Thermal Enhancement of Systems using Organic Flip-Chip Packages (FC-PBGA) with an Alternate Cooling Path through the Printed Wiring Board

Abstract

The thermal performance characteristics of organic flip-chip packages (FC-PBGA) incorporating thin (0.5 mm), high interconnect density (dense-core) organic substrates has been studied using 1-D calculations and 3-D numerical analysis. Of particular interest is the ability of the substrate to provide an effective thermal path to the printed wiring board (PWB) for high heat dissipation applications. The improvement in thermal impedance of dense core substrates vs. standard core substrates is quantified and shown to be approximately 2/spl times/. A package size of 50 mm and a chip size of 18 mm are assumed for the 3-D analysis. Two types of system boundary conditions, one with a heat sink attached to the top of the package, and one without are considered. For both cases, board-level enhancement is provided with a heat sink or cold plate. Numerical simulations are run to study the effect of the board heat sink on overall heat dissipation. The results indicate that the overall thermal resistance can be reduced by about 43% and that up to 73% or more of the heat dissipated in the chip can be diverted into the board even when a high performance (0.4 C/W) heat sink is used on top of the package. Comparisons are also made with packages with ceramic column grid array packages with similar wiring capability. Results indicate that thin, dense core packages can meet or exceed ceramic package thermal capability for the range of conditions studied here.