JPS5838957B2 - Method for manufacturing through-hole printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a through-hole printed wiring board that is inexpensive and easily obtains high reliability.

Conventionally, the manufacturing method for this type of wiring board is to drill holes at desired locations in a double-sided copper-clad laminate, and conductive plating is applied to the entire surface including the inner wall of the hole by a method such as chemical plating and/or electroplating after chemical plating. Then, in order to protect the inner wall of the through-hole plated hole, the inside of the hole is covered or filled with etching-resistant selectively soluble varnish or ink, and then etching resist is applied to both sides of the substrate in a desired pattern. There is a method in which the conductive layer other than the pattern is removed by etching, the remaining etching resist film is peeled off with a solvent, and then the soluble protective material such as varnish or ink is removed with a selective solvent.

More specifically, for example, Japanese Patent Publication No. 47-39672,
A method such as Japanese Patent Publication No. 49-26784, and a method in which a photosensitive resin film layer is attached to a release paper or a release film on a double-sided copper-clad board plated through holes, are coated with a photosensitive resin on the front and back surfaces of the board. After adhering the membrane layer side to the surface of the conductive layer to close the hole, removing the release paper or wall-type film, etc., and forming the desired pattern by exposure treatment,
The method disclosed in Japanese Patent Publication No. 3746/1983 was used to manufacture a through-hole printed wiring board by performing an etching process and then peeling off a photocured resist film.

However, the former method of Japanese Patent Publication No. 47-39672 and Japanese Patent Publication No. 49-26784 uses varnish or ink as a hole protection material, which not only requires expensive materials, but also requires the use of alcohol when removing the hole protection material. , it is necessary to treat with a solvent such as alkaline liquid using a sprayer, etc., and it is difficult to remove protective materials such as varnish and ink, especially when the substrate is thick or has small pores such as multilayer boards. becomes.

Furthermore, if even a small amount of protective material residue remains in the hole, it is an organic substance, and decomposition gas from the residue is sometimes generated during soldering, which impedes soldering properties in the through-hole and significantly deteriorates the reliability of the through-hole. It had drawbacks.

On the other hand, the latter method, disclosed in Japanese Patent Publication No. 46-3746, involves attaching a photosensitive resin film layer to so-called release paper or a dry film with release properties, and the photosensitive resin film layer side is attached to the front and back surfaces of the conductive layer. This is a method called the tenting method, in which the release paper or release film is removed after the hole is closed.
For example, since Liston is used, the material is extremely expensive, and the cost becomes high when mass-produced.

In addition, with a small difference between the hole and the land, a slight deviation in the hole position causes the etching liquid to flow into the hole, etching the copper on the inner wall of the hole, which significantly reduces the reliability of the through-hole. there were.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a through-hole printed wiring board that eliminates the drawbacks of the above-mentioned conventional methods and achieves high reliability through a simple process at low cost.

Hereinafter, an example of the manufacturing method of the present invention will be explained in order of steps based on the drawings.

FIG. 1, which shows the first step, shows a double-sided copper-clad laminate in which holes are drilled, and 1 indicates an insulating layer, 2 indicates a copper foil layer, and 3 indicates a drilled through hole.

In the second step, in order to provide conductivity to the entire surface of the double-sided steel-clad laminate including the holes, for example, electroless chemical copper plating and/or electroplating is applied on top of the electroless copper plating. This is a well-known method such as that in which conductive plating is applied as shown in FIG. 2, and numeral 4 indicates a copper plating layer that is electrically connected to the inner wall of the through hole.

The third step is to mix powder such as whitebait, diatomaceous earth, clay, mud, clay, rock, etc. into the holes of the through-hole plated substrate through water, and then fill or fill the holes by press-fitting. After coating and drying, inorganic powder and the like remaining on the front and back surfaces of the substrate are removed using a brush, puff, etc.

The third step is shown in FIG. In this drawing, 5 is a mixture of inorganic powder and water, and the particle size of this powder is preferably fine and preferably about 300 mesh.

