This application is based on Japanese Patent Application No. 2008-134113 filed on May 22, 2008, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of fabricating a printed wiring board, and more particularly, to a method of fabricating a printed wiring board which forms a via hole by laser machining.
2. Description of Related Art
Conventionally, a method of fabricating a printed wiring board which forms a via hole by laser machining is known.
As shown in
The insulation layer 111 of the core wiring board 110 is formed of an insulation resin and the like. The conductor circuit pattern 112 is formed of copper foil and the like.
As shown in
As shown in
A via hole 120 is formed on a predetermined region of the printed wiring board 101, and the plated pattern 105 is so formed as to cover the inner surface of the via hole 120. Thus, the copper-foil pattern 104 (the conductor circuit pattern 103) formed on the outer side of the insulation resin layer 102, and the conductor circuit pattern 112 formed on the inner side of the insulation resin layer 102 are electrically connected to each other.
Next, a method of fabricating the printed wiring board 101 as the conventional example is explained. First, as shown in
And, as shown in
Then, a resist layer 130 (see
Next as shown in
Then, as shown in
Then, a resist layer (not shown) is formed on a predetermined region of the surface of the plated layer 105a, and parts of the plated layer 105a and of the copper foil 104a are etched using the resist layer (not shown) as a mask. Thus, the conductor circuit pattern 103 (see
In the method of fabricating the printed wiring board 101 as the conventional example described above, because the copper foil 104a is laminated and bonded on the core wiring board 110 with the insulation resin layer 102 interposed therebetween, the copper foil 104a needs to have a predetermined thickness, and cannot be made thin excessively. Accordingly, the copper foil 104a usually has a thickness of about 18 μm to about 50 μm.
However, to form the hole portion 104b through the copper foil 104a by etching, usually, the inner diameter of the hole portion 104b is required to be several times as large as the thickness of the copper foil 104a. Besides, because the copper foil 104a has a thickness of about 18 μm to about 50 μm, the cross section of the hole portion 104b formed by etching has a mortar shape because of a side etching effect as shown in
Accordingly, in forming the via hole 120, if the copper foil 104a through which the hole portion 104b is formed is used as a mask, there is a problem that it is hard to form the minute via hole 120 having the inner diameter of dozens of micrometers with high accuracy.
The present invention has been made to cope with the conventional problems, and it is an object of the present invention to provide a method of fabricating a printed wiring board that is capable of forming a minute via hole with high accuracy.
To achieve the object, a method of fabricating a printed wiring board according to a first aspect of the present invention comprises: a step of preparing a core wiring board composed of a first conductor circuit pattern that is formed on at least one surface of an insulation layer; a step of forming an insulation resin layer on at least one surface side of the core wiring board to cover the first conductor circuit pattern; a step of forming a first resist layer on a predetermined region of a surface of the insulation resin layer; a step of forming a first metal layer with a plating method on a region of the surface of the insulation resin layer except the region where the first resist layer is formed; a step of forming a via hole by laser machining using the first metal layer as a mask to remove at least a predetermined region of the insulation resin layer and to expose part of a conductor layer formed on one side of the insulation resin layer that faces the core wiring board; a step of forming a second resist layer on a region of a surface of the first metal layer except the region around the via hole; a step of forming a second metal layer with a plating method on a region of the surface of the first metal layer except the region where the second resist layer is formed and on an inner surface of the via hole; a step of removing the second resist layer; a step of forming a third resist layer on a predetermined region of the surface of the first metal layer and on a surface of the second metal layer; and a step of forming a second conductor circuit pattern by etching the first metal layer using the third resist layer as a mask.
