JPH07302962A - Circuit board and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a circuit board in which a conductive defect is not caused, which can perform a high-density.mounting operation, which can be manufactured easily and whose yield is high. CONSTITUTION:A circuit board is provided with circuit patterns 2 formed on both faces of an insulating board 1, with lands 3 formed at end parts, on one side, of the circuit patterns 2 so as to be faced by sandwiching the insulating board 1 and with a through hole 4 formed in the insulating board 1 so as to be close to the lands 3. The inside diameter of individual opening parts 4a, 4b on both faces of the insulating board 1 of the through hole 4 is different, the inner wall face of the through hole 4 in a part close to the opening part 4a whose diameter is small out of the opening parts 4a, 4b swells and protrudes gently to the inside, and a small-diameter part 4c whose inside diameter is small is formed. A conductive paint 5 which is connected to the through hole 4 and to the lands 3 on both faces of the insulating board 1 and which has been hardened is provided.

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 circuit patterns formed on both sides of an insulating substrate, conductive through holes for electrically connecting the circuit patterns on both sides, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a conductive through hole of a through-hole circuit board is formed by punching a through hole in an insulating substrate, and a conductive paint is applied to the through hole a plurality of times by printing to conduct circuit patterns on both surfaces of the circuit board. (Japanese Utility Model Publication No. 55-44398, hereinafter referred to as "conventional example (a)").
Further, in order to improve the reliability of the conductive through hole, a method of press-fitting conductive paint into the through hole of the substrate from both front and back sides of the substrate with a pair of front and back squeegees (Japanese Patent Laid-Open No. 58-91696, hereinafter referred to as conventional example (b)). Or a method of applying conductive paint a plurality of times to the through holes of the substrate (JP-A-58-74097,
Hereinafter, referred to as a conventional example (C)), or when applying a conductive paint to the through holes of the substrate by using a screen printing method,
There is also a method of using a screen having a step in a mask hole corresponding to the through hole of the substrate (Japanese Patent Laid-Open No. 57-112096, hereinafter referred to as a conventional example (d)).

[0003]

As disclosed in the above publication, the formation of the conductive through holes by the printing of the above-mentioned conventional example (a) is highly reliable unless it is applied and cured a plurality of times. could not. In addition, there is a drawback in that the diameter of the conductive through hole cannot be reduced due to the printing misalignment caused by printing a plurality of times, and the man-hour and material cost increase.
Further, there is a drawback that bubbles are generated between the layers of the conductive paint or printing unevenness is caused by printing a plurality of times, and weak spots are formed on the strength and cracks easily occur. In addition, when printing is performed a plurality of times, the chances of causing short circuits between circuits due to the scattering of the conductive paint are increased, and the yield is deteriorated. In particular, when the through holes are small, the conductive paint is less likely to enter the through holes, thin portions of the conductive layer are likely to occur, and the possibility of disconnection increases.

In the conventional example (b), it was necessary to later remove the conductive paint attached to the places other than the through holes. Further, the conventional example (C) has the same drawbacks as those of the conventional example (A), and in the conventional example (D), it is troublesome to form a step in the mask hole of the screen.

The present invention has been made in view of the above-mentioned conventional technique, and provides a circuit board which is free from conductive defects and the like, enables high-density mounting, is easy to manufacture, and has a high yield, and a manufacturing method thereof. The purpose is to

[0006]

According to the present invention, there are provided a circuit pattern formed on both sides of an insulating substrate, and lands formed at one end of the circuit pattern so as to face each other with the insulating substrate sandwiched therebetween. It has a through hole formed in the insulating substrate close to the land, and the inside diameter of each opening on both sides of the insulating substrate of this hole is different, and it is close to the opening of the smaller diameter of these openings. A circuit board is provided with a small-diameter portion in which the inner wall surface of the through hole gently bulges inward to reduce the inner diameter, and is connected to the through hole and the lands on both sides of the insulating substrate and hardened conductive paint. The land is printed on the outside of the conductive paint.

Further, according to the present invention, a circuit pattern having a land is formed on at least one surface of an insulating substrate, the insulating substrate at the land forming portion is punched out, and through holes having different inner diameters are formed on both sides of the insulating substrate. A conductive paint is applied to the through hole through an opening with a large inner diameter in the direction opposite to the punching direction and through a screen, and then the conductive paint is cured to cure the conductive through. It is a method of manufacturing a circuit board in which holes are formed. Also, after applying and curing the conductive paint, the land connected to the insulating paint is formed by printing.

[0008]

The circuit board of the present invention has a strong bonding force between the insulating substrate and the conductive paint and is resistant to cracks and the like so that the conductive paint can be easily applied even if the diameter of the through hole is small. .

