Methodology for computation and measurement of thermal conductivity for thin film composite substrates

Thermal management of electronics very often incorporates thermal analysis using commercially available CFD softwares, which can perform conjugate heat transfer and fluid flow analysis. One of the big challenges in thermal modeling is the unknown material properties of many of electronic components. The paper describes the approach adopted to measure the thermal conductivity of flexible laminated layers commonly used in electronic applications. The small thickness, coupled with low thermal conductivity of the base material involved, makes the measurement of in-plane thermal conductivity challenging. Standard procedures like "laser flash" technique are not suitable due to the large uncertainty involved. A methodology was developed to measure the thermal conductivity of a 100 microns thick flex structure. An experimental set up was created wherein a temperature gradient was established across the flex layer and measured. A numerical model simulating the experimental conditions was created. Radiation and convective boundary conditions estimated by analytical means were imposed upon the model. By adjusting the thermal conductivity in the numerical model, the experimental temperature profile was matched with the numerical profile. The adjusted thermal conductivity was taken to be the thermal conductivity of the flex. Finally, an uncertainty analysis was performed and uncertainty bands were obtained for the thermal conductivity.