JP2002033566A - Method for forming wiring pattern of printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a wiring pattern without using a photomask which is high in cost and hard to handle and store. SOLUTION: This method has: an electroless plating stage where an electroless plating film 21 is formed on the top surface of a substrate 12; a laminated layer forming stage where a wiring pattern is formed on the top surface of the substrate by forming and laminating two-dimensional planes of wiring patterns, layer by layer, by forming slice data by slicing the solid shape of the wiring pattern by two-dimensional planes which are put one over another, making a scan with laser light 24 according to the slice data, and sintering copper powder 23 covering the substrat, and a polishing stage where the electroless plating film where the wiring pattern is not formed is polished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a wiring pattern on a printed wiring board.

[0002]

2. Description of the Related Art Conventionally, in general, a wiring pattern of a printed wiring board is formed by attaching a copper foil on a substrate and then patterning the copper foil by etching using a photolithography method. Formed by

FIG. 2 is a diagram showing a flow of a conventional method for forming a wiring pattern on a printed wiring board, and FIG. 3 is a sectional view showing a process of the conventional method for forming a wiring pattern.

First, in an artwork process, a photomask 11 is formed based on designed wiring pattern data.
Make one. The photomask 111 is made of glass, a resin film, or the like, and has a negative or positive wiring pattern.

On the other hand, in a wiring pattern forming step,
First, as shown in FIG. 3 (a), a copper foil 113 previously attached on a substrate 112 made of a dielectric is
A dry film 114 made of a photosensitive resin material is laminated.

Next, as shown in FIG. 3B, the photomask 11 manufactured in the above-mentioned artwork process is used.
1 is attached to the dry film 114.

Next, after exposing from above in FIG. 3B, the photomask 111 is removed, and the exposed dry film 114 is developed. As shown in FIG. An etching resist film 115 is formed.

Next, when wet etching is performed using the etching resist film 115 as a mask and using an etchant, as shown in FIG. 3D, the copper foil 113 immediately below the etching resist film 115 is removed. It is patterned according to the wiring pattern.

Finally, when the remaining etching resist film 115 is peeled (peeled) off, a printed wiring board having a wiring pattern 116 formed on a substrate 112 is obtained as shown in FIG. Can be.

[0010]

However, in the above-mentioned conventional method for forming a wiring pattern on a printed wiring board, it takes time and cost to manufacture the photomask 111 in the artwork process.
In particular, in the case of a trial printed wiring board, since the number of manufactured photomasks is small, the cost of manufacturing the photomask 111 is relatively high.

Further, a defect occurs in a wiring pattern drawn at the time of manufacturing the photomask 111, and when the photomask 111 is attached to the dry film 114, dust is generated between the photomask 111 and the dry film 114. Entering, the drawn wiring pattern is damaged,
The photomask 111 expands and contracts due to a change in temperature and humidity. In such a case, the wiring pattern 116 formed on the substrate 112 may be disconnected, missing, short-circuited, or the like.

[0012] Then, the dust adheres or is damaged,
In order to store the photomask 111 so that it does not expand or contract due to changes in temperature and humidity, special equipment is required, so that the cost is high and complicated.

Further, since the photomask 111 is flat and has poor flexibility, when the substrate 112 has a three-dimensional shape (three-dimensional shape) or when the surface of the substrate 112 is not flat, a wiring pattern must be formed. You will not be able to do it.

The present invention solves the problems of the conventional method for forming a wiring pattern of a printed wiring board, and uses a photomask which is expensive, difficult to handle and store, and cannot be applied to a three-dimensional shape. It is an object of the present invention to provide a method for forming a wiring pattern of a printed wiring board without using the same.

[0015]

For this purpose, in the method for forming a wiring pattern of a printed wiring board according to the present invention, an electroless plating step of forming an electroless plating film on the surface of a substrate, and a three-dimensional shape of the wiring pattern are superimposed. By creating slice data sliced on a plurality of two-dimensional planes, and scanning a laser beam based on the slice data to sinter the copper powder covering the substrate, the two-dimensional plane of the wiring pattern is formed as one layer. A lamination molding step of forming and laminating the electroless plating film on the electroless plating film, and a polishing step of polishing and removing the electroless plating film in a portion where the wiring pattern is not formed. .

