Dave, You are a cookin'. Love it, MoonMan ----- Original Message ----- From: "David Douthit" <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, March 06, 2002 12:56 PM Subject: Re: [TN] AUTOMOTIVE PACKAGING/SEALING REALIBILITY > Carl, > > Some quick points: > > 1. The boards are too dirty (clean them with heated DI water at a minimum). > 2. RTVS 27 - Is this a Room Temperature Vulcanization S??? potting compound? > If so be sure that the out gassing during the cure process does not contain acids. > 3. RTV does not absorb sudden shocks and vibration. It is forgiving during thermal changes. > 4. Your box leaks at numerous locations and RTV is very permeable to moisture and certain reactive > gases. > > David A. Douthit > Manager > LoCan LLC > > Carl VanWormer wrote: > > > Thanks to all for the recent comments, questions, and suggestions. Here's a > > "quick" update of my recent status and findings: > > > > Our unit is mounted in an aluminum box (4 screws into the top) with some > > style of heavy duty circular connectors (with rubber gaskets), and I've seen > > no board corrosion around that area. The system is potted with Insulcast > > RTVS 27, after treating the connector sides, box mating surfaces and holes, > > and sides of 4 led (that protrude thru box holes) with the "proper" primer. > > > > Previous batches of boards have been built, cleaned, then stocked. After > > final programming (a J-leaded PROM, hand soldered with water soluble flux), > > they are washed under hot, running water with vigorous brushing. Recent > > testing (yesterday, thanks to QPL) indicated ionic contamination levels of 5 > > ug. NaCl/sq.in, initially, and 15 ug. NaCl/sq.in after the PROM is added and > > "cleaned". This indicates that there is some bad stuff inside to start the > > process. This is like putting one bullet in your Colt 45 and playing > > Russian Roulette! > > > > Now we have 2 possibilities for the second half of the equation . . . either > > we are sealing enough moisture in the system to guarantee continued work for > > our repair tech, or water is getting in through our impervious barriers. > > Failure analysis shows the most common areas for the corrosion are in the > > area of the 4 LEDs that protrude through the box. I am suspicious of the > > quality of the adhesion to the "primered" LEDs, since they seem to pull > > clear of the potting compound leaving a smooth surface, not torn and ragged. > > Another area has been near the board (and box) edges, some of which have > > shown what appears to be oil incursion into potting fractures at the box top > > interface. I am wondering if vibration of the potting mass is causing > > fractures, even though it is hard to imagine when looking at the system. > > Has anyone seen anything like this with the Insulcast compound? > > > > Since I have to make some more units, I have cleaned a dozen (for a second > > time) and baked them overnight at 70 C, bagged them with desiccant to wait > > for potting. We are planning to flood the boards and box with primer, > > thinking that they may be more difficult to troubleshoot if they fail, but > > maybe they won't fail (at least at the present 30% rate). Any thoughts on > > this? > > > > Thanks for listening, > > Carl > > > > 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: Roger Stoops [mailto:[log in to unmask]] > > > > Carl, > > Been readin' what everbody else is saying about potting and encapsulating, > > thought I would jump into the fray. > > We build equipment that is mounted on 'dozer blades, behind and under > > motorgraders, and such. Pretty dirty and nasty environment. We have found > > that, for consistent reliability, potting or coating a board (really squeaky > > clean to begin with mind you), mounted in a custom aluminum enclosure, with > > a sealing ring or o-ring under the lid, and using Mil-style circular > > connectors (with gasket seal behind connector) seems to cure these problems. > > Of course this may be more expensive than what your product can afford, but > > illustrates how we solved such a problem. Even a small, inexpensive > > off-the-shelf aluminum enclosure with a simple gasket system would go a long > > way to reducing your problem with external moisture. > > We would like to hear later about your efforts in solving your dilemma. > > > > Roger M. Stoops, CID [log in to unmask] > > TRIMBLE NAVIGATION LLC > > Engineering and Construction Division > > http://www.trimble.com > > > > -----Original Message----- > > From: Carl VanWormer [mailto:[log in to unmask]] > > > > 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? > > > > -------------------------------------------------------------------------- ------- > > 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 > > -------------------------------------------------------------------------- ------- > > -------------------------------------------------------------------------- ------- > 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 > -------------------------------------------------------------------------- ------- > --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------