Peter, Voiding is worse with a poorly formed or damaged via/micro-via. I have seen some crushed vias where the side wall buckle produce some stupendous voiding. Voiding happens worse with vias that are narrower at the top surface of the board because solder has a more difficlt time filling the hole at solder printing. Remember most no-clean solder is 50% flux by volume and the volatiles need to do their thing and leave. Some think that trapped volatiles and flux when they cannot leave become viscous clumps in the via hole and then when the eutechtic BGA ball collapses the clump moves up into the ball. This gets worse with a site that goes through a double reflow process. One suggestion is to fill and plate over these vias so this cannot happen. Another suggestion is to offset the via from the center to about 2 mils from the pad edge so the clumping happens outside the component ball. Regards, Dorothy Lush -----Original Message----- From: Peter Lee [mailto:[log in to unmask]] Sent: Tuesday, December 18, 2001 11:20 PM To: [log in to unmask] Subject: [TN] Voiding on BGA with uVias Hello, We have encountered major BGA voiding issue. The void is sometimes up to 70% of the joint. Under X-ray inspection we found a blind 0.006" uVia, 0.01" deep under each void. Other BGA solder joint on board w/o uVias do not have any void problems. Board is gold over Nickel finish and 2mm thick. Things we tried: Reflow profile - WS/ no-clean paste, longer soak Washing/ baking the bare PCB Reworked by cleaning the uVias/pads and filled with solder but still seeing void Has anyone seen this before? Micro-sectioning clearly showed the void originated from the uVia. We are trying to convince the board house that it's not our process. Rgds, Peter _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------- -----