Printed wiring board and method for manufacturing the same

Abstract

To provide a printed wiring board that has a higher-definition conductive pattern, and a manufacturing method thereof.SOLUTION: A printed wiring board includes an insulating base material 11, a plating seed layer 13 formed of a photocurable resin and metal nanoparticles on the base material 11, and a plating layer 15 formed on the plating seed layer 13, and the plating seed layer 13 has a first region 13a that is a non-exposed region and a second region 13b that is an exposed region, and the plating layer 15 is not formed in the second region 13b but in the first region 13a.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a printed wiring board capable of forming a high-definition conductive pattern and a method for manufacturing the same.

Background Art

[0002] Conventionally, printed wiring boards have been manufactured by forming a metal layer on an insulating base material (base material) such as resin and then removing unnecessary portions of this metal layer by etching to form a wiring pattern. In this method, a large amount of water and excess metal discarded by etching are used, and many processes have to be undergone.

[0003] In contrast, the present applicant has proposed a technique of applying a conductive ink containing metal nanoparticles only to necessary portions by an inkjet method or the like, and further increasing the thickness of the metal layer by plating treatment to reduce the resistance value (Patent Document 1). This technique enables a significant simplification of the substrate manufacturing process, particularly significantly reducing the amount of water used and also succeeding in reducing the CO2 emission amount. The inkjet method is a reliable method capable of producing a small number of printed wiring boards on demand in a minimum of time and cost.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the precision expressed by the line and space achievable by the inkjet method has a limit of 200 to 200 μm, and it has been difficult to produce a conductive pattern with higher definition than this.

[0006] This invention was made against this background, and its objective is to provide a printed circuit board having a more detailed conductive pattern and a method for manufacturing the same. [Means for solving the problem]

[0007] To solve the above problems, the printed wiring board according to this disclosure comprises an insulating substrate, a plating layer formed on the substrate with a photocurable resin and metal nanoparticles, and a plating layer formed on the plating layer, wherein the plating layer has a first region which is a non-exposure region and a second region which is an exposure region, and the plating layer is not formed in the second region but is formed in the first region.

[0008] In this printed circuit board, the plating layer, formed from photocurable resin and metal nanoparticles, exhibits different plating properties depending on whether it is exposed or not. As a result, the patterned plating layer formed based on patterned exposure can become a highly detailed conductive pattern.

[0009] In one embodiment of the printed circuit board according to this disclosure, the plating layer is formed over the entire surface of the substrate.

[0010] In other embodiments of the printed circuit board according to this disclosure, the plating layer is formed in a pattern on the substrate.

[0011] The method for manufacturing a printed circuit board according to this disclosure comprises a coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of a substrate, an exposure step of exposing the substrate coated with the solution to a pattern, a firing step of firing the exposed substrate, and a plating step of plating the fired substrate, wherein in the plating step, no plating metal is deposited in the exposed areas, and plating metal is deposited in the unexposed areas.

[0012] In this method of manufacturing printed circuit boards, a solution containing a photocurable resin and metal nanoparticles is applied to the surface of a substrate, exposed to light in a patterned manner, and then fired. As a result, in the subsequent plating process, plating metal does not deposit in the exposed areas, while plating metal deposits in the unexposed areas. Consequently, a high-definition conductive pattern can be formed through patterned exposure.

[0013] In one embodiment of the method for manufacturing the printed circuit board, the exposure step is performed using a negative image of the desired wiring pattern.

[0014] In another embodiment of the method for manufacturing the printed circuit board, in the coating step, the solution is applied in a pattern on the substrate so as to encompass the desired wiring pattern, and in the exposure step, the applied pattern is exposed to a negative image of the wiring pattern.

[0015] In another embodiment of the method for manufacturing the printed circuit board, the method of coating the surface of the substrate is an inkjet printing method.

[0016] In another embodiment of the method for manufacturing the printed circuit board, silver nanoparticles are used as the metal nanoparticles, the photocurable resin contains a photopolymerization initiator, and the photopolymerization initiator contains sulfur or iodine as a component.

[0017] In another embodiment of the method for manufacturing the printed circuit board, copper nanoparticles are used as the metal nanoparticles, the photocurable resin contains a photopolymerization initiator, and the photopolymerization initiator contains iodine as a component. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a printed circuit board having a more detailed conductive pattern and a method for manufacturing the same. [Brief explanation of the drawing]

[0019] [Figure 1] This is a schematic cross-sectional view showing the general configuration of a printed circuit board according to an embodiment of the present invention. [Figure 2] It is a diagram schematically showing the schematic steps of the first manufacturing method of a printed wiring board according to an embodiment of the present invention. [Figure 3] It is a diagram schematically showing the schematic steps of the second manufacturing method of a printed wiring board according to an embodiment of the present invention. [Figure 4] It is a perspective view of the surface of a printed wiring board as a specific application example of the second manufacturing method of a printed wiring board according to an embodiment of the present invention. [Figure 5] It is a diagram showing photographs of samples before and after plating treatment in an embodiment of the present invention.

