JPH03165092A - Manufacture of throughhole printed wiring board - Google Patents

Abstract

PURPOSE:To improve considerably the reliability of throughhole connection and the yield of manufacture by performing thin electroless copper plating in advance after performing catalytic treatment in throughholes made in a laminated board that is covered with copper and again, performing electroless copper plating after forming each pattern that is required for both side layers of an insulating board. CONSTITUTION:Each throughhole is made at a laminated board which is obtained by bonding copper foils 9 on both side layers of an insulating board 8. Catalytic layers 11 are attached in order to deposit electroless copper plating over the whole surface and then, a 1st electroless copper metallic layer 12 having a thin film is deposited after being immersed in an electroless plating solution. Then, an etching resist 13 is applied to the whole surface and further, ultraviolet exposure and development treatment are performed by making a film where each desired pattern is formed come closely into contact with the above metallic layer and thus, a resist layer 13 that is resistance to etching properties is formed. Subsequently, the above board is treated with etching and a required circuit conductor layer is formed. Then a permanent resist layer 14 is formed selectively and further, its layer is immersed in the electroless copper plating solution and a 2nd electroless copper plating metallic layer 15 is deposited at each throughhole 10 and at a part of the circuit conductor layer 9 in the peripheral part of the throughhole 10.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to a method of manufacturing high density null-hole printed wiring "boards" used in a wide range of electronic equipment.

BACKGROUND OF THE INVENTION In recent years, with the rapid development of electronics technology, the demand for printed wiring boards has increased significantly.

In particular, there is an extremely high need for higher density printed wiring boards due to the recent trend toward smaller size and higher performance of electronic devices.
The need for high-density through-hole printed wiring boards that are oriented toward high multilayering and fine wiring is increasing more and more.

Conventionally, various methods have been used to manufacture such high-density null-hole printed wiring boards, and one example is a manufacturing method commonly called a part-additive method.

This typical manufacturing process is shown in Figures 2A-H.

In Fig. 2, 1 is an insulating substrate, 2 is a copper foil (circuit conductor layer), 3 is a through hole, 4 is a Fi catalyst layer, 6 is an etching-resistant resist, 6 is an electroless plating-resistant permanent resist layer, and 7 is an electroless It is a copper plated metal layer.

The printed wiring board produced by this part-additive method takes advantage of the characteristics of both printed wiring boards produced by the etching method and the additive method.

The typical manufacturing process is as follows.

That is, as shown in FIG. 2, copper foils 2 were bonded to both sides of an insulating substrate 1 such as a glass epoxy laminate substrate.

Using a so-called copper-clad laminate board, first, as shown in FIG. 2B, through-holes 3 are drilled at locations where null-hole connections are required, and then activated to include the through-holes 3. A catalyst layer 4 consisting of fine particle nuclei of metallic palladium is adhered to the entire copper-clad multilayer substrate, and then, as shown in FIG. An etching-resistant resist layer 6 is formed in the desired circuit diagram shape by a screen printing method, and the entire etching process is performed to dissolve and remove the necessary metal layer. After forming the through hole 3 and a part of the circuit conductor layer 2 around it, the other parts are coated with a permanent resist 6 that is resistant to electroless steel plating as shown in the second diagram. It is made by electroless copper plating to form a thick copper metal layer 7 on the inner wall surface of the through hole and the circuit conductor layer 2 in its surrounding area as shown in FIG. 2E. .

Problems to be Solved by the Invention However, in the through-hole printed wiring board according to the conventional example, when performing electroless copper plating on the through-holes and making through-hole connections, as a pre-treatment for depositing electroless copper plating. After the catalytic treatment and before electroless steel plating, the process of forming an etching resist,
It must go through many processes such as etching process, resist removal process, electroless copper plating resist formation process, etc., and the catalyst layer is activated by chemical treatment such as etching and thermal treatment during resist formation. There were problems in that the strength was reduced and the coverage of electroless copper plating deteriorated, resulting in a reduction in manufacturing yield and a lack of reliability in through-hole connections.

The present invention aims to solve these conventional problems and provide a method for manufacturing a high-density through-hole printed wiring board that can more reliably connect through-holes using electroless steel plating. be.

