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Predict Lead Free Solder Joint Life from Microstructure Evolution

Idea/Definition Information
Summary: 

This project aims to predict the remaining life of LF solder joints by microstructure analysis when a board has been in service for only a few years, not long enough to totally crack, but long enough to observe fatigue damage indication.  Test vehicles, as well as field returns, will be micro sectioned and analyzed for structural change.  Observed structural changes will be correlated to failure and field life.

If you are interested in this project and would like to subscribe to the project mailing list, please click here (members only) or email the project facilitator, Brian Smith - brians@hdpug.org.
 

Background: 

 Lead Free reliability is still controversial because:

·      No universal acceleration model yet
·      Complex factors such as dwell time, precondition, temperature rate have a significant influence on life

Not enough field failure data yet, especially non-consumer electronics

 

Problem: 

 

•The most important thing is field failure data, but it is only a few years after some products changing from tin lead to lead free, it’s still very long to know the full life performance.
 
•One way is to build the relationship between crack growth length/area and life Nf%; but still many problems: crack develop routes is more irregular than tin lead; different packages have different crack develop curves; always founds no crack initiate in a few years!
By Courtesy of Intel：ECTC08_Effect of Board and Package Attributes on Solder Joint
 
So the question is how to predict the full life if you only have a board worked for a few years without any failure or crack?
Correlate fatigue damage and life through microstructure evolution
Physical way to characterize accumulated fatigue damage
 
Recrystallization degree: for tin lead joints, grain coarsening nearly indicates 15% life passed; but how about lead free? maybe we can find similar rules to predict life through recrystallization.
IPC D279
 
 
For LF, we also see recrystallization.
We plan to study whether it can be used to predict life.
 
 
 
 
 
 
 
 
 
Approach: 

To predict the remaining life of LF solder joints by microstructure analysis when a board has been in service for only a few years, not long enough to totaly crack, but long enough to observe fatigue damage indication.

 
Test vehicles, as well as field returns, will be microsectioned and analysed for structural change.  Observed structural changes will be correlated to failure and field life.