Circuit board and method for manufacturing the same

Abstract

To provide a circuit board that can be properly created by a non-sub subtractive method using metal particle ink even on rigid base materials, and a method for manufacturing the same.SOLUTION: A circuit board 10 is composed of a substrate 11 made of glass epoxy, a resin layer 12 formed on the substrate 11 and containing epoxy resin, an electrical conductive film 13 consisting of a photo-sintered layer of metal particles formed on the resin layer 12, and a plating layer 14 formed on the electrical conductive film 13. In one aspect, the resin comprising the resin layer has a curing temperature in the range from room temperature to 190°C and has an endothermic peak within the region of more than 360°C and less than 450°C in a TG-DTA analysis of the resin.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a circuit board that can be appropriately produced by a non-subtractive method using an ink containing fine metal particles even on a rigid substrate, and to a method for producing the same. [Background technology]

[0002] Conventionally, circuit boards have been manufactured by a subtractive method in which a metal layer is formed on an insulating substrate (base material) such as resin, and then unnecessary parts of this metal layer are removed by etching to form a wiring pattern. This method requires the use of large amounts of water and excess metal that is discarded during etching, and requires many steps.

[0003] In response to this, the present applicant has proposed a method in which a conductive ink containing metal nanoparticles (metal fine particles) is applied only to the required parts of an insulating substrate made of a thermoplastic resin such as a polyimide film by an inkjet method or the like, and the metal layer is thickened by plating to further reduce the resistance value (Patent Document 1). This method (non-subtractive method), which differs from the conventional subtractive method, makes it possible to greatly simplify the board manufacturing process, and in particular has succeeded in significantly reducing the amount of water used and further reducing carbon dioxide emissions. Such a non-subtractive method can be said to be an environmentally friendly method for manufacturing circuit boards with a small number of steps. In addition, the inkjet method is a reliable method for producing small quantities of circuit boards on demand with minimal time and cost.

[0004] Patent Document 2 discloses a method of forming a circuit by applying an ink of metal nanoparticles onto a polyether ether ketone substrate, forming a photosintered film, and then forming a plating layer on the substrate, and improving the substrate by applying a resin layer (underlayer) called a primer. Photosintering is a method of sintering (firing) metal nanoparticles using a xenon lamp or the like as a heat source, and makes it possible to selectively heat the ink part of the metal nanoparticles while suppressing the temperature rise of the substrate. This allows sintering in a short time with minimal thermal effects even for substrates with low heat resistance. The reason for using a resin layer as the underlayer in Patent Document 2 is that when an ink of metal nanoparticles is directly applied to the substrate surface and photosintered (photosintering: PS), the adhesion strength of the plating layer to the substrate is insufficient. Patent Document 3 also discloses an example of improving sinterability by providing a resin underlayer with low thermal conductivity on the substrate. There is a description of using polyimide as this underlayer, but polyimide has the disadvantage of being weakly resistant to alkali, and other materials are desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6300213 [Patent Document 2] JP 2020-188074 A [Patent Document 3] Special Publication No. 2012-522383 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the case of rigid boards (RPCB) such as so-called glass epoxy boards that have been used for a long time, it has been difficult to manufacture circuit boards in exactly the same manner using the resin layer as a primer of Patent Document 2.

[0007] One of the reasons for this is that when a resin layer is applied as a primer similar to that used in conventional technology, the resin layer (and the metal nanoparticle layer) often blows away during photosintering, making it difficult to create a circuit board.

[0008] Figure 1 is a micrograph taken of the substrate surface after photosintering, showing that the resin layer and the metal nanoparticle layer applied thereon have been completely blown away during photosintering.

[0009] FIG. 2 is a micrograph (×20) of the substrate surface after photosintering, showing that the resin layer and the metal nanoparticle layer have been partially blown away.

[0010] Furthermore, even in cases where "blow-off" did not occur, the adhesion strength of the photosintered layer and plating layer formed after photosintering to the base material was very low, approaching nearly zero N / mm.

[0011] Another reason is that in rigid substrates, which are generally manufactured using a glass epoxy substrate, the weave of the glass fibers creates unevenness on the substrate surface, and due to this unevenness, photosintering of metal nanoparticles cannot be performed in the same way as with smooth polyimide films. Such unevenness on the substrate surface appears on the substrate surface after photosintering as a pattern as shown in the optical microscope photograph (x100) in Figure 3.