Mode for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described in detail. In the present embodiment, an approach of using an ink of a photocurable resin and containing metal nanoparticles therein is adopted. The photocurable resin contains a photoinitiator, and when predetermined light is applied thereto, a reaction occurs. The present inventors noticed that components such as photoinitiators may affect the catalyst for plating by metal nanoparticles in some cases, and based on this, they came up with the idea that a high-definition conductive pattern can be formed. Hereinafter, the configuration of the printed wiring board of the present embodiment and its manufacturing method will be specifically described.

[0021] <Configuration of Printed Wiring Board> FIG. 1 shows a cross-sectional view schematically showing the basic configuration of the printed wiring board according to the present embodiment. FIG. 1(a) shows a schematic configuration, and FIG. 1(b) shows a specific configuration example.

[0022] As shown in FIG. 1(a), the printed wiring board 10 basically includes an insulating base material 11, a plating seed layer 13 formed of a photocurable resin and metal nanoparticles on the base material 11, and a plating layer 15 formed on the plating seed layer 13. The plating seed layer 13 is formed based on an ink layer which is a layer of a solution (ink) containing a photocurable resin and metal nanoparticles. The plating layer 15 constitutes a conductive layer.

[0023] Figure 1(b) shows a simplified schematic configuration of a printed circuit board 10. An ink layer, which will form the base of the plating layer 13, is applied to the substrate 11, and this ink layer is exposed in a patterned manner. As a result, the plating layer 13 forms a first region 13a, which is an unexposed region, and a second region 13b, which is an exposed region. In the plating layer 13, only the metal nanoparticles in the first region 13a, which is an unexposed region, function as plating species, while the metal nanoparticles in the second region 13b, which is an exposed region, do not function as plating species. As a result, the plating metal is deposited only on the first region 13a, which is an unexposed region, forming a plating layer 15 as a conductive pattern.

[0024] The specific configuration of the components of the printed circuit board 10 is as follows:

[0025] (Insulating substrate 11) The insulating substrate (insulating base material) 11 can typically be made of a resin. Examples of such resins include polyimide, polyamide, polyester such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), nylon such as nylon 6-10 and nylon 46, polyether ether ketone, ABS, PMMA, and polyvinyl chloride.

[0026] The insulating substrate 11 used in this embodiment is not particularly limited, but a base film as a film-like substrate will be described as an example.

[0027] The thickness of the base film is preferably 5 μm to 3 mm, more preferably 12 μm to 1 mm, and most preferably 25 μm to 200 μm. If the base film is too thin, the strength will be insufficient, and distortion of the base film may become significant during the plating process. If the base film is too thick, there will be no particular problem in terms of performance, but the material cost will increase, and the volume and weight of the finished substrate may become unnecessarily large. However, this is a condition when the insulating substrate is a film-type substrate, and as mentioned above, the insulating substrate to which the present invention applies is not limited to a film-type substrate.

[0028] It is preferable to apply an easy-adhesion treatment to the surface of the base film in order to uniformly apply the ink described later. Examples of easy-adhesion treatments include corona treatment, plasma treatment, solvent treatment, and primer treatment. Instead of performing such an easy-adhesion treatment, a commercially available base film that has already undergone an easy-adhesion treatment may be used.

[0029] (Plating layer 13; ink layer; layer containing metal nanoparticles) The plating layer 13 is a layer formed by applying a photocurable resin ink (hereinafter also referred to as "UV-curable ink," "UV ink," or "nano-ink") as a solution containing a photocurable resin and metal nanoparticles. The photocurable resin ink is a solution applied to the surface of an insulating substrate to manufacture a printed circuit board 10, and is a solution in which a photocurable resin that hardens with light and metal nanoparticles that function as a plating agent are mixed. In this embodiment, the ink layer is partially exposed. In the exposed area, the catalytic activity of the metal nanoparticles is lost, and plating does not adhere to that area in the subsequent plating process. The photocurable resin contains a photopolymerization initiator, and depending on the type, some may inhibit (interfere) with plating. Among them, a type that releases inhibitory components upon exposure is used here.

[0030] In this embodiment, the light used for photocuring is ultraviolet light (UV), and hereafter, the photocurable resin will be referred to as UV-curable resin.

