I'd see it same way Bev ; perhaps with an addition of concern for the wafer itself : I can distinctly feel what would happen to my overheated head should some brute blast it with CO2, not only the legs/columns/balls would give up hold with mostly (in my "life")dissipative surfaces ; I would not guarantee the neural integrity therefore either . I know it sounds as that happened in my past already ; still : dear o dear, DT ; how could you ??? One of the hammerhead methods ? Paul Klasek http://www.resmed.com -----Original Message----- From: Bev Christian [mailto:[log in to unmask]] Sent: Wednesday, 28 July 1999 11:40 To: [log in to unmask] Subject: Re: [TN] Freeze Spray and BGAs Darrel, I can't claim to having seen the situation you describe below, but let me offer a wild scenario just to get people thinking... On one or more pads not enough solder paste was put down and/or some of the balls of the BGA were undersized. When reflow was finished there was just the barest mechanical (as opposed to metallurgical ) contact between the now melted and resolidified solder from the paste on the pad and the BGA ball. If the current was high enough going through a small enough contact area this might account for excess heating. Of course it could be just because you were looking for something it seemed hot to you, I don't know. Had you compared the feel of it to other identical BGAs used in the same circuit on different boards for a true comparison? Anyway, with this whisper thin contact any slight temperature change, board torsion, system vibration could have been making/breaking the connection or, even more unlikely, controlling current flow and thus giving squirrelly results. Once you hit it with freeze spray you shrunk the materials such that the contact area opened up, electrical flow stopped and perhaps an incredibly little piece of solder moved such that on rewarming to room temperature and re-expansion of the reflowed pad and BGA ball, connection could not be re-established to reheat the former connecting members. Anyone else willing to give their crazy (or maybe not so crazy ) scenario? regards, Bev Christian Nortel Networks > -----Original Message----- > From: Darrel Therriault [SMTP:[log in to unmask]] > Sent: Tuesday, July 27, 1999 8:01 PM > To: [log in to unmask] > Subject: [TN] Freeze Spray and BGAs > > TechNet, > > A curious situation happened when we used freeze spray on a BGA; it quit > working. > > The BGA seemed a bit hot to the touch and we were getting some flakey > operation, so > we decided to hit it with some freeze spray. It quit working altogether. > > I have not had a chance to check out the package for a failure mechanism, > but > I will be replacing it to see if it was that part causing the failure. > > Does anyone know of any specific thermal issues with using freeze spray on > BGAs?? > We use both TBGA and PBGA, so I thought I'd ask the question before I go > and > inadvertently destroy more of our parts. > > Regards......DT > > ############################################################## > TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c > ############################################################## > To subscribe/unsubscribe, send a message to [log in to unmask] with > following text in > the body: > To subscribe: SUBSCRIBE TECHNET <your full name> > To unsubscribe: SIGNOFF TECHNET > ############################################################## > Please visit IPC web site (http://www.ipc.org/html/forum.htm) for > additional > information. > If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or > 847-509-9700 ext.5365 > ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################