[0012] When the pattern on the substrate surface was further observed using an electron microscope photograph (×100), it became clear that it was caused by differences in the degree of photosintering. That is, the light-colored surface area 41 shown on the left side of Figure 4 is well sintered, while the dark-colored surface area 42 on the right side of the figure is insufficiently sintered. It was thus found that sintering unevenness occurs structurally in rigid substrates.

[0013] The reason for this uneven sintering is probably that the thermal conductivity of glass fiber and epoxy resin differs by an order of magnitude, causing the heat to be transferred differently depending on the location during light sintering. In other words, this uneven sintering reflects the internal structure of the glass fiber fabric. Incidentally, the thermal conductivity of epoxy resin is 0.17 to 0.21 W / mK, and that of glass is 1.03 W / mK.

[0014] In fact, as shown in Fig. 5, in the case where a thin resin layer was applied as a base layer and sintering unevenness became evident, an electron microscope photograph of the cross section of the substrate after photosintering showed metal nanoparticles periodically accumulating in depressions 51. This is also thought to indicate that photosintering was insufficient at the bottom of the periodic depressions created by the weave of the glass fibers.

[0015] Figure 6 shows a schematic diagram of surface sintering unevenness caused by light sintering in a glass epoxy substrate. Figure 6(a) shows a case where there is no resin layer (primer layer) and sintering unevenness occurs. A glass epoxy substrate 61 contains glass fibers 62, and due to the unevenness of the substrate surface formed by the woven fabric, unsintered parts 64 are partially generated in a metal nanoparticle layer (ink layer) 63. It is presumed that this type of structure is a factor in reducing the adhesion strength.

[0016] Figure 6(b) shows a case where uneven sintering does not occur thanks to the presence of a resin layer (not shown in the figure) that smooths out the unevenness of the substrate surface. However, if the problem of uneven sintering is attributed to the unevenness of the substrate surface and this is smoothed out by simply applying a resin or the like, the phenomenon of the resin layer being blown away during light sintering described above occurs, and it was found that this simple method cannot solve the problem.

[0017] The above problems can be briefly summarized as follows. That is, when a resin layer is provided that is thought to contribute to adhesion between the photosintered layer and the substrate during photosintering after application of metal nanoparticles (metal fine particles) in the ink, the resin layer may be blown off depending on the resin used. In addition, uneven sintering as described above always occurs. Systems with uneven sintering have very low adhesion strength. Also, although the three-dimensional unevenness can be eliminated by thickening the base resin layer, the phenomenon of "blow off" occurs when attempting to thicken the base resin layer for photosintering.

[0018] The present invention has been made against this background, and its object is to provide a circuit board and a manufacturing method thereof that can be appropriately produced by a non-subtractive method using an ink of metal fine particles, even on rigid substrates.

[0019] Another object of the present invention is to provide a circuit board and a manufacturing method thereof that can prevent the phenomenon in which a resin layer serving as a base layer is blown away during photosintering.

[0020] It is still another object of the present invention to provide a circuit board and a manufacturing method thereof that can increase the adhesive strength between the conductive film formed by the photosintering layer and the plating layer thereon and the substrate. Note that it is not necessary to achieve all of these multiple objects. [Means for solving the problem]

[0021] In order to solve the above problem, the inventors adopted an approach that tackles the problem from the material aspect. That is, since the same resin is used, but the substrate made of polyimide is less likely to blow off during light sintering, they realized that there is a compatibility between the substrate material and the resin material, and analyzed the characteristics of the resin used in the resin layer. Generally, substrates called rigid substrates are composites of glass fiber and epoxy resin, so they are called glass-epoxy substrates. It is easy to assume that an adhesive layer of epoxy resin will adhere to a substrate containing epoxy resin. However, it was experimentally found that even with the same epoxy resin, "blow off" may or may not occur depending on the composition and ingredients.

[0022] Therefore, the behavior of the epoxy resin from application to curing and the subsequent heating process was analyzed using TG-DTA (Thermogravimetry-Differential Thermal Analysis).

[0023] Figure 7 shows a typical thermogravimetric and differential thermal analysis (TG-DTA) chart for an epoxy resin that is prone to "blow-off" during photosintering. The TG curve (curve B) in this chart shows the percent weight change of the sample being analyzed as a function of increasing temperature (horizontal axis). Negative values ​​indicate weight loss. The DTA curve (curve A) shows the temperature difference between the sample and a reference material as a function of increasing temperature. This temperature difference is expressed as the electromotive force of the differential thermocouple in μV. The DTG curve (curve C) shows the time rate of change of the sample's weight (μg / min) as a function of increasing temperature. (The arrows extending left or right from each curve in the chart show the vertical axis that applies to that curve.)

