Until now, engineers generally assumed these two temperatures were the same, with the PCB acting as a perfect heat sink. The only other option, a detailed analysis of the problem, required sophisticated thermal simulation software that was often expensive and time consuming.
However, Custom MMIC’s new online calculator provides an easy and fast way of estimating the rise in temperature without the need for a full 3D thermal simulation environment. With this tool, engineers can now develop a reasonable estimate of temperature at the bottom of a package based upon the construction of the PCB.
Users simply select the package type, the power dissipation inside the package, the PCB board material, the via construction, and the base plate temperature (typically 85 ºC). The calculator then determines the temperature rise through the PCB to the bottom of the package, under the following assumptions: the PCB is plated with 1 oz. copper (1.4 mils [0.0014 in.] thick), the package is attached to the PCB with solder (2 mils [0.002 in.] thick), and the base plate is an ideal heat sink.
With this estimate, an engineer can then decide if a more detailed thermal analysis is required, which is probably the most useful aspect of this tool.
Custom MMIC; www.CustomMMIC.com