JP3059568B2 - Method of manufacturing multilayer printed circuit board - Google Patents

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 multilayer printed circuit board.

[0002]

2. Description of the Related Art Conventionally, as a multilayer printed circuit board,
2. Description of the Related Art A ceramic multilayer printed circuit board and a resin multilayer printed circuit board are known, and are manufactured as follows.

(A) Ceramic-based multilayer printed circuit board Thick-film multilayer method In this method, a conductive paste and an insulating paste are alternately printed and fired on a fired ceramic substrate to obtain a multilayer printed circuit board. Green sheet method In this method, a circuit was printed with conductive paste on an unfired ceramic sheet, a soft green sheet with a thickness of 200 to 300 μm, and a hole was made in the conductive part between layers to fill the conductive paste. A multi-layer printed circuit board is formed by laminating a plurality of substrates and firing them all at once at a high temperature of 600 to 1200 ° C.

(B) Resin-based multilayer printed circuit board This circuit board is composed of a plurality of double-sided printed circuit boards obtained by pattern etching a glass epoxy double-sided copper-clad board having a thickness of about 0.2 mm, with a prepreg interposed therebetween. After lamination and thermocompression bonding, it is manufactured by performing a drilling process and plating the inner surface of the hole to form a through hole.

[0005]

However, the method of manufacturing a ceramic-based multilayer printed circuit board by the thick-film multilayer method is cumbersome because printing and firing are repeated, and when the number of layers is large, unevenness on the surface becomes severe. As a result, printing becomes difficult, so that the number of layers cannot be increased.

In the method of manufacturing a ceramic-based multilayer printed circuit board by the green sheet method, when the number of laminations increases, the organic components contained in the green sheet are not sufficiently diffused, and a part of the organic components is left inside the circuit board. There is a problem in that carbonization occurs and carbonization occurs to degrade insulation between layers.
In this method, high dimensional accuracy cannot be obtained because the green sheet shrinks by about 10% by firing. Furthermore, since the dielectric constant of ceramic is as large as 5.7, the propagation delay time of the signal is large, and it is difficult to cope with high frequency and high speed circuits.

Further, the method of manufacturing a resin-based multilayer printed circuit board has a drawback in that the step of plating the inner surface of the hole is required to form the through hole, resulting in poor productivity and high cost.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for manufacturing a multilayer printed circuit board which solves the above-mentioned problems, and has a structure having a circuit conductor on one side of a plastic insulating film, A single-sided circuit film having an adhesive layer on the other surface, a through-stud formed of a conductive material at a position where conduction between the layers is formed, and a solder layer formed on the surface of the circuit conductor and the through-stud is formed by a metal plate, a circuit, A required number of layers are laminated on a substrate or other single-sided circuit film such as a single-sided circuit film, with the adhesive layer side facing the substrate sheet, and the laminate is heated and pressed at a temperature lower than the melting point of solder to form an interlayer. After the bonding, the layers are heated to a temperature higher than the melting point of the solder to perform soldering between layers.

[0009]

According to this method, a conductive path between the layers can be formed by laminating the circuit films, bonding between layers, and soldering between layers, so that it is not necessary to form through holes after lamination.
Even if the number of layers is increased, no unevenness on the surface is generated, so that a multilayer printed circuit board having a large number of layers can be obtained. In addition, since a plastic insulating film is used, the insulating layer hardly shrinks, high dimensional accuracy can be obtained, the dielectric constant is low, and interlayer insulation is reliable. Furthermore, since the conductors of adjacent layers are connected by soldering, the reliability of interlayer connection is high.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1A to 1F show a method for manufacturing a single-sided circuit film used in the present invention. In this method, first, as shown in (A), an insulating film 11 has a copper foil layer 13 on one surface and an adhesive layer 15 made of a thermoplastic adhesive or a semi-cured thermosetting adhesive on the other surface. Laminated film material 17
To manufacture.

In order to manufacture such a laminated film material 17, for example, a copper foil layer having a thickness of 0.2 to 1.0 μm is formed on one surface of a polyimide insulating film having a thickness of 25 to 125 μm by physical vapor deposition. , An imide adhesive as an adhesive layer on the other side
A method of coating to a thickness of 10 to 25 μm can be used.

Alternatively, for example, a copper foil may be bonded to a polyimide insulating film, or a polyimide precursor may be cast directly on the copper foil and then imidized.
It is also possible to obtain a flexible printed circuit board material obtained by integrating a copper foil and a polyimide insulating film, and coat the surface on the polyimide insulating film side with an epoxy-based adhesive to form a B stage.

Next, a hole is formed in a required position of the laminated film material 17 to form a hole 19 as shown in FIG.
Further, as shown in (C), after a dry film 21 for plating resist is laminated on the surface of the copper foil layer 13, imaging is performed by a known method, and a portion of the copper foil layer 13 left as a circuit is exposed.

Next, as shown in (D), a polymer conductive paste is filled in the holes 19 by a known screen printing method,
The through-stud 23 is formed by heating and curing. The steps (C) and (D) may be interchanged.

