JPH05129759A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To enable a printed wiring board to be kept high in electric reliability even if a second circuit pattern is printed by a method wherein a film of releasability and an insulating body provided with an insulating adhesive agent layer on its surface are made to overlap each other making the circuit pattern surface of the film confront the adhesive agent layer of the insulator and bonded together with pressure, and then the film is separated from the bonded body. CONSTITUTION:A conductive circuit pattern 1 is formed on the surface of a releasable film 4 on whose flat surface recesses 5 are provided at prescribed positions. On the other hand, an insulator 3 where an adhesive material 2 is applied and processed in a semi-cured state is prepared. The releasable film 4 and the insulator 3 are made to overlap each other bringing the circuit pattern 1 into contact with the adhesive material 2 and thermocompressed under vacuum. Then, the adhesive agent 2 in a semi-cured state is melted to flow, filled between the circuit patterns, and cured to bond. At the same time, the adhesive agent 2 is made to flow into the recesses provided to the releasable film 4 to form protrusions 6. Thereafter, the releasable film 4 is separated.

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, which is a printed wiring board in which an insulating material is filled between circuit patterns so as to be flush with the surface of the circuit pattern or vice versa. It is intended to provide a manufacturing method capable of selectively obtaining a printed wiring board having an insulator protruding at a predetermined position between them.

[0002]

2. Description of the Related Art As a method of manufacturing a printed wiring board having a circuit pattern formed thereon, as shown in FIG. 6, a Cu foil is formed on the surface of an insulator 3 such as a glass epoxy substrate, a paper phenol substrate or a thermoplastic resin film. After the predetermined circuit pattern 1 is formed by etching or by printing and hardening the conductive paste, the insulating resist 8 is printed and hardened to form an insulating coating. In the case of a circuit having a multilayer structure, the second circuit pattern 9 can be formed by printing and curing a conductive paste on the circuit.

When the electric component 11 is connected to the circuit pattern 1, the cream solder 10 is printed or applied at a predetermined position of the circuit pattern 1 and then the electric component 11 is connected.
The lead terminal 12 is placed and the cream solder 10 is melted and solidified by heat treatment such as reflow.

[0004]

However, as shown on the left side of FIG. 6, the conductive circuit pattern 1 provided on the surface of the insulator 3 is protruded by a predetermined thickness from the surface of the insulator when it is formed. Therefore, when the printing material in the subsequent step, for example, the insulating resist 8 is printed and cured, the insulating resist 8 is formed on the circuit pattern 1 due to the leveling effect or the like.
Tends to be thin. Therefore, when the second circuit pattern 9 is provided on the insulating resist 8 with a conductive paste or the like, since the insulating resist 8 is thin on the circuit pattern 1, the first circuit pattern 1 and the second circuit pattern 9 are not formed. Electrical insulation cannot be sufficiently secured between the circuit patterns 9, and a circuit short circuit or migration may occur. In particular, when the circuit pattern 1 has an acute-angled edge portion, this becomes more prominent. In order to prevent this, the insulating resist 8 is usually printed and cured at least twice to increase the film thickness.

Further, as shown on the right side of FIG. 6, when the lead terminals 12 having a fine pitch interval of the electric component 11 and the circuit pattern 1 are connected by the cream solder 10, insulation is provided between the circuit patterns 1. Even if the conductive resist 8 is printed, since there is no barrier between the adjacent cream solders, the solder bridge 10a may be formed on the insulating resist or fine solder balls may be generated depending on the processing conditions such as reflow. Electrical characteristics may be significantly deteriorated. For this reason, the defect rate at the time of mass production has been increased, and further manual correction has been required.
Here, it is possible to make the surface of the insulating resist 8 higher than the surface of the circuit pattern 1 by printing the insulating resist 8 thickly or by printing it several times. In some cases, the insulating resist 8 may cover even the surface of the circuit pattern 1 required for connecting the components due to the positional deviation or the surface deviation of the printing material.

[0006]

A method of manufacturing a printed wiring board according to the present invention for solving the above-mentioned problems includes a releasable film formed so that a conductive circuit pattern is projected on its surface, An insulating material having an insulating adhesive layer in a semi-cured state on the surface thereof, the circuit pattern surface of the film and the adhesive layer of the insulating material are pressure-bonded in a state of being overlapped to each other to bond the adhesive between the circuit patterns. After the filling, the film is peeled off to obtain a printed wiring board in which the circuit pattern is exposed from the adhesive layer on the insulator.

