JP2003198103A - Method for manufacturing printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a solder resist coating film on top of wiring conductors and a solder resist coating film filling gaps in between the conductors to be continuous in a heavy current printed circuit board with thickened conductors. <P>SOLUTION: A printed circuit board 1 is prepared, provided on one of its surfaces with an insulating layer 11 which is a thermosetting resin impregnated sheet type fabric substrate having metal foil conductors 12 (not less than 70 μm thick) printed on one of its surfaces. A prepreg 2 is prepared, for which a sheet type fabric substrate is impregnated with a thermosetting resin and is semihardened. On each side of the prepreg 2, a printed circuit board 1 with wirings printed on one side is bonded with the printed surfaces facing outward, and they are heated and pressed in between mirror-like boards 3 and are integrated. The insulating layer 11 is softened during this process and the printed conductors 12 are inserted in the direction of their thickness partially or wholly into the insulating layer 11. Steps on the resultant surfaces are so small that they do not make solder resisting coating film formation difficult. <P>COPYRIGHT: (C)2003,JPO

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 printed wiring board or a multilayer printed wiring board which can handle a large current.

[0002]

2. Description of the Related Art For a printed wiring board through which a large current (about 1 to 500 A) flows, a printed wiring conductor made of a metal foil having a thickness of 70 μm or more (for example, electrolytic copper foil or rolled copper foil) is used. , Is designed to withstand large currents. This printed wiring board is manufactured as follows. A sheet-shaped fiber base material is impregnated with a thermosetting resin, and the prepreg is prepared by curing the resin to a semi-cured state. The metal foil is laminated on one side or both sides of the layer of this prepreg and integrated by heat and pressure molding to obtain a metal foil-clad laminate. Then, the metal foil is etched to form a printed wiring conductor.

Electronic components are mounted on the printed wiring board by soldering, and a solder resist film is provided on the surface of the printed wiring board excluding the soldering portion so that the solder does not adhere to the portions unrelated to the soldering. . The solder resist coating is
For example, an epoxy-based resist ink is applied or printed to cover the surface of the printed wiring conductor and to fill the recesses between the conductors.

[0004]

However, the thickness of the solder resist coating which can be formed as described above is 50 at most even if it is thick.
The limit is about μm. As described above, a printed wiring board through which a large current flows has a printed wiring conductor thickness of 70 μm.
m or more, and in some cases the thickness exceeds 100 μm,
It may be 500 μm. However, since the solder resist coating is thin, the surface of the printed wiring conductor in the thickness direction is not covered with the solder resist and remains exposed. The solder resist coating on the upper surface of the printed wiring conductor and the solder resist coating filling the space between the conductors do not form a continuous coating, which causes electrolytic corrosion and cracks in the solder resist coating.

The problem to be solved by the present invention is, for a printed wiring board in which the printed wiring conductor is made thick to withstand a large current, a solder resist film on the upper surface of the printed wiring conductor and a solder resist for filling the space between the conductors. The coating is to be a continuous series of coatings.

[0006]

In order to solve the above problems, the method according to the present invention manufactures a printed wiring board through the following steps. The method for producing a printed wiring board according to the present invention is applicable to any method for producing a single-sided printed wiring board, a double-sided printed wiring board, or a multilayer printed wiring board having a printed wiring in an inner layer.

The method for producing a single-sided printed wiring board is as follows. First, a single-sided printed wiring is prepared by arranging a printed wiring conductor made of a metal foil having a thickness of 70 μm or more on one surface of an insulating layer holding a thermosetting resin in a sheet-shaped fiber base material layer. Prepare the board. Further, a prepreg is prepared by impregnating a sheet-shaped fiber base material with a thermosetting resin and curing the resin to a semi-cured state. Then, the single-sided printed wiring board is superposed on the layer of the prepreg so that the printed wiring surface is on the outside, and the superposed component is sandwiched between metal mirror-finished plates to be integrated by heat and pressure molding. At this time, a part or the whole of the printed wiring conductor in the thickness direction is embedded in the insulating layer.

