**4.2 External metallization**

The main raw material for building 3D structures piling up layers is PCBs; there are lots of commercial choices with different characteristics and heights depending on the working frequency and requirements of the prototype. These substrates are made of different components and have none, one (top or bottom), or two (top and bottom) thin layers of copper or other metals. The main idea is to stack different layers of different heights extracted from these substrates to create a whole 3D structure.

With the aim of building a metallic external wall, some layers must be externally metallized, and this can be done with a die cut system similar to the example shown in **Figure 13**. As it can be seen, the layer is almost fully metallized externally except for the small tabs located in the corners, which are needed to hold the structure to the PCB. The substrate around the external metallization of the prototype can be removed by simple exterior cuts shortened enough to hold the structure. The result is a completely metallized edge of these layers, but for the small corners as it was noted before.