[0007]

According to this structure, when the insulating resist is printed on the circuit pattern and further the second circuit pattern is printed to form the multilayer circuit, the release film having a flat surface is used. Thereby, a flat printed wiring board in which only the surface of the circuit pattern is exposed can be obtained. By printing an insulating resist on this, a uniform film having a designed film thickness can be formed, and electrical reliability can be ensured even if the second circuit pattern is printed.

When the lead terminals having a fine pitch of an electric component (for example, an IC) and the circuit pattern are connected by using cream solder or the like, a release film having a recess formed in a predetermined position is used. By using the printed wiring board, a printed wiring board having protrusions protruding from the surface of the circuit pattern between the respective lands can be obtained. The convex portion can effectively suppress the generation of a solder bridge when melting the cream solder.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings together with its manufacturing process.

First, as shown in FIG. 2, the recess 5 is formed only at a predetermined position between the circuit patterns 1 having a flat surface.
A conductive circuit pattern 1 is formed on the surface of a film 4 having a releasability, which is a semicircular shape (in the drawing, a shape). This circuit pattern 1 is obtained by printing a conductive paste containing Ag, Cu particles, etc. by screen printing and then heat-treating it, or pre-punching a metal foil of Cu, Al, etc. with an acrylic adhesive. It is prepared by fixing with an agent. The film 4 is made of a conventionally known thermoplastic resin, and has a releasability of itself such as polyethylene, polypropylene, fluorine-based resin, etc., or a type in which wax is kneaded inside or a fluorine-based or silicon-based resin on the surface. A PET, PI, PPS resin of a type coated with a release agent such as is used. Further, the processing of the concave portion 5 can be performed by cutting with a conventionally known drill or the like or by hot pressing using a jig having a convex shape.

On the other hand, as shown in FIG. 3, there is prepared an insulator 3 on the surface of which the adhesive 2 is applied and treated in a semi-cured state. The adhesive 2 is made of an insulating thermosetting resin such as an epoxy type, a polyester type, a polyurethane type or the like, and is easily semi-cured by an appropriate heat treatment. As the insulator 3, a conventionally known glass epoxy substrate, paper phenol substrate, PI film, PET film or the like is used.

The releasable film 4 and the insulator 3 obtained in the above steps are superposed so that the surfaces of the circuit pattern 1 side and the adhesive 2 side are in contact with each other as shown in FIG. As a result, only the semi-cured adhesive 2 melts and flows and is filled between the circuit patterns 1, and the adhesive can be adhered and cured while enclosing the periphery thereof. At the same time, the adhesive 2 is applied to the concave portion provided at a predetermined position of the release film 4.
Flows in to form the convex portion 6 corresponding to this shape.

Here, the vacuum heating press is a method used in a conventionally known process for producing a printed wiring board,
A prepreg-like plate-like body to be laminated, a film, a metal foil, or the like is laminated in a predetermined order by a predetermined number and then heated / pressed under reduced pressure to produce a laminated plate. As a result, it is possible to obtain a printed wiring board with almost no pinholes or the like and with very little warping and deformation.

Thereafter, the release film 4 is peeled off to obtain a printed wiring board 7 in which only the surface of the circuit pattern is exposed from the surface of the adhesive layer 2, as shown in FIG. On the left side of FIG. 5, fully cured adhesive 2
And the surface of the circuit pattern 1 are on the same plane and have a flat shape. On the other hand, on the right side of FIG. 5, similarly, only the surface of the circuit pattern 1 is exposed, but between each of the circuit patterns 1, convex portions 6 that are raised in a predetermined shape are formed.

