JPH05259614A - Resin filling method for printed wiring board - Google Patents

Abstract

PURPOSE:To provide excellent solder bonding by maintaining a conductive circuit at a potential which reduces an oxide layer which covers the surface of the conductive circuit into metal after forming a resin layer on an area other than the conductive circuit and removing the resin bulged out to the conductive circuit by Peeling. CONSTITUTION:A hole is made on a copper clad glass epoxy laminated board and electroless copper plating is performed on the whole plane including the inside of the hole. Then, a conductive circuit and a through hole are formed. The part other than the conductive circuit on the board including a land pitch 0.5mm, land pitch 0.3mm and a land pitch 0.2mm is print coated with liquid resin composition. Then, the liquid composition is hardened by heat. The other plane is printed and hardened by the same method. The board is impregnated with copper powder added aqueous solution which includes pH 13 formalin. The resin bulged out and peeled off on the conductive circuit is removed by buff polishing. Then, the conductive circuit is softly etched by ammonium persulfate solution.

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, and more particularly to a method for producing a printed wiring board suitable for surface mounting.

[0002]

2. Description of the Related Art In recent years, a surface mounting method has become mainstream for mounting on a printed wiring board. Further, with the progress of finer design, the lead terminal pitch of the semiconductor package is rapidly narrowing. Conventionally, in surface mounting of a package or the like, the lead terminal pitch was sufficiently large, so it was relatively easy to insert a resin for preventing solder bridges between the lands of the printed wiring board connecting them. Alternatively, the solder bridge was less likely to be generated without inserting resin between the lands.

However, when the pitch of the lead terminals becomes narrow, in order to prevent the solder bridge, resin is put between the lands of the printed wiring board connecting them or the land and the land become substantially flat. Such a structure has become indispensable. There are printing or photolin method etc. to put the resin between the lands, but when the land interval becomes narrow, the printing accuracy or negative accuracy becomes insufficient, and a part of the resin covers the land. The problem occurs. In such a situation, there is a problem that it is difficult to accurately solder the lead terminals of the package or the like.

On the other hand, a printed wiring board manufactured by the additive method disclosed in Japanese Examined Patent Publication No. 61-11480 is known as a printed wiring board which can cope with high density mounting of components.

[0005]

However, according to the method disclosed in Japanese Patent Publication No. 61-11480, it is easy to form a structure in which the lands are flat and the lands are flat, but a circuit is formed only by electroless copper plating. There is a problem in that there are many technically difficult points such as the fact that it has to be formed and the adhesion between the electroless copper plating and the base must be secured.

According to the present invention, when a package or the like is surface-mounted, a resin filling method between lands for manufacturing a printed wiring board in which a solder bridge or the like is unlikely to occur even in a narrow pitch land and the land is not covered with resin. Is provided.

[0007]

In order to solve the conventional technical problems, the present invention fills a resin in a gap between conductor circuits of a printed wiring board on which conductor circuits are formed in advance to form a substantially flat surface. In the resin filling method for forming the surface, after the resin layer is formed in the area excluding the conductor circuit portion, the conductor circuit portion is maintained at a potential that can reduce the oxide layer covering the surface of the portion to metal. Then, by peeling off and removing the resin that was formed protruding to the conductor circuit part,
It is characterized in that the conductor circuit portion is exposed.

In the present invention, the conductor circuit including the land for mounting the package can be manufactured by a usual general method. Here, in the conductor circuit, copper plating is performed in most cases in order to make the through holes conductive.

Next, a resin is formed on a region such as a land for mounting the package, which needs to be filled with the resin, or on the entire substrate including the conductor circuit such as the land. As the resin applicable here, there is an insulating resin having heat resistance, electrolytic corrosion resistance, etc., which is usually used as a solder resist. For example, epoxy resin, acrylate resin,
Methacrylate resins and melamine resins are available. As a method for forming the resin layer on the entire surface, there are roll coating, curtain coating, dip coating, and a method of laminating a film-shaped material. There are printing methods and the like for locally coating. When the resin is coated on the entire surface, exposure and development are performed by light rays to form a resin layer on the portion excluding the conductor circuit. Finally, the resin is cured by heat or light. Although the thickness of the resin layer depends on the thickness of the conductor circuit, there is substantially no problem as long as it is approximately the same as the thickness of the conductor circuit.