In another method for forming a wiring pattern on a printed wiring board according to the present invention, the wiring pattern is further formed on two opposing surfaces of the substrate.

In still another method of forming a wiring pattern on a printed wiring board according to the present invention, the surface of the substrate has a three-dimensional shape.

In still another method for forming a wiring pattern of a printed wiring board according to the present invention, the wiring pattern further has a portion having a different height.

In still another method of forming a wiring pattern for a printed wiring board according to the present invention, the wiring pattern further has irregularities on its surface.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a flow of a method of forming a wiring pattern on a printed wiring board according to a first embodiment of the present invention, and FIG. 4 is a sectional view of an electroless plating process according to the first embodiment of the present invention. FIGS. 5 and 6 are sectional views showing steps of the additive manufacturing process according to the first embodiment of the present invention, FIG. 6 is a sectional view explaining the operation principle of the additive manufacturing process, and FIG. 7 is a first embodiment of the present invention. It is a process sectional view of a polish process in a form.

In the present embodiment, as shown in FIG. 1, first, an electroless plating step of forming an electroless plating film 21 on the surface of the substrate 12 is performed, and then the electroless plating film 21 is formed. A laminate forming process for forming a wiring pattern thereon is performed, and finally, a polishing process for removing an unnecessary electroless plating film 21 is performed to form a wiring pattern 23a of the printed wiring board.

First, in the electroless plating step, FIG.
As shown in FIG. 1, a substrate 12 made of a dielectric material such as resin, prepreg, ceramics, or the like is immersed in, for example, a plating solution to form an electroless plating film 21 made of a thin copper film around the substrate 12. .

Next, in the additive manufacturing process, FIG.
As shown in (a), the substrate 12 on which the electroless plating film 21 is formed is placed on a lifting table 22, and the entire surface of the lifting table 22 is covered with copper powder 23. In this case, the upper surface of the substrate 12 is positioned about several μm below the surface of the copper powder 23. The lifting table 2
2 is moved upward or downward by a lifting drive source (not shown).

The lifting table 22 and the copper powder 2
The periphery of 3 is surrounded by a peripheral wall member (not shown) so that the copper powder 23 does not escape to the periphery.

A laser oscillator 24 is disposed above the elevation table 22 in the figure. The laser oscillator 24 may oscillate any type of laser, such as a YAG laser, a semiconductor laser, an excimer laser, etc., but from the viewpoints of wavelength, energy intensity, etc.
An O ₂ (carbon dioxide) laser oscillator is preferred. Further, the position where the laser oscillator 24 is provided may be any place, but a place where the optical path length of the laser beam 24a is not so long is desirable.

Further, a scanning mirror 25 is disposed above the elevation table 22 in the figure. The scanning mirror 25 is driven and oscillated by a mirror driving source (not shown) to reflect the laser beam 24 a from the laser oscillator 24 and scan the surface of the copper powder 23 covering the lifting table 22.

In this embodiment, a control device (not shown) is provided. The control device includes: an arithmetic unit;
It has a storage means, an input means, a display means, an input / output interface and the like, and controls the operations of the elevation drive source, the laser oscillator 24, the mirror drive source and the like.

On the other hand, slice data obtained by slicing a plurality of horizontal two-dimensional planes overlapping a three-dimensional shape of a wiring pattern formed on a printed wiring board is obtained by using a computer (not shown) such as a CAD device or the control device in advance. And stored in the storage means of the control device.

Then, based on the slice data,
By activating the laser oscillator 24, the mirror driving source and the lifting driving source, scanning the laser beam 24a and sintering the copper powder 23, two-dimensional planes of the wiring pattern are formed one by one and laminated, As shown in FIG. 5B, a wiring pattern 23a is formed on the electroless plated film 21 of the substrate 12 by the additive manufacturing for forming the wiring pattern on the surface of the substrate 12.

Here, the operation principle of the above-mentioned additive manufacturing process will be described.

First, slice data is sliced on a plurality of horizontal two-dimensional planes on which a three-dimensional shape to be formed is layered, and stored in the storage means of the control device.