During the heat and pressure molding, the insulating layer of the single-sided printed wiring board is softened to some extent. Therefore, a part or all of the printed wiring conductor projecting on the insulating layer in the thickness direction is easily immersed in the softened insulating layer. The back surface of the insulating layer projects at a position corresponding to the immersion, but the resin of the prepreg layer flows during the heat and pressure molding to absorb the projection so that the immersion can occur without trouble. As a result, the printed wiring conductor on the insulating layer is
Since the degree of protrusion from the surface of the insulating layer is reduced or the surface of the insulating layer is flush with the surface of the insulating layer, the step difference between the upper surface of the printed wiring conductor and the conductor is reduced or the recess is eliminated, and a uniform continuous solder resist film is formed. Can be formed.

Next, in the method for manufacturing a double-sided printed wiring board, first, as in the above, a single-sided printed wiring board in which a printed wiring conductor made of a metal foil having a thickness of 70 μm or more is arranged on one surface of an insulating layer is prepared. In addition, a prepreg is prepared in the same manner as above. Then, the single-sided printed wiring boards are superposed on both sides of the layer of the prepreg so that the printed wiring surfaces are on the outer sides, and the superposed components are sandwiched between metal mirror surface plates to be integrated by heat and pressure molding. At this time, a part or the whole of the printed wiring conductor in the thickness direction is embedded in each insulating layer.

During the heat and pressure molding, the insulating layer of the single-sided printed wiring board is softened to some extent. Therefore, a part or all of the printed wiring conductor projecting on the insulating layer in the thickness direction is easily immersed in the softened insulating layer. The back surface of each insulating layer protrudes at a position corresponding to the immersion, but the resin of the layer of the prepreg sandwiched by the insulating layers absorbs the protrusion by flowing during the heat and pressure molding, and the immersion is hindered. I'm trying to happen without. The layer of the prepreg is cured to become an insulating layer, which integrates the two single-sided printed wiring boards. As a result, the degree of protrusion of the printed wiring conductor on the insulating layer from the surface of the insulating layer is reduced, or the printed wiring conductor is flush with the surface of the insulating layer. The concave portions are eliminated, and it becomes possible to form a uniform and continuous solder resist film.

Further, the manufacturing method of the multilayer printed wiring board is as follows.
First, similarly to the above, a single-sided printed wiring board is prepared in which a printed wiring conductor made of a metal foil having a thickness of 70 μm or more is arranged on one surface of the insulating layer. In addition, a prepreg is prepared in the same manner as above. Also prepare a printed wiring board for the inner layer. Then, the layers of the prepreg and the single-sided printed wiring board are superposed on both sides of the inner layer printed wiring board so that the printed wiring surface is on the outer side, and the superposed composition is sandwiched between metal mirror surface plates. It is integrated by heat and pressure molding. At this time, a part or the whole of the printed wiring conductor in the thickness direction is embedded in each insulating layer.

