Systems for surface treatment with low-pressure plasma Plasma technology Contents Plasma technology 3 What is low-pressure plasma ? 4-5 Activation and/or modification 6-7 Cleaning 8-9 Etching 10 Coating 11 Standard systems 12-13 Inline systems 14 Special systems 15 2 Plasma technology Systems for low-pressure plasma surface treatment PINK GmbH Thermosysteme – founded by PINK operates internationally with a network Friedrich Pink – is located in Wertheim / Main of sectoral agencies in all major markets and is and has about 100 employees now. The a worldwide supplier of customized plants and product range includes low-pressure plasma systems. Well-known technology and research systems for surface treatment, systems companies rely on the high-quality and innova- for vacuum-supported soldering, sintering tive products of the company. systems as well as systems for drying and processing technology. PINK is the suitable partner for high-quality and customized low-pressure plasma systems of In the past years, the family business PINK any size and varieties of equipment configura- has grown steadily and successfully due to tions. PINK produces stand-alone units, continuous product improvements and reel-to-reel units as well as inline systems. View into the reaction chamber consequent customer orientation. of a low-pressure plasma system during a cleaning process Schematic structure of a low-pressure plasma system Process control High-frequency generator Process chamber Pressure control Gas flow control 3 What is low-pressure plasma ? The gentle power of the fourth aggregate state Matter changes its form of appearance at Low-pressure plasma: energy without heat specific temperatures. Generally, solid, liquid and gaseous aggregate states are known. At atmospheric pressure, plasma is hot – as in However, there is another state – the plasma. flames and arc discharges. Plasma is the ionized form of a gas and is also named as “fourth aggregate state”. The diffe- If pressure is reduced to around 100 Pa rence between neutral gas and plasma is the (1 mbar), plasma can be formed and sustained significantly higher electrical conductivity and even at room temperature. It is therefore chemical reactivity. also known as cold plasma or non-thermal plasma. However, the energy of the electrons Samples for naturally occurring plasmas are corresponds to a temperature of several lightning, northern lights or sun. However, in 1,000 K – forming a highly reactive medium. our everyday lives we also encounter plasma It enables both effective and gentle treatment in the form of fluorescent lamps, low-energy of polymers and other temperature-sensitive lamps or television. materials. The principle of low-pressure plasma O Plasmas known from 2 nature: lightning and northern lights. Electromagnetic energy + - O+O O2 + e O3 O2*, O* Dissociation Ionization High-energy products Excitation PLASMA Artificially produced plasmas are e.g. the plasma lamp and the electric arc in welding technology. 4 The efficient method for best results Wide range of application An especially high excitation frequency (GHz) promotes such reactions as it results in a high Low-pressure plasma is produced by electro- ion density in the plasma phase and therefore magnetic fields. The induced chemical reac- maximizes reactivity. Simultaneously, ion tions and physical effects depend on the energies remain low, so sputter effects and respective gas and excitation frequency used heat load are minimized or not incurred at all. for plasma formation. The used gas, for instance, determines if the Eco-friendly and efficient respective plasma is an oxidizing or reducing medium or neither of them (neutral). Such procedures of the low-pressure plasma technology are not only extremely efficient, but also ecologically neutral and economically Neutral plasmas useful because usually no polluting waste pro- ducts and no disposal costs incur therefore. Neutral plasma forms e.g. if a noble gas like argon is used. The major effect of neutral plasma is physical: Contaminants are removed Exemplary low-pressure plasma by a bombardment with heavy ions (sputter- treatment effects ing). Low excitation frequencies (kHz range) will boost this effect significantly as ions will • Removal of organic residues gain much more velocity before they impact • Activation by means of oxidation onto the surface. As fast and heavy ions of polymer chains transfer heat to the surfaces they collide with, • Coating by means of polymerisation this method is limited to suitable materials of suitable monomers and surfaces. • Removal of disturbing oxide layers by reduction • Etching by the use of aggressive gases Reactive plasmas and reaction conditions Reactive plasmas are formed from gases like oxygen, hydrogen or