Then, as shown in FIG. 6A, the laser oscillator 24 and the mirror driving source are operated, and the laser beam 24a from the laser oscillator 24 is reflected by the scanning mirror 25, and the copper powder 23 is removed. Scanning is performed according to the slice data. The copper powder 23 that has received the laser beam 24a is sintered, thereby forming the lowermost two-dimensional plane of the three-dimensional shape 23b to be formed.

The electroless plating film 2 of the substrate 12 is actually
When the wiring pattern 23b is formed on the substrate 1, the lowermost two-dimensional plane is located immediately above the electroless plating film 21 of the substrate 12, and is in close contact with the electroless plating film 21.

Next, as shown in FIG. 6B, the lifting table 22 is moved downward by one layer of the two-dimensional plane by the lifting drive source. In this case, the copper powder 2 is covered by one layer of the two-dimensional plane so that the height of the surface of the copper powder 23 covering the lifting table 22 does not change.
3 is replenished.

Subsequently, as described above, the laser light 2
4A, the copper powder 23 receiving the laser beam 24a is sintered, and a two-dimensional plane of the second layer from the bottom of the three-dimensional shape 23b is formed immediately above the two-dimensional plane of the lowermost layer. It adheres to the lowermost two-dimensional plane.

Thereafter, the three-dimensional shape 23b is formed by repeating the above-described formation of a two-dimensional plane for each layer by scanning with the laser beam 24a and downward movement of the lifting table 22 for one layer. Is done. That is, the laser beam 24a is scanned based on the slice data to
By sintering the copper powder 23 covering the surface, the two-dimensional planes of the three-dimensional shape 23b are formed one by one and laminated, and the three-dimensional shape 23b is formed on the elevating table 22. In this case, as the scanning range of the laser beam 24a is gradually changed for each layer, a three-dimensional shape 23b having a complicated cross section can be formed as shown in FIG.

Finally, in the polishing step, the unnecessary electroless plating film 21 is removed from the substrate 12 on which the wiring pattern 23a has been formed by the lamination molding step. That is, as shown in FIG. 7A (the same structure as FIG. 5B),
An electroless plating film 21 having an electroless plating film 21 therearound.
Abrasive (and) grains are sprayed from a direction perpendicular to the surface by general sandblasting on the entire surface of the substrate 12 on which the wiring pattern 23a is formed. Thus, the entire surface of the substrate 12 is polished. And the wiring pattern 2
When the sandblasting process is stopped when the portion of the electroless plating film 21 where the 3a is not formed is removed,
As shown in FIG. 7B, the substrate 12 on which the wiring pattern 23a is formed without the unnecessary electroless plating film 21 on the surface can be obtained.

As described above, in the present embodiment, the production of the photomask required for forming the wiring pattern 23a of the printed wiring board is not required, so that the artwork step is not required. Therefore, the wiring pattern 23a
The production time of the photomask in the formation of the photomask can be shortened, so that the productivity can be improved.

Further, since the photomask is not used, a defect occurs in the wiring pattern drawn at the time of manufacturing the photomask, dust is generated when the photomask is attached, or the drawn wiring pattern 23a is damaged. Or
Since the photomask does not expand or contract due to changes in temperature and humidity, the wiring pattern 23
There is no disconnection, loss, short circuit, etc. of a.

Furthermore, dust adheres or breaks,
Since no special equipment is required to store the photomask so that it does not expand or contract due to changes in temperature and humidity,
Cost can be reduced, and complicated work is not required.

Next, a second embodiment of the present invention will be described. The description of the same structure and the same method as in the first embodiment will be omitted.

FIG. 8 is a process sectional view of a lamination molding process according to the second embodiment of the present invention, and FIG. 9 is a process sectional view of a polishing process according to the second embodiment of the present invention.

First, by a method similar to that of the first embodiment, a lamination molding process is performed on one surface of the substrate 12 on which the electroless plating film 21 is formed, as shown in FIG. 8A. Thus, the wiring pattern 23a is formed on the electroless plating film 21. Next, the substrate 12 is inverted.
The other surface is also subjected to the additive manufacturing process to obtain the substrate 12 having the wiring pattern 23a formed on the electroless plating films 21 on both surfaces, as shown in FIG. 8B.

