METHOD FOR MANUFACTURING WIRING BOARD

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a wiring board.

2. Discussion of the Background

Japanese Laid-Open Patent Publication No. H11-214828 describes a method for manufacturing a wiring board as follows: forming an electroless plated film as a power-supply layer on an insulation layer with a roughened surface; forming plating resist having an opening portion on the electroless plated film; forming electrolytic plated film in the opening portion of the plating resist; and after the plating resist is removed, removing by wet etching a portion of the electroless plated film that was under the plating resist. The publication also describes a wiring board manufactured by such a method. The contents of Japanese Laid-Open Patent Publication No. H11-214828 are incorporated herein by reference in their entirety in this application.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method for manufacturing a wiring board includes forming an insulative resin layer, forming a power-supply layer on the insulative resin layer, forming a conductive layer made of electrolytic plating and having a conductive pattern on the power-supply layer such that the power-supply layer has an exposed portion not covered by a conductive portion of the conductive pattern, and irradiating the exposed portion of the power-supply layer with laser having a wavelength in a range of approximately 350 nm to approximately 600 nm at a pulse width in a range of approximately 0.1 picosecond to approximately 1,000 picoseconds such that the exposed portion of the power-supply layer is removed from the insulative resin layer.

According to another aspect of the present invention, a method for manufacturing a wiring board includes forming an insulative resin layer, forming a power-supply layer on the insulative resin layer, forming a conductive layer made of electrolytic plating and having a conductive pattern on the power-supply layer such that the power-supply layer has an exposed portion not covered by a conductive portion of the conductive pattern, forming a flow of one of a liquid and an inert gas over the exposed portion of the power-supply layer such that one of the liquid and the inert gas is in contact with the exposed portion of the power-supply layer, and irradiating the exposed portion of the power-supply layer with laser having a wavelength in a range of approximately 350 nm to approximately 600 nm such that the exposed portion of the power-supply layer is removed from the insulative resin layer.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view showing a wiring board manufactured by a method for manufacturing a wiring board according to a first embodiment of the present invention, along with a semiconductor device having such a wiring board;

FIG. 2 is a view showing positions of external connection terminals in the wiring board shown in FIG. 1;

FIG. 3 is a flowchart showing a method for manufacturing a wiring board according to the first embodiment of the present invention;

FIG. 4 is a cross-sectional view to illustrate a step for preparing an insulation layer in the manufacturing method shown in FIG. 3;

FIG. 5 is a cross-sectional view to illustrate a step for forming electroless plated film on the insulation layer in the manufacturing method shown in FIG. 3;

FIG. 6A is a cross-sectional view to illustrate a first step for forming a conductive pattern in the manufacturing method shown in FIG. 3;

FIG. 6B is a cross-sectional view to illustrate a second step subsequent to the step shown in FIG. 6A;

FIG. 6C is a cross-sectional view to illustrate a third step subsequent to the step shown in FIG. 6B;

FIG. 7A is a view to illustrate laser processing in the manufacturing method shown in FIG. 3;

FIG. 7B is a cross-sectional view taken at the A-A line in FIG. 7A;

FIG. 8A is a view to illustrate an example of a pulse width of laser light in the manufacturing method shown in FIG. 3;

FIG. 8B is a view to illustrate an example of scanning conditions of laser light in the manufacturing method shown in FIG. 3;

FIG. 9 is a view showing how filler functions as a stopper in the laser processing shown in FIG. 7A;

FIG. 10 is a view to illustrate a step for forming an insulation layer on the conductive pattern after the laser processing shown in FIG. 7A;

FIG. 11 is a graph showing relationships between a laser wavelength and the absorption rate of each material;

FIG. 12 is a table showing the results of irradiating a green laser respectively at insulation layers containing four different types of inorganic filler;

FIG. 13A is a view showing the result after electroless plated film is removed using a green laser;

FIG. 13B is a view showing the result after electroless plated film is removed using an excimer laser;

FIG. 13C is a view showing the result after electroless plated film is removed by a wet method;

FIG. 14A is an SEM (scanning electron microscope) photograph of a conductive pattern formed by a method for manufacturing a wiring board according to the first embodiment of the present invention;

FIG. 14B is an SEM photograph of a conductive pattern formed by a method for manufacturing a wiring board according to a comparative example;

FIG. 15 is a magnified photograph of FIG. 14A;

FIG. 16 is regarding a sample where a green laser is used and a sample where a wet method is used, a graph showing their respective results of measuring the existing amount of palladium as a catalyst used for forming a conductive pattern;

FIG. 17 is a view showing a first method for manufacturing a wiring board according to a second embodiment of the present invention;

FIG. 18 is a view to illustrate how to form a flow in the first method shown in FIG. 17:

FIG. 19 is a view showing a second method for manufacturing a wiring board according to the second embodiment of the present invention;

FIG. 20A is a view to illustrate a first example of how to form a flow in the second method shown in FIG. 19;

FIG. 20B is in the method for manufacturing a wiring board according to the second embodiment, a view to illustrate an example of how to irradiate laser light at a wiring board (power-supply layer) in liquid;

FIG. 21A is in the method for manufacturing a wiring board according to the second embodiment, a view to illustrate an example of how a portion irradiated by laser light makes contact with gas flow or liquid flow after the portion has been irradiated by laser light;

FIG. 21B is a view showing the injection tip of a nozzle shown in FIG. 21A;

FIG. 22A is a view to illustrate a modified example of laser processing to be conducted while keeping plating resist for electrolytic plating in the first embodiment of the present invention;

FIG. 22B is a view to illustrate a modified example of laser processing to be conducted while keeping plating resist for electrolytic plating in the second embodiment of the present invention;

FIG. 23A is a view to illustrate a first example of the shape of a conductive pattern in another embodiment of the present invention;

FIG. 23B is a view to illustrate a second example of the shape of a conductive pattern in yet another embodiment of the present invention;

FIG. 24 is a view to illustrate an example in which a wiring board to be manufactured is a wiring board having a core substrate in yet another embodiment of the present invention;

FIG. 25 is a view to illustrate an example in which filler is dispersed only in the surface-layer portion of an insulation layer in yet another embodiment of the present invention; and

FIG. 26 is a view to illustrate an example in which an insulation layer has crushed filler in yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

In the drawings, arrows (Z1, Z2) each indicate a lamination direction of a wiring board corresponding to a direction along a normal line (or a thickness direction of the core substrate) to main surfaces (upper and lower surfaces) of the wiring board. On the other hand, arrows (X1, X2) and (Y1, Y2) each indicate a direction perpendicular to a lamination direction (direction parallel to the main surfaces of the wiring board). The main surfaces of the wiring board are on the X-Y planes. Also, side surfaces of the wiring board are on an X-Z plane or a Y-Z plane.

