October 20, 2004
The low budget sputter coating apparatus
There are increasing requirements for sputter apparatuses at an affordable price. This is not only the case in research and development at universities and bigger companies – even small size enterprises have to install this technology in house. Sputter coatings (or films) are used to realise electrically conductive or insulating surfaces, for the metallization of plastics, for optical or mechanical purposes. The main criteria for the buyer are the reliability and the efficiency of the apparatus in combination with an affordable price. PT&B has met these requirements of its customers and offers the sputter coater SBA 40 at the revolutionary basic price of only 38.720 Euro:July 9, 2004
DLC coatings of superior surface quality
Injection moulding tools for the production of CD and DVD have highly polished surfaces of extreme low roughness. Nowadays, these tools are coated with a film of diamond-like carbon (the so-called DLC). For this purpose, an especial Plasma-CVD (also known as PCVD, PECVD ore PACVD) process has been designed in specific coating machines by other vendors. Recently, the R&D team of PT&B Ltd. was tasked to apply SilCor DLC coatings to these tools. The coating process was performed under standard conditions in one of the coating apparatuses, which is used for the series DLC coatings of machine components and cutting tools
View at a CD mirror coated with SilCor DLC. The surface mirrors the surrounding environment.
By means of visual evaluation one is able to recognise, that the coating process does not disturb the highly polished surface. The tool still works as a "mirror” showing the surroundings. The excellent surface quality of SilCor DLC is proven by investigations by atomic force microscopy (AFM): The deposition of a 1.5 µm thick film does not result in a significant increase of the surface roughness of the tool.
For the use of DLC coatings it is especially important to keep in mind that this surface roughness is available even in the standard coating process applied to tools and machine components.
Smooth DLC films are of extraordinary importance
Diamond like carbon shows - due to intermix of the properties of diamond and graphite - the unique combination of a hard, abrasion resistant coating with a wear reducing film. Therefore, it acts as hard material as well as a solid lubricant. It is well known that the coefficient of friction is strongly influenced by the surface roughness. The higher surface roughness increases the input of energy into the upper regions of the wear partners what results in increased abrasion. Therefore, even extreme hard coatings suffer from strong abrasion, when their surface is to rough.
Micrograph taken by atomic force microscopy (AFM) showing the surface topography of a region of 10 µm in square of the above CD mirror. The maximum difference in height amounts to only 0,1 µm.
The limits of PVD coatings
The technologies of physical vapour deposition (PVD) use solid material sources and generate a directed particle flux. This is the case in both, the Arc PVD employing a vacuum arc to evaporate cathode material and the Sputter PVD working on the ejection of atoms caused by an atomic collision cascade. The directed flux of atoms results in a growth of thin films containing columns of diameters in the micrometer-range. The tips of these columns drastically increase the roughness of the films. The growth of rough coatings is strongly enhanced, when DLC films are grown onto metallic under-layers deposited by Arc PVD. Because of the micro-particles (so-called droplets) generated by this process, such a coating appears under a microscope like a cake with crumble topping. A CD mirror coated this way has only a mat black surface, which does not show reflectance. Quite in contrast to PVD technique, Plasma CVD results in the deposition of very smooth films, what is caused by the isotropic flux of particles to the substrate. The formation of columns and pores even on the scale of nano-meters is widely suppressed. Therefore, the corrosion resistance of the latter films is far superior compared to PVD coatings.Conclusions for the use of DLC coatings
Hard diamond-like carbon films offer their full potential only in the case of a very low surface roughness. Good DLC coatings reveal a shimmering surface. There is absolutely no need for polishing these films after the deposition process. In the case the application of DLC appearing mat black or grey has not fulfilled the requirements of use, one should not judge DLC in general.For DLC coatings of the highest surface quality one should contact PT&B GmbH, where the requirements will be met.