Substrate for electroless plating, electroless plated structure, and electroless plating method

Abstract

The present invention relates to a substrate for electroless plating, which comprises a primer layer that is capable of coping with an electroless plating process. This substrate for electroless plating is composed of a base material and a primer layer that is formed on one surface or both surfaces of the base material. The primer layer contains a thermoplastic resin I which is a main agent component and a resin II which is a crosslinking agent component, and additionally contains a thermosetting resin III which is an adhesive component and has a bisphenol skeleton, and a titanium element or a zirconium element which is a reinforcing agent component. The resin III is preferably a bisphenol A type epoxy resin or a bisphenol F type epoxy resin. The titanium element or the zirconium element, which is a reinforcing agent component, is derived from a titanium alkoxide or the like, or a zirconium alkoxide or the like, each of which is contained in a primer liquid for forming the primer layer. The substrate for electroless plating according to the present invention can suppress deterioration of the base material, which is caused by diffusion of metal ions, by the action of the primer layer.

Description

Electroless plating substrate, electroless plating structure, and electroless plating method

[0001] The present invention relates to a substrate for forming a plating film by electroless plating, and more particularly to a substrate for electroless plating that has a primer layer of a predetermined composition, has good adhesion to a plating film, and is also excellent in durability.

[0002] The electrodes and wiring of circuit boards used in various semiconductor devices and electronic devices have a multilayer structure in which metal layers are stacked. A typical configuration requires a wiring metal layer that serves as the electrode or wiring, and many of them have a thin film made of a metal or metal compound called a barrier layer formed between the substrate and the wiring metal layer. Currently, copper (Cu) is the mainstream wiring metal. The barrier layer is designed to suppress the diffusion of metal ions (copper ions) from the wiring metal (copper) into other metal layers and the substrate. Nickel (Ni) thin films, nickel phosphorus (NiP) thin films, etc. are well-known materials for the barrier layer.

[0003] Recently, devices used in high-speed communication, AI, and autonomous driving technologies have seen remarkable development. They are using high-frequency bands as carrier waves for transmission signals to achieve ultra-high-speed, high-capacity information transmission and low-latency communications. Circuit boards used in these high-frequency bands are required to reduce transmission loss and insertion loss. Transmission loss is expressed as the sum of dielectric loss caused by the substrate and conductor loss caused by the metal layers forming the electrodes and wiring on the substrate. While improving the dielectric properties of the substrate (board) is effective in reducing transmission loss, it is equally important to reduce conductor loss by improving the wiring structure.

[0004] In light of these circumstances, recent years have seen growing discussion about the impact of barrier layers on transmission loss in device characteristics and the necessity for such layers. As mentioned above, metals and metal compounds such as nickel and nickel phosphorus are commonly used as materials for barrier layers. Nickel is a ferromagnetic material, which has a significant impact on devices in terms of high-frequency characteristics. Nickel phosphorus can also be nonmagnetic depending on its composition, but its high-frequency characteristics are unknown. Therefore, in circuit boards designed for high-speed transmission, it is necessary to consider eliminating the barrier layer below the wiring metal layer or changing its material.

[0005] The present applicant has proposed the application of an electroless plating process that applies a predetermined primer layer as a means for improving the circuit board manufacturing process (Patent Documents 1 to 3). Electroless plating has the advantage of being able to form a thin metal film (plating film) on a wide range of substrates, including conductive materials such as metals, as well as insulating materials such as plastics and ceramics. Therefore, electroless plating has become useful in recent years as a method for forming plating films on organic resin substrates in circuit boards for various devices.

[0006] The applicant of this application has proposed an electroless plating process that involves providing a suitable primer layer on a substrate prior to the electroless plating step and utilizing a pretreatment solution containing nano-sized precious metal colloid particles (Patent Document 1). In this electroless plating process, a resin with a glass transition temperature (Tg) of 40°C or higher and 430°C or lower is used as the primer layer. A pretreatment solution is then applied to the primer layer, and precious metal nanoparticles are adsorbed and fixed to the primer layer surface. These precious metal nanoparticles act as catalytic nuclei to promote the deposition and growth of the plating film. Furthermore, the primer layer is fluidized by heat treatment within a range of ±50°C of the resin's glass transition temperature, resulting in the precious metal nanoparticles sinking into the primer layer.

[0007] Furthermore, the electroless plating process developed by the applicant of the present application can be applied to the formation of fine circuits by compounding a specific resin with the resin constituting the primer layer described above (Patent Documents 2 and 3).Specific examples include a primer layer made of a two-component resin in which a thermoplastic resin such as polyester is used as the main component (base resin) and a crosslinking agent such as an amine-based resin, a guanamine-based resin, or a melamine-based resin is mixed into the thermoplastic resin.

