JPH10270852A - Multilayered printed wiring board for sheet coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high number of coil windings while maintaining the features of a sheet coil, i.e., light weight and thinness, by using an inner via hole which only connects adjoining layers at the time of pattern connecting a winding circuit of a coil from one layer to another. SOLUTION: A terminal 10a of a winding circuit 8a on a first layer 7a is connected with a start part 10b of a winding circuit 8b on a second layer 7b by an inner via hole. Interlayer connection between a third layer and a fourth layer and that of the subsequent layers are performed by inner via holes in the same manner. In this multilayered printed board for a sheet coil, the number of layers can be increased in response to the number of coil windings or the length of the prescribed coil wiring length can be set by changing the wiring pattern with the same number of layers. Thus, an area occupied by the holes can be suppressed at minimum as a whole wiring board, and as a result, the sheet coil can be miniaturized or higher number of coil windings can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed wiring board for a sheet coil using a thick copper foil for a conductive layer.

[0002]

2. Description of the Related Art Conventionally, a coil type of a coil type of various inductance elements such as a transformer and a choke coil used for a power supply circuit or the like is obtained by winding a copper wire insulated and coated many times with an insulator interposed therebetween. Coils have been used. However, in response to the recent demand for lighter, thinner and smaller electronic devices,
Inductor elements have also been required to be thin, small, and lightweight. Therefore, instead of the conventional winding type, a plate-shaped inductance using a multilayer printed wiring board type “sheet coil” in which conductive layers and insulating layers formed by patterning thick copper foil are alternately laminated. Devices have begun to be adopted. In this sheet coil, a through hole that penetrates a wiring board from top to bottom has been conventionally used to make electrical connection between the layers.

[0003] When it is necessary to increase the number of turns of the coil, in the conventional method of making electrical connection by through-holes, the number of turns is increased by the following two methods. First, as shown in FIG. 3, on the one-layer surface 12a,
Loop circuit 13a starting from land 14 and going to land 15a
And the first land 15a is connected to the land 15b provided on the next layer 12b by a through hole.
Loop circuit from land 15b to land 16b
The winding and then through the through hole the next layer 12c land
Connect with 16c. In the same manner, the circuit of each layer is connected in the same manner to form a coil pattern having a desired number of turns. The problem with this method is that the number of turns per layer is one.
Since the number of windings is limited, the number of layers is increased in order to increase the number of windings. In the second method, as shown in FIG.
By winding 9a several times, the number of turns per layer is increased. In this case, it is necessary to provide the land position of the end portion 21a, that is, the position of the through hole, inside the circuit. ), The wiring pattern passes through the gap, and the area of the wiring board must be increased, which makes it difficult to reduce the size of the sheet coil.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned problems, and maintains a characteristic of a sheet coil that is lightweight and thin, and is useful for producing a sheet coil capable of increasing the number of coil turns. It is intended to provide.

[0005]

In order to solve the above problems, a multilayer printed wiring board for a sheet coil according to the present invention is formed by alternately laminating a plurality of conductive layers formed by patterning copper foil and insulating layers. In a multilayer printed wiring board for a sheet coil, when a circuit of a coil is pattern-connected from one layer to the next, connection is made using inner via holes that connect only adjacent layers.

[0006] Where the conventional interlayer connection is made by through holes, a through hole penetrating from the uppermost layer to the lowermost layer is formed. On the other hand, in the case of the connection by the inner via hole according to the present invention, only the adjacent layers are formed by holes. Since the connection is made, the hole formation is limited to the connection point, and does not affect the pattern formation of other layers. As a result, the area occupied by holes in the entire wiring board can be minimized, so that the size of the sheet coil can be reduced. Alternatively, when compared with the same size, the number of turns of the coil can be larger than that of the conventional method.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of a multilayer printed wiring board for a sheet coil according to the present invention will be described with reference to FIG.
0b is connected to the inner via hole. Similarly, the interlayer connection between the third layer and the fourth and subsequent layers is also connected by the inner via hole.

In the multilayer printed wiring board for a sheet coil of the present invention, the number of layers may be increased or decreased in accordance with the number of turns of the coil, or the desired number of layers may be changed by changing the wiring pattern. The wiring length of the coil can be set.