[0024] In the chart of Figure 7, a convex peak indicating heat generation is observed in the region (range) below 200°C on the DTA curve (curve A), which indicates the heat generated when the epoxy monomer is thermally polymerized (curved). The TG curve (curve B), which indicates the weight change at this time, is flat, indicating that no material enters or leaves the sample. On the other hand, in the region between 360°C and 450°C, a large weight loss is confirmed on the TG curve, and according to the DTA curve, the heat in and out of this region is in the direction of heat generation. This can usually be considered to have occurred in this temperature region. Since heat generation is observed even after that at temperatures above 450°C, it is reasonable to consider that combustion continues to occur. This can be considered to have occurred when combustion occurs when the sample is suddenly heated by light sintering, as shown by the large, steep peak on the DTG curve (curve C), and if this occurs explosively, it can be considered to have caused the "blowout" phenomenon.

[0025] Figure 8(a) shows the case where the peak is in the heat generation (positive) direction from the baseline for the temperature range of 360°C to 450°C on the DTA curve (curve A) in Figure 7. It is best to draw the baseline from the low temperature side. Since heat generation is observed even after that, even at temperatures above 450°C, it is reasonable to assume that combustion continues to occur. In this case, if the heat generation peak is large, the endothermic peak shown earlier may be canceled out or the baseline may be difficult to draw, so the judgment is based only on the baseline from the low temperature side. Figure 8(b) shows the case where the peak in the same temperature range is in the heat generation (negative) direction from the baseline.

[0026] On the other hand, Figure 9 shows a typical TG-DTA chart of an epoxy resin that is less likely to "blow off" when irradiated with light at the same energy during light sintering. In this example, a large negative peak is observed in the DTA curve (curve A) in the range from 360°C to 450°C. This means that heat is absorbed, and it is thought that the resin does not burn immediately when it decomposes, but rather that the decomposition products, such as monomers, evaporate and endothermic heat is generated. In other words, rather than a sudden heat generation, the decomposition is relatively gentle due to the endothermic heat, and it is understood that "blow off" is less likely to occur during light sintering. Of course, in addition to evaporation, combustion must also be occurring in this region, and it is thought that the positive and negative peaks of both events overlap, resulting in the curve shown in the figure. In this way, it can be seen that the behavior of the DTA curve in the temperature range from 360°C to 450°C is deeply related to the presence or absence of "blow off".

[0027] Furthermore, in the case of Figure 9, when looking at the weight change in curve B (TG curve), it can be seen that most of the components have disappeared at around 400°C on the right end. In this case, there was no "blow-off," but it is believed that the resin layer that should support adhesion has disappeared. In other words, it was found that a certain amount of the resin layer remaining on the right end side of the TG curve is a condition for ensuring adhesion. According to experimental results, the average thickness is preferably 5 μm or more and 15 μm or less.

[0028] In the example in Figure 9, the resin solution contains 34% by weight of solvent, so a large weight change is observed due to evaporation of the solvent (see curves B and C) before the initial heat generation peak in the range below 200°C (see curve A). However, the presence of this solvent does not directly affect the occurrence of "blow-off" or adhesion.

[0029] From the above analysis, it is possible to predict and select a resin layer suitable for a glass epoxy substrate from the TGDTA analysis. That is, the circuit board and the manufacturing method thereof according to the present disclosure have the following aspects.

[0030] In a first aspect, the circuit board of the present disclosure includes a glass epoxy substrate, a resin layer containing an epoxy resin formed on the substrate, a conductive film consisting of a photosintered layer of metal particles formed on the resin layer, and a plating layer formed on the conductive film. With this configuration, a circuit board can be appropriately produced by a non-subtractive method using an ink of metal particles even on a rigid substrate.

[0031] In a second aspect of the circuit board, the resin constituting the resin layer has a curing temperature within a range of room temperature to 190° C., and in a TG-DTA analysis of the resin, has an endothermic peak within a range of 360° C. to 450° C. By using such a resin as a base layer for the photosintering layer, the phenomenon of the resin being blown away during photosintering is suppressed.

[0032] In the third aspect of the circuit board, the average thickness of the resin layer is 5 μm or more and 15 μm or less. By using such a resin as a base layer of the photosintered layer, the adhesive strength between the photosintered layer and the base material is improved. If the thickness is less than 5 μm, the resin layer is easily affected by the heat absorption of the base glass during photosintering, and if the thickness exceeds 15 μm, the epoxy resin is easily cured under the manufacturing conditions.