A conductive layer may include wiring that forms an electrical circuit (including ground), a pad, a land or like, or may include a plane conductive pattern that does not form an electrical circuit. A conductive pattern is formed with a conductive portion and a non-conductive portion (space).

Plating includes wet plating such as electrolytic plating and electroless plating along with dry plating such as PVD (physical vapor deposition) and CVD (chemical vapor deposition).

Laser light is not limited to visible light. Along with visible light, laser light includes electromagnetic waves with a short wavelength such as ultraviolet rays and X rays and electromagnetic waves with a long wavelength such as infrared rays. The absorption rate of laser light in each material is the value measured by an absorptiometer.

Other than a hole or a groove, an opening portion may be a notch, a slit or the like. A hole is not limited to being a penetrating hole, and it may also be a non-penetrating hole.

First Embodiment

Wiring board 100 manufactured in the present embodiment is a multilayer printed wiring board to be used for rewiring as shown in FIG. 1 and FIG. 2, for example. However, that is not the only option, and other wiring boards may be formed using the method of the present embodiment.

As shown in FIG. 1, semiconductor device 1000 is manufactured by mounting semiconductor chip 200 (semiconductor element) on wiring board 100 of the present embodiment and by encapsulating the chip with encapsulating resin 203. External connection terminal (102a) (pad) of wiring board 100 and electrode (200a) of semiconductor chip 200 are electrically connected to each other via solder 201, for example. Between wiring board 100 and semiconductor chip 200, insulative underfill material 202 is filled to mitigate mismatching of thermal expansion coefficients. Semiconductor device 1000 is used for a cell phone or the like, for example.

As shown in FIG. 2, terminal pitches of wiring board 100 are set to fan out from external connection terminals (102a) (pads) on the side of semiconductor chip 200 toward external connection terminals (102b) (pads) on the opposite side. Accordingly, semiconductor chip 200 with a dense terminal pitch is electrically mounted to a printed wiring board (such as a motherboard) with a sparse terminal pitch.

Wiring board 100 is manufactured, for example, by alternately building up conductive layers (101a˜101c) and interlayer insulation layers and by forming solder resist on the outermost layers. Conductive layers (101a˜101c) are formed by a method shown in later-described FIG. 3, for example.

The number of layers of wiring board 100 is not limited to three and may be any other number. For example, it may be six layers or eight layers. Also, the method shown in FIG. 3 may be applied to conductive patterns of all the layers (conductive layers 101a˜101c), or only to the outer layers (conductive layers 101a, 101c) or to the inner layer (conductive layer 101b). In addition, wiring board 100 of the present embodiment is a coreless wiring board that does not have a core substrate, but wiring board 100 may include a core substrate (see FIG. 24).

Wiring board 100, especially conductive layers (β101a-101c), is manufactured by the method shown in FIG. 3, for example.

In step (S11), insulation layer 10 is prepared as shown in FIG. 4, for example. In the present embodiment, insulation layer 10 is made of an insulative resin layer. In the following, one of the upper and lower surfaces (two main surfaces) of insulation layer 10 is referred to as first surface (F1) (on the Z1 side) and the other as second surface (F2) (on the Z2 side).

Here, insulation layer 10 includes filler (10a) and resin (10b). Insulation layer 10 is formed by combining filler (10a) in resin (10b). In the present embodiment, filler (10a) is mostly uniformly dispersed substantially throughout insulation layer 10. However, that is not the only option, and filler (10a) may be dispersed only in the surface-layer portion of insulation layer 10 (see later-described FIG. 25).

In the present embodiment, resin (10b) is made of thermosetting epoxy resin. The material for resin (10b) is not limited to a specific type, and instead of epoxy resin, the following thermosetting resins, for example, may be used as the material for resin (10b): phenol resin, polyphenylene ether (PPE), polyphenylene oxide (PPO), fluororesin, LCP (liquid crystal polymer), polyester resin, imide resin (polyimide), BT resin, allyl polyphenylene ether resin (A-PPE resin), aramid resin or the like.

Insulation layer 10 is preferred to contain filler (10a) at approximately 30 wt. % or greater. Especially, filler (10a) is preferred to be contained at approximately 50 wt. % or greater.

In the present embodiment, filler (10a) is made of inorganic filler. Therefore, since inorganic filler widely used as an insulative material for printed wiring boards is used as is, the present embodiment is advantageous from the viewpoint of cost and quality control.

The inorganic filler of the present embodiment is a silica-type filler. As for silica-type fillers, silicate minerals should preferably be used; especially at least any one of silica, mica, talc, kaolin and calcium silicate is preferred to be used. In the present embodiment, filler (10a) is made of spherical silica. However, the shape of filler (10a) is not limited specifically (see later-described FIG. 26). Here, the inorganic filler is not limited to a silica-type filler, and it may be a white-type filler, for example. The reflectance of a white-type filler is approximately the same as that of a silica-type filler.

The average particle width (diameter) of filler (10a) is preferred to be approximately 0.5 μm or greater and approximately 10 μm or smaller. When the average particle diameter of filler (10a) is in the above range, filler (10a) works favorably as a stopper that prevents the insulation layer from being damaged by laser energy. If filler (10a) is not shaped in a complete circle, an approximate value obtained from the volume is used as the particle diameter.

