JP2023178021A - Printed wiring board and manufacturing method thereof - Google Patents

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

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

Conventionally, printed wiring boards are produced by forming a metal layer on an insulating substrate (base material) such as resin, and then removing unnecessary parts of this metal layer by etching to form a wiring pattern. has been manufactured in. This method required many steps, using large amounts of water and excess metal that was discarded during etching.

In response, the applicant has proposed a method in which a conductive ink containing metal nanoparticles is applied only to the necessary areas using an inkjet method or the like, and a metal layer is increased by plating to further lower the resistance value. (Patent Document 1). This method has enabled a significant simplification of the substrate manufacturing process, and in particular has succeeded in significantly reducing the amount of water used and CO2 emissions. The inkjet method is a reliable method for producing printed wiring boards on demand in small quantities with minimal time and cost.

Patent No. 6300213

However, the precision expressed in lines and spaces that can be achieved with the inkjet method is limited to 200 to 200 μm, and it has been difficult to produce conductive patterns with higher definition than this.

The present invention was made against this background, and an object thereof is to provide a printed wiring board having a more precise conductive pattern and a method for manufacturing the same.

In order to solve the above problems, a printed wiring board according to the present disclosure includes an insulating base material, a plating seed layer formed of a photocurable resin and metal nanoparticles on the base material, and a plating seed layer formed on the plating seed layer. a plating layer, the plating seed layer has a first region that is a non-exposed region and a second region that is an exposed region, and the plating layer is not formed on the second region. The first region is formed in the first region.

In this printed wiring board, the plating seed layer formed of a photocurable resin and metal nanoparticles can be plated on exposed areas and non-exposed areas. Thereby, a patterned plating layer formed based on patterned exposure can become a high-definition conductive pattern.

In one aspect of the printed wiring board according to the present disclosure, the plating seed layer is formed on the entire surface of the base material.

In another aspect of the printed wiring board according to the present disclosure, the plating seed layer is formed in a pattern on the base material.

A method for manufacturing a printed wiring board according to the present disclosure includes a coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of a base material, and an exposure step of exposing the base material coated with the solution to light in a pattern. and a firing step of firing the exposed base material, and a plating step of plating the fired base material, wherein in the plating step, no plating metal is deposited on the exposed areas and no plating metal is deposited on the non-exposed areas. Plating metal is deposited.

In this printed wiring board manufacturing method, a solution containing a photocurable resin and metal nanoparticles is applied to the surface of the base material, exposed in a pattern, and baked. The plating metal does not precipitate in the exposed areas, but the plating metal precipitates in the non-exposed areas. As a result, a high-definition conductive pattern can be formed through patterned exposure.

In one aspect of the printed wiring board manufacturing method, in the exposure step, exposure is performed using a negative image of a target wiring pattern.

In another aspect of the method for manufacturing a printed wiring board, in the coating step, the solution is applied in a pattern on the base material so as to cover the intended wiring pattern, and in the exposure step, the applied pattern is On the other hand, exposure is performed using a negative image of the wiring pattern.

In another aspect of the method for manufacturing the printed wiring board, the method for coating the surface of the base material is an inkjet printing method.

In another embodiment of the method for manufacturing a printed wiring 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. do.

In another embodiment of the method for manufacturing a printed wiring 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.

According to the present invention, it is possible to provide a printed wiring board having a more precise conductive pattern and a method for manufacturing the same.

1 is a cross-sectional view schematically showing a schematic configuration of a printed wiring board according to an embodiment of the present invention. 1 is a diagram schematically showing the outline steps of a first manufacturing method of a printed wiring board according to an embodiment of the present invention. FIG. 6 is a diagram schematically showing the steps of a second method for manufacturing a printed wiring board according to an embodiment of the present invention. FIG. 3 is a perspective view of the surface of a printed wiring board as a specific application example of the second method for manufacturing a printed wiring board according to an embodiment of the present invention. It is a figure which shows the photograph of the sample before and after plating processing in embodiment of this invention.

Embodiments of the present invention will be described in detail below.
In this embodiment, an approach is adopted in which a photocurable resin ink is used and metal nanoparticles are contained therein. The photocurable resin contains a photopolymerization initiator, and when it is exposed to a certain amount of light, a reaction occurs. The present inventors noticed that some components such as photopolymerization initiators may affect the plating catalyst using metal nanoparticles, and based on this, they realized that high-definition conductive patterns can be formed. I came up with the idea. Hereinafter, the structure of the printed wiring board of this embodiment and its manufacturing method will be specifically explained.