[0033] In a first aspect, a manufacturing method for a circuit board according to the present disclosure includes the steps of forming a resin layer containing an epoxy resin on a glass epoxy substrate, forming a conductive film consisting of a photosintered layer on the resin layer by photosintering metal particles, and forming a plating layer on the conductive film.

[0034] In a second aspect of the method for producing a circuit board, the resin constituting the resin layer is cured at a temperature within a range of room temperature to 190°C.

[0035] In a third aspect of the method for producing a circuit board, the resin layer has an endothermic peak in a range of 360° C. or more and 450° C. or less in a TG-DTA analysis of the cured resin. Effect of the Invention

[0036] According to one aspect of the present invention, it is possible to provide a circuit board that can be appropriately produced by a non-subtractive method using an ink containing metal fine particles even on a rigid substrate, and a method for producing the same.

[0037] According to another aspect of the present invention, it is possible to provide a circuit board and a manufacturing method thereof that can prevent the phenomenon in which a resin layer serving as a base layer is blown away during photosintering.

[0038] According to yet another aspect of the present invention, a circuit board and a manufacturing method thereof can be provided that can increase the adhesive strength between the conductive film formed by the photosintered layer and the plating layer thereon and the substrate. [Brief description of the drawings]

[0039] [Figure 1] 1 is a micrograph of the substrate surface after photosintering (in the case of complete blow-off). [Diagram 2] 1 is a micrograph of the substrate surface after photosintering (in the case of partial blown-off). [Diagram 3] FIG. 13 is a diagram showing an optical microscope photograph of a case where a pattern is generated by photosintering. [Figure 4] Electron microscope photographs taken from above of the dark and light colored areas after photosintering. [Diagram 5] 1 is an electron microscope photograph of a cross section of a substrate after photosintering, in which sintering unevenness is evident. [Figure 6] 1 is a schematic diagram showing uneven sintering caused by light sintering in a glass epoxy substrate. FIG. [Figure 7] This is a typical TG-DTA chart of an epoxy resin that is prone to "blow-off" during photosintering. [Figure 8] FIG. 2 is an explanatory diagram of a DTA curve (curve A) in which (a) an exothermic peak appears relative to the baseline, and (b) an endothermic peak appears relative to the baseline. [Figure 9]This is a typical TG-DTA chart of an epoxy resin that is less likely to "blow off" during photosintering. [Figure 10] 1 is a cross-sectional view illustrating a schematic basic configuration of a circuit board according to an embodiment of the present disclosure. [Figure 11] FIG. 1 shows a profile (TG-DTA data) of the epoxy resin solution used in Example 1. [Figure 12] 1 is a photograph of a substrate surface after photosintering in Example 1. [Figure 13] 2 is an optical microscope photograph of a substrate surface after photosintering in Example 1. [Figure 14] FIG. 2 is a diagram showing the results of a peel test in Example 1. [Figure 15] 1 is an optical microscope photograph after photosintering in the case of a thinly applied resin layer in Comparative Example 1. [Figure 16] FIG. 1 shows a profile (TG-DTA data) of the epoxy resin solution used in Comparative Example 2. [Figure 17] 13 is an optical microscope photograph after photosintering in the case of the resin layer used in Comparative Example 2. [Figure 18] FIG. 1 shows the profile (TG-DTA data) of the epoxy resin solution of Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Hereinafter, an embodiment of the present invention will be described in detail. In this embodiment, an approach is adopted in which an underlying resin layer that meets specific conditions is used when applying ink containing metal nanoparticles as metal fine particles onto a glass epoxy substrate.

[0041] <Circuit board configuration> Fig. 10 is a cross-sectional view showing a schematic diagram of the basic structure of the circuit board according to the present embodiment, in which Fig. 10(a) shows a general structure, and Fig. 10(b) shows a specific example structure.

[0042] 10(a), the circuit board 10 is basically configured to include a glass epoxy base material 11 as an insulating base material, a resin layer 12 applied onto the base material 11, a photosintered layer 13 (conductive film) formed of a metal nanoparticle layer (ink layer) applied onto the resin layer 12, and a plating layer 14 formed on the photosintered layer 13. The plating layer 14 constitutes a conductive layer for the circuit.

[0043] FIG. 10(b) shows a cross-sectional view of a circuit board in a partially printed wiring state. In this figure, the photosintered layer 13a is formed by photosintering an ink layer 13a of a metal nanoparticle layer formed in a pattern. A plating layer 14a is formed on the photosintered layer 13a. The plating layer 14a is formed in a similar pattern to the photosintered layer 13a.

[0044] The specific configuration of the components of the circuit board 10 is as follows.

