JP7544544B2 - Planar Transformer - Google Patents

Description

The present invention relates to a planar transformer.

A well-known type of transformer is a planar transformer, whose windings are formed from a wiring pattern on a plane. Compared to conventional wound transformers, which have coils formed by winding ordinary electric wire around a core, planar transformers have the advantages of being able to be made smaller, having high magnetic coupling, generating less heat, and achieving high circuit efficiency.

In planar transformers, the primary and secondary coils are close to each other, so it is necessary to ensure insulation between them at high voltages. If a void occurs in the resin mold between the primary and secondary coils, corona discharge can occur in the void. Corona discharge can occur not only from the secondary coil (high voltage side) to the primary coil (low voltage side), but also from the secondary coil to conductive objects such as the core and fixtures.

When discharge occurs from the secondary coil to the core or fixture, it causes disadvantages such as increased power loss, deterioration of the insulating film, and increased heat generation in the core. For this reason, there is a demand for a planar transformer that can effectively suppress such discharge from the secondary coil to the core.

JP 2016-4928 A

The present invention provides a planar transformer that can effectively suppress discharge from the secondary coil to the core and fixture.

In order to solve the above problems, the planar transformer according to the present invention includes a multi-layer substrate formed by stacking a plurality of substrates with insulating layers therebetween, a first winding pattern having a conductive layer formed over a plurality of layers on a first substrate among the plurality of substrates and functioning as a primary coil for transmitting electric power, a second winding pattern having a conductive layer formed over a plurality of layers on a second substrate among the plurality of substrates and functioning as the primary coil, a third winding pattern having a conductive layer formed over a plurality of layers on a third substrate sandwiched between the first substrate and the second substrate and functioning as a secondary coil for receiving electric power from the primary winding pattern and the secondary winding pattern, and a core material disposed at the center of the first to third winding patterns. The third winding pattern has a size that is encompassed by the first winding pattern and the second winding pattern when viewed perpendicularly to the multi-layer substrate.

According to this invention, the third winding pattern as a secondary coil is arranged so as to be sandwiched between the first and second winding patterns as primary coils in the upper and lower layers, and the third winding pattern has a size that is encompassed by the first and second winding patterns when viewed from a direction perpendicular to the multilayer substrate. Therefore, discharge from the third winding pattern as a secondary coil can be made to tend toward the first and second winding patterns as primary coils rather than the core material, thereby suppressing power loss, preventing deterioration of the insulating film, and reducing the amount of heat generated.

Preferably, in this planar transformer, a slit is provided that divides the conductive film of the first winding pattern and the second winding pattern, and the position of the slit can be made different between the multiple layers of the primary winding pattern or the multiple layers of the secondary winding pattern. By making the positions of the slits different from each other, the risk of discharge from the third winding pattern as a secondary coil to the core material or the fixing device can be further reduced.

The present invention provides a planar transformer that can effectively suppress discharge from the secondary coil to the core and fixture.

1 is a schematic cross-sectional view illustrating a configuration of a planar transformer according to a first embodiment. 1 is a perspective view illustrating an outline of the structure and manufacturing process of a planar transformer according to a first embodiment. FIG. 1 is a cross-sectional view illustrating a cross-sectional structure of a multilayer substrate 10 of a planar transformer according to a first embodiment. FIG. 2 is a plan view illustrating an example of a planar layout of conductive layers CL1 to CL3. FIG. 11 is a plan view illustrating an example of a planar layout of conductive layers CL10 to CL12. FIG. 11 is a plan view illustrating an example of a planar layout of conductive layers CL4 to CL9. FIG. 2 is a plan view illustrating an example of a planar layout of conductive layers CL1 to CL12. FIG. 4 is a temperature distribution diagram illustrating the effect of the first embodiment. FIG. 11 is a plan view illustrating the configuration of a planar transformer according to a second embodiment.

Hereinafter, the present embodiment will be described with reference to the attached drawings. In the attached drawings, functionally identical elements may be indicated by the same numbers. Note that the attached drawings show embodiments and implementation examples according to the principles of the present disclosure, but these are for understanding the present disclosure and are in no way used to interpret the present disclosure in a restrictive manner. The descriptions in this specification are merely typical examples and do not limit the scope or application examples of the present disclosure in any sense.

In this embodiment, the disclosure is described in sufficient detail for a person skilled in the art to implement the disclosure, but it should be understood that other implementations and forms are possible, and that changes to the configuration and structure and substitutions of various elements are possible without departing from the scope and spirit of the technical ideas of the disclosure. Therefore, the following description should not be interpreted as being limited to this.

[First embodiment]
(Overall composition)
The structure of a planar transformer according to a first embodiment will be described with reference to Fig. 1. This planar transformer includes a multi-layer substrate 10, a first core material 20, a second core material 30, and a molding material 40. Fig. 2 shows an outline of the manufacturing process of the planar transformer.

