DLC (diamond-like carbon) coating technology is a professional technology applied in the field of die cutting tools. The industrial production of DLC coating began at the end of the 20th Century, compared with the hard coatings applied to the mold (such as TiN, TiAlN, CrN, TiCN, etc.), it is a new coating technology. In semiconductor packaging, pin cutting and forming process, high precision mold is the key to ensure product quality, and the surface quality of the mold also determines the quality of the product, the production efficiency and the product electrical performance. Therefore, the mould applied to the semiconductor packaging industry requires not only high precision, but also the development of the die edge parts to the surface with low friction factor and high hardness, and the coating with plasma DLC coating technology is the main solution for this problem.
The DLC treatment process includes substrate processing (polishing, cleaning) of the workpiece to be processed, selection of the target, setting of the forming process conditions, formation and post-forming inspection.
To get a high quality DLC coating, the quality of the workpiece substrate is very important. The workpiece should be polished to less than Ra0.2um, and after the coating, the workpiece can get satisfactory surface quality, which is very important for forming some parts with optical performance requirements.
The workpiece to be coated needs to be fully cleaned, and the cleaning process depends on the quality of the coating, the substrate and the geometric shape. The workpiece is mounted on a set fixture, which is designed on the basis of optimizing the size of the cavity loading and ensuring the uniformity of the coating. The vacuum chamber is evacuated to 10-6 Torr (high vacuum) to eliminate all pollutants in the system, and inert gas is added into the vacuum chamber and ionizes it, producing glow discharge (plasma). This is the gas cleaning phase and prepares the part for initial metal deposition.
High-current, low-voltage arcs are loaded on the target, the metal is vaporized and instantaneously ionized, and these metal ions enter the chamber through the inert gas or reactive gas under high energy, and then precipitate on the workpiece. In the deposition process, changing the volume or type of gas will change the properties of the film. Table 1 shows the process parameters used for different film layers.
After the coating is completed, the quality of the film after the formation of the workpiece needs to be measured, including the gloss of the workpiece, whether the thickness of the film is uniform and the size is within the control range, and whether the film is layered.
If the gloss of the film after forming is uneven and there is a pattern, it may be that the purity of the target is not enough and contains more impurities. Another possibility is that the coating equipment has a problem, and there is no stable process environment. In this case, the first thing is to check whether the equipment has a problem, if not, the target must be replaced. When the equipment is stable, the thickness of the film depends on the forming process time.
The most common and difficult problem to be solved is that the adhesion between the film and the workpiece is not strong, and occurs delamination phenomenon. There are many reasons for this problem. The main reason is that the workpiece is not cleaned cleanly and thoroughly, and the workpiece is not polished to the process requirements or there are defects, and the forming process parameters are not reasonable. In order to solve the problem of delamination between the substrate and the film, sometimes necessary to pre-treat the workpiece by coating the workpiece with a layer of metal in advance to eliminate the defect of the substrate.