Water cooling has been known in the PC world for many years.  
So why not equip the new Sixty One with an extremely quiet water cooling system?  
It sounds simple, and others have already done it.

As always, perfectionism plays a role. Others solder copper pipes onto the copper plate or simply mill a water channel into the copper plate.  
That may be enough for others, but not for me!  
The heat is generated exclusively under the LDMOS, so it must be quickly removed from there. The water must not flow somewhere else, but right under the LDMOS.  
If you want to increase the contact area between copper and water, you have to think about how to do that.

At this point, a greeting goes out to all companies, self-proclaimed experts, and copycats!  
To increase the area, ribs were milled into the copper under the LDMOS, significantly increasing the contact surface. However, one problem is the water flow, which must be evenly distributed over all ribs. This is very important to avoid temperature gradients that could stress the LDMOS unfavorably.  
Even if it looks simple in the pictures, simulation is absolutely necessary to achieve this goal. The smallest changes have a big impact.

As simulations show, the flow is absolutely harmonious.  
The video shows the moment the pump is turned on.  
With a well-thought-out cooling plate, the LDMOS stays cool, and the attenuator at the input also benefits from the water cooling.

Milled and highly polished copper plate

Water flow simulation, flow direction from right to left