JPH06326437A - Printed wiring board and manufacture thereof - Google Patents

Abstract

(57) [Summary] [Construction] In a printed wiring board having through holes 4 in which wiring circuit patterns respectively formed on different surfaces are electrically connected by a conductive paste 6, the above through holes 4 are replaced by the conductive paste 6. At the same time, the conductor fiber 7 is filled. [Effect] It is possible to provide a highly reliable and inexpensive printed wiring board having improved mechanical strength and no change in resistance value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board for mounting electronic parts and the like and a method for manufacturing the same, and more particularly to a printed wiring board having through holes which are electrically connected by a conductive paste and a method for manufacturing the same. Regarding the method.

[0002]

2. Description of the Related Art Conventionally, in various electronic devices such as a television receiver, a radio receiver, a cassette tape recorder, etc., a printed wiring board on which a predetermined wiring circuit pattern is formed for mounting a large number of electronic parts and the like. Is often used.

For example, in a printed wiring board having two or more surfaces, so-called plated through holes are used to connect the wiring circuit patterns formed on the different surfaces by metal plating such as copper.

The plated through hole is for plating the inner wall surface of the through hole formed in the substrate and conducting the wiring circuit pattern between different surfaces by this plating.

However, the plated through hole has a drawback that it is expensive because the plating work is troublesome because the inner wall surface of the through hole formed in the substrate is plated and the process is complicated.

Therefore, in order to reduce the cost, a so-called silver through-hole substrate or a copper paste through-hole substrate in which wiring circuit patterns on different surfaces are connected by a conductive paste is being used in the past.

In these silver through-hole substrates and copper paste through-hole substrates, conductive paste is filled in the through holes formed in the substrate by screen printing, and then the conductive paste is heat-cured to cure the conductive paste. It is made by making.

[0008]

However, in the method of connecting the front and back wiring circuit patterns with the conductive paste, there is brittleness peculiar to the paste, and reliability and resistance value change upon thermal shock pose a problem. For example, cracks in the conductive paste may change the resistance value or deteriorate the durability.

Therefore, the present invention has been proposed in order to solve the above-mentioned conventional problems, and it is an object of the present invention to provide a highly reliable printed wiring board having no change in resistance value and a manufacturing method thereof. .

[0010]

DISCLOSURE OF THE INVENTION The present invention has been proposed to achieve the above object, and is a through hole in which wiring circuit patterns formed on different surfaces are electrically connected by a conductive paste. In the printed wiring board having, the through hole is characterized by being filled with a conductive fiber together with a conductive paste.

Further, according to the present invention, in a method for manufacturing a printed wiring board having through holes formed by connecting conductive circuit patterns formed on different surfaces with a conductive paste, conductive fibers are provided in through holes formed in the board. The feature is that the conductive paste is filled after the temporary filling.

[0012]

In the printed wiring board according to the present invention, since the conductive fiber is filled in the through hole together with the conductive paste, the conductive fiber enhances the mechanical strength of the conductive paste. Also, since the conductor fiber is a conductor itself,
It contributes to conduction as a through hole and stabilizes the resistance value low. Therefore, it becomes strong against thermal shock and the like, and the resistance value does not change.

On the other hand, in the method of manufacturing a printed wiring board according to the present invention, it is only necessary to temporarily fill the through holes formed in the board with the conductive fibers and then to fill the conductive paste.
A highly reliable through hole with high mechanical strength can be easily obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described in detail below with reference to the drawings. As shown in FIG. 1, the printed wiring board of this embodiment has an insulating substrate 1 which is obtained by impregnating or coating an insulating material such as paper or glass cloth with a phenol resin, a polyester resin, an epoxy resin, or the like. By etching the copper foil formed on both sides of the copper foil, a wiring circuit pattern (only the through hole pads 2 and 3 are shown) is formed into a desired circuit pattern.

