Determination of the Thermal Properties of a PCB by Coupled Numerical and Experimental Approach

Electronic systems have been used extensively in many areas of industry such as aerospace, automotive, informatics and so on. Moreover, demand for electronics is increasing continuously. This fact necessitates the electronic systems to be placed narrower volumes intensively. The intenser electronic components set up in narrower enclosures, the higher temperature values reached in the system. Therefore, the design of electronics enclosures has to be made taking the thermal behavior of the system into account carefully. The thermal design of an electronic system is shaped by performing numerical analyses parametrically for different geometries and boundary conditions for the purpose of obtaining the best configuration at which the temperature of the system is minimized. In order to perform numerical analysis of an electronic system truthfully, initial conditions, boundary conditions and material properties of parts such that PCB (Printed Circuit Board), fastener, parts having high heat storage capacity etc. has to be known. If any of abovementioned parameters are unknown or include any unclarity, the value of that parameter has to be determined before attempting numerical analysis directly. In this paper, a method for obtaining thermal properties of a PCB, that is, coefficient of thermal conductivity and specific heat capacity, is presented. Since a PCB has generally a complex composite layup structure composed of conductive layers, generally made up of copper, and dielectric layers, generally made up of FR4, special methods are required to obtain overall coefficient of thermal conductivity and equivalent specific heat capacity value. Additionally, those methods may be destructive. In this study, above mentioned properties are obtained performing a simple non-destructive experiment and a numerical analysis instead of utilizing special and expensive methods. In the method, a small portion of PCB is sandwiched from one side at certain pressure by jaws. A couple of linear temperature profiles are applied to the jaws successively. Temperature values of predetermined points on the PCB are measured via thermocouples. Corresponding numerical analysis of the foregoing experiment is performed. The values of the coefficient of thermal conductivity and specific heat capacity which are unknown initially are iteratively modified staying within a physically acceptable range until the results of the analysis and the experiment match. The values for the coefficient of thermal conductivity and specific heat capacity which the experiment and numerical analysis results match can be said to be the actual values. From this point on, the PCB whose thermal properties are determined can be analyzed numerically for any desired geometry and boundary condition. A commercially available conduction based FEM (Finite Element Method) program is utilized for the numerical analyses.