[0008] This primer layer undergoes crosslinking and generates functional groups (amino groups) upon heat treatment or irradiation with light of 300 nm or longer. The functional groups act as acceptors that capture precious metal nanoparticles. These activated functional groups are then inactivated by irradiation with light of 300 nm or shorter (deep ultraviolet light irradiation). These functional groups, which can be activated and inactivated in this way, can impart selective film-forming properties to the primer layer surface, allowing for the formation of selective and fine plating films by applying a photomask or the like.

[0009] Patent No. 6312766 JP 2019-123909 A JP 2019-123910 A

[0010] As described above, the electroless plating process developed by the applicant of the present application strengthens the adhesion between the plating film and the substrate by applying a primer layer and controlling the state of precious metal nanoparticles. Furthermore, this electroless plating process can form a plating film more directly and efficiently than conventional film formation processes that use resist films. Furthermore, this electroless plating process is particularly useful for forming wiring in semiconductor devices and other devices, which are constantly required to be miniaturized.

[0011] Furthermore, the primer layer and plating film formed by this electroless plating process are expected to be able to eliminate the barrier layer in the wiring structure of the circuit board described above. Specifically, plating films formed by the electroless plating process include gold, palladium, etc., which are non-magnetic materials and therefore have little effect in the high frequency band. Furthermore, in addition to the plating film, it would be preferable if the primer layer also had the effect of suppressing the diffusion of metal ions from the wiring metal. Thus, the application of the electroless plating process can also contribute to the direct formation of wiring metal layers.

[0012] The present invention was made in light of the above-mentioned background, and proposes a specific means for eliminating the barrier layer in a structure in which multiple metal layers are stacked. Specifically, the present invention provides a substrate for electroless plating having a primer layer, which is developed by the applicant of the present application, that can suppress damage to the substrate due to diffusion of metal ions by optimizing the configuration of the primer layer.

[0013] The present inventors have considered that, in order to solve the above-mentioned problems, it is necessary to optimize the composition of the resin film that serves as the primer layer in the electroless plating process (Patent Document 1) developed by the applicant of the present application, thereby improving the adhesion (initial adhesion) between the plating film and the substrate. Generally, the adhesion strength between the substrate and the plating film tends to decrease over time, although to varying degrees. This tendency occurs regardless of whether or not the barrier layer is eliminated, and cannot be completely avoided. Given this, it is preferable to increase adhesion at the initial stage, while anticipating a certain degree of decrease in adhesion.

[0014] The initial adhesion of a primer layer is also discussed in the study of the electroless plating process in Patent Document 1 mentioned above. However, the method for evaluating adhesion in this document mainly relies on the relatively simple cross-cut method. The cross-cut method is a method for determining whether or not a cross-cut plating film peels off, and while it is an excellent test method in that it allows for a simple determination of relative superiority or inferiority, it does not specifically indicate adhesion strength. According to the inventors' studies, it is unclear whether such a test method and evaluation based on its results alone satisfy the adhesion strength required in various fields. Furthermore, as will be described later, according to the inventors' studies, the conventional primer layer in Patent Document 1 lacks adhesion strength even in the initial stage.

[0015] Therefore, in the present invention, priority should be given to examining the configuration of a primer layer with higher adhesion strength than conventional techniques, while conducting a more specific evaluation of adhesion strength. Furthermore, consideration should be given to not impairing the functions and properties of the primer layer in the electroless plating process. Here, the applicant's summary of the functions and required properties of the primer layer, taking into account the relationship between the primer layer and the substrate and the plating film that come into contact with the primer layer, includes the following four items (i) to (iv): (i) Adhesion at the interface between the substrate and the primer layer; (ii) Strength of the primer layer itself; (iii) Adsorption of precious metal nanoparticles (catalytic nuclei) on the primer layer surface; and (iv) Adhesion at the interface between the primer layer and the plating film.

[0016] After extensive research, the present inventors discovered that improving the adhesion strength of a plating film and ensuring the above-mentioned properties (i) and (iv) is achieved by improving the rigidity of the primer layer. Specifically, the present inventors found that adding a thermosetting resin as an adhesion agent component that favorably imparts rigidity to the primer layer is effective. Furthermore, the present inventors' research confirmed that adding an excessive amount of thermosetting resin improves rigidity but reduces adhesion. This indicates that a primer layer requires both rigidity (hardness) and toughness (flexibility), and that there is an appropriate range of addition amount that takes into account the balance between the two. Furthermore, the present inventors believed that optimizing this balance would lead to ensuring the properties (i) and (iv) as well as the strength of the primer layer itself (ii).

[0017] Furthermore, the inventors also considered identifying a thermosetting resin that does not impair the above characteristic (iii). The adsorption of precious metal nanoparticles on the primer layer surface is due to functional groups (acceptors) generated from the crosslinking agent in the primer layer. The type and amount of the thermosetting resin used as the adhesive agent, as well as the balance with the content of other resins, can affect whether or not acceptors are formed on the primer layer surface.

