Question about calculating Junction temperature and where you take the PCB temp?

[rbola35618]

I wanted to see how other folks are calculating junction temperatures. In the past, I have used the surface board temperatures, the ThetaJC and the ThetaCB to calculate the junction temperature.  Recently, I saw where instead of using the surface board temperature, they are using the mid-point internal temperature. For example, if the PCB uses 12 layers, then the temperature of the 6th layer is used as a reference. Using this temperature leads to higher ThetaCB because the reference is the 6th layer instead of the surface layer.

is there anybody out there that is using the mid-point layer as the reference for the board temperature?  What has been you experience. I welcome any feedback.

RB