JPH04112596A - Manufacture of multilayer printed wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing multilayer printed wiring boards used in a wide variety of electronic devices.

BACKGROUND OF THE INVENTION In recent years, as the demand for smaller size, higher functionality, and higher performance of electronic equipment has increased, the demand for multilayer printed wiring boards has increased significantly.

Conventional multilayer printed wiring boards are manufactured by various methods. As a typical manufacturing method, a six-layer multilayer printed wiring board is taken as an example, and its manufacturing process is shown in FIGS. 2A and 2B.

In FIGS. 2A and 2H, la and lb are insulating substrates, 2a,
2a', 2b, 2b' are inner circuit conductor layers, 3a, 3
b, 3c are prepreg insulating layers, 4a4b are metal copper foils, 5
is a through hole, and 6a and 6b are outermost circuit conductor layers.

This multilayer printed wiring board having 6 layers generally uses a so-called copper-clad laminate in which metal copper foil is adhered to both the front and back sides of an insulating substrate 1a1b such as a glass epoxy laminate, and is first insulated by photo-etching. Substrates 1a, l
Required inner circuit conductor layers 2a on the front and back surfaces of b,
2a, 2b, 2b' are formed, and these two inner layer circuit forming boards are interposed with three BRIBREK insulation sheets 3a, 3b, 3c as shown in FIG. , 4b are stacked, and the prepreg insulating layers 3a, 3b3c are cured and integrally molded by heating under pressure using a hot press. Thereafter, as shown in FIG. 2B, through-holes 5 are made at necessary locations, and electroless copper plating and electrolytic copper plating are combined to coat the surfaces of the outermost layer metal copper foils 4a and 4b and the inner wall surface of the through-holes 5. Metallic copper is deposited on the surface. Thereafter, unnecessary metal copper layers of the metal copper foils 4a and 4b are removed by photoetching, and the outermost layer is electrically connected to the inner circuit conductor layers 2a, 2a', 2b, and 2b' through the through-hole conductor layers. Circuit conductor layers 6a and 6b are formed.

Problems to be Solved by the Invention However, in the multilayer printed wiring board according to the conventional example described above, the mutual electrical connections between the inner circuit conductor layers 2a, 2a', 2b2b' are all performed by a through-hole connection method in which the through holes 5 are made conductive. Therefore, as the number of layers increases, the number of through holes for connecting the circuit conductor layers of each layer increases. Therefore, as the area occupied by the through holes in the board area increases, the degree of clarity of circuit design is restricted, and as a result, it becomes difficult to measure whether the circuit can be made denser. Further, in the case of through-hole connection, there is a drawback that the reliability of the electrical connection between the circuit conductor layers becomes poor due to the influence of smear generated during the hole processing process. On the other hand, in conventional multilayer printed wiring boards, the interlayer insulating layer uses a thick prepreg material made of glass fiber and epoxy resin.
There was a problem in that it was difficult to measure the thickness of the entire laminated multilayer printed wiring board.

The present invention solves the above-mentioned problems, and aims to provide a multilayer printed wiring board in which the area occupied by through holes is small and the thickness of the board is reduced.

Means for Solving the Problems In order to achieve this object, the present invention provides circuit conductor layers and insulating resin layers that are alternately formed on each of the front and back surfaces of an insulating substrate, and provided in the through holes of the insulating substrate and the insulating resin layer. An inner layer wiring board having an arbitrary number of layers is constructed so that the circuit conductor layers are electrically connected to each other through blind via holes, and metal copper foil is bonded to both the front and back layers of the inner layer wiring board via an adhesive layer. Thereafter, an outermost circuit conductor layer electrically connected to the inner circuit conductor layer is formed by photoetching.

As a result, it is no longer necessary to connect the inner circuit conductor layers to each other using only through holes, thereby reducing the number of through holes, increasing the density of the circuit, and increasing the reliability of the electrical connection between the interlayer circuit conductor layers. Furthermore, since prepreg insulation notes are not used in the interlayer insulation layer, the thickness can be reduced.

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

FIGS. 1A-B are cross-sectional views of the main manufacturing steps for explaining the method of manufacturing a six-layer multilayer printed wiring board in the first embodiment of the present invention.

