JPS60165793A - Method of producing multilayer circuit 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 a multilayer wiring board for configuring electronic circuits such as television receivers and video tape recorders.

(Conventional structure and its problems) In recent years, the demand for electronic devices to be lighter, thinner, shorter, and smaller in size has been increasing, and with this, it has become essential to increase the density of these electronic circuits. Under these circumstances, increasing the density of circuit boards that make up electrical circuits is considered the most important technical issue, and low-cost, highly reliable multilayer wiring boards are strongly desired. ing.

Regarding multilayer wiring boards, there have been many ifU
Although methods have been proposed and implemented, most of them connect interlayer circuit conductor layers with through holes. However, in recent years, a method of connecting circuit conductor layers between layers using via holes instead of through holes has been widely used. This type of via hole connection has the advantage of effectively increasing the density of the circuit because the area occupied by the circuit conductor layer required for connection is small, and all multilayer wiring boards based on ceramic substrates use via holes. It depends on the connection.

A typical manufacturing method thereof is shown in FIGS. 1(A) to 1(C). As shown in FIG. 1(A), this multilayer wiring board is manufactured by printing a metal glaze-based conductive paste in a desired wiring circuit shape on the surface of a ceramic insulating substrate 1, and baking it at a high temperature to form an inner circuit conductor layer 2. Figure 1 (T3
), an insulating paste containing glass as a main component is selectively applied to the surface of the inner circuit conductor layer so that a part of it is exposed, and then baked at a high temperature to form an insulator with pipe holes 3. The step of forming the body layer 4, as shown in FIG. 1(C),
A metal glaze type conductive paste is printed on the surface of the insulating layer 4 in the shape of a desired wiring circuit, and at the same time, the via holes 3 provided in the insulating layer 4 are also filled with the conductive paste.
By firing at a high temperature, the outermost circuit conductor layer 5 is formed (l), and the steps shown in FIGS. 1(B) and 1(C) are successively repeated to form a multilayer wiring circuit.

However, the multilayer wiring board manufactured by such a manufacturing method requires expensive materials such as metal glaze, and the process of forming the conductor layer and the insulator layer requires 800 microns each.
Because it requires baking at a high temperature of ~850°C for about 1 hour,
There were inconveniences such as the complicated process organization for sanitation.

As a method to solve this problem, a method has been proposed in which the outermost circuit conductor layer is formed using a conductive paste in which fine silver powder is dispersed in a resin. However, with the circuit conductor layer formed using this resin-based conductive paste, although it is possible to ensure electrical connection with the inner circuit conductor layer through the pie holes 4- provided in the insulator layer, on the other hand, the surface layer Since the silver powder is completely covered with resin, the solderability is extremely poor, and even if the surface is polished to expose the silver, so-called silver cracks will occur significantly. Furthermore, conductive pastes containing multiple layers of silver powder have problems such as reduced adhesive strength between circuit conductor layers and insulator layers, and there has been a strong desire to improve these problems.

(Objective of the Invention) An object of the present invention is to provide a method for manufacturing a multilayer wiring board in which the outermost circuit conductor layer has excellent soldering properties and excellent adhesion to an insulating layer.

(Structure of the Invention) The present invention provides a multilayer structure in which circuit conductor layers and insulator layers are alternately formed on at least one surface of an insulating substrate, and the circuit conductor layers between the layers are electrically connected through pie holes provided in the insulator layer. In a method of manufacturing a wiring board, the outermost circuit conductor layer is first filled with conductive resin in a via hole provided in an insulating layer, and then insulated so that it comes in contact with a part of the conductive resin layer. It is formed by applying adhesive to the desired wiring pattern, fixing metal powder to the surface, and then performing electroless plating to deposit a conductive metal layer on the metal powder layer. A multilayer wiring board with excellent solderability and adhesiveness can be realized.

(Description of Examples) Examples of the present invention will be described below with reference to the drawings.

FIGS. 2(A) to 2(F) show a series of manufacturing steps for a multilayer wiring board according to an embodiment of the present invention.
6 is an insulating substrate, 7 is an inner circuit conductor layer, 8 is an insulator layer, 9
10 is a conductive resin layer, 11 is an adhesive layer, 12 is a metal powder layer, 13 is a conductive metal layer, and 14 is an outermost circuit conductor layer.

Next, the manufacturing method will be explained in detail. First, Figure 2 (
As shown in A), a desired inner circuit conductor layer 7 is formed on the main surface of the insulating substrate 6. As the insulating substrate 66, a synthetic resin substrate such as a paper-phenol laminate or a glass-epoxy laminate, or a ceramic substrate such as alumina porcelain can be used. In the case of a synthetic resin substrate, an electrolytic copper foil is bonded to the entire surface. The inner circuit conductor layer 7 is formed by etching the material and dissolving and removing unnecessary portions of the copper foil. On the other hand, in the case of a ceramic substrate, a metal glaze-based conductive paste made of silver or silver-palladium 11 is applied in the desired wiring circuit shape by screen printing, and then baked at a high temperature in air at 800 to 850°C. The inner circuit conductor layer 7 is formed by the following steps.

Next, as shown in FIG. 2(B), the main surface 1 of the insulating substrate 6 is
An insulator layer 8 is formed on the surface of the inner circuit conductor layer 7 formed on the inner circuit conductor layer 7 in which a pie hole 9 is provided so that a part of the inner circuit conductor layer 7 is exposed. In this embodiment, the insulating layer 8 is made of a photosensitive resin regardless of the material of the insulating substrate 6 used, such as an acrylic resin or a photosensitive resin having a two-layer structure of a cyclized rubber-based polybutadiene resin and an acrylic resin. Insulating film was used. These photosensitive insulating films are laminated on the entire surface of the insulating substrate 6 on which the inner circuit conductor layer 7 has been formed, a prescribed mask film for forming via holes is attached to this surface, and UV exposure and development treatment are carried out. By this process, a pie hole 9 having a fine diameter was formed, and an insulator layer 8 provided with the pie hole 9 was formed.

