ADVANCES IN USING A POLYMERIC TAPE FOR LASER-INDUCED DEPOSITION AND ABLATION

Transcription

1 ADVANCES IN USING A POLYMERIC TAPE FOR LASER-INDUCED DEPOSITION AND ABLATION Arne Koops, tesa AG, Hamburg, Germany Sven Reiter, tesa AG, Hamburg, Germany 1. Abstract Laser systems for industrial materials processing are today s state-of-the-art technology driving innovation and productivity. tesa AG has combined some of the major positive advantages of laser and polymeric tape technology to create an innovative marking technique for the industry. The new laser marking process has been enjoyed by all sectors of industry including automotive, electronics and aerospace. In this presentation, we will discuss the chemical and physical interaction between a laser beam at µm wavelength and polymeric tapes for direct writing on glass, ceramics, metals and polymeric materials. 2. Introduction Laser technology has attracted a great number of people interested in industrial applications, mainly in automotive and electronics. Industrial application of lasers, mainly in cutting, welding and marking, are well established techniques [1]. It is interesting to look at the evolution of laser interactions with materials as it applies to materials processing in the time since the lasers were discovered. In the `60 - `80, the laser interaction for materials processing could be described as being based on the primary laser material interaction such as etching and cutting. For the last 20 years the laser material interaction has expanded to include secondary effects such as laser ablation for film formation and laser-induced deposition for surface treatments. Here, the laser-material interaction is used to do subsequent processing of materials. In the last few years an argument could be made that this secondary effect has been expanded to include laser interactions with novel materials. One of the novel materials is polymeric & adhesive film. Figure 1 shows a simple graphic description of the evolution of laser interactions used to process materials. Laser Material Processing 1 st Order Laser Interaction with Materials, Primary (Etching, Cutting) 2 nd Order Laser Interaction with Materials, Secondary-Novel (Ablation, Deposition) Laser Interaction 3 rd Order with Materials, Secondary (Welding, Marking) trendsetter technologies with polymeric&adhesive films? Discovery of the Laser Figure 1. `60 `80 `00 A graphic description of the evolution of lasers used in processing materials

2 2.1. Laser Basics Lasers are efficient marking and engraving tools and their application dominates sectors such as plastics, metals, alloys, silicones, and satisfies requirements of speed, quality, flexibility and price. Some of these qualities are not seen in traditional technologies. pump source: flashlamp, laser diode galvanometer deflection mirrors highly reflective mirror Laser medium (crystal): Nd:YAG, Nd:YVO4,.. beam expander partially reflective mirror continuous wave (cw) pulsed laser beam (Q-switch) field projection lense output output image processing area (workpiece) time time Figure 2. Typical Laser Marking Schematic Fig. 2 above illustrates a typical layout for a laser marking system (solid-state laser). A laser beam is collimated and directed into an industrial scanner unit. Within this unit are two high-speed galvanometric scanning mirrors, which deflect the beam into a focussing lens. The laser is thus moved rapidly relative to the work piece, and by controlling the laser parameters a high quality mark can be created Mechanisms for Marking Mechanisms for marking can be divided into two categories: marking by surface removal, and marking by surface modification. In the first instance removing material with a laser creates a visible mark: either by melting, vaporisation or photochemical decomposition. The resulting surface morphology or substrate structure creates a readable high contrast mark. In the second instance the laser radiation affects the material composition to create a high contrast mark without material removal. It may locally melt the material, causing it to oxidise or chemically alter to form a visible mark [2]. Novel products can realize marks through laser-induced ablation and deposition processes on new surfaces. Engraving Foaming Fading Ablation Deposition laser Figure 3. Principles of laser marking

3 3. Experimental Set-up Design of experiment was employed for the marking study on glass Processing Systems and Conditions To examine the effect of ablation and deposition, one YAG-laser system was used for the experiments. Laser Model Violino 3 Laser Medium Nd:YVO 4 Wavelength 1064 nm Nominal Power 20 W +/- 5% Polarization Linear (>100:1) Modulation 20 khz to 200 khz Laser Pumping Diode Laser Focal distance 296 +/- 4 mm Marking Area 170 x 170 mm 2 Min. Spot Diameter 40 µm Speed 100 to 4000 mm/sec Table 1. General specifications and feature (overview) of laser equipment Laser control software is as important as any hardware component in the marking system. For processing for the marking files, some software was used like CorelDRAW, Adobe Photoshop, AutoCAD, and Smartist that is the laser controlling CAD/CAM system. All essential laser parameters such as pulse frequency, speed, peak power, pulse energy, spot overlap and focus diameter are adjusted by a laser matrix (Fig. 4). current (A) V= const. = 4000 mm/sec Hz at 1000 mm/sec &spot = 100 µm process area khz Hz at 1000 mm/sec 9 8 marking length 1mm frequency (khz) Figure 4. Overlap and process area for marking settings (example)