fluorocarbons. Varying process gases and excitation frequen- The oxidizing, reducing or functionalizing cies, there is a broad selection of possible effects originate from the ions and radicals plasma effects. Verification of the desired present in plasma which readily react with plasma effect on the actual substrate should the substrate material or the topping conta- never be skipped as thorough process develop- minant. After plasma treatment, surfaces ment may be necessary. PINK warrants its are activated, passivated or particularly developed processes and therefore safeguards clean, respectively. customer’s investments in PINK equipment. Plasma properties regarding different excitation frequencies Low frequency (LF) Radio frequency (RF) Microwave (MW) 40 kHz 13.56 MHz 2.45 GHz Plasma density Low Medium High Heat load High Medium Low Sputtering Considerable Medium Low 5 Activation with low-pressure plasma Individual modification or activation of surfaces Bonding improvement on polymers Plasma activation – for excellent bonding properties in adhesive applications The surfaces of countless industry-relevant plastics such as polyolefins (PE, PP, EPDM or In order to achieve adhesion between PTFE) are nonpolar so they cannot be adequa- surfaces of unpolar plastics and adhesives, tely wetted by paints, printing inks or adhe- lacquers, paints, etc., polar groups must sives. Bio-organic materials or metals are also be created on the surfaces. This results in often very difficult to coat or only with the aid an increase of the interfacial energies and A hydrophobic polymer surface of costly, specialized polymer products. therefore in an increase in affinity. prior a treatment with low-pres- sure plasma. With the aid of low-pressure plasma tech- If this, in addition, results in the formation nology, it is possible to simply and efficiently of covalent chemical bonds between the sub- obtain an activation or chemical modification strate and the adhesive or coating, particularly of polymer surfaces. In numerous industrial good adhesion properties can be expected. applications, this process has already proven Under such circumstances, the bond only itself in terms of improved polymer processing breaks under high mechanical loads. It will not properties (bonding, printing, painting, etc.). break at the interface but within the bonding components. The same surface has hydro- Areas of application With low-pressure plasma technology, polar philic properties after plasma functional groups can be integrated into the treatment. • Automotive and surface of plastics. Depending on the gas ap- automotive component industry plied, these may include oxygen groups such • Medical technology as –OH or nitrogen groups such as –NH2. This • Electronic industry effect is limited to the surfaces themselves. • Electrical engineering The polymer bulk material is unaffected. • Chip card production • Plastics processing • R & D With the activation in low-pres- sure plasma, the surface tensi- on increases and O-functional groups are incorporated into the PE surfaces. This improves bonding of the imprint. In medical technology, numerous plastic components are plasma treated in order to achieve improved hydrophilic properties on surfaces of microtiter plates, syringe hubs, etc. 6 Long-term behavior of plasma-activated surfaces Plasma activation produces covalent chemical Physical deactivation bonds between oxygen and carbon atoms allowing interactions between the substrate Directly after activation, all functional groups surface and the coating material because of responsible for the activity are oriented their polarity. Such chemical bonds are stable towards the interface of the material. Over over time and there is no degradation under time, a statistic distribution of this orientation normal storage conditions. However, storage is achieved by means of rotations along the stability is influenced by the following factors: polymer chains around chemical single bonds. The groups are randomly oriented then and • Subsequent contamination from outside only a small part is available for interaction • Subsequent contamination from inside with the environment. Heat accelerates such • Physical processes in the material processes because heat increases the mobility of the polymer chains. Contamination from outside ESCA analysis of a polypropylene surface Subsequent contamination from outside may occur due to improper storage or handling: Contact with contaminated objects or hands, dirty atmosphere in the storage room, transfer CHx C-O- CHx C-O- C=O COOH of volatile material components of the packag- ing material. Contamination from inside untreated after plasma treatment Today, many plastics are optimized for special properties by means of aggregates: plasticizers, UV