JP4046827B2 - Planar coil and planar transformer - Google Patents

Description

[0001]
BACKGROUND 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 that operate with a small power of 10 W or less.
[0002]
[Prior art]
The planar coil is widely used for a power source or a signal for a two-axis actuator of a digital audio disk or an artificial satellite.
By the way, recently, as the demand for precision components of planar coils increases, it is expected that a plurality of so-called high aspect conductor patterns having a narrow width and a large thickness are formed in parallel at narrow intervals. It has become. Until now, such a planar coil has been obtained by depositing a conductive thin film on an insulating substrate, applying a negative photoresist layer thereon, forming a resist pattern in accordance with a conventional method, and then etching the conductive thin film. Are etched, and then the resist pattern is removed.
[0003]
However, in the planar coil obtained in this way, when etching the conductor thin film, the etching solution enters the portion covered with the resist pattern and dissolves and removes the conductor of the portion as a result. It is inevitable that the cross section becomes a trapezoid and the interval between the coil patterns is greatly increased.
[0004]
In order to improve such a defect, a method of selectively plating a conductive thin film using the difference in electrical resistance between the insulating substrate and the conductive thin film has been proposed (Japanese Patent Laid-Open No. 58-86). No. 12315), the plating base film is thin, especially when a spiral pattern is formed, the wiring resistance of the base increases, the plating current cannot be increased, and there is no anisotropy in the growth rate of the plating. The pattern thickness cannot be increased.
[0005]
In addition, a metal thin film is provided on the entire surface of the insulating substrate, a thick resist pattern is formed on the insulating substrate, a high aspect conductor is formed by pattern plating, the resist is removed, and then dry etching such as ion milling is used to remove the gap between the lines. Although a method for removing a metal thin film is also known, the thickness of the resist is limited to 50 μm at the maximum, so that 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 thickness of the coil conductor itself, and a conductor pattern is formed by etching. Therefore, the interval between the filaments constituting the coil conductor is determined by the layer thickness of the coil conductor. Therefore, the space factor in the spatial sense of the coil conductor portion is low, the direct current resistance is inevitably increased, and good electrical characteristics cannot be obtained.
[0006]
[Problems to be solved by the invention]
The present invention provides a high-performance planar coil having a small DC resistance and a high-performance transformer using the same by increasing the layer thickness of the coil conductor and narrowing the interval between the wires constituting the coil conductor. It was made for the purpose.
[0007]
[Means for Solving the Problems]
As a result of intensive research in order to obtain a high-performance planar coil, the present inventor has grown each filament of the coil conductor anisotropically and formed it in a mushroom-like cross section, so that the height of the coil conductor is 50 μm. As described above, it has been found that 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, and the present invention is made based on this finding. It came.
[0008]
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 surface or both surfaces of an insulating substrate with an aspect ratio (H / G) of 1 or more of the gap portion, and the surface is optionally a metal-plated thin film. In a planar coil covered with a layer, the coil conductor wire has a mushroom-shaped cross section, the width (L) of the head of the cross section is 2 to 5 times the width (l) of the neck, and the height of the head The planar coil, which is 0.5 to 1.5 times the length (H) and 4 to 10 times the minimum distance (G) between the coil conductor wires, and the planar coil, an insulating film A planar transformer is provided which is formed by stacking a plurality of layers and sandwiching the whole with a thin ferromagnetic core.
Here, the mushroom-shaped cross section means a shape in which the eaves portion bulges greatly and the leg portion, that is, the neck portion is narrow and short, as shown in FIG.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
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 with a metal thin film layer 2 interposed therebetween. 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 2 to 5 times the width (l) of the neck and the height (H) of the head. 0.5 to 1.5 times, it is necessary that 4 to 10 times the minimum distance (G) between the coil conductor filament.
[0010]
FIG. 2 shows an example of a method for producing a planar coil according to the present invention. First, a through hole 7 is formed on a disk-shaped insulating substrate 1, and then a metal-plated thin film layer 2 is provided on the substrate. Further, a structure in which the photoresist pattern layer 6 is formed is formed (a).
