Hi Werner, How is life in Florida? In response to your e-mail, I do agree that all things being the same, a higher stand-off will decrease the magnitude of the localized stress and thus increase the reliability of the joints according to published data... but I do disagree with your statement about 'having nothing to do' with the other input that people have given...increasing stand-off height may be the most important, but it is not the only reason.... there is a lot that the industry still do not know about reliability... reliability is application dependent...and I wish that the only issue with using ceramic BGAs with high temp solder (balls or columns) was stand-off height...but we know better now, but we still need to keep conducting reliability tests to know even more... marcelo -----Original Message----- From: Werner Engelmaier [SMTP:[log in to unmask]] Sent: Tuesday, September 15, 1998 12:42 PM To: [log in to unmask] Subject: Re: [TN] X-ray for open joints on BGA's ? Hi 'eholton', Marcelo, & Steve, Lets remember why there are high-melt solder balls and columns on CBGAs; it is to reduce the strains on the solder joints due to the large thermal expansion mismatch between the ceramic and the FR-4 by assuring large solder joint heights (stand-offs). It has nothing to do with cleaning, package weight, or devices generating heat. For BGAs, particularly CBGAs, a reflow profile with a peak temperature of 219C is too low even for eutectic Sn/Pb solder. Even with high-melt solder balls you should get nice fillets because of the eutectic solder paste. The reliability of the solder joints goes up roughly with the square of the stand-off height. 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] ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################ ################################################################ TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################