Dear Marianne Quite a while ago ( on Thu, 25 Jul 1996 to be more specific ) the Technet SIR-Guru ( Doug Pauls ) provided a extensive answer to your question. I think it's the best I just make a "copy paste" of his E-Mail to Technet: >> information regarding the calculation of accelerated aging factors in SIR testing. I referred to the Arrhenius model and the Eyring model. The following is taken from the SIR Handbook (IPC-9201). I apologize for not getting this out sooner. 3.4.1 Arrhenius Model. This model is based on the logarithmic nature of chemical reactions. Simply put, for every 10oC rise in temperature, the simulated test time is cut in half. One year of service / storage at 35 oC and 85% RH can be simulated by 6 months at 45 oC and 85% RH, three months at 55 oC and 85% RH, and so on. This should be used as a general ěrule of thumbî. 3.4.2 Eyring Model. The Eyring model is based on a modified Arrhenius rate equation. References 9, 10, and 11 go into greater depth on these models. The Eyring equation is: t2 = t1 x exp[(j/K)*(1/T1 - 1/T2)] x exp[b * (1/RH1 - 1/RH2)] x [A2*Ec2/A1*Ec1] where: t2 = Accelerated Test Time t1 = Simulated test time j = activation energy in electron volts (eV) K = Boltzmannís constant (8.63 x 10-5 eV/K) T2 = Accelerated Aging Temperature (K) T1 = Normal Temperature (K) b = Humidity acceleration constant RH2 = Accelerated aging relative humidity (%) RH1 = Normal relative humidity (%) A = voltage acceleration constant Ec2 = Accelerated Elec. Field in Corrosion Region (V) Ec1 = Normal Electric Field in corrosion region (V) This model was developed by Nickolas Lycoudes, Motorola Reliability Department. A discussion of the use of the model can be found in "Evaluation of a No-Clean Soldering Process Designed to Eliminate the Use of Ozone Depleting Chemicals", Ron Iman, Sandia National Laboratories, November 1992. The applicable references are: N. Lycoudes, Solid State Technology, October 1978 E.W. Kimball, "Accelearated Vs. Real Time Aging Tests", 1980 IEEE Proceedings of Reliability and Maintainability Symposium I hope this fulfilled peoples needs. Doug Pauls CSL [log in to unmask] << 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. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################