JPH10313152A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately set the pattern width according to the current capacity and ensure an insulation distance in the thickness direction by making a thin- walled conductor continuous in the widthwise direction, and dividing an increasingly thick plated layer in sections in the widthwise direction. SOLUTION: A circuit board has thin-walled circuit patterns 23A, 23B for low currents and thick-walled circuit patterns 25A, 25B for high currents on both sides of an insulation board 13. The patterns 23A, 23B are composed of Cu foils 3A, 3B of specified circuit patterns with a Cu-plated layer 19. The patterns 25A, 25B have increasingly thick Cu plated layers 7A, 7B on the Cu foils 3A, 3B of thin wall conductor (3A, 19; 3B, 19) of specified circuit patterns. The broader thick-walled circuit pattern 25A has thin-wall conductors 3A, 19 continuous in the widthwise direction, while the thick walled plated layer 7A is divided in sections in the widthwise direction. This ensures required insulation distance in the thickness direction, without increasing the thickness of the board 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board having a thick circuit pattern for supplying a large current.

[0002]

2. Description of the Related Art As the use of electronic circuits is rapidly expanding to the fields of industrial machinery and automobile parts, inverter circuits and power supply devices need to be reduced in space and power, so that they can be mounted on the same insulating substrate. A composite circuit board on which a thin circuit pattern for a current (for a signal) and a thick circuit pattern for a large current are mixed has been widely used.

[0003] There are various types of thick circuit patterns used for this type of circuit board. One of them is electroplating on one surface of a thin conductor (copper foil) formed in a predetermined circuit pattern. The thing provided with the thick plating layer for thickening is known.

[0004]

However, in the case of a thick circuit pattern of this form, if a relatively thick plating layer is to be formed on a thin conductor by electroplating, the plating is performed at the center of the width of the circuit pattern rather than at both sides. The thickness tends to be thin. This tendency becomes remarkable as the width of the circuit pattern increases. Therefore, when the width of the thick circuit pattern is wide,
There is a problem that the plating thickness on both sides becomes relatively thick, and it becomes difficult to secure a required insulation distance in the thickness direction of the insulating substrate when the thickened plating layer is embedded in the insulating substrate. This problem can be avoided by increasing the thickness of the insulating substrate, but increasing the thickness of the insulating substrate is not preferable because it increases the size and weight and increases the cost. In addition, when thick circuit patterns having different widths coexist on the same substrate due to the above tendency, a difference occurs in the average plating thickness of each pattern. That is, the plating thickness of the thick circuit pattern having a small width becomes too thick, and the above-described problem of the insulation distance also occurs. If the plating thickness varies greatly within the same substrate, it is difficult to set a pattern width according to the current capacity at the time of designing.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a circuit board having a thick circuit pattern composed of a thin conductor and an increased plating layer. In addition to reducing the variation in the thickness of the thickened plating layer, it is possible to accurately set the pattern width according to the current capacity, and to secure the insulation distance in the thickness direction without increasing the thickness of the insulating substrate. Is to do so.

[0006]

In order to achieve this object, the present invention comprises an insulating substrate and a thick circuit pattern for a large current, wherein the thick circuit pattern is formed in a predetermined circuit pattern. The thin conductor is provided with a thick plating layer on one surface, and the thin conductor is continuous in the width direction, and the thick plating layer is divided into a plurality of pieces in the width direction. .

In the case where the thickness of the thick circuit pattern is wide, dividing the thick plating layer into a plurality of parts in the width direction makes it possible to reduce variations in thickness when forming the thick plating layer. The above-mentioned problem can be solved.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] FIG. 1 shows an embodiment of the present invention. This circuit board is provided with thin circuit patterns 23A and 23B for small current and thick circuit patterns 25A and 25B for large current on both surfaces of the insulating substrate 13. The thin circuit patterns 23A and 23B are composed of copper foils 3A and 3B formed in a predetermined circuit pattern and a copper plating layer 19.

The thick circuit patterns 25A, 25B are thin conductors (3A, 19, 3B) formed in a predetermined circuit pattern.
And 19) the copper thick plating layer 7 on the copper foil 3A, 3B side.
A and 7B are provided. Thick circuit pattern 25
The thin conductors 3A and 19 of A and 25B protrude from the surface of the insulating substrate 13 like the thin circuit patterns 23A and 23B, and the thickened plating layers 7A and 7B are embedded in the insulating substrate 13.

The relatively thick (upper right in FIG. 1) thick circuit pattern 2 of the thick circuit patterns 25A and 25B
5A shows that the thinned conductors 3A and 19 are continuous in the width direction, while the thickened plating layer 7A has a plurality (three) in the width direction.
It has a divided form. This is a feature of this circuit board. In this example, a wide thick circuit pattern 2
5A and a thick plating layer 7A provided on a narrow thick circuit pattern 25A.
A has almost the same width.

Hereinafter, a method for manufacturing the circuit board will be described with reference to FIGS. 2 to 7 in order to clarify the specific structure of the circuit board. First, as shown in FIG. 2, two support plates 1A and 1B are prepared, and 1 ounce (nominal thickness 35 μm) general-purpose copper foils 3A and 3B are attached to one surface of each of them by an adhesive or the like. The material of the support plates 1A and 1B is a stainless plate, an aluminum plate, a bake plate, or the like.