[0031] The thickness of the plating layer 13 is preferably 100 nm to 20 μm, more preferably 200 nm to 5 μm, and most preferably 500 nm to 2 μm. If this layer is too thin, the mechanical strength may decrease. Conversely, if the ink coating layer is too thick, the manufacturing cost may increase because metal nanoparticles are generally more expensive than ordinary metals.

[0032] Suitable materials for metal nanoparticles include gold (Au), silver (Ag), copper (Cu), palladium (Pd), and nickel (Ni). They may contain one or more metals, but gold, silver, and copper are preferred from the viewpoint of conductivity. Silver is preferable because it is less prone to oxidation than copper and cheaper than gold, but it is even better if cheaper copper can be used.

[0033] The average particle size of the metal nanoparticles is preferably between 1 nm and 200 nm, and more preferably between 10 nm and 100 nm. If the particle size is too small, the reactivity of the particles may increase, potentially negatively affecting the storage and stability of the ink. If the particle size is too large, it may become difficult to form a uniform thin film, and precipitation of the ink particles may occur more easily.

[0034] The viscosity of the UV-curable resin ink containing metal nanoparticles is preferably 1 cps to 50 cps. When using an inkjet method in the coating process, it is preferably 2 cps to 20 cps.

[0035] In conventional inks, even when metal nanoparticles are mixed in, there is no reason for the metal nanoparticles to strongly adhere to a resin substrate such as polyimide. Adhesion to the resin substrate is only possible after a large number of metal nanoparticles have been sintered. Furthermore, while inks using binders can fix metal particles with a certain degree of strength, this is not the case when the concentration of metal nanoparticles is reduced. If the metal nanoparticles are not sintered, they will fall off or leak out, resulting in a lack of adhesion and potentially adversely affecting the plating tank. On the other hand, it is thought that using UV ink or a heat-curable binder can prevent the leakage of metal nanoparticles in the next process, and as a result, it is estimated that adhesion can be obtained even without a sintered layer of metal nanoparticles.

[0036] For plating to adhere to a plating layer, metal nanoparticles must be located near its surface. Even if there is a protective film of coating material on the surface of the ink layer or on the surface of the metal nanoparticles near it, this protective film will be removed by firing. However, if too much fully cured resin is applied on top of the metal nanoparticles, the metal nanoparticles will be located deep below the surface of the ink layer, and plating will not adhere. This is thought to be the reason why plating does not adhere if the curing rate of the photocurable resin is too high.

[0037] Regarding the concentration of metal nanoparticles in UV ink, while a higher concentration of metal nanoparticles as a plating catalyst is desirable in the plating process, fewer metal nanoparticles can be incorporated into the ink from the perspective of not excessively blocking UV light and from a cost standpoint.

[0038] From this perspective, we conducted various experiments to determine the appropriate range of metal nanoparticles (weight concentration) to add to UV ink.

[0039] For example, in a system where bisphenol A dialkyl ether (53 wt%), Shin-Etsu Chemical's tetrafunctional epoxy monomer KR-470 (5 wt%), oxetane (40 wt%), and a photopolymerization initiator (2 wt%) were mixed with silver nanoink to a concentration of 5 wt% silver nanoparticles, UV curing occurred, but electroless plating did not adhere after 1 hour.

[0040] This electroless plating method uses a standard copper sulfate solution with formaldehyde as a reducing agent, adjusted to a pH of 10 or higher. With the same composition but 5 wt% silver nanoparticles, microscopic observation of the same plating solution revealed only a slight beginning of plating. At 8 wt%, successful plating was achieved, and sufficient plating was obtained after 3 hours in the same plating solution. From this, the practical lower limit for plating was determined to be 8 wt%. On the other hand, at 20 wt% or higher, the UV ink stopped curing, so this was set as the limit. More preferably, around 10 wt% is considered optimal.

[0041] These experiments revealed that the minimum necessary content of metal nanoparticles in the ink is preferably between 8% and 20% by weight (wt%). This reduction in weight concentration leads to a reduction in the cost of expensive metal nanoparticles. However, if the weight concentration falls below the lower limit of this range, the plating layer may cease to function as a conductive layer.

[0042] In this embodiment, the plating layer 13 (after exposure and firing) formed with the ink within the specified weight concentration range does not need to function as a conductive layer itself; it is sufficient that the final plated layer 15 functions as a conductive layer.

[0043] (Plating layer 15) The plating layer 15, which serves as a conductive layer, is formed on the plating layer 13 by a plating process (electrolytic plating or electroless plating).

[0044] While copper, nickel, tin, silver, and gold can be used as plating metals, copper is the most preferable from the viewpoint of economy and conductivity.