In FIG. 1, 7 is an insulating substrate, 8 is a through hole provided in the insulating substrate, 9a and 9b are plating-resistant resist layers, 10
a, 10b are first inner circuit conductor layers formed by electroless copper plating; 11. a and 11b are interlayer insulating films made of insulating resin layers; 12a and 12b are second plating-resistant resist layers;
3a, 13b are second inner circuit conductor layers, 14a, 14b
15a and 15b are adhesive layers, 15a and 15b are metal copper foils, 16 is a through hole, 17 is a copper-plated metal layer, and 18a and 18b are outermost circuit conductor layers.

A detailed example of a manufacturing method for the six-layer multilayer printed wiring board having the above structure will be described below.

In this embodiment, first, as shown in FIG. 1A, through-holes 8 are made at necessary locations in an insulating substrate 7 made of synthetic resin such as a glass epoxy laminate, a paper phenol laminate, or a glass polyimide laminate. by applying adhesive to or roughening its surface by chemical, physical or mechanical methods,
This is sequentially immersed in a hydrochloric acid solution of stannous chloride and palladium chloride to deposit a catalyst layer consisting of fine particle cores of metal balanrum on both the front and back surfaces, and then dried. Thereafter, the first and second plating resist layers 9a and 9b are formed into a reverse wiring diagram shape on both the front and back layers of this insulating substrate by screen printing or photo method.
The substrate is immersed in an electroless copper plating solution of pH 12 to 13 consisting of an alkaline solution of a copper complex salt and formalin to coat the catalyst layer or the exposed front and back surfaces of the insulating substrate 7 and the inner wall surface of the through hole 8 with metal. Copper is deposited to form the second inner circuit conductor layers 10a and 10b in which the through holes 8 are made conductive.

In this case, the plating resist layers 9a and 9b may or may not be removed after electroless copper plating, but in this example, the resist layers 9a and 9b are not removed in order to smooth the inner circuit conductor layers 10a and 10b. Plating resist was used.

Since the resist material needs to have alkali resistance, an epoxy resin is used, and a paste is made by kneading this resin with inorganic fillers such as alumina, phosphorus, carbonate, etc., and screen printing is performed. Both the front and back surfaces of the insulating substrate 7 were coated in the shape of a reverse wiring diagram using a method.

Next, insulating resin layers 11a and llb are selectively formed on the respective circuit conductor surfaces of the first inner circuit conductor layers 10a and 10b so that a portion thereof is exposed, or the method for forming them is as described above. Similar to the electroless plating resistant Lenst, Evokin resin is kneaded with inorganic fillers such as alumina, phosphoric acid, and calcium carbonate to form a paste, which is then selectively applied using screen printing to create blind buyer holes. Insulating resin layer 11a11b
Adopt a method to form a

On the other hand, as another example of the method of forming blind buyer holes in the insulating resin layers 11a and 11b, a film is thickly coated with an acrylic-modified photosensitive epoxy resin, and this is first coated using a hot roll. After the insulating resin is transferred to the entire surface of the inner circuit conductor layers 10a and 10b, it is partially irradiated with ultraviolet rays and developed, and a part of the insulating resin layer is removed to provide a blind buyer hole with a fine diameter. Layers 11a and llb may also be formed.

Then, the surfaces of the interlayer insulating resin layers 11a and llb are finely roughened by a scientific, physical or mechanical method, and activated to adhere catalyst nuclei for electroless plating to the entire surface. do.

and second plating-resistant lens by screen printing method)
After coating 12a and 12b in a reverse wiring diagram shape and curing, electroless copper plating is performed to form insulating resin layers 11a and llb.
forming second inner circuit conductor layers 13a, 13b electrically connected to the first inner circuit conductor layers 10a, 10b through micro holes (blind buyer holes) provided in 4;
An inner layer wiring board having multiple circuit conductor layers is obtained.

Then, as shown in FIG. 1B, metallic copper foils 15a15b coated with adhesive 14a14b on one side are stacked on both the front and back surfaces of the four-layer inner layer wiring board, and pressed and heated using a hot press. After performing the integral molding, through-holes] 6 are drilled at necessary locations, and the inner wall surface of the through-hole 16 and the metal copper foils 15a, 15b are coated using a combination of electroless copper plating and electrolytic copper plating.
Copper-plated metal layers 17 are deposited on both the front and back surfaces.

