Good Day,

Last week, a number of individuals requested more 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 "rule of thumb".

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 = Boltzmann's 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
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