JPH0365673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing printed wiring boards used in various electronic devices.

Conventional structure and its problems In recent years, printed wiring boards with conductive paint on both sides are easy to manufacture and require little capital investment.
Because it can be mass-produced, it has come to be used in large quantities in devices that consume relatively little power, such as calculators, remote controls, radios, tape recorders, and toys.

The manufacturing method for this type of printed wiring board is to form a circuit by etching the copper foil of the conductive laminate on one or both sides, then create a through hole in the board, and apply conductive paint such as silver paint inside the through hole. There is a known method in which the film is coated to form a gaseous connection on both sides of the board. For example, in the copper foil 1 and hard insulating base material 2 of a double-sided copper-clad laminate shown in FIG. 1a, an etching resist 3 is printed in a circuit shape on the surface of the copper foil 1 as shown in FIG. After that, this etching resist 3
is removed to form circuit patterns on both sides as shown in FIG. 1c. Next, as shown in Fig. 1d, the insulating base material 2
A through hole 4 is formed by drilling, as shown in Fig. 1 e.
As shown in the figure, silver paint is filled and applied into the through holes 4, and the front and back sides are electrically connected through the silver through holes 5. Thereafter, a solder resist 6 is printed on the silver through-holes 5 and on the necessary circuits, and the external shape is processed to produce a double-sided printed wiring board.

However, in the above method, since the silver through holes 5 are formed after etching the copper foil 1, the curing time of the conductive paint for the silver through holes 5 is long and the temperature is high, so that the insulating base material 2
Dimensional shrinkage is severe, making it difficult to guarantee dimensional accuracy for printed wiring boards in recent years, which require highly accurate dimensions. Moreover, since the dimensional change is large, the warping behavior during the process is severe, making it extremely difficult to print the solder resist 6 and process the external shape in the process after the conductive paint is cured. In addition, when trying to form the external shape and component insertion holes by press working after the conductive paint has hardened, the insulating material 2 deteriorates due to heat curing and becomes hard and brittle, making it difficult to work with and making it difficult to form between the component insertion holes. Due to the occurrence of cracks, cracks, and chipping of the board, the press punching conditions and circuit design conditions had to be extremely limited.
In recent years, printed wiring boards have become increasingly automated with the automatic insertion of components and the automatic mounting of small chip components, requiring extremely high precision dimensions, and there has been a strong desire to solve the above-mentioned drawbacks.

OBJECTS OF THE INVENTION In view of the above-mentioned conventional drawbacks, the present invention provides a method for manufacturing a printed wiring board in which through-holes can be formed using highly accurate conductive paint.

Structure of the Invention In order to achieve this object, the method for manufacturing a printed wiring board of the present invention involves drilling holes in the thickness direction of a copper-clad laminate, and only forming holes in the copper foil surface area within and around the processed holes. After filling and applying copper paint, heat treatment is performed to harden the conductive paint, an etching resist is formed on the conductive paint and the copper foil, and an etching process is performed to form a predetermined circuit pattern on the copper foil. It is something that forms. According to this manufacturing method, when the conductive paint is hardened by heat treatment, the copper foil remains on the entire surface of the insulating base material, so the copper foil suppresses the dimensional shrinkage of the insulating base material, and due to the heat dissipation effect of the copper foil, It is possible to prevent thermal deterioration inside the insulating base material and reduce warpage.

DESCRIPTION OF EMBODIMENTS A method of manufacturing a printed wiring board according to an embodiment of the present invention will be described below with reference to the drawings. FIGS. 2a to 2f are process diagrams showing a method for manufacturing a printed wiring board in an embodiment of the present invention. The hard type shown in Figure 2a is made by drilling holes in the copper foil 1 and insulating base material 2 of a double-sided copper-clad laminate in the thickness direction of the insulating base material 2, as shown in Figure 2b. form 4. Next, as shown in Figure 2c, silver paint is filled and applied only to the inside of the processed through hole 4 and the surface area of the copper foil around the processed through hole 4, and this silver paint is cured in a heat oven at 150°C for 1 hour. , through holes 5 are formed to electrically connect the front and back sides. Thereafter, as shown in FIG. 2d, an etching resist 3 was printed on the through holes 5 and on the copper foil 1, and then an etching process was performed, and the etching resist 3 was removed to form a circuit pattern as shown in FIG. 2e. Thereafter, as shown in FIG. 2f, a solder resist 6 was printed on the through holes 5 and the necessary circuit patterns, and the external shape and parts insertion holes were processed by press punching.

According to the method for manufacturing a printed wiring board as described above, since the copper foil 1 remains on the entire surface of the insulating base material 2 when the conductive paint is cured, the shrinkage of the dimensions of the insulating base material 2 is small, and the paper phenol 0.15 to 0.15 when through holes are formed after conventional etching on the substrate.
While the shrinkage was 0.30%, the shrinkage rate was 0.04-0.05%. Furthermore, the amount of warpage of the insulating base material 2 during the process is small, and a process of rewarping is not required, making the work easier. In the final process of press punching, paper phenol boards and paper epoxy boards, which are most often used for this type of printed wiring board, are easily cracked when punching with a 2.5 mm pitch between component insertion holes in conventional manufacturing methods. However, in this example, due to the heat dissipation effect of the copper foil 1, thermal deterioration was small and no cracks occurred. In addition, a hole pitch of 1.78 mm was also possible. As described above, according to this embodiment,
Dimensions are stable and higher density circuit patterns can be formed.

Although the present embodiment has been described using a double-sided copper-clad laminate, the same effect can be obtained using a single-sided copper-clad laminate.

Effects of the Invention As described above, the present invention forms through holes with conductive paint before etching the conductive foil, and since the conductive foil remains on the entire surface, the insulation base material shrinks in size due to the heat treatment of the conductive paint. It reduces the warpage of the insulating base material during the holding process, and the heat dissipation effect of the copper foil prevents thermal deterioration inside the insulating base material, improving workability in press punching etc., making it possible to create high-density This method has great practical effects as a method for manufacturing high-precision printed wiring boards.

[Brief explanation of drawings]

Figures 1 a to f are cross-sectional views for explaining the steps of a conventional printed wiring board manufacturing method, and Figures 2 a to f
FIG. 2 is a cross-sectional view for explaining the steps of a method for manufacturing a printed wiring board in an embodiment of the present invention. 1... Copper foil, 2... Insulating base material, 3... Etching resist, 4... Through hole, 5... Silver paint through hole, 6... Solder resist.

Claims (1)

[Claims] 1 Drill holes in the thickness direction of the copper-clad laminate,
After filling and applying conductive paint only to the surface of the copper foil in and around the processed through holes, heat treatment was performed to harden the conductive paint, forming an etching resist on the conductive paint and the copper foil. 1. A method for manufacturing a printed wiring board, comprising: thereafter performing an etching process to form a predetermined copper foil circuit pattern.