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Glossary: P, Q

Here you are going to find explications of important terms in plasma technology:

I,J

P,Q

X,Y,Z

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PCB: Printed circuit board. In the production of PCBs, plasma treatment is applied for borehole cleaning, etching of the tracks, and the cleaning of metal surfaces from organic contaminations before the contacting process.
PE (polyethylene): Polyethylene (short: PE) is a semi-crystalline thermoplastic, generated through polymerisation of ethene. It belongs to the group of polyolefins.
permeation: Permeation is the transport of substances through solid materials on the molecular scale.
The permeation process can be described in three phases:
-Adsorbtion:
Gases, vapour, or chemicals or suspended substances diluted in liquids are absorbed on the surface of the plastic part.
-Diffusion:
The adsorbate exhausts as a gas on the other side of the work piece.
Through plasma, permeation barrier layers can be generated.
photoresist: Often photoresists are used for the structuring and treatment of samples. These are polymers dissolved in a solvent that are superimposed onto the samples by a spin coater, via sputtering or dipping. Adjacently, the solvent is tempered so that a photosensitive layer is developed. Through UV- or electron radiation, the molecules embedded into an organic matrix are either cross-linked (negative resist) or disconnected (positive resist), so that their properties towards solvents are changed.
If the applied photo resist is a positive resist, the areas exposed to light are dissolved in a developer bath. With negative resists, the unexposed areas are dissolved in the developer. The structure thus obtained in the varnish can serve as a protection layer (photoresist-mask) on a functional layer (a multilayer, e.g.) for adjacent processes such as argon ion etching (dry etching). Alternatively, a functional layer can be superimposed on the lacquer structure; after the subsequent removal of the lacquer, this layer will stay in those areas of the sample where there was no photo-resist afore (lift-off process).
For lift-off processes, a special positive resist was developed, whose edges strongly decline in the lacquer and have a kerf, so as to prevent bonding with the functional layer and facilitate the removal of lacquer and layer structure.
physical etching: With the aid of inert gas ions (e.g. Ar), an etching attack is made on the substrate by the kinetic energy. This process is performed only physically. Since no volatile product is generated, a part of the sputtered layer is accumulated in direct vicinity.
pin holing: Moistening disturbances starting on the substrate’s surface, e.g. surface active particles or adsorbate hydrocarbons. The most well-known ones are siliconeous hydrocarbons in particular.
plasma (- physics): In physics, plasma means a gas that contains a noteworthy part of free charge carriers such as ions or electrons. More than 99% of the visible matter in the universe is in the plasma state. The term plasma traces back to Irving Langmuir (1928). The plasma state is called the fourth state of aggregation.
plasma ashers: see „ashing“
plasma boration: One of the plasma diffusion techniques is plasma boration. Boron trichloride is used here as boron donator. With 700°C to 900°C, the treatment temperature lies significantly under the common temperatures for boration. During the treatment of steel, a session layer of FeB and Fe2B is generated that is, because of differences in diffusion speeds, interlocked with the ground material. Thereby, an extremely high adhesion, especially against shear forces, is provided. The treatment takes place in several steps which reduces considerably the risk of pore building through the formation of iron chloride. During the plasma boration of titan, TiB and TiB2 are formed. Plasma boration of stellites (Co-based alloys) results in a Co2B phase and CrB.
plasma carbonitration: Plasma carbonitration is a technique for the hardening of steel analogous to plasma carburisation (see there) where nitrogen is added accessorily. This facilitates the diffusion of carbon into the steel.
plasma carburisation = plasma case hardening: Hardening of the surface of steels by increasing the carbon content via plasma diffusion of hydrocarbon gases and adjacent quenching. In comparison to conventional carburisation of steel, plasma carburisation causes no noteworthy oxidation of the surface, and the process goes faster. Mostly, the surface’s hardness is a little lower than if it was treated by the nitration method, the diffusion layer, however, is mostly thicker.