[0045] (Base material 11) The insulating substrate (insulating substrate) 11 in this embodiment is a woven glass fiber impregnated with epoxy resin, and is typically woven in a plain weave, but is not necessarily limited to this. The substrate 11 may be of various types depending on the degree of modification of the epoxy resin and additives, but is not particularly limited to this. The thickness is typically about 0.2 mm to 1.6 mm, but is not necessarily limited to this.

[0046] (Resin layer 12 (primer, undercoat layer)) The composition of the resin solution for the resin layer 12 as a primer in this embodiment is an epoxy resin monomer with 1 to 5% by weight of an amine-based curing agent added, which is diluted to 50% by weight with ethylene glycol monoethyl ether.

[0047] Modified epoxy resin monomers can be used as the epoxy resin monomer, and oligomers or monomers with different odd functionalities can be mixed and used. The curing agent can be other than amine-based. Note that in the embodiment of the present invention, polymers (molecular weight of 10,000 or more) are not included.

[0048] (Metal nanoparticle layer 13: ink layer: layer containing metal nanoparticles: photosintered layer: conductive film) In this embodiment, the thickness of the metal nanoparticle 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 be reduced. Conversely, if the ink coating layer is too thick, the manufacturing cost may increase because metal nanoparticles are generally more expensive than normal metals.

[0049] Materials for metal nanoparticles (metal fine particles) include gold (Au), silver (Ag), copper (Cu), palladium (Pd), and nickel (Ni), and may contain one or more metals. From the viewpoint of electrical conductivity, however, gold, silver, and copper are preferred. Silver is less susceptible to oxidation than copper and is cheaper than gold, and if even cheaper copper can be used, that is even better.

[0050] The average particle size of the metal nanoparticles is preferably 1 nm to 200 nm, more preferably 10 nm to 100 nm. If the particle size is too small, the reactivity of the particles may be high, which may adversely affect the storage stability of the ink. If the particle size is too large, it may be difficult to form a uniform thin film, and the ink particles may be more likely to settle.

[0051] (Plating layer 14) The plating layer 14 as a conductive layer is formed by plating (electrolytic plating or electroless plating) on ​​the metal nanoparticle layer 13. For electroless plating, a standard copper sulfate solution with formaldehyde as a reducing agent and a pH of 10 or higher can be used.

[0052] As the plating metal, copper, nickel, tin, silver, gold, etc. can be used, but from the viewpoints of economy and electrical conductivity, it is most preferable to use copper.

[0053] The thickness of the plating layer 14 is preferably 3 μm to 100 μm, and more preferably 3 μm to 35 μm. If the plating layer 14 is too thin, the mechanical strength may be insufficient and the electrical conductivity may not be sufficient for practical use. Conversely, if the plating layer 14 is too thick, the time required for plating may be long, and the manufacturing cost may increase. In general, electrolytic plating requires less time than electroless plating, so that electrolytic plating can handle thicker plating layers at a realistic cost. However, electroless plating has the advantage that it can plate not only connected electrode lines but also floating areas as islands.

[0054] <Manufacturing method of circuit board> (Primer application process) A resin solution for the resin layer 12 as a primer is applied to the surface of a glass epoxy substrate. The method of applying the primer is not particularly limited, but since a rigid substrate is hard, a sheet-fed printing method is often used. For example, screen printing is considered to be suitable. Alternatively, gravure printing or offset printing can be used. The applied resin layer as a primer is cured at a temperature within a range of room temperature to 190°C. Here, room temperature to 200°C is a suitable temperature range for curing the epoxy resin as a primer, but the glass epoxy substrate melts or burns when heated above 200°C, so the upper limit of the curing temperature is set to 190°C. It is preferable to use a resin composition used as a primer that cures within a range of room temperature to 190°C.

[0055] (Ink application process) In this process, ink containing metal nanoparticles is applied to the surface of the substrate on which the primer has been applied and cured. This application can be done either over the entire surface of the substrate or in a pattern. When applying in a pattern, a printing method can be used, typically an inkjet method. However, this is not necessarily limited to the inkjet method, and other application methods may also be used. In the experiments described below, application was also performed using a bar coater.

[0056] After the ink containing metal nanoparticles is applied to the substrate, a drying process is performed to remove the solvent, if any. This process is similar to the known drying process for metal nanoparticle ink. Methods for drying the ink containing metal nanoparticles include heating in an oven or drying with hot air.

