GB2083952A

GB2083952A - Microcoil Assembly

Info

Publication number: GB2083952A
Application number: GB8127246A
Authority: GB
Original assignee: Asahi Chemical Industry Co Ltd; Asahi Kasei Kogyo KK
Current assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Priority date: 1980-09-11
Filing date: 1981-09-09
Publication date: 1982-03-31
Also published as: NL185747C; KR830008358A; NL8104176A; DE3135962A1; GB2083952B; NL185747B; KR890004585B1

Abstract

A microcoil assembly comprises as one body, at least one spiral- patterned flat conductor 1 (shown in section) having a conductor width of 20 to 200 mu m, a conductor-to- conductor spacing of 0.5 to 100 mu m, and a conductor thickness of 15 to 400 mu m, with layers of magnetic material 4, for example ferrite material, placed directly on or near the spiral-patterned flat conductor on both sides. A plurality of spiral coils may be stacked between a pair of magnetic layers, with intervening insulation, and the layers may be connected in series or parallel and provide the windings of a transformer. Details are given for possible conductor materials, magnetic materials, insulating materials and substrates. <IMAGE>

Description

SPECIFICATION Microcoil Assembly The present invention relates to a small-sized microcoil structure having high performance and high reliability, and more particularly to thick film printed coil structure or microcoil assembly.

In recent years, with the advance in integration of active elements such as used in an IC or LSI, there is a growing tendency that passive elements are included as discrete components in a hybrid circuit having miniaturized chips to realize highdensity mounting and automatic mounting.

Accordingly, it is strongly desired to develop a microcoil which is small in size and high in performance and reliability.

A transformer obtained by combining two coils transmits electrical energy through magnetism serving as a medium, and performs such important functions in circuit technology as an abrupt change in voltage or current, impedance matching, electrical insulation, and phase shifting.

Accordingly, the microcoil is very important.

A conventional wire-wound discrete coil becomes large in size when it has a large inductance and a small d.c. resistance, and therefore cannot be used in hybrid circuit. Further, a printed coil or flat coil, which is formed of an evaporated thin metal film, is small in size but large in d.c. resistance, and therefore cannot be used in the hybrid circuit (see, for example, U.S.

Patent No. 3,947,934). A transformer including two wire-wound coils is inevitably large in size, and moreover has drawbacks that the coupling coefficient thereof and the amount of coils mountable in unit area are small. A transformer used for VTR rotary coils is required to have a coupling coefficient of 0.9 to 0.95.

For these reasons, the development of microcoils has been desired, but no satisfactory product has been obtained hitherto. However, the inventors of the present invention have found that a small-sized high-performance microcoil assembly can be obtained by providing a magnetic material or magnetic members uniformiy over upper and lower sides of a spiralpatterned flat conductor having a high wiring density and a high mounting density, and further providing the magnetic material or magnetic members at a selected position, if necessary.

According to the basic construction of the present invention, there is provided a microcoil assembly comprising a spiral-patterned flat conductor having a conductor width of 20 to 200 a a conductor-to-conductor spacing of 05 to 100 ,sum, and a conductor thickness of 1 5 to 400 ym, and a magnetic material provided at least on both sides, namely, upper and lower sides of the spiral-patterned flat conductor. It is preferable that the magnetic material is an insulator and has high magnetic permeability. Ferrite is generally used as the magnetic material. Amorphous metal may also be used.

A microcoil assembly according to an aspect of the present invention has dimensions 5 mmx5 mm, a thickness of 1 to 1.1 mm, and an inductance of hundreds of microhenries.

According to another aspect of the present invention, there is provided a microtransformer in which two coils formed on an insulating substrate and each formed of a spiral patterned flat conductor having a conductor width of 20 to 200 ym, a conductor-to-conductor spacing of 0.5 to 100 ,um and a conductor thickness of 1 5 to 200 ,um are operatively and integrally disposed so that mutual induction may be generated between the two coils when activated. A magnetic material is provided in a magnetic flux path established by the microcoils, and the shape and size of the magnetic material are determined in accordance with the application.

According to a further aspect of the present invention, there is provided a microcoil assembly in which two or more insulating substrates each provided thereon with a spiral-patterned flat conductor having a conductor width of 20 to 200 a a conductor-to-conductor spacing of 0.5 to 100 ,um and a condcutor thickness of 15 to 200 ym are piled so as to form a laminate, the spiral patterned flat conductors formed respectively on the insulating substrates are connected so that respective spiral patterns on the insulating substrates extend in the forward direction, and members of magnetic material are provided at least on the uppermost and lowermost spiral patterned flat conductors of the laminate so that the laminate and the magnetic members are integrally formed.