As described below, the multilayer substrate 10 is composed of multiple substrates, each of which includes multiple conductive layers, with an interlayer insulating layer sandwiched between them. The conductive layers formed across the multiple layers are formed into loops to form the primary coil and secondary coil, as described below. Terminals T1 and T2, which are connected to the primary coil and secondary coil, are formed on the surface of the multilayer substrate 10. The aforementioned core material is arranged so as to pass through the center of the primary coil and secondary coil.

The multilayer substrate 10 has a circular through hole H near its center (FIG. 2(a)). After the protrusion of the second core material 30 passes through this through hole H (FIG. 2(b)), the first core material 20 covers the top of the multilayer substrate 10 and the second core material 30 (FIG. 2(c)). The first core material 20 and the second core material 30 form a core material. The multilayer substrate 10, the first core material 20, and the second core material 30 are then sealed with a molding material 40 (FIG. 2(d)). When power is transmitted between the primary coil and the secondary coil, the first core material 20 and the second core material 30 become a magnetic path for the magnetic flux generated by the current flowing through the primary coil. The first core material 20 and the second core material 30 can be made of a material such as manganese zinc ferrite.

(Configuration of multi-layer substrate 10)
The cross-sectional structure of the multilayer substrate 10 of the planar transformer of the first embodiment will be described with reference to Fig. 3. As described above, the multilayer substrate 10 includes a plurality of substrates 11, 12, and 13, and interlayer insulating layers 14 and 15 sandwiched therebetween. The number of substrates is three here, but this number is merely an example and is not limited to this number. The interlayer insulating layers 14 and 15 may be formed of a material such as polyimide.

It is preferable that the interlayer insulating layers 14 and 15 have a flat interface and a uniform thickness in the stacking direction, at least near the region where the conductive layer CL is formed. If the interfaces of the interlayer insulating layers 14 and 15 are uneven and the thickness is non-uniform, electric field concentration occurs at the positions of the unevenness and in the parts of the non-uniform thickness, and heat concentration due to discharge is likely to occur. It is also preferable that the interlayer insulating layers 14 and 15 are formed so that the dielectric constant is constant overall. If a dielectric with a different dielectric constant is formed in some parts, electric field concentration is likely to occur in those parts.

Each of the substrates 11 to 13 is constructed by laminating multiple conductive layers CL with insulating layers IL sandwiched therebetween. Each conductive layer CL is formed by patterning a thin film (conductive film) of copper (Cu) deposited to a thickness of about several hundred μm on the insulating layer IL into a roughly loop shape. Conductive layers CL1 to 3 and CL10 to CL12 that function as primary coils are formed on the substrates 11 and 13, and conductive layers CL4 to CL9 that function as secondary coils are formed on the substrate 12 sandwiched between the substrates 11 and 13. The conductive layers CL1 to 3 form a first winding pattern that functions as a primary coil. The conductive layers CL10 to CL12 form a second winding pattern that similarly functions as a primary coil.

The conductive layers CL4-CL9 form a third winding pattern that functions as a secondary coil that receives power from the primary coil (first winding pattern, second winding pattern). That is, in this planar transformer, the two primary coils (first winding pattern and second winding pattern) are formed so as to sandwich the secondary coil (third winding pattern) from above and below. Note that the number of conductive layers CL formed on the substrates 11-13 is 3 (primary coil), 6 (secondary coil), and 3 (primary coil) respectively in the illustrated example, but this is just an example and is not limited to a specific number.

These conductive layers CL1 to CL12 are connected to via contacts BC formed through the substrates 11 to 13 and the interlayer insulating layers 14 and 15. The via contacts BC are arranged to contact the conductive layers CL1 to CL12, for example, thereby connecting adjacent conductive layers CL to form a primary coil or a secondary coil. The material of the via contacts BC can be aluminum (Al), cobalt (Co), tungsten (W), etc., but is not limited to these. The number of conductive layers CL included in each of the substrates 11 to 13 is not limited to the above. Instead of connecting a single or a small number of via contacts BC with a large diameter to the conductive layer CL, it is preferable to arrange a large number of via contacts BC in a lattice (matrix) over a wide area, as shown in Figures 4 to 6. Here, the lattice or matrix is not limited to a square lattice, but is used to broadly include a plurality of via contacts arranged vertically and horizontally. This is because when a single or a small number of via contacts BC with a large diameter are connected to the conductive layer CL, the electric field tends to concentrate in that area.

