Temperature Cycling as An Accelerating Stress

[ggross]

I want to run an accelerated life test, using temperature cycles as the accelerating factor (normal temp rise during use is approx 20C versus a temperature delta of 100C during the ALT). I would like to use ALTA 6 to empirically determine what the AF is, versus using Coffin Manson and some arbitrary coefficient that I pick (it would only be a guess).

Any advice on how to set this up (should I have more than one thermal cycle profile for more than one level of stress), and can ALTA 6 handle the analysis part?

Thanks!

[Pantelis]

I am assuming that you are treating it as a constant stress test (i.e. the temp delta is constant and the only stress). If this is the case you would need at least two different deltas. And yes you can do it in A6.

[ggross]

In my mind I was thinking that the IPL is the correct model to use here, so the temperature delta is the temperature rise the product sees during use (due to self heating) and the temperature delta it sees during the ALT is the difference in low to hot temperature extremes I am driving it to during the test. I would then try to relate the number of cycles to failure on test to the number of cycles to failure during actual use. I have ALTA 6 standard and not ALTA pro, so that is why I was wondering if there was a way to do it with the package I have?

And I was thinking that, for example, if I needed two different ALT stress levels I would pick something that is about 2-3 times the normal use temp delta for stress #1 and something about 5 times normal use for stress#2. For example:
Normal Use: 20C delta (23C off to 43C when equipment is on)
Stress#1: temperature cycles of 0C to +50C
Stress#2: temperature cycles of -35C to +65C

Does that sound like a reasonalble approach?

Thanks!

[Pantelis]

From an experimental prespective it sounds like reasonable approach and you should be able to analyze it in A6 St.

Now, I have no idea what you are testing and what the physics are, so from that prespective I cannot comment.

[ggross]

Thanks Pantelis!

This is a multi-material detector that has CTE issues which causes delamination and fracture propagation issues. So the stresses induced by temperature cycling are the main driver in the failure process (as I think is the case in a lot of electronics). In fact, since this is so common in the electronics field, I am a little surprised I haven't found a good example of this is any of the literature for ALTA standard. If there is something that I missed in the Standard ALTA documents (or even on-line), perhaps you can point me in the right direction?

One confusing thing I found when setting up ALTA was the ability to select Thermal Cycles as the Stress To Use. This seems, at first light, to be what I want, but then when you look at the folio this creates you end up with needing to enter time to failure, which in my case will be cycles, and then a column for the Thermal Cycle stress. This confuses me, so I guess that I need to use Temperature as the stress, with the Max-Min delta of my temperature cycle as the stress and the normal Use stress being the normal Max-Ambient temperature delta the product sees in the field. I would then select Inverse Power Law as the analysis model to use. Correct?

This gets me wondering, is there a good example of how ALTA has been used with Thermal Cycles being used as the stress? I'd love to read how it has been used in this fashion.

Thanks again for all your help.

BTW - Since receiving our software and training from Adam Mettas last year, I have been using Weibull++ extensively and love it! I am now just getting a chance to work with ALTA!