Now various embodiments of the present invention will be explained below with reference to the accompanying drawings, in which: Fig. 1 is a plan view showing an example of a spiral-patterned flat conductor used in the present invention; Fig. 2 is a sectional view showing the structure of a fundamental microcoil according to the present invention; Figs. 3A and 3B are plan views respectively showing typical examples of a spiral-patterned flat conductor formed on an insulating substrate; Figs. 4 and 5 are sectional views respectively showing different embodiments of a microcoil assembly according to the present invention in which a magnetic material is provided on both sides of spiral-patterned conductors;; Fig. 6A is a plan view showing a further embodiment of a microcoil assembly according to the present invention in which a magnetic material forms a closed magnetic circuit, and Fig.

6B is a sectional view of Fig. 6A, taken along the line VIB--VIB; Fig. 7 is a sectional view showing a laminate obtained by piling substrates each provided with a spiral-patterned conductor; Figs. 8 and 9 are sectional views respectively showing different methods for connecting the spiral-patterned conductors of the laminate shown in Fig. 7; Fig. 10 is a sectional view showing another embodiment of a microcoil assembly according to the present invention; Figs. 11 and 1 2 are sectional views respectively showing different embodiments of a microtransformer assembly according to the present invention in which a plurality of printedcoil mounted substrates are piled in the longitudinal direction;; Fig. 13 is a sectional view showing a further embodiment of a microtransformer assembly according to the present invention in which a plurality of printed-coil mounted substrates are arranged in the transverse direction and a magnetic material is provided on the path of magnetic flux generated by the coils; Fig. 14 is a plan view for showing a microcoil connecting structure in the case where a plurality of coils each having the structure shown in Fig. 4 or 5 are juxtaposed and electrically connected to each other; and Fig. 15 is a view showing an external appearance of an embodiment of the present invention in which a plurality ofcoils juxtaposed and connected as shown in Fig. 14 are provided on a cylindrical surface.

Hereinafter, like reference numerals designate like parts throughout the drawings.

Fig. 1 shows a fundamental spiral-patterned flat conductor 1, and Fig. 2 shows in section, a fundamental microcoil structure according to the present invention. Referring to Fig. 2, on both sides of the spiral-patterned flat conductor 1 which is a fine-patterned thick film conductor, provided are magnetic material layers 4a and 4b each formed of, for example, ferrite, and the conductor 1 and the magnetic material layers 4a and 4b are unitarily formed by an insulating adhesive material 5. The magnetic material layers 4a and 4b may be arranged symmetrically relative to the pattern surface of the conductor 1, or may be disposed asymmetrically. According to the necessity, a plate of conductor pattern 1 may be adhered directly to the surface of the magnetic material, or a thick film of conductor pattern 1 may be deposited thereon.

Figs. 3A and 3B show in plan views, different examples of the spiral-patterned flat conductor 1 formed on an insulating substrate 2. Referring to Figs 3A and 38, the spiral-patterned conductors 1 have inner ends 1 a, 1 c and outer ends 1 b, 1 d, and are provided on the insulating substrate 2 which may be flexble or non-flexible. The outer end which is usually as an external lead terminal connected to an external electrode, is provided at positions selected to connect a plurality of spiralpatterned, conductors as described later. Figs. 3A and 3B show typical positions of the outer ends 1b, 1d.

In usual, the spiral-patterned conductor 1 is formed on both surfaces of the insulating substrate 2. The conductors 1 on both surfaces of the substrate 2 are arranged so that electric current can flow through the two spiral-patterned conductors in the same direction or in the forward direction to increase the resulting magnetic flux.

Normaily, respective inner ends 1 a or 1 c of the spiral-patterned conductors are connected to each other by a thru-hole 3, and respective outer ends 1 b or 1 d of the conductors form external lead terminals. In the case where a conductor having the pattern shown in Fig. 3A is formed on one surface of an insulating substrate, a conductor having the same pattern is arranged on the other surface of the insulating substrate concentrically with the above-mentioned conductor, but respective outer ends are disposed at both ends of one side of the spiral pattern. A similar arrangement is employed in the case of using a conductor having the pattern of Fig. 3B.

Figs. 4 and 5 show structures in which a magnetic body 4 is formed on both sides of a pile of spiral-patterned conductors through an insulating adhesive material 5. The drawings show sectional views of coil assembly having spiral-patterned conductors formed on both surfaces of an insulating substrate, taken along the line IV--IV in Fig. 3A. In Fig. 4A, the magnetic material is provided over only upper and lower surfaces of the conductors, while in Fig. 5, the spiral-patterned conductors are fully covered by the magnetic material.