[0057] (Photosintering process) After the ink application and drying processes, the photo-sintering process is carried out. For this purpose, a commercially available photosintering (PS) device, such as the photo-sintering device (B0320-A) manufactured by Ushio Inc., can be used. The distance between the substrate and the lamp is set, and the voltage and irradiation time are adjusted. Photo-sintering is completed instantly, so the time required to proceed to the next process is short.

[0058] (Plating process) The formed photosintered layer is subjected to a plating process. This causes a plating metal to be deposited on the surface and inside of the sintered layer. The plating method is the same as a known plating process using a known plating solution, and specifically may include electroless copper plating, electrolytic copper plating, electrolytic nickel plating, etc.

[0059] Next, a specific example of performing photosintering and plating treatment using the resin layer (underlayer) of this embodiment will be described.

[0060] Example 1 In Example 1, a glass epoxy substrate of ES-33515 (manufactured by Risho Kogyo Co., Ltd.) of 100 mm x 100 mm was used as a substrate made of glass epoxy resin. A solution containing 50% by weight of monomers, oligomers, and polymers that would become an epoxy resin layer (underlayer) was applied to this substrate, and cured at 150°C for 1 hour. The coating method was to wash the substrate with acetone, and then apply the coating at a speed of 40 mm / sec using a bar coater and a Bevs1818S Miniautomatic Applicator (manufactured by Bevs Co., Ltd.) to a thickness of 30 μm before drying. When measured with a micrometer, the thickness of the underlayer varied from 11 μm to 15 μm due to unevenness. In an electron microscope photograph of this cross section, the thickness was 8 μm, and this result was different from the value measured with a micrometer. In the thickness measurement with a micrometer in this embodiment, the average value of measurements at five or more points was obtained. To measure thickness using an electron microscope photograph, two lines were drawn at the upper and lower boundaries of the layer to be measured and the distance between the two lines was measured.

[0061] The epoxy resin used as a primer here is a mixture of epoxy monomers with a bisphenol A skeleton, bifunctional monomers and trifunctional monomers necessary for three-dimensional hardening, and an amine-based hardener is used. The solvent is ethylene glycol monoethyl ether, initially 66% by weight, and then the same solvent was added to make it 50% by weight before coating.

[0062] The characteristics (profile) of this epoxy resin are shown in the TG-DTA chart in Figure 11.

[0063] This resin solution contains about 30% by weight of solvent, and on the chart it evaporates at temperatures above 100°C, causing a decrease in weight (see curve B), and it can be seen that heat is absorbed (see curve A). However, an endothermic portion is confirmed above 400°C, after which heat is observed to be generated (see curve A). The heat generated around this temperature can be interpreted as being due to combustion. The endothermic portion is thought to be the heat absorbed when some of the resin components that had hardened by 200°C decompose and evaporate.

[0064] Such epoxy resins are not limited to a specific composition as long as they can be identified by the TG-DTA results. As long as equivalent TG-DTA results are obtained, they may be modified with various additives.

[0065] After the resin layer (undercoat layer) was cured, a 15% by weight copper nanoparticle ink was applied to the substrate with a coating thickness of 10 μm using a bar coater. After confirming that the solvent had dried at room temperature, the coated substrate was dried in a 60°C oven for 30 minutes. Ethylene glycol monobutyl ether was used as the solvent for this nanoparticle ink.

[0066] After drying, the substrate was set in a photosintering device B0320-A (manufactured by Ushio Inc.) and photosintering was performed at a voltage between 2700 V and 3000 V. Specifically, the voltage and irradiation time (milliseconds) were adjusted using a thermal sensor L50(150)A-LP2-35 manufactured by Ohir Inc. so that the light output of the xenon lamp was in the range of 1.2 W ±0.02 W. The distance from the xenon lamp to the sample surface was set to 5 cm.

[0067] In severe cases, the resin layer was easily visible, but in subtle cases, a digital microscope (VHX-8000, manufactured by Keyence Corporation) was used to take an optical microscope photograph to confirm the defect. The resistance value was measured using a four-terminal resistance meter RM3544 (manufactured by Hioki E.E. Corporation).

[0068] As a result, in Example 1, there was no blow-off, and a conductive film made of a photosintered layer (photosintered film) with a resistance value of 0.5 Ω or less could be obtained.

[0069] Figure 12 shows a photograph of the substrate surface after light sintering in Example 1. From the reflection of light, even though sintering was performed under good conditions, the texture of the substrate can be seen on the surface. In other words, this photograph shows that large undulations on the substrate surface are still visible. On the other hand, as shown in Figure 13, in the optical microscope photograph (x100), it can be seen that the uneven sintering shown in Figure 3 is almost invisible.