[0018] Based on the above points, the inventors have investigated suitable thermosetting resins and the amounts of thermosetting resins to be added, and have concluded that initial adhesion strength can be ensured in a substrate having a primer layer containing an appropriate amount of a thermosetting resin having a bisphenol skeleton as an adhesive component.

[0019] Once it has been confirmed that adding an appropriate thermosetting resin can ensure the initial adhesion of the plating film, the next step is to address the issue of metal ion diffusion from the wiring metal. This also requires that the primer layer satisfy the characteristics (i) to (iv) described above. Furthermore, it is also necessary to ensure that the initial adhesion improvement effect of adding a resin, which acts as an adhesive agent, is not hindered.

[0020] The present inventors conducted studies while keeping the above-mentioned points in mind, and as a result, they concluded that adding a reinforcing agent to the resin component when forming a primer layer would enable the formation of a primer layer that can suppress the diffusion of metal ions. They then discovered that a reinforcing agent that strengthens the primer layer without impairing the properties (i) to (iv) of the primer layer and the effects of the adhesion agent component is suitable for containing titanium element (Ti) derived from a specified organotitanium compound or zirconium element (Zr) derived from a specified organozirconium compound. The present inventors arrived at the present invention based on the above-mentioned studies.

[0021] That is, the present invention provides a substrate for electroless plating comprising a base material and a primer layer formed on one or both sides of the base material, the primer layer containing a thermoplastic resin I as a main component and a resin II as a crosslinker component, wherein the primer layer contains, in addition to resins I and II, a thermosetting resin III having a bisphenol skeleton as an adhesion agent component, and a titanium element or a zirconium element as a reinforcing agent component, the content of resin III in the primer layer being 10% by mass or more and 48% by mass or less based on the mass of the entire primer layer, and the content of the titanium element or zirconium element calculated as a metal being 0.5% by mass or more and 3.0% by mass or less based on the mass of the entire primer layer.

[0022] The structure and manufacturing method of the electroless plating substrate according to the present invention will be described below. Also, an electroless plating method using the electroless plating substrate according to the present invention and an electroless plated structure manufactured thereby will be described.

[0023] A. Constitution of the Electroless Plating Substrate According to the Present Invention As described above, the present invention essentially comprises a substrate and a primer layer formed on the substrate.

[0024] A-1 Substrate The substrate for electroless plating can be made of either a conductive material such as metal or an insulating material such as resin. By utilizing the properties of electroless plating, resin, plastic, glass, ceramic, cellulose, fabric, and composites of these can be suitably used as insulating materials.

[0025] In particular, in the field of electronic materials, etc., substrates made of insulating resins are increasingly being used. Both thermoplastic and thermosetting resins can be used as insulating resin substrates. Examples of thermoplastic resins include polypropylene, polyethylene, polystyrene, acrylic, polyethylene terephthalate, polyphenylene ether, nylon, polyamide, polycarbonate, polyacetal, polyester, polybutylene terephthalate, polyphenylene sulfide, polyether ether ketone, polyurethane, polyimide, polyamide-imide, cyclic polyolefin, polyvinyl chloride, polyvinyl acetate, liquid crystal polymer, fluororesin, ABS resin, and AS resin. Examples of thermosetting resins include epoxy resin, phenolic resin, melamine resin, unsaturated polyester, urea resin, alkyd resin, polyurethane, and thermosetting polyimide. Damage caused by metal ions to wiring metals such as copper is a particularly significant problem with resin substrates such as polyimide. Therefore, the present invention is preferably applied to electroless plating substrates made of such resins.

[0026] There are no particular limitations on the shape and dimensions of the substrate. The substrate may be transparent, translucent, or opaque. There are also no particular limitations on the shape, and the substrate may be in the form of a plate, film, or the like.

[0027] A-2 Primer Layer The primer layer of the present invention essentially contains the three resins, Resin I, Resin II, and Resin III, and further contains titanium or zirconium as a reinforcing agent. Each component will be described below.

[0028] A-2-1 Resin I (Main Component) Resin I is a main component that serves as the framework for establishing the primer layer as a structure. Resin I, the main component, is a thermoplastic resin, and specific examples of the resin that can be used include polyester resin, polyimide resin, LCP resin, and polyethylene terephthalate resin.

[0029] A-2-2 Resin II (Crosslinking Agent Component) Resin II, the crosslinking agent component, is a component that crosslinks intramolecular and intermolecular bonds of the resin that constitutes the primer layer through a crosslinking reaction, thereby insolubilizing the resin. In the electroless plating process of the present invention, it also functions as a component that generates functional groups (amino groups) during the crosslinking reaction. The generated functional groups act as acceptors that capture precious metal nanoparticles, as described below, and promote the formation of a plated thin film.

