Transient thermal + fatigue analysis in ASONIKA

Specify a name for the project

Select 3d model to import

Quarter-symmetry model of PCB + BGA Package

Specify initial temperature for entire model (20 degrees C)

This temperature will be also used as reference temperature for thermal stress calculation

Select external surfaces and set the thermal condition:convection and radiation (from these surfaces) to the environment

Specify film coefficient, emissivity, view factor and ambient temperature values

Surfaces with thermal conditions become meshed

Symmetry planes should not have thermal conditions

Select the volume (that represent the silicon chip) and set it as a heat power source

For transient thermal analysis heat power source can be time dependent

Input heat power vs time curve.In this example two thermal cycles are modeled. Time dependent heat power will cause cyclic temperatures and stresses. Cyclic thermal stresses are used for fatigue calculation

One thermal (heat power) cycle has range of 8-18 Watt (2-4.5 Watt for quarter symmetry model)

Set material properties for all parts of the model For solder balls the following parameters will be used:

Run automatic FE mesh generation procedure

Set solution parameters

Specify the end time of the analysis, the time integration step and the number of thermal cycles contained in the solution interval

Temperatures plot

Temperature – time curve at nodes

Two arbitrary nodes were selected Temperature vs time curves for two nodes

Stress plot

Stress-time curve

Two arbitrary nodes were selected Stress vs time curves for two nodes

Fatigue plot

Plot shows minimum fatigue life (451.9 thermal cycles) in solder balls