JPH11204337A - Planar coil and planar transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and high-performance planar coil with a small DC resistance and a high-performance transformer by making a coil conductor large in larger thickness and making each lines constituting the coil conductor small in interval. SOLUTION: A plurality of coil conductor lines 3, 3' and 3" with a thickness of 50 to 400 μm are provided on one surface or both surfaces of an insulation substrate 1 with an aspect ratio (H/G) of 1 or more in the cap part, and a planar coil is covered with a metallic plating thin-film layer 2 on its surface as desired. The coil conductor lines 3, 3' and 3" have a mushroom-like cross section, where a width L of a head part thereof is two times or more than that a width 1 of a neck part, 1.5 times or less than a height H of the head part and two times or more than a minimum distance G between the coil conductor lines 3, 3' and 3". The planar coil is stacked in plural number via an insulation film interposed, and the entire body is made tight by a thin ferromagnetic core, to form a planar transformer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar coil and a planar transformer, and more particularly to a planar coil and a planar transformer operating with a small power of 10 W or less.

[0002]

2. Description of the Related Art A planar coil is widely used as a power source or a signal source for a two-axis actuator of a digital audio disk or an artificial satellite. By the way, recently, as the demand for precision parts for planar coils has increased, it has been demanded that a plurality of so-called high-aspect conductor patterns having a narrow width and a large thickness, formed in parallel at a narrow interval, are required. It has become Heretofore, such a planar coil has been formed by applying a conductive thin film on an insulating substrate, applying a negative photoresist layer thereon, forming a resist pattern according to a conventional method, and etching the conductive thin film. Is etched, and then the resist pattern is removed.

[0003] However, in the planar coil obtained in this manner, when the conductor thin film is etched, the etchant enters the portion covered with the resist pattern, and the conductor in that portion is also dissolved and removed. The cross section of the conductor is trapezoidal, and the interval between the coil patterns is inevitably increased.

In order to improve such a drawback, a method has been proposed in which a thick conductive film is selectively applied to a conductive thin film by utilizing the difference in electric resistance between the insulating substrate and the conductive thin film (Japanese Patent Application Laid-Open No. H11-163873). Japanese Patent Application Laid-Open No. 58-12315), the plating underlayer is thin, especially when a spiral pattern is formed, the wiring resistance of the underlayer increases, the plating current cannot be increased, and the plating growth rate has anisotropy. Therefore, the thickness of the conductor pattern cannot be increased.

In addition, after a metal thin film is provided on the entire surface of an insulating substrate and a thick resist pattern is formed thereon,
It is also known to form a high-aspect conductor by pattern plating, remove the resist, and then remove the metal thin film between the lines by dry etching such as ion milling. However, the thickness of the resist is at most 50 μm. Since this is the limit, the thickness of the conductor pattern is only about 40 μm. As described above, in the conventional planar coil, it is difficult to increase the layer thickness of the coil conductor itself, and since the conductor pattern is formed by etching, the interval between the filaments constituting the coil conductor is limited by the layer thickness of the coil conductor. Since the limit is about twice as large as the above, the space factor of the coil conductor portion in the spatial sense is low, the DC resistance is inevitably increased, and good electrical characteristics cannot be obtained.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a high-performance flat coil having a small DC resistance and a small DC resistance by increasing the layer thickness of the coil conductor and narrowing the distance between the wires forming the coil conductor. The purpose is to provide a high-performance transformer used.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to obtain a high-performance planar coil. As a result, it has been found that each filament of the coil conductor is grown anisotropically to form a mushroom-shaped cross section. By this, it was found that the height of the coil conductor can be formed at 50 μm or more and the interval between the filaments can be formed at 20 μm or less, and therefore, the apparent space factor can be increased to improve the electrical characteristics. The present invention has been made based on the findings.