In the present embodiment, approximately 50 wt. % or greater of filler (10a) is spherical filler (spherical silica). When the main ingredient (more than half) of filler (10a) is spherical filler, filler (10a) works favorably as a stopper in a later-described step of laser irradiation (see FIG. 9). As a result, conductor, catalyst or the like seldom remains on insulation layer 10.

In an example of the structure of insulation layer 10, the base resin is epoxy resin, the curing agent is phenolic novolac, the filler is spherical silica, the amount of filler contained is 42 wt. % and the flame retardant is an organic phosphorous type. Insulation layer 10 contains two types of filler having diameters of 0.5 μm and 5 μm, for example.

First surface (F1) of insulation layer 10 is roughened by etching, for example. In particular, first surface (F1) of insulation layer 10 is etched through immersion using a permanganic acid solution, for example. However, the roughening method is not limited specifically to etching. For example, treatments such as polishing, oxidation or oxidation/reduction may be used to roughen first surface (F1) of insulation layer 10.

A catalyst is adsorbed on first surface (F1) (roughened surface) of insulation layer 10 through immersion, for example. Such a catalyst is made of palladium, for example. For immersion, a solution of palladium chloride, a palladium colloid or the like is used. To immobilize the catalyst, thermal treatment may be conducted after the immersion.

A power-supply layer is formed on insulation layer 10 (insulative resin layer) in step (S12) in FIG. 3.

In particular, as shown in FIG. 5, electroless copper-plated film 1001 (power-supply layer), for example, is formed on first surface (F1) (roughened surface) of insulation layer 10 by a chemical plating method, for example. As for the plating solution, for example, a copper sulfate solution with an added reduction agent or the like is used. As for the reduction agent, for example, formalin, hypophosphite, glyoxylic acid or the like is used.

The thickness of electroless plated film 1001 is preferred to be in the range of approximately 0.1 μm to approximately 1.0 μm. Since electroless plated film 1001 works as a power-supply layer for electrolytic plating, if the thickness of electroless plated film 1001 is approximately 0.1 μm or greater, conductive resistance is reduced, and the thickness tends to become more uniform in electrolytic plated film (conductive pattern 22 shown later in FIG. 6C) to be formed on electroless plated film 1001. Also, if the thickness of electroless plated film 1001 is approximately 1.0 μm or less, removal by laser processing (step (S14) in FIG. 3) is easier.

In step (S13) in FIG. 3, a conductive pattern is formed on electroless plated film 1001 (power-supply layer) through electrolytic plating.

In particular, as shown in FIG. 6A, plating resist 1002 is formed on electroless plated film 1001. Plating resist 1002 has opening portion (1002a) at a predetermined spot. Opening portion (1002a) is positioned to correspond to conductive pattern 22 to be formed (see FIG. 6C).

As shown in FIG. 6B, by electrolytic copper plating, for example, conductive portion (22a) of conductive pattern 22 (see FIG. 6C) is formed in opening portion (1002a) in plating resist 1002. More specifically, copper (such as high phosphorous copper) as the material to be plated is connected to an anode, and electroless plated film 1001 as a power-supply layer is connected to a cathode, and then they are immersed in a plating solution. Then, direct voltage is applied between both electrodes to flow current, and copper is deposited on electroless plated film 1001 exposed at the cathode. In doing so, conductive portion (22a) is formed on electroless plated film 1001. As for the plating solution, for example, a copper sulfate solution, a copper pyrophosphate solution, a copper cyanide solution, copper fluoroborate or the like is used.

As shown in FIG. 6C, using a predetermined removing solution, for example, plating resist 1002 is removed. Accordingly, conductive pattern 22 having conductive portion (22a) and non-conductive portion (22b) is formed. This step may be omitted, and plating resist 1002 may be removed by subsequent laser processing (step (S14) in FIG. 3) (see later-described FIGS. 22A and 22B).

By black oxide treatment, for example, the surfaces (their entire surface, for example) of electroless plated film 1001 and conductive pattern 22 are blackened. Accordingly, laser absorbency is enhanced and efficiency during laser processing is improved.

In step (S14) in FIG. 3, by irradiating laser light having a wavelength in the range of approximately 350 nm to approximately 600 nm and a pulse width in the range of approximately 0.1 picosecond (approximately 100 femtoseconds) to approximately 100 picoseconds (hereinafter referred to as a short pulse), a portion of electroless plated film 1001 (power-supply layer) which is not covered with conductive pattern 22 (conductive portion 22a) is removed.

In particular, electroless plated film 1001 is sublimed by laser irradiation. When laser light is irradiated with a short pulse, it is easier to mitigate energy concentration than when laser light is irradiated at a shorter pulse width than the short pulse (a pulse width shorter than approximately 0.1 picosecond). Thus, laser light is less likely to further sublime inorganic filler.

Also, the surface of conductive pattern 22 (in particular, main surface (F11) of conductive pattern 20) is roughened through abrasion by laser irradiation. Electroless plated film 1001 (power-supply layer) is preferred to be made of material which requires less energy to sublime than conductive pattern 22. Accordingly, effects from abrasion by laser light are suppressed in conductive pattern 22.

In the present embodiment, laser light having the above wavelength is irradiated without using a mask on the entire surface of the object (insulation layer 10 or the like), namely on electroless plated film 1001 and conductive pattern 22 formed on electroless plated film 1001. The second harmonic of a fundamental wave with an approximate wavelength of 1064 nm, namely, laser light having an approximate wavelength of 532 nm (hereinafter referred to as green laser) is used as an example of the present embodiment.

In the present embodiment, as shown in FIG. 7A and FIG. 7B (a cross-sectional view taken at the A-A line in FIG. 7A), for example, conductive pattern 22 is formed with multiple straight lines positioned substantially parallel to each other. However, a conductive pattern is not limited to such and may be determined freely (see later-described FIGS. 23A and 23B).