Finally, in the polishing step, FIG.
As shown in FIG. 8 (b), a substrate 12 having an electroless plating film 21 therearound and having a wiring pattern 23a formed on the two opposing electroless plating films 21
Abrasive particles are sprayed on the entire surface of the substrate by sandblasting to remove the electroless plating film 21 at the portion where the wiring pattern 23a is not formed. Then, as shown in FIG. 9B, the wiring patterns 23a are formed on the two opposing surfaces.
Can be obtained.

As described above, in the present embodiment, it is not necessary to manufacture two photomasks which are necessary when forming the wiring pattern 23a on the two opposing surfaces of the substrate 12. Therefore, the manufacturing time of the photomask when the printed wiring board is a double-sided printed wiring board can be shortened, and the productivity can be improved.

Next, a third embodiment of the present invention will be described. The description of the same structure and the same method as in the first and second embodiments will be omitted.

FIG. 10 is a sectional view showing a process of an electroless plating process according to a third embodiment of the present invention, FIG. 11 is a sectional view showing a process of an additive manufacturing process according to the third embodiment of the present invention, and FIG. It is a process sectional view of a polish process in a 3rd embodiment of the present invention.

First, in the electroless plating step, FIG.
As shown at 0, an electroless plating film 21 made of a copper thin film is formed around a substrate 31 having a substantially triangular cross section.

Next, in the additive manufacturing process, FIG.
As shown in (a), the substrate 31 on which the electroless plating film 21 is formed is placed on a lifting table 22, and the lifting table 22 is covered with copper powder 23. In this case, the upper surface of the outermost peripheral portion of the substrate 31 has several μm of the surface of the copper powder 23.
m, and the central portion of the substrate 31 is a copper powder 2
3 to be exposed from the surface.

Then, based on slice data obtained by slicing a plurality of horizontal two-dimensional planes in which a three-dimensional shape of a wiring pattern prepared in advance is layered, the copper powder 23 is sintered by scanning with a laser beam 24a. Copper powder 23
A one-layer two-dimensional plane of the wiring pattern 23a is formed on the upper surface of the outermost peripheral portion of the substrate 31 covered with.

Thereafter, the formation of a two-dimensional plane for each layer by scanning with the laser beam 24a and the downward movement of the lifting table 22 for one layer are repeated, as shown in FIG. Substrate 3 having a substantially triangular cross section
The wiring pattern 23a is gradually formed from the peripheral portion toward the central portion.

Finally, in a polishing step, a substrate 31 having a substantially triangular cross-sectional shape in which a wiring pattern 23a is formed on the surrounding electroless plating film 21 as shown in FIG. Abrasive grains are sprayed to remove the electroless plating film 21 at the portion where the wiring pattern 23a is not formed. And FIG.
As shown in (b), the substrate 31 on which the wiring pattern 23a is formed can be obtained.

As described above, in the present embodiment, since a photomask having low flexibility is not required, the substrate 31
Has a three-dimensional shape (three-dimensional shape), or when the substrate 31 is bent or distorted (distorted).
The wiring pattern can be formed even when the surface of the substrate 1 is not flat but has a three-dimensional shape.

Next, a fourth embodiment of the present invention will be described. The description of the same structure and the same method as those of the first to third embodiments will be omitted.

FIG. 13 is a sectional view showing a step of a lamination molding process according to the fourth embodiment of the present invention, and FIG. 14 is a sectional view showing a polishing step according to the fourth embodiment of the present invention.

First, in the additive manufacturing process, FIG.
As shown in (a), the substrate 12 on which the electroless plating film 21 is formed is arranged on a lifting table 22, and the lifting table 22 is covered with copper powder 23. Subsequently, based on slice data sliced on a plurality of horizontal two-dimensional planes in which a three-dimensional shape of a wiring pattern created in advance is formed, a two-dimensional plane is formed for each layer by scanning with a laser beam 24a. By repeating the downward movement of the lifting table 22 for one layer, the wiring patterns 23a having different heights are formed as shown in FIG. 13B.

Finally, in the polishing step, wiring patterns 23a having different heights are formed on the surrounding electroless plating film 21 as shown in FIG. 14A (the same structure as FIG. 13B). Abrasive particles are sprayed onto the transparent substrate 21 by sandblasting to remove the electroless plating film 21 at the portion where the wiring pattern 23a is not formed. Then, as shown in FIG. 14B, the substrate 21 on which the wiring patterns 23a having different heights are formed can be obtained.

