to unmask]<mailto:[log in to unmask]>>
To: <[log in to unmask]<mailto:[log in to unmask]>>
Date: 05/15/2013 04:38 PM
Subject: Re: [TN] Conformal Coating Question
Sent by: TechNet <[log in to unmask]<mailto:[log in to unmask]>>
Dale,
Based on my experience as an end user who works at a facility on the Pacific Coast 85 feet above the ocean, the use of edge coating is almost a
requirement. Over time I have noted more than one instance of moisture
intrusion on the edge of a circuit card, in some instances causing the traces to un-bond and in some instances causing the board to swell, I have seen numerous boards that have had the edges of circuit cards, green stuff
along the edge of the traces. Rusty component leads are also a problem,
areas uncoated and areas where the plating was damaged.
Pat Goodyear
Control Technician
Diablo Canyon Power Plant
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of lduso - Diamond-MT.com
Sent: Wednesday, May 15, 2013 12:35 PM
To: [log in to unmask]<mailto:[log in to unmask]>
Subject: Re: [TN] Conformal Coating Question
Dale, this was just brought up about a month ago but it was not the main topic. I think it was part of the large discussion about coating that Doug started. Here at Diamond-MT we are a conformal coating application house, that's all we do. We coat for everyone from the big guys to the small mom and pop shops. They send us the boards with a spec and we coat them in whatever they want. That being said, of the thousands of different part numbers we have coated over the years, I'd say less than ten required coating on the edge. As a matter of fact, we have more part-numbers that require us to leave the edges coating-free than be coated. Unless you have something conductive exposed on the edge, there really isn't a reason to coat it. (Of course we are talking about all liquids, parylene is a different matter.)
Lloyd Duso
Diamond-MT
Plant Manager
(814) 535-3505
www.Diamond-mt.com
On Wed, May 15, 2013 at 3:08 PM, Dale Ritzen <[log in to unmask]<mailto:[log in to unmask]>> wrote:
> Hello Technetters,
> Don't know if this has come up before or not (nothing in the
> archives), but we are researching any conformal coating requirements
> specifying that the edges - not just the surfaces - of the boards be
> covered. With the emergence of automated coating equipment, i.e.
> moving away from the spray or dunk coating processes, we are finding
> it hard to identify a coating machine that can do board edges. So...
>
> 1. Is there a valid need to coat the board edges, or is this simply a
> customer driven requirement? (I'm waiting for an "It depends..." on
> this
> one.)
> 2. Are there any IPC standards that address this specific question?
> J-STD-001E, section 10, covers coating to "all areas designated for
> coverage on the assembly drawing/documentation", and does not
> specifically mention board edges. I don't have copies of HDBK-830 or
> CC-830B for reference, so am relying on your inputs and experience with
this question.
> I would be glad to do some reading up on this if anyone has any
> suggestions for white papers or other documents that cover this (pun
intended).
>
> We'd really like to understand what the industry-wide requirements are
> for conformal coat in this regard. Might be a lost cause already as we
> have been getting the boards sprayed for years, so the customer is
> used to seeing every surface coated, including edges. But, the only
> spec they've quoted so far is the old Mil-I-46058C which was removed
> from service back in the 1990's. After reading through it though, I
> don't find anything that specifically addresses this question.
>
> Any feedback would be appreciated!
>
> Dale Ritzen, ASQ CQA
> Manager | Quality Group and ISO Management Representative
> _____________________________________________
> Austin Manufacturing Services
>
>
>
> ______________________________________________________________________
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