Chemicals and materials of the type used in the production of Printed Circuit Boards (PCBs), as follows: a. PCB composite substrates made of glass fibre or cotton (e.g. FR-4, FR-2, FR-6, CEM-1,G-10, etc.); b. Multilayer PCB substrates, containing at least one layer of any of the following materials: b.1. Aluminium; b.2. Polytetrafluoroethylene (PTFE); or b.3. Ceramic materials (e.g. alumina, titanium oxide, etc.); c. Etchant chemicals; c.1. Ferric chloride (7705-08-0); c.2. Cupric chloride (7447-39-4); c.3. Ammonium persulphate (7727-54-0); c.4. Sodium persulphate (7775-27-1); c.5. Chemical preparations specially designed for etching and containing any of the chemicals included in c.1 to c.4. d. Copper foil with a minimum purity 95 % and of a thickness less than 100 μm; e. Polymeric substances and films thereof of less than 0.5 mm of thickness, as follows: e.1. Aromatic polyimides; e.2. Parylenes; e.3. Benzocyclobutenes (BCBs); e.4. Polybenzoxazoles.