EP1090387B1 - Method for applying an attenuating coating on surface wave components - Google Patents

Description

The present invention relates to a method for damping Coating of surface wave components.

Surface wave components, for example surface wave filters, are electronic components of processing serve high-frequency electrical signals. Such components are commonly found in televisions and video devices as well as cell phones used. The electrical signal carrying the information is transformed into mechanical vibrations, so-called surface waves, converted. For electroacoustic conversion or to generate the surface waves are interdigital converters used on piezoelectric substrates, which consist of certain ceramics or crystalline materials, for example from lithium niobate. By a suitable one Structure of the converter, especially by a special geometric Design of the sound generating transducer surface affects the acoustic properties of this transducer. Thereby it is possible to specifically modify the acoustic signal and special wavelength ranges from the entire spectrum filter out.

Surface waves that are reflected at the chip edges, interfere with the function of a surface acoustic wave component. to Attenuation of such unwanted surface waves and The surface is reduced by reflections and echo effects of the transducer element in certain areas with a damping material provided, which the energy of the leaking Consumes waves and reduces reflections and echo effects.

Organic materials are used to create such damping structures with a suitable dynamic-mechanical property profile required. In EP 0 360 037, for example proposed two-component epoxy-based resins to use which is base catalyzed with carboxylic acids and acidic esters can be crosslinked. These two-component resins can be acoustically adjusted in the desired manner and lead to the required damping, but on the other hand prepare Processing problems. Mixing the two resin components leads to increased effort in production, Resins with a limited service life are obtained. The solvent content of the reactive resins requires one lengthy flash-off and hardening procedure, in addition there is a risk that the in a special three-dimensional Damping structures applied to geometry not permitted and then the desired damping properties or no longer have the required geometry precision.

EP 0 098 599 A2 proposes for the damping structures of surface wave components UV-curing Use acrylic resin mixtures and these to a high To optimize the modulus of elasticity and a high density. so manufactured and hardened damping structures show in the Practice, however, too high a brittleness and a too low one Liability on chip and converter material. The structures will namely preferably finished on a wafer and then isolated by sawing. If necessary sawing required damping structures to their flaking and peeling and thus to damage the lead entire component.

In DE-A 44 43 946.6, or WO 9618182 A, a UV-initiated cationic curing agent is used Epoxy resin described, which due to its viscosity property for printing damping structures on surface wave components using the screen printing process.

These organic masses must be used with regard to the application process - precision, reliability, rationality, automatability, Costs - the further processing of the Components - sawing through, packaging - the damping effect - Preservation of the filter characteristics, path attenuation of the surface wave, no impermissible reflections - and the lifespan of the components - corrosion of the finger structures, permanent adhesion - be optimized. In this point there is hence the constant need for new developments.

There are several known methods of applying the Damping structure on a surface wave component. Earlier fittings were cut from an extruded material, applied to the transducer surface and then in a thermal step by melting with the surface firmly connected. This step must be done for each component performed individually is cumbersome and time consuming.

According to the current state of the art, the organic Masses to create a damping structure mainly in Screen printing process on the surfaces of surface acoustic wave components applied. Applying the damping structure Screen printing has several disadvantages.

This is how this type of application results in many resins Bubbles, which in unfavorable cases have the required damping effect compromise. Waiting for bubbles to go away can be undesirable and uneconomical for the process Waiting times. UV-curable, solvent-free Screen printing resins tend to bleed. To that To remedy this, inorganic thixotropic agents are added to the resins to. However, the thixotropy is too damping effect critical. Generally you get with the use of the screen printing process in terms of Structure resolution, the position accuracy and the producible Layer thickness to technical limits. There are unfavorable ones Dependencies on the structure height, the sieve tolerances, the flow of the mass, etc. When printing relatively thick Layers, the resolution is limited, very thin layers are hardly feasible. In addition, the screen printing process own for a variety of filter types Masks are needed and every component design change makes new ones Screen masks required. This is particularly evident in the production of prototypes or products that are only available in small quantities are generated as disadvantageous. The sieves must be cleaned and dried. The screen films and Screen fabrics also only have a finite service life.

The object of the present invention is accordingly a method for the damping coating of surface acoustic wave components indicate the high structure resolution and position accuracy enables, and with what layers of 0.2-100 microns, preferably 20-50 microns can be realized.

The invention accordingly relates to a method for damping Coating of surface wave components by Coating the surface acoustic wave component with a damping, photo-curable resin and curing of the resin accordingly the required damping structure by imagewise exposure with one moving relative to the substrate surface Beam of light and removal of the unhardened areas.

In a preferred embodiment of the invention Process for the damping coating of surface acoustic wave components becomes a cationically curable, solvent-free Epoxy resin in a thin layer on the surface the surface wave component applied and with the help a computer-controlled UV laser according to the required Damping structure exposed imagewise.

Further embodiments of the invention are the subclaims refer to.

With the method according to the invention, damping coatings that are precise and automatable generate on surface acoustic wave devices that have a high Structure resolution and position accuracy. The Procedure is when using a computer controlled UV laser for exposure is used without any effort at possible component design changes customizable. Changeover times in production, as with screen printing, as well as screen storage and logistics are eliminated.

The photocurable resin can be essentially anything that meets the usual requirements for a damping mass. That the resins must be in electronic quality be available and for example a suitable glass transition temperature exhibit. Also should be used to separate the component structures for example sawing through the substrate be possible without the damping layer tearing and flaking off the piezoelectric material.