Through holes 4 for electrically connecting the respective wiring circuit patterns formed on both surfaces of the insulating substrate 1 are formed on the printed wiring board.

The through hole 4 has a conductive paste 6 and a conductive fiber 7 in a circular through hole 5 formed through the insulating substrate 1 at the center of the through hole pads 2 and 3 of the wiring circuit pattern. After filling, it is formed by heat curing treatment.

The conductive paste 6 is formed so as to cover the inner wall surface of the through hole 5 and is laminated on the through hole pads 2 and 3 provided at the peripheral edge of the opening of the through hole 5, The upper and lower wiring circuit patterns are electrically connected.

The conductive paste 6 is mixed with conductive fibers 7 made of, for example, fibrous metallic copper. The conductor fiber 7 enhances the mechanical strength of the conductive paste 6, and contributes to the conduction as the through hole 4 because it is a conductor itself, and functions to stabilize the resistance value at a low level. Therefore, the reliability at the time of thermal shock is significantly improved, the resistance value change is extremely small, and the reliability is high.

In this printed wiring board,
Solder resists 8 and 9 for forming windows for mounting electronic components are formed on both surfaces of the insulating substrate 1.

Next, a method for manufacturing the above-mentioned printed wiring board will be described. First, as shown in FIG. 2, a so-called double-sided copper-clad laminate in which copper foils 2 and 3 are formed on both surfaces of an insulating substrate 1 is prepared.

Next, as shown in FIG. 3, the insulating substrate 1
Through holes 5 for forming through holes are formed at predetermined positions. The processing position and the hole diameter of the through hole 5 are controlled with high accuracy by a drill controlled by NC (numerical value).

Subsequently, as shown in FIG. 4, a predetermined circuit is formed on the copper foils 2 and 3 on both sides by the subtractive method. Next, as shown in FIG. 5, solder resists 8 and 9 are formed by printing on predetermined portions of the wiring circuit pattern except the through-hole pads 2 and 3.

Before the conductive paste 6 is filled in the through holes 5, the conductive fibers 7 made of, for example, fibrous metallic copper are temporarily filled in the through holes 5. To temporarily pack the conductor fibers 7, as shown in FIG. 6, for example, the insulating substrate 1 is adsorbed on the air-permeable mat 10 by air or the like,
Due to the suction force, the conductive fibers 7 scattered on the surface on which the one through-hole pad 2 is formed are forcibly sucked into the through hole 5.

When the conductor fibers 7 have been sucked into the through holes 5 to some extent, the excess conductor fibers 7 remaining on one of the through hole pads 2 are blown off in the direction of the arrow X by air or the like, as shown in FIG. As a result, FIG.
As shown in, the conductor fiber 7 is filled. It is not necessary to fill the conductive fibers 7 to such an extent that the through holes 5 are densely filled, and the conductive fibers 7 may be sufficiently filled with mechanical strength of the conductive paste 6 to be filled in the through holes 5 in a step described later. Good.

Next, as shown in FIG. 9, a conductive paste 6 such as a silver paste or a copper paste is filled in the through holes 5 by screen printing. The filling operation of the conductive paste 6 is performed from the side where one wiring circuit pattern is formed.

As a result, the through holes 5 in which the conductor fibers 7 are temporarily filled are filled with the conductive paste 6 and the through holes pads 3 and 4 provided above and below the through holes 5 are also electrically conductive. Paste 6 is laminated.

Next, the conductive paste 6 is heat-cured. Then, as shown in FIG. 1, the solvent contained in the conductive paste 6 flies and the conductive paste 6 is solidified.
At this time, since the conductor fiber 7 filled in the through hole 5 is fixed so as to strengthen the through hole portion, the mechanical strength of the through hole portion is increased. In addition, the conductor fiber 7 is
Since it is a conductor itself, it contributes to conduction as the through hole 4 and can be stabilized with a low resistance value.

