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.