As described above, in the present embodiment, since the wiring patterns 23a having different heights can be formed, it is possible to locally thicken an arbitrary portion of the wiring pattern 23a, and to perform printed wiring. It is possible to arbitrarily change electrical characteristics, circuit characteristics, and the like of an arbitrary portion of the wiring of the board.

Next, a fifth embodiment of the present invention will be described. The description of the same structure and the same method as those of the first to fourth embodiments will be omitted.

FIG. 15 is a sectional view showing a step of lamination molding according to the fifth embodiment of the present invention, FIG. 16 is a sectional view showing a polishing step according to the fifth embodiment of the present invention, and FIG. FIG. 13 is a cross-sectional view showing a state where components are mounted on a wiring pattern formed according to the embodiment.

First, in the additive manufacturing process, FIG.
As shown in (a), the substrate 12 on which the electroless plating film 21 is formed is placed on a lifting table 22, and the lifting table 22 is covered with copper powder 23. Subsequently, based on slice data obtained by slicing a plurality of horizontal two-dimensional planes in which the three-dimensional shape of the wiring pattern created in advance is layered, forming a two-dimensional plane for each layer by scanning the laser beam 24a, By repeating the downward movement of the elevating table 22 for one layer, a wiring pattern 23a in which irregularities are formed on the surface of each wiring is obtained as shown in FIG.

Finally, in the polishing step, the wiring pattern 23a was formed on the surrounding electroless plating film 21 as shown in FIG.
6 (a) (same structure as in FIG. 15 (b)) is sprayed with abrasive grains by sandblasting on the substrate 21 to remove the electroless plating film 21 in the portion where the wiring pattern 23a is not formed. . Then, FIG.
As shown in (2), it is possible to obtain a substrate 21 having a wiring pattern 23a in which irregularities are formed on the surface of each wiring. In addition, the shape of the unevenness may be any shape.

Then, the wiring pattern 2 of the printed wiring board
As shown in FIG. 17, when a component 35 such as a QFP, a BGA, or a CSP is mounted on, for example, a pad portion 3a, a solder ball 36 attached to the component 35 is placed in a concave portion on the surface of the wiring. The fitting 35
In addition to improving the positioning accuracy, the molten solder does not dissipate and the contact area increases, so that the solderability is also improved.

As described above, in the present embodiment, 1
Since irregularities of an arbitrary shape can be formed on the surface of the wiring of each book, any portion of the wiring pattern 23a can be locally thickened, and the electrical characteristics of an arbitrary portion of the wiring of the printed wiring board can be improved. , Circuit characteristics and the like can be arbitrarily changed, and the component 3
5, the positioning accuracy of the component 35 is improved, and the solderability is also improved.

The present invention is not limited to the above embodiment, but can be variously modified based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0067]

As described above in detail, according to the present invention, in the method for forming a wiring pattern of a printed wiring board, an electroless plating step of forming an electroless plating film on the surface of a substrate, By creating slice data sliced on a plurality of two-dimensional planes overlapping a three-dimensional shape, by scanning a laser beam based on the slice data and sintering copper powder covering the substrate, two-dimensional of the wiring pattern A lamination molding step of forming and laminating planes one by one and forming the wiring pattern on the surface of the substrate, and a polishing step of polishing and removing the electroless plating film in a portion where the wiring pattern is not formed. And

In this case, the production of a photomask becomes unnecessary, so that an artwork process becomes unnecessary, and the production time of the photomask in forming a wiring pattern can be shortened, so that productivity can be improved. .

Further, since a photomask is not used, a defect occurs in a wiring pattern drawn at the time of manufacturing the photomask, dust is generated when the photomask is attached, and the drawn wiring pattern is damaged. Since the photomask does not expand or contract due to changes in temperature and humidity, disconnection, loss, short circuit, and the like of the wiring pattern due to these does not occur.

Further, dust adheres or breaks,
Since no special equipment is required to store the photomask so that it does not expand or contract due to changes in temperature and humidity,
Cost can be reduced, and complicated work is not required.

