Gentle Ablation of Surface Coatings
Laser decoating is mainly used for selective ablation, where the carrier medium may not be influenced. “Selective ablation” means that an exactly and strictly measured area or even single functional layers of one layer composition are decoated (when ablating single layers, the layer to be removed must be outwards). This method has the advantage that basic materials are not damaged and chemical additions as well as the treatment of wastes (besides the removed substance) are not necessary. The method is used for example for the production of solar cells, TFT monitors or high-strength tailored blanks.
Here, q-switched solid-state lasers with high powers are used, which remove those layers from the carrier with higher intensity and ablation rates of often 50 cm2/s due to very short laser pulses. During this process, due to the incoupling of preferably much energy into a small volume the temperature escalates in the material to be removed.
This creates plasma, which ablates or blasts the upper layers or plies of the coating with a shock wave.
Decoating by contact-free laser beams can be done with very fine structures (20 µm minimal gauge), e.g. for solar cells with medium powers of 20 Watt. For a (large) area ablation clearly higher laser powers of up to 800 watt are required that can achieve pulse peak performances during pulse operation. With up to 3 MW these can be a thousandfold of that of the CW laser power.
Decoating of Tailored Blanks
- For the ideal welding preparation of new, high strength Tailored Blanks out of manganese-boric steel the metallic coating of aluminum-silicium is ablated completely, quickly and efficiently. This coating protects the surface in further process steps from scaling and corrosion, but minimizes the resistance of the welding joint when mixed with the basic material. Therefore, it must be ablated in the area of the welding seam
Decoating of Solar Cells
- Today, thin film solar cells consist of glass substrate as well as diverse functional layers. For clean lamination of the active panel with a glass panel as counterpart, all functional layers must be removed circularly at a width of 10 to 20 mm. This is the only way to securely protect the thin film cell from entering moisture and against contact of conducting components.
Decoating of LCD Displays
- Further application areas are structuring of Flat Panel Displays, especially liquid crystal and plasma displays.