[0045] The thickness of the plating layer 15 is preferably 3 μm to 100 μm, and more preferably 3 μm to 35 μm. If the plating layer 15 is too thin, the mechanical strength may be insufficient, and the conductivity may not be practically sufficient. Conversely, if the plating layer 15 is too thick, the time required for the plating process will increase, which may increase manufacturing costs. Generally, electrolytic plating requires less time than electroless plating, so electrolytic plating can accommodate thicker plating layers at a more realistic cost. However, electroless plating has the advantage of being able to plate not only connected electrode lines but also floating regions as islands.

[0046] <Manufacturing method for printed circuit boards> The method for manufacturing a printed circuit board according to this embodiment comprises a coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of a substrate, an exposure step of exposing the substrate coated with the solution in a patterned manner, a firing step of firing the exposed substrate, and a plating step of plating the fired substrate, wherein in the plating step, no plating metal is deposited in the exposed areas, and plating metal is deposited in the unexposed areas.

[0047] More specifically, the exposure process involves exposure using a negative image of the target conductive pattern.

[0048] (Ink application process) As described later, UV-curable ink containing metal nanoparticles can be applied to the surface of a substrate in two ways: full-surface application or patterned application. For patterned application, printing methods can be used, typically employing inkjet technology. However, the method is not necessarily limited to inkjet technology; other application methods may also be used. Furthermore, in the experiments described later, application using a bar coater was also performed.

[0049] After applying the UV-curable ink containing metal nanoparticles to a base film as a substrate, a drying process is performed to remove any solvent present. This process is the same as the drying process for known metal nanoparticle inks. Methods for drying the UV-curable ink containing metal nanoparticles include heating in an oven or hot air drying.

[0050] (UV exposure process) In the UV exposure process for UV-curable ink containing metal nanoparticles, patterned exposure is performed. The exposure method is selected based on the sensitivity wavelength of the photopolymerization initiator contained in the UV-curable resin. Patterned exposure may be performed using a mask or by optical drawing using a light-drawing device described later. Furthermore, the exposure pattern is a negative image of the desired conductive pattern. In this UV exposure process, the UV-curable resin is not over-cured, resulting in an incompletely cured state.

[0051] (Burning process of UV-curing resin) In the firing process following the UV exposure process, the UV-curable resin undergoes further curing, and cracks are created in the resin on the surface of the ink layer. Metal nanoparticles connect to the surface through these cracks, and it is presumed that in the subsequent plating process, metal is deposited on the surface of the plating layer through these cracks. It is presumed that the incomplete curing state of the UV-curable resin before firing assists in creating these cracks. However, in this embodiment, due to the plating inhibitory effect in the exposed area, plating metal does not deposit in the exposed area.

[0052] Furthermore, this firing process is expected to improve the adhesion between the plating layer and the substrate. As mentioned above, in some cases, such as with copper nanoparticles, a protective film may be formed on the surface of the metal nanoparticles due to a coating material. The coating material may include, for example, organic acids. In the firing process, in order to allow such metal nanoparticles to function as plating materials, this protective film is removed by firing after UV exposure and before plating.

[0053] The firing temperature is approximately 160°C to 260°C, and the firing time is 10 minutes to 1 hour. In the case of UV-curing inks, a firing temperature of 160°C is insufficient, and 260°C or higher is preferable. This firing process is also expected to improve the adhesion between the plating layer and the substrate. After this process, the process moves on to the subsequent plating process.

[0054] (Plating process) After the ink application and UV exposure processes described above, the plating layer formed on the base film is subjected to a plating treatment (electrolytic plating or electroless plating). This deposits the plating metal on the surface and within the plating layer.

[0055] The plating method is the same as known plating treatments using known plating solutions, and specifically may include electroless copper plating, electrolytic copper plating, electrolytic nickel plating, etc.

[0056] UV-curing resins contain photoinitiators, and when UV light strikes them, a reaction occurs, essentially initiating the curing of the resin. However, as mentioned above, the photoinitiator can sometimes affect the catalyst for plating using metal nanoparticles. This depends on the combination of metal and photoinitiator. As a result, the areas of the plating layer that are exposed to light (exposed regions) will not be plated even when immersed in electroless plating solution, while the areas that are not exposed to light (unexposed regions) will be plated. In other words, this method allows for the creation of conductive patterns because the possibility of plating differs between exposed and unexposed regions. Since the UV light beam can be focused, this technique can be used to create even finer conductive patterns, such as patterns of 1 μm or less, which is currently possible. However, in this case, plating does not adhere to the exposed areas, and plating adheres to the unexposed areas, so the exposed pattern becomes a so-called positive-negative inverted pattern (negative image). This pattern can be formed by exposure using a mask corresponding to the desired conductive pattern, or it can be formed on demand by drawing with UV LEDs using a drawing device. Examples of such drawing devices include the MicroWriter ML, a small LED direct drawing device manufactured in the UK.