Next, centering on the portion where the metal plating thin film layer 2 is exposed, the same metal as this is preferably subjected to bright electroplating, thereby forming the strips 3, 3 ', 3 "... having a mushroom-like cross section. Form them in parallel (b).
Next, after removing the remaining resist (c), a selective etching process is performed to remove only the metal plating thin film layer between the filaments (d).
In this case, if desired, after the high aspect plating, a protective metal is plated to cover the surface of the coil conductor wire.
[0011]
As described above, when performing bright electroplating around a portion where the photoresist layer is removed and the metal plating thin film layer is exposed in a coil pattern, if the plating conditions are appropriate, the growth rate in the height direction is increased in the width direction. As compared with the growth rate, the plating portion expands, and a mushroom-like coil conductor wire having a low direct current resistance is formed even in a single treatment.
[0012]
The plating conditions at this time depend on the composition of the plating bath, the shape of the plating tank, and the stirring conditions of the bath, but the optimum conditions can be easily selected by repeating preliminary tests. As for the current density at this time, anisotropic growth is performed at 70% or more of the limit current density.
[0013]
In addition, the width of the neck portion of each line of the coil conductor at this time is first selected to be the minimum width of the exposed metal thin film on the resist pattern in consideration of the resolution of the resist and the strength when the coil conductor is formed, We examined the plating conditions in this pattern, set the conditions with the largest aspect ratio, grown to the prescribed film thickness, measured the minimum value of the spacing between each line, and reduced the design value to this The value is adjusted by increasing the width of the exposed metal thin film on the resist pattern.
[0014]
In this case, the plating bath is not particularly limited as long as it is a bright plating bath with a low resistance metal. However, in the case of a matte plating bath, if the spacing between the strips of the coil conductor is narrow, It cannot be used because it is short-circuited.
[0015]
The reason why the planar coil of the present invention has a large aspect ratio can be considered as follows. That is, in through-hole plating, when the aspect ratio of the hole is large, the film thickness in the hole is smaller than the external film thickness, and this tendency becomes more prominent as the aspect ratio increases. In the case of forming by bright plating, similar development occurs, and the plating grows isotropically at the beginning. However, as the film thickness increases, the groove aspect increases and anisotropic growth occurs. However, by forming the head, this tendency is gradually promoted and the aspect ratio increases more and more.
FIG. 3 is a plan view showing an example of a planar coil according to 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 used.
The planar coil thus obtained can also be used by being sandwiched between thin ferromagnetic cores. As this thin ferromagnetic core, for example, a NiZn ferrite having a thickness of 1.2 mm is used.
[0016]
Next, if a plurality of planar coils of the present invention are laminated via an insulating film and the whole is sandwiched between thin ferromagnetic cores, a planar transformer having very excellent electrical characteristics can be obtained.
As the insulating film at this time, a plastic film such as a polyester film having a thickness of 0.05 mm is suitable, and the same thin film as described above can be used as the thin ferromagnetic core.
[0017]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0018]
Example 1
In order to manufacture 284 coils on a 3-inch substrate, the following processing was performed. That is, a through hole having a diameter of 0.2 mm was formed at a predetermined position of an unclad FR4 substrate (thickness: 100 μm), and a copper layer having a thickness of 1 μm was formed on both sides thereof with an electroless copper plating solution.
On top of this, a positive photoresist was spin-coated so as to have a dry film thickness of 5 μm.
Next, at the same time as removing the resist around the through hole, 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 in order to form a coil portion. Here, the through hole is used to connect the copper layers on both sides. The pattern of the resist removal portion that becomes the coil portion is a circular spiral, the radius of the innermost circumference is 0.9 mm, and the number of turns is 11.5.
This was plated with a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 70 g / l, and the solution temperature is 25 ° C. A pipe with a small hole was installed in the vicinity of the cathode, from which a plating solution was ejected at 20 mm / second, and plating was performed at a current density of 2.5 A / dm ² until the film thickness reached 150 μm. The conductor interval at this time was 10 μm.
