A METHOD OF PRODUCING AN LC-CIRCUIT

Abstract: A method is provided of producing an LC-circuit in form of a single component, in which the inductor and capacitor elements are arranged atop one another, and where the inductor elements are formed by ferromagnetic zones made of layers (6, 8) of ferrite of a high permeability, and between which electrode layers (7) are provided, and where the capacitor elements are formed by dielectric zones made of layers (9) of dielectric with electrode layers (4, 5) on both sides, said inductor and capacitor elements being produced by way of tape- or thick-film technology. According to the invention, the capacitor elements are initially provided and being subjected to a sintering at a relatively high temperature, whereafter the inductor elements (6, 7, 8) are applied and a sintering is performed at a considerably lower temperature. In this manner undesired reactions are avoided between the two zones.

Description: Title: A method of Producing an LC-circuit. Technical Field. The invention relates to a method of producing an LC-circuit in form of a single component, where the inductor and capacitor elements are arranged atop one another, and where the inductor elements are formed by ferro¬ magnetic zones composed of layers of ferrite of a high permeability, elec¬ trode layers being provided between said layers of ferrite, and where the capacitor elements are formed by dielectric zones made of dielectric paste with electrode layers on both sides, said inductor and capacitor elements being produced by means of tape or thick-film technology or combinations thereof. Background Art The use of ferrimagnetic materials for structuring chip components com¬ prising both inductors and capacitors has previously been limited by the difficulty in using ferrimagnetic materials in connection with dielectric materials. The inductors are often made of a ferrite and are used by way of known printing methods for structuring layer structures including inter¬ nal conducting paths. These inductors have low inductances due to the low permeability of the ferromagnetic material. EP-PS No. 297 565 dis- closes for instance a ferrimagnetic material of a relatively low permeability caused by a very small granular size and a high content of glass. Attempts have been made at obtaining a higher permeability by raising the sintering temperature or increasing the sintering period, but from a productional point of view such procedures are disadvantageous or necessitate the use of cost-intensive electrode materials, such as Pd. Thus the material described in EP-PS No. 297 565 requires a sintering period of 30 -220 min., which makes a production under usual thick-film conditions difficult. Furthermore, the final components have a relatively poor mechanical strength Moreover chip components comprising both inductors and capacitors suffer from delamination and distortion at the interface zone between the ferrimagnetic and the dielectric zones. Chip components comprising both inductors and capacitors are furthermore encumbered with problems due to reactions at the interface between the ferrimagnetic and the dielectric zones, whereby the characteristics of these materials are deteriorated These problems can be set right by the ferrimagnetic zones being separ¬ ated from the dielectric zones of the capacitors by means of a blocking layer, cf Danish Patent Application No 908/91 . Brief Description of the Invention Such an additional blocking layer should, however, be avoided, and a method of the above type is according to the invention characterised by initially providing the capacitor elements, which are sintered at a relatively high temperature, whereafter the inductor elements are applied followed by a sintering at a considerably lower temperature. In this manner undesired reactions are avoided between the two zones. Furthermore you have a free hand concerning the choice of dielectrics for the capacitor elements in such a manner that desired properties, such as high dielectric constants, i.e high capacity values, in the same number of layers can be optimized According to a particularly advantageous embodiment, the capacitor elements are provided by means of dielectric having e R > 250, such as a ceramic powder of the type TAM X7R 21 2 L, which is mixed with a binder and cast in thin layers, whereafter an electrode material is applied The resulting LC-circuit presents particularly high capacity values for the same number of layers In addition, low cut-off frequencies can thereby be obtained. Brief Description of the Drawings The invention is explained in greater detail below with reference to the accompanying drawings, in which Fig. 1 is an exploded view of a multilayer -LC-circuit according to the invention, Fig. 2 illustrates an equivalence diagram of the LC-circuit, and Fig. 3 shows the final LC-circuit in form of a single component. Best Mode for Carrying Out the Invention The multilayer LC-circuit of Fig. 1 comprises at least one ferromagnetic and at least one dielectric zone forming inductors and capacitors, respect¬ ively. Previously, it has been difficult to use ferrimagnetic materials in connection with dielectric materials. According to the invention, the pro- cess conditions have been divided such that undesired reactions between the materials have been avoided. An Example is described below where the principle is used for the produc¬ tions of multilayer Pi- filters containing two capacitors C 1 ( C 2 and one inductor (L - cf. Fig. 2) . The two capacitors C, , C 2 are produced by means of multilayer tape, whereas the inductor L is produced by way of serigra- phy technology. The process steps are as follows: a) A ceramic powder for instance of the type X7R 21 2L is mixed with a PVB binder for instance of the type MSI B73221 in the ratio of 55 weιght% of ceramic powder to 45 weιght% of binder in a container with zirconium balls for about 1 6 hours The mixture is then cast in thin layers of a thickness of about 35 - 40 μm on a carrier film, such as a mylar film The ceramic layers are removed from the carrier film and adhered to frames, cf. the article "Production of ceramic multilayer chip-capacitors" by Ole Pedersen, Ferrope- rm in Elektronik 1 , 1 983) , whereafter the ceramic tape on the inner side is applied an electrode material, which is for instance Gwent C301 1 1 D 1 (70% AG, 30% Pd) After air - drying of the applied electrode, the layers are individually punched in a matrix. Then the layers are laminated together into a block at a pressure of about 3000 psi and a tempera- ture of about 70°C. Subsequently, a slow burning off of the binder in the final multilayer block is performed The block is then sintered in an oven at a temperature of about 1 1 00°C for about 2 hours. b) The used ferrite paste is for instance composed of Lι 0 5 ( 1 + t _ c) , Zn 2 , Mn m , Tι t , Co c , Fe ( 1 . 0 2z 0 6t 0 4m.0 2c . e) , where 0 < t < 0.2; 0.2 < x < 0.5; 0.2 < n <0.4; 0.02 < c < 0.05, and ε are of the magnitude 0.06. c) On the rear side of the ceramic substrate, electrodes 4 of Ag/Pd/Pt are serigraphed, such as DuPont, which is to serve as frame termi- nation The internal frame electrodes are connected later on to the frame termination by means of rim terminations. The frame termina¬ tion are burnt on at about 750°C. Then the substrate is turned, and a plurality of ferrite layers 6 are serigraphed until the thickness is about 0. 25 mm Internal silver electrodes and necessary cutting marks are serigraphed twice, whereafter a plurality of ferrite layers 8 are again serigraphed until the total thickness of the ferrite layers is about 0.5 mm. The entire structure is then sintered at a tempera¬ ture which is below the melting point of silver, such as 91 0°C, for one to two hours. d) The ceramic substrate with the applied and sintered ferrite material is adhered to a steel plate with a glass base by means of shellac. By means of a diamant cutting machine a cutting is initially carried out in one direction through some cutting masks applied together with the silver electrodes, whereafter the plates are turned 90 ° and a cutting is performed in the opposite direction. The items cut out are washed in ethanol and subjected to a rim- end termination by means of Ag/Pd/Pt termination paste of the type DuPont 4933 D. Covering power: The ceramic material is typically barium titanate-based, such as TAMTRON X7R 1 62L product No. 52563 TAMTRON X7R21 2L product No. 52675 TAMTRON X7R262L product No. 52625 TAMTRON X7R422L product No. 52628 i.e. materials sintering at temperatures above 1 000 °C. Other ceramic materials can be used. As ferrite material is used LiMe 2 0 4 , such as FERROPERM A/S: L34 (lithium spinel ferrite) FERROPERM A/S: L48 i.e. materials sintering at temperatures below 960° C. Other ferrite materials can, however, also be used. As conducting material in the capacitor elements is used Ag/Pd, such as Gwent: C301 1 1 D 1 70Ag/30Pd ESL: 9637-B As conducting material in the inductor elements is used Ag/Pd, such as DuPont: 61 60 ( 1 00% Ag) ESL: 991 2-f ( 1 00% Ag) ESL: 9990 ( 1 00% Ag) Other conducting materials in the inductor elements can, however, also be used, such as gold. The conductor paths 7 can for instance be meander-shaped, cf. Fig. 1 . The inductor L is typically of 100 nH whereas the capacitors C C 2 ty¬ pically are o 2 x 1 0 nF. Fig. 1 illustrates furthermore the interconnections of the components. During the production, a temperature difference must apply by the pro¬ cesses at the capacitor elements and the inductor elements, respectively, of at least 50°C. In this manner undesired reactions are avoided between the two zones.