During the heat and pressure molding, the insulating layer of the single-sided printed wiring board is softened to some extent. Therefore, a part or all of the printed wiring conductor projecting on the insulating layer in the thickness direction is easily immersed in the softened insulating layer. The back surface of each insulating layer protrudes at a position corresponding to the immersion, but the resin of the prepreg layer sandwiched between the printed wiring board for the inner layer and the insulating layer flows during heat and pressure molding to absorb the protrusion. However, the immersion is made to occur without any trouble. There is no concern that the protrusion damages the printed wiring of the printed wiring board for the inner layer. The layer of the prepreg is cured to become an insulating layer, which integrates the inner layer printed wiring board and the two single-sided printed wiring boards. As a result, the degree of protrusion of the printed wiring conductor on the insulating layer from the surface of the insulating layer is reduced, or the printed wiring conductor is flush with the surface of the insulating layer. The concave portions are eliminated, and it becomes possible to form a uniform and continuous solder resist film.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In carrying out the method according to the present invention, a single-sided printed wiring board is manufactured as follows. A prepreg made by impregnating a sheet-like fiber base material (glass woven fabric, glass non-woven fabric, etc.) with a thermosetting resin (epoxy resin, phenol resin, polyimide, unsaturated polyester, etc.) and curing the resin to a semi-cured state. prepare. A metal foil having a thickness of 70 μm or more is overlaid on one side or both sides of the layer of this prepreg, and this is integrated by heat and pressure molding to obtain a single-sided metal foil-clad laminate. Then, the metal foil is etched to form a printed wiring conductor. The metal foil is an electrolytic copper foil or a rolled copper foil. When the above-mentioned one-sided metal foil-clad laminate is molded, two one-sided metal foil-clad laminates are pseudo-molded as a double-sided metal foil-clad laminate with a mold release film sandwiched therebetween, The single-sided metal foil-clad laminate can be subjected to an etching treatment for forming a printed wiring conductor while being integrated. After the etching treatment, the release film is peeled off to obtain two single-sided printed wiring boards. The single-sided metal foil-clad laminate is
Since the layer structure in the thickness direction is asymmetric, the warp tends to be large. However, if the double-sided metal foil-clad laminate is artificially formed as described above, the warp can be handled in a small state.

(Embodiment 1) A method for manufacturing a single-sided printed wiring board according to the present invention includes a single-sided printed wiring board 1 (a printed wiring conductor 12 is arranged on an insulating layer 11) prepared as described above. 1 (a) (b) using prepreg 2
It is manufactured through the steps shown in. The single-sided printed wiring board 1 is superposed on the layer of the prepreg 2 so that the printed wiring surface is on the outer side, and the superposed composition is sandwiched between the metal mirror surface plates 3 to be integrated by heat and pressure molding. A mold release film is arranged between the layer of the prepreg 2 and the mirror surface plate 3, and a mold release film is arranged also between the one-sided printed wiring board 1 and the mirror surface plate 3 as necessary to perform heat and pressure molding. . Up to this stage, the thermosetting resin of the insulating layer 11 may be kept in an insufficiently cured state so as to be easily softened by the heat and pressure molding. Since it softens to a certain extent by pressurization, in any case, part or the whole of the printed wiring conductor 12 in the thickness direction is immersed in the softened insulating layer 11 by the heat and pressure molding. Figure 1 (b)
Shows a state in which the printed wiring conductor 12 is immersed in the same surface as the insulating layer 11. On this single-sided printed wiring board, component mounting holes are appropriately opened, and a solder resist film is applied or printed on the surface. There is no step between the printed wiring conductor 12 and the insulating layer 11, and the solder resist coating can be formed well even if the coating is thin.

On the opposite surface of the insulating layer 11 in which the printed wiring conductor 12 is immersed, a corresponding portion is projected, and the above-mentioned projection allows the immersion to be performed without trouble. The resin of the layer of the prepreg 2 flows during the heat and pressure molding to absorb the protrusion. The prepreg 2 is the insulating layer 1
Although the same prepreg as that of No. 1 may be used, it is preferable that the amount of resin contained be larger than that. A large amount of resin serves as a cushioning material at the time of heat and pressure molding, which is convenient for favorably immersing the printed wiring conductor 12 into the insulating layer 11. It is also effective to stack the prepregs 2 and to thicken the prepregs 2. These matters can be similarly adopted in the following embodiments.

