Darrel Looking at the phase diagram for Pb-Sn-Ag at the low silver end except for the 3 eutectics with L/S temps. of 304, 221 and 179 degrees C, I do not see any phase that would cause the solidus temperature to be different than the Sn-Pb binary composition. ie. when you reach 10 % tin the solidus temp is 268 Deg. C, at 15% it drops to 225 Deg. C and at 19% it drops to the the 183 Deg C. Obviously the liqidus temperature is higher, but when any melting occurs the joint strength is essentially zero. If you are soldering components with leads with a tin-lead coating or tin electroplate the probability of the solder reaching a low solidus temperature by mixing with the Pb is very good. The diffusion of the solder during SM is poor and you can have localized areas with high tin and high lead in the same joint when using the HMP solders and tin or tin-lead coated leads. Even with good difusion and mixing the tin content of the solder joint could reach 20 % easily, especially if you have components with 500 micron [0.020inch] of tin electroplate. Therefore, you could be using HMP solder to solder joints that really have a solidus temperature of 179-183 Deg. C. Any other question or thoughts give me a ring at 520-745-1013 Phil Hinton Hinton "PWB" Engineering. *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************