[0030] The crosslinking agent is not particularly limited as long as it has the above-described crosslinking reaction and functional group generation effects. Examples of suitable crosslinking agents include melamine-based crosslinking agents, amine-based crosslinking agents, guanamine-based crosslinking agents, and glycoluril-based crosslinking agents. Melamine-based crosslinking agents are particularly suitable. Examples of melamine-based crosslinking agents include methoxyalkyl melamines such as hexamethoxymethylmelamine, hexamethoxyethylmelamine (HMM), dimethoxymethylmelamine, trimethoxymethylmelamine, tetramethoxymethylmelamine, pentamethoxymethylmelamine, and hexamethoxymethylmelamine. Other examples include alkoxymethylglycolurils such as tetramethoxymethylglycoluril, 1,3-bismethoxymethyl-4,5-bismethoxyethyleneurea, and bismethoxymethylurea.

[0031] A-2-3 Resin III (Adhesion Agent Component) The above-mentioned Resin I and Resin II have been used as components of the primer layer in the electroless plating process (Patent Document 1) by the applicant of the present application. The resin constituting the primer layer in the present invention is a three-component resin that further contains Resin III, which serves as the adhesion agent component. The adhesion agent component does not itself function as a so-called adhesion agent. The adhesion agent component in the present invention is a component that improves the adhesion strength between the substrate and the plating film by imparting appropriate rigidity and toughness to the primer layer composed of Resin I and Resin II.

[0032] Resin III, an adhesive component, is a resin that imparts rigidity to the primer layer. Resin III is a thermosetting resin having a bisphenol skeleton. The bisphenol skeleton is a skeleton composed of two phenol groups, as shown in the following formula (1), and is known to include bisphenol A, bisphenol B, bisphenol C, bisphenol E, bisphenol F, bisphenol M, bisphenol P, bisphenol S, bisphenol Z, and phenoxy resins depending on the substituent R. The bisphenol skeleton is a structure that is effective in imparting rigidity and toughness to the resin.

[0033]

[0034] Resins III in the present invention are preferably resins having a bisphenol skeleton, and particularly preferably resins having a bisphenol A skeleton or a bisphenol F skeleton. Specifically, resins III are preferably bisphenol A-type epoxy resins or bisphenol F-type epoxy resins having epoxy groups. Known thermosetting resins having epoxy groups include biphenyl-type epoxy resins, glycidyl ester-type epoxy resins, and alicyclic epoxy resins, but these resins without a bisphenol skeleton are ineffective. Furthermore, resins having an epoxy equivalent of 150 to 3,000 are preferred, and those having an epoxy equivalent of 170 to 500 are particularly preferred.

[0035] In the present invention, suitable adhesion to the plating substrate is imparted by controlling the content of Resin III in the primer layer. As described above, the addition of a thermosetting resin is effective in increasing the rigidity of the primer layer, but if the content is too high and the rigidity is too high, adhesion decreases. By appropriately adjusting the content of the thermosetting resin, the toughness of the primer layer can be ensured and optimal adhesion can be achieved. The content of Resin III is 10% by mass or more and 48% by mass or less, based on all resins constituting the primer layer. Preferably, it is 15% by mass or more and 40% by mass or less, and particularly preferably, it is 18% by mass or more and 38% by mass or less.

[0036] The contents of Resin I and Resin II in the primer layer are not particularly limited as long as they are within the range of the Resin III content. They may be set within a range that allows each resin to exert its function. Resin I is preferably 30% by mass or more and 80% by mass or less, more preferably 45% by mass or more and 75% by mass or less. Resin II is preferably 2% by mass or more and 25% by mass or less, more preferably 3% by mass or more and 20% by mass or less.

[0037] Furthermore, in the primer layer of the present invention, which is composed of a three-component system of resins I, II, and III, the ratio of the content of resin I to the content of resin III (resin I / resin III) is preferably 1 or more and 7 or less, and particularly preferably 1 or more and 4 or less. Resin I, the main component, is the resin that forms the framework of the primer layer. The primer layer inherently exhibits adhesion as an intermediate layer between the plating film and the substrate, and also functions to capture and fix precious metal nanoparticles, which serve as catalyst nuclei. If the content of resin I is low relative to resin III, this basic function of the primer layer may be reduced, resulting in a decrease in the adhesion strength of the plating film. Therefore, the ratio of the content of resin I to the content of resin III is preferably 1 or more. On the other hand, in order for resin III, the adhesion agent component, to fully exert its function, it may be undesirable for the content of resin I, the main component, to be too high relative to resin III. Therefore, the ratio is preferably 7 or less, and particularly preferably 4 or less.