Fig. 6a shows an embodiment of a microcoil structure including a closed magnetic circuit, and Fig. 6B shows a section taken along the line VIB--VIB in Fig. 6A. In Figs. 6A and 6B, a magnetic material 4 is provided in such a manner that spiral-patterned flat conductors are fully enclosed by the magnetic material 4 and a hole bored through an insulating substrate 2 at a central portion thereof (which is near respective inner ends of the spiral-patterned conductors and is not occupied by the spiral-patterned conductors) is filled with the magnetic material 4.

Thus, a closed magnetic circuit is formed, and the inductance of the microcoil assembly is enhanced. External electrodes 6a, 6b are provided on a side face of the magnetic material 4, and connected to respective lead terminals of the spiral-patterned conductors by a conductive paste or solder loaded in thru-holes which are provided in the magnetic material 4.

Figs. 7 to 13 show various embodiments of the present invention in which a plurality of flat coils each having a structure that a spiral-patterned conductor is formed on each of upper and lower surfaces of an insulating substrate as shown in Figs. 3A, 3B, 4 and 5, are piled. In these flat coils, when the spiral-patterned conductor of Fig. 3A is formed on the upper surface of the insulating substrate, the conductor is also formed on the lower surface. When the spiral-patterned conductor of Fig. 3B is formed on the upper surface, the conductor is also formed on the lower surface. The patterned conductors on the upper surface and on the lower surface are connected by a thru-hole 3 so that an electric current flows through these spiral-patterned conductors in the same direction. Now, let us consider the case where a plurality of flat coils are piled, that is, a plurality of insulating substrates each provided on both surfaces thereof with spiral-patterned conductors are piled. When the flat coils are connected in parallel, electric currents can be readily passed through the flat coils in similar directions by piling insulating substrates each having the spiral-patterned conductor shown in Fig. 3A, or by piling insulating substrates each having the spiral-patterned conductor shown in Fig. 3B. When the flat coils are connected in series, an electric current can be readily passed through the flat coils in the same direction by piling an insulating substrate having the spiralpatterned conductor shown in Fig. 3A and an insulating substrate having the spiral-patterned conductor shown in Fig. 3B alternatively.The flat coils thus piled are connected to each other by a stepped connection shown in Fig. 8 or by a thruhole connection shown in Fig. 9. The parallel connection of flat coils is used mainly to reduce the d.c. resistance, and the series connection is used generally to increase the inductance. The above parallel connection and series connection may be appropriately combined.

Fig. 7 indicates a structure in which two flat coils are piled through an insulating adhesive material 5, taken along the line Vil-VIl shown in Fig. 3A, Fig. 8 indicates in section, a connecting part in the case where two flat coils are connected by the stepped connection using a conductive material 7, taken along the line VI Il- VIII shown in Fig. 3A. Fig. 9 indicates a section of a connecting part in the case where two flat coils are connected by the thru-hole connection using a thru-hole conductor 8, in place of the stepped connection shown in Fig. 8.

Fig. 10 shows an embodiment of a microcoil assembly in which two fundamental flat coils each having such a structure as shown in Figs. 6A and 6B are piled. The connection between the flat coils and the connection of lead terminals to external electrodes are made in the abovementioned manner. The microcoil assembly shown in Fig. 10 is small in d.c. resistance and large in inductance, since the assembly includes two flat coils each having a closed magnetic circuit.

Figs. 11 and 12 show microtransformers, taken in the same direction as in Fig. 7. In order to allow mutual induction between the primary and secondary coils of the microtransformer, the two coils may be piled in the longitudinal direction, or may be arranged in the transverse direction. In either case, the two coils are integrally formed through an insulating adhesive material. In the case where the primary and secondary coils are piled in the longitudinal direction, a laminated primary coil (a) and a laminated secondary coil (b), each of which has a structure as shown in Fig.

8, may be piled as shown in Fig. 11. Alternatively, a primary coil (a), a secondary coil (b), another primary coil (a') and another secondary coil (b') may be piled as shown in Fig. 12. In this case, the primary coils (a) and (a') are connected to each other to form a unified primary coil of a microtransformer according to the present invention, and the secondary coils (b) and (but) are also connected to each other to form a unified secondary coil of the microtransformer. In Figs.

11 and 12, T1 designates two end terminals of a primary coil, and T2two end terminals of a secondary coil.

The performance of the above-mentioned microtransformers can be improved by providing a magnetic material on the path of magnetic flux generated by the microtransformers. It is preferable to arrange the magnetic material so that mutual induction is effectively generated between the primary and secondary coils and a closed magnetic circuit is formed.

