Two thoughts/questions cross my mind (quickly, because the mind is small)
on this one -
1) Are the edible traces anywhere near the areas where you used no-clean
soldering? I categorise potting as similar in principal to coating inasmuch
as you're sealing any no-clean residues onto the board surface, and it's
never really recommended to use no-clean chemistry if you're also sealing
the unit afterwards.
2) Is your potted unit potted into a sealed container, or is it just
hanging out with the potting exposed to the elephants, I mean elements? Is
your potting permeable? - it probably is, in which case moisture (and
there's plenty gets thown up by truck wheels, along with Gawdnosewot
contaminants) will be transpiring nicely through the potting and nurturing
your trapped residues to the point where they'll get hungry and eat your
traces, leaving all kinds of pooh behind. If the potting isn't permeable,
then you've probably sealed in moisture that can't escape. It's then gone
stir-crazy and destroyed its surroundings.
Have you analysed the green, red and white deposits? Do their compounds
bear any relation to the chemistries used on the units prior to potting?
I'm no chemist at all, but salts and oxides? Acids and metals? Any truck
batteries nearby?
Physical damage is an obvious consideration from debris kicked up by the
wheels, but you don't mention it, so I take it the units are protected from
this in some way. Can you tell us how? If the units or the potting have
been physically damaged in any way, anything could have got inside to do
the damage.
Can help with any good literature, sorry to say, but I'ld make sure you use
water-soluble fluxes throughout your manufacturing of this unit, make sure
it's very clean and dry before you pot, use a suitable potting primer to
ensure good keying, but not an etchant type unless you can guarantee to
neutralise it, make sure the potting is properly out-gassed, and don't
mount the finished product in a more exposed position than neccesary.
How was the product qualified?
My 2 cents worth, and good luck with finding a solution.
Peter
Carl
VanWormer To: [log in to unmask]
<[log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST
COM> Aero/ST Group)
Sent by: Subject: Re: [TN] AUTOMOTIVE PACKAGING/SEALING
TechNet REALIBILITY
<[log in to unmask]
ORG>
03/06/02
12:35 AM
Please
respond to
"TechNet
E-Mail
Forum.";
Please
respond to
Carl
VanWormer
I got excited after seeing the subject, but I haven't seen enough, yet . .
.
We have a "potted" product that rides behind the wheels of a truck. All
our
best protection efforts have yielding significant failure rates. Returned
units have had traces eaten off the board, with various colors of crud left
over. The green is probably copper oxides. Some of the copper seems to
have turned into a red powder. There is a lot of white crust around some
of
the lost traces and vias. We are guessing that the boards were not
cleaned
well enough before potting (Insulcast RTVS 27 thermally conductive potting
compound). We believe the boards were produced with a water soluble flux,
then washed, then a few hand-ads were installed with a "no-clean" flux. We
think that either (1) moisture sealed inside the potted units may be
"helping" the corrosion, or (2) moisture (with or without extra corrosive
elements) is leaking it through poorly sealed boundaries of the potting
compound. (we are using "primer" around the known "edges" of the units)
I know that "Detroit" has solved this problem many times. Where can I find
a "guide book" or a knowledgeable vendor to help me out of this board
cleaning/potting mess?
Carl Van Wormer
Cipher Systems
1815 NW 169th Place, Suite 5010
Beaverton, OR 97006
Phone (503)-617-7447 Fax (503)-617-6550
-----Original Message-----
From: Earl Moon [mailto:[log in to unmask]]
Sent: Tuesday, March 05, 2002 6:35 AM
To: [log in to unmask]
Subject: Re: [TN] AUTOMOTIVE PACKAGING/SEALING REALIBILITY
Brian,
Thanks for the site/company/info. Just what I've been looking for and
should
do the job well. Also, not too far away, like you.
You noticed the reduced number of participants on this forum? Can't
remember
seeing it this low. I remember when Steve said we are getting close to the
2000 member mark and was only off by a few hundred or so. I suspect you've
been stealing them away to your environmental forum.
In any event, everyone says the economy is back on track. Of course,
contract engineers are being offered half what they made one year ago and I
don't see too many jobs available but for JSF, power, drugs, and some
strange stuff I've never heard of before.
Just thinking, a self flattery statement, on paper,
MoonMan
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send e-mail to [log in to unmask]:
SET Technet NOMAIL
To receive ONE mailing per day of all the posts: send e-mail to
[log in to unmask]: SET Technet Digest
Search previous postings at: www.ipc.org > On-Line Resources & Databases >
E-mail Archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700
ext.5315
---------------------------------------------------------------------------------
[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