[0038] The contents of resins I, II, and III in the primer layer described above can be measured by Fourier transform infrared spectroscopy (FT-IR), near infrared spectroscopy (NIR), gas chromatography mass spectrometry (GC-MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), nuclear magnetic resonance spectroscopy (NMR), or the like.

[0039] A-2-4 Titanium or Zirconium Element (Reinforcing Agent Component) The titanium or zirconium element contained in the primer layer as a reinforcing agent component is added to exert an inhibitory effect on the diffusion of metal ions by improving the physical and chemical strength of the resin that constitutes the primer layer.

[0040] As described below, the primer layer of the present invention is formed by applying and baking a primer liquid in which the above-mentioned Resins I to III are dissolved. The titanium or zirconium element serving as a reinforcing component in the primer layer is introduced by adding an organotitanium compound or organozirconium compound described below to the primer liquid. That is, the titanium or zirconium element serving as a reinforcing component in the present invention is an element derived from an organotitanium compound or organozirconium compound described below. The titanium or zirconium element exists in the primer layer in the form of a compound with the constituent elements and resins of the primer layer (titanium oxide, zirconium oxide, etc.) or in the form of atomic metal (metallic titanium, metallic zirconium).

[0041] In the present invention, the reinforcing effect of the titanium or zirconium element derived from an organotitanium compound or organozirconium compound in the primer layer is exerted based on the binding ability of the organometallic compound with other substances. Titanium and zirconium alkoxides and chelates are organic compounds capable of binding with a variety of substances, and can bond with the resin that constitutes the primer layer and crosslink various resins to form a rigid molecular structure. This increases the strength of the primer layer and reduces the mobility of metal ions. Titanium and zirconium alkoxides and chelates can also strengthen the bond between the primer layer and the substrate. The primer layer, which has these reinforcing effects, suppresses metal ion diffusion while strengthening the interface with the substrate, improving durability. Furthermore, titanium and zirconium alkoxides and chelates can also contribute to improving adhesion to plating films.

[0042] Furthermore, titanium and zirconium alkoxides and chelates are unlikely to interfere with the formation of an electroless plating film on a primer layer. In this regard, components other than organometallic compounds are also generally known to be capable of improving the strength of resins. For example, fillers (glass fillers) can be mixed and dispersed, or inorganic compounds can be mixed in the form of a basic solution. However, additives other than these organometallic compounds deteriorate the adsorption of precious metal nanoparticles supplied as catalytic nuclei before plating. In other words, the above-mentioned characteristic (iii) cannot be ensured. In contrast, titanium and zirconium alkoxides and chelates do not inhibit the adsorption of catalytic nuclei. Furthermore, titanium and zirconium alkoxides and chelates are highly stable and sufficiently soluble in resin solutions, and do not deteriorate the adsorption of catalytic nuclei or the surface roughness of the substrate.

[0043] The content of titanium or zirconium in the primer layer is 0.5% by mass or more and 3.0% by mass or less, calculated as metal, based on the total mass of the primer layer. This range is set because a content less than 0.5% by mass results in a poor function as a reinforcing component, while a content greater than 3.0% by mass results in an excessively high rigidity of the primer layer, which may result in reduced toughness and reduced adhesion. The content of titanium or zirconium in the primer layer is preferably 0.8% by mass or more and 2.5% by mass or less. The content of titanium or zirconium in the primer layer can be measured by X-ray fluorescence analysis (XRF), inductively coupled plasma (ICP)-optical emission spectroscopy (ICP-OES), inductively coupled plasma (ICP)-mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), or gravimetric analysis.

[0044] A-2-5 Other Components of Primer Layer The primer layer of the electroless plating substrate of the present invention essentially comprises the above-mentioned Resin I, Resin II, Resin III, and titanium or zirconium element, but may also contain other components (resins / compounds) to more effectively exert the effects of these components. Specifically, the primer layer of the electroless plating substrate of the present invention may contain the following components:

[0045] A-2-5-1 Curing Agent Component The curing agent component is a component that increases the hardness of the resin film that is the primer layer, thereby further improving heat resistance. As the curing agent component, an imidazole compound is contained in the primer layer. The imidazole compound particularly acts as a curing agent for the thermosetting resin having a bisphenol skeleton, which is the above-mentioned adhesion agent component (resin III). Although the thermosetting resin having a bisphenol skeleton is a resin that can be cured by heating without the use of a curing agent, the addition of a curing agent allows it to be cured more quickly and with a high degree of hardness. Here, improved heat resistance refers to adhesion at high temperatures of 150°C or higher.

[0046] Specific examples of imidazole compounds that serve as curing agent components include 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-benzyl-2-phenylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole. When adding a curing agent component to the primer layer, its content is preferably 2.0 mass% or less based on the mass of the entire primer layer. Adding more than 2.0 mass% can excessively increase the rigidity of the primer layer, potentially affecting adhesion. Depending on the resin composition of the primer layer, heat resistance may be exhibited even without the curing agent component, making the curing agent component an optional component.

