I'm trying to do a simple DC self-heating calculation. The design manual for my process says:
Tself = P * Rth
P (mW / um) = power through device = Id * Vd
Rth (degC/mW / um) = 100
The units are confusing to me. It seems like to get Tself to be units of temperature, Rth should be degC * um / mW. They use Tself later on as a pure temperature unit since it's added to Tamb... is it just a mistake in the manual or am I missing something? The way they spaced it (degC/mW / um) made it seem like it was done purposely.
what is the part number of the transistor? the calculation is not straightforward, and depends on the air flow, emmisivity etc.
the delta junction to ambient will give you a fair idea, (power X junction to ambient)
The thermal impedance of a small transistor (and most are small in relation to
wafer thickness) is a messy thing to calculate, and that's if there are no other
local heaters messing with you. It's a spreading geometry problem (at simplest)
unless your transistor is wider and longer than the wafer is tall.