[Structure of Conductive Layer CL]
An example of a planar layout of the conductive layers CL1-12 will be described with reference to Figures 4 to 6. As shown in Figure 4, the conductive layers CL1-CL3 formed on the top substrate 11 have a loop-shaped wiring pattern, a part of which is in contact with the contact BC to form a primary coil of a planar transformer. The loop wiring parts of the conductive layers CL1-CL3 present on the substrate 11 (parts excluding the lead-out part for connection to the terminal T1) each have a width D1 in the X direction and a width H1 in the Y direction, and have an opening AP1 corresponding to the through hole H at their center. In addition, the loop wiring parts of the conductive layers CL1-CL3 are formed with a wiring width W1 or more.

The conductive layers CL1 to CL3 also have slits SL1 to SL3 that divide the loop-shaped wiring pattern. These slits SL1 to SL3 are all formed at different positions in the planar direction. Here, the expression "formed at different positions" is used to mean that the slits SL1 to SL3 adjacent to each other in the vertical direction only cross each other, and the slits SL1 to SL3 do not coincide in the planar direction over a distance that is sufficiently longer than their width direction.

As shown in FIG. 5, the conductive layers CL10-CL12 formed on the bottom substrate 13 also have a loop-shaped wiring pattern, with a contact BC in contact with a part of the pattern to form the primary coil of the transformer. The loop wiring portions of the conductive layers CL10-CL12 on the substrate 13 (excluding the portion drawn out for connection to the terminal T1) each have a width D2 in the X direction and a width H2 in the Y direction, and have an opening AP2 in the center corresponding to the through hole H. Similarly to the conductive layers CL1-3, the conductive layers CL10-CL12 each have a slit SL10-SL12 that divides the loop-shaped wiring pattern. These slits SL10-SL12 are all formed at different positions in the planar direction. The loop wiring portions of the conductive layers CL10-CL12 are formed with a wiring width W2 or more.

As shown in FIG. 6, the conductive layers CL4-CL9 formed on the intermediate substrate 12 have a loop-shaped wiring pattern with contacts BC in contact with part of it, forming the secondary coil of the transformer. The pattern of the conductive layers CL4-CL9 present on the substrate 12 has a width D3 in the X direction and a width H3 in the Y direction in the loop wiring portion (excluding the leads DL6 and DL7). In addition, the pattern of the conductive layers CL4-9 has an opening AP3 in its center that corresponds to the through hole H.

The width D3 is smaller than the width D1 of the conductive layers CL1-CL3 and the width D2 of the conductive layers CL10-CL12 (D1>D3, D2>D3). The width H3 is also smaller than the width H1 of the conductive layers CL1-CL3 and the width H2 of the conductive layers CL10-CL12 (H1>H3, H2>H3). That is, as shown in FIG. 7, the conductive layers CL4-CL9 are arranged so as to be included in the conductive layers CL1-CL3 and the conductive layers CL10-CL12 when viewed in a direction perpendicular to the main plane of the multilayer substrate 10 (excluding the lead line patterns DL6, DL7 (not shown in FIG. 7) of the conductive layers CL6, CL7). The loop wiring portion of the conductive layers CL4-CL9 is formed with a wiring width W3 or less. This wiring width W3 is smaller than the wiring widths W1 and W2 mentioned above (W1>W3, W2>W3).

In this manner, in this embodiment, the conductive layers CL4 to CL9 constituting the secondary coil are sandwiched vertically between the conductive layers CL1 to CL3 and CL10 to CL12 constituting the primary coil. Furthermore, the conductive layers CL4 to CL9 are given a size such that they are included in the conductive layers CL1 to CL3 and CL10 to CL when viewed from a direction perpendicular to the multilayer substrate 10. This allows the corona discharge based on the high voltage of the secondary coil to reach mainly the primary coil, rather than toward the core or other fixed materials. Furthermore, the slits SL1 to SL3 formed in the conductive layers CL1 to CL3 are arranged at different positions in the planar direction, which prevents the discharge from the secondary coil from passing through the primary coil and reaching the core material or other fixed materials. Furthermore, the slits SL10 to SL12 formed in the conductive layers CL10 to CL12 are arranged at different positions in the planar direction, which prevents the discharge from the secondary coil from passing through the primary coil and reaching the core material or other fixed materials.

Figure 8 is a temperature distribution diagram for explaining the effect of the first embodiment. Figure 8 is a temperature distribution diagram (heat map) showing the temperature distribution of the multilayer substrate 10. Figures 8(a) and 8(c) show the temperature distribution in the planar transformers of the first and second comparative examples, respectively, and Figure 8(b) shows the temperature distribution in the planar transformer of the first embodiment. The first comparative example of Figure 8(a) has a structure in which the secondary coil is sandwiched between the primary coils on the top and bottom, as in the first embodiment, but the size of the secondary coil is approximately the same as that of the primary coil. In the second comparative example of Figure 8(c), the primary coil and secondary coil are each arranged on one substrate, and the secondary coil is not sandwiched between the primary coils.