It should be noted that, as shown in FIG.
In the printed wiring board shown in FIG. 11 in which the conductive paste 6 is filled in and heat-cured, the brittleness peculiar to the paste causes reliability and resistance value change at the time of thermal shock. However, both the mechanical strength and the change in resistance value can be improved by temporarily filling the through holes 5 with the conductive fibers 7 and then filling the conductive paste 6.

Next, a protective coating process called an overcoat is applied to the through hole portion. The protective coating process is an operation of applying a protective resist on the conductive paste 6 in the through holes in order to protect the conductive paste 6 from heat generated by solder.

Finally, after the symbol printing,
In order to form the outer shape of the printed wiring board into a desired shape, the outer shape is processed by pressing to finish it. As a result, the printed wiring board is completed.

[0031]

As is apparent from the above description, in the printed wiring board of the present invention, since the conductive fiber is filled together with the conductive paste, the conductive fiber enhances the mechanical strength of the conductive paste. As a result, the reliability of the through hole portion against thermal shock and the like can be significantly improved. Further, since the conductor fiber is a conductor itself, it contributes to conduction as a through hole and can stabilize the resistance value at a low level.

On the other hand, in the method of manufacturing a printed wiring board according to the present invention, it is possible to easily increase the mechanical strength by simply filling the through holes formed in the board with the conductive fibers and then filling the conductive paste. It is possible to obtain a reliable and inexpensive printed wiring board having through holes.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of a printed wiring board to which the present invention is applied.

FIG. 2 is an enlarged cross-sectional view showing the steps of manufacturing a double-sided copper-clad laminate, showing the steps of manufacturing a printed wiring board to which the present invention is applied in sequence.

FIG. 3 is an enlarged cross-sectional view showing a through-hole forming step, which sequentially shows the steps for manufacturing a printed wiring board to which the present invention is applied.

FIG. 4 is an enlarged cross-sectional view showing a wiring circuit pattern forming step, which sequentially shows the steps for manufacturing a printed wiring board to which the present invention is applied.

FIG. 5 is an enlarged cross-sectional view showing a solder resist forming step, which sequentially shows the steps for manufacturing a printed wiring board to which the present invention is applied.

FIG. 6 is an enlarged cross-sectional view showing a step of temporarily filling conductor fibers, which sequentially shows a manufacturing process of a printed wiring board to which the present invention is applied.

FIG. 7 is an enlarged cross-sectional view sequentially showing the steps of manufacturing a printed wiring board to which the present invention is applied, showing a step of blowing excess conductor fibers after temporary filling of the conductor fibers.

FIG. 8 is an enlarged cross-sectional view showing a step of manufacturing a printed wiring board to which the present invention is applied, in a state of being filled with conductive fibers.

FIG. 9 is an enlarged cross-sectional view showing a conductive paste filling step, which sequentially shows the steps for manufacturing a printed wiring board to which the present invention is applied.

FIG. 10 is an enlarged cross-sectional view showing a state where the through holes are simply filled with a conductive paste.

FIG. 11: After simply filling the through holes with the conductive paste,
It is an expanded sectional view showing the state where this was heat-hardened.

[Explanation of symbols]

 1 ... Insulating substrate 2, 3 ... Through hole pad 4 ... Through hole 5 ... Through hole 6 ... Conductive paste 7 ... Conductor fiber 8, 9 ... Solder resist 10. ··mat

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hironori Miho 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (2)

[Claims] 1. A printed wiring board having through holes formed by connecting conductive circuit patterns respectively formed on different surfaces with a conductive paste, wherein the through holes are filled with conductive paste and conductive fibers. A printed wiring board characterized by the above. 2. A method for manufacturing a printed wiring board having through holes formed by connecting conductive circuit patterns formed on different surfaces with a conductive paste, wherein conductive fibers are provisionally packed in through holes formed in the board. After that, a method of manufacturing a printed wiring board, characterized by filling a conductive paste.