That is, according to the present invention, a plurality of coil conductor wires having a thickness of 50 to 400 μm are provided on one or both surfaces of an insulating substrate at an aspect ratio (H / G) of a gap portion of 1 or more, and the surface thereof is optionally formed. In a planar coil covered with a metal plating thin film layer, the coil conductor has a mushroom-shaped cross section, and the head width (L) of the cross section is twice or more the neck width (l), A planar coil, wherein the planar coil is 1.5 times or less the height (H) and at least twice the minimum distance (G) between the coil conductors, and the planar coil is interposed by an insulating film. And a flat transformer formed by stacking a plurality of thin ferromagnetic cores and sandwiching the whole with a thin ferromagnetic core.

[0009]

Next, the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an enlarged partial cross-sectional view of a planar coil according to the present invention, in which coil conductor wires 3, 3 ', 3 "... Are provided in parallel on an insulating substrate 1 via a metal thin film layer 2. Each of the filaments has a mushroom-shaped cross section composed of a head 4 and a neck 5, and the width (L) of the head is twice or more, preferably 2 to 5 times, the width (l) of the neck. 1.5 times or less of the height (H), preferably 0.5 to 1.
It is necessary to be 5 times, more than 2 times, preferably 4 to 10 times, the minimum distance (G) between the coil conductor wires.

FIG. 2 shows an example of a method of manufacturing a planar coil according to the present invention. First, a through hole 7 is formed on a disc-shaped insulating substrate 1 and then a metal plating thin film layer 2 is formed on the substrate.
Is formed, and a structure having the photoresist pattern layer 6 formed thereon is formed (a). Next, the same metal as this is preferably subjected to bright electroplating with a focus on a portion where the metal plating thin film layer 2 is exposed, so that the filaments 3, 3 ', 3 "having a mushroom-shaped cross section are formed. Next, after the remaining resist is stripped (c), selective etching is performed to remove only the metal plating thin film layer between the lines (d). After the high aspect plating, if desired, a protective metal is plated to cover the surface of the coil conductor wire.

Thus, the photoresist layer is removed,
When performing bright electroplating centering on the part where the metal plating thin film layer is exposed in the coil pattern, if the plating conditions are appropriate, the growth rate in the height direction will be greater than the growth rate in the width direction, and Expands to form a mushroom-shaped coil conductor strip having a small DC resistance even in a single treatment.

In this case, the plating conditions include the composition of the plating bath,
Although it depends on the shape of the plating tank and the stirring conditions of the bath, the optimum conditions can be easily selected by repeating preliminary tests. Regarding the current density at this time, anisotropic growth is performed at 70% or more of the limit current density.

At this time, the width of the neck portion of each wire of the coil conductor is first determined by taking the width of the exposed metal thin film on the resist pattern into consideration in consideration of the resolution of the resist and the strength when the coil conductor is formed. After examining the plating conditions for this pattern, setting the conditions with the largest aspect ratio, and growing it to a predetermined thickness, measure the minimum value of the interval between the filaments, Is adjusted by increasing the width of the exposed metal thin film on the resist pattern by a value obtained by subtracting.

The plating bath at this time is not particularly limited as long as it is a bright plating bath of a metal having a low resistance. In the case of a matte plating bath, the interval between the filaments of the coil conductor is narrow. If this happens, it will not be possible to use it because it will cause a short between the filaments.

The following can be considered as a reason why a coil having a large aspect ratio can be obtained in the planar coil of the present invention. That is, in the through-hole plating, when the aspect ratio of the hole is large, the film thickness in the hole becomes smaller than the external film thickness, and this tendency becomes more remarkable as the aspect ratio becomes larger. Even when formed by bright plating, similar development occurs, and plating grows isotropically at first, but as the film thickness increases, the aspect of the groove increases and anisotropic growth occurs. It is performed, and the head is formed,
This tendency is gradually promoted, and the aspect ratio is further increased. FIG. 3 is a plan view showing an example of the planar coil of the present invention. In this figure, the coil pattern is formed in a circular spiral shape. Any shape used in a conventional planar coil such as a spiral shape or a polygonal line shape can be adopted. The planar coil thus obtained can be used while being sandwiched between thin ferromagnetic cores. As this thin ferromagnetic core, for example, NiZ having a thickness of 1.2 mm is used.
An n-type ferrite or the like is used.

