JPH01315191A - Manufacture of high density printed wiring board - Google Patents

Abstract

PURPOSE:To increase an alignment accuracy of a solder resist and to prevent the resist from hanging in a small-diameter via-hole prior to a plating process by irradiating ultraviolet rays onto a surface opposite to a surface on which an ultraviolet-ray cured plating and soldering resist is applied. CONSTITUTION:An ultraviolet-ray cured plating and solder resist film 5 is applied to the whole surface of one face of a printed wiring board. A through- hole portion is masked from the other face of the board. Then, ultraviolet rays is irradiated from the masked face and an uncured portion of the resist film 5 is removed by using a solvent such as a chlorothane. In the same manner, the resist film 5 is formed on a face opposite to the face on which the resist film is formed and a thick copper plating film 8 is formed on a conductive portion not coated with the resist film 5. Then, a thermosetting solder resist is applied to the whole surface. By this method, a very accurate resist can be formed. Therefore, the resist hanging in the through-hole before a thick chemical copper plating process is prevented from remaining and a high reliability can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a printed wiring board, and particularly to a manufacturing method suitable for application to a high-density printed wiring board having small diameter via holes.

[Conventional technology]

The printed wiring board has a through hole for mounting the mounted component, and is formed on the printed wiring board at the open end of this through hole, and the surface mounting has a terminal for electrical connection with the mounted component. A land has been formed. In addition, in order to improve the soldering properties of the mounted components, copper plating is applied to the inside of the through hole and the land portion.

In conventional printed wiring board manufacturing methods, for example, as described in Japanese Patent Publication No. 5O-26O22, a thermosetting solder resist is used to protect circuit conductors except for land areas and through-hole areas. Then, chemical copper plating was used to form copper plating on the land portion and the his-through hole portion.

Furthermore, Japanese Patent Application Laid-Open No. 12791/1983 discloses a technique using an ultraviolet curing solder resist.
Here, it is used in the step of patterning the exposed resist film after copper plating is formed in the through hole.

[Problem to be solved by the invention]

In the first conventional technology, a thermosetting solder resist is used, and the substrate to which it is applied is a through hole with a large diameter and a land (hole diameter α9rnm, land diameter 1.4 nm).
mco). The alignment accuracy is
Since a printing method is used, it is approximately ±[L15m111.

On the other hand, the hole diameter of the small diameter through hole (small diameter via hole) for connecting the conductor circuits on the front and back sides of the printed wiring board is OJmm, the land diameter is (15mm), and the alignment accuracy of the solder resist is at least (lL1f
fIm or more is required. Therefore, after forming the solder resist, plating is performed on the land portions and in the through-hole portions, and in the 5-part additive method, the thermosetting solder resist using the conventional printing method is used to form small-diameter via holes that require strict alignment accuracy. It cannot be applied to printed wiring boards.

In addition, in order to solve the problem of peeling, there is a method in which copper plating is formed on the lines, lands, and through holes by chemical copper plating before forming the solder resist, and then the solder resist is formed. However, in this case, when plating is applied, the plating also adheres to the side surfaces of the line and the line width becomes thicker, so it is necessary to take this into consideration and form the line portion to be that much thinner during etching. This causes an increase in circuit disconnections and the like, which is a major problem with thinning patterns.

The purpose of the present invention is to improve the alignment accuracy of solder resist, prevent the resist from sagging into small-diameter via holes before the plating process, and provide high-density printed wiring boards with small-diameter via holes with high connection reliability. Our goal is to provide the following.

[Failure to solve the problem]

In order to achieve the above object, the method for manufacturing a high-density printed wiring board of the present invention includes the steps of forming through holes in a substrate on which copper foil is formed on both the front and back surfaces (first surface and second surface); a step of forming a catalyst layer for chemical copper plating in the hole, a step of forming the steel foil into a predetermined circuit shape, a step of forming a thin copper plating film in the hole and on the copper foil by chemical copper plating, A step of applying an ultraviolet curing plating resist/solder resist film to the entire first surface of the substrate, masking the hole from a second surface opposite to the first surface, and irradiating ultraviolet rays from the second surface side. and removing an uncured portion of the resist film on the first surface, further applying an ultraviolet curable plating resist/solder resist film to the entire surface of the second surface, and removing the uncured portion of the resist film from the first surface. a step of masking and irradiating ultraviolet rays from the first surface side; a step of removing an uncured portion of the resist film on the second surface; The method is characterized by comprising a step of forming a copper plating film, and a step of forming an exposed resist film except for a predetermined portion.

