SI22288A - Method and device for selective etching of composite materials with laser ablation - Google Patents

Abstract

The subject of invention is a method for surface treatment of composite materials having a polymer matrix and a device with which selective etching of a composite surface is carried out. The method is based on surface treatment of a composite with a jet of energetic particles, first of all a bundle of laser rays, i.e. with laser ablation. Polymer is selectively partly or completely removed from the surface and fillers are left almost intact. Such changes of surface lead to the essential change of surface properties, first of all adhesion and porosity of various coatings on a composite.

Description

METHOD AND DEVICE FOR LASER ABLASION SELECTIVE CORNING OF COMPOSITE MATERIALS

The object of the invention is a method and apparatus for selective etching of composite materials by laser ablation, that is, a method for surface treatment of composite materials with a polymer matrix and a device for achieving selective etching of the surface. The method is based on the surface treatment of a composite with a pulsed jet of energy particles from a laser beam, called laser ablation. During treatment with selected pulse parameters or additional sources of energy particles and / or gases that allow increased particle densities to interact on the surface, the composition and morphology of the surface part of the composite changes. The polymer is partially or completely removed from the surface, leaving only fillers on the surface. This process is called selective etching of composites. Such surface changes, however, lead to a significant change in the surface properties, especially the adhesiveness and porosity of the various coatings on the composite.

DISPLAY OF THE PROBLEM

Polymer matrix composite materials (hereinafter referred to as "composites") have established themselves in various industries. Composites consist of a polymer matrix in which various particles, called fillers, are arbitrarily distributed. Fillers may be organic or inorganic particles of various shapes and sizes. The properties of each composite depend on the type of polymer matrix, the type and concentration of fillers, and the distribution, sometimes orientation, of the fillers in the polymer matrix. The surface properties of composites (composition, morphology, surface tension), however, depend mainly on the properties of the polymer matrix, since the polymer usually completely covers the fillers. Examples are found in composite coatings such as different paint coatings containing several different fillers. Selective surface treatment allows us to remove the polymer from the surface so that we can characterize the surface for e.g. the quality and homogeneity of the distribution of the fillers in the polymer matrix. We often want to change the surface properties of a composite to increase the adhesiveness of a composite with an applied layer of different materials. In these cases, it is advantageous to remove the polymer from the surface, leaving only the fillers disclosed on the surface, to which the applied layer will better adhere.

The polymer can be removed from the surface in various ways, for example by chemical etching or mechanical removal. These procedures are environmentally unfriendly, of poor quality or cost-effective and, above all, make local etching difficult. Plasma etching is more environmentally friendly but does not guarantee the selective removal of material in smaller areas and is more suitable for selective etching of larger areas. However, a problem arises when we want to remove material equally selectively at individual sites or holes, which is a standard problem for microelectronic devices.

BACKGROUND OF THE INVENTION

The classic method of etching polymers from the surface of composites is wet chemical etching. Such etching e.g. used for surface treatment of superconducting composites (US6214249 and VV002071462) or prior to application of metal coatings (US6080836). The polymer can also be removed from the composite surface by oxidation. They use flame, corona discharge or wet chemical etching for these purposes. The etching of polymers is often used in microelectronics, for example in the manufacture of integrated circuits. They may use multi-stage processes such as etching with high-frequency discharge, i.e. plasma (US2002055263, US5705428 in

US2002125207). Plasma etching of polymers, e.g. also used for processing polyethylene (UHMPE) fiber / vinyl ester resin composites to improve surface wettability. In this case, plasma etching is a step in the fabrication process which allows the fiber surface to be so wettable that it can be impregnated with vinyl ester resin (US5221431). Selective plasma etching of composites is found in patent DE10320483, where the surface is treated with reactive gas radicals.

