Integrated flow-thermomechanical analysis of solder joints fatigue in a low air flow C4/CBGA package

This paper presents an integrated flow-thermomechanical analysis of ansiothermal fatigue behavior of ceramic ball grid array (CBGA) solder joints in a 32mm C4/CBGA package under a mini power cycled load of one to three watts at a frequency of three cycles per hour. A computational fluid dynamics model was used for conjugate conduction-convection heat transfer analysis to determine the local heat transfer coefficients of package under various low air flow conditions of 0.1 to 0.5m/s. The determined local heat transfer coefficients were specified as the thermal boundary conditions in a thermomechanical model for transient heat transfer and nonlinear thermal stress analyses to predict the local temperature profiles and associated viscoplastic deformation of CBGA solder joints. Using a deformation base lifetime analysis method, the predicted mean fatigue life of the power cycled solder joints are compared to that of the temperature cycled solder joints under a 0/100°C load. Predictions of temperature cycled solder mean life show good agreements with experimental data. Analysis shows that the leading edge and trailing edge CBGA solder joints in the package have different fatigue behavior. This air flow induced orientation effect grows significantly as the air flow velocity increases. Both temperature cycled and power cycled solder fatigue results were used to estimate the equivalent solder fatigue lives of the C4/CBGA packages with application to the laptop and desktop computer systems at an average onoff temperature rise DT of 20°C and 30°C.

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