In the method of fabricating a printed wiring board according to this one aspect, as described above, the step of forming the first resist layer on the predetermined region of the surface of the insulation resin layer, and the step of forming the first metal layer with the plating method on the region of the surface of the insulation resin layer except the region where the first resist layer is formed are employed. Usually, a resist layer can be formed minutely, and the side surfaces of the resist layer can be formed substantially vertically. Accordingly, according to the above structure, the inner diameter of the part (the part where the resist layer is formed) of the first metal layer where the via hole is to be formed can be made sufficiently small, and it is possible to prevent the part (the part where the resist layer is formed) from having a mortar shape in cross section. As a result of this, it is possible to form a minute via hole with high accuracy by laser machining using the first metal layer as the mask.
In the method of fabricating a printed wiring board according to the above one aspect, as described above, the thickness of the first metal layer can be made sufficiently small by forming the first metal layer with the plating method compared with a case where the first metal layer is formed of, for example, metal foil. Thus, in forming the second conductor circuit pattern by etching the first metal layer, it is possible to form the second conductor circuit pattern easily and minutely.
In the method of fabricating a printed wiring board according to this one aspect, as described above, the step of forming the second metal layer with the plating method on the region of the surface of the first metal layer except the region where the second resist layer is formed and on the inner surface of the via hole. Thus, because the first metal layer that forms the second conductor circuit pattern, and the second metal layer that is formed on the inner surface of the via hole can be formed of separate layers, it is possible to form the second conductor circuit pattern easily and minutely securing a thickness of the second metal layer that is formed on the inner surface of the via hole.
In the method of fabricating a printed wiring board according to the above one aspect, it is preferable that at least an electroless plating method is used in the step of forming the first metal layer. According to this method, it is possible to easily form the first metal layer on the surface of the insulation resin layer.
In this case, it is preferable that both electroless plating method and electrolytic plating method are used in the step of forming the first metal layer. According to this method, it is possible to easily shorten the plating time required for forming the first metal layer.
In the method of fabricating a printed wiring board according to the above one aspect, it is preferable that a step of removing the first resist layer is further employed before the step of forming the via hole. According to this method, it is possible to easily remove the insulation resin layer to form the via hole by laser machining using the first metal layer as a mask.
In the method of fabricating a printed wiring board according to the above one aspect, it is preferable that the step of forming the via hole includes one step of removing the first resist layer and a predetermined region of the insulation resin layer by laser machining with the first metal layer used as a mask. According to this method, it is possible to curb increase in the number of steps for forming the via hole.
In the method of fabricating a printed wiring board according to the above one aspect, it is preferable that at least an electroless plating method is used in the step of forming the second metal layer. According to this method, it is possible to easily form the second metal layer on the region of the surface of the first metal layer except the region where the second resist layer is formed and on the inner surface of the via hole.
In this case, it is preferable that both electroless plating method and electrolytic plating method are used in the step of forming the second metal layer. According to this method, it is possible to easily shorten the plating time when forming the second metal layer to a large thickness.
In the method of fabricating a printed wiring board according to the above one aspect, it is preferable that the step of forming the via hole includes a step of forming the via hole by exposing part of the first conductor circuit pattern with laser machining. According to this method, it is possible to easily connect electrically the first conductor circuit pattern and the first metal layer (the second conductor circuit pattern) with each other through the via hole.
In the method of fabricating a printed wiring board according to the above one aspect, it is preferable that a step of roughening and dehydrating the surface of the insulation resin layer is further employed before the step of forming the first metal layer. By forming the first metal layer after the surface of the insulation resin layer is roughened, it is possible to raise the bonding strength between the first metal layer and the insulation resin layer. Thus, in the step of forming the via hole, even if the first metal layer is subjected to a large thermal stress due to laser light or pressurized by a machining gas, it is possible to prevent the first metal layer from peeling off the insulation resin layer. In a case where the bonding strength between the first metal layer and the insulation resin layer is small, if the first metal layer is subjected to a large thermal stress due to laser light or pressurized by a machining gas in the step of forming the via hole, there is a possibility that the first metal layer peels off the insulation resin layer in the part around the via hole. Because the bonding strength between the first metal layer and the insulation resin layer can be raised, it is possible to increase the peeling-off strength of the first metal layer. Besides, by forming the first metal layer after dehydrating the insulation resin layer, it is possible to prevent the first metal layer from peeling off the insulation resin layer because of the curbed vaporization (expansion) of water absorbed in the insulation resin layer even if the insulation resin layer is heated by laser light in the step of forming the via hole.