Means for Solving the Issues In order to achieve this object, the present invention provides through holes at predetermined positions of a copper-clad laminated board in which copper foil is bonded to the outermost layer of the front and back surfaces of a resin-based insulating board, and A first copper metal thin film layer is formed on the entire front and back surfaces of the copper-clad multilayer substrate including the inner wall surface of the hole by electroless copper plating, and a desired layer is formed on the inner wall surface of the through hole and both the front and back surfaces of the copper-clad multilayer substrate. An etching-resistant resist layer is formed in the shape of a wiring circuit diagram, and the first copper metal thin film layer that is not covered by the resist layer is dissolved and removed by an etching method, and then the resist layer is removed to form a circuit conductor layer. A permanent resist layer with electroless plating resistance is selectively coated on the through hole and at least a part of the circuit conductor layer around the through hole, and then electroless copper plating is applied again. A second copper metal thick film layer is formed on the surface layer of the circuit conductor layer exposed through the through hole.

Function: Immediately after catalytic treatment of the through-holes in the copper-clad laminate board, a thin layer of electroless copper plating is applied in advance to confirm whether or not the through-hole connection has been established. By forming the necessary patterns on both the front and back layers and finally applying thick electroless copper plating, a thick copper layer is formed on the necessary parts of the circuit conductor layer, including through holes.
Electroless copper plating will significantly improve the reliability and manufacturing yield of through-hole connections.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIGS. 1M to 1F are cross-sectional views showing the manufacturing process of a null-hole printed wiring board in a first embodiment of the present invention.

In FIGS. 1A to 1F, 8 is an insulating substrate, 9 is a copper foil (circuit conductor layer), 1o is a through hole, 11 is a catalyst layer, 12 is a first electroless copper plating metal layer, 13 is an etching-resistant resist layer, 1
4 is an electroless copper plating resist layer, and 16 is a second electroless copper plating metal layer.

The manufacturing method for the through-hole printed wiring board configured as described above will be explained in detail below.

According to the first embodiment, as shown in FIG. Using a so-called copper-clad laminate to which a copper foil 9 with a thickness of 10 to 36 μm is adhered, first, as shown in FIG. A through hole 10 having an arbitrary diameter is drilled for hole connection. After this, 1 fine particles of metallic palladium are sequentially immersed in an activation treatment solution consisting of, for example, dichloromethane and palladium chloride to deposit electroless copper plating on the entire surface of the copper-clad multi-layered substrate including the through holes 1o. A catalyst layer 11 consisting of is deposited.

Next, this copper-clad multi-layer board is immersed in an ordinary electroless copper plating solution consisting of an alkaline solution of a copper complex salt and formalin, so that the entire copper-clad multi-layer board including the through-holes 101 is coated with about 1 to A first electroless copper plating metal layer 12 consisting of a thin film of about 2 μm is deposited.

As shown in the first diagram, an etching resist 1 having high resolution is applied to the entire surface of the substrate including the inner wall surface of the through hole 1o.
3 is applied, the film with the desired pattern is brought into close contact with the film, exposed to ultraviolet rays, and developed to form 1 through hole 1o.
Then, an etching-resistant resist layer 13 is formed in a desired wiring circuit diagram shape on both the front and back surfaces of the copper-clad multilayer board that has been subjected to electroless copper plating.

In this case, the etching resist layer 13 can be formed using an IED method (electrodeposition method), a dry film method coated with a photosensitive resist, a method using a liquid resist material, or a method in which easily removable ink is applied to the through holes 10. It is possible to fill the substrate and apply etching resist ink in a pattern to both the front and back surfaces of the substrate by screen printing.

Then, this substrate is immersed in a ferric chloride or cuprous chloride solution to perform an etching process, and as shown in FIG. form a circuit conductor layer.

In forming this circuit conductor layer, if it is necessary to form a fine pattern, it is preferable to use a copper-clad laminate in which the thickness of the copper foil is made as thin as possible.

In this embodiment, since it was necessary to form a circuit conductor layer having a pattern width of at least 60 μm, a copper-clad laminate board with 18 μm copper foil bonded thereto was used.

Then, as shown in FIG. 1F, the through holes 10 and the circuit conductor layer around them, and the circuit conductor surface that does not have the through holes, are exposed by thin electroless copper plating. A permanent resist layer 14 having resistance to electroless copper plating is selectively formed on other parts so as to do so.

In this case, it is desirable that the permanent resist layer 14 has excellent properties such as not only chemical resistance but also electrical insulation and heat resistance, and in this example, epoxy resin, epoxy modified resin, etc. These resist materials are selectively formed by screen printing or photography using acrylic resin.

Then, the substrate selectively coated with this permanent resist layer 14 is further immersed in an electroless copper plating solution, and a second electroless copper plating metal layer is applied to the through hole 10 and a portion of the circuit conductor layer 9 around the through hole 10. A high-density printed wiring board with null-hole connections was completed by depositing to a thickness of about 16110 to 30 μm.

