BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a surface acoustic wave component. Electrically conductive structures are disposed on a substrate and encapsulated, i.e., sealed against environmental influences, by a cap cover. The SAW component is provided with a cover metallization which acts as an RF shield.
An earlier, commonly owned application No. 08/743,540 (see international published application WO 95/30276) describes an encapsulation for electronic components with a cap that seals component structures on a substrate. The cap is formed by a cover which is provided on the substrate and has cutouts accommodating the component structures in regions thereof. Such an encapsulation protects the component structures against environmental influences, with the result that electronic components encapsulated in such a way can be used directly in further applications, without the need for an additional housing.
When such components are fitted in a ceramic casing and the casing is sealed with glass solder for cost reasons, then the component is not effectively RF shielded since the cover is then composed of ceramic and there is no conductive connection to the cover. When the casing is formed of plastic material, then an analogous situation results.
German published non-prosecuted patent application DE 31 38 743 A1 discloses a SAW filter enclosed in a metallic casing and sealed on all sides which avoids the above disadvantages.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of producing a surface acoustic wave component, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type and which provides for an effective RF shield for electronic components of this type.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electrical component, in particular a SAW component operating with surface acoustic waves, comprising:
a substrate, electrically conductive structures disposed on the substrate, and a cap cover encapsulating and sealing the electrically conductive structures against environmental influences; and
an RF shielding metallization disposed on the cap cover, the metallization being a layer sequence formed with a layer of titanium/tungsten, a layer of a metal selected from the group consisting of copper and nickel, and a layer of gold.
In accordance with an added feature of the invention, the layer of titanium/tungsten and the copper layer have a layer thickness of less than 0.1 μm, the layer of nickel has a layer thickness of approximately 1 μm, and the layer of gold has a layer thickness of about 0.05 μm.
In accordance with an additional feature of the invention, the conductive structures include a ground connecting pad for electrically connecting the conductive structures, the cap cover has a window formed therein, and the metallization is electrically connected to the pad via a through-plated hole through the window in the cap cover.
With the above and other objects in view there is also provided, in accordance with the invention, a method of producing a surface acoustic wave component, which comprises:
providing a substrate and forming electrically conductive SAW structures on the substrate, encapsulating and sealing the structures against environmental influences with a cap cover; and
forming an RF-shielding metallization on the cap cover, by initially vapor-depositing a material layer sequence of TiW, Cu or Ni and Au, and reinforcing with a process selected from the group consisting of a current-less process and a galvanic process.
In accordance with a concomitant feature of the invention, the metallization is formed by vapor depositing the layer sequence of TiW, Cu or Ni and Au, structuring the metal layer by pulsed laser radiation, and non-electrically reinforcing the vapor deposited layer with Cu.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method of producing a surface acoustic wave component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is seen a surface acoustic wave (SAW) component which, in principle, comprises a piezoelectric substrate 1 and conductive structures 3 disposed on the substrate. Such conductive structures 3 which may be, for example, the electrode fingers of interdigital transducers, resonators or reflectors. As already described in the above-mentioned copending application No. 08/743,540 (herewith incorporated by reference), the electrically conductive structures 3 are covered by a cap 2 which protects the structures against environmental influences. The component, together with the cover 2 and the substrate 1, may be directly used as a “casing”, or it can be fitted into a casing.