Hi Ramon Any coating at 33% solids or more is unlikely to penetrate fully beneath a BGA even when dip coating - with the exception of silicones as they have really low surface energy. To rely on "natural product shrinkage" to avoid any fillets would be a little risky and how could you know for sure? Kindest regards, Graham Naisbitt [log in to unmask] On 22 Nov 2006, at 14:21, Dehoyos, Ramon wrote: > Hi Graham: > I have not made detailed experiments as you and > Brian have. CC at 33% solids and 66% solvents when squirted under > the BGA will adhere to all surfaces when wet. When it dries it > shrinks significantly leaving plenty room for expansion. My > question: Wouldn't it work based on the fact that the CC is shrunk? > Best Regards, > Ramon > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Graham Naisbitt > Sent: Tuesday, November 21, 2006 12:32 PM > To: [log in to unmask] > Subject: Re: [TN] BGA and conformal coating > > Vered > > This is an old and thorny subject much debated on the TechNet in > the past. > > The TCE of apretty much all conformal coatings is >300ppm/DegC but > the TCE of silicones are huge at ~300-350ppm/°C Solder being only > ~16 ppm/°C this is a pretty significant TCE mismatch. > > As for silicones as debated by Brian Ellis and myself some time > ago, Brian said: They have a unique property that however soft they > feel, they are rock-hard when subjected to mechanical shock (hence > super- bouncing balls and bouncing putty) At only slightly elevated > temperatures there would be tension on a BGA-ball-pad combination, > that would increase by orders of magnitude should it be subjected > to a small shock at the same time > > If you must under-fill, then a soft purpose developed epoxy is the > probable answer, check with Brian Toleno - wherever he is hiding > these days? > > Having said all of that, I have had aerospace customers who apply a > very thin coating, diluting the coating and dipping at very slow > speeds, that can ensure (as far as one can without removing the > device to check!) coverage under the device. They then apply a > "conventional" spray coat to complete the job. > > I hope this helps > > Regards, > > Graham Naisbitt > > Gen3 Systems - Engineering Reliability in Electronics > > [log in to unmask] > > > > On 20 Nov 2006, at 16:40, Vered BS wrote: > >> looking for reviews/articles or case studies regarding conformal >> coating on BGA for military/aerospace environment Appreciate any >> comment or sharing your experiance Thanks Vered >> >> --------------------------------------------------- >> Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 1.8e > 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 1.8e > 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 1.8e 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 -----------------------------------------------------