plasma chemistry: Research field in chemistry that deals with the behaviour of chemical elements that are in the fourth state of aggregation, the plasma state. New material properties appear in a plasma.
plasma cleaner: see „precision cleaning“
plasma coating: see „functionalisation“
plasma diffusion: Amongst others, plasma diffusion serves to give metallic surfaces higher hardness and resistance against wear by nitration, boration or carburisation. The plasma activates the molecules of the process gas and partly splits them into their components. When the atoms of the process gas impinge then on the part’s surface, they can diffuse into it.
plasma etching: see „dry etching“
plasma etching: A dry etch technique in which reactive atoms or ions (e.g. oxygen, chlorine, fluorine) are generated in a gas discharge (mostly operated with a high frequency). Reactive ion etching makes use of the fact that ions are accelerated in the boundary layer between plasma and substrate with high directivity and are thus able to create deep grooves with steep walls.
plasma hardening: During plasma hardening, a metal is exposed to a gas discharge where e.g. O or N ions are released and permeate into the surface of the work part. Through this, the surface gets harder than the inside of the metal (edge layer hardening).
plasma oven: see „low-pressure plasma“
plasma polymerisation: Plasma polymerisation is a process in which gaseous monomers, activated by a plasma, precipitate on arbitrary substrates as highly networked layers. Precondition for this process is the presence of concatenating atoms like carbon, silicon, or sulphur, in the process gas. Since the biggest part of the monomer molecules in the plasma are split, the chemical structure of the original gas is retained only partially, which leads to networking and an orderless structure. Conservation of the structure and degree of cross-linking can be controlled via process parameters like pressure, process gas flow, and supplied electric power, so that so-called gradient layers can be generated as well which show e.g. a degree of cross-linking increasing with thickness.
plasma precision cleaning: see „precision cleaning“
plasma sandblasting: see „precision cleaning“
plasma spray coating: Method for the coating of surfaces with metals and ceramics. Herein, the powdered coating material is introduced into a gas stream of a high energetic plasma (about 12000 K). The coating material melts and is propelled onto the substrate’s surface where it solidifies immediately. Particularly useful in the manufacture of hard protecting coatings with well-defined coating thickness. The process can be applied under ambient pressure (air plasma spraying – APS) or in vacuum under an inert gas (vacuum plasma spraying – VPS).
plasma strippers: see „ashing“
plasma technology: Collective name for a number of industrial applications of plasma. In plasma technology, technical plasmas are used for a multitude of applications. Contrary to natural plasmas (sun, flash), technical plasmas don't ignite by themselves. Here, ignition is done by electric discharge. DC, medium, or high frequency current supplies can be applied for the firing of plasma.
plasma treatment: see “surface treatment”
plastics: There are thermoplastic, duroplastic and elastomerlike polymers. They differ with regard to their chemical composition, their crystalline structure and cross-links. Additives are added to the ground polymer to adjust it to the technical requirements.
polyamide (PA): Besides ABS and PP compounds, polyamides are ranked to belong to the top flight of materials. The material group polyamide 6 (PA 6) offers all-purpose materials for mechanical functional parts in mechanical engineering: polyamides are cold, shock, and impact resistant, abrasion-proof even in combination with a rough sliding partner, and they possess a high working capacity. Pre-treatment of polyamides by plasma yields excellent results and outstandingly improved adhesion properties.
polybutylene terephthalat (PBT): PBT has properties similar to PET, but is more convenient for injection moulding because of its more advantageous cooling behaviour; it is used preferably for precision mechanics component parts. PBT shows high dimensional stability, low slip resistance, high mechanical strength and stiffness, and it is very resistant against abrasion. The adhesion of bondings and varnishings on PBT can be substantially improved by plasma treatment.
polycarbonate (PC): Polycarbonate (PC) is a transparent amorphous thermoplastic. Its most important properties are an extremely high impact resistance and mechanical strength, good optical properties, a high temperature resistance, and it is self-extinguishing, yet scratch sensitive. PC can be pre-treated via plasma in order to improve adhesion of e.g. scratch-resistant layers.