4 4. Results / Discussion 4.1. Laser-induced Deposition and Ablation A process was developed to indirectly inscribe glass using pigment foil and Nd:YAG laser. This method stands out from other processes and it is a completion for conventional methods like screen printing, etching and mechanical grinding [3]. The developed pigment foils make it possible to create a black to gray colored, free of stress inscription on various glass types. The inscription has a high bonding power, a good quality of resolution and a good contrast. The characteristics of use and the inscribing quality are proofed with different assessment methods. The general scheme of the new process on laser ablation and deposition at atmospheric pressure is shown in Fig. 5. (1) Nd:YAG Pulse 1064 nm (2) transmittion glass substrate (receiving material) Laser Transfer Matrix Figure 5. Scheme of marking process We have termed this technique LTF Lasertransferfilm and present its historical evolution from pulsed laser deposition. The colored marking process of the new LTF Technology is based on a laser supported pigment transfer by using a polymeric tape. In a first step the Lasertransferfilm is fixed to the substrate. The substrate is positioned direct to the film surface. The 2nd step is the marking process by a YAG-Laserbeam. When the laser energy is passed through the glass substrate, the laser sensitive pigments are transferred to the substrate by a chemical and physical interaction. The innovative laser technology provides a particularly strong pigment anchoring. After the removal of the film the receiving substrate is marked permanently and tamper proof. The glass is neither strained mechanically nor are critical chemicals being used. The product design of the Lasertransferfilm in a way resembles the ink ribbon of a typewriter even though on a technologically completely different level. The LTF product consists of a marking material coated onto the backing of a tape. The coating can be slightly self-adhesive. The first layer of the LTF product is a special 50 µm thick polymeric film.

5 The pigment layer contains pigment A and pigment B. The laserbeam is focused onto this pigment layer. The laser settings are then preferentially tuned to interact with the solid laser transfer matrix. Ideally, the pigment layer should evaporate or be decomposed into a volatile material, carried away by a purge gas and form a marking on glass under a new bond formation of A + B. The glass is marked in a highly controllable fashion. The close-up schematic of Fig.6 shows the important steps of the pigment transfer and marking formation. (3) evaporated matrix (5) deposition on glass (3) evaporated matrix (1) Nd:YAG Pulse 1064 nm (2) transmittion (1) Nd:YAG Pulse 1064 nm (2) transmittion (4) bond formation A + B = AB (4) bond formation A + B = AB glass substrate (receiving material) Laser Transfer Matrix glass substrate (receiving material) Laser Transfer Matrix Figure 6. Schematic diagram of the basic LTF process To illustrate some of the effects of the laser deposition to the receiving substrate, we show a LTF with evaporated zones (Fig. 7) and the result on glass (Fig. 8). Figure 7. LTF matrix with evaporated zones (alphanumeric characters)

6 Figure 8. Example of surface structure occurring in the deposition zone under usage of laser pulses The marking thickness is between 100 up to 1000 nm and is extremely resistant to mechanical abrasion, chemicals, solvents, temperatures and atmospheric exposures. 5. Summary There are many advantages to LTF compared to other existing direct write technologies. These advantages include the ability to do adherent depositions at room temperature and in atmospheric pressure. The latter is accomplished because LTF is a dry technique meaning there is no interval of time required for transferring one layer on the surface of another. Today, the ultimate resolution of the LTF approach can be as small as µm line width. The technique is 100% computer controlled and can process different designs on various glass and ceramic substrates. The LTF equipment is based on an industrial laser system. We have demonstrated that by combining some of the major positive advantages of lasers and polymeric films, that we could produce a novel laser driven direct writing technique termed LTF. We have also shown that LTF can fabricate high contrast marks on glass substrates. Also the marking is created at the surface without damages to glass like expansion cracks and influence to mechanical stability of the substrate. Compared to direct laser marking processes and printing processes, LTF is an energetically soft and dry laser based marking technique.

7 Acknowledgements [1] Hillmann, R., Diodengepumpte Festkörper-Beschriftungslaser, Bayrische Laserseminare (2004), [2] Haefer, Rene A., Oberflächen- und Dünnschicht-Technologie, Springer Verlag, (1987) pp [3] Dumont Th., Laser writing of 2D data matrices, Thin Solid Film (2004), [4] Böhme R., Zimmer K., Ultraglatt und hochpräzise: Laserabtrag an der Rückseite transparenter Dielektrika, Lasertechnik (2003), 50-52

8