Hi Paul, This is a common problem in the industry when the customer asks for the via holes to be plugged with soldermask & if the PBW fabricator does not do a good job of plugging the holes you will end with solder balls. Basically when plugging is done it is done from one side either component side or solder side depending on the board design, fine pitch devices, closely spaced features etc., would end up having soldermask smear after the plugging process, hence it would be plugged from the non-critical side. When the vias are not plugged sufficiently (%hole fill), solder from the subsequent HASL process wold get entrapped inside these vias which are attached to the plugged soldermask inside the vias & may not be visible to the naked eye, these solder balls would then pop-out during the IR reflow process at the assembly side, those that are visible would be entrapped inside but attached to the hole wall copper & would not pop-out during the IR reflow process at the assembly side. Normally you would see that when the plugging is done from the component side & top-side is being reflowed the solder balls will pop-out on the solder side or bottom side making it difficult to print solder paste on the bottom-side. The only way out here is increase the %hole fill by the fabricator to ensure no solder entrapment & for those boards that have been already fabricated & in WIP to send them through the IR reflow as bare boards to pop-out the solder balls & take a plastic paper cutter or non-metallic knife & run it across the board to remove the popped out solder balls & then your assembly would not have any problems. Baking the boards will not help as you need temperature & gravity for the solder ball to pop out & make sure you place the boards with the plugging side facing top during the IR reflow process. Hope this helps. Thanks, Krishnan -----Original Message----- From: Reuven ROKAH [mailto:[log in to unmask]] Sent: Thursday, September 25, 2003 1:08 PM To: [log in to unmask] Subject: Re: [TN] Solder Balls Hello Paul, The reason is : Vial holes, plugged by solder that come from the HASL process. You have to instruct the PCBs fab to increase the air pressure during the HASL. Other reason is, when you have plugging via holes requirement and the HASL process is done after the plugging process and not before. Best Regards ROKAH Reuven Chief Engineer ECI Telecom LTD. Operations Division 30 Hasivim St. Petah-Tikva 49517 ISRAEL Tel: 972-3-9266734 Mobile:972-55-786734 Fax: 972-3-9266480 e mail: [log in to unmask] "Black, Paul" <[log in to unmask] To: [log in to unmask] OM> cc: Sent by: TechNet Subject: [TN] Solder Balls <[log in to unmask] > 24/09/2003 14:57 Please respond to "TechNet E-Mail Forum."; Please respond to "Black, Paul" Hi TechNet Gurus, Has anyone experienced solder balls resulting from the board fabrication process? We have been getting them from our offshore supplier for a few months now and have had to add a wash step to our no-clean process. We know that it's fro the board because we have run bare boards through the reflow oven using the normal reflow recipe from that board and we are seeing 25-60 random solder balls on our 9" x 7", 8 layer, .062", HASL FR4 board. We believe the problem is caused by uncured solder mask that erupts when exposed to reflow temperatures but have been unsuccessful trying to eliminate the problem. We have tried baking the board @ 320 F for anywhere from 1.5 - 6 hours. This has reduced the number of solder balls to maybe a dozen or less. Anyone have a suggestion? Thank you, Paul Black Manufacturing Engineer Kronos --------------------------------------------------- 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- 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 847-509-9700 ext.5315 -----------------------------------------------------