JPH0754873B2 - Method for manufacturing multilayer printed board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a method for producing a multilayer printed board having few voids and good heat dissipation.

(Prior Art) As the density and precision of multi-layer printed circuit boards have increased, the circuit width and inter-circuit width have become narrower, and many parts that generate heat per unit area are mounted. Is likely to accumulate in. Therefore, there is a tendency to thicken the copper foil of the inner layer circuit board for dissipating this heat.

However, if the thickness of the copper foil used for the inner layer circuit board is 35 μm or more, and if it is thicker than 70 μm, voids tend to occur when the prepreg is overlaid and molded on the inner layer circuit board. That is, as shown in FIG. 2 for explaining the state at the time of molding, the recesses 12 other than the copper foil circuit 11 of the inner layer circuit board 10 are likely to become voids. The air present in the recess 12 is replaced with the resin due to the decrease in the viscosity of the resin in the prepreg 13 and the molding pressure during the heat and pressure molding, and is mostly discharged out of the multilayer printed board. However, the direction in which the resin flows into the recess and the direction in which the air is discharged are opposite, and the copper foil circuit 11
As a barrier, air tends to remain. This tendency is not so much affected when the copper foil circuit 11 is thin, but is adversely affected as the copper foil circuit 11 is thickened. If the copper foil circuit is thick, the volume of the recess 12 that must be filled with the resin in the prepreg 13 increases, and if the number of prepregs 13 is the same, the amount of resin in the prepreg 13 that fills the recess 12 is constant The thicker the foil circuit 11 is, the more likely it is to form voids. In order to improve these drawbacks, recently, a method for manufacturing a multilayer printed board by vacuum molding has been carried out and the occurrence of voids has been remarkably reduced.
As the thickness increases to 105 μm, 140 μm, etc., it cannot be said that the void suppression is sufficient.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances, and even when the copper foil of the inner layer circuit board has a thickness of 70 μm or more, no void is generated, and a multilayer structure excellent in heat dissipation and electric characteristics is provided. It is intended to provide a method for manufacturing a printed board.

[Structure of the Invention] (Means for Solving the Problems) As a result of earnest studies to achieve the above-mentioned object, the present inventor applied a resin to the step caused by the copper foil circuit thickness, The inventors have completed the present invention by finding that the resin layer formed by vacuum molding suppresses the generation of voids and that the formed resin layer has an excellent insulating effect. That is, the present invention is a method for producing a multilayer printed board using an inner layer circuit board having a copper foil circuit having a thickness of 70 μm or more and a prepreg, and a gel time of 80 to 80 on the surface of the inner layer circuit board after the blackening treatment.
The method for producing a multilayer printed board is characterized in that the same heat-resistant resin as used for the prepreg and the inner layer circuit board is applied for 150 seconds to a thickness of 40 to 60% of the copper foil. And it is a manufacturing method of a multilayer printed board which can be pressure-reduced if necessary.

As the inner layer circuit board used in the present invention, a prepreg obtained by impregnating and drying a thermosetting resin such as an epoxy resin or a polyimide resin on a base material, and a copper foil having a thickness of 70 μm or more are superposed on each other to form a single body under heat and pressure. After that, a circuit is formed by etching. The inner layer circuit board is blackened and then a heat resistant resin is applied.

The heat-resistant resin used in the present invention is the same resin as used for the prepreg or the inner layer circuit board, for example, an epoxy resin, a polyimide resin, a modified resin thereof and a mixed resin thereof, and the gel time thereof is 80 to 150 seconds. Is desirable. More preferably, the gel time is 90 to 120 seconds. If the gel time exceeds 150 seconds, it is generally possible to sufficiently fill and reduce the generation of voids, but the resin flow is too large and the inner layer circuit board is likely to slip during molding, which is dangerous. Further, in a special case, it becomes difficult to fill all the concave portions of the inner layer circuit board, resulting in poor heat resistance and electric characteristics, which is not preferable. On the other hand, when the gel time is less than 80 seconds, the resin flow decreases, the recesses are not sufficiently filled, and voids are easily generated, which is not preferable.