[0057] (First method for manufacturing printed circuit boards) Figure 2 schematically shows the general steps of the first manufacturing method of a printed circuit board according to this embodiment.

[0058] This printed circuit board is formed by applying an insulating substrate (base film) 11 and an ink layer 13 onto the insulating substrate 11 using UV-curable ink containing metal nanoparticles. In this example, the UV-curable ink is applied to the entire surface of a base film such as polyimide by spin coating or the like. Next, the pattern is exposed by drawing a negative image pattern of the desired conductive pattern with UV light. This deactivates the plating catalyst in the exposed areas 13b. After that, the entire surface is cured by heat curing through firing. In this way, the plating layer 13 is formed. Then, by applying plating (electroless plating in this case), the plating metal is deposited in the unexposed areas 13a, forming a plating layer 15 as a wiring pattern 15a. The unexposed areas of the UV-curable ink are considered to have been heat-cured. In this way, the printed circuit board is completed.

[0059] The thickness ratios of each layer shown in Figure 2 are merely illustrative, and the present invention is not limited to these ratios. Similarly, the width and spacing of the conductive lines are also illustrative.

[0060] This method currently allows for the formation of wiring patterns with a resolution of 0.6 μm to 1 μm. The figure shows an example with a line width of 3 μm.

[0061] (Second method for manufacturing printed circuit boards) Figure 3 schematically shows the general steps of the second manufacturing method of a printed circuit board according to this embodiment.

[0062] In the first manufacturing method shown in Figure 2, UV-curable ink containing metal nanoparticles was applied to the entire substrate. However, in the second manufacturing method shown in Figure 3, an ink pattern 13c is formed by applying UV-curable ink containing metal nanoparticles in a patterned manner only to the necessary areas using a line-and-space printing method such as inkjet printing.

[0063] More specifically, UV-curable ink is applied in a pattern based on an ink pattern 13c that encompasses the target conductive pattern. The printing of this ink pattern can be low resolution. With this method, the UV-curable ink does not need to be applied to the entire surface, but only to the minimum necessary areas at a low resolution. This eliminates waste of UV-curable ink containing metal nanoparticles compared to the first manufacturing method. In the subsequent exposure step, the low-resolution ink pattern is exposed with a negative image of a high-resolution wiring pattern (conductive pattern). This creates unexposed areas 13a and exposed areas 13b in the ink pattern 13c. As a result, in the next plating step, a plating layer 15 consisting of the target higher-resolution conductive pattern 15a can be formed in the same line.

[0064] Figure 4 shows a perspective view of the surface of a printed circuit board as a specific application example of the second manufacturing method. In this case, an ink pattern 13c is drawn on the surface of the substrate 11 using an inkjet method, and then the ink layer 13 is exposed to LED light (UV LED drawing) with a negative image of the target conductive pattern. That is, the target conductive pattern (linear portion) 13a is left exposed, and the surrounding portion 13b is exposed. The line and space of the ink pattern 13c in the ink layer 13 is 200-200 μm, but the line width of the unexposed region 13a corresponding to the conductive pattern is considerably narrower, for example, about 3 μm. In the subsequent plating process, the plating metal is deposited on the unexposed region 13a corresponding to the conductive pattern, so the line width of the resulting wiring pattern is also about 3 μm.

[0065] Next, we will show an experimental example of plating using the UV-curing ink of this embodiment.

[0066] (Experimental Example 1) This experimental example uses a radical polymerization UV-curing ink. A PI (polyimide) film was used as the base film, and the following was used as the UV-curing ink (Composition 1): A commercially available ink containing silver or copper nanoparticles was used (1-17 wt%). As the UV-curing base resin, an acrylic resin-based UV-curing ink was prepared. A mixture of difunctional acrylic acid ester (40 wt%), cresol novolac epoxy resin (2.5 wt%), trifunctional acrylic acid ester (1 wt%), and monofunctional acrylic acid ester (15 wt%) was prepared, to which a photopolymerization initiator: phosphorus-based photopolymerization initiator A (5 wt%) containing phosphorus was added. These ratios are examples and do not limit the present invention. A dispersant may be added to this ink for the metal nanoparticles. The ink prepared in this way was applied to the base film with a No. 10 bar coater (OSP-10: manufactured by OSP), exposed with an Hg lamp, and baked in an oven at 260°C for 60 minutes to cure the uncured portion of the UV-curing resin. At this time, even if there is a protective film made of a coating material on the surface of the ink layer or on the surface of metal nanoparticles near it, this protective film is removed by firing.