[0047] Although known methods for curing thermosetting resins having a bisphenol skeleton include the addition of acid anhydrides such as tetrahydrophthalic anhydride and low-molecular-weight amine compounds such as dicyandiamide, these are not applicable to the present invention. Acid anhydrides may excessively increase the rigidity of the primer layer, reducing adhesion. Furthermore, low-molecular-weight amine compounds may affect the generation of acceptors (functional groups) in the primer layer. The addition of these curing agents, which affect the function of the primer layer, is not applicable to the present invention.

[0048] A-2-5-2 Photoacid Generator / Sensitizer As described below, the primer layer is formed by applying and baking a primer liquid in which each resin component is dissolved. The primer liquid, which serves as the precursor of the primer layer, may contain a photoacid generator (PAG) or a sensitizer as a reaction initiator. In such cases, compounds derived from these may be contained in the primer layer. The photoacid generator may also function as a curing accelerator for the above-mentioned resin III. Examples of photoacid generators include onium salts (sulfonium salts, iodonium salts, diazonium salts, etc.), nitrobenzyl esters, diazomethane, triazines, and the like, used alone or in combination. Examples of sensitizers include 9-methylanthracene, anthracenemethanol, acenaphthylene, thioxanthone, methyl-2-naphthyl ketone, 4-acetylbiphenyl, 1,2-benzofluorene, and the like. In the primer layer, the content of these compounds as reaction initiators is preferably 0.4% by mass or more and 10% by mass or less based on the total mass of the resins constituting the primer layer.

[0049] A-2-6 Primer Layer A preferred thickness for the primer layer formed on the substrate in the present invention is 0.05 μm or more and 1.5 μm or less. A thickness of less than 0.05 μm makes it difficult to form a plating film with sufficient adhesion in the subsequent electroless plating process. On the other hand, a primer layer exceeding 1.5 μm is undesirable because it may result in poor hardness and a loss of thin film and smoothness. The primer layer is more preferably 1.0 μm or less. The thickness of the primer layer can be adjusted by the concentration of the resin in the primer liquid and the application conditions, which will be described later. The glass transition temperature (Tg) of the primer layer having the above configuration is preferably 50°C or more and 350°C or less.

[0050] B. Method for manufacturing electroless plating substrate according to the present invention The electroless plating substrate according to the present invention can be manufactured by applying a primer liquid containing the above-mentioned components and baking (pre-baking) it at a predetermined temperature. The primer liquid is a precursor of the primer layer, and is a solution obtained by mixing and dissolving Resin I, Resin II, Resin III, an organic titanium compound consisting of at least one of titanium alkoxide and titanium chelate, or an organic zirconium compound consisting of at least one of zirconium alkoxide and zirconium chelate, and appropriate additives (curing agent component, reaction initiator) in a solvent. In this case, the substrate described above is used.

[0051] Regarding the composition of the primer liquid, the resin I, resin II, resin III, and additives used are those described above.

[0052] On the other hand, titanium or zirconium, which is a reinforcing component of the primer layer, is introduced by adding an organic titanium compound or an organic zirconium compound to the primer liquid. The organic titanium compound is at least one of titanium alkoxide and titanium chelate. The organic zirconium compound is at least one of zirconium alkoxide and zirconium chelate.

[0053] Titanium alkoxide and zirconium alkoxide are M(OR) ４ (M=Ti or Zr) in which an alkoxide ligand (OR) is coordinated to titanium-zirconia. In the present invention, R of the alkoxide ligand is preferably a hydrocarbon group having 1 to 6 carbon atoms. Specific examples of the hydrocarbon group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a pentyl group, and a hexyl group.

[0054] In the present invention, preferred titanium alkoxides include titanium tetramethoxide, titanium tetra-n-propoxide, titanium tetraisopropoxide, titanium tetraisobutoxide, titanium tetra-n-butoxide, titanium tetraethoxide, titanium tetra-2-ethylhexoside, and tetra-tert-butyl titanate. These may be used alone or in combination of two or more. Furthermore, preferred zirconium alkoxides include zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra-n-propoxide, zirconium tetraisopropoxide, and zirconium tetra-n-butoxide. These may be used alone or in combination of two or more.

[0055] Titanium chelates and zirconium chelates are organometallic compounds in which at least one ligand (chelating agent), such as β-diketone, β-ketoester, polyhydric alcohol, alkanolamine, or oxycarboxylic acid, is coordinated with titanium-zirconia. In the present invention, titanium chelates and zirconium chelates in which at least one β-diketone is the ligand are preferred. Examples of β-diketone ligands include 2,4-pentanedione, 2,4-hexanedione, 2,4-heptanedione, dibenzoylmethane, thenoyltrifluoroacetone, 1,3-cyclohexanedione, and 1-phenyl-1,3-butanedione.