As an example of the present embodiment, a green laser is irradiated at a pulse width of 15 picoseconds. FIG. 8A shows distribution of light intensity (see line L1) when a laser is irradiated with a short pulse (pulse width D1), and another distribution of light intensity (see line L2) when a laser is irradiated at pulse width (D2) which is longer than pulse width (D1). As shown in FIG. 8A, since laser light with a short pulse gives the ability to infuse higher energy per unit time, when laser light with a short pulse is irradiated at electroless plating 1001, the portion irradiated by the laser light is sublimed instantaneously. Accordingly, such processing allows reaction (decomposition) to be finished before heat is conveyed to the object (hereinafter referred to as non-thermal processing). Then, by such non-thermal processing, it is easier to suppress a material of electroless plating 1001 from becoming a drift (plume), and to suppress the drift from being attached again to the conductive pattern. The pulse width of laser light is preferred to be in the range of approximately 0.1 picosecond to approximately 1,000 picoseconds, more preferably in the range of approximately 0.1 picosecond to approximately 100 picoseconds.

When laser light scans the entire surface of an object, for example, it is preferred to fix the object and to move the laser light (more precisely, its aiming range); alternatively, to fix the laser light (more precisely, its aiming range) and to move the object. When moving the laser light, it is preferred that the laser light be moved by using a galvanomirror, for example. In addition, when moving the object, it is preferred to set the laser light as a linear beam using a cylindrical lens, for example, and to move the object by conveyor while the laser light is irradiated at predetermined portions.

Here, an example of the conditions is described for laser light to be moved using a galvanomirror. In FIG. 8B, spot diameter (d11) of the laser light is approximately 30 μm, for example. In such an example, the scanning direction of the laser light is set along a direction X. Unit moving amount (d12) in a direction X (distance between irradiation centers P of adjacent spots) is approximately 20 μm, for example. In addition, unit moving amount (d13) in a direction Y (distance between irradiation centers P of adjacent spots) is approximately 20 μm, for example. The scanning speed of the laser light is approximately 1500 mm/sec., for example.

Taking an example of laser irradiation under the above conditions, an example of laser irradiation is described as follows.

First, a laser is irradiated at a first line on the X-Y plane of an object, for example, from (0, 0) through (XX, 0) in this example. In particular, a laser is irradiated at a first irradiation spot (0, 0) and then the laser is moved toward the X2 side by unit moving amount (d12) and is irradiated at next irradiation spot (20, 0). Then, as shown with arrows in FIG. 7A, by repeating laser irradiation and movement toward the X2 side, a laser is irradiated spot by spot at each irradiation spot designated along a direction X of the object. Accordingly, when laser irradiation is finished for the entire region in a direction X of the object, laser irradiation on the first line is completed.

Laser irradiation is conducted on a second line on the X-Y plane of the object, for example, from (0, 20) through (XX, 20). In particular, as shown with arrows in FIG. 7A, the laser is returned to the original point of the X coordinate from the final irradiation point (XX, 0) of the first line, while moving the Y coordinate toward the Y1 side by unit moving amount (d13). Then, the laser is scanned from the irradiation spot (0, 20) toward the X2 side the same as for the first line. Accordingly, by conducting laser irradiation one line after another, the entire main surface (X-Y plane) of the object is irradiated by laser light.

Here, an example has been shown in which a laser is scanned along a direction X, which is perpendicular to the longitudinal direction (direction Y) of a conductive pattern. However, a laser may be scanned along a direction Y parallel to the longitudinal direction of the conductive pattern. Alternatively, laser irradiation is not limited to spot irradiation. For example, laser light may be set as a linear beam along a direction X or a direction Y using a cylindrical lens, and using the linear beam, the object may be scanned along a direction Y or a direction X.

Here, laser intensity (amount of light) is preferred to be adjusted by pulse control. In particular, for example, to modify laser intensity, the number of shots (irradiation number) is changed without changing laser intensity per shot (one irradiation). Namely, if required laser intensity is not obtained with one shot, laser light is irradiated again at the same irradiation spot. If such a control method is used, the throughput improves, since time for modifying irradiation conditions is omitted. However, adjusting laser intensity is not limited specifically to the above. For example, irradiation conditions may be determined for each irradiation spot, while the irradiation number is set constant (for example, one shot per one irradiation spot). Also, if multiple laser shots are irradiated at the same irradiation spot, the laser intensity may be modified for each shot. Moreover, without completely setting the laser focus at the irradiation spot, the object may be processed using light that is out of focus in a direction Z (defocused light). If defocused light is used, since its spot diameter is enlarged while the laser intensity is weakened, soft processing is achieved.

Using the above conditions, a green laser is irradiated at the entire surface of the object (insulation layer 10 or the like), namely, electroless plated film 1001 and conductive pattern 22 formed on electroless plated film 1001. Accordingly, electroless plated film 1001 between portions of conductive pattern 22, namely, portions of electroless plated film 1001 (power-supply layer) which are not covered by conductive pattern 22, are removed. As a result, as shown in FIG. 9, conductive pattern 21 is formed and conductive pattern 20 having a double-layer structure of conductive pattern 21 and conductive pattern 22 is formed. Conductive pattern 20 is formed with conductive portion (20a) having main surface (F11) and side surfaces (F12) along with non-conductive portion (20b) (space) (see FIG. 10).

In the present embodiment, laser irradiation not only removes electroless plated film 1001 (power-supply layer), but also shaves the surface of insulation layer 10 beneath electroless plated film 1001. Accordingly, resin residue on the surface of insulation layer 10 is removed, while recess (P1) is formed on the surface of insulation layer 10, as shown in FIG. 9. However, recess (P1) is not always required to be formed.