Heat-resistant resin is applied on the inner layer circuit board after blackening treatment,
The coating method is not particularly limited, and any method such as spraying, flow coater and curtain coater can be used well. Among these coating methods, a curtain coater is preferably used from the viewpoint of accuracy of coating thickness. The coating thickness of the heat resistant resin is preferably 40 to 60% of the thickness of the copper foil used for the inner layer circuit board. If the coating thickness is less than 40%, the resin may not be sufficiently filled in the recesses, causing voids, which is not preferable. Further, if it exceeds 60%, the inner layer circuit board may slip when molding the inner layer circuit board, the prepreg and the copper foil, which is dangerous and not preferable. After coating both surfaces of the inner layer circuit board, it is dried in a drying furnace such as a horizontal tunnel furnace. At this time, care should be taken to dry the resin at a temperature of 60 to 80 ° C. so as not to harden it by increasing the air volume, volatilize the solvent and dry the inner circuit board so that it can be handled.

The heat resistant resin-coated inner layer circuit board thus obtained, the prepreg, and the copper foil are superposed on each other and integrated by heat and pressure to produce a multilayer printed board.

If the thickness of the copper foil used for the inner layer circuit board is less than 105 μm, the effect of the present invention can be sufficiently obtained by applying the heat resistant resin, but if it is 105 μm or more, the application of the heat resistant resin is sufficient. Since it may not be obtained in some cases, the effect can be sufficiently expected if vacuum molding is performed at the same time as the application of the heat resistant resin.

(Operation) Next, the operation will be described with reference to the drawings. As shown in FIG. 1 (A), the heat resistant resin 3 is formed on the blackened inner layer circuit board 1.
By coating and semi-curing the copper foil circuit 4 so as to fill a part of the concave portion 2 so that the heat-resistant resin 3 on the copper foil circuit 4 is filled into the remaining portion of the concave portion 2 during molding. To Then, as shown in FIG. 1 (B), after molding, the heat-resistant resin 3 is sufficiently filled and filled in the recesses, and the entire inner layer circuit board 1 having no voids is covered with the heat-resistant resin 3, so that the adhesion between the prepreg and the inner layer circuit board is improved. And has the effect of improving heat resistance and electrical characteristics.

(Example) Next, the present invention will be described with reference to an example.

Examples 1 to 4 In the structure shown in the multilayer printed board construction in Table 1, the same epoxy resin as that used for the prepreg and the inner layer board was subjected to the blackening treatment as shown in the heat resistant resin in Table 1 for the inner layer board. Was coated on both front and back sides, and integrally molded under a reduced pressure and molding conditions shown in Table 1 to produce a multilayer printed board.
The resulting multilayer printed board was evaluated for appearance, heat resistance, electrical characteristics, and inner layer slip during molding. The results are shown in Table 1, and the effects of the present invention were confirmed in all cases.

Comparative Examples 1 to 6 Multilayer printed boards were manufactured in the same manner as in Examples 1 to 4 according to the configuration of the multilayer printed board shown in Table 1. Further, the multilayer printed board obtained in the same manner was evaluated. The results are shown in Table 1. However, in the comparative example, voids were generated, the appearance was poor, and the heat resistance and electric characteristics were poor.

[Effects of the Invention] As is clear from the above description and Table 1, according to the method for manufacturing a multilayer printed board of the present invention, the inner copper foil has a thickness of 70.
It was possible to produce a multilayer printed board having excellent heat resistance and electrical characteristics without generation of voids even when the thickness was more than μm.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (A) and 1 (B) are sectional views of a resin-coated inner layer plate for explaining a resin filling state in the method of the present invention, and FIG. 2 illustrates a void generation state in a conventional method. FIG. 3 is a cross-sectional view of a main part of a multilayer printed board for the purpose of: 1 , 10, ... Inner layer circuit board, 4, 11 ... Copper foil circuit, 2, 12 ... Recessed portion, 3 ... Heat resistant resin, 13 ... Prepreg.

Claims (3)

[Claims] 1. A method for producing a multilayer printed board using an inner layer circuit board having a copper foil circuit having a thickness of 70 μm or more and a prepreg, wherein the gel time is 80 to 150 seconds on the surface of the inner layer circuit board after blackening treatment. The same heat-resistant resin used for the prepreg and the inner layer circuit board is used for 40-60% of the copper foil.
% Coating method for producing a multilayer printed board. 2. The method for producing a multilayer printed board according to claim 1, wherein the heat resistant resin is an epoxy resin, a polyimide resin or a mixed resin thereof. 3. A method for producing a multilayer printed board using an inner layer circuit board having a copper foil circuit having a thickness of 70 μm or more and a prepreg, wherein a gel time is 80 to 150 seconds on the surface of the inner layer circuit board after blackening treatment. The same heat-resistant resin used for the prepreg and the inner layer circuit board is used for 40-60% of the copper foil.
% Of thickness and vacuum forming, which is a method for producing a multilayer printed board.