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

As shown in FIG. 1(a), the printed wiring board 10 basically includes an insulating base material 11 and 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 that is a layer of a solution (ink) containing a photocurable resin and metal nanoparticles. The plating layer 15 constitutes a conductive layer.

FIG. 1(b) shows a schematic configuration of a simplified printed wiring board 10. As shown in FIG. An ink layer that is the source of the plating seed layer 13 is applied onto the base material 11, and this ink layer is exposed in a pattern. As a result, the plating seed layer 13 is formed with a first region 13a that is a non-exposed region and a second region 13b that is an exposed region. In the plating seed layer 13, only the metal nanoparticles in the first region 13a, which is a non-exposed region, function as a plating seed, and the metal nanoparticles in the second region 13b, which is an exposed region, do not function as a plating seed. As a result, the plating metal is deposited only on the first region 13a, which is the non-exposed region, to form the plating layer 15 as a conductive pattern.

The specific configuration of the components of the printed wiring board 10 is as follows.

(Insulating base material 11)
The insulating base material (insulating base material) 11 can typically be made of resin. Examples of the resin 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. Examples include resins such as.

Although the insulating base material 11 used in this embodiment is not particularly limited, a base film as a film-like base material will be described as an example.

The thickness of the base film is preferably from 5 μm to 3 mm, more preferably from 12 μm to 1 mm, and most preferably from 25 μm to 200 μm. If the thickness of the base film is too thin, the strength will be insufficient and there is a risk that the base film will be significantly distorted during the plating process. If the base film is too thick, there is no particular problem in terms of performance, but there is a risk that the material cost will increase and the volume and weight of the completed substrate will become unnecessarily large. However, this is a condition when the insulating base material is a film-like base material, and as described above, the insulating base material to which the present invention is applied is not limited to a film-like base material.

The surface of the base film is preferably subjected to adhesion-facilitating treatment in order to uniformly apply the ink described below. As the adhesion-facilitating treatment, for example, corona treatment, plasma treatment, solvent treatment, and primer treatment can be used. Instead of performing such an adhesion treatment, a commercially available base film that has been subjected to an adhesion treatment may be used.

(Plating seed layer 13; ink layer; layer containing metal nanoparticles)
The plating seed layer 13 is formed based on application of a photocurable resin ink (hereinafter also referred to as "UV curing ink" or "UV ink" or "nano ink") as a solution containing a photocurable resin and metal nanoparticles. It is a layer. The photocurable resin ink is a solution applied to the surface of an insulating base material to manufacture the printed wiring board 10, and is composed of a photocurable resin that is cured by light, and metal nanoparticles that function as plating seeds. is a mixed solution. In this embodiment, the ink layer is partially exposed. The catalytic activity of the metal nanoparticles disappears in the exposed area, and no plating is applied to that area in the subsequent plating process. The photocurable resin contains a photopolymerization initiator, and depending on the type, some may inhibit (obstruct) plating. Among these, those that release inhibitory components upon exposure to light are used here.

The light for photocuring in this embodiment is ultraviolet (UV) light, and hereinafter the photocuring resin will be referred to as UV curing resin.

The thickness of the plating seed layer 13 is preferably from 100 nm to 20 μm, more preferably from 200 nm to 5 μm, and most preferably from 500 nm to 2 μm. If this layer is too thin, the mechanical strength may be reduced. On the other hand, if the ink coating layer is too thick, the manufacturing cost may increase because metal nanoparticles are generally more expensive than ordinary metals.

Materials for metal nanoparticles include gold (Au), silver (Ag), copper (Cu), palladium (Pd), nickel (Ni), etc., and may contain one or more metals; From this point of view, gold, silver, and copper are preferable, and silver, which is less likely to oxidize than copper and is cheaper than gold, is preferable, but it is even better if copper, which is even cheaper, can be used.

The average particle diameter of the metal nanoparticles is preferably from 1 nm to 200 nm, more preferably from 10 nm to 100 nm. If the particle size is too small, the reactivity of the particles may increase, which may adversely affect the storage life and stability of the ink. If the particle size is too large, it may be difficult to form a thin film uniformly, and the ink particles may be more likely to precipitate.

