Hi Werner, I'm a little confused on the solder wetting. Can solder become liquidous and not form a metallurgical bond because either not enough time while liquidous or insufficient peak temperature? Or is a metallurgical bond formed as soon as the solder becomes liquidous unless some other controlling factor prevents the bond? Kind Regards Ryan Grant Advanced Technology Engineer MCMS (208) 898-1145 [log in to unmask] > -----Original Message----- > From: Werner Engelmaier [SMTP:[log in to unmask]] > Sent: Thursday, May 31, 2001 4:05 PM > To: [log in to unmask] > Subject: Re: [TN] Package reliabilty... > > Hi Pete and Steve, > Just to make sure that misinformation does not get disseminated.In a > message > dated 05/30/2001 23:44:39, [log in to unmask] writes: > >BGA's, especially CBGA's have given us a real headache, mostly because > the > >assembly process has to be spot on. We're making VME conduction-cooled > >cards with both PBGA's (35x35mm 1.27mm pitch) and CBGA's (21x21mm 1.27mm > >pitch), that are used in an avionics box. We had some boards made where > the > >manufacturing process was OK for the other components but the BGA solder > >joints looked a little rough for avionics quality standards. They > survived > >initial temperature cycling, but failed very quickly with only gentle, > >single axis vibration perpendicular to the board surface. The poor joints > >were blamed and we're working on improving the process with a different > >board stuffer. > Vibration failures do not occur in real solder joints, that is solder > joints > that truly metallurgically bond. Your failures are, I bet, interfacial > failures of "SJs" that never properly wetted. Most likely bec ause the > CBGAs > have a larger thermal mass and acted as heat sinks letting the solder > balls > never reach proper reflow conditions. > > >From more long-term experience in a previous prison camp, it was LCC's, > >particularly 20 pin LCC's that showed signs of solder joints cracking > under > >qualification testing (15g accelerations and thermal cycling from -40 to > >+125 deg). The problem was improved by putting a pad underneath to lift > >them off the board surface and using a stepped solder stencil to deposit > 10 > >mils paste on the pads for these devices. The higher solder joints gave > >greater flexibility. > Nothing new about reducing the strains in solder joints from a given > thermal > expansion mismatch by making them taller. It is NOT greater "flexibility," > but reduced strain. > > 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 1.8d > 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 ---------------------------------------------------------------------------------