Hi Dave,

Thanks for your response, and a couple others I have received. This is certainly appreciated. I think my question is something a bit different. I agree with you that the failure mechanisms are different in the thermal shock vs thermal cycling domains. I don't think I am shocking the parts as the ramp rate (delta temp / delta time) is always 20C / 30 minutes = less than a degree C per minute, during both heating and cooling phases. 

I think what I am asking is there a general predictive SMT leaded/leadless solder fatigue model that applies for cases where both the following conditions apply:

(1) there is no real "dwell time" or temperature plateau, either in operational usage or accelerated testing. So the soak time and the Td (half-cycle dwell time) parameter in E-W is zero.
(2) there is no accelerated testing data available, over any temperature range, or for any ramp rate.

I suspect that the Engelmaier-Wild model (IPC-D-279, Appendix A-3.1) doesn't really apply here per item 1 above. So in the absence of both (1) and (2) above, are there any predictive models that can be used?   

Another way of asking this question is, are there any generally accepted, published and/or standardized methods and analysis models that can be applied here, or is this not possible (e.g., highly application dependent, too many variables, very ad-hoc/custom, or proprietary?) How were these issues addressed when SMT was in it's infancy? I'm trying to track down a few leads on this. 

Thanks again for any helpful thoughts on this topic. 

John Nieznanski


---- "David D. Hillman" <[log in to unmask]> wrote: 
> Hi John - the solder joint fatigue testing a fair majority of the industry 
> conducts is thermal cycle testing - as you detailed in your email, we 
> allow the solder joints to stabilize at a given temperature limit for a 
> specific time period. Your question focuses on a second conditioning 
> protocol - thermal shock testing. The IPC-9701 specification defines 
> thermal cycle testing as temperature transition rates below 20C per minute 
> and thermal shock testing as temperature transition rates greater than 20C 
> per minute. The failure modes for thermal cycle testing and thermal shock 
> testing are very different so any accelerated testing needs to replicate 
> the thermal conditions that your product will experience. The IPC-9701 
> specification can be used for both test methodologies.
> 
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
> 
> 
> 
> 
> John Nieznanski <[log in to unmask]> 
> Sent by: TechNet <[log in to unmask]>
> 06/23/2012 09:13 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
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> 
> 
> To
> <[log in to unmask]>
> cc
> 
> Subject
> [TN] solder fatigue analysis for continuously ramping temperature swings
> 
> 
> 
> 
> 
> 
> Hello TechNet,
> 
> Has anyone had any success predicting, measuring and correlating solder 
> fatigue wearout for circuits that are continuously ramping up or down in 
> temperature (linearly) between fixed thermal limits over fixed time 
> periods? The fixed time periods are stable and repeatable as is the 
> temperature change over these periods. 
> 
> As an example, a normal ramp-up time is 30 minutes and the temperature 
> ramps linearly from 20C to 40C. Then the temperature immediately ramps 
> down from 40C to 20C over the next 30 minutes. This pattern repeats.
> 
> The Engelmaier method described in IPC-D-279, IPC-SM-785 assumes cyclic 
> temperature swings between two fixed temperature limits.  The solder joint 
> temperatures stabilize at each temperature limit for a fixed interval 
> before periodically switching to the other temperature limit for the same 
> interval.  How can be solder fatigue wearout be quantified in solder 
> joints that instead of ?soaking? or stabilizing at each of the temperature 
> limits, are always either heating up or cooling down between these known 
> limits in a predictable, linear way?  Intuitively, it seems that creep and 
> stress relaxation should be less, but how to quantify when solder joint 
> wearout occurs (N50, mean lifetime)?
> 
> Thanks.
> 
> John Nieznanski
>  
> 
> 
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