Next, by stacking a plurality of the planar coils of the present invention via an insulating film and sandwiching the whole with a thin ferromagnetic core, a planar transformer having extremely excellent electric characteristics can be obtained. . In this case, a plastic film such as a polyester film having a thickness of 0.05 mm is suitable as the insulating film, and the same thin film ferromagnetic core as described above can be used.

[0017]

Next, the present invention will be described in more detail by way of examples.

Example 1 The following process was performed to manufacture 284 coils on a 3-inch substrate. That is, a through hole having a diameter of 0.2 mm was formed at a predetermined position on an unclad FR4 substrate (thickness: 100 μm), and 1 μm was formed on both surfaces thereof using an electroless copper plating solution.
The thickness of the copper layer was formed. A positive photoresist was spin-coated thereon to a dry film thickness of 5 μm. Next, at the same time as removing the resist around the through hole and forming the coil portion, the resist pattern width 9 was used.
0 μm, resist pattern interval (line width of exposed conductor)
A 20 μm pattern was formed by photolithography. Here, the through holes are used to connect the copper layers on both sides. The pattern of the resist removal portion serving as the coil portion is a circular spiral shape, the innermost radius is 0.9 mm, and the number of turns is 11.5. This was plated in a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 70 g / l, and the temperature of the solution is 25 ° C. Place a pipe with a small hole near the cathode, and apply plating solution 20m from here
The plating was performed at a current density of 2.5 A / dm ² until the film thickness reached 150 μm. The conductor spacing at this time was 10 μm. Next, the resist was peeled off, the underlying copper film was etched by ion milling to form a coil conductor, and then cut into a single planar coil. The 284 planar coils thus obtained each have an outer dimension of 3.1 × 3.1 × 0.4 mm, a thickness (H) of the coil conductor layer of 150 μm, and an interval between the coil conductor wires. (G) is 10 μm, head width (L) is 100 μm, neck width (l) is 20 μm, L / l ratio is 5, L / H ratio is 0.
67, L / G ratio was 5. The electrical characteristics of this device are DC resistance 0.1Ω, inductance value 0.37μ.
H. For comparison, a coil having the same pattern was formed by a normal method of manufacturing a printed wiring board using a FR4 substrate having a thickness of 100 μm and a copper foil of 36 μm attached to both sides. Although the yield was greatly reduced due to the fine pattern, the DC characteristics were 1.1 Ω and the inductance value was 0.37 μH when the electrical characteristics of good products were measured. The external dimensions are 3.1 × 3.1 × 0.2 mm. From this, the planar coil of the present invention has a DC resistance that is 1/10 that of a coil manufactured by a normal printed wiring board manufacturing method.
It can be seen that the following can be done.

COMPARATIVE EXAMPLE In Example 1, a coil having a conductor having the same cross-sectional neck width as the head width was formed by pattern plating. That is, an underlying copper film was formed on the same substrate in the same manner as in Example 1, and a thickness of 35 μm and a width of 10 μm
Was formed, and a 30 μm-thick plating was applied to the resist pattern under the same conditions as in the example. This was repeated five times, the resist was peeled off, and the underlying copper film between the conductors was etched by ion milling to form a coil having a cross-section having the same neck width as that of the head in Example 1 on one side. At this time, the warpage of the substrate was 1.2 mm. On the other hand, a coil was formed only on one side by the same method as in Example 1, and the warpage of the substrate was measured to be 0.25 mm. It can be seen that the amount of warpage of the substrate is reduced to 1/5 by making the neck thinner.