The viscosity of the UV curable resin ink containing metal nanoparticles is preferably 1 cps to 50 cps. When an inkjet method is used in the coating process, the speed is preferably 2 cps to 20 cps.

With normal ink, even if metal nanoparticles are mixed, there is no reason for the metal nanoparticles to strongly adhere to a resin base material such as polyimide, and it only adheres to the resin base material after a large number of metal nanoparticles are sintered. be able to. Further, with ink using a binder, it is possible to fix metal particles with a certain degree of strength, but this is not the case when the concentration of metal nanoparticles is reduced. If the metal nanoparticles are not sintered, the metal nanoparticles will fall off or flow out, and not only will adhesion not be obtained, but there is a risk that it will have an adverse effect on the plating bath. On the other hand, when UV ink or a thermosetting binder is used, it is thought that it is possible to prevent the metal nanoparticles from being washed away in the next process, and as a result, there is no sintered layer of metal nanoparticles. It was estimated that adhesion could be obtained even if

In order for plating to adhere to the plating seed layer, metal nanoparticles must be located near the surface of the plating seed layer. Even if there is a protective film made of a coating material on the surface of the ink layer or the surface of the metal nanoparticles in the vicinity thereof, this protective film is removed by baking. However, if too much completely cured resin is placed on the metal nanoparticles, the metal nanoparticles will be located deep from the surface of the ink layer and will not be plated. This is thought to be the reason why plating does not adhere if the curing rate of the photocurable resin is too high.

Regarding the concentration of metal nanoparticles in UV ink, it is better to have more metal nanoparticles as a plating species (plating catalyst) in the plating process, but from the viewpoint of not blocking UV light excessively and from the viewpoint of cost, it is possible to add more metal nanoparticles to the ink. The fewer metal nanoparticles the better.

From this point of view, various experiments were repeated to determine the appropriate range of the amount (weight concentration) of metal nanoparticles to be added to the UV ink.

For example, silver nano ink is mixed into a system containing bisphenol A dialkydyl ether (53 wt%), Shin-Etsu Chemical's tetrafunctional epoxy monomer KR-470 (5 wt%), oxetane (40 wt%), and a photopolymerization initiator (2 wt%). In a system in which silver nanoparticles were mixed at a concentration of 5 wt %, UV curing occurred, but the plating did not adhere after 1 hour of electroless plating.

This electroless plating is a standard method in which a copper sulfate solution using formaldehyde as a reducing agent has a pH of 10 or more. When using the same plating solution with the same composition but containing 5 wt% of silver nanoparticles, it was observed that plating had begun to form slightly when observed under a microscope. Further, at 8 wt%, plating was successful, and it was found that sufficient plating was obtained after 3 hours using the same plating solution. From this, the lower limit for practical plating was determined to be 8 wt%. On the other hand, if the content exceeds 20 wt%, the UV ink will not be cured, so this is the limit. More preferably, it is around 10 wt%.

As a result of such experiments, it was found that the content ratio of metal nanoparticles in the ink is preferably 8% to 20% in terms of weight concentration (wt%) as the minimum necessary range. This reduction in weight concentration leads to a reduction in the cost of expensive metal nanoparticles. However, if the weight concentration is below the lower limit of this range, the plating layer may not function as a conductive layer.

Note that in this embodiment, the plating seed layer 13 (after exposure and baking) formed with the ink in the weight concentration range itself does not have to function as a conductive layer, and the plating layer 15 finally generated is conductive. It is sufficient if it functions as a layer.

(Plating layer 15)
The plating layer 15 as a conductive layer is formed on the plating seed layer 13 by a plating process (electrolytic plating or electroless plating).

As the plating metal, copper, nickel, tin, silver, gold, etc. can be used, but copper is most preferably used from the viewpoint of economy and conductivity.

The thickness of the plating layer 15 is preferably from 3 μm to 100 μm, more preferably from 3 μm to 35 μm. If the plating layer 15 is too thin, it may lack mechanical strength and may not have sufficient electrical conductivity for practical use. On the other hand, if the plating layer 15 is too thick, the time required for the plating process will be longer, which may increase manufacturing costs. Generally, electrolytic plating requires less time for plating than electroless plating, so electrolytic plating can accommodate thicker plating layers at a more realistic cost. However, electroless plating has the advantage that it can plate not only connected electrode lines but also floating areas as islands.