In another wiring pattern forming method for a printed wiring board, the wiring pattern is formed on two opposing surfaces of the substrate.

In this case, it is not necessary to manufacture two photomasks, which is necessary when forming a wiring pattern on two surfaces of the substrate. Therefore, when the printed wiring board is a double-sided printed wiring board, the photomask is not used. Since the manufacturing time can be shortened, productivity can be improved.

In still another method for forming a wiring pattern on a printed wiring board, the surface of the substrate has a three-dimensional shape.

In this case, since a photomask having poor flexibility is not required, a wiring pattern can be formed even if the surface of the substrate is not flat.

Further, in still another method of forming a wiring pattern on a printed wiring board, the wiring pattern has portions having different heights.

In this case, an arbitrary portion of the wiring pattern can be locally thickened, and the electrical characteristics, circuit characteristics, and the like of the arbitrary portions of the wiring of the printed wiring board can be arbitrarily changed.

In still another method for forming a wiring pattern on a printed wiring board, the wiring pattern has irregularities on the surface.

In this case, when components are mounted on the wiring pattern, the positioning accuracy of the components is improved, and the solderability is also improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of a method for forming a wiring pattern on a printed wiring board according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a flow of a conventional method for forming a wiring pattern on a printed wiring board.

FIG. 3 is a process sectional view of a conventional wiring pattern forming method.

FIG. 4 is a process sectional view of an electroless plating process according to the first embodiment of the present invention.

FIG. 5 is a process sectional view of the additive manufacturing process according to the first embodiment of the present invention.

FIG. 6 is a process cross-sectional view for explaining the operation principle of the additive manufacturing process according to the first embodiment of the present invention.

FIG. 7 is a process sectional view of a polishing process in the first embodiment of the present invention.

FIG. 8 is a process cross-sectional view of the additive manufacturing process according to the second embodiment of the present invention.

FIG. 9 is a process sectional view of a polishing process according to the second embodiment of the present invention.

FIG. 10 is a process sectional view of an electroless plating process according to a third embodiment of the present invention.

FIG. 11 is a process cross-sectional view of a layered manufacturing process according to the third embodiment of the present invention.

FIG. 12 is a process sectional view of a polishing process according to a third embodiment of the present invention.

FIG. 13 is a process cross-sectional view of a layered manufacturing process in a fourth embodiment of the present invention.

FIG. 14 is a process cross-sectional view of a polishing process according to a fourth embodiment of the present invention.

FIG. 15 is a process cross-sectional view of a layered manufacturing process in the fifth embodiment of the present invention.

FIG. 16 is a process sectional view of a polishing process in a fifth embodiment of the present invention.

FIG. 17 is a sectional view showing a state where components are mounted on a wiring pattern formed according to a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Substrate 21 Electroless plating film 23 Copper powder 23a Wiring pattern 23b Three-dimensional shape 24 Laser beam

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E339 BC02 BD03 BD08 BE03 EE05 5E343 AA02 AA12 BB16 BB24 BB71 BB78 DD33 DD69 DD76 ER45 ER47 FF11 GG11

Claims (5)

[Claims] (A) an electroless plating step of forming an electroless plating film on the surface of a substrate; and (b) creating slice data obtained by slicing a plurality of two-dimensional planes in which a three-dimensional shape of a wiring pattern is overlaid; By scanning a laser beam based on the slice data and sintering the copper powder covering the substrate, two-dimensional planes of the wiring pattern are formed and laminated one by one, and the wiring pattern is formed on the electroless plating film. Forming a wiring pattern on a printed wiring board, comprising: a lamination modeling step of forming a wiring pattern; and (c) a polishing step of polishing and removing the electroless plating film in a portion where the wiring pattern is not formed. Method. 2. The method according to claim 1, wherein the wiring patterns are formed on two opposing surfaces of the substrate. 3. The method according to claim 1, wherein the surface of the substrate has a three-dimensional shape. 4. The method for forming a wiring pattern on a printed wiring board according to claim 1, wherein said wiring pattern has portions having different heights. 5. The method for forming a wiring pattern on a printed wiring board according to claim 1, wherein the wiring pattern has irregularities on the surface.