Next, solder plating is performed using the copper foil layer 13 as an electrode to form a solder layer 25 having a thickness of 5 to 20 μm on the surface of the copper foil layer 13 and the surface of the through stud 23 as shown in FIG. When silver paste is used as the polymer conductive paste for the through stud 23, in order to prevent diffusion of silver into the solder, after forming a barrier layer such as copper plating on the surface of the through stud, the solder plating is performed. Good.

Next, after the dry film 21 is dissolved and removed,
When the exposed portion of the copper foil layer 13 is etched, a single-sided circuit film 27 as shown in FIG. The present invention is to manufacture a multilayer printed circuit board using such a single-sided circuit film 27.

FIGS. 2 and 3 show an embodiment of the present invention. In this manufacturing method, first, as shown in FIG.
29 on the single-sided circuit film manufactured as described above
27 are laminated with the adhesive layer 15 facing the metal plate 29 side. The laminated body is heated to a temperature of 170 ° C. by a vacuum press and pressed, and the adjacent layers are bonded by the adhesive layer 15.
Thereafter, the laminate is passed through a reflow furnace or dipped in hot oil and heated to a temperature equal to or higher than the melting point of solder to melt the solder layer 25 and perform soldering between layers. Then, a metal-based multilayer printed circuit board as shown in FIG. 3 is completed.

In the embodiment shown in FIGS. 2 and 3, a copper foil is used in place of the metal plate 29, and after laminating and bonding, the copper foil is etched into a desired circuit pattern. A printed circuit board can be manufactured. In addition, a single-sided or double-sided printed circuit board can be used instead of the metal plate 29.

FIGS. 4 and 5 show another embodiment of the present invention. In this manufacturing method, the above-described single-sided circuit film 27 is laminated on both sides of a double-sided printed circuit board 31 to manufacture a multilayer printed circuit board. Double-sided printed circuit board
31 is the circuit conductor 3 on both sides of the plastic insulation film 33
A through stud 39 is formed by drilling and filling with a polymer conductive paste at a position where the circuit conductors 35 and 37 on both sides are conductive, and a solder layer 25 is formed on the surface of the circuit conductors 35 and 37 and the through stud 39. It has.

The structure of each single-sided circuit film 27 is the same as in the above embodiment. Such a single-sided circuit film 27 is laminated on both sides of the double-sided printed circuit board 31 with the adhesive layer 15 facing the double-sided printed circuit board 31 side, and the laminate is heated and pressed in the same manner as in the above-described embodiment. After bonding, the solder layer 25 is further melted to perform soldering between layers. Then Figure 5
A multilayer printed circuit board as described above is obtained.

[0021]

As described above, according to the present invention, a plurality of single-sided circuit films are laminated on a base sheet such as a metal plate, a circuit board, or another single-sided circuit film, and interlayer adhesion and interlayer soldering are performed. In this way, a conductive path between the layers can be formed, so that it is not necessary to form a through hole by plating after lamination, so that a multilayer printed circuit board can be manufactured efficiently and inexpensively, and even if the number of laminations is increased, unevenness of the surface, etc. Since this does not occur, there is an advantage that a multilayer printed circuit board having a large number of layers can be easily manufactured.

Further, since the insulator of each layer is a plastic insulating film, a multilayer printed circuit board with little shrinkage and high dimensional accuracy can be manufactured, the insulation between the circuit conductors of each layer is good, and the dielectric constant of the insulating layer is good. And a multi-layer printed circuit board having a small size can be obtained. Furthermore, since the conductors in adjacent layers are connected by soldering, the interlayer connection is strengthened, and a highly reliable multilayer printed circuit board free from increase in conductor resistance and disconnection even when a thermal shock or the like is applied can be obtained.

[Brief description of the drawings]

1 (A) to 1 (F) are cross-sectional views showing an example of a method for manufacturing a single-sided circuit film used in the present invention in the order of steps.

FIG. 2 is a sectional view showing one embodiment of the manufacturing method of the present invention.

FIG. 3 is a sectional view of a multilayer printed circuit board manufactured by the manufacturing method of FIG. 2;

FIG. 4 is a sectional view showing another embodiment of the manufacturing method of the present invention.

FIG. 5 is a sectional view of a multilayer printed circuit board manufactured by the manufacturing method of FIG. 4; 11: Plastic insulation film 13: Copper foil layer 15: Adhesive layer 19: Hole 21: Dry film for solder plating resist 23: Through stud 25: Solder layer 27: Single-sided circuit film 29: Metal plate 31: Double-sided printed circuit board

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/46

Claims (1)

(57) [Claims] 1. A plastic insulating film having a circuit conductor on one surface, an adhesive layer on the other surface, a through stud made of a conductive material at a position where electrical conduction is provided between the layers, and a circuit conductor and a through stud. A required number of single-sided circuit films having a solder layer formed on a surface thereof are laminated on a base sheet such as a metal plate, a circuit board or another single-sided circuit film, with the adhesive layer side facing the base sheet side. And a method of manufacturing the multilayer printed circuit board, wherein the laminate is heated and pressed at a temperature lower than the melting point of the solder to bond the layers, and then heated to a temperature higher than the melting point of the solder to perform the soldering between the layers.