JPH06326460A - Manufacture of printed wiring board - Google Patents

Abstract

(57) [Summary] [Construction] In a method of manufacturing a printed wiring board having through holes 8 in which wiring circuit patterns respectively formed on different surfaces are conducted by a conductive paste 7, a conductive paste is formed in through holes 4. Immediately after filling with 7, ultrasonic vibration is applied. [Effect] The protrusion amount of the conductive paste protruding on the printed surface of the printed wiring board and the back surface on the opposite side can be made substantially the same, and the reliability of the through hole portion and the surface mountability can be significantly improved. it can.

Description

Detailed Description of the Invention

[0001]

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

[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 such as silver paste or copper paste is filled in the through holes formed in the substrate by screen printing, and then heat-cured. It is produced by curing the conductive paste.

[0008]

However, when the conductive paste is filled by screen printing, the thickness of the conductive paste is different between the printing surface on the printing side and the back surface on the opposite side. That is, the thickness of the conductive paste is thin on the printed surface side, and the thickness of the conductive paste is large on the back surface side.

For this reason, the reliability of the through-hole corner portion is deteriorated due to the insufficient thickness on the printing surface side, and the excessive thickness on the back surface side causes a problem in mounting an electronic component or the like. To do.

Therefore, the present invention has been proposed to solve the problems of the prior art, in which the protruding amounts of the conductive paste protruding on the printed surface and the back surface of the printed wiring board are made substantially uniform. An object is to provide a printed wiring board having excellent surface mountability.

[0011]

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 method for manufacturing a printed wiring board having the above, the method is characterized in that the through hole formed in the board is filled with a conductive paste and then vibrated.

[0012]

In the present invention, since the substrate is vibrated immediately after the conductive paste is filled in the through holes formed in the substrate, the conductive paste filled in the through holes is vibrated, and the printed surface and the back surface are And, the protruding amounts of the conductive paste become substantially equal.

[0013]

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. The printed wiring board of this example is manufactured by the following procedure. First, as shown in FIG. 1, 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.

In this embodiment, the insulating substrate 1 has a thickness of 1.
A 2 mm paper phenol substrate was used, and the thickness of the copper foils 2 and 3 was 35 μm.

Next, as shown in FIG. 2, the insulating substrate 1
Through holes 4 for forming through holes are formed at predetermined positions. The processing position and the hole diameter of the through hole 4 are controlled with high precision by a drill under NC (numerical value) control.

Subsequently, as shown in FIG. 3, a predetermined wiring circuit pattern (only the through-hole pads 2 and 3 are shown) is formed on the copper foils 2 and 3 on both sides by a subtractive method. Next, as shown in FIG. 4, solder resists 5 and 6 are formed by printing on predetermined portions of the wiring circuit pattern except the through hole pads 2 and 3.

After that, as shown in FIG. 5, the through holes 4 are filled with a conductive paste 7 such as a silver paste or a copper paste by screen printing. The filling operation of the conductive paste 7 is performed from the side where one wiring circuit pattern is formed. In this example, a copper paste (trade name TH1259) manufactured by Tatsuta Electric Wire Co., Ltd. was used as the conductive paste 7.

As a result, the through hole 4 is filled with the conductive paste 7, and the conductive paste 7 is also laminated on the through hole pads 2 and 3 provided above and below the through hole 4. In this screen printing state, the thickness of the conductive paste 7 becomes thin on the side of the printed surface on which the one through-hole pad 2 is provided, and the thickness of the conductive paste 7 becomes extremely thick on the opposite side, the back surface. Therefore, in the next step, the thickness of the conductive paste 7 is made uniform on the front and back surfaces.

That is, immediately after filling the conductive paste 7, the insulating substrate 1 is vibrated. In this embodiment,
While holding the end portion of the insulating substrate 1, ultrasonic vibration was rapidly applied for 5 seconds. The vibration applied to the insulating substrate 1 is not limited to ultrasonic vibration, but may be forced mechanical vibration, for example. Further, at this time, it is more effective to turn the front and back of the insulating substrate 1 so that the printing surface is directed in the direction of gravity and vibrate.

