THERMAL DESIGN UNDER NATURAL CONVECTION CONDITIONS IN ELECTRONIC SWITCHING SYSTEM.

To determine natural convection conditions in an electronic switching system (ESS), radiant heat transfer effect between transverse adjacent printed wiring boards (PWBs) and convective heat transfer effect between longitudinal printed wiring boards were quantitatively investigated. It was found that the semiconductor junction temperature should be directly measured to get strict measurement values, especially for radiant heat transfer. Fully reproducible evaluating equations based on a quantitative method were also obtained, effective for variation in PWB depth, variation in PWB mounting pitch, PWB materials and nonuniform power consumption distribution. Results have been applied to the thermal designs in individual ESSs, such as ND, NXE, and NEAX system.