I should point out that the "glob" reference is not mine, just the viewpoints of some of our floor operators when adding silicone adhesives. From long experience at the IPC, I will say that the 1-5 mils you see so commonly referenced in IPC documents, represents generally accepted industry practices, not necessarily limits that THOU SHALT NOT TRANSGRESS. There is nothing magical that makes a coating absolutely wonderful at 4.9 mils, but a nightmare at 5.1 mils. Qualification documents usually specify 1 mil minimum and 5 mils maximum because that is where most people use them. This is NOT to say that you cannot make thicker conformal coatings work perfectly well. We do it here all the time as Dave indicates (not that we like to). The biggest problem comes when people, in the interest in manufacturing velocity, try to put on a thick coating in a single pass. That is very bad karma and this is where most coating horror stories start. Cracking of coating, poor adhesion, dewetting, underfilling parts with coating, etc. If you build up coating in thin layers, it can be just as reliable. It all depends on what you qualified your product with. If you did all your qual testing with 8 mil thick coating, and it passes all your tests, its Miller Time. On the other hand, if you qualified product with 3 mils of coating, but are somehow now applying 8 mils, then you have a potential problem. Your signals might change, you might change the resonant frequency of the board in vibration, you add weight, etc. Doug (Gotta Straighten Out Hillman Again) Pauls "David D. Hillman" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/30/2007 08:00 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask] To [log in to unmask] cc Subject Re: [TN] bubbles in conformal coating Hi Joel! I can pass on this experience with the use of excess conformal coating. I have witnessed design teams mandate the use of conformal coating in excess of 5 mils due to humidity qualification testing failures. The conformal coating becomes a "potting material" rather than a use environment coating. Most conformal coating materials are not designed to functional as potting materials and the typical result is a loss of solder joint integrity due to a conformal coating CTE impact. A phase that Doug Pauls uses to emphasis this misapplication is "the bigger the glob, the better the job" - bigger is not always better. Dave Hillman Rockwell Collins [log in to unmask] Joel Alexander <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/30/2007 07:49 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to [log in to unmask] To [log in to unmask] cc Subject Re: [TN] bubbles in conformal coating Please humor my question regarding coating thickness. Besides adding weight to the end product, what is the significance of listing a maximum thickness to conformal coating? Why would 0.010 be less reliable then the maximum thickness of 0.005? Joel Alexander Quality Assurance Manager TT APSCO, INC. Edward Mines <[log in to unmask]> 04/29/2007 12:54 PM To [log in to unmask] cc Subject Re: [TN] bubbles in conformal coating Joel- The thickness you are using is far greater rthan the maximum coating thickness called out by MIL-I-46058 & IPC-CC-830. Some customers would reject the coating for that reason alone. Contact Dymax. Ed [log in to unmask] wrote: We are using Dynamax Multi-Cure 984LVUF and it is about 10 mils thick on the flat section. I know this sounds thick but the machine drop dispenses so the coating will not run into keep our areas. Joel Alexander Quality Assurance Manager TT APSCO, INC. Edward Mines <[log in to unmask]> 04/27/2007 10:17 AM To [log in to unmask] cc Subject Re: [TN] bubbles in conformal coating Joel- You're right. 830 (the son of MIL -I-46058) is used by manufacturers to qualify the material. As a former employee of a manufacturer I know this document very well. I am less familiar with IPC-A-610. 46058 used to be on the internet. The versions of IPC-CC-830 that I am familiar with (there may be a newer one) followed the same format as 46058. Near the very beginning in MIL-I-......it states something like "the coating must be free from etc." Our interpretation was that this applied to the users too.That MIL SPEC is vague on many other things like thickness. Our interpretation was that the thickness the SPEC called out was on flat area of the board. I think foam is mentioned in the statement "the coating must be free from....." I know of many instances where coaters did things that weren't specifically prohibited that would adversely effect coating performance. Which coating are you using? Is the thickness on flat sections within the 1-3 mil range? Some HumiSeal polyurethane coatings do not cure properly if they are too thick. To the best of my knowledge no document says you have to follow the manufacturers instructions but if the don't the coating may not provide the protection for which the coating was designed. Ed [log in to unmask] wrote: IPC-CC-830 is a standard used by the manufacturer of the conformal coating to qualify their material. Can these also be applied to the application by the end user. IPC-A-610 states that bubbles are acceptable as long as they do not bridge adjacent conductors. Also is there a specific reference that states anything about the appearance of foam? Joel Alexander Quality Assurance Manager TT APSCO, INC. Edward Mines <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 04/25/2007 10:26 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to Edward Mines <[log in to unmask]> To [log in to unmask] cc Subject [TN] bubbles in conformal coating MIL-I-46058 & now IPC-CC-830 say conformal coatings should be "bubble free". Some have interpreted this as meaning that a few small bubbles away from components are acceptable. Foam is not acceptable. Some polyurethane conformal coatings generate gas as they cure. They should not be coated on very humid days. Bubbles are also apt to form in conformal coatings when the coating is too thick. I've seen this happen in between closely spaced tall components even when the coating on most of the board is within customary limits and has no bubbles. The solution was to change the application technique. Get the coating and equipment manufacturers involved. They want your future business. Ed Mines Ahhh...imagining that irresistible "new car" smell? Check out new cars at Yahoo! Autos. ForwardSourceID:NT000B489E Ahhh...imagining that irresistible "new car" smell? Check out new cars at Yahoo! Autos. ForwardSourceID:NT000B49D2 --------------------------------------------------- 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] 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] 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 -----------------------------------------------------