FIG. 1 shows a state in which a multilayer circuit is printed on the printed wiring board 7 and a state in which electric parts are mounted. On the left side of FIG. 1, after the insulating resist 8 is printed and cured, the second circuit pattern 9 made of a conductive paste is used.
Is formed. Here, since the surface of the printed wiring board 7 on which the circuit pattern 1 is formed is extremely smooth, the insulating resist 8 is printed with a uniform film thickness. For this reason, the electrical insulation between the first circuit pattern 1 and the second circuit pattern 9 can be sufficiently secured by only one printing of the insulating resist 8, and in the right side of FIG. The fine pitch lead terminals 12 fixed to the component 11 and the circuit pattern 1 are connected by the cream solder 10, and the convex portions 6 formed by the adhesive 2 exist between the circuit patterns 1. . Since this convex portion 6 acts as a barrier, the melted cream solder does not move onto the adjacent circuit pattern 1 when it is heat-treated by reflowing or the like, and moreover, the melted cream solders are cooled and solidified by each other. There is no contact to form a solder bridge. Further, even if a solder ball is generated, it slides down the slope of the convex portion 6 to reach the circuit pattern and is integrated with the already melted cream solder. Similarly, the flux contained in the cream solder does not remain as a flux residue between the patterns after the reflow. In the past, an insulating resist was printed between each of the circuit patterns 1, but it is not necessary to print the insulating resist because the convex portions 6 exhibit the above effects.

Here, the cream solder 10 is printed by a conventionally known screen printing method or a metal mask printing method in a shape substantially the same as the circuit pattern, or in a strip shape continuous to both ends of a large number of circuit patterns (commonly called). , Single-character printing), or a fixed amount may be directly dropped on the circuit pattern using a dispenser.

Instead of the cream solder, Ag,
Even when a conductive adhesive containing fine metal particles such as Cu is used, surface sagging can be prevented and similar effects can be obtained.

In the present embodiment, a printed wiring board having both characteristics is shown, but a printed wiring board having only a flat surface or a printed wiring board having a convex portion having a solder bridge preventing effect is used. It may be created separately.

Further, although the case where the cross section of the convex portion 6 has a semicircular shape is shown, the present invention is not limited to this, and may be trapezoidal, triangular or the like.

[0020]

As described above, according to the present invention, the circuit pattern can be made flat without protruding from the surroundings, and the insulating printing material can be printed with a uniform film thickness. The electrical insulation between the circuit pattern and the second circuit pattern is improved. In addition, convex portions that are higher than the surface of the circuit pattern can be easily and selectively formed between the fine-pitch circuit patterns. It is possible to prevent solder bridges that occur in the.

[Brief description of drawings]

FIG. 1 is a side sectional view of a printed wiring board manufactured by a method for manufacturing a printed wiring board according to the present invention, in which electrical components are mounted.

FIG. 2 is a side sectional view of a film in one manufacturing process of one embodiment of the method for manufacturing a printed wiring board of the present invention.

FIG. 3 is a side sectional view of an insulator in another manufacturing process of the same embodiment.

FIG. 4 is a side sectional view of a printed wiring board in still another manufacturing process of the same embodiment.

FIG. 5 is a side sectional view of a printed wiring board in still another manufacturing process of the same embodiment.

FIG. 6 is a side sectional view of a conventional printed wiring board on which electrical components are mounted.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Circuit pattern 2 Adhesive 6 Convex part 7 Printed wiring board 8 Insulating resist 10 Cream solder 11 Electric parts

Claims (3)

[Claims] 1. A circuit pattern of the film, comprising a releasable film formed so that a conductive circuit pattern is projected on the surface, and an insulator having a semi-cured insulating adhesive layer on the surface. A layer of the adhesive on the insulator by peeling the film after the adhesive is filled between the circuit patterns by pressure bonding in a state where the surface and the adhesive layer of the insulator are superposed on each other. A method for manufacturing a printed wiring board, characterized in that a printed wiring board having the exposed circuit pattern is obtained. 2. A recess is provided in advance at a predetermined position on the film surface between circuit patterns, and when the film is peeled off, an adhesive layer protruding from the surface of the circuit pattern is simultaneously formed at a position corresponding to the recess. The method for manufacturing a printed wiring board according to claim 1, wherein. 3. A circuit pattern of the film, comprising a releasable film having a conductive circuit pattern protruding on the surface thereof, and an insulator having a semi-cured insulating adhesive layer on the surface. A layer of the adhesive on the insulator by peeling the film after the adhesive is filled between the circuit patterns by pressure bonding in a state where the surface and the adhesive layer of the insulator are superposed on each other. A method for manufacturing a printed wiring board, which comprises obtaining a more exposed circuit pattern, applying an insulating layer at a predetermined position of the circuit pattern, and forming a second circuit pattern on the insulating layer.