Eliminating the most obvious, which is the nitrogen curtain brushing over the components at the end of the tunnel, and the board is massive enough to retain heat such that the components are still in liquidus, and there are no "dust bunnies" hanging down near the exhaust stack, then: 1. Is the copper layout balanced for the BGA pads? If several ground and power planes are connected to one side of the BGA, they sometimes cause such a major delay in the solder paste obtaining liquidus between one side of the pad pattern and the other that they can literally pull the BGA off of it pads. 2. Is the solder mask below the lateral line of the bottom of the component body? With .020" ball diameter, the part can literally bottom out on top of the mask if the mask is even .010" above the pad surface. If there is flux or solder fines as a result of slightly misregistered paste print, the component will move around as the solder fines are agglomerating together, like a board on top of marbles. 3. Is the print properly registered on the pads? If not, again the surface tension may be enough to shift the part to one side during initial liquidus. 4. This package is very small in terms of mass. If steps are not taken to keep the solder paste under control, it can absorb a certain amount of moisture that leads to voiding. The violent boiling out of this moisture can cause very small components to literally blow around during the reflow process. Check the X-rays for presence of voids. If they are present, then it is a good bet that some of the problems you are seeing is due to the volatility of the solder paste. This is more prevalent when using a water wash paste, but can also happen with alcohol-based no-clean paste as well. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Le Thanh Tung Sent: Sunday, August 21, 2005 8:16 PM To: [log in to unmask] Subject: [TN] Sifted part at BGA location Hello everybody. At present, we are facing to one problem as below: BGA component is shifted after go through reflow machine. We have checked 100% mounting condition at BGA location before reflow, we sure the BGA is not shifed but after reflow the shifted part defect still happened. although we lost much time to investigate but the problem is still not be overcome. The detail of BGA is as below: - BGA size: 15 x 15 - Pitch: 1 mm - Ball dia.: 0.49 mm - Product: RoHS PCBA Anyone who have this experience? Thanks --------------------------------------------------- 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 -----------------------------------------------------