Thermal Based Optimization of Functional Block Distributions in a Non-Uniformly Powered Die

Abstract

Microprocessors continue to grow in capabilities, complexity and performance. The current generation of microprocessors integrates functional components such as logic and level two (L2) cache memory into the microprocessor architecture. The functional integration of the microprocessor has resulted in better performance of the microprocessor as the clock speed has increased and the instruction execution time has decreased. However, the integration has introduced a layer of complexity to the thermal design and management of microprocessors. As a direct result of function integration, the power map on a microprocessor is highly non-uniform and the assumption of a uniform heat flux across the chip surface is not valid. The objective of this paper is to minimize the thermal resistance of the package by optimizing the distribution of the uniformly powered functional blocks. In order to model the non-uniform power dissipation on the silicon chip, the chip surface area is divided into a 4 × 4 and 6×6 matrix with a matrix space representing a distinct functional block with a constant heat flux. Finally, using a FEM code, an optimization of the positioning of the functional blocks relative to each other was carried out in order to minimize the junction temperature Tj. This analysis has no constraints placed on the redistribution of functional blocks. The best possible Tjmax reduction could thus be found. In reality (and at a later date) constraints must be placed regarding the maximum separation of any 2 (or more) functional blocks to satisfy electrical timing and compute performance requirements. Design guidelines are then suggested regarding the thermal based optimal distribution for any number of functional blocks. The commercial finite element code ANSYS® is used for this analysis.