In the multilayer printed wiring board for sheet coil of the present invention, the thickness of the copper foil at the coil wiring portion is 35.
μm or more and 210 μm or less, and the thickness of the insulating layer is 30 μm.
It is desirable that it is not less than m and not more than 300 μm. Copper foil is 2
If it exceeds 10 μm, the substrate becomes too thick and the effect of miniaturization is small, and if it is less than 35 μm, practicality is lost in terms of electric capacity and the like. On the other hand, if the thickness of the insulating layer exceeds 300 μm, the substrate becomes too thick, and the effect of miniaturization is reduced. If the thickness is less than 30 μm, the reliability of insulation is reduced. The thickness of the copper foil in the shield layer and the land part of the outermost layer is not particularly limited, but may be the thickness normally used in the copper foil in the wiring part.
For example, a thickness of 18 μm is preferably used.

In the method of manufacturing a multilayer printed wiring board for a sheet coil according to the present invention, a wiring pattern including a predetermined coil pattern is formed on a single-sided or double-sided copper-clad laminate by using a conventional etching process or the like. By repeating the process, a required number of coil wiring boards and, if necessary, a wiring board for a shield layer and a copper foil are prepared, and then necessary parts are connected using inner via holes, and these elements are connected. The method includes a step of forming a land pattern on the outermost layer after laminating the prepreg with the prepreg sandwiched therebetween, and then heating and compressing to form a laminate. The thickness of the insulating layer in the finished product is 30 μm to 3
In order to make it 00 μm, one or more prepregs having a thickness of 60 μm to 200 μm may be used.

Further, among the elements used in the method for manufacturing a sheet coil printed wiring board of the present invention, the copper foil and copper plating of the copper-clad laminate serve as a conductive layer, and the base portion of the copper-clad laminate and the prepreg are used. Function as an insulating layer. The prepreg bonds the wiring board elements together, and at the same time, fills voids such as inner via holes with the resin component that has flowed during lamination molding, and plays a role of forming an insulating layer integrally with the base material.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of a method for manufacturing a multilayer printed wiring board for sheet coils according to the present invention will be described. First, one unpatterned copper foil, two double-sided copper-clad laminates with primary coil wiring patterns formed on the front and back, one single-sided copper-clad laminate with a shield layer pattern, and a secondary One double-sided copper-clad laminate with coil wiring patterns formed on the front and back and one copper foil without patterning were prepared, and necessary parts were connected using the inner via holes 4a and 4b, and shown in FIG. As described above, the above-described components were stacked in that order with the prepreg interposed therebetween in the above-described order by heating and compression. Thereafter, a land pattern was formed on the outermost layer. In this way, lands for lead extraction are provided on the upper and lower outermost layers, and four layers of primary coil wirings are provided on the inner layer.
One layer of the shield layer and two layers of the wiring for the secondary side coil were sequentially formed, and a multilayer printed wiring board was formed in which each layer was connected by an inner via hole. The thickness of each layer is such that the thickness of the outermost copper foil 1 and the thickness of the copper foil 5 of the shield layer is 18 μm, the thickness of the copper foils 6a and 6b of the coil portion is 105 μm, and the thickness of the base materials 3a and 3b is The thickness of prepreg 2 was 60 μm.

[0013]

As can be seen from the above description, in the multilayer printed wiring board for sheet coil of the present invention, since the adjacent layers are connected by the inner via holes, the formation of holes is limited to the connection points, and the pattern formation of other layers is performed. Has no effect. As a result, the area occupied by holes in the entire wiring board is minimized, so that the size of the sheet coil can be reduced. Alternatively, when compared with the same size, the number of turns of the coil can be larger than that of the conventional method.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a layer structure of a wiring board according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an arrangement of adjacent two-layer circuits and lands in the embodiment of the present invention.

FIG. 3 is a schematic diagram showing an arrangement of adjacent three-layer circuits and lands in a conventional example.

FIG. 4 is a schematic diagram showing an arrangement of adjacent two-layer circuits and lands in a conventional example.

[Explanation of symbols]

 9 Start land on 1st layer 11 Terminal land on 2nd layer 12c 3rd layer 13c Circular circuit on 3rd layer 17 Terminal land on 3rd layer 18b 2nd layer 19b Circular circuit on 2nd layer 21b Start land on 2nd layer 22 End land on 2nd layer 23 Penetration Surhole

Claims (3)

[Claims] 1. A multilayer printed wiring board for a sheet coil in which a plurality of conductive layers formed by patterning a copper foil and insulating layers are alternately laminated, adjacent layers are electrically connected to each other by inner via holes. A multilayer printed wiring board for sheet coils, characterized in that: 2. The insulating layer has a thickness of 30 μm or more and 300 μm or more.
The multilayer printed wiring board for a sheet coil according to claim 1, wherein: 3. The thickness of the copper foil at the wiring portion of the coil is 35 μm.
2. The structure according to claim 1, wherein the thickness is not less than m and not more than 210 μm.
Or a multilayer printed wiring board for sheet coils according to 2.