Low cycle fatigue
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Transcript of Low cycle fatigue
LOW CYCLE SOLDER JOINT FEA FATIGUE FAILURE ANALYSIS OF
AN INTEGRATED CIRCUIT PACKAGE
using a strain energy method
06/18/2005
GOALS Evaluate the possibility of
extremely low cycle (<100 cycles) fatigue failure in an integrated circuit package
Such damage has been seen during installation and extraction of a parent printed wiring board assembly.
Typical failure
Solder joint fractures
Host pwb asy joint loading
Bending about this lineDuring insertion in
Back plane
FEA mesh
Hinge line / flex axis
Component detail
Strain energy contours
Peak solder strainpredicted in corner land
Deflection @ 700X mag
reference
hysterisis
Dwell time as a variable
The larger the area the higher the damage
Strain Energy testing see ref.
Estimate for 25 cycles
Assume a failure after 25 flexes of
the board at the connector edge.
The accumulated strain energy
density in a solder joint
must be at failure:580,000 joules/cu-
meteror
23,200 joules/cu-meter
in each flex
Board handling insertion flexure
Plastic strain energy in solder has shown to be cumulative in eutectic solders.
A flexure of only .014 inches per cycle will result in a strain energy sufficient to cause a fracture in the solder joint after approximately 25 cycles.