Hey Doug and Dave, out of curiosity- So why not use an underfill material as the coating? Do you not trust the electrical properties of the underfill, or is it a processing issue (e.g. wetting,voids...)? Chris -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls Sent: Monday, November 30, 2009 11:52 AM To: [log in to unmask] Subject: Re: [TN] BGAs & Conformal Coating Thank you Steve for posting the pictures. Here are the links. http://stevezeva.homestead.com/files/deformed_Balls.jpg http://stevezeva.homestead.com/files/Squished_Ball_1.jpg http://stevezeva.homestead.com/files/Squished_Ball_2.jpg To give a little background, we have certain design engineers who absolutely, positively believe that every ball on a BGA must be coated with conformal coating or it will fail in humidity. They put silly notes on the engineering drawing to this effect, resulting in conformal coating being used like an underfill or a potting material. Dave Hillman and I did an internal study this last year to demonstrate the effects. We forceably filled the area under the BGAs with conformal coating, one a popular solvent based acrylic, the other a water based acrylic urethane. We left the material come to a tack free condition, fully cured the material, and then put it through thermal cycling, monitoring resistance. The cycle was -55C to +125C, 15 min dwells at either extreme, 8-10C/min ramp rates. The test ran for a little over 2100 cycles. The solvent based acrylic had a 73% failure rate by the end of the test. The water based acrylic urethane had none. The pictures are all of the solvent based acrylic, which has a higher CTE than the acrylic-urethane. We tested BGAs, QFPs, a couple of QFNs, and some SOICs. The only significant failures were for the BGAs. Can't really say much more than this. Doug Pauls Rockwell Collins "Steve Gregory" <[log in to unmask]> 11/30/2009 07:33 AM To "'TechNet E-Mail Forum'" <[log in to unmask]>, <[log in to unmask]> cc Subject RE: [TN] BGAs & Conformal Coating Hi Doug! Send them here: [log in to unmask] Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls Sent: Monday, November 30, 2009 8:29 AM To: [log in to unmask] Subject: Re: [TN] BGAs & Conformal Coating Good morning Juan, I suspect that Xilinx wants you do do a thermal cycle study on solder joint reliability when conformal coating gets under the BGA. The stresses brought about by a mismatches in the coefficient of thermal expansion (CTE) can rip a BGA off the board and can severely deform the balls. Hillman and I did such a study here a few years ago. I can share a few pictures of what happens, if Steve Gregory would be kind enough to forward his present e-mail address for the photos. Not sure I have the right one. Doug Pauls "Juan T. Marugán" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> 11/26/2009 11:53 AM Please respond to TechNet E-Mail Forum <[log in to unmask]>; Please respond to "Juan T. Marugán" <[log in to unmask]> To [log in to unmask] cc Subject [TN] BGAs & Conformal Coating Hi, I've read in a Xilinx guide that: "Xilinx has no experience or reliability data on flip-chip BGA packages on board after exposure to conformal coating. It is recommended that the end-user should characterize the board level reliability performance of Xilinx packages before production use." Does anybody know any infomation or study related with this topic? Thank you. Juan T. Marugán Indra Sistemas SA Espańa --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------