In the present embodiment, since laser light is irradiated without using a mask on the entire surface of the object (see FIGS. 7A and 7B), a short-pulse green laser is also irradiated at conductive pattern 22. Then, due to abrasion by laser irradiation, recessed portions (anchors) are formed in the surface of conductive pattern 22 (specifically, main surface (F11) of conductive pattern 20). In the present embodiment, removing electroless plated film 1001 (power-supply layer) and roughening conductive pattern 22 are simultaneously conducted by irradiating laser light. By employing point irradiation with a short pulse for laser processing, recessed dots tend to be formed on the surface of conductive pattern 22, and because of such recessed dots, the surface of conductive pattern 22 tends to be roughened. At that time, the surface roughness (Ra) of conductive pattern 22 is approximately 0.1 μm, for example. When point irradiation is conducted for processing, the finish tends to be neat at the boundary between conductive pattern 22 and electroless plated film 1001 (power-supply layer). Also, if the spot of point irradiation is shaped as a square, the number of times to overlap decreases compared with a circular shape. As a result, manufacturing efficiency is improved.

After irradiating the laser, as shown in FIG. 10, for example, insulation layer 30 is formed on insulation layer 10 and conductive pattern 20 without roughening treatment. Insulation layer 30 may be an upper interlayer insulation layer of conductive pattern 20 or may be solder resist. Here, if the surface of conductive pattern 22 (especially main surface (F11) of conductive pattern 20) is roughened, adhesiveness tends to improve between conductive pattern 22 and insulation layer 30 formed thereon. Especially when insulation layer 30 is made of resin, adhesiveness tends to improve.

In the present embodiment, since electroless plated film 1001 is removed by short-pulse laser processing instead of wet etching, side etching and undercutting tend to be suppressed without making electroless plated film 1001 thinner in advance. Then, as a result, a conductive pattern with excellent electrical characteristics tends to be obtained.

In addition, because side etching and undercutting tend to be suppressed, the line width of conductive pattern 20 seldom becomes thinner. As a result, a fine pattern is easily formed at a high yield rate without requiring a highly clean room. Also, by removing electroless plated film 1001 (power-supply layer) through non-thermal treatment, electroless plated film 1001 is suppressed from reattaching. Moreover, reattaching particles tend to be fine particles such as 100 nm or smaller. Making reattaching particles finer is effective in improving adhesiveness with an upper insulation layer (resin).

In the present embodiment, by conducting laser processing using a green laser, filler (10a) works as a stopper and insulation layer 10 under electroless plated film 1001 tends to be suppressed from being excessively removed. Also, since it is easier to completely remove the catalyst which tends to remain between conductive portions (20a) of conductive pattern 20, short circuiting between wiring lines tends to be suppressed. The reasons for those are described as follows by referring to FIG. 11 and others.

FIG. 11 is a graph showing the relationship between a wavelength of laser light and its absorption rates when the laser light is irradiated respectively on epoxy resin (line L11), copper (line L12) and silica (line L13). Here, if epoxy resin is replaced with other resins, or if silica is replaced with other inorganic fillers, substantially the same effects are achieved.

First, laser light (LZ3) with an approximate wavelength of 532 nm (green laser) and laser light (LZ4) with an approximate wavelength of 10640 nm are compared. As the light source for laser light (LZ4), a CO₂laser is used, for example.

As shown in FIG. 11, the absorption rate of laser light (LZ4) is high in both epoxy resin (line L11) and silica (line L13); however, the absorption rate of laser light (LZ3) is high in epoxy resin (line L11) and low in silica (line L13). Especially, in laser light (LZ3), the absorption rate of silica (line L13) is kept at approximately 20% or less, specifically at approximately 10%. Since insulation layer 10 contains resin (10b) (epoxy resin) as well as filler (10a) (a silica-type filler) in the present embodiment, when laser light (LZ3) is irradiated at insulation layer 10, filler (10a) works as a stopper to suppress progress of the decomposition reaction (photochemical reaction) in insulation layer 10. Namely, as shown in FIG. 9, for example, filler (10a) reflects laser light and suppresses excessive removal of insulation layer 10 at the irradiation spot. To use filler (10a) as a stopper, the absorption rate of laser light in resin (10b) is preferred to be approximately seven times or greater the absorption rate of laser light in filler (10a).

Also, the absorption rate in copper (line L12) is higher in laser light (LZ3) than in laser light (LZ4). When irradiating a laser to pattern electroless copper-plated film 1001, the absorption rate of laser light in copper is preferred to be higher to a certain degree. That is because removal of conductor (copper) becomes more efficient. However, if the absorption rate of laser light in copper is too high, disadvantages such as excessive shaving of copper occurs. Thus, the absorption rate of laser light in the material (copper) for conductive film is preferred to be in a certain range so that the laser light is appropriately absorbed in copper; specifically, a range of approximately 30% to approximately 65% is preferred. For that matter, since the absorption rate of laser light (LZ3) in copper is approximately 50%, it is suitable for patterning a conductive layer made of copper.

Also, laser light with a wavelength of approximately 1064 nm or shorter decomposes the object mainly by a photochemical reaction, and laser light with a wavelength longer than approximately 1064 nm decomposes the object mainly by a thermal reaction. If the two reactions are compared, energy efficiency is higher in a photochemical reaction, which uses light as is, than in a thermal reaction, which uses light by converting it to heat. Accordingly, laser light (LZ3) is also excellent for energy efficiency. Furthermore, by conducting non-thermal treatment using a laser light having the same wavelength but a short pulse, energy efficiency is enhanced even more.

Laser light (LZ1) with an approximate wavelength of 200 nm, laser light (LZ2) with an approximate wavelength of 355 nm (UV laser) and laser light (LZ3) with an approximate wavelength of 532 nm are compared. As the light source of laser light (LZ1), an excimer laser is used, for example. In addition, as laser light (LZ2), the third harmonic of YAG laser is used, for example.

