Factors affecting the calculation of effective conductivity in printed circuit boards [thermal analysis]

A comparative study is presented that demonstrates the importance of including both the material resistance and the spreading resistance in the calculation of effective thermal conductivity for printed circuit board applications. An analytically based Fourier series model is used to calculate effective conductivity in three dimensional test coupons. Results show that models based exclusively on cross-plane and in-plane resistive networks are not adequate for predicting effective conductivity in multilayer laminated printed circuit boards. The mixed boundary conditions found in most microelectronics applications accentuate the importance of spreading resistance between heat sources and the convective boundaries. Discrepancies between commonly used methods of calculating effective conductivity and methods incorporating both the bulk material and spreading resistance can be greater than 100% for geometries typically found in microelectronics applications.