In this case, the second electroless copper plating 16 is thickened to ensure the reliability of through-hole connections, but the physical properties of the copper coating are such as ductility and ductility to ensure reliability of through-hole connections. It must have excellent elongation properties, and in this example, as an electroless steel plating method that meets this purpose, a small amount of 2.2 Chatter Seal is added as an additive to a basic bath consisting of a copper-EDT complex salt and formalin. Immersion plating is carried out for 8 to 10 hours at a pH of 12.0 to 13.0 and a bath temperature of 70° C. using the added plating bath. The printed wiring board with through-hole connections under these conditions is -55"C ~ 1
It was found that there was almost no change in the through-hole resistance value in any of the severe thermal shock tests such as the heat cycle test at 50°C and the oil dip test at 260"C, and good reliability could be ensured.

On the other hand, in the second embodiment, a multilayer wiring board in which an arbitrary number of circuit conductor layers are previously formed on the inner layer of the multilayer board is used as the multilayer board on which copper foil is bonded to the entire surface of the outermost layer.

After bonding copper foil to the outermost layer on both the front and back sides, a through hole is made to expose a part of the inner circuit conductor layer on the inner wall surface of this through hole, and the entire surface of the laminated board including this through hole is electroless. A thin copper film layer is formed by copper plating, a desired circuit conductor layer is formed by the same method as in the first embodiment described above, and finally a thick layer of electroless copper plating is applied to the necessary areas to form a null layer. -Complete high-density multilayer printed wiring boards using hole connections.

Multilayer printed wiring boards made using this method can uniformly and reliably plate through-holes on the inner wall surfaces even if the through-hole diameter is small, and the reliability of null-hole connections in multilayer printed wiring boards with high aspect ratios is improved. could be significantly improved.

Effects of the Invention As described above, the through-hole printed wiring board according to the present invention has the following properties: Immediately after catalytic treatment is applied to the entire surface of a copper-clad laminate board provided with through-holes, electroless copper plating is applied thinly and uniformly in advance. Since pattern formation is performed using an etching method, the activation ability of the catalyst layer attached to the inner wall surface of the through hole is reduced compared to the conventional method in which electroless copper plating is performed through many steps from catalyst treatment. It is possible to prevent through-hole connections and proceed to subsequent processes after confirming that the through-hole connections have been made reliably, improving manufacturing yields.

The effect of significantly improving the reliability of through-hole connections can be obtained.

Furthermore, by applying the present invention to through-hole connections in multilayer wiring boards, it is possible to significantly improve the reliability of through-hole connections between inner circuit conductor layers of multilayer wiring boards with small hole diameters relative to board thickness, that is, high aspect ratios.

[Brief explanation of the drawing]

Figures 1 to (F) are cross-sectional views showing the manufacturing process for explaining one embodiment of the through-hole printed wiring board according to the present invention, and Figures 2 (A) to <Tg are through-hole printed wiring boards according to the conventional example. It is a sectional view showing a manufacturing process of a wiring board. 8... Insulating substrate, 9... Copper foil (circuit conductor layer), 10... Through hole, 11... ... Catalyst layer, 12 ... First electroless copper plating metal layer, 1
3... Etching resist layer, 14...
- Electroless plating resistant resist layer, 16... second electroless copper plating metal layer.

Claims (2)

[Claims] (1) A through-hole is provided at a predetermined position of a copper-clad laminate board in which copper foil is bonded to the outermost layer of the front and back surfaces of a resin-based insulating board, and the entire front and back surfaces of the copper-clad laminate board, including the inner wall surface of the through-hole, are forming a first copper metal thin film layer by electroless copper plating;
Forming an etching-resistant resist layer in a desired wiring circuit diagram shape on the inner wall surface of the through hole and on both the front and back surfaces of the copper-clad laminate board, and forming a first copper metal thin film layer not covered with the resist layer. After dissolving and removing it by an etching method, the resist layer is removed to form a circuit conductor layer, and a permanent resist that is resistant to electroless plating is applied to the through hole and at least a portion of the circuit conductor layer in the surrounding area. A through-hole printed wiring board characterized in that the layer is selectively coated, and then a second copper metal thick film layer is formed on the through-hole and the exposed surface layer of the circuit conductor layer by electroless copper plating again. manufacturing method. (2) The copper-clad laminated board has an arbitrary number of circuit conductor layers laminated on its inner layer, and a part of the inner circuit conductor layer is exposed on the inner wall of the through hole. A method for manufacturing a through-hole printed wiring board.