Next, the resist was peeled off, the base copper film was etched by ion milling to form a coil conductor portion, 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, the thickness (H) of the coil conductor layer is 150 μm, and the spacing between the coil conductor wires. (G) was 10 μm, head width (L) was 100 μm, neck width (l) was 20 μm, L / l ratio was 5, L / H ratio was 0.67, and L / G ratio was 5. . The electrical characteristics of this product were a direct current resistance of 0.1Ω and an inductance value of 0.37 μH.
For comparison, a coil having the same pattern was prepared by a normal printed wiring board manufacturing method using a FR4 substrate having a thickness of 36 μm and a 36 μm copper foil pasted on both sides. Although the yield was greatly reduced due to the fine pattern, the electrical characteristics of the non-defective product were measured to have a DC resistance of 1.1Ω and an inductance value of 0.37 μH. The external dimensions are 3.1 × 3.1 × 0.2 mm.
From this, it can be seen that the planar coil of the present invention can reduce the direct current resistance to 1/10 or less as compared with that produced by the ordinary method for producing a printed wiring board.
[0019]
In Comparative Example 1, a coil in which the width of the neck of the cross-sectional shape of the conductor was the same as the width of the head was formed by pattern plating. That is, a base copper film is formed on the same substrate by the same method as in Example 1, and a resist pattern having a thickness of 35 μm and a width of 10 μm is formed in the gap position of the coil conductor wire, and the thickness is increased under the same conditions as in the Example. A thickness of 30 μm was applied. This was repeated 5 times, the resist was peeled off, and the underlying copper film between the conductors was etched by ion milling. In Example 1, a coil having a cross-sectional shape with the same neck width as the head width was formed on one side. The warpage of the substrate at this time was 1.2 mm. On the other hand, when the coil was formed only on one side by the same method as in Example 1 and the warpage of the substrate was measured, it was 0.25 mm. It can be seen that the amount of warpage of the substrate is reduced to 1/5 by narrowing the neck.
[0020]
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, and a copper layer having a thickness of 1 μm was formed on both sides thereof with an electroless copper plating solution.
A positive photoresist was spin-coated thereon so as to have a dry film thickness of 5 μm, and a pattern having a resist pattern width of 110 μm and a resist pattern interval (line width of exposed conductor) of 20 μm was formed by a photolithography method. Here, the through hole is used to connect the copper layers on both sides. The pattern of the resist removal portion that becomes the coil portion is a circular spiral, the radius of the innermost circumference is 0.9 mm, and the number of turns is 11.5.
This was plated with a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 70 g / l, and the solution temperature is 25 ° C. A pipe with a small hole was installed in the vicinity of the cathode, from which a plating solution was ejected at 20 mm / second, and plating was carried out at a current density of 2.5 A / dm ² until the film thickness reached 200 μm. The conductor interval at this time was 10 μm. Compared with Example 1, the length (L) of the head is 10 μm longer, so that the conductor height can be increased.
Next, the resist was peeled off, the base copper film was etched by ion milling to form a coil conductor portion, 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, the thickness (H) of the coil conductor layer is 200 μm, and the spacing between the coil conductor wires. (G) was 10 μm, head width (L) was 100 μm, neck width (l) was 20 μm, L / l ratio was 5, L / H ratio was 0.5, and L / G ratio was 10. . The electrical characteristics of this product were a DC resistance of 0.06Ω and an inductance value of 0.36 μH.
For comparison, a coil having the same pattern was prepared by a normal printed wiring board manufacturing method using a FR4 substrate having a thickness of 36 μm and a 36 μm copper foil pasted on both sides. Although the yield was greatly reduced due to the fine pattern, the electrical characteristics of the non-defective product were measured to have a DC resistance of 0.9Ω and an inductance value of 0.37 μH. The external dimensions are 3.1 × 3.1 × 0.2 mm.
From this, it can be seen that the planar coil of the present invention can reduce the direct current resistance to 1/10 or less as compared with that produced by the ordinary method for producing a printed wiring board.
[0021]
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, and a copper layer having a thickness of 1 μm was formed on both sides thereof with an electroless copper plating solution.