Example 2 A through hole having a diameter of 0.2 mm was provided at a predetermined position on the same unclad FR4 substrate as used in Example 1,
A copper layer having a thickness of 1 μm was formed on both surfaces with an electroless copper plating solution. On top of that, a positive photoresist is dried at a thickness of 5 μm.
m, and spin the resist pattern width 1
A pattern with a resist pattern interval of 10 μm and a line width of the resist pattern (line width of the exposed conductor) of 20 μm was formed by photolithography. Here, the through holes are used to connect the copper layers on both sides. The pattern of the resist removal part that becomes the coil part is a circular spiral shape, and the innermost radius is 0.9 mm.
And the number of turns is 11.5. This was plated in a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 70 g / l, and the temperature of the solution is 25 ° C. Place a pipe with a small hole near the cathode, and apply plating solution from here
The plating was performed at a current density of 2.5 A / dm ² until the film thickness reached 200 μm. The conductor spacing at this time was 10 μm. Since the length (L) of the head is 10 μm longer than in the first embodiment, a large conductor height can be obtained. Next, the resist was peeled off, the underlying copper film was etched by ion milling to form a coil conductor, and then cut into a single planar coil. Each of the 284 planar coils thus obtained has an outer dimension of 3.1.
× 3.1 × 0.4 mm, the thickness (H) of the coil conductor layer is 200 μm, the interval (G) between the coil conductor wires is 10 μm, the width of the head (L) is 100 μm, and the width of the neck ( l) is 20 μm, L / l ratio is 5, L / H ratio is 0.5,
The L / G ratio was 10. In addition, the electrical characteristics of this device are DC resistance 0.06Ω, inductance value 0.36μ.
H. For comparison, a coil having the same pattern was formed by a normal method of manufacturing a printed wiring board using a FR4 substrate having a thickness of 100 μm and a copper foil of 36 μm attached to both sides. Although the yield was greatly reduced due to the fine pattern, the DC characteristics were 0.9Ω and the inductance value was 0.37 μH when the electrical characteristics of good products were measured. The external dimensions are 3.1 × 3.1 × 0.2 mm. From this, the planar coil of the present invention has a DC resistance that is 1/10 that of a coil manufactured by a normal printed wiring board manufacturing method.
It can be seen that the following can be done.

Example 3 A through hole having a diameter of 0.2 mm was provided at a predetermined position on the same unclad FR4 substrate as used in Example 1,
A copper layer having a thickness of 1 μm was formed on both surfaces with an electroless copper plating solution. On top of that, a positive photoresist is dried at a thickness of 5 μm.
m and a resist pattern width of 9
0 μm, resist pattern interval (line width of exposed conductor)
A 20 μm pattern was formed by photolithography. Here, the through holes are used to connect the copper layers on both sides. The pattern of the resist removal portion serving as the coil portion is a circular spiral shape, the innermost radius is 0.9 mm, and the number of turns is 11.5. This was plated in a bright high-speed copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 110 g / l
And the liquid temperature is 35 ° C. Place a pipe with a small hole near the cathode, and apply 5 parts of plating solution from here.
It was jetted at 0 mm / sec and plated at a current density of 9 A / dm ² until the film thickness became 150 μm. The conductor spacing at this time was 10 μm. Next, the resist was removed, and the underlying copper film was etched by ion milling to form a coil conductor. The planar coil thus obtained has an outer dimension of 3.1 × 3.1 × 0.4 mm, a thickness (H) of the coil conductor layer of 150 μm, and a gap (G) between the coil conductor wires.
Is 10 μm, the head width (L) is 100 μm, the neck width (l) is 20 μm, the L / l ratio is 5, and the L / H ratio is 0.6.
7, L / G ratio was 5. The electrical characteristics of this device are DC resistance 0.1Ω, inductance value 0.37μH
Met. For comparison, a coil having the same pattern was formed by a normal method of manufacturing a printed wiring board using a FR4 substrate having a thickness of 100 μm and a copper foil of 36 μm attached to both sides. Although the yield was greatly reduced due to the fine pattern, the DC characteristics were 1.1 Ω and the inductance value was 0.37 μH when the electrical characteristics of good products were measured. The external dimensions are 3.1 × 3.1 × 0.2 mm. From this, the planar coil of the present invention has a DC resistance that is 1/10 that of a coil manufactured by a normal printed wiring board manufacturing method.
It can be seen that the following can be done.