Fig. 13 shows another embodiment of a microtransformer according to the present invention, in which two flat coils each having a structure that spiral-patterned conductors 1 are, as shown in Fig. 3A, formed on both surfaces of a substrate 2 and electrically connected to each other by a thru-hole 3 provided in the ventral part of the substrate, are piled in the longitudinal direction to form a laminated flat coil. The two flat coils are electrically connected to each other as shown in Fig. 8, a hole is bored through each substrate in the central part thereof where the spiral-patterned conductors are not present. The thus laminated flat coils are used as the primary and secondary coils 9 and 10 and are juxtaposed.

A magnetic material 4 is provided around the primary and secondary coils 9 and 10 and loaded in the holes as bored.

When the two coils each formed of finepatterned thick film conductors on an insulating substrate are united in one body so that mutual induction is generated between the coils, smallsized transformers with high performances can be obtained with high manufacturing accuracy.

Fig. 14 shows another embodiment in which a plurality of flat coils are juxtaposed in a plane.

Each of the flat coils have a structure that spiralpatterned conductors are, as shown in Fig. 3A or 3B, formed on both sides of an insulating substrate and connected to each other at their inner ends by the thru-hole connection. The lead terminal on the back side of a flat coil is connected by the thru-hole connection to the lead terminal on the front side of the next flat coil. A magnetic material (not shown) is provided on the back and front sides of the flat coils.

Fig. 1 5 shows the case where a plurality of spiral-patterned conductors are juxtaposed on each of back and front sides of a cylindrical substrate. In the present invention, a spiralpatterned conductor is usually formed on a flat substrate, but may be formed on various kinds of surfaces according to the needs. Two such cylindrical substrates may be combined co-axially to allow signal transformation or electro-magnetic signal transmission.

General aspects of the present invention will be explained below. A chip structure of providing external electrodes on the outside of the magnetic material, enhances the packing density and facilitates the automatic mounting. Such a chip structure is specifically desired when the present microcoil or microtransformer is used in a hybrid circuit.

A plurality of flat coils each having spiralpatterned flat conductors may be piled depending on the application, and the flat coils thus piled are electrically connected to each other by the thruhole connection or stepped connection. In this case, the parallel connection of the flat coils is used mainly to decrease the d.c. resistance, and the series connection of the flat coils is used mainly to increase the inductance. The abovementioned parallel connection and series connection are made so that electric current flows through all the flat coil in the same direction of clockwise or counter-clockwise.

Fig. 7 shows a coil assembly in which two flat coils are arranged in the longitudinal direction and mutual induction is generated between the two flat coils. In this structure, the flat coils form two inductive circuits which are electrically independent of each other, and thus form a transformer structure. In order to establish mutual inductance between two flat coils, the two flat coils may overlap each other, or may be placed side by side.

By the above arrangements of the two flat coils small-sized, large-coupling-coefficient microtransformer can be obtained.

The spiral-patterned flat conductor used in the present invention may be any conductive material. Preferable materials are silver, gold, copper, nickel, tin and others. Copper is most preferable from the view points of conductivity and economy. The width of conductor, the spacing between parallel parts of conductor, and the thickness of conductor have significant relation with the characteristics of microcoil. It is preferable that the width and thickness of conductor are made as large as possible and the spacing between parallel parts of conductor is made as small as possible to provide a high mounting density as far as electrical insulation between adjacent conductors is insured.In order to obtain a small-sized high-performance microcoil, it is required to make the thickness of conductor as large as possible for the purpose of decreasing the d.c. resistance, since the width of conductor and the wiring density are related to each other.

However, the dimensions of conductor meeting the above requirements are restricted to the fabrication processes. The range of the width of conductor is 20-200 pm, preferably 40-200 pm, the range of the interconductor spacing is 0.5-100 pm, preferably 1-60 pm, and the range of the conductor thickness is 1 5--400 pm, preferably 35--400 pm.

The spiral-patterned flat conductor can be formed by electroplating using a high cathode current density. The spiral-patterned flat conductor is not always required to be formed on an insulating substrate, but it is preferable to form the conductor on the insulating substrate for the convenience of handling.

The insulating substrate may be ceramic, ferrite, glass, polymer film, or a metal plate coated with an insulating thin film. In the case where a plurality of insulating substrates each provided with a spiral-patterned flat conductor are piled, the polymer film is especially preferable. Any polymer film such as polyester film, epoxy film, polyimide film, polyamide-imide film, polyparabanic acid film, or triazin film can be used. The polyimide film, polyamide-imide film, polyparabanic acid film and triazin film are preferable for their flexibility and heat resistance.

In order to obtain a small-sized, high-performance microcoil, it is preferable to make the thickness of polymer film as small as possible, since the high inductance and high timing thinning characteristics of the microcoil are affected by a conductor mounting density in the transverse area of the microcoil assembly. A preferable range of film thickness is 5-200 pm, more preferably 10-150pm.