First, a structure of a printed wiring board according to an embodiment of the present invention is explained with reference to
A printed wiring board 1 according to an embodiment of the present invention is used for electronic devices and the like. As shown in
The insulation layer 11 of the core wiring board 10 is formed of, for example, a glass-fiber reinforced resin material. The core wiring board 10 may be formed of another material such as a polyimide resin and the like besides the glass-fiber reinforced resin material. The conductor circuit pattern 12 is formed of copper foil and the like.
As shown in
Here, in the present embodiment, as shown in
Via holes 20 are formed on predetermined regions of the printed wiring board 1, and the plated layer 4 is so formed as to cover the inner surface (surface of the conductor circuit pattern 12 included) of the via hole 20. Thus, the conductor circuit pattern 3 formed on the outer side of the insulation resin layer 2 and the conductor circuit pattern 12 formed on the inner side of the insulation resin layer 2 are electrically connected with each other.
In the present embodiment, the plated layer 4 is formed on a surface of part of the conductor circuit pattern 3 that is located around the via hole 20.
The plated layer 4 includes an electroless plated layer 4a that is formed on a predetermined region of the surface of the conductor circuit pattern 3 and on the inner surface of the via hole 20, and an electrolytic plated layer 4b formed on a portion of the surface of the electroless plated layer 4a.
The electroless plated layer 4a is formed to a thickness of, for example, about 0.05 μm to several micrometers, and the electrolytic plated layer 4b is formed to a thickness of, for example, about 5 μm to about 50 μm. The thicknesses of the electroless plated layer 4a and the electrolytic plated layer 4b are determined by taking performance such as current capacity, impedance and the like necessary for the printed wiring board 1 into account. Depending on circumstances, the electroless plated layer 4a may be formed to a necessary thickness without forming the electrolytic plated layer 4b.
A part 4c of the plated layer 4 that is located on a portion of the surface of the conductor circuit pattern 3 functions as a via-hole land.
Next, a method of fabricating the printed wiring board according to an embodiment of the present invention is explained with reference to
First, as shown in
In the present embodiment, as shown in
Then, in the present embodiment, as shown in
Besides, the plating resist layer 30 can be formed of, for example, a light-sensitive resin and can also be formed into a minute shape on a desired position with an accuracy to several micrometers or fewer. The plating resist layer 30 can also be formed of, for example, a plating resist that includes an acryl-denatured novolak-epoxy resin which is commercially available for electroless copper plating.
And, in the present embodiment, the surface of the insulation resin layer 2 is roughened by using a chromic-acid surface-roughening agent that is commercially available, and then, neutralized and washed. And, the insulation resin layer 2 and the core wiring board 10 are dehydrated by performing heat treatment (drying treatment) at a temperature of about 120° C. for 1 hour or longer.
Then, in the present embodiment as shown in
Depending on laser machining conditions described later, after the copper plated layer 3a is formed with the electroless plating method, a copper layer and other metal layers may be formed on the copper plated layer 3a. Here, electrolytic plating may be performed using the copper plated layer 3a as an electricity-feeding layer. As described above, if the electrolytic plating is performed after the electroless plating is carried out, when forming the layers (the copper plated layer 3a, the copper layer and the other metal layers) that serve as the masks at the time of laser machining described later, it is possible to shorten the plating time.
And, the plating resist layer 30 is peeled off by using a plating-resist peeling solution. Thus, as shown in
Next, as shown in
The laser used here is a laser that is suitable for the machining of the insulation resin layer 2. For example, in a case where a polyimide resin is used for the insulation resin layer 2, it is preferable to use a YAG laser.