Those laser lights (LZ1˜LZ3) have common properties such as decomposing the object mainly by photochemical reaction. However, regarding the absorption rates in epoxy resin (line L11), copper (line L12) and silica (line L13) respectively, laser light (LZ1) has the highest, laser light (LZ2) has the second highest, and laser light (LZ3) has the lowest, as shown in FIG. 11. More specifically, absorption rates of laser lights (LZ2, LZ3) are listed in epoxy resin (line L11), copper (line L12) and silica (line L13) in descending order. However, the absorption rates of laser light (LZ1) are listed in epoxy resin (line L11), silica (line L13) and copper (line L12) in descending order. Moreover, when laser light (LZ1) is used, there is little difference between the absorption rate in epoxy resin (line L11) and the absorption rate in silica (line L13). Therefore, if laser light (LZ1) is used in the previous step of laser irradiation, filler (10a) does not function as a stopper. On the other hand, if laser light (LZ2) or (LZ3) is used in the previous step of laser irradiation, filler (10a) works as a stopper, and phenomena such as deep-cut epoxy resin seldom occur. Also, the ratio of the absorption rate in copper (line L12) to the absorption rate in silica (line L13) (copper/silica) is preferred to be approximately five to one or greater.

Considering the above, the laser light to be used in laser irradiation for removing unnecessary electroless plated film 1001 is preferred to be a type which decomposes the object mainly by photochemical reaction, namely, laser light with a wavelength of approximately 1064 nm or shorter. Also, considering the efficiency of removing the conductor (copper), the absorption rate of laser light in the material for conductive film (copper) should preferably be in the range of approximately 30% to approximately 60%. If the wavelength of laser light is in the range of approximately 350 nm to approximately 600 nm (range R21), the absorption rate of the laser light is in the range of approximately 30% to approximately 60%. Furthermore, considering the use of filler (10a) as a stopper and the efficiency and the like of removing the conductor, it is more preferable if the range is approximately 500 nm to approximately 560 nm (range R22).

The light source may be a solid laser, a liquid laser or a gas laser. Specifically, YAG laser, YVO₄laser, argon ion laser, semiconductor laser, fiber laser, disc laser or copper vapor laser is preferable as a light source. For example, by using the second harmonic of YAG laser or YVO₄laser, laser light with an approximate wavelength of 532 nm is obtained, and by using the third harmonic of YAG laser or YVO₄laser, laser light with an approximate wavelength of 355 nm is obtained. Also, by using an argon ion laser, laser light with a wavelength in the range of approximately 488 nm to approximately 515 nm is obtained. In addition, by using a semiconductor laser, high efficiency is achieved despite its compact size. Also, by using a copper vapor laser, laser light with a wavelength in the range of approximately 511 nm to approximately 578 nm is obtained. However, the light source is not limited to those, and it is preferred to select a type appropriate to the required wavelength of the laser light.

FIG. 12 is a table showing the results when a green laser with an average output of 5 W and a short pulse is respectively irradiated at insulation layers 10 containing four different inorganic fillers. In those tests, epoxy resin was used as resin (10b), and SiO₂powder (silica-type filler), CaCO₃powder (calcium-carbonate filler), BaSO₄powder (barium-sulfate filler) and Al(OH)₃powder (aluminum-hydroxide filler) were used as filler (10a). In addition, regarding the SiO₂powder, the above laser irradiation was conducted respectively at insulation layers 10 containing four different amounts of filler (10a). The scanning speed of laser light was set at approximately 50 mm/sec. and the laser intensity was set at approximately 60 times that of the manufacturing process.

As shown in FIG. 12, when SiO₂powder was not contained in resin (10b) (approximately 0 wt. %), or SiO₂powder was contained in resin (10b) at approximately 15 wt. %, carbonization was observed on the surface of resin (10b) irradiated by laser. On the other hand, when SiO₂powder was contained in resin (10b) at approximately 30 wt. % or approximately 50 wt. %, carbonization was not observed on either surface of resin (10b) irradiated by laser. From those results, by adding filler (10a) at approximately 30 wt. % or more to resin (10b), resin (10b) is suppressed from being carbonized. Also, when white-type fillers such as calcium-carbonate filler, barium-sulfate filler and aluminum hydroxide filler are used, substantially the same results are obtained.

Laser processing and a wet method using an etching solution are compared. When a wet method is employed, it is a substantially isotropic processing, unlike an anisotropic processing by laser processing (in particular processing mainly in a direction Z). Thus, conductor tends to be excessively removed through side etching or the like as shown in FIG. 13A. As a result, wiring width is reduced from the required width. For that matter, since the line width is suppressed from locally becoming thinner when a laser is used, it is easier to design a fine pattern and to achieve impedance matching. Moreover, since effects from side etching are few, the smoothness of the side surfaces of the wiring is enhanced.

To improve the smoothness of the side surfaces of the wiring, it is effective to employ laser processing rather than a wet method, especially laser processing using laser light with a wavelength in the range of approximately 500 nm to approximately 560 nm. In particular, when a laser having such a wavelength is used, since filler (10a) tends to work as a stopper, undercutting does not occur and it is easier to form conductive pattern 20 with a required width as shown in FIG. 13B. By contrast, when laser light with a wavelength shorter than approximately 500 nm (such as excimer laser) is used, since filler (10a) has difficulty in working as a stopper, undercutting occurs as shown in FIG. 13C.

In addition, to improve the smoothness of the side surfaces of the wiring, irradiating laser light with a short pulse is preferred. FIG. 14A is an SEM photograph showing conductive pattern 20 obtained by removing electroless plated film 1001 through laser irradiation at a pulse width of 10 picoseconds. Also, FIG. 14B is an SEM photograph showing conductive pattern 20 obtained by removing electroless plated film 1001 through laser irradiation at a pulse width of 10 nanoseconds. FIG. 15 is a magnified photograph of FIG. 14A. As shown in FIGS. 14A and 14B, when laser light is irradiated with a short pulse (such as a pulse width of 10 picoseconds) (FIG. 14A), the smoothness of the side surfaces of the wiring improves compared with when laser light is irradiated at a pulse width longer than a short pulse (such as a pulse width of 10 nanoseconds) (FIG. 14B).

Also, if a laser is used when removing unnecessary electroless plated film 1001, the catalyst (such as palladium) used for forming electroless plated film 1001 remains less than when a wet method is used. The reasons for that are described in the following by referring to FIG. 16.

Regarding sample A where a green laser is used and sample B where a wet method is used, FIG. 16 is a graph respectively showing the results of the remaining amounts of a catalyst (palladium here) measured on the surface of insulation layer 10 exposed in non-conductive portion (20b) of conductive pattern 20 (hereinafter referred to as a detection surface).