Laser light is used in many applications to remove material. More specific is laser ablation or a combination thereof with other types of sources. A mixture of laser light technology and electrical discharge where a laser plasma is created between the sample and the anode to process the material is found in JP11197947. In general, laser ablation is widely used in printing (JP10291319, US5836249, JP9118017, US6165687) and lithography (DE19817756), where composite materials are concerned. Also known is the application of laser ablation materials to form composites (JP5179429, VV02004042785) or to apply materials (DE3915261, FR2816756). Laser ablation is used as a medical device primarily for tissue processing (VV003101529, US5807379) or catheter ablation (US2003199755, US6701176, WO09638193). This honey also produces nanostructured materials such as carbon nanotubes (JP2003054922), sintered materials (US2004081573), and synthesized compact films such as e.g. for use as optical conductors, treating polymers (US5106211). Often, the method is also used to remove material from two-layer composites where the bottom layer is transparent to laser light (JP2001300749).

Selective laser ablation is used in the fabrication of microelectronic or semiconductor devices where the surface is sampled (EP0542656, US5348609,

VVO9803271), cover (VVO9719269) or remove material by selective ablation of metallization layer or polymer material thereon (US6057173, US4568409, US5035918, US5348609, EP0337658). Selective removal is used to produce integrated electro-optical devices (US2003048974, US5281798) where multilayer composites or only optical devices are used to form a polycrystalline diamond (US5500157, EP0618043). Also used for marking and opening packaging (WO0168460). Laser-assisted etching in halocarbon environments (gases) is also used in semiconductor fabrication to improve etching efficiency (US5348609). Selective etching of substrate surface layers can also be performed with a light flash having sufficient high energy for ablation, and selectivity is assured by different wavelengths of light (US5281798), which is used to remove paint from the aircraft without damaging or degrading the underlying layers, typically lightweight aluminum.

Most of the work relates to multilayer composites used in the semiconductor and microelectronics industries. There is no information on selective laser ablation or selective surface treatment with a combined jet of energy particles for polymer matrix composites that are no longer layered but whose fillers are arbitrarily distributed. In an article in the journal J. Phys. D: App. Phys., 14 (1981) p. 2341 by K.C.A.Crane and J.R. Brown describes laser ablation on a composite fiber with an epoxy matrix, but they do not achieve process selectivity. Partial selective removal of the PEEK polymeric matrix was achieved by the authors P.E. Dyer et al. in an article by J. Mater. Really. 5 (1992) p. 1152, where the laser beam energies are too high and do not activate the surface.

The object and object of the invention is a method and device for selective etching of composite materials by laser ablation, that is, a method for treating the surface of composite materials with a polymer matrix and a device that enables selective removal of the polymer from the surface and activates it additionally.

According to the invention, the problem is solved by a method and device for selective etching of composite materials with a polymeric material with laser ablation according to independent claims.

According to the invention, the polymer of the composite material is partially or completely removed from the surface so that only fillers remain on the surface. This means a significant change in the surface properties of the composite, especially the adhesiveness and porosity of the various coatings on the composite.

DESCRIPTION OF THE PROBLEM SOLUTION

The invention encompasses a method and apparatus for processing composites. The surface of the composites is treated with a jet of energy particles. Photons and ions can be taken as energy particles. During the processing, the composition and morphology of the surface of the composite changes due to the interaction of the energy particles. Due to the selective interaction, the polymer is partially or completely removed from the surface, leaving only fillers on the surface that remain mostly intact. Selective interaction is mainly due to rapid local warming, where a quasi-equilibrium state with high particle densities is created at the interface between the surface and the vacuum. In the localized area, concentrations of charged particles and even atoms appear in the laser pulse induction, which further corrode, cleave surface bonds, and produce polar groups if gases are additionally initiated. This phenomenon is called surface activation. Etching also increases the surface roughness. Such surface changes lead to significant changes in the surface properties, especially the adhesiveness and porosity of the various coatings on the composite.

The invention will be described by way of example and pictures showing:

Figure 1. Cross-sectional diagram of a composite with a polymer matrix and two types of fillers.