<Manufacturing method of printed wiring board>
The method for manufacturing a printed wiring board according to the present embodiment includes a coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of a base material, and an exposure step of exposing the base material coated with the solution to light in a pattern. a firing step of firing the exposed base material, and a plating step of plating the fired base material, wherein in the plating step, the plating metal does not precipitate on the exposed area and the non-exposed area Plating metal is deposited on the surface.

More specifically, in the exposure step, exposure is performed using a negative image of the target conductive pattern.

(Ink application process)
The application of the UV curable ink containing metal nanoparticles to the surface of the base material may be applied over the entire surface of the base material or in a pattern, as described below. When applying in a pattern, a printing method can be used, and typically an inkjet method is used. However, the coating method is not necessarily limited to the inkjet method, and other coating methods may be used. Furthermore, in the experiments described below, coating was also performed using a bar coater.

After applying a UV-curable ink containing metal nanoparticles to a base film as a substrate, a drying process is performed to remove any solvent. This step is similar to the known drying step of metal nanoparticle ink. As a method for drying the UV-curable ink containing metal nanoparticles, heating using an oven or the like, hot air drying, or the like can be employed.

(UV exposure process)
In the UV exposure process of UV curable ink containing metal nanoparticles, patterned exposure is performed. At that time, the exposure means is selected depending on the sensitivity wavelength of the photopolymerization initiator contained in the UV curing resin. A mask may be used for the patterned exposure, or optical drawing may be performed using an optical drawing device described later. Further, as the exposure pattern, exposure is performed using a negative image of the target conductive pattern. In this UV exposure step, the UV curable resin is not cured too much and is in an incompletely cured state.

(Baking process of UV cured resin)
In the baking step that follows the UV exposure step, the UV-curable resin is additionally cured and cracks are created in the resin on the surface of the ink layer. It is assumed that the metal nanoparticles are connected to the surface through these cracks, and in the subsequent plating process, metal is deposited on the surface of the plating seed layer through these cracks. It is presumed that the effect of causing this tear is aided by the fact that the UV-cured resin before firing is not over-cured and is in an incompletely cured state. However, in this embodiment, the plating metal does not precipitate in the exposed areas due to the plating inhibiting effect in the exposed areas.

In addition, this firing step is expected to improve the adhesion between the plating seed layer and the base material. As described above, some metal nanoparticles, such as copper nanoparticles, may have a protective film formed with a coating material on their surfaces. The coating material includes, for example, organic acids. In the baking process, such a protective film is removed by baking after UV exposure and before plating, in order to make these metal nanoparticles function as plating seeds.

The firing temperature is about 160°C to 260°C, and the firing time is 10 minutes to 1 hour. In the case of UV-curable ink, a firing temperature of 160°C is insufficient and a firing temperature of 260°C or higher is preferable. This firing step is also expected to improve the adhesion between the plating seed layer and the base material. After this step, the process moves to the subsequent plating step.

(Plating process)
After the ink application step and UV exposure step, a plating treatment (electrolytic plating or electroless plating) is performed on the plating seed layer formed on the base film. Thereby, plating metal is deposited on the surface and inside of the plating seed layer.

The plating method is similar to a known plating process using a known plating solution, and specifically may include electroless copper plating, electrolytic copper plating, electrolytic nickel plating, etc.

UV-curable resins contain photopolymerization initiators, and when exposed to UV light, a reaction occurs and basically the resin begins to harden. However, as mentioned above, the photopolymerization initiator may affect the plating catalyst by metal nanoparticles in some cases. This is determined by the combination of metal and photoinitiator. As a result, the portions of the plating seed layer that are exposed to light (exposed areas) will not be plated even if immersed in an electroless plating solution, and the areas that are not exposed to light (non-exposed areas) will be plated. That is, according to this method, it is determined whether or not plating is possible in the exposed area and the non-exposed area, so that a conductive pattern can be produced. Since the beam of UV light can be narrowed down, by using such a technique, it is possible to create conductive patterns with higher definition, for example, patterns with a diameter of 1 μm or less at present. However, in this case, the exposed areas are not plated and the non-exposed areas are plated, so the exposure pattern becomes a so-called positive-negative reversal pattern (negative image). This pattern can be formed by exposure using a mask corresponding to the desired conductive pattern, or can be formed on demand by drawing with a UV light LED using a drawing device. An example of such a drawing device is Microlighter ML, a small LED direct drawing device manufactured in the UK.