In this case, the adhesive layers 14a and 14b applied to one side of the metal copper foils 15a and 15b not only have excellent adhesion to the metal copper foils, but also have excellent properties such as insulation properties and heat resistance. In this example, an epoxy resin was used as an adhesive that satisfies these characteristics.

On the other hand, in other embodiments, the adhesives 14a, 14b
Metallic copper foil 15a, 1 using prepreg insulation
5b was adhered to the front and back surfaces of the inner layer wiring board.

As a result, we were able to create a multilayer printed wiring board with excellent interlayer insulation properties, heat resistance, and adhesive properties.

Then, as shown in FIG. 1C, the unnecessary outermost copper-plated metal layer is dissolved and removed by a known method such as photoetching, and the necessary outermost circuit conductor layers 18a, 1 are removed.
8b was formed to complete a six-layer multilayer printed wiring board.

The multilayer printed wiring board made by this method is one in which the outermost circuit conductor layers 18a, 18b or the metal copper foils 15a, 15b are strongly bonded to the inner layer wiring board with adhesives 14a, 14b, and then circuits are formed by etching. Therefore, the reliability of the circuit conductor layer is sufficiently ensured.

As is clear from the above description, the multilayer printed wiring board according to the present example has circuit conductor layers formed by electroless copper plating and insulating layers formed by insulating resin layers alternately formed on both the front and back sides of an insulating substrate. constitute an inner layer wiring board in which the circuit conductor layers between the layers are electrically connected through through holes provided in the insulating substrate and non-penetrating micro holes provided in the insulating resin layer,
This is a multilayer wiring board in which a metal copper foil is bonded to the outermost layer of this inner wiring board via an adhesive layer, and then a circuit conductor layer is formed by photoetching.

Therefore, in the multilayer printed wiring board according to the present invention, the inner circuit conductor layers are connected not only by through holes but also by micro holes provided in the insulating resin layer, so the number of through holes is significantly reduced. At the same time, this connection type has the effect of eliminating connection failures due to smearing and improving the reliability of interlayer connections between circuit conductor layers. In addition, since a thick ξ prepreg sheet is not used for the inner interlayer insulating layer, multilayer printing is possible. This provides an unprecedented effect of making the wiring board thinner and thinner.

Effects of the Invention As described above, according to the present invention, it is no longer necessary to connect the inner circuit conductor layers to each other or only through the through holes, thereby reducing the number of through holes and increasing the density of the circuit. The reliability of the electrical connection between the circuit conductor layers is improved, and furthermore, since no Flipreg insulating sheet is used for the interlayer insulating layer, the thickness can be reduced.

[Brief explanation of the drawing]

FIGS. 1A-C are cross-sectional views illustrating the manufacturing process of a multilayer printed wiring board according to an embodiment of the present invention, and FIGS. 2A-B are sectional views illustrating the manufacturing process of a multilayer printed wiring board according to a conventional example. It is. 7...Insulating substrate, 8...Through hole provided in the insulating substrate, 9a, 9b...-th plating resistant resist, 10a10b...first inner layer circuit conductor layer,
lla, llb...Insulating resin layer, 12a, 12
b... Third set of plating resists, 13a, 13b
...Second inner circuit conductor layer, 14 a, 14
b...---Adhesive layer, 15a, 15b...
・Metal copper foil, 16...Through hole, 17...
- Copper plated metal layer, 18a, 18b... Outermost circuit conductor layer. Name of agent: Patent attorney Haruaki Koebi and 2 others IO /

Claims (2)

[Claims] (1) A circuit conductor layer and an insulating resin layer are alternately formed on each of the front and back surfaces of an insulating substrate, and the circuit conductor layers are electrically connected to each other through a through hole in the insulating substrate and a blind via hole provided in the insulating resin layer. An inner layer wiring board with an arbitrary number of layers is constructed as shown in FIG. A method for manufacturing a multilayer printed wiring board, which forms an outermost circuit conductor layer that is connected to the outermost circuit conductor layer. (2) The method for manufacturing a multilayer printed wiring board according to claim 1, wherein a prepreg insulating sheet is used as the adhesive layer.