According to the above method, the resin layer is formed on the portion other than the conductor circuit portion, but in reality, when the circuit becomes finer,
It is difficult to perfectly align the positions, and the resin layer protrudes on the circuit. Usually, the resin layer adheres sufficiently to the conductor circuit, so it is difficult to selectively remove the resin layer on the conductor circuit. The metal on the conductor circuit is usually oxidized,
The conductor circuit and the resin layer are in close contact with each other through the oxide film.

The present invention is intended to remove the resin layer on the conductor circuit by reducing the adhesion of the resin layer by reducing the oxide film layer to a metal. Copper is generally used for the conductor circuit, but the oxide can be made into metallic copper by making it more base than the reduction potential of copper. In order to make this possible, there is a method in which the conductor circuit is energized for reduction or it is immersed in a solution containing a reducing agent. Examples of the reducing agent include dimethylamine borane, sodium borohydride, formalin, hypophosphite and hydrazine. The resin layer is peeled off by immersing in a solution containing these reducing agents. Here, the lower the potential, the easier the peeling.
Further, the more the time and temperature are sufficient, the easier the peeling is. For example, with a 20 g / l dimethylamine borane aqueous solution, it is easy to sufficiently peel off at 50 ° C. for about 1 hour. Finally, the resin on the conductor circuit can be completely removed by brush polishing, buff polishing, or the like. By this method, the conductor circuit surface such as a land and the resin-filled surface between them can be made substantially flat.

[0012]

The present invention will be described in detail below. 1.6m
A hole was made in a required portion of the m-thick copper-clad glass epoxy laminate, and electroless copper plating with a thickness of 30 μm was performed on the entire surface including the inside of the hole. Next, a conductor circuit and a through hole were formed by a normal tenting method. Continued, liquid resin composition (Taiyo Ink, solder resist, S-222
N), land pitch 0.5 mm (distance between lands 0.2
mm), land pitch 0.3 mm (land distance 0.1
2 mm), land pitch 0.2 mm (distance between lands: 0.
(08 mm) was printed and applied to a portion except the conductor circuit on the substrate. Here, the thickness of the liquid resin composition is 3 between lands.
The printing conditions were adjusted to be 0 μm or more. Then
The liquid resin composition was thermoset. Subsequently, the other surface was printed and cured in the same manner. Then, add 70 ml of an aqueous solution containing copper powder containing 20 ml / l of formalin of pH 13
It was immersed at 0 ° C. for 2 hours. As a result,
The voltage was kept below 0.5V. Next, the peeled resin protruding on the conductor circuit including the land was removed by buffing.
Further, a conductor circuit of about 1 μm was soft-etched with an aqueous solution of ammonium persulfate to complete resin filling.

In the printed wiring board manufactured according to the above-mentioned embodiment, the resin covering on the land in the land portion where the resin is filled has a land pitch of 0.5, 0.3 and 0.2 m.
It was not observed in any of the cases. For the purpose of forming a substantially flat surface having a height within 10 μm from the land surface, a method of directly forming a photosensitive resin between the lands by a lithographic method was used for comparison. as a result,
With a 500 mm square substrate and a land pitch of 0.5 mm, a resin with a width of 0.1 mm could be inserted between the lands, but with land pitches of 0.3 and 0.2 mm, 0.0
An attempt was made to put a resin having a width of 7 mm between the lands, but most of the resin fell on the lands, and the lands could not be flattened.

[0014]

The printed wiring board manufactured by the method of the present invention can perform good solder connection without a solder bridge or soldering failure in the package surface mounting at the land portion. In addition, this method is not limited to double-sided printed wiring boards
It can also be applied to a multilayer printed wiring board.

[Brief description of drawings]

1A to 1D are cross-sectional views of a printed wiring board showing an embodiment of the present invention.

[Explanation of symbols]

 1. Insulation layer 2. Copper foil layer 3. Plating film 4. Insulating resin

Claims (1)

[Claims] 1. A resin filling method for forming a substantially flat surface by filling resin in a gap between conductor circuits of a printed wiring board on which conductor circuits are formed in advance, and a region excluding the conductor circuit portion. After the resin layer is formed on the conductor, the conductor circuit portion is maintained at a potential that can reduce the surface oxide of the portion to metal, and the resin formed by protruding to the conductor circuit portion is peeled off and removed. A resin filling method for a printed wiring board, which comprises exposing a circuit portion.