Enhanced Plastic Ball Grid Array Research Articles

Thermal Study of Enhanced Plastic Ball Grid Array Package with Flat Heat Spreader

Three-dimensional finite element simulations are performed to study the thermal performance of a thermally enhanced plastic ball grid array (EPBGA) package with a flat heat spreader adhered to the top surface of the package. Variables available for modification during simulation include heat spreader thickness, heat spreader conductivity and airflow. Specific study is made of the relative effects on thermal resistance of variation of heat spreader conductivity (from 0 to 350 W/m.K), heat spreader thickness (from 0 to 5.5 mm) and airflow speed (from 0 to 3 m/s). Improved thermal performance by use of a heat spreader is confirmed and dangerous package hot spots are minimized. Increasing the thermal conductivity of the heat spreader is found significant at levels up to around 100 W/m.K, but beyond this value the thermal performance improvement is negligible. Increasing heat spreader thickness is found to have a positive effect on thermal performance, but over the range (thickness >0.2 mm) the improvement is small. Increasing the airflow has a positive effect on thermal performance, but again the level of improvement decreases as the airflow increases.

Optimization of high pin count cavity-up enhanced plastic ball grid array (EPBGA) packages for robust design

Three-dimensional (3-D) nonlinear finite element models of epoxy encapsulated enhanced plastic ball grid array (EPBGA) packages with and without an aluminum lid have been developed using ANSYS finite element simulation code. The model has been used to optimize the packages for robust design and to determine design rules to keep package warpage within acceptable limits. An L/sub 18/ Taguchi matrix has been developed to investigate the effect of die attach and encapsulant properties along with the substrate, encapsulant, die attach, and internal copper plane thicknesses on the reliability of the package during temperature cycling. For package failures, simulations performed represent temperature cycling from 165/spl deg/C to -65/spl deg/C. This condition is approximated by cooling the package mounted on a multilayer printed circuit board (PCB) from 165/spl deg/C to -65/spl deg/C. For coplanarity analysis, simulations have been performed without the PCB and the lowest temperature of the cycle is changed to 20/spl deg/C. Predicted results indicate that for an optimum design, that is low stress in the package and low package warpage, encapsulant as well as die attach material should have low Young's modulus and low coefficient of thermal expansion. Furthermore, it is found that the substrate and the die attach epoxy thicknesses should be increased beyond the current design. In addition to the optimization analysis, plastic strain distribution on each solder ball has been determined to predict the location of the possible first solder ball failure.

Thermal performance comparison of high pin count cavity-up enhanced plastic ball grid array (EPBGA) packages

Three-dimensional finite element models of cavity-up enhanced plastic ball grid array (EPBGA) packages have been developed using ANSYS finite element simulation code. The models have been used for thermal characterization of different designs of high pin count EPBGA packages under different air flow conditions with and without an external heat sink. In addition to the design evaluations, the simulations have been repeated to quantify the effect of populated and unpopulated boards on the thermal performance of each EPBGA package with and without a heat sink. For the unpopulated board case, a single package has been modeled on a 10 cm/spl times/10 cm/spl times/0.16 cm (4"/spl times/4"/spl times/0.062") multilayer printed circuit board (PCB). For the populated board, the size has been reduced to the size of the package footprint, and no heat transfer is permitted along the board periphery. Further parametric studies have been performed to predict the thermal performance of EPBGA packages as a function of solder ball counts in the inner solder ball matrix (underneath the cavity). In conjunction, the optimum number of solder balls in the inner matrix has been determined for better heat dissipation through the package to the board via the thermal balls. In addition to the solder ball counts, the importance of the package internal vias connected to the solder balls in the inner matrix is quantified. The predicted results have been plotted as functions of the junction-to-ambient resistance (/spl theta//sub JA/) and the air speed for different package designs. It is also found that the junction-to-case resistance (/spl theta//sub JC/) significantly drops when the solder bails are placed in the inner matrix underneath the die. The thermal performance would not be significantly improved when more than 48 solder balls are placed underneath the die region.