Dan It is clear that the actual stresses after soldering a far lower that what you expect when you take only the difference in elongation during solidification. Solder creeps above 20°C very fast. This means that the solder joint will not build up stress during cool down but a continuous relaxation takes place. The higher the stress and the temperature the faster the relaxation. Thus HOOKE's law is not applicable for tin lead solder. The elastic deformation is negligible compared to the creep deformation occurring. However, forced cooling after soldering may result in a temperature gradient that leads to a considerable stress that may damage a weak component ( Again, Captain Hook has not his fingers in this game. Its just that a higher temperature ramp causes a higher strain rate and thus in creep a higher stress ). Leaded components do not see the problem a severe as those without leads since the leads are elastic enough to deform thus storing the deformation of the CTE mismatch as elastic deformation ( in the lead not in the solder ). But the stress needed for the deformation is low especially in copper leads. Thus no damage occurs due to the global CTE mismatch of component and PCB. On the other hand.........well there is a lot to say but it might be too much for TECHNET, as you said this might go very much in depth. Gotta shut up now. Best regards Guenter ############################################################## 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 ##############################################################