Next, as shown in FIG. 2(C), a conductive resin 10 made by dispersing and mixing fine silver or copper powder in an epoxy resin or the like is used as an insulator using a screen printing method or a dispenser. In addition to filling the pie hole 9 provided in the layer 8, if necessary, it is also applied to a part of the surrounding area, and the conductive +11 resin is heated and cured.

The pie holes 9 thus formed in the insulator layer 8 are filled with conductive resin 10 and covered, and the inner circuit conductor layer 8 is
After completely shielding from the outside, as shown in FIG. 2(D), an adhesive 11 made by dispersing and mixing carbon powder in an insulating resin is applied to the surface of the outermost insulating layer 8 by screen printing. 1/- to form a desired wiring pattern so that a part of the conductive resin layer IO is in contact with a part of the conductive resin layer IO.

Before the adhesive 1 has hardened, fine metal powder 12 of copper, iron, nickel, silver, etc., for example, is sprinkled on its surface as shown in FIG. 2(E), and it is pressed with a roller.
Remove metal fine powder adhering to unnecessary parts of the insulator layer 8,
The adhesive 11 is heated and cured.

The metal powder used in this step must be a metal that will serve as the catalyst nucleus for the electroless plating in the next step, but in this example, dendritic electrolytic copper powder with a particle size of about 10 μm was used. This made it possible to form a circuit conductor layer with a good surface condition and excellent adhesive strength.

Finally, as shown in FIG. 2(F), electroless copper plating is performed on the metal fine powder layer 12 fixed to the surface of the adhesive 11 to deposit a conductive metal layer 13 made of metal steel, and the outermost layer is A circuit conductor layer 14 is formed.

In this example, a two-layer structure was described in which a circuit conductor layer was formed only on one main surface of an insulating substrate, and an insulating layer and a circuit conductor layer were sequentially formed on the surface of the insulating substrate. The circuit is not limited to a multilayer wiring board having a structure of The present invention is also applied to a multilayer wiring board in which conductor layers are multilayered and circuit conductor layers formed on the front and back sides of an insulating substrate are connected through holes penetrating the insulating substrate. Furthermore, in such a multilayer wiring board, a ceramic substrate is used as the base insulating substrate, and a circuit conductor layer is formed with a thick film conductor made of metal glaze made of silver thread on the front and back surfaces of the ceramic substrate, and a circuit conductor layer is formed on the same surface. A circuit conductor layer may be formed by forming a ruthenium oxide resistor layer by screen printing and insulating it with an insulating resin to form a multilayer circuit conductor layer. One of the major features is that it is possible to create multilayer circuit boards with built-in resistors, and we have actually manufactured multilayer circuit boards with built-in resistors, and have obtained good results.

(Effects of the Invention) As is clear from the above description, the present invention provides circuit conductor layers and insulator layers that are alternately formed on the main surface of an insulating substrate, and circuit conductors between layers that are passed through pie holes provided in the insulator layer. Regarding the manufacturing method of a multilayer wiring board that connects layers, only the via holes of the outermost circuit conductor layer are filled with conductive resin to completely cover the inner circuit conductor layer, and then the conductive resin is Apply adhesive so that it touches a part of the adhesive resin,
It is formed by fixing metal powder on the surface and then applying electroless plating, and by forming the outermost circuit conductor layer using this method, the adhesiveness between the insulator layer and the circuit conductor layer is improved. In addition, since the conductor layer is formed by electroless plating, the solderability is significantly improved.

[Brief explanation of the drawing]

FIGS. 1(A) to (C) are diagrams showing a series of manufacturing steps of a multilayer wiring board according to a conventional example, and FIGS. 2(A) to (F) are diagrams showing a series of manufacturing steps of a multilayer wiring board according to an embodiment of the present invention. It is a diagram showing a series of manufacturing steps. 6...Insulating substrate, 7...Inner circuit conductor layer, 8
...Insulator layer, 9...Piere hole, 10...
・Conductive resin layer, 11... Insulating adhesive layer, 12...
- Fine metal powder layer, 13... Conductive metal layer, 14... Outermost circuit conductor layer. Patent applicant: Matsushita Electric Industrial Co., Ltd. Figure 1 (Figure 2)

Claims (4)

[Claims] (1) A multilayer wiring board in which a circuit conductor layer and an insulator layer are formed at an intersection If on at least ten sides of an insulating substrate, and the circuit conductor layers between the layers are electrically connected through a pie hole provided in the insulator layer. In the manufacturing method, the outermost circuit conductor layer is
Fill the via holes in the insulator layer with conductive resin,
An insulating adhesive is applied in the desired wiring diagram shape so as to be in contact with a part of the conductive resin layer, a total bending powder is fixed on the surface, and the metal powder layer is subjected to thermal electrolytic plating. 1. A method for manufacturing a multilayer wiring board, characterized in that the multilayer wiring board is formed by: (2) The multilayer circuit board according to claim (1), wherein a synthetic resin board is used for the insulating board, and the inner circuit conductor layer is formed by etching a copper foil. Production method. (3) A ceramic substrate is used as the insulating substrate, 1- The inner circuit conductor layer is formed of a 71% film conductor of metallurgy 1 nose type, and the outermost insulator layer is formed of an insulating f1 resin. Claim No. 1 characterized in (
1) The method for manufacturing a multilayer circuit board as described in item 1). (4) Manufacturing a multilayer circuit board according to claim (3), wherein a resistor layer is formed on the same surface as the thick film circuit conductor layer formed on the ceramic substrate. Method.