In order to more improve the reliability, the entire surface of the coil conductor is coated with an insulating layer made of polymer such as polyimide, polyamide-imide, epoxy resin, phenol resin, or polyurethane, if necessary.

When the spiral-patterned flat conductor is formed on the insulating substrate, the conductor may be formed on one surface of the insulating substrate. However, it is preferable to form the spiral-patterned flat conductor on both surfaces of the insulating substrate as shown in Fig. 4. In this case, it is required that a hole is bored through the insulating substrate and two spiral-patterned flat conductors are electrically connected to each other by the thru-hole connection. In the case where a plurality of spiral-patterned conductors are formed on a single insulating substrate as shown in Figs. 14 and 15, it is preferable to form spiral-patterned conductors on both surfaces of the insulating substrate and to electrically connect a spiral-patterned conductor on one surface to a spiral-patterned conductor on the other surface by the thru-hole connection.

As required, a plurality of flat coils each having a structure that spiral-patterned flat conductors are formed on an insulating substrate, may be piled. In this case, the flat coils are piled through an insulating layer, and are electrically connected so that electric current flows through all the coils in the same rotatational direction. When the flat coils are piled, they are adhered to each other by the thermo-compression bonding using an insulating adhesive material. The insulating adhesive material is preferably a material having high heat resistance, high humidity resistance and high adhesive force such as polyester-isocyanate resin, phenol resin-butyral, phenol resin-nitrile rubber, epoxy-nylon, or epoxy-nitrile rubber. As has been previously mentioned with respect to the thickness of insulating substrate, the characteristic of the laminated structure formed by piling fiat coils is affected by the conductor mounting density in the cross-sectional area of the laminated structure. Therefore, it is preferable to make the thickness of insulating adhesive material as small as possible. However, when this thickness is made too small, the adhesive force is decreased and insulation is deteriorated.

Accordingly, a preferable range of thickness of insulating adhesive material is 1-50m, more preferably 5-30 ,um.

The electrical connection between flat coils in a laminated structure may be made by a thru-hole connection, in which a thru-hole is provided in an electrode portion of the laminated structure and is filled with a conductive material such as solder or conductive paste, or electroplated with a conductive material to connect the flat coils.

Alternatively, the connection may be made by a stepped connection, in which a recess is formed at an electrode portion of the laminated structure and is filled with a conductive material such as solder or conductive paste to connect the flat coils.

In order to generate mutual induction between flat coils, the flat coils are arranged in the longitudinal or transverse direction. In this case, it is required that they are electrically independent of each other. When the flat coils are required to produce mutual induction therebetween, they may be united in one body by an insulating adhesive material, or may be separately fixed after concentrically arranged or juxtaposed.

The magnetic material used in the present invention may be any ordinary magnetic material, for example, pure iron, silicon steel, iron-cobalt alloy, iron-nickel alloy, iron-aluminium alloy, ironaluminium-silicon alloy, and metal oxides such as Mn-Zn ferrite, Ni-Zn ferrite, Cu-Zn ferrite, ferroxplana and garnet. The ferrite is most preferable. The magnetic material is required to have high saturation magnetization, high magnetic Curie temperature, temperatureimmunity, low coercive force, high magnetic permeability, and small high-frequency loss.

The magnetic material is provided at least on the upper and lower surfaces of a flat coil or laminated structure in such a manner that a thin plate made of magnetic material is sticked on each surface with an insulating adhesive material, that the surfaces are coated with a magnetic paste obtained by dispersing powders of the magnetic material in a resin, or that the surfaces are plated with the magnetic material. Further, these methods may be combined.

A microcoil having satisfactory characteristics can be obtained oniy by providing the magnetic material on the upper and lower surfaces of a flat coil or laminated structure. It is preferable to form a closed magnetic circuit as shown in Fig. 6B for the purpose of improving the characteristic of the microcoil. It is a feature of the present invention that such a closed magnetic circuit can be readily formed.

A microcoil according to the present invention is small in size, and has an excellent performance and high reliability. In other words, the present invention provides a microcoil and microtransformer for use in a hybrid circuit which are small in size, high in inductance, and low in d.c. resistance. Further, the present invention provides a rotary transformer for VTR which requires a high coupling coefficient, a triggering transformer for triac, various resonators, a high frequency filter, and the like.

The spiral-patterned conductor used in the present invention can be formed by the techniques disclosed in our copending patent application no. 8041120 published as GB2066583A. In this copending application it is proposed that, after a thin film conductor having a thickness of 0.1 to 1 0 ,um has been formed, a conductive material is electroplated on the thin film conductor using a cathode current density of not less than 5A/dm2 to obtain a fine-patterned thick film conductor having a density of not less than 3 conductor lines/mm, preferably not less than 5 conductor lines/mm.

