FACTORS AFFECTING THE CALCULATION OF EFFECTIVE CONDUCTIVITY IN PRINTED CIRCUIT BOARDS

A coniparative study is presented that denionstrates the importance of including both the inaterial resistance aiid the spreading resistance in the calcula.tion of effective conductivity for printed circuit board applica,tions. An analytically based Fourier series model is used to calculate effective conductivity in three dimensional test coupons. Results show that. inodels based exclusively on cross- plane and iii-plane rcsistivc nctworlcs are not adequate for predicting effective conductivity in multilayer, laminated printed circuit boards. The mixed boundary conditions fouiid in most, inicroelect,ronic applications accentuate the iniportaice of spreading resistance between heat sources and tlie convective boundaries. Discrepancies between co1111nonly used methods of calculating effective conduc- tivity and methods incorporating both the bulk material and spreading resistance can be greater t,han 100% for ge ometries typically found in microelectronics applications.