Question

A 50mm x 150mm multilayered printed circuit board (PCB) is densly populated with BGAs on its two faces. The BGAs collectively dissipate 40W by conduction into the PCB. The PCB is composed of 5, 2oz copper layers, 10, 1oz copper layers, and 14, 6mil layers of epoxy with a thermal conductivity of 0.8W/m•K. You may assume that cut-outs for vias and signal line definition require removing approximately 40% of each copper layer.

The two short edges of the PCB are attached to a "cold bar" and cooled by conduction to these surfaces. The surrounding air is at a room temperature of 25^oC.

1. Find the lateral and perpendicular thermal conductivities of the PCB.
2. Assuming that both edges of the PCB are cooled symmetrically to 35^oC and that both sides are convectively cooled with a heat transfer coefficient of 6 W/m²•K, find the location and value of the peak PCB temperature.
3. Neglecting Convection and assuming that one edge of the PCB is cooled to 25^oC and the other to 45^oC, find the location and value of the peak PCB temperature.

Answer 1