Then, in the present embodiment, as shown in
And, the inside of the via hole 20 is cleaned and washed, and pre-plating treatment is performed. Then, as shown in
Specifically, the electroless plated layer 4a having a thickness of, for example, about 0.05 μm to several micrometers is formed with the electroless plating method on the region of the surface of the copper plated layer 3a except the region where the plating resist layer 31 is formed. Here, the electroless plated layer 4a is also formed on the inner surface (surface of the conductor circuit pattern 12 included) of the via hole 20.
In addition, the electrolytic plated layer 4b having a thickness of, for example, about 5 μm to about 50 μm is formed with the electrolytic plating method on the surface of the electroless plated layer 4. Here, the copper plated layer 3a and the electroless plated layer 4a are used as electricity-feeding layers.
Thus, the plated layer 4 including the part 4c that functions as a via hole land is formed.
Then, the plating resist layer 31 is peeled off by using a plated-resist peeling solution.
And, in the present embodiment, an etching resist layer 32 is formed on predetermined regions of the surface of the plated layer 4 and of the surface of the copper plated layer 3a. Thus, the structure shown in
Then, part of the copper plated layer 3a is etched by using the etching resist layer 32 as a mask to form the conductor circuit pattern 3. Here, in the present embodiment, because the layer (the copper plated layer 3a) to be etched is formed of copper, an etching solution containing cupric chloride or ferric chloride is used. And, the etching resist layer 32 is removed.
As described above, the printed wiring board 1 according to the embodiment of the present invention shown in
In the present invention, as described above, the step of forming the plating resist layer 30 on the predetermined region of the surface of the insulation resin layer 2, and the step of forming the copper plated layer 3a by using the electroless plating method on the region of the surface of the insulation resin layer 2 except the region where the plating resist layer 30 is formed are employed. Thus, the plating resist layer 30 can be minutely formed, and the side surfaces of the plating resist layer 30 can be formed substantially vertically, thereby not only the inner diameter of the part (the hole portion 3b) of the copper plated layer 3a where the via hole 20 is to be formed can be made sufficiently small but also the sectional shape of the part (the hole portion 3b) where the via hole 20 is to be formed can be prevented from having a mortar shape. Consequently, it is possible to form the minute via hole 20 with high accuracy by laser machining using the copper plated layer 3a as the mask.
Besides, in the present embodiment, it is possible to make the thickness of the copper plated layer 3a sufficiently small by forming the copper plated layer 3a using the electroless plating method compared with a case where, for example, metal foil is used to form the copper plated layer 3a. Thus, when forming the conductor circuit pattern 3, it is possible to form easily and minutely the conductor circuit pattern 3 by etching the copper plated layer 3a.
In the present embodiment, as described above, the copper plated layer 3a (the conductor circuit pattern 3) and the plated layer 4 formed on the inner surface of the via hole 20 are formed of separate layers, thereby the conductor circuit pattern 3 can be formed easily and minutely securing the desired thickness of the plated layer 4 formed on the inner surface of the via hole 20.
In the present embodiment, as described above, it is possible to increase the bonding strength between the copper plated layer 3a and the insulation resin layer 2 by forming the copper plated layer 3a after the surface of the insulation resin layer 2 is roughened. Thus, in the step of forming the via hole 20, even if the copper plated layer 3a is subjected to a large thermal stress due to laser light or pressurized by a machining gas, it is possible to prevent the copper plated layer 3a from peeling off the insulation resin layer 2. In a case where the bonding strength between the copper plated layer 3a and the insulation resin layer 2 is small, if the copper plated layer 3a is subjected to a large thermal stress due to laser light or pressurized by a machining gas in the step of forming the via hole 20, there is a possibility that the copper plated layer 3a peels off the insulation resin layer 2 in the part around the via hole 20. Because the bonding strength between the copper plated layer 3a and the insulation resin layer 2 can be raised, it is possible to increase the peeling-off strength of the copper plated layer 3a. Besides, by forming the copper plated layer 3a after dehydrating the insulation resin layer 2, it is possible to prevent the copper plated layer 3a from peeling off the insulation resin layer 2 because of the curbed vaporization (expansion) of water absorbed in the insulation resin layer 2 even if the insulation resin layer 2 is heated by laser light in the step of forming the via hole 20.
