Hi Ian In our applications we have used one of three options depending on what the product is and where it is going: 1) underfill the BGA with a purpose made material, not with conformal coating. 2) parylene coat the assembly (which, by virtue of it being a vacuum deposition process, will coat under the BGA) 3) spray coating on the board and accept that the BGA underside is shadowed. #3 isn't without precedent, we don't typically worry much about old style boards with pin grid array components... I would not underfill a BGA with a regular coating material. This has been discussed in the past on TechNet, one of the concerns is the expansion with temperature putting stress on the joints. Good luck! regards, Graham Collins Process Engineer, L-3 Communications Electronic Systems Inc. Halifax (902) 873-2000 ext 6215 >>> [log in to unmask] 07/19/05 01:23PM >>> Fellow techies, a BGA related question. We're just starting to design BGA's into some new designs which are class 3 high rel assemblies and I am asking myself questions about the ability to adequately conformally coat under the packages. Our standard coating is a solvent based acrylic and we are using a 456PBGA device and a 429CBGA device, both on 1.27mm pitch, as the maximum sizes so far and I'd be interested to hear what other class 3 builders have experienced when applying the coating. Regards Ian Fox Goodrich ECS Birmingham UK --------------------------------------------------- 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 -----------------------------------------------------