Werner, I see that you and Dan Quail attended the same school (potatoe). Marion Graybeal ----- Original Message ----- From: Werner Engelmaier <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, July 28, 1999 10:07 AM Subject: Re: [TN] Freeze Spray and BGAs >Hi Darrelt, >What happened to your BGA is pretty obvious. Just consider what is physically >happening when you hit iot with the freeze spray. >You hit the BGA with the freeze spry from the top, I am sure. This quickly >cools the top layer of the BGA, the rest of the BGA to a lesser degree. That >sets up differential thermal shrinking (the opposite of thermal expansion on >heating), which causes the BGA to warp like a potatoe chip with the top >surface being concave. This puts tremendous tensile stresses on the solder >joints, as well as on other parts in the BGA depending on construction. On >top of which, the PCB does not cool very much at all (the BGA shields it from >the freeze spray) and sets up shear stresses between the BGA and the PCB. >I would not at all be surprised if failure analysis shows fractured solder >joints. likely in combination of soldering pads ripped out of the polymer >matrix. > >Werner Engelmaier >Engelmaier Associates, L.C. >Electronic Packaging, Interconnection and Reliability Consulting >7 Jasmine Run >Ormond Beach, FL 32174 USA >Phone: 904-437-8747, Fax: 904-437-8737 >E-mail: [log in to unmask], Website: www.engelmaier.com > >############################################################## >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 ##############################################################