Further, the mixing ratio with water is about 1:0.5 to 1:1 by weight for good workability.

In the fourth step, an etching resist having etching resistance is applied to the conductive layers on both sides of the substrate, which holds a filler or coating such as an inorganic powder in the through hole, to form a desired circuit pattern as shown in 6 of FIG. Form and adhere to the surface.

The method for applying this etching resist is to screen print an etching-resistant ink.

Alternatively, a method may be used in which a photosensitive liquid resist is applied and required portions are cured and developed by exposure.

In the fifth step, etching is performed using an inexpensive etching solution such as ferric chloride solution, and the copper conductive layer other than that covered by the resist film is dissolved and removed, as shown in Figure 5, to form a circuit section. .

As the sixth step, since a resist film is adhered on the circuit part, this resist film is removed using an organic solvent or the like.
Peel off as shown in the figure.

Finally, in the seventh step, the inside of the hole of the substrate is cleaned by spraying with pressurized water or dipping in water to easily remove the filler or coating such as inorganic powder inside the hole. , the desired through-hole printed wiring board as shown in FIG. 7 is obtained.

According to the manufacturing method of the present invention, the hole of a through-hole plated substrate can be filled or covered with an inorganic powder, which is easily available anywhere, and water as a medium, instead of the conventional organic material. It is extremely inexpensive compared to varnishes, inks, etc., is not harmful, and unlike varnishes, inks, etc., there is no need for concentration adjustment, and workability is significantly improved.

In addition, when the holes are coated with varnish, ink, etc., the varnish, ink, etc. remaining on the front and back surfaces of the substrate are removed by polishing, but in the method of the present invention, polishing is not necessary and the inorganic powder is used. It can be removed with a brush, puff, etc. Compared to hole protection materials such as varnish and ink, there is less shrinkage on the upper and lower surfaces of the hole after drying, and the etching resin is uniform as a substrate with smooth front and back surfaces. There is no chance of resist breakage at the shoulder of the hole.

Next, there is a concern that uneven etching may occur if a trace amount of organic residue is present on the conductive layer of the substrate during etching, but the method of the present invention can be operated without even considering such concerns.

In the method of the present invention, the waste liquid after removing inorganic powder, etc. as a pore protection material by washing with water is extremely easy to dispose of, unlike organic material varnishes, inks, etc., and there is no need for pollution or sanitary equipment, and it does not cause sedimentation. It has the advantage of being recyclable through processing.

In addition, soldering inside the holes to ensure the attachment of components on the through-hole flint wiring board is difficult. Even if a small amount of residue remains inside the through-hole, it will not affect the soldering process because it is an inorganic material and will not be chemically applied to the copper. No effect occurs.

As described above, the method of the present invention overcomes the many drawbacks of the conventional manufacturing method of this type of wiring board, and achieves reliability by using extremely inexpensive materials and improving workability in a short period of time and with a highly reliable manufacturing method. This makes it possible to manufacture a through-hole printed wiring board with high performance, and contributes to the simplification of equipment and a significant reduction in costs, making it extremely useful.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 7 are longitudinal sectional views illustrating the order of each step of the method for manufacturing a through-hole printed wiring board according to the present invention. In the above drawings, 1 is an insulating layer, 2 is a copper foil layer, 3 is a through hole, 4 is a conductive plating layer, 5 is a mixture of inorganic powder and water, and 6 is an etching resist.

Claims (1)

[Claims] 1. Fill or cover the holes of a copper-clad laminate board with a conductive material film coated on the inner wall of the through hole and on the front and back surfaces of the board with water interposed therebetween, and after drying this, After removing inorganic powder etc. remaining on the substrate, an etching resist film with a desired pattern is deposited on the conductive material film on the front and back surfaces of the substrate, and after etching away the exposed conductive material film, the etching resist film is removed. A method for manufacturing a through-hole printed wiring board, which comprises peeling and removing a resist film using a solvent, and then washing and removing inorganic powder, etc. to be filled or coated.