how to use TO-254 Power MOSFET and DIODE's full current capacity?
I had an application that required MOSFETs in an H-Bridge at 15A capabilities. Instead of mounting them with wires I used the following setup on my prototype board where the legs of the MOSFETS went directly into the PCB.

The above prototype was designed to permit a plate to be screwed to the top of the heatsinks with a fan mounted on it that would force air flow down around the heatsinks.
I had a similar application years earlier where MOSFETs were mounted to a heatsink with two fans atop it. In that appliction the MOSFETs were rated for 200A in very similar packages with legs right into the PCB. That application required surge currents of over 150A and at first testing with the motor loaded the legs of the MOSFETs blew completely away like fuses. It turns out that manufacturers often specify current capabilities for devices that far outstrip the physical limits of the package.
Often times you have to find devices that are rated well beyond the current levels of your application and in suitable packages that you can connect them properly. I built myself an adjustable constant current sink that I use for testing power supplies and battery discharge curves. That device is intended for use at voltages up to 15VDC at 10A max. The MOSFET used is in a package like that shown below and mounted on a heatsink that has two 40mm fans blowing air into the heatsink fins.

I happened to get lucky and found those FETs at an electronics surplus outlet for $2.95 each. Needless to say I bought all they had despite the fact that they were pulls out of some equipment. The devices were rated at 200A and 100V.