Hi Bill, You are technically right when you say: >1. Some people try to manipulate Coffin-Manson for time dependency by >using modified slopes of the graph. Some people call this a modified Coffin-Manson equation; this is not correct, because historically the Coffin-Manson equation was not modified, but the solder joint fatigue results lead to a power law similar to the Coffin-Manson equation, which is actually a simplification of the more complete but less well known Morrow equation. I developed this Engelmaier-Wild fatigue relationship for solder based on Roger Wild's data with the exponent being able to account for the time- and temperture-dependencies of solder creep-fatigue. >2. Do you mean strain range not stress to equate to the temperature range? It certainly is more strain range based than stress range based, but for solder joints with compliant leads, it is necessary to consider the cyclic visco-plastic strain energy (hysteresis loop). >3. I think that if there are different rates of heating and cooling (lower than those >for shock) then there could be an effect because of the imbalance in time >dependence effects. This phenomenon certainly occurs in mechanical fatigue. Different rates of heating and cooling would have a role in shaping the cyclic hysteresis loop, and thus the cyclically accumulating fatigue damage. Werner Engelmaier ############################################################## 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 Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ##############################################################