In order to make the embodiments of the present invention more clear, specific examples will be explained below although the invention is not limited to these examples but various modifications can be made.

Example 1 A thin ferrite plate having a thickness of 0.5 mm was surface treated and electroless plated with copper (to a thickness of 5,us). Then, a desired spiral pattern was formed by the photoetching technique. Thereafter, copper was plated to a thickness of 65 ym using a Harshaw Murata pyrophosphoric acid copper plating bath under the condition of a cathode current density of 1 4 A/dm2 to form a spiral-patterned conductor having a conductor width of 72 ssm, a conductorto-conductor spacing of 8 ,um, a conductor thickness of 70 ,"m and the number of turns equal to 25. For the patterning the method according to the above-referenced-application was used.Then, another thin ferrite plate having a thickness of 0.5 mm was attached on the upper surface of the spiral-patterned conductor with an epoxy adhesive material to form a microcoil assembly.

The microcoil assembly has a size of 4.5x4.5x1.1 mm. The resulting microcoil had an inductance of 39.0,us and a d.c. resistance of 1 .02. The inner end of the spiral-patterned conductor was connected to a lead electrode through a thru-hole provided in one thin ferrite plate, and the outer end was connected directly to another lead electrode.

Example 2 On both sides of Esso Chemical polyparabanic acid film "Tradron" having a thickness of 25 ,um as a substrate, phenol resin-nitrile rubber adhesive material "XA-564-4" prepared by Bostik Japan Co. was applied to have a dried thickness of 5 ym on each side. Then a thru-hole was punched, and copper was evaporated to form a thin conductive layer having a thickness of 0.3 Mm. Then, a resist film was formed on areas other than a desired spiral-patterned area by the photoresist technique.Thereafter, copper was electroplated on the above desired area to a thickness of 50 ,um using a Harshaw-Murata pyrophosphoric acid copper plating bath under the condition of a cathode current density of 7 A"dm2. Then, the resist film was removed off and the thin conductive layer on the areas other than the desired area was etched away. Thus, a spiralpatterned conductor having a conductor width of 85,us, a conductor-to-conductor spacing of 15 a a conductor thickness of 50 ,um and the number of turns equal to 20 was formed on each side of the film substrate, and respective inner ends of the spiral-patterned conductors on both sides of the film substrate were connected to each other by a thru-hole connection.Thereafter, a hole was bored through the film substrate at the inner ends of the spiral patterns. A magnetic paste containing 8 parts of ferrite powder and 2 parts of epoxy resin by weight was put in the above hole and applied around the spiralpatterned conductors, and then hardened to form a microcoil assembly. The resulting microcoil assembly had dimensions of 4.7 mm x4.7 mmxO.5 mm and exhibited an inductance of 100 ,uH, and a d.c. resistance of 1.94 Q.

Example 3 On both sides of Esso Chemical polyparabanic acid film "Tradron" having a thickness of 25 ,am as a substrate, phenol resin-nitrile rubber adhesive material "XA-564-4" prepared by Bostik Japan Co. was applied to have a dried thickness of 5 ,um on each side. Then, Perstorp very thin copper foil "40E5" of a structure that a 5-,um thick copper layer was formed on a 40-,um thick aluminium foil was adhered on each surface of the film substrate by the thermocompression bonding. Aluminium was etched away, and then the copper layer was etched by the photoetching technique to form a desired spiral pattern. Further, a thru-hole was provided in the film.Thereafter, copper was electroplated to a thickness of 125 ,um using a Harshaw-Murata pyrophosphoric acid copper plating bath under the condition of a cathode current density of 14 A/dm2. Thus, a spiral-patterned conductor having a conductor width of 120,am, a conductor-to conductor spacing of 5 ,um a conductor thickness of 130 ,um and the number of turns equal to 16 was formed on each side of the film substrate, and the spiral-patterned conductors on both sides of the film substrate were electrically connected to each other by a thru-hole connection. Then, the conductor-pattern film substrate was applied with the insulating material "XA-5644", subjected to an activation treatment, and then electroless plated with nickel.Thereafter, an iron-nickel alloy acting as the magnetic material was electroplated, so that the above structure was enclosed by an iron-nickel layer as shown in Fig.

5. The conductor pattern is electrically isolated from the iron-nickei layer with the "XA-564- 4" layer. The resulting microcoil assembly had an inductance of 64.0,uH and a d.c. resistance of 0.42Q.

