Greenwich university and (National Physical Laboratory
have done a lot of work in this area, Copy and paste above into Google to
see


Regards


Mike 


 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Nieznanski
Sent: Saturday, June 23, 2012 3:14 PM
To: [log in to unmask]
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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