(First manufacturing method of printed wiring board)
FIG. 2 schematically shows the steps of the first method of manufacturing a printed wiring board according to this embodiment.

This printed wiring board includes an insulating base material (base film) 11 and an ink layer 13 formed by applying a UV curable ink containing metal nanoparticles onto the insulating base material 11. In this example, UV curable ink is applied over the entire surface of a base film such as polyimide by spin coating or the like. Next, exposure is performed in a pattern by drawing a negative image of the desired conductive pattern with UV light. As a result, the plating catalyst in the exposed region 13b, which is the exposed portion, is deactivated. After that, all parts are hardened by thermosetting by firing. In this way, the plating seed layer 13 is formed. Next, by performing plating (here, electroless plating), plating metal is deposited in the non-exposed region 13a, thereby forming a plating layer 15 as a wiring pattern 15a. The non-exposed portions of the UV-curable ink are considered to have been thermally cured. In this way, the printed wiring board is completed.

Note that the ratio of the thickness of each layer shown in FIG. 2 is just an example, and the present invention is not limited to the ratio shown. Furthermore, the width of the conductive lines and the line spacing are merely examples.

According to this method, it is currently possible to form wiring patterns with a resolution of 0.6 μm to 1 μm. The figure shows an example in which the line width is 3 μm.

(Second manufacturing method of printed wiring board)
FIG. 3 schematically shows the steps of the second manufacturing method of the printed wiring board according to the present embodiment.

In the case of the first manufacturing method shown in Figure 2, UV-curable ink containing metal nanoparticles was applied to the entire surface of the substrate, but in the second manufacturing method shown in Figure 3, printing methods such as inkjet methods can be used. The ink pattern 13c is formed by applying UV curable ink containing metal nanoparticles in a line-and-space pattern only to necessary portions.

More specifically, UV curable ink is applied in a pattern based on the ink pattern 13c that includes the intended conductive pattern. This ink pattern may be printed at low resolution. According to this method, the UV-curable ink is not applied to the entire surface, but only to the minimum necessary area with low resolution. Thereby, compared to the first manufacturing method, it is possible to eliminate waste of UV-curable ink containing metal nanoparticles. In the subsequent exposure step, this low-resolution ink pattern is exposed using a negative image of a high-definition wiring pattern (conductive pattern). As a result, a non-exposed portion 13a and an exposed portion 13b are generated in the ink pattern 13c. As a result, in the next plating process, the plating layer 15 consisting of the desired conductive pattern 15a with higher resolution can be formed in the line.

FIG. 4 shows a perspective view of the surface of a printed wiring board as a specific application example of the second manufacturing method. This is obtained by drawing an ink pattern 13c on the surface of the base material 11 by an inkjet method, and then exposing the ink layer 13 to LED light (UVLED drawing) with a negative image of the desired conductive pattern. That is, the target conductive pattern (linear portion) 13a was left and the surrounding portion 13b was exposed. Although the line and space of the ink pattern 13c of the ink layer 13 is 200 to 200 μm, the line width of the non-exposed region 13a corresponding to the conductive pattern is much narrower than this, for example, about 3 μm. In the subsequent plating step, plating metal is deposited on the non-exposed region 13a corresponding to this conductive pattern, so the line width of the resulting wiring pattern is also about 3 μm.

Next, an experimental example in which plating is performed using the UV curable ink of this embodiment will be shown.

(Experiment example 1)
This experimental example is an example using a radically polymerized UV curing ink. A PI (polyimide) film was used as the base film, and the following UV-curable ink was used (composition 1). Commercially available inks of silver or copper nanoparticles were used (1-17 wt%). As the UV curing base resin, an acrylic resin-based UV curing ink was prepared. Bifunctional acrylic ester (40wt%), cresol novolak epoxy resin (2.5wt%), trifunctional acrylic ester (1wt%), and monofunctional acrylic ester (15wt%) are blended to initiate photopolymerization. Agent: A product containing phosphorus-based photopolymerization initiator A (5 wt%) containing phosphorus was prepared. These ratios are examples and do not limit the invention. The ink may also include a dispersant for the metal nanoparticles. The ink prepared in this way was applied onto the base film using a No. 10 bar coater (OSP-10: manufactured by OSP), exposed to light using an Hg lamp, and baked in an oven at 260°C for 60 minutes to remove the uncured portion. The UV cured resin was cured. At this time, even if there is a protective film made of a coating material on the surface of the ink layer or the surface of the metal nanoparticles in the vicinity thereof, this protective film is removed by baking.