[Effect]

By irradiating ultraviolet rays from the opposite side of the surface fully coated with ultraviolet curing plating resist and solder resist,
The conductor circuit part including the land part and line part on the resist coated surface serves as a kind of artwork for resist formation, achieving ideal alignment accuracy (±001 mm).
A resist can be formed by

In addition, in the process of forming thick copper plating, the line portion is exposed on the surface and a plating layer is formed on it, but the side surface of the line portion is embedded with a resist film, so The plating does not precipitate, and the line width does not become thicker even after the plating process.Therefore, when etching a conductor circuit, it is only necessary to form it according to the finished dimensions, and unlike conventional methods, the line width becomes thicker due to plating precipitation. Since there is no need to form the wire thinner in advance in anticipation of the wire breakage, the problem of wire breakage can be solved.

In the process of the present invention, a thin plating film is formed.

Furthermore, the reason why the through-hole is masked is that the resist film inside the through-hole is irradiated with ultraviolet rays, which hardens the resist film and prevents it from remaining.

〔Example〕

FIGS. 1(A) to 1(H) are process cross-sectional views showing one embodiment of the method for manufacturing a high-density printed wiring board of the present invention.

First, through holes (including small-diameter via holes) are formed using a drill or the like at predetermined positions on a copper-clad laminate 10 in which copper foil 1 is formed on both the front and back sides of a base material layer 3 made of an insulator. A catalyst layer 2 for chemical copper plating is formed in the hole (FIG. 1(A)).

Next, the copper foil 1 is etched using a known tenting method to form a desired conductor circuit pattern, and copper is deposited on the patterned conductor (including land and line parts) and in the through holes by chemical copper plating. The plating film 4 is formed thinly (thickness (L5 to 2.5 μm)) (FIG. 1(B)).

Next, a solder resist film 5 that also serves as an ultraviolet curing plating resist is applied to the entire surface of one side of the printed wiring board, the through-holes are masked from the opposite side, and ultraviolet rays 7 are irradiated from the masked surface (see Fig. 1). C)).

Next, the uncured portion of the resist film 5 is removed using a solvent such as chlorocene (FIG. 1(D)).

Next, a resist film 5 is similarly formed on the surface opposite to the surface on which the resist film 5 was formed, resulting in the results shown in FIGS. 1(E) and 1(F).

Next, the conductor parts not covered with the resist film 5 are subjected to chemical copper plating to form a thick copper plating film 8 (FIG. 1(G)).

Next, apply thermosetting solder resist to the entire surface of the component (top surface in the figure) except for the large-diameter through holes for mounting the mounted components, and then
Figure 1 (H) is obtained by applying a thermosetting solder resist to the entire surface except for the large-diameter through holes and their lands.

According to this embodiment, since the resist can be formed with high precision, the thick resist film can be prevented from remaining in the through holes before the chemical copper plating process, and reliability can be improved. In addition, copper plating is deposited on the line part, but since the plating is not deposited on the side of the line, there is no need to narrow the line width in advance to the plated part as in the conventional method, and therefore, the possibility of wire breakage at the line part increases. There's nothing to do.

Regarding the resist film formed in FIG. 1(H),
It is better to use a thermosetting resist, which has stronger adhesion to the copper surface than an ultraviolet curable resist.

〔Effect of the invention〕

As explained above, according to the manufacturing method of the present invention, the alignment accuracy of the resist can be dramatically improved from the conventional level (L15mo+) to the level (L01ffIIT+). There is no residual resist film hanging down into the via hole, and the chemical copper plating is deposited well, allowing the formation of highly reliable small-diameter via holes.In addition, the line width increases after the copper plating process. Therefore, there is no need to take into account the increase after the plating process and thin the wire in advance, so a printed wiring board with a high yield and less disconnection can be obtained.

[Brief explanation of the drawing]

FIGS. 1(A) to 1(H) are sectional views showing the manufacturing process of a high-density printed wiring board according to an embodiment of the present invention. 1... Copper foil 2... Catalyst for chemical copper plating 3... Base material layer 4... Thin material is chemical copper plating film 5... Ultraviolet curing type plating resist/solder resist film 6... Through-hole mask 7...UV light 8...Thick chemical copper plating film 9...Thermosetting solder resist film 10...Copper-clad laminate: )

Claims (1)

[Claims] 1. A process of making a through hole in a substrate with copper foil formed on both the front and back sides (first and second sides), a process of forming a catalyst layer for chemical copper plating in the hole, and a process of forming the copper foil into a predetermined circuit shape. a step of forming a thin copper plating film in the hole and on the copper foil by chemical copper plating; and a step of applying an ultraviolet curable plating resist and solder resist film to the entire first surface of the substrate; a step of masking the hole from a second surface opposite to the first surface and irradiating ultraviolet rays from the second surface side; and a step of removing an uncured portion of the resist film on the first surface; , applying an ultraviolet curable plating resist and solder resist film to the entire surface of the second surface, masking the holes from the first surface, and irradiating ultraviolet rays from the first surface side; a step of removing an uncured portion of the resist film, a step of forming a thick copper plating film on the copper foil not covered with the resist film, and a step of forming a solder resist film except for a predetermined portion. A method for manufacturing a high-density printed wiring board, comprising: