Steve, I have been working this issue with some very large 'glob top' BGA's and had to modify the first cool down zone to get the BGA's to flatten out. Some oven manufacturers (like mine) seem to have a race to get the boards back to room temp after solder (a marketing ploy) and blast the board with relatively cold room air right out of the spike zone. You don't see much effect with the thermocouples buried under the BGA, but try placing one on top and watch the temperature dive. This top/bottom temperature differential is what caused my warpage. My fancy 8 heating zone/2 cooling zone oven had no provisions for adjusting the cooling zone so I used wire cutters to disable the two top blowers. What a difference! Works for me. Jim Kittel -----Original Message----- From: Stephen R. Gregory [mailto:[log in to unmask]] Sent: Tuesday, February 27, 2001 2:34 PM To: [log in to unmask] Subject: [TN] Heat-sinked BGA Bridging... Hi all! This topic is a "moldy-oldie", but I've started to experience bridges again with this TI DSP (TMS320C6201GJC200). I've been doing okay up unil recently. We build these boards in work orders of around 25 pieces. Our last run we had 7 boards bridged out of 25!! Sent the boards out to be reworked. I asked that they be x-rayed before and after, and to my surprise after looking at the x-ray images, they were all bridging in the same general area. It's a 4-row periphery BGA, and the bridges are occuring on the inner two rows, around the center of the part, at the same side of the part. What's funny, is that the vendor we use to rework the boards for us is having difficulty as well. We've been asking him to remove, re-ball, and re-install the part, they said they've been having about a 50% success rate doing this...they've been getting the bridges too. They have a nice full-blown SRT BGA rework station and do this for a living. I print 6-mils of paste (square apertures for the BGA), have a Conceptronic HVN-70 which I run: 150 160 170 180 240 150 160 170 180 240 25-in. per min We never have had these problems before...it all started when TI put the heatsink into the top of the part. I've looked at our paste print and it's dead on, placement is dead on too, we verify that with a Ersascope. My question is could there be something wrong with the part? Warping causes bridges at the corners, right? Why would it bridge in the interior rows at the same general area? Thanks in advance! -Steve Gregory- ---------------------------------------------------------------------------- ----- 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 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- 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 ---------------------------------------------------------------------------------