Furthermore, the method of manufacturing a circuit board according to the present invention is
The conductive paint can be easily and surely applied to the through holes having a small inner diameter, and the conductive paint is firmly adhered to the wall surface roughened by punching.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 and 2 are partial cross-sectional views of a through-hole circuit board of this embodiment, in which a circuit pattern 2 made of copper foil is formed on both surfaces of an insulating substrate 1, and one end of this circuit pattern 2 is a land 3. It is This land 3
Has a doughnut-shaped central portion that is hollowed out, and the diameter of the hollowed-out portion 3a is slightly different on each surface of the insulating substrate 1. Here, the diameters D1 and D2 in the drawing are shown.
Is D1 <D2. The through hole 4 is formed by punching out the insulating substrate 1 in the hollow portion 3a.
The through holes 4 have diameters D1 and D of the cut-out portion 3a of the land 3.
The inner diameter is smaller than 2, and the inner diameter is d1 of the opening 4a on one side and the inner diameter d of the opening 4b on the other side.
The relationship of 2 is d1 <d2, and the inner diameter of the inside of the substrate further bulges so that the inner diameter closer to the opening 4a is gradually reduced to form a small diameter portion 4c. Therefore, the inner diameter d3 of the small diameter portion 4c is d3 <d1.

A conductive paint 5 containing silver, copper, nickel, carbon or the like in a thermosetting resin or an ultraviolet curable resin is applied to the through hole 4, and the conductive paint 5 is the insulating substrate 1. Conductive through holes 6 connected to lands 3 on both sides of
Is formed. Depending on the viscosity and the inner diameter of the through hole 4, the conductive paint 5 may block the through hole 4 as shown in FIG. 1 or may have holes as shown in FIG. About 60 poise is preferable, and electrical performance is also good.

A method of manufacturing a through-hole circuit board having the conductive through-hole 6 having the above-described structure will be described with reference to FIGS.
It will be described based on. First, as shown in FIG. 3A, the circuit pattern 2 and the land 3 are formed on the insulating substrate 1, and the larger diameter of the cutout portion 3a of the land 3 is set to the lower side.
As shown in FIG. 3 (B), it is set in a press working machine.
The punch 7 of the press machine is located above the upper land 3, and the die 8 is located below the lower land 3 having the large-diameter cutout 3a.

After that, the punch 7 is operated to punch out the insulating substrate 1 inside the cutout portion 3a of the land 3. At this time, as shown in FIG. 3C and FIG. 1, since a clearance is provided between the punch 7 and the die 8, the diameter d2 of the opening 4 is larger than the diameter d1 of the opening 4a. After punching, the inner wall surface of the through hole 4 slightly rises inward to form the small diameter portion 4c. This small diameter portion 4c is
Slip of the tissue near the surface of the insulating substrate 1 at the beginning of shearing occurs obliquely in a V shape with respect to the shearing direction, and as the shearing progresses, a portion smaller than the diameter of the punch 7 is pushed outward, and punching is completed. This is caused by a slight bulge of this pushed portion, and it appears remarkably when the inner diameter of the through hole is small.

Next, a conductive paint 5 is applied to the through holes 4 of the insulating substrate 1. At this time, as shown in FIG. 4A, the conductive paint 5 is applied from the direction opposite to the direction punched by the punch 7. To apply the conductive paint 5, a screen 9 is placed on the surface of the through-hole 4 on the side of the large-diameter opening 4b, the position is aligned, and the conductive paint 5 is scraped off with an elastic squeegee 10 such as rubber. On the other hand, the conductive paint 5 is applied from the transmissive portion 9a of the screen 9 into the through hole 4 by a single operation.
At this time, the squeegee 10 is pressed against the insulating substrate 1 as shown in the drawing so that the angle with the screen 9 becomes smaller at the tip end portion, and the pressure for applying is increased. Then, as shown in FIG. 4B, the conductive paint 5 passes through the through hole 4 and slightly spreads at the opening 4 a on the opposite side, and is just connected to the land 3. At this time, a relief portion 12 is formed on the base 11 so that the conductive paint spreads to the land 3. The shape of the base 11 can be changed as appropriate.

Finally, as shown in FIG. 4C, the conductive paint 5 is heated or cured by ultraviolet rays to complete the conductive through holes 6.

The conductive through hole 6 of this embodiment has a diameter of the through hole 4 which is d2 in FIG. 1 in response to the recent demand for high density packaging.
The diameter is set to d2 = 0.8 mm, and d1 is d2
It is set about 5 to 10% smaller than that. And
The clearance x between the hollow 3a of the land 3 and the through hole 4 is 0.
Set to 05 mm to 0.3 mm. With this setting, the swelling in the through hole 4, which was not seen in the conventional through hole having an inner diameter of about 1.5 mm, becomes remarkable,
By appropriately setting the clearance between the punch 7 and the die 8, the through hole 4 is rounded as shown in the drawing, and the corners of the openings 4a and 4b of the through hole 4 are also rounded. As a result, even if the insulating substrate 1 shrinks due to heating and drying, the conductive paint is not cracked at the corners.

Further, in the manufacturing method of this embodiment, the conductive paint 5 is applied to the through-hole 4 through the screen 9 by one operation, so that it can be applied easily. Moreover,
Since the coating is applied from the direction opposite to the punching direction, the conductive paint flows in from the larger one of the openings of the through holes 4, and pressure is applied to the conductive paint at the small diameter portion 4c, so that the through holes 4 that are rough surfaces are extremely damaged. It is filled with conductive paint smoothly and without gaps. In particular, it is possible to reliably apply even a small through hole that cannot be applied by inserting a pin as in the conventional case.