It must be thought that the embodiment disclosed above is an example in all respects and is not limiting. The scope of the present invention is not indicated by the above explanation of the embodiment but by the claims, and all modifications within the scope of the claims and the equivalent meaning and scope are included.
For example, in the embodiment described above, the core wiring board that includes the conductor circuit patters formed on both surfaces of the insulation layer is used. However, the present invention is not limited to this structure, and a core wiring board that includes the conduction circuit pattern formed, for example, on only the upper surface of the insulation layer.
In the embodiment described above, the insulation resin layers and the copper plated layers (the copper plated patterns) are formed on both surfaces of the core wiring board. However, the present invention is not limited to this structure, and the insulation resin layer and the copper plated layer (the copper plated pattern) may be formed on, for example, only the upper surface of the core wiring board.
In the present embodiment described above, the copper plated layers (the copper plated patterns) are formed on both surfaces of the core wiring board, that is, one layer on one surface and the other layer on the other surface of the core wiring board with the insulation resin layer interposed therebetween. However, the present invention is not limited to this structure, and a plurality of insulation resin layers and a plurality of copper plated layers (copper plated patterns) may be laminated alternately on both surfaces of the core wiring board.
In the embodiment described above, the via hole is so formed as to connect the conductor circuit pattern of the core wiring board and the copper plated layer (the copper plated pattern). However, the present invention is not limited to this structure, and is applicable to a case where a via hole is so formed as to connect a copper plated layer (a copper plated pattern) formed on the inner surface (which faces the core wiring board) of a predetermined insulation resin layer and a copper plated layer (a copper plated pattern) formed on the outer surface of the predetermined insulation resin layer if a plurality of insulation resin layers and a plurality of copper plated layers (copper plated patterns) are formed alternately on both surfaces of the core wiring board as described above.
In the present embodiment described above, the plating resist layer is peeled off before laser machining is performed using the copper plated layer as the mask. However, the present invention is not limited to this method, and laser machining may be performed using the copper plated layer as the mask without peeling off the plating resist layer. In other words, the plating resist layer and the predetermined region of the insulation resin layer may be removed in one step by laser machining using the copper plated layer as the mask. In this case, it is possible to curb increase in the number of steps for forming the via hole.
In the present embodiment described above, the surface of the insulation resin layer is roughened before the copper plated layer is formed on the surface of the insulation resin layer. However, the present invention is not limited to this method, and the surface of the insulation resin layer may not be roughened.
In the present embodiment described above, the insulation resin layer and the core wiring board are dehydrated before the copper plated layer is formed on the surface of the insulation resin layer. However, the present invention is not limited to this method, and the insulation resin layer and the core wiring board may not be dehydrated.
In the present embodiment described above, the copper plated layer (the copper plated pattern) is formed on the surface of the insulation resin layer. However, the present invention is not limited to this structure, and a plated layer (a plated pattern) formed of a metal other than copper may be formed on the surface of the insulation resin layer.
In the present embodiment described above, the core wiring board on which the conductor circuit pattern is formed of copper foil is used. However, the present invention is not limited to this structure, and a core wiring board on which the conductor circuit pattern is formed of metal foil made of a metal other than copper or a plated layer may be used.
In the present embodiment described above, the core wiring board through which a through hole is formed is used. However, the present invention is not limited to this structure, and a core wiring board through which no through hole is formed may be used.
Number | Date | Country | Kind |
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2008-134113 | May 2008 | JP | national |