[0070] The substrate thus obtained, on which the photosintered layer (conductive film) containing metal nanoparticles was formed, was treated with 10% sulfuric acid for 10 seconds and washed with water. Then, a pre-dip was performed in an electroless copper plating solution, and electroless copper plating was performed at a solution temperature of 65°C for 4 hours using an electroless copper plating solution mainly composed of copper, alkali, and formaldehyde. Then, the substrate was immersed in a discoloration prevention agent at room temperature for 1 minute and then dried.

[0071] As a result, a plating layer was formed on the surface of the substrate after photosintering by plating, ensuring electrical conductivity suitable for use in normal devices.

[0072] The substrate thus completed was annealed at 200°C for 1 hour and subjected to a peel test, which resulted in a stable adhesion strength of 0.4 N / mm or more, as shown in Figure 14(a). This strength exceeds the US UL standard (0.35 N / mm). For comparison, Figure 14(b) shows the result before annealing, when there was almost no peel strength (0.113 N / mm).

[0073] Comparative Example 1 Comparative Example 1 describes a case where a 5% by weight solution was applied to a coating thickness of 10 μm using a bar coater using the epoxy resin layer of Example 1. There are no other differences from Example 1. The thickness of the resin layer in Comparative Example 1 was 2 μm or less, measured with a micrometer and an electron microscope photograph of the cross section. Figure 15 shows an optical microscope photograph of Comparative Example 1 after photosintering. In this photograph, in addition to uneven sintering, some of the copper has been blown off, leaving holes.

[0074] In this case, the result of the peel test after plating was almost 0.0N / mm. Therefore, it was found that even if the same resin is used, if the resin layer is thin, the effect on the adhesive strength is small and no strength is obtained at all.

[0075] Comparative Example 2 The experimental method of this Comparative Example 2 is the same as that of Example 1, but the TG-DTA profile of the epoxy resin of the resin layer used in the primer is different, as shown in Figure 16. In this example, there is a heat generation peak at 300°C or higher, and it is considered that the resin is mainly decomposed by combustion. In this case, it was confirmed that explosive combustion occurs during light sintering, and "blowout" is likely to occur.

[0076] In this case, the applied film thickness was 10 μm using a bar coater, and as can be imagined from the TG-DTA profile, the film has a tendency to be easily blown off, so uneven sintering was clearly observed after photosintering. Figure 17 shows an optical microscope image of this resin layer after photosintering.

[0077] The substrate on which the ink layer containing metal nanoparticles was formed was cleaned with running water for 1 minute. After that, a pre-dip was performed in electroless copper plating solution, and electroless copper plating was performed for 180 minutes at a solution temperature of 60°C using an electroless copper plating solution whose main components are copper, alkali, and formaldehyde. After that, the substrate was immersed in a discoloration prevention agent at room temperature for 1 minute and then dried.

[0078] In this case, even after annealing at 200℃ for 1 hour after plating, the result of the peel test was a small value of 0.066N / mm. Before annealing, it was 0.018N / mm. Therefore, it was found that when the TG-DTA profile was poor and the resin layer was thin, sufficient adhesive strength could not be obtained.

[0079] Example 2 In this Example 2, a solution containing 50% by weight of monomers, oligomers, and polymers that will become the epoxy resin layer (underlayer) was applied to a glass epoxy substrate of 100 mm x 100 mm ES-33515 (manufactured by Risho Kogyo Co., Ltd.) as a substrate made of glass epoxy resin, and cured at 150°C for 1 hour. The coating method was to wash the substrate with acetone, and then use a bar coater that coats a thickness of 30 μm before drying, and apply the coating at a speed of 40 mm / sec using a Bevs1818S Miniautomatic Applicator (manufactured by Bevs). When measured with a micrometer, the thickness of the underlayer was 11 μm to 15 μm, with variation due to unevenness.

[0080] The epoxy resin used as the primer here is a mixture of epoxy monomers with a bisphenol A skeleton, bifunctional monomers and trifunctional monomers necessary for three-dimensional curing, as in Example 1, and an amine-based curing agent, but the mixture is slightly different from that in Example 1. The solvent was also ethylene glycol monoethyl ether, initially 66% by weight, and then the same solvent was added to make it 50% by weight before coating.

[0081] The characteristics of this epoxy resin are shown in the TG-DTA chart in Figure 18.

[0082] According to the DTA curve of this chart, an endothermic portion is recognized above 400°C, followed by the observation of heat generation (see curve A). The heat generation around this temperature can be interpreted as being due to combustion. The endothermic portion is thought to be the heat absorption caused by some of the resin components that hardened by 200°C decomposing and evaporating.