polyethylene terephthalat (PET): Transparent thermoplastic with a permanent-use temperature of up to 120°C. Amongst many other applications suitable for the production of drinks bottles. With the aid of plasma, barrier layers against oxygen and CO2 are applied, respectively the adhesion of such layers is substantially improved.
polymerisation: Polymerisation is a process of reacting simpler structured chemical compounds (monomers) together, under development of real covalent bonds, finally forming polymer chains of macromolecules, e.g. ethylene reacts to the plastic polyethylene. Polymerisation via plasma: see "plasma polymerisation".
polyolefins: Polyolefines are semi-crystalline thermoplasts that are distinguished by good chemical endurance and good electrical isolation properties. They are very cheap and easy to work with the conventional processing techniques. Therefore, they are applied very often and rated amongst the most important plastics. To the group of polyolefines belong: PE, PP, PB, PMP. The adhesion properties of polyolefines for varnishings and bondings can be increased substantially by a plasma treatment.
Polyoxymethylene (POM): Polyoxymethylene (short POM, also called polyacetal, or polyformaldehyde) is a semi-crystalline thermoplastic. It is distinguished by high stiffness, strength, and hardness in a wide temperature range. It keeps its high viscosity down to -40°C, features a high abrasion resistance, a low friction coefficient, a high shape stability against heat, good electrical and dielectrical properties, as well as a low water absorption. POM is known under the trade names Delrin, Ultraform, and Hostaform. It is very difficult to agglutinate, only after a corresponding pre-treatment.
polypropylene (PP): Polypropylenes are semi-crystalline thermoplastics that are generated through polymerisation of propylene in the presence of Ziegler-Natta catalysts. Polypropylenes belong to the group of thermoplastics. Isotactic polypropylenes are multi-purpose standard polymers with a balanced property level. At a low price, they offer an average stiffness, strength, and impact resistance, low density, a very good resistance against chemicals, a special folding endurance (10 million folds), good resistance to stress cracking (better than PE), yet very poor cold properties. PP's adhesion properties for varnishings and bondings can be increased substantially by a plasma treatment.
polystyrene (PS): Polystyrene is a plastic that was developed in 1930, generated through radical polymerisation of styrene. Pure polystyrene (PS) is hard, colourless, and brittle. Remarkable is the brilliant surface gloss. Polystyrene is resistant against acids, lyes, and alcohol. But it is vulnerable by many non-polar solvents. PS is a transparent material of high stiffness and hardness. It features low viscosity, is therefore sensitive to cracking under impact stress, and shows a transparency light as water. Varnishings, coatings, or bondings have better adhesion results on PS after a plasma treatment.
polytetrafluorethylene (PTFE): PTFE = Teflon (trade name by DuPont), a chemically very stable polymer with a very low friction coefficient. Surface energy about 19 mN/m. The vapours generated in fires are toxic.
Even though PTFE's workability is limited and costly, this homopolymer has the highest resistance of all high-performance plastics against chemicals and an extremely low adhesion. PTFE is a soft thermoelastic, a sintering material with a low mechanical property level. PTFE's capability of flowing is low after melting, so it can not be applied in injection moulding or extrusion.
Elaborated sintering methods have to be applied for PTFE. PTFE has a very high fluorine content and its most significant properties are resistance against almost all chemicals, a very high temperature stability (UL 94 V-0), a low friction coefficient, and extremely low adhesion. Unfortunately, the material features low strength and hardness, and high sliding abrasion. A pre-treatment via plasma for the improvement of adhesion in following processes is possible.
positive column: The self-sustaining part of a gas discharge, in which ionization by electron impact and material loss by diffusion equilibrate.
powder coating: Environmentally friendly alternative to varnishing. Electrostatically charged plastic powders are deposited on metallic surfaces and then melted.
