This is a 250W 30 dB attenuator up to 2 GHz. I used copper for connecting the attenuator with the bottom side of the microstrip (which is all copper) . Also I used a small copper piece to connect the bottom side of the microstrip with the N connectors (you can see it at the foto).  I will like to thank SV3IBS for cutting the aluminum used for cooling.

      As you can see in the previous fotos the 2 of the four screws are not used. The reason is that is impossible to put the nut as you can not hold it as it is inside the box. The solution is to use a rivet nut tool that puts a nut that fixed to the Aluminium box. I use nuts for M3 srews.