Next, in order to form a thick plating layer on the copper foils 3A and 3B, a plating resist 5 is formed so that a pattern (mirror pattern) opposite to the thick plating layer to be obtained remains.
A and 5B are formed. The plating resists 5A and 5B are formed by attaching a dry film on the copper foils 3A and 3B, exposing and developing a mirror pattern of a thick circuit pattern. The thickness of the plating resists 5A and 5B can be set by the number of laminated dry films, and is set to be equal to or larger than the thickness of a thick plating layer to be formed later.

Incidentally, a plating resist pattern for forming the thickened plating layer may be formed according to the following concept. First, the narrowest thick circuit pattern is selected from the thick circuit patterns, and the width of the pattern is set as a reference width. On the other hand, the following items (1) to (5) are considered for the thick circuit patterns having a width wider than the reference width.

When the width of the thick circuit pattern is not less than twice the reference width, the thick plating layer to be formed is divided into a plurality of parts in the width direction. A thin island of resist (5A1 in FIG. 2 corresponds to this) is arranged. The width of the island of the plating resist should be equal to or larger than the minimum width at which the plating resist itself can be developed accurately and sufficient peel strength from the copper foil can be obtained. For example, when the thickness of the plating resist is about 150 μm, the width is preferably 0.5 mm or more. When thin islands of the plating resist are arranged, it is necessary to widen the width of the thick circuit pattern in order to compensate for the decrease in the cross-sectional area of the thick plating layer due to this. If the width of the plating resist island is wide,
Since the width of the thick circuit pattern must be increased by that amount, it is practical to set the width of the island to about 0.5 to 1.0 mm.

For a solid pattern that is not subjected to through-hole processing and has no purpose such as shielding, a circular, square or other shape of a plating resist island may be arranged. However, when the number of islands is large and the size of each is small, when the thickened plating layer is embedded in the insulating substrate, the flow of the resin and the followability of the prepreg are adversely affected, and the peel strength may be reduced. Therefore, care must be taken.

In the process of manufacturing a circuit board, for a land having a circular shape or other shape to be subjected to through-hole processing, an island of plating resist having a diameter of [through-hole diameter of -1 mm] (5A2 and 5B2 in FIG. The provision of (equivalent) makes it possible not only to make the plating thickness uniform, but also to reduce the plating area and the load on the working drill.

As described above, the plating resists 5A, 5A
After forming B, electroplating is performed using the thin copper foils 3A and 3B as electrodes. Thereby, the plating resists 5A, 5B
Copper thick plating layers 7A and 7B are formed in the areas not covered with the metal as shown in FIG. In this embodiment, the width of each of the thickened plating layers 7A and 7B is made substantially the same in accordance with the width of the narrowest thickened plating layer. Although the thickness tends to be thick, the variation in thickness can be small.

On the other hand, as shown in FIG. 8, when the thickened plating layers 7A and 7B include a narrow one and a wide one, for example, the wide thickened plating layer 7A (upper left of FIG. 8) In this case, the swelling of the plating layers on both side edges becomes large, but the swelling of the plating thickness on both side edges becomes small in the adjacent thickened plating layer 7A having a small width. As a result, when a circuit board is finally formed using this, as shown in FIG. 9, both side edges of the wide thick plating layer 7 </ b> A penetrate deeply into the insulating substrate 13, so that the insulation distance in the thickness direction is secured. There is a problem that it becomes impossible.

In this embodiment, as shown in FIG. 3, since the portion corresponding to the wide thick plating layer 7A is divided into three in the width direction, the thickness of the thick plating layers 7A and 7B varies. Becomes smaller.

Next, when the plating resists 5A and 5B are removed, as shown in FIG. 4, the thickened plating layers 7A and 7B having a pattern corresponding to the thick circuit pattern to be obtained on the copper foils 3A and 3B are formed. can get. Then, a guide hole (not shown) using a laminated film for positioning during lamination
To form The guide holes may be formed in advance in the previous step.

Next, as shown in FIG.
The prepregs 9 are stacked with an appropriate number of prepregs 9 interposed therebetween with the surfaces on which the A and 7B are formed facing inside. It is preferable that holes 11 for receiving the thick plating layers 7A and 7B are formed in the prepregs of the uppermost layer and the lowermost layer among the prepregs to be laminated. Also, prepregs having different layer thicknesses may be used at the time of superposition so that the fibers can follow the projections of the thickened plating layer.

The copper foils 3A and 3B and the thick plating layer 7
The surfaces of A and 7B are preferably subjected to a surface roughening treatment such as a blackening treatment before lamination in order to improve the adhesion to the prepreg 9.

Next, the laminate as shown in FIG. 5 is heated and pressed by a hot press, and then the support plates 1A and 1B are removed to obtain a copper-clad laminate as shown in FIG. In this copper-clad laminate, the thickened plating layers 7A and 7B are embedded in the thickness of the insulating substrate 13, and the copper foils 3A and 3B are laminated on the surface of the insulating substrate 13.