Example 4 Ni having a diameter of 3 inches, a thickness of 350 μm, and a relative magnetic permeability of 800
A 1 μm thick copper layer was formed on both surfaces of a Zn-based ferrite substrate using an electroless copper plating solution. A positive photoresist was spin-coated thereon to a dry film thickness of 5 μm, and a pattern having a resist pattern width of 90 μm and a resist pattern interval (line width of exposed conductor) of 20 μm was formed by photolithography. The pattern of the resist removal portion serving as the coil portion is a circular spiral shape, the innermost radius is 0.9 mm, and the number of turns is 5.75. This was plated in a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution was 70 g / l, the solution temperature was 25 ° C., and the current density was 2.5 A / dm ² and the film thickness was 150 μm as in Example 1.
Until plating. The conductor spacing at this time is 10 μm
Met. Next, the resist was removed, and the underlying copper film was etched by ion milling to form a coil conductor. Furthermore, a photosensitive epoxy resin including a gap portion is applied thereon by a curtain coating method, and after a temporary curing, at a predetermined position,
A contact hole was formed by a conventional photolithography method, and this was hardened. Next, the same method as described above was repeated using the photosensitive epoxy resin as an insulating substrate to form a second coil layer, thereby producing a laminated planar coil assembly. One planar coil obtained by dividing this assembly has an outer dimension of 3.1 × 3.1 × 0.7 mm, a thickness (H) of the coil conductor layer of 150 μm, and a space between the coil conductor wires. Are 10 μm, the head width (L) is 100 μm, the neck width (l) is 20 μm, the L / l ratio is 5, and the L / H ratio is 0.1 μm.
67, L / G ratio was 5. The electrical characteristics of this device are DC resistance 0.1Ω, inductance value 0.6μH
Met. This has an inductance value increased by about 50% as compared with the planar coil of the first embodiment.

Example 5 A 1 μm thick copper layer was formed on a 3 inch diameter, 300 μm thick NiZn-based composite ferrite substrate (70 volume% ferrite powder and 30 volume% epoxy resin) with an electroless copper plating solution. . A positive photoresist was spin-coated thereon to a dry film thickness of 5 μm, and a pattern having a resist pattern width of 90 μm and a resist pattern interval (line width of exposed conductor) of 20 μm was formed by photolithography. The pattern of the resist removal portion serving as the coil portion is a circular spiral shape, the innermost radius is 0.9 mm, and the number of turns is 5.75. This was plated in a bright copper sulfate plating bath. The plating was performed at a current density of 2.5 A / dm ² and a film thickness of 150 μm in the same manner as in Example 1 except that the concentration of copper sulfate in the plating solution was 70 g / l and the solution temperature was 25 ° C. The conductor spacing at this time was 10 μm. next,
The resist was removed, and the underlying copper film was etched by ion milling to form a coil conductor. Further, a photosensitive epoxy resin including a gap portion was applied thereon by a curtain coating method, and after provisional curing, a contact hole was formed at a predetermined position by a conventional photolithography method, followed by main curing. Next, the same method as described above was repeated using the photosensitive epoxy resin as an insulating substrate to form a second coil layer, thereby producing a laminated planar coil assembly. One planar coil obtained by dividing this assembly has an outer dimension of 3.1 × 3.
1 × 0.6 mm, and the thickness (H) of the coil conductor layer is 1
50 μm, the interval (G) between the coil conductors is 10 μm,
Head width (L) is 100 μm, neck width (l) is 20 μm
m, L / l ratio is 5, L / H ratio is 0.67, L / G ratio is 1
It was 0. The electrical characteristics of this product were a DC resistance of 0.1Ω and an inductance value of 0.48 μH. This has an inductance value increased by about 30% as compared with the planar coil of the first embodiment.

