Prasad,

Given the right circumstances I would guess high cycle fatigue could
occur in soft solders. The worst situation would probably be if you had
an environment with a high level of vibration together with a constant
low temperature. Any significant change in temperature or interuption
to the vibration cycling is likely to result in (creep) plasticity
around the forming crack tip thereby "resetting the clock" on its
development.

In tests I did 10 years ago bending PCBs with 1206 & 1812 chip components
average cycles to failure went from about 3000 cycles at one cycle/hour
to 5000 cycles at 30/hour and 100,000 cycles at 600/hour (which is starting
to get into high cycle territory - certainly not much time for creep at
room temperature). Unfortunately I didn't do any mixed cycle rate tests
which might have confirmed my guess about plasticity.

David Whalley
Loughborough University


>      The other day I was asked me the following questions on fatigue 
>     properties of solder (joints and bulk):
>     
>     Why is there no data on High Cycle Fatigue (stress or load controlled, 
>     high frequency fatigue) of solder? 
>     
>     My contention was that this (stress controlled failure) is not a 
>     realistic mode because  fatigue failures of solder joints are 
>     strain-driven.  EWven at room temperature, the large component of 
>     temperature-dependent creep drives these stresses to near zero, 
>     thereby making it a strain-driven failure and not stress related.
>     
>     Having being told so, they still want to either generate this data 
>     themselves or want to located published data in the literature?
>     
>     Do you know of any source?
>     
>     How would you answer the question?
>     
>     Thanks for your help.
>     
>       Prasad Godavarti

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