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
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John Nieznanski <[log in to unmask]> 
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06/23/2012 09:13 AM
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[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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