Yes to near-edge. However, one must see the design engineer's situation. If given a fixed space for the board, and you have a lot, lot of objects to press into that space, I think you bless every millimeter that can be used. We have a thumb rule that says 'no closer than 0.5 mm to the edge' for inner traces and 'no closer than 1.0 mm from any metal for the top traces' , which points at rack mechanisms of course. If there is plenty of space, then there is no reason for running close to the edge. Inge ----- Original Message ----- From: "Glidden, Kevin" <[log in to unmask]> To: <[log in to unmask]> Sent: Thursday, October 21, 2010 2:31 PM Subject: Re: [TN] Conformal Coating Board Edges Hallelujah Brother Doug.... Thanks for that post. Not to make light of your problem, but it was GREAT for a morning laugh. I feel your pain. LEAN can be a double-edged sword. And to provide just one man's opinion on some your questions: I agree with your reasoning around NOT coating board edges that are routed vs coating edges of boards that are V-scored or mouse-bite. One caveat to the routed edges is that different designs can have widely varying minimum edge spacing to inner conductors. Much of the reliability, I would imagine, would depend on that edge spacing, the dielectric strength of the laminate, and the stack-up/resin content, and lastly the quality of the PCB lamination. Also, and I'm not certain how common this is, but I've seen PCBs where the designers require the ground layers extend all the way to the edge for EMI purposes. That sounds like a great candidate for edge coating. Re. "how harsh an environment has to be in order to coat the edges?"...is it really a limit? Is there a magic number? 5= good, 4.5 = bad? I think it's relative. Any humid or condensing environment deserves the consideration. -----Original Message----- From: Douglas Pauls [mailto:[log in to unmask]] Sent: Wednesday, October 20, 2010 5:40 PM To: [log in to unmask] Subject: Re: [TN] Conformal Coating Board Edges Thank you all for your responses. As indicated earlier, how I wish I would have had this kind of resource back in the 80s. Here are my thoughts on the matter. At Rockwell, home of truth justice and the American way, we do a great deal of coating by hand. A classic case of LEAN principles applied wrong, though I am told it made sense at the time. I am working on bringing back spray coating, but it is tough to change an entrenced culture. We have often required coating the board edges on our drawings, generally because "we have always done it that way". We may have done it for some of the reasons you all have given, but the technical rationale is probably buried somewhere in our archives. However, this edge coat requirement is selective in application. When the edges of the board have metal clad areas on top and bottom, such as with card guides, the edges are not coated, because it is very difficult to coat just the edge and not get any on the top or bottom card guide. Similarly, if we have a large high density connector on the board edge, that is flush mounted to the board, we do not coat the edge under that connector as it is next to impossible to do without flooding the connector surfaces. It is not unusual to have three out of four sides of an assembly uncoated (two card guides, one connector, one coated edge). So our apparent philosophy is to coat board edges unless it is too hard. One of the things that having a LEAN philosophy as a driver does for you is that you are constantly evaluating processes asking "is this really necessary?", or "is this value added?". For us, coating the edges of the board takes additional time and effort. It can also lead to rework or touch up activities as well. I cannot say we have ever had field failures or problems from board edges that are uncoated. Since we deal with some pretty harsh environments, if this had truly been a failure mechanism, such as for moisture ingress, we would have seen it by now. One of the key points for me, is that we are dealing with board edges that are routed, which has a tendency to seal the board edge, as opposed to punching or V-scoring, which can leave exposed fibers and has a greater risk of moisture intrusion. If I had punched or scored/snapped edges, I would consider edge coating to be necessary. But since I have routed edges, I ask myself the question of whether edge coating is value added. Would you agree with my reasoning? Inge, when you say board that are sensitive to water ingress, what do you mean? Is there a particular laminate material, such as Teflon or the high speed laminates, that is a consideration? Second, how do you determine how harsh an environment has to be in order to coat the edges? As for Parylene, remember, a nightmare is also a dream............. Now, to be perfectly honest, I can't really pass all this questioning off as high minded LEAN driven noble pondering. It's actually because I messed up last week. I used this reasoning on one, ONE mind you, program to relax the edge coat requirement for a tough application. Now I have a hundred requests, many along the lines of "Why do I have to coat my board edges if Donna does not have to coat hers, huh, huh?". There are some days here I REALLY don't want to be the coating expert......... Doug Pauls Inge <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 10/20/2010 03:46 PM Please respond to Inge <[log in to unmask]> To [log in to unmask] cc Subject Re: [TN] Conformal Coating Board Edges Well, it depends.. example 1: boards sensitive to water ingress via edges: we used multilayers of cc along edges example 2: boards with rough edges damaged the rack slides: we used cc along edges example 3: boards with smooth edges, no harsh environment: we did not use cc along edges there are more examples of course Conformal coating the edges was tricky, because of the sharp edges. The viscosity was therefore very important. Someone mentioned Parylene, that one has no such problem. Parylene is a dream stuff. Lately, we have skipped edge coating, except when the customer wants it. I had a look into MoonMan's POD, which covers most about PCB manufacturing. Strange enough, nothing about edge coating. Inge ----- Original Message ----- From: "Douglas Pauls" <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, October 20, 2010 8:20 PM Subject: [TN] Conformal Coating Board Edges > Good afternoon all, > > I am glad we all appreciate Inge and the time he puts into making this a > fun and interesting forum. To sum up: Ditto. > > I have a question related to conformal coating, a sort of survey. For > those of you that conformally coat your assemblies, do you coat the edges > of the boards? Why or why not? > > There is an internal debate here and I wanted some other viewpoints before > offering my own. > > Doug Pauls > Rockwell Collins > > ______________________________________________________________________ > This email has been scanned by the MessageLabs Email Security System. > For more information please contact helpdesk at x2960 or [log in to unmask] > ______________________________________________________________________ > > --------------------------------------------------- > 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 > ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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 ----------------------------------------------------- ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. 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For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ --------------------------------------------------- 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 -----------------------------------------------------