Figure 2. SEM image of the surface of the composite with the polymer matrix before processing.

Figure 3. Roughness analysis of the untreated polymer composite matrix composite sample from

FIG. 1.

Figure 4. SEM image of a polymer matrix composite surface after laser jet treatment.

FIG. 5. Roughness analysis of the composite sample after treatment with the laser jet of FIG. 4.

FIG. 6. Schematic diagram of an apparatus for treating a composite with a jet of energy particles.

Figure 1 shows a schematic of a typical composite. The composite generally contains a polymer matrix 1 in which the various fillers 2 and 3 are dispersed. The surface of the composite is typically covered with a polymer layer, which is typical especially for composites made by the process of pressing at elevated temperature. The surface properties of such a composite (such as morphology and surface tension) depend on the type of polymer matrix, not the type of fillers. As the polymer softens during compression at elevated temperature, the surface of the composite is quite smooth. The surface energy of the composite, however, corresponds to the surface energy of the polymer, which is typically very low, i.e. less than 40mN / m. Such polymers are e.g. Paraffin, PTFE, PMDS, PP, PE, PPS, PMMA, etc. Fillers, however, are typically of a very wide range, from organic color pigments to carbon compounds.

Figure 2 presents a SEM (electron microscope) image of the surface of a simple untreated PP composite composite polymer and a single filler, in this case graphite. The surface is relatively smooth and no filler particles are visible on it.

The surface of the untreated composite is relatively smooth. This can be seen from Figure 3, which represents the roughness of the raw composite measured by the needle displacement method over the sample surface. It can be seen from the figure that the average roughness is less than 1pm, which is much less than the typical dimension of fillers, which in our case is about 10pm.

If the untreated composite of Figure 2 is exposed to laser light, selective etching of the surface is obtained. Figure 4 presents a SEM image of the surface of a treated composite exposed to laser ablation or. laser light beam with an energy of 40mJ / mm ² . The source of the laser ablation laser was an excimer laser with a wavelength of 308nm (Lambda Physik 105E). It can be seen from Figure 4 that no polymer is visible on the surface, only filler particles exiting the surface.

The change in surface roughness is seen in Figure 5, which represents the roughness of the treated composite analyzed by the needle displacement method over the sample surface. The figure shows that the transverse roughness is about δμιτι, which is the same order of magnitude as the typical dimension of the filler, which is about 10μιτι. Additionally, an increased surface wettability occurs, indicating an increase in surface energy through removal and also activation.

Comparison of Figures 2 and 3 with Figures 4 and 5 shows that laser ablation treatment of the composite significantly changed the morphology and composition of the composite surface. Before treatment, the surface was covered with a layer of polymer, and after laser ablation treatment, no polymer was found on the surface, but only filler particles. The roughness of the composite also changed accordingly. This change is due to the different physical and chemical properties of the polymer matrix and the fillers. The polymer always has a lower melting point than the fillers, while having a significantly higher vapor pressure than the fillers. When the surface of the composite is exposed to pulsed laser light with a wavelength of 308 nm, the surface is heated locally. The penetration depth of laser light with such a wavelength is extremely small, so most of the beam energy is released in the surface layer. Both polymer and surface fillers are highly heated. Because the vapor pressure of the polymer is extremely high at elevated temperature, the polymer evaporates from the surface while the fillers remain virtually undamaged, since the vapor pressure of the filler at this temperature is still low. The improved properties of selective etching of the composite are achieved by the addition of reactive gases, which increase the local high concentrations of the particles, which help to better and faster decompose the aged parts of the surface and further activate the surface. These reactive gases are typically oxygen, nitrogen, water vapor, nitrogen oxides, and mixtures of these gases with inert gases, primarily argon. This also prevents the surface from abrasion from being etched on the surface, which remains completely clean after ablation. The vapors of the polymer protruding from the surface of the composite could, under ordinary air pressure, bind back to the surface of the composite and thus slow the etching by laser ablation. The gas added or the gas mixture should preferably be less than 150 Pa.

