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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Posted by: Ian ( )
Date posted: Wed Aug 23 11:15:37 US/Eastern 2000
Subject: Arrenhius-Lawson Equation
I have to date came across 2 different versions of the Arrenhius-Lawson equation, where one uses an acceleration humidity factor of 0.00044 and the other 5000 (both believed to default values). Could anybody provide me with a definitive Arrenhius-Lawson Equation and the correct default acceleration humidity factor or a source of reference for both. Thanks in advance.


Subject: Lawson Humidity Acceleration Model
Reply Posted by: Jack Farrell ( )
Organization: Reliability Analysis Center
Date Posted: Wed Aug 23 15:30:21 US/Eastern 2000
In 1974, Robert W. Lawson presented a paper at the 12th annual Reliability Physics Symposium entitled "The Accelerated Testing of Plastic Encapsulated Semiconductor Components". In this paper he presented a humidity acceleration model of "Tm = To exp - [n(RH)^2]". n was defined as a constant for the water absorption of a material with a typical value of .00001 for silicone and .0001 for epoxy. In 1976 he presented an update to his research at the Symposium on Plastic Encapsulated Semiconductor Devices. This paper, entitled "The Qualification Approval of Plastic Encapsulated Semiconductor Components For Use In Moist Environments", presented the humidity acceleration model as "Tx = T' exp - [.00044(RH)x^2]". In reviewing this paper most of the data presented was for epoxy and one can assume that the .00044 was the water absorption constant for epoxy. In conclusion, the above does not support a constant value of 5000. Also, the Arrhenius acceleration model you mention is used when temperature is the accelerating environment.

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