**3. Layer manufacture**

As it was explained formerly, to create a 3D structure, an undetermined number of layers have to be piled up. These layers can have different heights and can be manufactured using the same or different substrates, with a careful alignment of them being necessary. **Figure 9** shows an exploded schematic view of a prototype. It shows different layers with different geometries and different heights making up the whole 3D structure.

**Figure 10** shows a full assembled prototype besides a euro coin to compare sizes, where it is possible to observe how different layers with different heights (among 0.5 mm and 0.8 mm) are assembled.

These layers are manufactured using standard PCB processes such as cutting, drilling, milling, and plating. Once the layers are manufactured in the PCB, they are carefully extracted to be piled up. **Figure 11** shows the prototype layers before being extracted from the PCB. These PCBs are slabs that can be none, single, or twice metallized. Metallized substrates present a thin metal layer in one or both faces, usually copper. Later on, these PCBs can be additionally metallized such as the slab at the right in **Figure 11** using the process explained in section 2.1.7.

**Figure 9.** *Exploded view of the layers of a prototype.*

**Figure 10.** *Assembled prototype.*