As for the measuring method, ESCA (electron spectroscopy for chemical analysis) was employed. More specifically, X rays were irradiated at the detection surface of each sample, and a narrow-band spectrum was measured in the energy range where the peak particular to palladium appears (especially its 3d^5/2orbit). In that graph, the vertical axis shows photoelectron intensity (the number of photoelectrons) and the horizontal axis shows binding energy of electrons. Also, line (L21) shows the measurement results of sample A and line (L22) shows the measurement results of sample B.

Since line (L21) shows no peak, it is found that there is no substantial amount of palladium on the detection surface of sample A. By contrast, since line (L22) shows a peak in the spot particular to palladium, it is found that palladium exists on the detection surface of sample B. In addition, as a result of conducting quantitative analysis from peak intensity, concentration per unit area and the like, the remaining amount of palladium on the detection surface of sample B was 4.39 μg/cm².

From the above test results, the remaining amount of palladium is less when a laser is used than when a wet method is used. Accordingly, using a laser, there is a decrease in risks such as short circuiting between conductive portions (20a) of conductive pattern 20 caused by Ni or the like being deposited abnormally around palladium as a core.

Also, since using a wet method generates waste liquid, laser processing is preferred in consideration of environmental issues.

Second Embodiment

The second embodiment of the present invention is described focusing on differences with the above first embodiment. Here, the same numerical reference is applied to the same element as shown in above FIG. 1 and others, and when a portion is already described, namely its description would be redundant, such a description is omitted or simplified.

The manufacturing method according to the present embodiment includes the steps shown in FIG. 3 and the like, the same as the manufacturing method according to the first embodiment. However, during laser irradiation in the present embodiment (step (S14) in FIG. 3), a portion where laser light is irradiated (hereinafter referred to as a processing portion) is set in contact with liquid flow or current from inert gas. In the following, such laser irradiation is described in detail. In the present embodiment, laser light is also irradiated at an object in a manner as shown in FIG. 7A, for example, the same as the manufacturing method according to the first embodiment. Namely, irradiation of laser light is conducted multiple times by changing irradiation spots. In addition, laser irradiation in the present embodiment is performed at a pulse width on the order of nanoseconds (such as 10 nanoseconds) instead of short-pulse laser irradiation.

The laser irradiation of the present embodiment is performed, for example, while a portion to be irradiated by laser light is in contact with liquid flow or current from inert gas. More specifically, as shown in FIG. 17, for example, prior to laser irradiation, flow (P12) is formed on a surface of a wiring board in a direction (direction X) that is perpendicular to the irradiation direction (direction Z) of laser light (P11). Then, laser light (P11) is irradiated on the surface of the wiring board. For example, as shown in FIG. 18, flow (P12) (liquid flow) is formed on the surface of the wiring board, by flowing a liquid (such as water) in a vertical direction (direction X) while the wiring board is placed to be in a standing position and gravity is used. However, forming flow (P12) is not limited specifically to the above.

For example, flow (P12) may be formed by injecting gas (such as air or inert gas) pressurized by a compressor, a tank or the like. Alternatively, using gas such as helium which is lighter than air, flow (P12) as an ascending current may be formed.

The direction of flow (P12) is not limited specifically. For example, as shown in FIG. 19, flow (P12) may be formed in a direction (direction Z) parallel to the irradiation direction of laser light (P11). Such flow (P12) is formed by blowing gas (such as air or inert gas) on the surface of a wiring board to be irradiated by laser light (P11), for example. However, forming flow (P12) is not limited specifically to the above.

For example, as shown in FIG. 20A, a gas lighter than air (such as helium) may be flowed on the surface of a wiring board so that flow (P12) as an ascending current is formed.

According to the manufacturing method of the present embodiment, if a drift or the like is generated during laser processing, such a drift is removed by flow (P12) and the original condition of the processing portion is substantially restored. Also, the temperature at the processing portion is suppressed from rising by adjusting temperatures using flow (P12). By maintaining the condition of the processing portion in a preferred condition, it is easier to suppress the drift generated during laser processing from being reattached to the conductive pattern, or from damaging insulation layer 10 (resin insulation layer).

In addition, a wiring board (including a power-supply layer) may be set in a liquid where the liquid is flowing, and laser light may be irradiated at the wiring board (power-supply layer) in the liquid. For example, as shown in FIG. 20B, a wiring board is placed in liquid 1004 (such as water) and flow (P12) (liquid flow) may be formed in any selected direction by blending or the like. By placing the wiring board in a liquid, it is easier to enhance the efficiency of removing the drift or cooling the processing portion.

It is not always required that the processing portion to be irradiated by laser light be in contact with liquid flow or current from inert gas prior to laser irradiation. For example, after irradiating laser light, the portion irradiated by laser light may be set in contact with liquid flow or current from inert gas. After laser light is irradiated, if the processing portion is set in contact with liquid flow or current from inert gas prior to the next irradiation, even if the portion to be irradiated next is close to the prior irradiation portion, the above drift is seldom reattached.

In such a case, as shown in FIG. 21A (a view showing a side surface of nozzle 1003) and FIG. 21B (a view showing the injection tip of nozzle 1003), for example, it is effective to form flow (P12) by using nozzle 1003 which emits laser light (P11) and liquid (such as water) in concentric circles. In that case, the direction of flow (P12) is parallel (direction Z) to the irradiation direction of laser light (P11) (see FIG. 19). Using such nozzle 1003, the processing portion tends to make contact with flow (P12) shortly after the irradiation of laser light (P11). In the example shown in FIGS. 21A and 21B, laser light (P11) passes the center of nozzle 1003 and the liquid flows around it. However, inversely, the liquid may flow in the center of nozzle 1003 and laser light (P11) may pass around the liquid flow. Alternatively, gas may be flowed instead of liquid.