As a result, the conductive paste 7 filled in the through-holes 4 is vibrated by ultrasonic vibration, as shown in FIG.
As shown in, the amount of protrusion is equal on the printing surface and the back surface. That is, the distance T ₁ from the through hole pad 2 formed on the printing surface side to the tip of the conductive paste 7 and the distance T ₂ from the through hole pad 3 formed on the back surface side to the tip of the conductive paste 7 are approximately Will be equal.

Next, the conductive paste 6 is heat-cured. Then, as shown in FIG. 7, the solvent contained in the conductive paste 7 is blown away to open a hole in the center, and the hardened conductive paste 7 covers the inner wall surface of the through hole 4 and the through hole pads 2, 3 The conductive paste 7 is also laminated on the top.

As a result, a through hole 8 is formed in which the wiring circuit patterns respectively formed on both surfaces of the insulating substrate 1 are conducted by the conductive paste 7.

Next, the through-hole portion is subjected to a protective coating treatment called overcoating. The protective coating process is an operation of applying a protective resist on the conductive paste 7 in the through hole portion in order to protect the conductive paste 7 from heat generated by solder.

And finally, after performing 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.

Here, after actually manufacturing the printed wiring board, it was humidified under the conditions of 40 ° C., 90% and 96 hours, and then,
The solder was immersed in the condition of 245 ° C. for 5 seconds, and the resistance value was measured. Immediately after the conductive paste 7 was filled, solder was dipped under the same conditions for the printed wiring board that was produced without applying vibration.

As a result, in the printed wiring board produced without applying vibration, the resistance value was 65 mΩ / hole. On the other hand, in the printed wiring board manufactured through the above-mentioned steps, it was improved to 31 mΩ / hole. This is because the conductive paste 7 projecting on the printed surface of the insulating substrate 1 and the back surface of the insulating substrate 1 on the opposite side have substantially the same projecting amount.

[0027]

As is apparent from the above description, in the method of the present invention, vibration is applied immediately after filling the through holes of the insulating substrate with the conductive paste. Are vibrated, and the projection amount of the conductive paste projecting on the printed surface of the substrate and the back surface opposite to the printed surface becomes substantially the same. Therefore, the reliability of the through hole is significantly improved in terms of resistance and the like, and the protrusion amount of the conductive paste on the back surface side can be suppressed, so that the surface mountability can be significantly improved.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing the steps of manufacturing a printed wiring board to which the present invention is applied in sequence and showing the steps of manufacturing a double-sided copper-clad laminate.

FIG. 2 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. 3 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. 4 is an enlarged cross-sectional view showing a solder resist forming step, which sequentially shows steps of manufacturing a printed wiring board to which the present invention is applied.

FIG. 5 is an enlarged cross-sectional view showing a conductive paste filling step, which sequentially shows manufacturing steps of a printed wiring board to which the present invention is applied.

FIG. 6 is an enlarged cross-sectional view showing a process of manufacturing a printed wiring board to which the present invention is applied in sequence and showing a process of applying ultrasonic vibration.

FIG. 7 is an enlarged cross-sectional view showing the steps of manufacturing a printed wiring board to which the present invention is applied, in sequence, showing the steps of thermosetting the conductive paste.

[Explanation of symbols]

 1 ... Insulating substrate 2, 3 ... Copper foil 4 ... Through hole 5, 6 ... Solder resist 7 ... Conductive paste 8 ... Through hole

Claims (1)

[Claims] 1. A method of manufacturing a printed wiring board having through holes formed by connecting conductive circuit patterns formed on different surfaces with a conductive paste, wherein through holes formed in the board are filled with the conductive paste. rear,
A method of manufacturing a printed wiring board, characterized by applying vibration.