JPH07212040A - Pattern connecting method of circuit board - Google Patents

Abstract

PURPOSE:To enable a method of electrically connecting conductive patterns provided to the front and rear of a circuit board together through a plated through-hole to be improved so as to restrain excess plating from attaching to the circuit board. CONSTITUTION:A resist film 7 is previously formed as shown in a Figure (A), a through-hole 4 is bored as shown in a Figure (B), and the through-hole 4 is plated with copper 5' through an electroless plating method as shown in a Figure (C). An excess copper plating 5' is restrained from being formed by the action of the resist film 7, and a product with no useless copper plating can be obtained as shown in a Figure (D).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of producing a circuit board having circuit patterns on the front and back sides of an insulating plate without adversely affecting the circuit pattern on the front side and the circuit pattern on the back side. The present invention relates to a method for electrically connecting these elements to each other so as to make them conductive. However, in the present invention, the front side and the back side of the insulating plate or the circuit pattern are not defined to be strictly distinguished from each other, and the names are for convenience of explanation, and if either one is set as the front side, the other side is the back side. , Can exchange names with each other.

[0002]

2. Description of the Related Art A classical method for electrically connecting two electric circuits to make them electrically conductive is to connect them with electric wires for soldering, which are provided on the front and back of a circuit board. A through-hole plating method is generally used to bring the circuit patterns into conduction with each other. In this method, through holes are formed in the insulating plate by penetrating through the conductive patterns facing the front and back of the insulating plate, and electroless plating is performed on the through holes. As a result, the circuit patterns formed by the conductive patterns on the front and back of the insulating plate are conducted by the plating film. More specifically, when making a circuit board,
After forming a metallic conductive film on the front and back of the insulating plate, apply a photoresist to this, and after exposing, developing and etching, remove the photoresist film to form a conductive pattern to form a circuit pattern. To do. The through-hole plating is performed before the conductive film is etched to form the circuit pattern. Therefore, although the above-mentioned through-hole plating conducts the circuit pattern, it is an operation to electrically connect the conductive film to be the circuit pattern (conductive pattern) in advance so as to be conductive. The application target of the present invention is not a finished product of a circuit board but an unfinished product before the etching treatment, which is called a circuit board semi-finished product. 2A and 2B are process diagrams of the through-hole plating operation. FIG. 2A is a state before processing, FIG. 2B is a state in which through holes are formed, and FIG. 2C is a state in which electroless plating is performed.
(D) is a cross-sectional view schematically illustrating a state in which an electrolytic plating layer is formed on the electroless plating layer.
The front side conductive coating 2 and the back side conductive coating 3 are formed on both surfaces of the insulating plate 1 as shown in FIG.
And electroless plating (electroless copper plating in this example) 5 is applied as shown in FIG. At this stage, the conductive coatings 2 and 3 on the front and back sides are electrically connected by the thin layer of the electroless copper plating 5. Further, as shown in FIG. 3D, electrolytic plating (electrolytic copper plating in this example) 6 is overlaid to reinforce the electroless copper plating 5, and the electrical resistance is reduced to complete conduction.

[0003]

In the method of connecting a conductive pattern (more specifically, a conductive film to be a conductive pattern) by through-hole plating of the conventional example shown in FIG.
A necessary and sufficient condition in the stage of FIG. 3C is that electroless copper plating is formed on the inner peripheral surface of the through hole 4 so that the front and back conductive films are electrically connected. However, in this conventional technique, as shown in FIG. 7C, unnecessary portions, that is, the front and back conductive films 2 are covered with the electroless copper plating 5. As a result, the front and back conductive coatings 2 and 3 are covered with the electroless copper plating 5 and the electrolytic plating 6 as shown in FIG. Thus, unnecessary plating leads to waste of plating chemicals and plating current. Not only that, but these useless platings are not easy to control the thickness of the coating film.
No. 3 has an excessive thickness in the uncontrolled or incompletely controlled state, and the film thickness uniformity is impaired. If the film thickness dimension is not uniform, it becomes difficult to form a high-density and high-precision circuit pattern in a subsequent process, which is extremely undesirable. The present invention has been made in view of the above circumstances, the front edge plate, the conductive coating to be the circuit pattern on the back, electrically connected by a necessary and sufficient plating layer, to make it conductive. An object of the present invention is to provide a circuit pattern connecting method in which a useless and harmful plating layer is not attached to the conductive film. As a result, it is expected that the waste of the plating chemical liquid will be reduced, and that the circuit pattern as the final product will have a high density and high accuracy, which will contribute to the improvement of the circuit board manufacturing technology.

[0004]

In order to achieve the above-mentioned object (prevention of unnecessary plating), a circuit board pattern connecting method according to the present invention comprises a conductive coating for forming a circuit pattern on each of the front and back of an insulating plate. Is provided with a through hole in the circuit board semi-finished product, electroless plating is applied to the circuit board semi-finished product to form an electroless plating layer on the inner peripheral surface of the through hole, and the electroless plating layer is interposed. In the method of connecting and electrically connecting the circuit patterns on the front and back sides of the insulating plate, prevent the electroless plating from adhering to the conductive coating on the front and back sides before the electroless plating is performed by making holes in the semi-finished circuit board. Form a resist film,
Prevents electroless plating from adhering to the flat surface of the conductive coating provided on each of the front and back of the insulating plate to form a layer,
An electroless plating layer is formed only on the inner peripheral surface of the through hole, and conductive patterns on the front and back of the circuit board are connected to and electrically connected to the inner peripheral surface of the through hole via the electroless plating layer. .