The support plates 1A, 1B after hot pressing
In order to facilitate the removal, copper foil 3
When attaching A and 3B, it is preferable to use a type of adhesive (for example, an adhesive in which a thermosetting resin is blended) whose adhesive strength is reduced when heated. Then, the heat when the laminate of FIG. 5 is heated and pressurized causes the support plates 1A and 1B and the copper foil 3
A, since the adhesive strength with 3B decreases, the support plates 1A, 1B
Can be easily peeled off. In order to remove the support plates 1A and 1B, it is also conceivable to use an adhesive having a low adhesive strength.

The subsequent steps are the same as the ordinary circuit board manufacturing steps. That is, after a through hole for a through hole is formed at a predetermined position, a copper plating layer 19 is provided on the inner surface of the through hole as shown in FIG. 7 to form a through hole. This copper plating layer 19 is also formed on the surfaces of the copper foils 3A and 3B. Next, a dry film is adhered to both sides, and pattern exposure and development are performed to form an etching resist having a pattern corresponding to a thin circuit pattern (for small current) and a thick circuit pattern (for large current). Thereafter, etching is performed to remove unnecessary regions of the thin conductors 3A and 19, 3B and 19, and then the etching resist is removed to obtain a composite circuit board as shown in FIG.

This composite circuit board has thin circuit patterns 23A and 23B for small current and thick circuit patterns 25A and 25B for large current on both sides of the insulating substrate 13. As is clear from FIG. 1, the thickness of the thin circuit patterns 23A and 23B is a thickness in which the copper plating layers 19 are added to the copper foils 3A and 3B, respectively. Also, the thick circuit pattern 25
The thicknesses of A and 25B are the thicknesses obtained by adding the thicker plating layers 7A and 7B and the copper plating layer 19 to the copper foils 3A and 3B, respectively. Among the thick circuit patterns, there is also a thick circuit pattern 25A having a large width (upper right in FIG. 1). However, this thick circuit pattern 25A is formed by dividing the thickened plating layers 7A and 7B into three in the width direction and increasing the thickness. Since the variation in the height is small, the insulating substrate 13
It is easy to secure the required insulation distance in the thickness direction.

In this circuit board, the thin circuit patterns 23A and 23B project from the surface of the insulating substrate 13 by the thickness. The thick circuit patterns 25A and 25B have the same thickness as the thin circuit patterns 23A and 23B of the entire thickness protruding from the surface of the insulating substrate 13, and the remaining thickness is embedded in the insulating substrate 13. . Therefore, the surfaces of the thin circuit patterns 23A and 23B and the surfaces of the thick circuit patterns 25A and 25B are located at the same level.

This composite circuit board is then subjected to solder resist formation, silk character printing, non-through hole drilling, surface treatment such as a solder leveler, outer shape processing, and the like. Since the thickness of the circuit pattern protruding from the surface of the insulating substrate is as thin as that of a normal circuit board, and there is no step on the surface of the circuit pattern, the processing can be easily performed using ordinary equipment.

[Other Embodiments] In the above embodiment,
Thick circuit patterns 25A, 25B on both sides of insulating substrate 13
However, the thick circuit pattern may be provided only on one side of the insulating substrate. Further, in the above-described embodiment, the case where the circuit pattern has two layers is shown. However, if the circuit patterns of some layers are embedded in the insulating substrate, a circuit board having three or more circuit patterns may be used. It is possible.

[0030]

As described above, according to the present invention, in a circuit board having a thick circuit pattern composed of a thin conductor and a thick plating layer, the thickness of the thick plating layer of the thick circuit pattern is increased. Therefore, the required insulation distance in the thickness direction can be ensured without increasing the thickness of the insulating substrate.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing an initial stage of manufacturing the circuit board of FIG. 1;

FIG. 3 is a sectional view showing the next stage of FIG. 2;

FIG. 4 is a sectional view showing the next stage of FIG. 3;

FIG. 5 is a sectional view showing the next stage of FIG. 4;

FIG. 6 is a sectional view showing the next stage of FIG. 5;

FIG. 7 is a sectional view showing the next stage of FIG. 6;

FIG. 8 is a cross-sectional view showing a problem when a circuit board having a thick circuit pattern is manufactured.

FIG. 9 is a sectional view showing a problem of a circuit board having a thick circuit pattern.

[Explanation of symbols]

 1A, 1B: support plate 3A, 3B: copper foil 5A, 5B: plating resist 7A, 7B: thicker plating layer 9: prepreg 13: insulating substrate 19: copper plating layer for through hole 23A, 23B: thinner for small current Circuit pattern 25A, 25B: Thick circuit pattern for large current

Claims (1)

[Claims] An insulating substrate (13) and a thick circuit pattern (25A) for a large current, wherein said thick circuit pattern (2) is provided.
5A) is formed by providing a thickened plating layer (7A) on one surface of a thin conductor (3A, 19) formed in a predetermined circuit pattern, and the thin conductor (3A, 19) is continuous in the width direction. Wherein the thickened plating layer (7A) is divided into a plurality in the width direction.