Example 6 A hole was formed in the center of the coil prepared in Example 1, and the coil was sandwiched between NiZn-based EI type ferrite cores having an outer dimension of 3.2 × 3.2 × 1.3 mm to form a planar coil. did. At this time, the inductance value is 11 μH, and the inductance value is increased about 30 times.

Example 7 A through hole having a diameter of 0.2 mm was provided at a predetermined position on the same unclad FR4 substrate as used in Example 1,
A copper layer having a thickness of 1 μm was formed on both surfaces with an electroless copper plating solution. On top of that, a positive photoresist is dried at a thickness of 5 μm.
m, and spin the resist pattern width 2
A pattern of 00 μm and a resist pattern interval (line width of exposed conductor) of 20 μm was formed by photolithography. Here, the through holes are used to connect the copper layers on both sides. The pattern of the resist removal part that becomes the coil part is a circular spiral shape, and the innermost radius is 0.9 mm.
The number of turns is six. This was plated in a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution was 70 g / l, the temperature of the solution was 25 ° C., and the solution was stirred at a speed of 3 mm / sec with a stroke of 100 mm and a current density of 2.5 A / d.
The plating was performed until the film thickness became 150 μm at m ² . The conductor spacing at this time was 10 μm. Next, the resist was removed, and the underlying copper film was etched by ion milling to form a coil conductor. The external dimensions are 3.1 x 3.1 x 0.
4 mm, and the electrical characteristics were a direct current resistance of 0.05Ω. This was perforated at the center of the planar coil obtained in Example 1 through an insulating film, and then laminated. The whole was coated with a NiZn-based EI type ferrite core having an outer dimension of 3.2 × 3.2 × 1.7 mm. A flat transformer was formed by clamping. The coupling coefficient was 0.95 measured at a frequency of 500 kHz.

REFERENCE EXAMPLE For the coil conductor wire having a head width (L) of 110 μm (A) and 170 μm (B), plating was performed by identifying the conductor wire spacing (G) as 10 μm. ,
(L-1) / 2, that is, the change in the thickness (H) of the conductor was measured by changing the length of the eaves of the mushroom cross section, and the results are shown as a graph in FIG. In this graph, the result of isotropic growth is shown as C for reference. As a result, by increasing the length of the eaves of the overhang portion, the growth rate of the plating in the lateral direction is suppressed.As a result, it is possible to increase the thickness of the conductor while keeping the conductor interval constant. It can be seen that a planar coil having a small DC resistance can be obtained. Also, it is understood that the thickness of the conductor can be increased as the length of the eaves is increased.

[0027]

According to the planar coil of the present invention, the thickness of the conductor can be increased while keeping the interval between the coil conductors small, so that the DC resistance can be reduced. When the transformer is configured, there is an advantage that excellent electrical characteristics are obtained particularly at a small power of 10 W or less.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a planar coil of the present invention.

FIG. 2 is a process chart of an example of a method for manufacturing a planar coil according to the present invention.

FIG. 3 is a plan view showing an example of the shape of the planar coil of the present invention.

FIG. 4 is a graph showing the relationship between the eave length and the conductor height in the planar coil of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 insulating substrate 2 metal thin film layer 3, 3 ′, 3 ″ coil conductor wire 6 photoresist pattern layer 7 through hole

Claims (3)

[Claims] 1. A thickness of 50 to 4 on one or both sides of an insulating substrate.
In a planar coil in which a plurality of coil conductors of 00 μm are provided with an aspect ratio (H / G) of a gap portion of 1 or more,
The coil conductor wire has a mushroom-shaped cross section, and the head width (L) of the cross section is twice or more the neck width (l), 1.5 times or less the head height (H), and A planar coil characterized by being at least twice as long as the minimum distance (G) between each coil conductor wire. 2. The planar coil according to claim 1, wherein the coil conductor wire is covered with a protective metal plating thin film layer. 3. A planar transformer comprising a plurality of the planar coils according to claim 1 or 2 laminated via an insulating film and entirely sandwiched between thin ferromagnetic cores.