That device has a very low thermal resistance from junction to case, \$R_{thJC}\$=0.125 ºC/W (max), which means that, for every watt dissipated, the junction will only be 0.125 ºC (max) above the case temperature. So, for instance, for \$I_C\$=300 A, \$V_{GE}\$=15 V, and \$T_J\$=125 ºC (see Fig. 2) \$V_{CE}\$ will only be about 1.55 V. That's a power of P=300·1.55=465 W being dissipated (yes, more than some electric heaters). So, the junction will be 465·0.125=58.125 ºC (max) above the case temperature, which is a very low differential, for that massive dissipation.
However, in order for the junction temperature not to exceed its limit (of 150 ºC), the thermal resistance from case to ambient, \$R_{thCA}\$, which depends on the heat sink used, also has to be very low, because otherwise the case temperature would rise well above the ambient temperature (and the junction temperature is always above it). In other words, you need a very good heat sink (with a very low \$R_{th}\$), in order to be able to run this creature at 300 A.
The thermal equation is:
$$
T_J=P_D·(R_{thJC}+R_{thCA})+T_A
$$
with
\$T_J\$ : Junction temperature [ºC]. Has to be < 150 ºC, according to the datasheet.
\$P_D\$ : Power dissipation [W].
\$R_{thJC}\$ : Thermal resistance from junction to case [ºC/W]. This is 0.125 ºC/W (max), according to the datasheet.
\$R_{thCA}\$ : Thermal resistance from case to ambient [ºC/W]. This depends on the heat sink used.
\$T_A\$ : Ambient temperature [ºC].
For instance, on an ambient temperature of 60 ºC, if you want to dissipate 465 W, then the heat sink has to be such that \$R_{thCA}\$ is at most 0.069 ºC/W, which implies a very large surface in contact with air, and/or forced cooling.
As far as the terminals, the approximate dimensions of their thinnest part are (L-L1)·b1·c. If they were made of copper (just an approximation), the resistance of each one would be:
\$R_{min}\$=16.78e-9*(19.79e-3-2.59e-3)/(2.59e-3*0.74e-3)=151 \$\mu\Omega\$
\$R_{max}\$=16.78e-9*(21.39e-3-2.21e-3)/(2.21e-3*0.43e-3)=339 \$\mu\Omega\$
At \$I_C\$=300 A, each one of them would dissipate between 13.6 and 30.5 W (!). That's a lot. Twice of it (for C and E) can be as high as 13% of the 465 W being dissipated (in this example) at the IGBT itself. But, usually, you will solder them so that that thin part is shorter than (L-L1).
The voltage rating is for the resistor series typically and specifies the maximum peak voltage you can apply without danger of damaging the resistor due to corona, breakdown, arcing, etc.
The power rating is completely independent of the voltage rating. It specifies the maximum steady state power the package is able to dissipate under given conditions.
You have to conform to both specs. If placing the maximum voltage across the resistor results in more power than the spec allows you have to reduce the voltage until you meet the spec. Likewise you can't increase the voltage above the rating just because you're not hitting the maximum power limit.
Best Answer
Component package designations are a situation where you have several different partly overlapping "standard" conventions, and then a bunch of manufacturers who have created their own schemes.
The "SC" designation is a JEDEC convention, the SOT designation is, I believe, IPC, and there are a handful of other pseudo-standards that have cropped up to cover various configurations that don't exactly match the standards. Many manufacturers have their own more tightly-standardized packages, with their own designations.
Even when two devices claim the exact same designation, the exact dimensions may differ slightly or have different tolerances, so it's important to always check the drawing in the datasheet to verify that the dimensions are close enough. If you've designed a PCB footprint for a device that is on the small side of the standard range, then you may wind up with insufficient fillets if you later switch to a device that is on the larger side. 0.65mm SOT parts are small enough that the tolerances DO matter here.
The only time you can really be sure that a device is going to be in exactly the same package as another is if it's from the same manufacturer and references the exact same manufacturer's drawing.
Regarding the part characteristics, don't rely on what Digikey has chosen to list in their catalog. It's very difficult to distill a device's performance down to a handful of numbers. The datasheet probably lists several different values for each of the parameters that Digikey has chosen to list, at different operating points. In order to compare a single parameter between parts--say, the output power--you need to ensure that those parameters were measured under equivalent conditions. Consider the catalog numbers to be a very rough guideline, and dig into the datasheet to make sure that the device's performance will meet your needs under the conditions in which you intend to use it.