[0083] Such epoxy resins are not limited to a specific composition as long as they can be identified by the TG-DTA results. As long as equivalent TG-DTA results are obtained, they may be modified with various additives.

[0084] After the resin layer (undercoat layer) was cured, a 15% by weight copper nanoparticle ink was applied to the substrate with a coating thickness of 10 μm using a bar coater. After confirming that the solvent had dried at room temperature, the coated substrate was dried in an oven at 60°C for 30 minutes. Ethylene glycol monobutyl ether was used as the solvent for this nanoparticle ink.

[0085] The dried substrate was set in a photosintering device B0320-A (manufactured by Ushio Inc.) and photosintering was carried out at a voltage between 2700 V and 3000 V in the same manner as in Example 1. As a result, a conductive film was obtained that was free of blow-off and consisted of a photosintered layer (photosintered film) with a resistance of 0.5 Ω or less.

[0086] (Thickness of resin layer (base layer)) Table 1 shows the experimental results (within a 100 mm x 100 mm substrate sample) for the thickness (film thickness) of the resin layer (undercoat layer). [Table 1]

[0087] As explained in the above-mentioned Example 1, when a 50 wt% epoxy resin solution was applied using a 30 μm bar coater, the thickness of the undercoat layer (after drying and curing) was measured with a micrometer to be 11 μm to 15 μm in an experimental example with an adhesion strength of about 0.4 N / mm, and the cross-sectional SEM measurement value was 8 μm.

[0088] In contrast, a 30μ bar coater was also used for applying two coats of the base layer and for directly applying the undiluted solution, but the film thickness was very large.

[0089] In samples with a base layer thickness of over 100 μm, "blow-off" was likely to occur during light sintering, making adjustments difficult. It is thought that light sintering conditions are easier to adjust when the base layer is 20 μm or less. In this situation, we tried to create a sample with a film thickness of 20 to 100 μm, but it was difficult and difficult to reproduce, but in the case of the 25 μm thickness obtained by chance, the sample was blown off, so it is thought that the thicker the film, the more likely it is to be blown off.

[0090] When the same epoxy resin undercoat was applied at 5% by weight, the thickness of the undercoat was 3 to 4 μm, as determined by cross-sectional observation with an electron microscope. In this case, there was less "blow-off," but the effect of improved adhesion strength was not obtained.

[0091] Based on the above experimental results, from the viewpoints of adjusting the light sintering conditions and adhesion strength, it is considered appropriate that the average film thickness of the resin layer as the underlayer is 5 μm or more and 15 μm or less.

[0092] (Modification) Although the preferred embodiment has been described above, various modifications and changes other than those mentioned above are possible. The materials, lengths, thicknesses, ratios, temperatures, times, etc. used are merely examples and are not necessarily limited to these. [Explanation of symbols]

[0093] 10 Circuit Board 11 Substrate (insulating substrate) 12 Resin layer (primer, base layer) 13 Metal nanoparticle layer (ink layer, photosintered layer, conductive film) 14 Plating layer 14b Wiring pattern (conductive pattern) 41,42 Surface area 51 Hollow 61 Glass epoxy substrate 62 Glass Fiber 63 Metal nanoparticle layer (ink layer, photo-sintered layer, conductive film) 64 Unsintered part 65 Plating layer A curve (DTA curve) B curve (TG curve) C curve (DTG curve)

Claims

1. A glass epoxy substrate, a resin layer formed on the substrate and containing an epoxy resin; a conductive film formed on the resin layer and including a sintered layer of metal fine particles; a plating layer formed on the conductive film; A circuit board comprising:

2. The circuit board according to claim 1, wherein the resin constituting the resin layer has a curing temperature within a range of from room temperature to 190°C, and a TG-DTA analysis of the resin shows an endothermic peak within a range of from 360°C to 450°C.

3. 3. The circuit board according to claim 1, wherein the resin layer has an average thickness of 5 [mu]m or more and 15 [mu]m or less.

4. forming a resin layer containing an epoxy resin on a glass epoxy substrate; forming a conductive film made of a sintered layer on the resin layer by sintering metal fine particles; forming a plating layer on the conductive film; A method for manufacturing a circuit board comprising:

5. 5. The method for manufacturing a circuit board according to claim 4, wherein the resin constituting the resin layer is cured at a temperature within a range of from room temperature to 190.degree.

6. 6. The method for manufacturing a circuit board according to claim 4, wherein the resin layer has an endothermic peak in the range of 360° C. or higher and 450° C. or lower in TG-DTA analysis of the resin after curing.

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