Printed wiring boards, more commonly referred to as printed circuit boards or PCBs, are the electrical boards used to install integrated circuits in electronic systems. PCBs form the "guts" of all computers and electrical equipment, small and large. They consist of integrated circuits connected through small strips of conductive material. These small strips are referred to as PCB traces. The traces carry electrical current and electrical current flow produces heat. Thermal conductivity calculations involve calculating and quantifying this heat.
Instructions
1 Find the thickness of the PCB board and the thickness of the copper traces on the board. Refer to the manufacturer's schematics for the PCB to find these variables. To use this information in follow-on calculations, call the thickness of the PCB board the variable Z and the thickness of the copper traces the variable ZCu.
2 Calculate the thermal conductivity parallel to the plane of the board using the formula Kp = 0.8 + 350 (ZCu/Z) where the variable "Kp" represents thermal conductivity parallel to the plane of the board. This formula include conversion factors that produce thermal conductivity in units of watts per meter Kelvin or W/mK. As an example calculation, assume Z = 5 centimeters and ZCu is 7 micrometers.
Kp = 0.8 + 350 (ZCu/Z) = 0.8 + 350 (7/50,000) = 0.8 + 350 (0.00014) = 0.849 W/mK.
Note: Both Z and ZCu must have the same units. For this reason, it was necessary to convert 5 centimeters into 50,000 micrometers using the conversion factor 1 centimeter = 10, 000 micrometers.
3 Calculate the thermal conductivity perpendicular to the plane of the board using the formula Kn = 1/[1.69 (1 -- ZCu/Z)) + 0.0026 (ZCu/Z)] where the variable "Kn" represents thermal conductivity perpendicular to the plane of the board. Continuing with the example numbers:
Zn = 1/[1.69 (1 -- 0.00014)) + 0.0026 (0.00014)] = 1/[1.69 (0.99986) + 0.000000364] = 1/1.689 = 0.592 W/mK.
Note: Kp and Kn represent two PCB board orientations in which you can calculate the thermal conductivity.