The base film on which the plating seed layer containing metal nanoparticles was formed was cleaned with running water for 1 minute. Thereafter, pre-dipping with an electroless copper plating solution was performed, and electroless copper plating was performed at a solution temperature of 65° C. for 180 minutes using an electroless copper plating solution containing copper, alkali, and formaldehyde as main components. Thereafter, it was immersed in a discoloration inhibitor for 1 minute at room temperature, and then dried.

In this case, the combination with the photocuring agent was good, the plating was adhered, and the conductivity was also ensured.

(Experiment example 2)
This Experimental Example 2 is also an example using a radically polymerized UV-curable ink. A PI film was used as the base film, and the following UV-curable inks were used (compositions 3 to 4). Copper nanoparticles or silver nanoparticles reduced with hydrazine were used as the material for the metal nanoparticles (4.5 to 25 wt%). As the UV curing base resin, an acrylic resin-based UV curing ink was prepared. A mixture of bifunctional acrylic ester (40wt%), cresol novolac epoxy resin (2.5wt%), trifunctional acrylic ester (1wt%), and monofunctional acrylic ester (15wt%), which contains sulfur. A sample containing sulfur-based photopolymerization initiator C (5 wt%) was prepared. These ratios are merely examples, and the present invention is not limited thereto. This UV-curable ink may include a dispersant for the nanoparticles. The UV curable ink thus prepared was applied onto the base film using a No. 10 bar coater, exposed to light using an Hg lamp, and the uncured portion of the UV curable resin was cured in an oven at 260° C. for 60 minutes.

The base film on which the plating seed layer containing metal nanoparticles was formed was cleaned with running water for 1 minute. Thereafter, pre-dipping with an electroless copper plating solution was performed, and electroless copper plating was performed at a solution temperature of 65° C. for 180 minutes using an electroless copper plating solution containing copper, alkali, and formaldehyde as main components. Thereafter, it was immersed in a discoloration inhibitor for 1 minute at room temperature, and then dried.

In this case, the combination with the photocuring agent was good, the plating was adhered, and the conductivity was also ensured.

(Experiment example 3)
In Experimental Example 3, a cationic polymerization type photopolymerization initiator was used (composition 2). The UV curing ink base contains oxetane (40 wt%), bisphenol A-dialkidyl ether (53 wt%), Shin-Etsu Chemical's tetrafunctional epoxy monomer KR-470 (5 wt%), and iodine photoinitiator B (2 wt%). ) was used to prepare a resin base. Note that these ratios are merely examples, and the present invention is not limited thereto. Copper or silver nano ink was mixed into this resin base at a ratio of 2 to 10 wt% to form a UV-curable ink.

The UV curable ink prepared in this way was applied onto the base film using a No. 10 bar coater, partially exposed to a 254 nm UV lamp, and placed in an oven at 260°C for 60 minutes to remove the uncured portion of the UV curable resin. hardened.

The base film on which the plating seed layer containing metal nanoparticles was formed was cleaned with running water for 1 minute. Thereafter, pre-dipping with an electroless copper plating solution was performed, and electroless copper plating was performed for 180 minutes at a solution temperature of 60° C. using an electroless copper plating solution containing copper, alkali, and formaldehyde as main components. Thereafter, it was immersed in a discoloration inhibitor for 1 minute at room temperature, and then dried.

Through this experiment, it was confirmed that plating was applied only to the non-exposed areas of the ink application area and no plating was applied to the exposed areas. It is presumed that the photopolymerization initiator photoreacted in the exposed area, and the released component (iodine in this example) inhibited plating. That is, it is thought that the photopolymerization initiator reacts in the exposed area, and the component is released, bonds to the surface of the metal nanoparticle, and changes the potential, thereby inhibiting plating. On the other hand, in the non-exposed area, this reaction does not occur, and therefore no plating inhibition effect occurs.

