Digital moiŕ subtraction interferometry (DMS) for electronics cooling applications in enclosures

Optical noninvasive temperature measurement techniques, such as interferometry, are particularly advantageous in obtaining temperature information noninvasively from enclosed low velocity flows induced by thermal sources, as commonly arise in electronic systems. The single greatest restriction in the application of interferometry as a standard measurement methodology has been the enormous cost associated with the optical equipment required. This cost is due to the quality of the optics required, which exhibits an exponential dependence on size. Digital Moiŕ subtraction is a technique, which removes the restriction on the use of high quality optics, thereby, enabling reasonably large fields of view. In this paper, a digital Moiŕ subtraction interferometer configuration is presented with a 140 mm field of view. First, the ability of the interferometer to accurately measure the free convection temperature field about an isothermal horizontal cylinder is examined through a comparison with measurements from literature using classical interferometry. The technique is then applied to the thermal interaction between 2D components representing BGAs mounted on a vertical printed circuit board (PCB). Qualitative and quantitative evaluation of the interferograms show the significant influence of in-plane PCB conductivity on the temperature field about the PCB. The spacing to length ratio above, which upstream components on a PCB experience enhanced cooling, is reduced from 4 to 3 for a PCB with a high effective in-plane conductivity (15 W/m K).