The cooling rate of solder directly effects the resulting metallurgical microstructure of the solder joint. In solder, a rapid cooling (not quenching, but of several degrees C per second) results in a lamellar eutectic microstructure, where there are very fine, ordered grains of Sn and Pb rich areas. (The grains look like fine lines throughout the solder). A slower cooling rate will cause the microstructure to have coarse, globular grains of Sn and Pb in a basically random arrangement. The lamellar microstructure (from fast cooling) is much better at resisting the motion of dislocations, and thus gives a stronger, more creep resistant structure. Also, the faster cooled solder will look shinier - which makes the QA people happy, while it is not necessarily a great indicator of how fatigue resistant the actual joints are. Here's the kicker - at time, especially with elevated temperatures, the lamellar microstructure will grow fairly quickly. (They'll even coarsen at room temperature.) Thus the quicker cooled solder joints will have superior initial strength, but over time and temperature will have comparable strength to the slower cooled solder joints. Brett Goldstein EVI, Inc. > Technet, > > I have recently read in an article that the most favourable type of solder > joint is formed from rapid cooling of the solder. > > I am a bit confused with this as I have always been under the impression > that rapid cooling of metals results in tight compact grain structures > (very hard, but brittle). This is in contrast to slow cooling that forms > long grain structures resulting in a stronger and tougher material (which > I would have thought is what would be ideal for a solder joint - good > shock resistance). > > Regards.... > > > Clayton Gardner > Engineering Manager > > A.E.M.S > 11-13 Fiveways Boulevard > Keysborough VIC 3173 > AUSTRALIA > Ph. 61 +3 9701 5499 > Fx. 61 +3 9701 5422 > Mb. 0416044552 > Email: [log in to unmask] > WEB: www.aemspl.com.au > ############################################################## 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 ##############################################################