Even when the iodine-based photoinitiator B used here was mixed with the UV-curable ink of Experimental Example 1 (which already contains a radical polymerization initiator), no plating was attached to the exposed areas, and no plating was attached to the non-exposed areas. I confirmed that it is attached. This suggests that components released upon exposure inhibit plating, regardless of the polymerization method.

(Experiment example 4)
As Experimental Example 4, the principle of performing mask exposure in the exposure process will be shown. A resin base was made by mixing 1 g of tetrafunctional epoxy monomer KR-470 (Shin-Etsu Chemical) and 9 g of bifunctional epoxy monomer .4g to prepare a UV-curable ink. Using a bar coater, a sample was coated onto a polyimide film to a thickness of 10 μm, masked and only a portion was exposed to UV light, and a sample without exposure was prepared. These were fired at 260° C. for 1 hour and electroless plated for 3 hours. The results are shown in FIG.

FIG. 5(a) shows a photograph of the sample before plating treatment, and FIG. 5(b) shows a photograph of the sample after plating treatment. The samples on the left were partially masked and exposed to UV light, and the samples on the right were exposed to UV light without masking.

As shown in FIG. 5(b), the sample without UV exposure (right) has plating on the entire ink application area, and the sample with partial UV exposure (left) has plating on the unexposed area (center area 51). Comes with plating. That is, it is presumed that the photopolymerization initiator photoreacted in the exposed area of the ink application area, and the released component (sulfur in this example) inhibited plating.

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

The UV curable ink prepared in this manner was applied onto the base film using a No. 10 bar coater, partially exposed to a 254 nm UV lamp, and left in an oven at 160°C for 60 minutes to coat the uncured portion of the UV curable resin. hardened.

The base film on which the plating seed layer containing metal nanoparticles was formed in this manner was cleaned with running water for 1 minute. Thereafter, pre-dipping with an electroless copper plating solution was performed, and electroless copper plating was performed at a solution temperature of 60° C. for 60 minutes using an electroless copper plating solution containing copper, alkali, and formaldehyde as main components. Thereafter, it was immersed in a discoloration inhibitor for 1 minute at room temperature, and then dried.

Through this experiment, it was confirmed that plating was applied only to the non-exposed areas of the ink application area, and no plating was applied to the exposed areas. In this case as well, it is presumed that the photopolymerization initiator photoreacted in the exposed area, and the released component (iodine in this example) inhibited plating. We confirmed that it is possible to create wiring patterns according to this principle. At the same time, it was confirmed that the same effect could be obtained using different UV curing methods.

Even when the iodine-based photoinitiator B used here was mixed with the UV-curable ink of Experimental Example 1 (which already contains a radical polymerization initiator), no plating was attached to the exposed areas, and no plating was attached to the non-exposed areas. I confirmed that it is attached.

Other experimental results with the above compositions and combinations are also summarized in Table 1 (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 exposure light is different. Photopolymerization initiator: "A" is a phosphorus-based photopolymerization initiator that generates radicals at a wavelength of 365 m, and "B" is an iodine-based photopolymerization initiator containing iodine that generates radicals and cations at 254 nm. Further, "C" is a sulfur-based photopolymerization initiator that generates radicals and cations at a wavelength of 365 m. As can be seen from Table 1, whether or not plating is possible depends on the combination of each reagent and exposure wavelength.

(Possibility of plating on exposed areas under various experimental conditions)

As can be seen from this experimental result, an appropriate printed wiring board can be realized by combining various experimental conditions, including whether or not plating is possible.

(Other embodiments)
In the above-described embodiment, a printed wiring board using UV ink and a method for manufacturing the same have been described, and the formation of a high-definition conductive pattern by plating non-exposed areas using a negative image has been described. On the other hand, as yet another embodiment, a combination of nanoparticle metal and photopolymerization initiator (photocuring agent) components that improves the deposition of plating metal on exposed areas will be described.

In this embodiment, in the ink application step, an ink layer is applied (printed) in the form of a positive image pattern that matches the intended conductive pattern. Unlike the above embodiments, UV irradiation in the exposure step does not necessarily have to be performed in a pattern, and may be performed over the entire surface (full surface exposure).