Claims: Claims 1. A method of producing an LC-circuit in form of a single component, in which the inductor and the capacitor elements are arranged atop one another, and where the inductor elements are formed by ferro- magnetic 5 zones composed of layers (6, 8) of ferrite of a high permeability, and where electrode layers (7) are provided between said ferrite layers, and where the capacitor elements are formed by dielectric zones made of layers of dielectric with electrode layers on both sides, said inductor and capacitor elements being produced by way of tape or thick-film technology 10 or combinations thereof, c h a r a c t e r i s e d by initially providing capacitor elements which are sintered at a relatively high temperature, whereafter the inductor elements are applied and a sintering is performed at a considerably lower temperature. 2. A method as claimed in claim 1, c h a r a c t e r i s e d by the 15 temperature difference between the sintering temperatures being at least 50°C, and typical 200°C. 3. A method as claimed in claim 1, c h a ra cte ri s e d in that the capacitor elements (9, 4, 5) are sintered at a temperature above 1000°C, such as 1100°C, whereas the entire structure after the application of the 0 inductor elements (6, 7, 8) is sintered at a temperature below about 960°C, such as 910°C. 4. A method as claimed in one or more of the preceding claims, ch aracte rised in that the capacitor elements (9, 4, 5) are provided by means of dielectric of e R >250, such as a ceramic powder of the type ~5 TAM X7R212L, which is mixed with a binder and cast in thin layers, whereafter electrode material (4, 5) is applied.

Inventors: HOLM JENS PETER, HOLM, JENS, PETER
Applicants: HOLM JENS PETER, WHITAKER CORP, HOLM, JENS, PETER, THE WHITAKER CORPORATION
Application year: 1997
Main classification: H01G4
IPC codes: H01F27, H01F41, H01G4, H03H3, H03H7