[0005]

When the present invention is applied, a thin film of resist is formed on the conductive film before the conductive film is provided on both surfaces of the semi-finished circuit board and perforated and prior to through-hole plating. Therefore, the plating does not adhere to the front and back conductive films covered by the resist. As a result, through-hole plating is applied only at necessary and sufficient places to prevent waste of plating chemicals and plating power, and since the plating does not adhere to the conductive coating, the conductive coating is precisely etched. A high-density, high-precision circuit pattern can be obtained.

[0006]

EXAMPLE An example of the method of the present invention will be described in detail with reference to FIG. FIG. 1 is a process diagram showing one embodiment of a circuit board pattern connecting method according to the present invention.
(A) shows a state where conductive films are formed on the front and back of the insulating plate,
(B) is a cross-sectional view schematically illustrating a state in which through holes are formed in the insulating plate, (C) is a state in which electroless plating is performed, and (D) is a state in which electrolytic plating is finished. Is.
In FIG. 1A, a thin layer 7 of resist is formed as compared with FIG. (B) As shown in the drawing, the through holes 4 are formed through the front and back conductive films 2 and 3 and the thin layer 7 of resist.

Next, electroless copper plating 5'is applied to the circuit board semi-finished product shown in FIG. At this time, (C) is applied to the front and back conductive films 2 and 3 covered with the thin layer 7 of the resist.
The electroless copper plating 5 "as shown by the phantom line in the figure does not adhere. The electrolytic copper plating 6'is formed as shown in FIG. As a result, a lean product can be obtained.

Here, the fact that the electroless plating does not adhere to the front and back conductive coatings 2 and 3 does not necessarily guarantee that the electroless plating does not adhere to the thin layer 7 of the resist.
Therefore, it is desirable to select the electroless plating agent and the type of resist and use a resist that does not adhere to electroless plating.

[0009]

When the present invention is applied, a thin layer of resist is formed on the conductive film before the conductive film is provided on both surfaces of the semi-finished circuit board and perforated, and prior to through-hole plating. Therefore, the plating does not adhere to the front and back conductive films covered by the resist. This allows
Through-hole plating is applied only at necessary and sufficient places to prevent waste of plating chemicals and plating power, and since plating does not adhere to the conductive coating, the conductive coating can be precisely etched, It has an excellent practical effect of obtaining a circuit pattern with high density and high accuracy.

[Brief description of drawings]

FIG. 1 is a method 1 of a pattern connection method for a circuit board according to the present invention.
It is process drawing which shows an Example.

2A and 2B are process diagrams of the through-hole plating operation, in which FIG. 2A is before processing, and FIG.
(C) is a cross-sectional view schematically showing a state where electroless plating is applied, and (D) a state where an electroplating layer is formed on the electroless plating layer.

[Explanation of symbols]

1 ... Insulating plate, 2 ... Front side conductive coating, 3 ... Back side conductive coating, 4
... through holes, 5,5 'electroless copper plating, 5 "... extra electroless copper plating, 6,6' ... electrolytic copper plating, 7 ... resist.

Claims (4)

[Claims] 1. A circuit board semi-finished product having a conductive coating for forming a circuit pattern on each of the front and back sides of an insulating plate is provided with a through hole, and the circuit board semi-finished product is electroless plated to form a through hole. In the method of forming an electroless plating layer on the inner peripheral surface and connecting and electrically connecting the circuit patterns on the front and back of the insulating plate through the electroless plating layer, the electroless plating is performed by forming a through hole in the semi-finished circuit board product. Before applying, a resist film that prevents the adhesion of electroless plating is formed on the front and back conductive films, and electroless plating is applied to the flat surface portions of the conductive films provided on the front and back of the insulating plate, respectively. A conductive pattern on the front and back of the circuit board is formed by forming an electroless plating layer only on the inner peripheral surface of the through hole to prevent adhesion and layering, and through the electroless plating layer on the inner peripheral surface of the through hole. A circuit board pattern that connects and conducts Connection method. 2. The circuit board according to claim 1, wherein, after the electroless plating is applied, electrolytic plating is applied on the electroless plating to reinforce the electroless plating layer to ensure conduction. Pattern connection method. 3. The circuit board pattern connection method according to claim 1, wherein the conductive films provided on the front and back of the insulating plate are made of copper. 4. The resist has a function of covering a conductive coating of a circuit board semi-finished product to prevent adhesion of electroless plating to the conductive coating, and a function of preventing adhesion of electrolytic plating. The pattern connection method for a circuit board according to claim 2, wherein the resist film itself has a property such that electroless plating does not adhere thereto.