Principle of anodic alumina blackening
The theory of the AAO blackening is to further oxidize the anodized aluminium oxide layer with a film thickness of 5-20μm and changes the texture of the surface material in a short period of time by focusing the laser beam with high energy density laser. The principle of the aluminium blackening is based on the nanometer effect, because the laser treatment has made the oxide particle size at the nanometer level, the material's light absorption performance increases, hence the visible light irradiated to the material is absorbed, with very less reflected visible lights left, so that it appears to be black in our naked eye observation, so called the AAO blackening .As for the thickness of the oxide layer and the surface treatment process of the AAO, generally speaking, with a thickness range of 5um to 20um, the film thickness directly determines the effect and efficiency of blackening, often, it is very easy to blacken when the film thickness is between 10um and 20um, if the film thickness is less than 8um, then the oxide film is too thin, which is easy to break and contributes to the phenomenon of white spots, in view of this, laser parameters are needed for compensation. Additionally, the surface treatment process of the AAO will directly affect the blackening effect. since sandblasting and surface drawing are common processes, the thickness of sandblasting will have different effects on the marking effect, which means the finer the sandblasting particles are, the better the blackening effect enjoys . It is recommended that the film thickness of the anode aluminium to be 10-15μm, so that the overall blackness effect is better.
The applications of laser marking ofblack trademark, model, and text on the surface of the AAO has been widely and early used by electronic manufacturers such as Apple, Huawei, ZTE, OPPO, VIVO, and others for electronic products shells. For these applications, MOPA fiber lasers are currently utilized for processing. Because the MOPA laser has a wide range of pulse width and pulse frequency adjustment, the black marking on the surface of the work piece can be realized by adopting the narrow pulse width and high frequency parameters. Also various effects of gray levels can be achieved through different combinations of parameters.
With the current development and the market requirements, the previous silk screen printing process was gradually replaced by the laser marking. Laser marking, as a modern precise processing method, compared with the traditional processing methods such as printing, mechanical engraving, and electric discharge processing, has unparalleled advantages. Due to the advantages of maintenance-free, high flexibility and high reliability, Laser marking machine is especially suitable for areas with high requirements for precision, depth and smoothness. The personal electronic products represented by mobile phones have changed and facilitated people's lives, with the developing orientation of functionalization, intelligence, and smart appearance. As the technological progress of the microelectronics industry and people's pursuit of personalized mobile phones, precise laser marking processing technology will play an increasingly important role in mobile phone manufacturing. (Source: Laser Fabrication Network)