Abstract
The main objective of the present study is to construct a heat transfer correlation to be used as boundary condition in the three-dimensional conduction simulation to simulate the thermal field within the flip chip BGA package. First, the thermal field of the flip chip BGA package is simulated using CFD model under the laminar flow regime, where the radiant and gravitational effects are ignored, and the simulated results are used to extract the heat transfer coefficients along the surfaces in contact with the airflow. Then, based on the heat transfer coefficients, a new group of accurate heat transfer coefficients correlations that include the effects of different substrate sizes and package components thermal conductivities is proposed.This will be used as the boundary conditions for the three dimensional conduction equation to replace the commonly adopted flat plate formula. Due to the package geometry configuration, there are four important local heat transfer coefficients needed to be considered. They are Hdie, Hsub, Hpcbup, Hpcbdown, which mean the heat transfer coefficients on the surface of the die, substrate, upper surface of PCB and lower surface of PCB, respectively. A best fitting interpolation procedure is applied to determine the Hsub, Hpcbup, and Hpcbdown under different thermal component conductivities, when the substrate size is fixed.Three-dimensional conduction simulations for flip-chip BGA package using the flat plate formula indicates that when the free stream velocity increases the maximum predicted junction temperature error increases up to 12 %. However, when the components thermal conductivities increase, the maximum predicted error decreases down to 3 %. If the newly developed heat transfer coefficients correlations are used as boundary condition in the 3-D conduction simulations of the flip-chip BGA package, the maximum predicted junction temperature error is less than 1 %. Therefore, if the requirement of simulation accuracy is very restrict, it is not advisable to use the flat plate formula to predict the heat transfer coefficients h, instead the newly proposed formula should be adopted.