The device that enables us to do such processes is shown in Figure 6, which shows the scheme of the device. The apparatus consists of a vacuum container 4 in which the composite materials are treated 11. The vacuum vessel is pumped with one or more vacuum pumps 7, which is separated from the system by a valve 8 and a recombination system 9, which enables the recombination of reactive radicals and the removal of undesirable substances from the system . Air is vented into the reactor system via valve 10. Prior to treatment, the composite 11 is mounted on a flexible carrier 12 so that any part of the surface of the composite can be precisely reached by a particle jet. The primary source of the energy particle jet is laser 5 with a suitable wavelength, which is fed through the optical laser system 6. An additional source of energy particles for selective etching, in particular, to increase the particle density near the surface is a low energy ion cannon 17 fed through the system 18. In exceptional cases, an electronic top 19 powered by the system 20 may also be used, where additional heating of the individual part is required. There is also the combined possibility of mounting an additional ion source at the electron gun position to achieve a homogeneous etching using an ion cannon 17. After attaching the composite 11 to the support 12, evacuate the vacuum chamber 4 to obtain a suitable pressure (typically below 1 Pa). , and the surface is treated primarily with a pulse jet of energy photons from source 5. The processing time or the number of laser pulses and their length and energy or energy. the intensities depend mainly on the type of composite 11. Since the intrusion depth of the energy particles from all sources is small, only the surface of the composite 11 is changed by treatment without significantly changing its lower layer properties. By leaking additional reactive gas or gas mixture from cylinders 13, 14 via shut-off 15 and inlet 16 valves, the machining conditions and also additional surface activation can be modified to achieve the desired properties of the corrosive composite. Reactive gases 13 are typically oxygen, water vapor, nitrous oxide, nitrogen, these gases used in mixtures with one another, or combinations thereof with inert gases, typically argon 14. By moving the carrier 12 or even the particle jet 17, any part of the surface of the composite can be treated. , so that with the device shown in Fig. 6, we can draw any exact area on the composite 11 on which we want to change the surface properties. The precision of the area depends only on the width of the beam of energy particles, primarily the laser beam in the ablation, which colminates with quartz lenses.

Claims (8)

PATENT APPLICATIONS METHOD AND DEVICE FOR LASER ABLASION SELECTIVE CORNING OF COMPOSITE MATERIALS 1. A method for selectively etching composite materials with a polymeric matrix, characterized in that the composite material is exposed to a pulsed jet of energy photons from a laser source, the ablation photon source being a laser of any wavelength, preferably of such wavelength, at which the inlet depth of the photon jet is small compared to the thickness of the composite, preferably of the order of magnitude of the thickness of the fillers in the composite, and are bundles of electrons or electrons combined. 2. Composite treatment method according to claim 1, characterized in that the vacuum reactor vessel is pumped to a pressure lower than 1Pa and the whole or part of the surface is exposed to a particle jet. Composite treatment method according to claims 1 and 2, characterized in that a reactive gas or mixture of gases whose total pressure does not exceed 150Pa is discharged into the vacuum reactor vessel to increase the particle density and selective etching efficiency. Composite treatment method according to claims 1, 2 and 3, characterized in that the reactive atmosphere is oxygen, nitrogen, water vapor, nitrous oxide or a mixture of these gases. 5. Composite treatment method according to claim 4, characterized in that in the reactive atmosphere a mixture of one or more reactive gases with inert gases, preferably argon. Composite treatment method according to claims 1 to 5, characterized in that the reactive atmosphere is in the plasma state. 7. A selective etching device for composite materials, characterized in that it consists of a reactor-vacuum vessel (4), pumped with one or more vacuum pumps (7), a gas metering system and three combined sources of energy particles and a recombination system (9 ) of reaction products .. Device according to claim 7, characterized in that the sources of the energy particles are photonic, ionic or electronic sources.