precision cleaner: see „precision cleaning“
precision cleaner: In order to obtain high-purity surfaces, a surface can be cleaned by plasma. This precision cleaning can be achieved e.g. by fogging (sputtering) of the contamination, thus through accelerated particles impinging on the surface. Furthermore, the organic impurities like oil and grease can be removed from the sample via cold combustion by radicals and activated atoms which are available in a plasma. Precision-cleaning by plasma cleanses surface gently, without environmentally harmful detergents and solvents.
pre-treatment: The term „pre-treatment“ is scientifically not clearly defined. Depending on the industrial sector, it is used in different ways. In the range of adhesion enhancement for splicing, pre-treatment can stand for precision cleaning + activation.
pre-treatment of plastics: Processing, like e.g. the agglutination, flocking, varnishing, coating of plastics, often causes problems. Plastics have mostly non-polar surfaces. That’s why adhesives and varnishes are often incapable to generate sufficient adhesion to these surfaces.
Through certain pre-treatment methods, polar groups are built up on the surface that improve adhesion without affecting the plastic material. Else, an increase in adhesion can be achieved through cleaning the surface. This precision cleaning can be achieved e.g. by fogging (sputtering) of the contamination, thus through accelerated particles impinging on the surface.
Furthermore, the organic impurities like oil and grease can be removed from the sample via cold combustion by radicals and activated atoms which are available in a plasma. Precision-cleaning by plasma cleanses surface gently, without environmentally harmful detergents and solvents. Another possibility to give a surface defined and designed mechanical, optical, chemical, and physical properties is to provide them with a coating.
This can be done by superimposing molecules (silanes, SiOx) onto the surface, e.g. through vaporisation, deposition from a gas phase or through application of some special precursor-gas (TEOS, HMDSO) via plasma. These coating layers can have e.g. scratch resistant, barrier, hydrophobic, or hydrophilic properties.
principle of the plasma process: If a plasma is brought into contact with a surface, then the latter is freed from adsorbates and the real surface can be changed chemically. Too low impact of plasma yields insufficiently cleaned surfaces. If surfaces are treated for too long a time, they can melt again (overtreatment). The reasonable contact time decreases with increasing process pressure. Under atmospheric pressure, contact times of a few ms are sufficient in some cases.
printed circuit board (PCB): Non-conductive carrier material with selectively conducting coated tracks which connect the electric and electronic components. There are single- and multiple-layer designs.
printing: A treatment by atmospheric plasma renders possible adhesion on nonpolar plastics as well. Quality and durability of the print are substantially improved.
printing on silicone: A large application field of silicone are flexible keyboards. Silicone has a low surface energy and it is thus difficult to obtain good adhesion of printing inks. Here, an activation of the surface preceding the printing process is helpful.
printing Teflon: see „etching Teflon“
process gas: The chemical reactions in the plasma and thus also on the surface are defined decisively by the process gas. In principle, all gases and gasifiable liquids are applicable as plasma gas. Under atmospheric conditions, air has proved of value, since it yields good cleaning and activation results and is cheap.
proton: Positively charged elementary particle (symbol: p; mass: 1.67·10-27 kg; charge: +1.6·10-19 As).
PTFE coating: Coating with PTFE can be done in vacuum plasma through the polymerisation of fluorinated gases. Commonly, household appliances are keyed by sandblasting and the PTFE is applied by high pressure.
PVC: Polyvinyl chloride, cheap amorphous thermoplastic polymer used in large scale production; good weldability; good bonding results with solvent glues; depending on fillers and plasticisers from hard to elastically modifiable; via plasma pre-treatment significant increases in adhesion as well to methylene-chloride-free varnishes and adhesives possible; attention: often high content of UV stabilisers and plasticisers that can make a pre-treatment very difficult.
PVD coating: Physical vapour deposition, a solid material is vapourised in high vacuum under energy input and is then deposited on the part to be coated.