For example, there are photocurable (meth) acrylates, polyimides or polybenzoxazoles in question. Are preferred according to the invention however, epoxy resins with one on the exposure source adapted photoinitiator system used. such Epoxy resins are described for example in DE-A 44 43 946.6, to which full reference is made here. The corresponding epoxy resin compositions are there structured by screen printing on the respective piezoceramic Applied substrates.

For an embodiment according to the invention, the resins contain especially additives for the lateral limitation of hardening to increase the structure resolution. These additives are preferred alkaline in nature and can be selected from the group of salt-like Hydroxides and organic amines can be selected. For example one uses ethanolamine or its organic substituted derivatives.

According to the present invention, the reaction resin composition through the most varied of methods to be damped Substrates are applied. For example, the job done by spin coating, but also by other coating processes, like roller or curtain coating. Conceivable is also still an order in the screen printing process, whereby here the application is unstructured or roughly structured can be done, for example, to save material, Keep edges clear etc.

The required layer thickness can be applied by modification the epoxy resin composition, as far as this modification does not influence the damping effect or only influences it insignificantly, and the type of order can be influenced.

The required damping structure is then by pictorial Exposure of the applied resin layer generated. The photo structuring of organic layers, both positive as well as negative, is known per se and is used in manufacturing of electronic components and circuit boards in used in many ways. A scanning photo structure is not for the damping coating of Surface wave components and not in combination with the selected resin formulations. Rather is up No system has been found today to match the one outlined above Features and performance combination.

Laser stereo lithography is a method of generation three-dimensional structures made of liquid, photosensitive Resins and is for example in DE-A 195 41 075.0 described. In the context of the present invention a single-layer, damping Coating also created by scanning exposure. To do this, you wear the selected damping reaction resin in one thin layer of 0.2 to 100 microns, preferably 20 to 50 µm on the surface of a surface wave substrate. The wafer is then suitably positioned under the Laser exposure device. This is similar, for example as described in DE-A 195 41 075.0, from a focused Laser with a suitably designed transfer optics.

For example, a helium-cadmium laser can be used as the laser light source with a wavelength of 325 nm can be used. The radiant power is preferably between 1 and 100 mW. alternative lasers would also be suitable for this purpose, in which the laser power in the specified range or above and for their Suitable photoinitiators are available. On an alternative UV laser would be, for example, an argon ion laser with a wavelength at 351 and 364 nm. Others too Intense UV light sources are for the method according to the invention suitable. Short-wave visible light can also be used be used when making photoinitiation effective is possible. The light beam is also on one Focus diameter from 5 to 200 microns, preferably 20 to 50 microns focused.

The focused light beam is now controlled by a computer Mirror system and a transfer optics in one the required damping structure the surface wave component coated with reactive resin directed. Of course, one or more can do this both relative directions of movement are carried out by the wafer. With such an exposure process, only such Places hardened on the resin-coated component, where damping structures should arise.

After the resin layer has cured imagewise, this can unexposed resin according to all known in the art Methods are removed, i.e. the damping structure developed become. Suction, blowing off are conceivable, for example or washing off the unexposed resin in the solvent vapor, or in cascade washers, so to some extent unused resin can be recovered.

In the method according to the invention there is no bleeding generated structures, especially no different Flow behavior on different substrates. This property creates a scope for development selectable resin formulations because of the flow behavior, in particular the viscosity can be varied within wide limits can and does not have to be optimized for precise screen printing. This means that the application is bubble-free and homogeneous possible of a high quality acoustic damping as well as good liability.

If necessary, the exposure can be such that none the exposed areas are completely cured. This variation is due to modification of the resin itself or the exposure intensity and / or duration possible. Through the then the required thermal aftertreatment proceeds Resin slightly, so that damping structures with special low-reflection edges arise.

After the essentials based on the previous description Features and advantages of the invention have been presented , it can be stated that the method according to the invention in terms of flexibility and economy previously known and in the prior art for the generation of damping coatings on surface acoustic wave components the method used is far superior.

Claims (8)

1. Method for applying an attenuating coating on surface wave components by coating the surface wave component with an attenuating, photocurable resin and curing the resin in a way corresponding to the required attenuation structure by imagewise exposure with a light beam moved in a scanning manner in relation to the substrate and removing the uncured regions.
2. Method according to Claim 1, characterized in that the structuring exposure is carried out by means of laser light.
3. Method according to either of Claims 1 and 2, characterized in that the photocurable resin is selected from (meth)acrylates, polyimides, polybenzoxazoles or epoxy resins.
4. Method according to either of Claims 1 and 2, characterized in that an epoxy resin composition with a suitable photoinitiator system is selected.
5. Method according to Claim 4, characterized in that the epoxy resin composition comprises at least a liquid epoxy compound, a polyhydroxyl compound soluble therein with at least two aliphatic OH groups and a photoinitiator or a photoinitiator system for the cationic curing.
6. Method according to Claim 5, characterized in that the epoxy resin composition further comprises additives for the lateral limitation of the curing.
7. Method according to Claim 6, characterized in that the additives for the lateral limitation are selected from the group of salt-like hydroxides and/or organic amines.
8. Method according to one of Claims 1 to 7, characterized in that, if appropriate, the coating is subsequently subjected to thermal treatment to produce edges of very low reflection, with the said coating running away slightly.