Way back in the early '70 some jet fighter were having crazing up to 12" into boards. Fighters diving form high altitude to warm jungle environment and back to altitude were "pumping" water down the fiber glass weave resulting in shorts. We did not have a word for it back them but it was most likely CAF. PWBs had edges dipped in epoxy to prevent humid air from condensing as water in the glass fibers during the climb back to altitude. PR -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls Sent: Tuesday, June 09, 2009 8:35 AM To: [log in to unmask] Subject: Re: [TN] Conformal coating of PCB edges Kevin, I don't know that I would go as far as to say it is a deeply entrenched military requirement. For the aerospace industry, Boeing, Airbus, Sikorsky, etc., can be just as demanding in their commercial requirements as any of our military customers. As my esteemed colleague, Mr. Hillman, is fond of saying, we don't have a switch on the solder machine that selects between military solder joints and commercial solder joints. Same philosophy applies to conformal coating. We don't coat a military assembly any different (well, in most cases) than we do a commercial assembly. In fact, because many of our military boxes are more nearly hermetic in design, vs. the open construction of commercial boxes, the challenge to the conformal coating is often greater for the commercial hardware. Our commercial customers put some pretty odd requirements in their packages when they come to us. Enough to make me wonder sometimes what they were sniffing when drafting the design package. Sometimes the customer has wanted us to coat the edges because they could not give us a tolerance on how close to the edge we had to be with the coating. Others have indicated that they thought it gave them greater insurance that the edge of the coating will not delaminate during thermal cycling if the coating lapped over the edge. Again, not really traceable to a failure anywhere, but that is what the customer wants. Doug Pauls Rockwell Collins Kevin Glidden <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/09/2009 07:20 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Kevin Glidden <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Conformal coating of PCB edges Many thanks, as always, to all for responding. This confirms what I suspected - no real documented industry requirement or recommendation, but instead a deeply entranched military "requirement" that became somewhat of a standard practice. Of course like anything, there is no "one size fits all" rule for all the different applications. In the end, a little extra protection can't hurt, with exception of the card guides and tight fits. Thanks, Kevin Glidden -----Original Message----- From: Douglas Pauls [mailto:[log in to unmask]] Sent: Monday, June 08, 2009 2:24 PM To: [log in to unmask] Subject: Re: [TN] Conformal coating of PCB edges For our applications, the card guides are metal and are not coated so as not to interfere with card insertion into rail guides. Same as you. I would agree that coating the edges is usually overkill. I would be hard pressed to find an example of failures attributed to lack of coating on an edge of a board. But it would be too hard to roll that boulder up the hill. Speaking as one who has tried it and been flattened by the boulder. Painfully. Repeatedlly. Doug Pauls Rockwell Collins Keith Calhoun <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/08/2009 12:50 PM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Keith Calhoun <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Conformal coating of PCB edges In my previous employment we built military electronics systems, airborne and shipboard, and in most cases masked off the board edges before coating to allow the boards to slide into various types of card guides or clamps. I never recall a failure attributable to moisture intrusion through the card edges, and we used to see some amazing failures in our legacy products. Keith S. Calhoun Product Engineer SoPark Corporation 3300 South Park Avenue Buffalo, New York 14218 Phone: 716-822-0434 Ext. 237 Fax: 716-822-5062 email: [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls Sent: Monday, June 08, 2009 11:41 AM To: [log in to unmask] Subject: Re: [TN] Conformal coating of PCB edges Kevin, For our applications, if the board is coated, the edges of the board are coated as well, except in certain situations, such as where connectors are at the edge of the board. Why? Well, the time honored "we have always done it this way". Part of the rationale is that at the board edge, you have the glass bundles of the laminate exposed and water can potentially wick into those glass bundles, creating problems over the long haul. In most cases, I think that if the boards are routed from the panel, the routing process tends to seal the edges and conformal coat is not needed. However, if you are shearing or punching the board out, then those fibers are not sealed (in my opinion) and should be coated to seal the edges. In order for me to change that stance, I would have to have to prove to our ever skeptical design engineers that not coating a board edge will never create a problem in any environment for any of the 20-30 years design life we use on any product we have ever made. Then change an entire corporate culture. I am already burned in effigy 2-3 times per week. Doug Pauls Rockwell Collins Kevin Glidden <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 06/05/2009 10:30 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Kevin Glidden <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Conformal coating of PCB edges No takers on this one, so maybe I will reword it... How many are requiring conformal coat application to PCB edges, and why? Thanks! -----Original Message----- From: Kevin Glidden [mailto:[log in to unmask]] Sent: Wednesday, June 03, 2009 1:47 PM To: [log in to unmask] Subject: [TN] Conformal coating of PCB edges Can anyone point me to an industry document where this is mentioned / required / recommended, or is this left entirely up to choice? I believe most consider this a good and desirable thing? How do automated selective spray systems accomplish this? --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] 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