Junction to case thermal resistance (Rjc) is a key parameter when characterizing a package. It can be expressed as the temperature difference between the two locations over the heat dissipation.
I am confused as in where this 'case' is supposed to be. Most of these packages have a copper plating on the back, which is an effective thermal passage. The 'case temperature' there is much higher and much closer to the junction temperature. If the 'case temperature' is measured on the front side on the plastic, the measurement is likely lower.
I was considering using a case temperature measurement and estimated heat loss to back track junction temperature with the help of Rjc, but I am not sure which case temperature is more valid in this calculation. Maybe an average works better?