[0067] A base film with a plating layer containing metal nanoparticles was cleaned with running water for 1 minute. Then, it was pre-dipped in an electroless copper plating solution. Electroless copper plating was then performed for 180 minutes at a solution temperature of 65°C using an electroless copper plating solution primarily composed of copper, alkali, and formaldehyde. Afterward, it was immersed in a discoloration inhibitor at room temperature for 1 minute, and then dried.

[0068] In this case, the combination with a photocuring agent worked well, resulting in successful plating and ensuring conductivity.

[0069] (Experimental Example 2) This experimental example 2 also uses a radical polymerization UV-curing ink. A PI film was used as the base film, and the following UV-curing inks were used (compositions 3-4). As the material for the metal nanoparticles, copper nanoparticles or silver nanoparticles reduced with hydrazine were used (4.5-25 wt%). As the UV-curing base resin, an acrylic resin-based UV-curing ink was prepared. A mixture of difunctional acrylic acid ester (40 wt%), cresol novolac epoxy resin (2.5 wt%), trifunctional acrylic acid ester (1 wt%), and monofunctional acrylic acid ester (15 wt%) was prepared, to which a sulfur-containing sulfur-based photopolymerization initiator C (5 wt%) was added. These ratios are just examples, and the present invention is not limited thereto. A dispersant may be added to this UV-curing ink for the nanoparticles. The UV-curing ink prepared in this way was applied to the base film with a No. 10 bar coater, exposed with an Hg lamp, and cured in a 260°C oven for 60 minutes to cure the uncured portion of the UV-curing resin.

[0070] A base film with a plating layer containing metal nanoparticles was cleaned with running water for 1 minute. Then, it was pre-dipped in an electroless copper plating solution. Electroless copper plating was then performed for 180 minutes at a solution temperature of 65°C using an electroless copper plating solution primarily composed of copper, alkali, and formaldehyde. Afterward, it was immersed in a discoloration inhibitor at room temperature for 1 minute, and then dried.

[0071] In this case, the combination with a photocuring agent worked well, resulting in successful plating and ensuring conductivity.

[0072] (Experimental Example 3) In this experimental example 3, a cationic polymerization-based photopolymerization initiator was used (composition 2). The UV-curable ink base was prepared using oxetane (40 wt%), bisphenol A-dialkylidyl ether (53 wt%), Shin-Etsu Chemical's tetrafunctional epoxy monomer KR-470 (5 wt%), and iodine-based photopolymerization initiator B (2 wt%). Note that these ratios are just examples, and the present invention is not limited to these. Copper or silver nanoink was mixed into this resin base in a ratio of 2 to 10 wt% to produce a UV-curable ink.

[0073] The UV-curing ink prepared in this way was applied to the base film using a No. 10 bar coater, partially exposed to a 254nm UV lamp, and cured in a 260°C oven for 60 minutes to cure the uncured UV-curing resin.

[0074] A base film with a plating layer containing metal nanoparticles was cleaned with running water for 1 minute. Then, it was pre-dipped in an electroless copper plating solution. Electroless copper plating was then performed at 60°C for 180 minutes using an electroless copper plating solution primarily composed of copper, alkali, and formaldehyde. Afterward, it was immersed in a discoloration inhibitor at room temperature for 1 minute, and then dried.

[0075] This experiment confirmed that plating adhered only to the unexposed areas of the ink-coated region, while not to the exposed areas. It is presumed that in the exposed areas, the photopolymerization initiator underwent a photoreaction, and the released component (iodine in this example) inhibited the plating process. In other words, it is thought that in the exposed areas, the photopolymerization initiator reacts, releasing the component, which then binds to the surface of the metal nanoparticles, changing the potential and inhibiting the plating. In contrast, this reaction does not occur in the unexposed areas, so there is no inhibition of plating.

[0076] The iodine-based photopolymerization initiator B used here was found to not form a plating on the exposed areas, but did form on the unexposed areas, when mixed with the UV-curable ink (which already contains a radical polymerization initiator) used in Experimental Example 1. This suggests that, regardless of the polymerization method, the components released upon exposure inhibit the plating process.

[0077] (Experimental Example 4) As Experimental Example 4, the principle of mask exposure in the exposure process is shown. A resin base was prepared by mixing 1 g of tetrafunctional epoxy monomer KR-470 (Shin-Etsu Chemical) and 9 g of bifunctional epoxy monomer X40-2669 with 0.2 g of sulfur-based photopolymerization initiator C to create a resin base. 0.6 g of this base was weighed out and mixed with 0.4 g of commercially available silver nano-ink to create a UV-curable ink. Using a bar coater, this ink was applied to a polyimide film to a thickness of 10 μm. Samples were prepared by masking and partially exposing them to UV light, and samples were prepared without exposure. These were fired at 260°C for 1 hour, followed by electroless plating for 3 hours. The results are shown in Figure 5.