Example 4 A thin ferrite substrate having a thru-hole and a thickness of 0.5 mm was surface treated, and then both surfaces of the substrate were electroless plated with copper (to a thickness of 5 yam). Thereafter, each copper layer thus formed was etched by the photoetching technique to form a desired spiral pattern, and then copper was electroplated to a thickness of 65 ,um using a Harshaw-Murata pyrophosphoric acid copper plating bath under the condition of a cathode current density of 14 A/dm2.Thus, a spiralpatterned conductor having a conductor width of 75 ym, a conductor-to-conductor spacing of 5 ym, a conductor thickness of 70 um and the number of turns equal to 10 was formed on each side of the substrate, and the spiral-patterned conductors on both sides of the substrate were electrically connected to each other by the thruhole connection, to produce a flat coil as a subassembly. Two flat coils were prepared.

Phenol resin-nitrile rubber adhesive material "XA--5644-4" prepared by Bostik Japan Co.

was applied to one of the flat coils to a dried thickness of 20 ym. Thereafter, two flat coils were piled through the above-mentioned adhesive material, and adhered to each other by the thermo-compression bonding to form a laminated structure of flat coils. Then, a thru-hole was provided at a connecting portion of the laminated structure and filled with solder so that the flat coils were electrically connected in series and electric current could flow through the flat coils in the same direction. Thereafter, a ferrite plate having a thickness of 0.5 mm was adhered to each side of the laminated structure with an epoxy adhesive material to sandwich the laminated structure. The resulting microcoil assembly exhibited an inductance of 100 ,uH and a d.c. resistance of 0.96 Q.

Example 5 A phin ferrite substance having a thru-hole and a thickness of 0.5 mm was surface treated, and then both surfaces of the substrate were electroless plated with copper to a thickness of 5 ,um. Thereafter, each copper layer thus formed was etched by the photoetching technique to form a desired spiral pattern, and then copper was electroplated to a thickness of 75 ,um using a Harshaw-Murata pyrophosphoric acid copper plating bath under the condition of a cathode current density of 14 A/dm2. Thus a spiral patterned conductor having a conductor width of 75 ,um, a conductor-to-conductor spacing of 5 a a conductor thickness of 80 ,um and the number of turns equal to 20 was formed on each side of the substrate, and the spiral-patterned conductors on both sides of the substrate were electrically connected to each other by the thru hole connection to thereby produce a flat coil as a subassembly. Two flat coils were prepared.

Phenol resin-nitrile rubber adhesive material "XA05644" prepared by Bostik Japan Co. was applied to one of the flat coils to a dried thickness of 20 ym. Thereafter, two flat coils were piled through the adhesive material, and were then adhered to each other by thermo-compression bonding to form a laminated coil structure. Then, a thru-hole was provided at a connecting portion of the laminated coil structure and filled with solder, so that the flat coils are electrically connected in series and electric current could flow through the flat coils in the same direction.

Thereafter, two laminated structures each made in the above-mentioned manner were placed side by side in two ferrite cores, which faced each other and each of which has a U-shaped cross section. Then, the laminated structures were adhered to the ferrite cores with a magnetic paste containing 8 parts of ferrite powder and 2 parts of epoxy resin by weight, and a thru-hole provided at a central portion of each laminated structure was filled with the magnetic paste to form a highperformance microtransformer (Fig. 13). Each of the primary and secondary coils of the microtransformer had an inductance of 400 yH and a d.c. resistance of 2.39Q.

Example 6 On both sides of Esso Chemical polyparabanic acid film "Tradron" having a thickness of 25 ,um as a substrate, phenol resin-nitrile rubber adhesive material "XA-564-A" prepared by Bostik Japan Co. was applied to have a dried thickness of 5 m on each side. Then, Perstorp very thin copper foil "40E5" (having a structure that a 5-,am-thick copper layer was formed on a 40-,um-thick aluminum foil) was bonded to each surface of the film by thermo-compression bonding. Aluminum was etched way, and then the copper layer was etched by photo-etching techniques to form a desired spiral pattern. A thru-hole was provided in the film substrate.

Thereafter, copper was electroplated to a thickness of 1 25 ,um using a Harshaw-Murata pyrophosphoric acid copper plating bath under the condition of a cathode current density of 14 A/dm2. Thus, a spiral-patterned conductor havinga conductor width of 120 ,um, a conductorto-conductor spacing of 5 ,um a conductor thickness of 130 ,um and the number of turns equal to 15 was formed on each side of the film substrate, and the spiral-patterned conductors on both sides of the film were electrically connected to each other by the thru-hole connection to form a flat-coil in the form of subassembly.

Further, other three flat coils each having the above-mentioned structure were prepared. The adhesive material "XA-564-4" was applied to each side of one of the flat coils to a dried thickness of 20 ym. Thereafter, three flat coils were piled through the above adhesive material, and were then adhered to each other by thermocompression bonding to form a laminated structure. Then, thru-holes were provided at connecting portions of the laminated structure and filled with Epoxy Technology conductive paste "Epotec H-3 1 D", so that the flat coils were connected in series and electric current could flow through these flat coils in the same direction. Then, the conductive paste was hardened by heating.