[0056] In the present invention, preferred titanium chelates include titanium tetraacetylacetonate, titanium diisopropoxybis(acetylacetonate), titanium diisopropoxybis(ethylacetoacetate), etc. These may be used alone or in combination of two or more. Furthermore, preferred zirconium chelates include zirconium tetraacetylacetonate, zirconium dibutoxybis(ethylacetoacetate), zirconium tributoxymonoacetylacetonate, etc. These may be used alone or in combination of two or more.

[0057] The above-mentioned organotitanium compounds and organozirconium compounds may contain hydrolysates and partial condensates, such as tetra-n-butoxytitanium tetramer (a tetramer), tetra-n-butoxytitanium heptamer (a heptamer), and tetra-n-butoxytitanium decamer (a decamer).

[0058] Suitable solvents for the primer liquid that dissolve the above-described resins I, II, and III and the organic titanium compound or organic zirconium compound include ketones, ethers, esters, and aromatic hydrocarbons. Specific examples of the solvent include methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, cyclopentanone, cyclohexanone, 2-methoxy-1-propylene acetate, 2-methoxyethanol, 2-ethoxyethanol, 2-ethoxyethyl acetate, 1-methoxy-2-propyl acetate, 1,2-dimethoxyethaneethyl acetate, cellosolve acetate, propylene glycol monoethyl ether acetate, propylene glycol methyl ether acetate, methyl lactate, ethyl lactate, methyl pyruvate, ethyl pyruvate, ethyl 3-methoxypropionate, N-methyl-2-pyrrolidone, 1,4-dioxane, ethylene glycol monoisopropyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol dimethyl ether, and toluene.

[0059] As a result of dilution with the solvent, the concentration of each resin in the primer liquid differs from the content of the primer layer formed, but the blending ratio of each resin is the same. Therefore, with regard to the composition of the primer liquid, the concentration of each resin relative to the total resin in the liquid is preferably 0.06% by mass or more and 17% by mass or less for Resin I, more preferably 2% by mass or more and 10% by mass or less for Resin II. Resin III is preferably 0.2% by mass or more and 12% by mass or less, more preferably 0.7% by mass or more and 6% by mass or less for Resin III. Furthermore, the concentration of the reaction initiator is preferably 0.007% by mass or more and 2% by mass or less, more preferably 0.02% by mass or more and 0.1% by mass or less for Resin III. The concentration of the solvent is preferably 80% by mass or more and 90% by mass or less for Resin II.

[0060] The concentration of the organic titanium compound (titanium alkoxide, titanium chelate) or organic zirconium compound (zirconium alkoxide, zirconium chelate) in the primer liquid is preferably 0.5% by mass or more and 5.0% by mass or less, and more preferably 1.0% by mass or more and 3.5% by mass or less.

[0061] Furthermore, when an imidazole compound, which is a curing agent component, is introduced into the primer layer, the imidazole compound is dissolved in the primer liquid. In this case, the concentration of the imidazole compound is preferably 1.0 mass% or less. Since the curing agent component is an optional component of the primer layer, it is not essential to add the imidazole compound to the primer liquid. Therefore, the lower limit of the concentration of the imidazole compound in the primer liquid is 0 mass%.

[0062] The primer liquid can be prepared by sequentially adding and mixing each resin to a solvent. There is no restriction on the order in which the resins are added. Alternatively, stock solutions of each resin dissolved in a solvent may be mixed. Furthermore, a highly concentrated primer liquid may be prepared in advance and then diluted with a solvent.

[0063] The primer liquid can be applied to the substrate by various methods such as spraying, dipping, spin coating, roll coating, and various printing methods (screen printing, gravure printing, flexographic printing, inkjet printing, etc.).

[0064] The primer liquid applied to the substrate is then baked to form a primer layer, resulting in the electroless plating substrate of the present invention. The baking temperature is 150°C or higher and 260°C or lower. At temperatures below 150°C, it is difficult to form a good primer layer with sufficient adhesion. Furthermore, at temperatures above 260°C, it becomes difficult for the catalyst for plating deposition to adsorb. The baking temperature is preferably 180°C or higher and 240°C or lower. The baking process can be carried out in the air, or under reduced pressure or in a non-oxidizing atmosphere. During the baking process described above, the solvent in the primer liquid volatilizes and the resins harden. Furthermore, the crosslinking agent generates active functional groups (amino groups) on the surface of the primer layer, forming acceptors for the catalyst nuclei.