A positive photoresist was spin-coated thereon so as to have 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 a photolithography method. Here, the through hole is used to connect the copper layers on both sides. The pattern of the resist removal portion that becomes the coil portion is a circular spiral, the radius of the innermost circumference is 0.9 mm, and the number of turns is 11.5.
This was plated with a bright high-speed copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 110 g / l, and the solution temperature is 35 ° C. A pipe with a small hole was installed in the vicinity of the cathode, from which a plating solution was ejected at 50 mm / second, and plating was performed at a current density of 9 A / dm ² until the film thickness reached 150 μm. The conductor interval at this time was 10 μm.
Next, the resist was peeled off, and the base copper film was etched by ion milling to form a coil conductor portion. 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 an interval (G) between the coil conductor wires. The head width (L) was 10 μm, the neck width (l) was 20 μm, the L / l ratio was 5, the L / H ratio was 0.67, and the L / G ratio was 5. The electrical characteristics of this product were a direct current resistance of 0.1Ω and an inductance value of 0.37 μH.
For comparison, a coil having the same pattern was prepared by a normal printed wiring board manufacturing method using a FR4 substrate having a thickness of 36 μm and a 36 μm copper foil pasted on both sides. Although the yield was greatly reduced due to the fine pattern, the electrical characteristics of the non-defective product were measured to have a DC resistance of 1.1Ω and an inductance value of 0.37 μH. The external dimensions are 3.1 × 3.1 × 0.2 mm.
From this, it can be seen that the planar coil of the present invention can reduce the direct current resistance to 1/10 or less as compared with that produced by the ordinary method for producing a printed wiring board.
[0022]
Example 4
On a NiZn ferrite substrate having a diameter of 3 inches, a thickness of 350 μm, and a relative magnetic permeability of 800, a copper layer having a thickness of 1 μm was formed on both sides with an electroless copper plating solution.
A positive photoresist was spin-coated thereon so as to have 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 a photolithography method. The pattern of the resist removal portion to be a coil portion is a circular spiral, the innermost radius is 0.9 mm, and the number of turns is 5.75.
This was plated with a bright copper sulfate plating bath. 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 with a copper sulfate concentration of 70 g / l and a solution temperature of 25 ° C. The conductor interval at this time was 10 μm.
Next, the resist was peeled off, and the base copper film was etched by ion milling to form a coil conductor portion. Further, a photosensitive epoxy resin including a gap portion was applied thereon by a curtain coating method, and after temporary curing, a contact hole was formed at a predetermined position by a conventional photolithography method, followed by main curing. Next, using the photosensitive epoxy resin as an insulating substrate, the same method as described above was repeated to form a second coil layer to produce 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 between the coil conductor wires. The gap (G) is 10 μm, the head width (L) is 100 μm, the neck width (l) is 20 μm, the L / l ratio is 5, the L / H ratio is 0.67, and the L / G ratio is 5. there were. The electrical characteristics of this product were a DC resistance of 0.1Ω and an inductance value of 0.6 μH. This has an inductance value increased by about 50% compared to the planar coil of the first embodiment.
[0023]
Example 5
A copper layer having a thickness of 1 μm was formed with an electroless copper plating solution on a NiZn composite ferrite substrate (70% by volume ferrite powder and 30% by volume epoxy resin) having a diameter of 3 inches and a thickness of 300 μm.
A positive photoresist was spin-coated thereon so as to have 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 a photolithography method. The pattern of the resist removal portion to be a coil portion is a circular spiral, the innermost radius is 0.9 mm, and the number of turns is 5.75.
This was plated with a bright copper sulfate plating bath. 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 with a copper sulfate concentration of 70 g / l and a solution temperature of 25 ° C. The conductor interval at this time was 10 μm.