[0078] Figure 5(a) shows a photograph of the sample before plating, and Figure 5(b) shows a photograph of the sample after plating. In each figure, the sample on the left was exposed to UV light with a portion of it masked, while the sample on the right was exposed to UV light without a mask.

[0079] As shown in Figure 5(b), in the sample without UV exposure (right), plating adhered to the entire ink-coated area, while in the sample partially exposed to UV light (left), plating adhered only to the unexposed area (central part 51). This suggests that in the exposed area of ​​the ink-coated region, the photopolymerization initiator underwent a photoreaction, and the released component (sulfur in this example) inhibited the plating process.

[0080] (Experimental Example 5) Experimental Example 5 is an example using a cationic polymerization-based photopolymerization initiator (composition 2). The UV-curable ink base used was oxetane (30-40 wt%), bisphenol A-dialkylidyl ether (40-55 wt%), tetrafunctional epoxy monomer KR-470 (Shin-Etsu Chemical) (2-5 wt%), and iodine-based photopolymerization initiator B (1-2 wt%). Note that these ratios are just examples, and the present invention is not limited to these. Silver nano ink was mixed into this resin base at a ratio of 2-10 wt% to produce a UV-curable ink.

[0081] The UV-curing ink prepared in this way was applied to the base film using a No. 10 bar coater, partially exposed to a 254nm UV lamp, and cured in a 160°C oven for 60 minutes to cure the uncured UV-curing resin.

[0082] The base film, which had a plating layer containing metal nanoparticles formed in this manner, was cleaned with running water for 1 minute. Then, it was pre-dipped with an electroless copper plating solution, and electroless copper plating was performed for 60 minutes at a solution temperature of 60°C using an electroless copper plating solution mainly composed of copper, alkali, and formaldehyde. After that, it was immersed in a discoloration inhibitor at room temperature for 1 minute and then dried.

[0083] This experiment confirmed that plating adhered only to the unexposed areas of the ink-coated region, while not to the exposed areas. In this case, it is presumed that the photopolymerization initiator reacted with light in the exposed areas, and the released component (iodine in this example) inhibited the plating process. Following this principle, it was confirmed that wiring patterns could be created. At the same time, it was confirmed that the same effect could be obtained with different UV curing methods.

[0084] The iodine-based photopolymerization initiator B used here was found to not form a plating on the exposed areas, but did form a plating on the unexposed areas, when mixed with the UV-curable ink from Experimental Example 1 (which already contains a radical polymerization initiator).

[0085] Table 1 summarizes the results of other experiments using the above compositions and combinations (the above experimental examples do not necessarily correspond to the "experiment numbers" in Table 1). Some systems contain two types of photocuring agents, but the light used for exposure was different for each. Photopolymerization initiators: "A" is a phosphorus-based photopolymerization initiator that generates radicals at a wavelength of 365 nm, "B" is an iodine-based photopolymerization initiator containing iodine that generates radicals and cations at 254 nm, and "C" is a sulfur-based photopolymerization initiator that generates radicals and cations at a wavelength of 365 nm. As can be seen from Table 1, the success or failure of plating depends on the combination of each reagent and exposure wavelength.

[0086] (Feasibility of plating in the exposed area under various experimental conditions) [Table 1]

[0087] As these experimental results show, a suitable printed circuit board can be realized by combining various experimental conditions, including whether or not plating is possible.

[0088] (Other embodiments) In the embodiments described above, a printed circuit board using UV ink and a method for manufacturing the same were described, in which a high-definition conductive pattern is formed by plating the unexposed areas using a negative image. In contrast, as yet another embodiment, a combination of nanoparticle metal and a photopolymerization initiator (photocuring agent) that improves the deposition of plating metal on the exposed areas will be described.

[0089] In this embodiment, the ink application process involves applying (printing) a patterned ink layer of a positive image that matches the desired conductive pattern. Unlike the above embodiment, UV irradiation in the exposure process does not necessarily have to be performed in a patterned manner; it may be full-surface irradiation (full-surface exposure).

[0090] This embodiment aims to achieve good plating using a plating layer with an ink (solution) containing a photocurable resin and metal nanoparticles. More specifically, as shown in Experimental Examples 1 and 2 above, and Experimental Numbers 1, 2, 6-9 in Table 1, an enhancing effect on the plating catalyst was found in specific combinations of nanoparticle metals and photopolymerization initiators (photocuring agents).

[0091] The photocurable resin in such an ink contains phosphorus when the metal nanoparticles are silver nanoparticles, and phosphorus or sulfur when the metal nanoparticles are copper nanoparticles. The resulting plating layer on the substrate (printed circuit board) will have either a first composition containing silver nanoparticles and phosphorus, or a second composition containing copper nanoparticles and phosphorus or sulfur.