(Embodiment 2) Next, in the method for manufacturing a double-sided printed wiring board according to the present invention, the single-sided printed wiring board 1 and the prepreg 2 are used in the same manner as described above, and as shown in FIGS. It is manufactured through the steps shown. The single-sided printed wiring boards 1 are superposed on both sides of the layer of the prepreg 2 so that the printed wiring surfaces are on the outside, and the superposed components are sandwiched between the metal mirror-like plates 3 to be integrated by heat and pressure molding. Then, a part or the whole of the printed wiring conductor 12 in the thickness direction is immersed in the insulating layer 11 softened by the heat and pressure molding. In FIG. 2B, the printed wiring conductor 12 is connected to the insulating layer 11.
It shows a state in which the same surface is immersed. Each,
On the opposite surface of the insulating layer 11 in which the printed wiring conductor 12 is immersed, the corresponding portion projects, and the resin of the layer of the prepreg 2 flows during the heat and pressure molding to absorb the projection. The manufactured double-sided printed wiring board is provided with appropriate component mounting holes and through holes for connecting the printed wiring conductors on both sides,
A solder resist coating is formed on the surface.

(Third Embodiment) In the method for manufacturing a multilayer printed wiring board according to the present invention, the single-sided printed wiring board 1 and the prepreg 2 are used, and the inner layer printed wiring board 5 is prepared in the same manner as described above. , And is manufactured through the steps shown in FIGS. The inner layer printed wiring board 5 may be the printed wiring board manufactured in the above-described first and second embodiments in which the printed wiring conductor and the surface of the insulating layer are on the same surface, or the printed wiring conductor is insulated. A printed wiring board protruding from the layer surface may be used, but the former is preferable. Prepregs 2 are provided on both sides of the inner layer printed wiring board 5, respectively.
Layer, and further, the single-sided printed wiring board 1 is superposed such that the printed wiring surface is on the outside, and the superposed composition is sandwiched by the metal mirror plate 3 to be integrated by heat and pressure molding.
Then, a part or the whole of the printed wiring conductor 12 in the thickness direction is immersed in the insulating layer 11 softened by the heat and pressure molding. FIG. 3B shows a state in which the printed wiring conductor 12 is immersed in the same surface as the insulating layer 11. On the opposite surface of the insulating layer 11 in which the printed wiring conductor 12 is immersed, the corresponding portion projects, and the resin of the layer of the prepreg 2 flows during the heat and pressure molding to absorb the projection. It is convenient that the printed wiring conductor of the inner layer printed wiring board 5 is flush with the surface of the insulating layer because it is unlikely to be affected by the protrusion of the insulating layer 11. The manufactured multilayer printed wiring board is provided with component mounting holes, through holes for connecting printed wiring conductors between the inner layer and the surface or between the both surfaces, and a solder resist film is formed on the surface.

(Embodiment 4) Since a large amount of heat is generated by passing a large current, in the above-mentioned printed wiring board, a thermosetting resin forming an insulating layer contains a non-conductive inorganic filler. Therefore, the thermal conductivity of the insulating layer may be improved and the heat dissipation may be improved. The inorganic filler is fine powder of silica, talc, aluminum hydroxide, magnesium hydroxide or the like.

(Embodiment 5) The single-sided printed wiring board, the double-sided printed wiring board, and the multilayer printed wiring board according to the above-described embodiments of the present invention all have a small surface unevenness due to the printed wiring conductors, and therefore have a uniform continuous shape. The solder resist film can be formed well. This means that
It also means that a thin-layer electric component can be satisfactorily applied to the surface. That is, even if an insulating layer is added to the surface of the printed wiring board, the surface of the insulating layer is smooth and has no irregularities, and thin-layer electrical components (coils, capacitors, etc.) can be accurately formed on the surface of the insulating layer. can do. The addition of the insulating layer to the surface of the printed wiring board can be carried out by integration of the prepreg by heat and pressure molding, sticking of a resin film, printing or coating of an insulating paint. The formation of the electric component can be performed by the following technique.
For example, it is a technique for etching a metal foil integrated with the insulating layer, a technique for electroless plating or vapor deposition on the insulating layer, and a technique for printing or applying a conductive paint on the insulating layer.

