Characterization of Heat Dissipation From a Microprocessor Chip Using Digital Interferometry

Electronic circuit boards of computers consist of components which generate substantial amounts of heat during their operation. Among these, the microprocessor chip is one of the major sources of heat generation. In high-performance processor chips, the rates of heat generation are also correspondingly high. The performance of the chips themselves, as well as that of the neighboring electronic components are affected by the temperature levels attained, which in turn depend on the heat dissipation capability. Effective thermal management of microprocessor chips, following precise thermal characterization, is essential to avoid their untimely failure due to overheating. The selection of an appropriate cooling methodology and the design of an efficient cooling system for the microprocessor chip essentially require a clear knowledge of the heat dissipation rates during its operation. A comprehensive database of heat dissipation from microprocessor chips as a function of the activity level, based on actual measurements, is rare to find in the literature. A major reason for this is that conventional intrusive measurements on and around the chip are quite insufficient, as they will alter the performance, while the system is under operation. To overcome this, a nonintrusive digital interferometric measurement has been devised in this paper for obtaining the in situ temperature distributions and the heat dissipation patterns around the microprocessor chip, while it is under operation. The interferometric method utilizes interference of coherent laser beams to make measurements in the thermal field around the heat-dissipating component. An Intel Pentium 4 microprocessor with its integrated heat sink was used for experimentation. The computational load on the processor was varied utilizing a software package, thus varying the heat generation rates, and the base temperature of the fins in the heat sink attached to the microprocessor. Interferometric measurements were made to obtain the temperature distribution in the medium, and the patterns of heat dissipation from the fins' surfaces. Indicators of the heat transfer behavior, namely, the local heat flux values and the heat transfer coefficients were obtained from the experiments, using digital image processing techniques. Experiments were conducted at various fin-base temperatures, under free and forced convection conditions, to characterize the effect through a database of the heat dissipation level. In essence, a nonintrusive temperature measurement method coupled with digital image processing techniques has been successfully used for convective heat transfer studies on the microchip while the microchip is under operation.