The above-mentioned single flat coil and threelayered laminated structure were pierced with a hole at their central portion, and were then piled in two ferrite cores, which faced each other and each of which had an E-shaped cross section.

Then, the single flat coil and laminated structure were adhered to the ferrite cores with a magnetic paste containing 8 parts of ferrite powder 2 parts of epoxy resin by weight, to form a microtransformer (Figs. 11 and 12). The resulting microtransformer exhibited a high coupling coefficient, that is, a coupling coefficient of 0.99.

Claims

1. A microcoil assembly comprising: at least one spiral-patterned flat conductor having a conductor width of 20 to 200 ym, a conductor-to-conductor spacing of 0.5 to 100 ym and a conductor thickness of 1 5 to 400 m and forming a microcoil; members of a magnetic material provided on at least upper and lower sides of said spiralpatterned flat conductor, said members being integrally formed in close proximity or directly with said spiral-patterned flat conductor; and electrode lead means connected respectively to inner and outer ends of said spiral-patterned flat conductor for providing electrodes of the microcoil.

2. A microcoil assembly according to Claim 1, wherein said spiral-patterned flat conductor is formed on an insulating substrate.

3. A microcoil assembly according to Claim 1 or 2, wherein said spiral-patterned flat conductor is covered with an adhesive insulating layer.

4. A microcoil assembly according to Claim 1 or 2, wherein a plurality of spiral-patterned flat conductors are arranged in close proximity to each other with an insulating layer therebetween, and said lead means of one of said spiralpatterned flat conductors are separated from said lead means of the other spiral-patterned flat conductor.

5. A microcoil assembly according to Claim 1 or 2, wherein said spiral-patterned flat conductor is copper.

6. A microcoil assembly according to Claim 1 or 2, wherein said magnetic material member is ferrite.

7. A microcoil assembly according to Claim 2, wherein said insulating substrate is a polymer film.

8. A microcoil assembly according to Claim 1 or 2, wherein said magnetic material member includes the electrode on its outer surface.

9. A microcoil assembly according to Claim 1 or 2, wherein a plurality of the spiral-patterned flat conductors having the same structure are piled, and wherein respective inner ends of said spiral-patterned flat conductors are connected to each other or respective outer ends of said spiralpatterned flat conductors are connected to each other so that electric current flows through said spiral-patterned flat conductors in the same direction.

10. A microcoil assembly according to Claim 9, wherein said spiral-patterned flat conductors which are piled, are electrically connected to each other by a thru-hole connection.

11. A microcoil assembly according to Claim 9, wherein said spiral-patterned flat conductors which are piled, are electrically connected to each other by a stepped connection.

12. A microcoil assembly according to Claim 2, wherein said spiral-patterned flat conductor is formed on each side of said insulating substrate so that said spiral-patterned flat conductor formed on one side and said spiral-patterned flat conductor formed on the other side are concentrically arranged but are 1 800 out of phase with each other, and respective inner ends of said spiral-patterned flat conductors are electrically connected to each other by thru-hole connection.

13. A microcoil assembly according to Claim 12, wherein said concentrically arranged spiralpatterned flat conductors are used as one coil unit, and a plurality of coil units are juxtaposed.

14. A microcoil assembly according to Claim 13, wherein said coil unit has first and second outer lead terminals on one of two sides of said insulating substrate, and wherein said first terminal is an outer end of said spiral-patterned flat conductor formed on said side and said second terminal is connected by the thru-hole connection to an outer end of said spiralpatterned flat conductor formed on the other side.

15. A microcoil assembly comprising: (a) an insulating substrate; (b) a pair of spiral-patterned flat conductors formed on both sides of said insulating substrate, each of said spiral-patterned flat conductors having a conductor width of 20 to 200 ym, and a conductor-to-conductor spacing of 0.5 to 100 ym and a conductor thickness of 1 5 to 400 ym, said spring-patterned flat conductors being concentrically aligned, respective inner ends of said spiral-patterned flat conductors being connected to each other so that spiral-patterned flat conductors extends in the forward direction through said inner ends to provide a microcoil; (c) external lead terminals given respectively by outer ends of said spiral-patterned flat conductors; and (d) a magnetic material covering said spiralpatterned flat conductors and inserted into a thruhole, said thru-hole being provided in said insulating substrate at a portion thereof near said inner ends.

16. A microcoil assembly according to claim 1, substantially as described herein with reference to any one of the Figures of the accompanying drawings.

17. A microcoil assembly according to claim 1, substantially as described in any one of the Examples.

18. A hybrid circuit comprising a microcoil assembly according to any one of claims 1 to 1 7.