Finite element thermal analysis of 144 pin plastic flat packs

A numerical thermal analysis of a 144-pin plastic flat pack using the finite-element method is presented. A 3-D model capturing details of the leadframe and internal structure was developed using solid elements. The symmetry of the chip package was utilized in the model to create only a 1/8 section of the package. The thermal conductivities for the silicon chip, metal leadframe and leads, and the epoxy encapsulating material are assigned to the elements. Appropriate adiabatic boundary conditions are assumed on the surface planes of symmetry, and suitable heat transfer rates are prescribed for the remaining surfaces. The models are then solved to determine the internal temperatures at steady state under various thermal conditions. A comparison between the calculated temperature contours and an infrared picture of the actual package showed similar temperature contours. Experimental measurement of the temperature rise differences between locations on the internal chip and the center package surface at varying heat transfer rates were compared with the results of numerical simulations, and it was found that the numerical solutions showed very similar trends.<>