Such heat spreaders are made of metals with good thermal conductivity, such as copper or aluminum. They can also be gold-coated for better heat diss ipation. Heat dissipation plates distribute the heat generated over the entire surface of the heat spreader, from where it is dissipated with heat sinks or by means of air cooling.
On top of the heat spreader plate, there are other heat sinks such as tubular heat sinks that dissipate the heat from the heat spreader. They thus protect the processor from thermal damage.