Next, the resist was peeled off, and the base copper film was etched by ion milling to form a coil conductor portion. Further, a photosensitive epoxy resin including a gap portion was applied thereon by a curtain coating method, and after temporary curing, a contact hole was formed at a predetermined position by a conventional photolithography method, followed by main curing. Next, using the photosensitive epoxy resin as an insulating substrate, the same method as described above was repeated to form a second coil layer to produce 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, a coil conductor layer thickness (H) of 150 μm, and between coil conductor wires. The gap (G) is 10 μm, the head width (L) is 100 μm, the neck width (l) is 20 μm, the L / l ratio is 5, the L / H ratio is 0.67, and the L / G ratio is 10. there were. The electrical characteristics of this product were a direct current resistance of 0.1Ω and an inductance value of 0.48 μH. This has an inductance value increased by about 30% compared to the planar coil of the first embodiment.
[0024]
Example 6
A central portion of the coil prepared in Example 1 was punched and sandwiched between NiZn-based EI type ferrite cores having outer dimensions of 3.2 × 3.2 × 1.3 mm to form a planar coil. The inductance value at this time is 11 μH, and the inductance value increases about 30 times.
[0025]
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, and a copper layer having a thickness of 1 μm was formed on both sides thereof with an electroless copper plating solution.
A positive photoresist was spin-coated thereon so as to have a dry film thickness of 5 μm, and a pattern having a resist pattern width of 200 μm and a resist pattern interval (line width of exposed conductor) of 20 μm was formed by a photolithography method. Here, the through hole is used to connect the copper layers on both sides. The pattern of the resist removing portion to be a coil portion is a circular spiral, the innermost radius is 0.9 mm, and the number of turns is six.
This was plated with a bright copper sulfate plating bath. The concentration of copper sulfate in the plating solution is 70 g / l, the solution temperature is 25 ° C., and the agitation is performed with a cathode lock at a stroke of 3 mm / second, a stroke of 100 mm, a current density of 2.5 A / dm ² and a film thickness of 150 μm. Plated until. The conductor interval at this time was 10 μm.
Next, the resist was peeled off, and the base copper film was etched by ion milling to form a coil conductor portion. The external dimensions were 3.1 × 3.1 × 0.4 mm, and the electrical characteristics were DC resistance 0.05Ω.
This was laminated after punching the central portion of the planar coil obtained in Example 1 through an insulating film, and the whole was formed of a NiZn-based EI type ferrite core having an outer dimension of 3.2 × 3.2 × 1.7 mm. The planar transformer was formed by sandwiching. The coupling coefficient was 0.95 measured at a frequency of 500 kHz.
[0026]
Reference Example For the coil conductor wire with a head width (L) of 110 μm (A) and 170 μm (B), the conductor wire spacing (G) is identified as 10 μm and plated (L -L) / 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 result is 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 eave length of the overhang portion, the growth rate of the plating in the lateral direction is suppressed. As a result, the conductor thickness can be increased while keeping the conductor interval constant. It can be seen that a planar coil with low DC resistance can be obtained.
It can also be seen that the conductor thickness can be increased as the length of the eaves is increased.
[0027]
【The invention's effect】
Since the planar coil of the present invention can increase the thickness of the conductor while reducing the spacing between the coil conductor wires, the direct current resistance can be reduced, and when a planar transformer is configured using this, In particular, there is an advantage that excellent electrical characteristics are exhibited at a small power of 10 W or less.
[Brief description of the drawings]
FIG. 1 is a partial sectional view of a planar coil of the present invention.
FIG. 2 is a process chart of an example of a method for producing a planar coil of 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]
DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Metal thin film layer 3, 3 ', 3 "Coil conductor filament 6 Photoresist pattern layer 7 Through hole

Claims (3)

In a planar coil in which a plurality of coil conductor wires having a thickness of 50 to 400 μm are provided on one or both sides of an insulating substrate with an aspect ratio (H / G) of 1 or more in the gap portion, the coil conductor wires have a mushroom-like cross section. The width (L) of the head of the cross section is 2 to 5 times the width (l) of the neck, 0.5 to 1.5 times the height (H) of the head, and between the coil conductor wires. A planar coil characterized by being 4 to 10 times the minimum gap (G). 2. The planar coil according to claim 1, wherein the coil conductor wire is coated with a protective metal plating thin film layer. A planar transformer configured by laminating a plurality of planar coils according to claim 1 or 2 through an insulating film, and sandwiching the whole with a thin ferromagnetic core.

Images