[0092] Preferably, the concentration of the nano-ink is 8% to 20% by weight, as in the above embodiment.

[0093] As described in Examples 1 and 2, the UV-curable resin of the nano-ink is cured to some extent by the UV exposure process, and then the uncured portion is cured in the subsequent firing process.

[0094] In the firing process of this embodiment, additional curing is performed after UV curing, and cracks are created on the surface of the plating layer to facilitate the subsequent plating process.

[0095] This embodiment can take the following forms. (1) An insulating substrate and A plating layer formed on the substrate with a photocurable resin and metal nanoparticles, The system comprises a plating layer formed on the aforementioned plating layer, The aforementioned plating layer has a first composition comprising silver nanoparticles and phosphorus, or a second composition comprising copper nanoparticles and phosphorus or sulfur. substrate. (2) A coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of an insulating substrate, An exposure step of exposing a substrate coated with the aforementioned solution, A firing step for firing the exposed substrate, The process includes a plating step for plating the aforementioned fired substrate, The photocurable resin contains phosphorus when the metal nanoparticles are silver nanoparticles, and contains phosphorus or sulfur when the metal nanoparticles are copper nanoparticles. A method for manufacturing a circuit board. (3) The method for manufacturing a substrate according to (2), wherein the metal nanoparticles in the solution are present in a weight concentration of 8% to 20%. (4) The method for manufacturing a substrate according to (2), wherein the solution is applied in a pattern in the coating step. (5) The method for manufacturing a substrate according to (2) or (4), wherein the method for applying the substrate to the surface is an inkjet printing method. (6) A solution applied to the surface of a substrate for manufacturing a substrate, A photocurable resin that hardens with light and metal nanoparticles that function as a plating agent are mixed together. The photocurable resin contains phosphorus when the metal nanoparticles are silver nanoparticles, and contains phosphorus or sulfur when the metal nanoparticles are copper nanoparticles. solution. (7) The solution according to (6), wherein the metal nanoparticles are present in a weight concentration of 8% to 20%. (8) A printed circuit board formed using the substrate described in (1).

[0096] (modified version) While preferred embodiments of the present invention have been described above, various modifications and changes are possible beyond those mentioned above. The materials, lengths, ratios, temperatures, times, etc., used are illustrative and not necessarily limited to these. [Explanation of symbols]

[0097] 10 Printed circuit boards 11. Substrate (insulating substrate) 13 Plating layer (ink layer) 13a First region (unexposed region, unexposed area) 13b Second region (exposure region, exposure area) 13c Ink Pattern 15 Plating layer 15a Wiring pattern (conductive pattern)

Claims

1. An insulating substrate, A plating layer formed on the substrate with a photocurable resin and metal nanoparticles, The system comprises a plating layer formed on the aforementioned plating layer, The plating layer has a first region which is a non-exposed region and a second region which is an exposed region, and the plating layer is formed in the first region but not in the second region. Printed circuit board.

2. The printed circuit board according to claim 1, wherein the plating layer is formed on the entire surface of the substrate.

3. The printed wiring board according to claim 1, wherein the plating layer is formed in a pattern on the substrate.

4. A coating step in which a solution containing a photocurable resin and metal nanoparticles is applied to the surface of a substrate, An exposure step in which the substrate coated with the aforementioned solution is exposed in a patterned manner, A firing step for firing the exposed substrate, The process includes a plating step for plating the aforementioned fired substrate, A method for manufacturing a printed circuit board, wherein, in the aforementioned plating process, no plating metal is deposited in the exposed areas, and plating metal is deposited in the non-exposed areas.

5. The method for manufacturing a printed circuit board according to claim 4, wherein the exposure step is performed using a negative image of the target wiring pattern.

6. In the coating step, the solution is applied in a patterned manner onto the substrate so as to encompass the desired wiring pattern. The method for manufacturing a printed circuit board according to claim 4, wherein in the exposure step, the coated pattern is exposed with a negative image of the wiring pattern.

7. The method for manufacturing a laminate according to claim 4, wherein the method for applying the material to the surface of the substrate is an inkjet printing method.

8. The method for manufacturing a printed circuit board according to claim 4, wherein silver nanoparticles are used as the metal nanoparticles, the photocurable resin contains a photopolymerization initiator, and the photopolymerization initiator contains sulfur or iodine as a component.

9. The method for manufacturing a printed circuit board according to claim 4, wherein copper nanoparticles are used as the metal nanoparticles, the photocurable resin contains a photopolymerization initiator, and the photopolymerization initiator contains iodine as a component thereof.

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