This embodiment is intended to realize good plating with a plating seed layer using an ink (solution) containing a photocurable resin and metal nanoparticles. More specifically, as shown in Experimental Example 1, Experimental Example 2, and Experimental Numbers 1, 2, and 6 to 9 in Table 1, specific nanoparticle metals and photopolymerization initiators (photocuring agents) It was discovered that the effect of enhancing the plating catalyst was found in the combination of the following components.

The photocurable resin in such an ink contains phosphorus when the metal nanoparticles are silver nanoparticles, and contains phosphorus or sulfur when the metal nanoparticles are copper nanoparticles. The plating seed layer of the substrate (printed wiring board) thus formed has a first composition containing silver nanoparticles and phosphorus, or a second composition containing copper nanoparticles and phosphorus or sulfur. It turns out.

Regarding the concentration of the nanoink, preferably, the weight concentration of the metal nanoparticle component is 8% to 20% as in the above embodiment.

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 portions are cured in the subsequent baking process.

In the firing step in this embodiment, additional curing is performed after UV curing, and fissures are created in the surface of the plating seed layer to aid the subsequent plating process.

This embodiment can take the following aspects.
(1) An insulating base material,
a plating seed layer formed of a photocurable resin and metal nanoparticles on the base material;
a plating layer formed on the plating seed layer,
The plating seed layer has a first composition containing silver nanoparticles and phosphorus, or a second composition containing copper nanoparticles and phosphorus or sulfur.
(2) a coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of an insulating base material;
an exposure step of exposing the substrate coated with the solution;
a firing step of firing the exposed base material;
a plating step of plating the fired base material,
The photocurable resin contains phosphorus when the metal nanoparticles are silver nanoparticles, and contains phosphorus or sulfur when the metal nanoparticles are copper nanoparticles. The method for manufacturing a substrate.
(3) The method for manufacturing a substrate according to (2), wherein the metal nanoparticle component in the solution has a weight concentration of 8% to 20%.
(4) The method for manufacturing a substrate according to (2), wherein in the coating step, the solution is applied in a pattern.
(5) The method for manufacturing a substrate according to (2) or (4), wherein the method of applying the coating onto the surface of the base material is an inkjet printing method.
(6) A solution applied to the surface of a substrate for manufacturing the substrate,
A photocurable resin that is cured by light and metal nanoparticles that function as a plating species are mixed,
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 component of the metal nanoparticles has a weight concentration of 8% to 20%.
(8) A printed wiring board formed using the substrate according to (1).

(Modified example)
Although the preferred embodiments of the present invention have been described above, various modifications and changes can be made in addition to those mentioned above. The materials, lengths, ratios, temperatures, times, etc. used are examples, and are not necessarily limited to these.

10 Printed wiring board 11 Base material (insulating base material)
13 Plating seed layer (ink layer)
13a First area (non-exposed area, non-exposed part)
13b Second area (exposure area, exposure part)
13c Ink pattern 15 Plating layer 15a Wiring pattern (conductive pattern)

Claims (9)

an insulating base material,
a plating seed layer formed of a photocurable resin and metal nanoparticles on the base material;
a plating layer formed on the plating seed layer,
The plating seed layer has a first region that is a non-exposed region and a second region that is an exposed region, and the plating layer is not formed on the second region but on the first region. Printed wiring board. The printed wiring board according to claim 1, wherein the plating seed layer is formed on the entire surface of the base material. The printed wiring board according to claim 1, wherein the plating seed layer is formed in a pattern on the base material. a coating step of applying a solution containing a photocurable resin and metal nanoparticles to the surface of the base material;
an exposure step of exposing the substrate coated with the solution in a pattern;
a firing step of firing the exposed base material;
a plating step of plating the fired base material,
A method for producing a printed wiring board in which, in the plating step, plating metal does not precipitate in exposed areas, but plating metal precipitates in non-exposed areas. 5. The method for manufacturing a printed wiring board according to claim 4, wherein in the exposure step, exposure is performed using a negative image of a target wiring pattern. In the coating step, the solution is coated on the base material in a pattern so as to cover the desired wiring pattern,
5. The method for manufacturing a printed wiring board according to claim 4, wherein in the exposure step, the applied pattern is exposed with a negative image of the wiring pattern. 5. The method for producing a laminate according to claim 4, wherein the method for applying the coating onto the surface of the base material is an inkjet printing method. The method for producing a printed wiring 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 thereof. . 5. The method for manufacturing a printed wiring 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.