Sådan fungerer fordampningsbåde

Fordampningsbåde er keramiske komponenter, der fungerer som beholdere til metallet (rent aluminium), der skal fordampes. De fungerer som elektriske modstandsvarmere. Fordampningsbåden og en kontinuerligt tilført aluminiumtråd opvarmes under højvakuum af strøm, så tråden først smelter og derefter fordamper. På grund af speciel overfladestruktur og tekstur dannes et smeltebad og fordeles optimalt over båden, hvorved der sikres en homogen dampsky. Metaldampen aflejres derefter på et substrat placeret over dampskyen.

Materialer til fordampningsbåde

Der er forskellige krav, som fordampningsbåde skal opfylde. For at princippet om modstandsopvarmning skal virke, skal de være elektrisk ledende; samtidig har de brug for en tilstrækkelig høj grad af elektrisk modstand til overhovedet at gøre det muligt at opvarme dem. Desuden skal de være modstandsdygtige over for høje temperaturer og inerte over for smeltet metal. For at kombinere disse egenskaber fremstilles blandet keramik af to eller tre komponenter.

Two-component evaporation boats contain titanium diboride and BORON NITRIDE. Due to its bonding structure, titanium diboride offers excellent resistance to high temperatures and remains inert even to non-ferrous metal melts. It also improves the wettability of the evaporation boat through liquid aluminum and ensures a melting bath with an extensive surface. For example, when used for aluminum vapor deposition, it's completely wetted by liquid aluminum. In addition, titanium diboride is a very good electrical conductor. Boron nitride is added as a non-conductive material to set the electrical resistance of the evaporation boat.

Three-component mixed ceramics also include aluminum nitride. This material has very good thermal conductivity which makes it particularly suitable for large evaporation boats to ensure they heat up quickly and uniformly. Compared to two-component evaporation boats, the three-component versions have a shorter lifespan, with lower evaporation rates and less corrosion resistance. At the same time, the wettability of the evaporator is significantly improved and there's greater homogeneity of the vapor-deposited layers. Three-component evaporators are therefore primarily used in the manufacture of capacitors, since this requires a particularly high level of homogeneity in the coatings.