As is clear from FIG. 8(b), in the structure of the first embodiment, high heat is generated only in the conductive layer constituting the primary coil or secondary coil and in its immediate vicinity. Almost no high heat is generated in the core material or other fixing materials. On the other hand, from FIG. 8(a) and FIG. 8(c), it can be seen that in the first comparative example and the second comparative example, high heat is also generated in areas other than the conductive layer and its vicinity (e.g., the core material and other fixing materials). This tendency is particularly noticeable in the second comparative example (FIG. 8(c)). Such generation of high heat can cause deterioration of the insulating film and a decrease in circuit efficiency.

[effect]
As described above, according to this embodiment, in the multiple boards of the multilayer board, the secondary coil made of multiple conductive layers is sandwiched between the primary coils made of multiple conductive layers on the top and bottom, and is smaller in size than the primary coil. Therefore, most of the discharge from the secondary coil to which a high voltage is applied is directed toward the primary coil, and not toward the core material or other fixing members. This makes it possible to provide a planar transformer that effectively suppresses discharge from the secondary coil to the core or fixing members, reduces power loss, and suppresses deterioration of the insulating film and increases in heat generation.

[Second embodiment]
Next, a planar transformer according to a second embodiment of the present invention will be described with reference to FIG. 9. The overall configuration of the planar transformer of the second embodiment may be the same as that of the first embodiment (FIGS. 1 and 2). The cross-sectional structure of the multilayer substrate 10 may also be the same as that of the first embodiment. The second embodiment differs from the first embodiment in that the conductive layers CL formed on each substrate 11-13 are not circular, but have a substantially rectangular shape that is long in the Y-axis direction, unlike the first embodiment. This structure also provides the same effects as the first embodiment.

The present invention is not limited to the above-described embodiments, and includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and are not necessarily limited to those having all of the configurations described. It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

10... multilayer substrate 11-13... substrate 14, 15... interlayer insulating layer 20... first core material 30... second core material 40... molding material AP1-3... opening BC... via contacts CL1-CL12... conductive layer,
SL1-3, SL10-12...Slit

Claims (5)

A planar transformer including a multi-layer substrate having a low-voltage primary coil and a high-voltage secondary coil , and a core material penetrating the multi-layer substrate,
the multilayer substrate includes a first substrate portion having a first primary coil, a second substrate portion having a second primary coil, a third substrate portion having a secondary coil, a first interlayer insulating layer, and a second interlayer insulating layer;
the first substrate portion is provided on a front surface side of the multilayer substrate, and has a first winding pattern formed thereon that functions as a primary coil for transmitting electric power by conductive layers formed across a plurality of layers, and has a through hole through which the core material can pass;
the second substrate portion is provided on a back surface side opposite to the front surface side of the multilayer substrate, and has a second winding pattern formed thereon that functions as a primary coil for transmitting electric power by conductive layers formed across a plurality of layers, and has a through hole through which the core material can pass;
the third substrate portion is provided between the first substrate portion and the second substrate portion, and has a third winding pattern formed by a conductive layer formed across a plurality of layers, the third winding pattern functioning as a secondary coil that receives power from the first winding pattern and the second winding pattern, and has a through hole through which the core material can pass;
the first interlayer insulating layer is provided between the first substrate portion and the third substrate portion, and has a through hole through which the core material can pass;
the second interlayer insulating layer is provided between the third substrate portion and the second substrate portion, and has a through hole through which the core material can pass;
a third winding pattern having a size that is encompassed by the first winding pattern and the second winding pattern when viewed in a direction perpendicular to a main plane of the multilayer substrate; each of the first winding pattern and the second winding pattern includes a slit that divides a wiring pattern ;
2. The planar transformer according to claim 1, wherein the positions of the slits are different among the first winding patterns in the multiple layers or the second winding patterns in the multiple layers. the first winding pattern, the second winding pattern, and the third winding pattern each include a via contact that connects the conductive layer formed across a plurality of layers;
The planar transformer according to claim 1 , wherein the via contacts are arranged in a matrix and connected to the conductive layers. 4. A planar transformer as described in any one of claims 1 to 3, wherein the first interlayer insulating layer and the second interlayer insulating layer have flat interfaces in areas overlapping with the first winding pattern, the second winding pattern, and the third winding pattern when viewed in a direction perpendicular to the main plane of the multilayer substrate, and have a uniform thickness in the direction perpendicular to the main plane of the multilayer substrate. 5. A planar transformer as described in any one of claims 1 to 4, wherein the through holes formed in the first substrate portion, the second substrate portion, the third substrate portion, the first interlayer insulating layer and the second interlayer insulating layer are of the same size and are arranged in positions that overlap when viewed from a direction perpendicular to the main plane of the multilayer substrate.