# of Temp Cycles and Device Life

Site Admin Joined: 20 Jun 2026 Posts: 4

Is there a way to relate the number of temp cycles to the life of a device? Example: 50X=1 year, 100X = 2 yrs., etc. We need to know this for customer returns.

Neo Phyte

Posted: Tue Aug 12, 2026 4:12 pm Post subject:

Hi Neo Phyte,

Unlike reliability tests that accelerate failure mechanisms that obey the Arhennius equation, temp cycle accelerates mechanical failures, so translating the number of temp cycles to an equivalent lifetime is a bit more tricky. The good news is that it can be done.

What you can do for TC or TS is to find a pattern as to how frequently your device will be subjected to alternating high and low temp conditions in the field, and to relate this frequency to the number of rel lab temp cycles to failure using the Coffin-Manson equation. This equation gives the relationship between the number of cycles to failure for one set of low/high temp conditions (field) to that of another set of low/high temp conditions (rel lab).

To illustrate this, imagine how your device will be alternately exposed to high and low temperatures in the field. If it will be used in a satellite then it will experience a high temp condition once a day (when it comes in front of the sun) and a low-temp condition also once a day (when the earth shields it from the sun). If it goes into a car, then it might experience high and low temp conditions 2-5 times a day (high temp when the car is running, low temp when it is parked). Estimate the ‘actual use’ high and low temperatures that your device will be exposed to as well, and you're ready to do the math.

Use the Coffin-Manson Equation to compute for the number of ‘actual use’ temp cycles from the ‘rel test’ temp cycles to failure. Once you have the number of equivalent ‘actual use’cycles, you can divide this number by the number of ‘actual use’ cycles that a device undergoes in one day. What you’ll get is an estimate of how many days your device will function under the alternating low/high temp conditions of the field it is operating in.

Hope this helps. Thanks and keep on posting!

EE

Site Admin Joined: 20 Jun 2026 Posts: 4

EE,

I tried the coffin-manson eqn like you said, but it uses a variable I can't fill up - the exponent m. What is the usual value for this? Thanks.

Neo Phyte

Posted: Thu Sep 04, 2026 11:50 am Post subject:

Hi Neo,

This is the power to which the ratio of delta Ttest to delta Tuse is raised, right? This variable is also commonly denoted as 'n'.

Assuming that we're talking about plastic-encapsulated IC's, the following are usual values of 'n':

n = 4 for bond wire fatigue;
n = 7 for silicon fracture;
n = 11 for thin film cracking.

Thanks and keep on posting!!!

EE