Thermal design of a broadband communication system with detailed modeling of TBGA packages

Abstract

This paper presents a thermal modeling of a broadband network communication box partitioned into two stacked modules. A printed circuit board (PCB) is inside each module where an array of 16 tape ball grid array (TBGA) packages is surface mounted to the PCB. The TBGA package dissipates 6 W power each. In addition, 12 W of power is dissipated from four plastic ball grid array (PBGA) packages on the PCB. Pin-fin heat sinks are attached to the TBGA packages using silica-filled epoxy to enhance heat dissipation. Pin-fin heat sinks are also attached to the PBGA packages. Two exhaust fans are mounted at the flow exit to draw ambient air into the system at approximately 200 linear feet per minute (LFM) of velocity. The full Navier–Stokes equations for airflow are solved to simulate the forced convection cooling in the electronic module. Buoyancy effect was considered in the numerical model by incorporating Boussinesq-approximation. The TBGA packages are modeled in detail in order to obtain the package junction temperatures for system reliability evaluation and thermal design optimization. Detailed models of the attached pin-fin heat sinks and the epoxy interfaces are also utilized in this study. Compact heat sink model composed of a base plate and a resistance fluid volume is applied to model heat dissipation from the heat sinks attached to the four PBGA packages. System fan curve is used to simulate the fan operating conditions. The effect of changing system thermal design on the TBGA package junction temperatures as well as the hydraulic operating conditions of the system fans are examined and reported herein. The effect of radiation heat transfer is also examined. The importance of detailed modeling of the high power TBGA packages is demonstrated in this study. Simulation results were compared with JEDEC thermal test data under similar conditions of airflow.