Further, in the circuit board according to the present invention, as shown in FIGS. 5 and 6 (B), the land 31 of the circuit pattern 21 on one surface is the upper and outer sides of the conductive paint 5 at the edge of the conductive through hole 6. It may be formed by printing on top of.

Further, the manufacturing method is as shown in FIG.
As shown in (A) and (B), the circuit pattern 22 is formed only on one surface of the insulating substrate 1, and the insulating substrate 1 is punched out together with the land 32 to form the hollow portion 3a and the stab-like through hole 4. At the same time, the conductive coating material 5 is applied and cured in the same manner as described above, and then the insulating substrate 1 is formed.
Land 31 on the surface where the circuit pattern is not yet formed
Circuit pattern 21 so that it overlaps the conductive paint 5.
May be formed by printing. Here, the circuit pattern 22 formed before forming the through holes 4 may be on any surface of the insulating substrate 1.

Further, as shown in FIGS. 7A and 7B, the circuit patterns 2 are formed on both surfaces of the insulating substrate 1, and the cut-out portions 3a of the lands 3 facing each other through the insulating substrate 1 are provided with the through holes 4. Is also formed at the time of drilling, and then the conductive paint is applied from the large-diameter opening 4b side of the through hole 4 in the same manner as described above,
A method of carrying out a curing treatment is also possible.

In the manufacturing method of the above two examples, since the hollow portion 3a of the land 3 is also formed when the through hole 4 is formed, the step of forming the hollow portion 3a in advance can be omitted.

The circuit pattern of the present invention may be not only a copper foil but also a circuit pattern printed with a conductive paint, or may be formed by another method which has been conventionally used. Further, the amount of the conductive paint can be arbitrarily set, and the viscosity and the angle and speed of the squeegee at the time of application may be appropriately set according to the diameter of the through hole and the like.

It is also possible to drop the corners with a drill or slightly scrape the small diameter portion in order to adjust the shape of the through holes formed by punching the through holes, and to apply the conductive paint. Processing such as facilitation is optional.

[0024]

Since the circuit board of the present invention has a bulge inside the through hole of the insulating substrate, the conductive paint is not cracked or peeled off. Therefore, there is no problem even if the inspection of the conductive through holes is performed only by visually observing the appearance from the front and back surfaces, the yield in the manufacturing process of the circuit board and the mounting process of components is improved, and the reliability of the circuit board is also increased. Further, in the method for manufacturing a circuit board according to the present invention, the conductive paint is applied from the direction opposite to the punching direction of the through holes of the insulating substrate, so that the printing can be performed once from the widest opening of the through holes. Conductive paint flows in smoothly,
Conductive paint can be applied to even extremely small holes. As a result, the diameter of the conductive through hole can be reduced, the packaging density of the circuit board can be improved, and the productivity of the circuit board can be significantly improved.

[Brief description of drawings]

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

FIG. 2 is a partial cross-sectional view showing another state of the conductive through hole in the first embodiment of the present invention.

FIG. 3 is a partial cross-sectional view showing the manufacturing process of the circuit board according to the first embodiment of the present invention.

FIG. 4 is a partial cross-sectional view showing the manufacturing process of the circuit board according to the first embodiment of the present invention.

FIG. 5 is a sectional view of a conductive through hole portion in another embodiment of the circuit board of the present invention.

FIG. 6 is a partial cross-sectional view showing main work steps in another embodiment of the method for manufacturing a circuit board according to the present invention.

FIG. 7 is a partial cross-sectional view showing main work steps in still another embodiment of the method for manufacturing a circuit board of the present invention.

[Explanation of symbols]

 1 Insulating Substrate 2, 21, 22 Circuit Pattern 3, 31, 32 Land 4 Through Hole 4a, 4b Opening 4c Small Diameter 5 Conductive Paint 6 Conductive Through Hole 9 Screen 10 Squeegee

Claims (4)

[Claims] 1. A circuit pattern formed on both sides of an insulating substrate, lands formed on one end of the circuit pattern so as to face each other with the insulating substrate sandwiched between the circuit pattern, and an insulating substrate close to the land. There is a formed through hole, the inner diameter of each opening on both sides of the insulating substrate of this through hole is different, and the inner wall surface of the through hole close to the opening of the smaller diameter is gently inside. A circuit board, characterized in that a small-diameter portion having a small inner diameter is formed by swelling to the through hole and a conductive paint which is hardened by being connected to the lands on both sides of the insulating board. 2. The circuit board according to claim 1, wherein the land is formed by printing on the outside of the conductive paint. 3. A circuit pattern having a land is formed on at least one surface of an insulating substrate, and the insulating substrate at the land forming portion is punched out to form through holes having different inner diameters on the both sides of the insulating substrate. A conductive paint is applied to the through hole by a squeegee through a screen from an opening having a large inner diameter in a direction opposite to the punching direction, and then the conductive paint is cured to form a conductive through hole. Circuit board manufacturing method. 4. The circuit board according to claim 3, wherein a land connected to the insulating paint is formed by printing after applying and curing the conductive paint.