The printed wiring board having the thin-layer electric component formed on the surface of the insulating layer as described above can also be employed as the inner layer printed wiring board 5 used in the third embodiment of the invention. As a result, it becomes possible to manufacture a multilayer printed wiring board which accommodates a large current and has electric components built in the insulating layer.

[0021]

As described above, according to the method of the present invention, even when the thickness of the printed wiring conductor is increased to withstand a large current, the step difference between the upper surface of the printed wiring conductor and the surface of the insulating layer is reduced. It is possible to favorably form the solder resist coating on the surface of the printed wiring board by eliminating steps or steps.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating an embodiment of a manufacturing method according to the present invention.

FIG. 2 is a sectional view illustrating another embodiment of the manufacturing method according to the present invention.

FIG. 3 is a cross-sectional view illustrating still another embodiment of the manufacturing method according to the present invention.

[Explanation of symbols]

1 is a single-sided printed wiring board 11 is an insulating layer 12 is a printed wiring conductor 2 is prepreg 3 is a mirror plate 4 is a release film 5 is a printed wiring board for the inner layer

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Claims (6)

[Claims] 1. A step of preparing a single-sided printed wiring board in which a printed wiring conductor made of a metal foil having a thickness of 70 μm or more is arranged on one surface of an insulating layer holding a thermosetting resin in a sheet-shaped fiber base material layer, sheet-shaped fiber Step of preparing a prepreg in which a base material is impregnated with a thermosetting resin and curing of the resin is progressed to a semi-cured state, and the single-sided printed wiring board is overlaid on the layer of the prepreg so that the printed wiring surface is on the outside. A step of combining, a step of sandwiching the superposed composition between metal mirror-finished plates to integrate by heat and pressure molding, and a step of burying a part or the whole of a printed wiring conductor in a thickness direction in an insulating layer. Manufacturing method of printed wiring board. 2. A step of preparing a single-sided printed wiring board in which a printed wiring conductor made of a metal foil having a thickness of 70 μm or more is arranged on one surface of an insulating layer in which a sheet-shaped fiber base material layer holds a thermosetting resin, sheet-shaped fibers A step of preparing a prepreg in which a base material is impregnated with a thermosetting resin and curing of the resin has progressed to a semi-cured state, and the one-sided printed wiring board has the printed wiring surface on the outside on both sides of the layer of the prepreg. A step of superposing the printed wiring conductors in a thickness direction and burying a part or the whole of the printed wiring conductor in an insulating layer. Characteristic printed wiring board manufacturing method. 3. A method for manufacturing a printed wiring board, wherein a thin-layer electric component and a conductor are added to the surface of the printed wiring board manufactured through the process according to claim 1 or 2 via an insulating layer. 4. A step of preparing a single-sided printed wiring board in which a printed wiring conductor made of a metal foil having a thickness of 70 μm or more is arranged on one surface of an insulating layer holding a thermosetting resin on a sheet-shaped fiber base material layer, sheet-shaped A step of preparing a prepreg obtained by impregnating a fiber base material with a thermosetting resin and curing the resin to a semi-cured state, a step of preparing an inner layer printed wiring board, on both sides of the inner layer printed wiring board, respectively. A layer of the prepreg, and a step of superimposing the single-sided printed wiring board so that the printed wiring surface is on the outer side, and the superposed component is sandwiched between metal mirror-faced plates to be integrated by heat and pressure molding and a single-sided printed wiring. A method of manufacturing a printed wiring board, comprising a step of burying a part or the whole of a printed wiring conductor of the board in a thickness direction in an insulating layer. 5. An inner layer printed wiring board according to claim 1.
The method for manufacturing a printed wiring board according to claim 4, wherein the printed wiring board manufactured by the method according to any one of claims 3 to 5 is used. 6. A method of manufacturing a printed wiring board, wherein a thin-layer electric component and a conductor are added to the surface of the printed wiring board manufactured through the process according to claim 4 or 5 via an insulating layer.