Carl, Inspection of Underfill can be carried out by X-Ray if you have a system with bags of resilution and excellent computer enhancement capabilities, but the recommended method is by using a Scanning Accoustic Microscope. I haven't found any specs for accept/reject criteria either, so had to draw up my own. Of prime consideration was the amount of rework involved should you decide to reject an underfill because of voiding. Using "Flow" type underfill (fill the air gap underneath a part after the soldering operation) is bad enough to rework - you have to remove the BGA, clean up the site to remove epoxy as well as solder, re-ball the BGA, re-attach, re-underfill and re-inspect. "No FLow" type underfills are worse because they're not reworkable. Once you fill a BGA with this stuff, it's meant to be there for keeps. I decided that "failure" occurs where a void leaves one or more balls more than 50% by surface area unsupported. Multiple small voids are not significant, but should be minimised. Void-free underfilling is not actually critical, but the permissible degree of voiding is up to the product engineers to determine from their Qualification tests. As a rule of thumb, I used the same acceptance/rejection criteria as for voids in the BGA solder joints, but gave a bit more lattitude/benefit of the doubt before rejecting. After all, underfill voiding will not directly cause a functional failure, though too many voids of the wrong size or in the wrong places may reduce the enhanced reliability of the BGA's solder joints. Solder joint life will still be longer than with no underfill under conditions of temperature cycling. Does this help any? Peter Carlr Ray <[log in to unmask]> 24/05/2003 02:01 AM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to Carlr Ray To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: [TN] Checking and measuring voids in underfil Hey Techer's, Currently I an assisting with the development of a underfilling a FPBGA. As part of the qualification I was wondering what amount of voiding should I expect and accept. I have been unable to find any standards for underfil voids and methods of detection. Any information would be greatly appreciated. Carl Ray Sr. Manufacturing Engineer Huntsville, AL 35807 Phone: 256-882-4800 ext. 8845 Cell: 256-990-1990 --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------