To simplify manufacturing steps, it is preferred that laser light (P11) be irradiated while the processing portion is in contact with flow (P12) (liquid flow or current from inert gas). However, if the processing portion makes contact with liquid flow or current from inert gas after laser light (P11) is irradiated, attenuation of laser light (P11) by flow (P12) tends to be suppressed.

In addition, regarding structure and treatments the same as in the first embodiment, substantially the same effects as those described above in the first embodiment are also achieved in the present embodiment. The pulse width of laser light in the present embodiment may also be a short pulse.

Other Embodiment(s)

In each of the above embodiments, a laser is irradiated after plating resist 1002 for electrolytic plating is removed. However, that is not the only option. For example, as shown in FIG. 22A or 22B, while plating resist 1002 remains, laser light is irradiated (step (S14) in FIG. 3), and plating resist 1002 and electroless plated film 1001 may be removed through the laser irradiation. In doing so, a step to remove plating resist 1002 (FIG. 6C) is omitted. Also, plating resist 1002 tends to be removed completely. In such a case, plating resist 1002 is preferred to be made of material which is easy to remove by laser, for example, acrylic resin.

In each of the above embodiments, laser light is irradiated without using a mask on the entire surface of an object. However, that is not the only option, and a shading mask, for example, may be used. In addition, laser irradiation is paused in a non-irradiation portion and laser light may be selectively irradiated only at the portion to be irradiated. Other than those, irradiation spots, the method for controlling laser intensity and the like are determined freely.

Conductive pattern 20 is not limited to being a linear pattern, and any other pattern may be employed.

For example, as shown in FIG. 23A (a plan view corresponding to FIG. 7A), conductive pattern 20 may also be a U-shaped conductive pattern.

In addition, as shown in FIG. 23B (a plan view corresponding to FIG. 7A), non-conductive portion (20b) (space) of conductive pattern 20 may be a hole.

Wiring board 100 to be manufactured is not always required to be a coreless wiring board as shown in FIG. 1. For example, it may be a double-sided wiring board having core substrate (100a) as shown in FIG. 24. In such a case as well, conductive layers (101a˜101f) are each formed by the above-described method for forming conductive pattern 20 (see FIG. 3). In addition, the above-described method for forming conductive pattern 20 may be applied not to the conductive patterns of all the layers (conductive layers 101a˜101f), but only to the conductive patterns of the outer layers (conductive layers 101a, 101f) or inner layers (conductive layers 101b˜101e), or only to the conductive patterns of core substrate (100a) (conductive layers 101c, 101d).

Basically, wiring board 100 to be manufactured is selected freely as long as it is a wiring board having a conductive pattern on an insulation layer made of resin, for example. Therefore, it may be a rigid wiring board or a flexible wiring board. Also, it may be a double-sided wiring board, or a single-sided wiring board. The number of conductive patterns and insulation layers is determined freely.

It is not always required to disperse filler (10a) substantially throughout insulation layer 10. For example, as shown in FIG. 25, insulation layer 10 may include first layer 11 that does not contain filler (10a) (resin layer) and second layer 12 that contains filler (10a) (filler layer). In such an example, first layer 11 is made mainly of resin (10b) and second layer 12 is made mainly of filler (10a) and resin (10b). Then, second layer 12 is formed on first layer 11. Alternatively, multiple resin layers and multiple filler layers may be alternately formed.

As for filler (10a), filler in a shape other than spherical may also be used. For example, as shown in FIG. 26, instead of spherical filler, crushed filler (such as crushed silica) may be used as filler (10a).

As for filler (10a), it is preferred to use at least one from among spherical silica, crushed silica, fused silica and crystalline silica. However, inorganic filler other than a silica-type filler may also be used as filler (10a). Also, other than a silica-type filler, inorganic fillers such as the following may be used: filler made from calcium carbonate (hereinafter referred to as calcium-carbonate filler); filler made from barium sulfate (hereinafter referred to as barium-sulfate filler); filler made from aluminum hydroxide (hereinafter referred to as aluminum-hydroxide filler); and the like. Alternatively, two or more inorganic fillers selected from among the above silica-type fillers, calcium-carbonate filler, barium-sulfate filler and aluminum hydroxide filler may be contained in insulation layer 10. Especially, if at least one of calcium-carbonate filler, barium-sulfate filler and aluminum hydroxide filler is contained in addition to a silica-type filler, it is effective in lowering the cost of insulation layer 10.

As the material for conductive pattern 20, conductors other than copper may be used. As long as relationships substantially the same as those shown in FIG. 11 are obtained, effects substantially the same as those described earlier are achieved.

Regarding other factors such as the structure of semiconductor element 1000, the types of its structural elements, quality, measurements, material, shapes, number of layers, positions or the like may be freely modified within a scope that does not deviate from the gist of the present invention.

The method for manufacturing wiring board 100 is not limited to the order and contents shown in FIG. 3, and the order and contents may be freely modified within a scope that does not deviate from the gist of the present invention. Also, some processes may be omitted depending on usage or the like.

Each of the above embodiments and each modified example may be combined freely. It is preferred to select an appropriate combination according to usage or the like.

A method for manufacturing a wiring board according to an embodiment of the present invention includes the following: forming an insulative resin layer; forming a power-supply layer on the insulative resin layer; forming a conductive pattern on the power-supply layer through electrolytic plating; and removing the power-supply layer between portions of the conductive pattern by irradiating laser light with a wavelength in the range of approximately 350 nm to approximately 600 nm at a pulse width in the range of approximately 0.1 picosecond to approximately 1,000 picoseconds.

A method for manufacturing a wiring board according to another embodiment of the present invention includes the following: forming an insulative resin layer; forming a power-supply layer on the insulative resin layer; forming a conductive pattern on the power-supply layer through electrolytic plating; and removing the power-supply layer between portions of the conductive pattern by irradiating laser light having a wavelength in the range of approximately 350 nm to approximately 600 nm. In such a manufacturing method, a portion to be irradiated by the laser light is set in contact with liquid flow or current from inert gas when irradiating the laser light.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

METHOD FOR MANUFACTURING WIRING BOARD

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