[0065] C. Electroless Plating Method According to the Present Invention In the electroless plating method according to the present invention, catalytic nuclei composed of noble metal nanoparticles are adsorbed onto the above-described electroless plating substrate, and then a plating film is formed by electroless plating. This electroless plating method may use a pre-prepared electroless plating substrate, or may be performed continuously from the preparation of the electroless plating substrate to the electroless plating step. In the latter case, the preparation of the electroless plating substrate is the same as that described above, and therefore, to avoid redundant description, the following will describe the steps after the preparation of the electroless plating substrate.

[0066] C-1 Pretreatment of Electroless Plating Substrate (Optional Step) As described above, the primer layer of the electroless plating substrate according to the present invention has functional groups (amino groups) on its surface that act as catalyst nuclei acceptors due to the action of Resin II as a crosslinker component. The functional groups generated by the application and baking of the primer solution are active and can adsorb precious metal nanoparticles in this state. The functional groups on the primer layer are then inactivated by irradiation with deep ultraviolet light having a wavelength of 300 nm or less. The inactivation of such functional groups by light irradiation contributes to the selective fixation of precious metal nanoparticles. That is, by performing patterning using a photomask or the like and selectively inactivating the functional groups by irradiation with deep ultraviolet light, it is possible to form a pattern of active functional groups on the substrate. Therefore, by performing the patterning and light irradiation before adsorption of precious metal nanoparticles, a desired wiring pattern can be formed using an electroless plating film. This step of forming a pattern of functional groups by irradiation with deep ultraviolet light is optional.

[0067] When irradiating the primer layer with deep ultraviolet light having a wavelength of 300 nm or less to inactivate the functional groups on the primer layer, the process can be the same as that commonly used in the semiconductor field. As a light source, ultraviolet lamps such as low-pressure mercury lamps and excimer lamps can be used. Low-pressure mercury lamps can irradiate ultraviolet light with wavelengths of 185 nm and 254 nm. As an excimer lamp, Xe ２ Examples of light sources that can be used include an excimer lamp (wavelength 172 nm), a KrBr excimer lamp (wavelength 206 nm), a KrCl excimer lamp (wavelength 222 nm), and a KrF excimer lamp (wavelength 248 nm). Using these light sources and an appropriate photomask, a desired functional group pattern can be formed. Patterning is also possible using ultraviolet laser light or the like.

[0068] C-2 Noble Metal Nanoparticle Adsorption Process Noble metal nanoparticles that serve as catalytic nuclei for plating film deposition are adsorbed onto the primer layer surface of a substrate that has been appropriately patterned, etc. The noble metal nanoparticles are fine particles made of a noble metal, with an average particle size of 1 nm to 100 nm. Preferable noble metals are Au, Pt, and Pd, which have suitable catalytic properties. The noble metal nanoparticles are preferably in a monodispersed state, and since particles with a particle size that is too small tend to aggregate, the particle size should be 1 nm or greater. Furthermore, noble metal nanoparticles with an excessively large particle size have a reduced ability to bond with functional groups in the primer layer. The average particle size of the noble metal nanoparticles is more preferably 3 nm to 30 nm.

[0069] A preferred method for adsorbing and fixing precious metal nanoparticles to the primer layer is to apply a dispersion of precious metal nanoparticles to the surface of the primer layer. In this case, an aqueous solution containing a sugar alcohol is preferred as the dispersion medium for the dispersion of precious metal nanoparticles. The sugar alcohol acts as a protective agent (dispersant) surrounding the precious metal nanoparticles and suppresses aggregation of the precious metal nanoparticles in the dispersion. Furthermore, the sugar alcohol bonded to the precious metal nanoparticles in the dispersion is substituted with functional groups on the surface of the primer layer, promoting bonding between the precious metal nanoparticles and the functional groups of the primer layer. Examples of sugar alcohols that can be used as such protective agents include glycerin, erythritol, xylitol, sorbitol, and mannitol. The dispersion medium is preferably an aqueous solution containing 0.1 g / L or more and 20 g / L or less of a sugar alcohol.

[0070] The dispersion of noble metal nanoparticles can be applied by spraying, dipping, using a spin coater, a roll coater, etc. After application of the dispersion, drying and washing may be carried out as necessary.

[0071] C-3 Electroless Plating Process A plating film is formed by electrolessly plating a substrate onto which noble metal nanoparticles have been adsorbed. The present invention can be applied to the electroless plating of various metals. Metals that can be used to form films by electroless plating include noble metals such as Au, Ag, Pt, and Pd, and base metals such as Cu, Ni, and Co. Known compositions of the electroless plating solution and electroless plating methods and conditions for the electroless plating of these metals can be applied.

[0072] For example, autocatalytic electroless plating solutions are widely known as electroless plating solutions for Au plating films. Autocatalytic electroless plating solutions contain an Au salt (Au ions), a reducing agent for reducing the Au ions, and appropriate additives. Preferably, a non-cyanide electroless plating solution is used. Suitable Au salts for autocatalytic plating solutions include tetrachloroauric acid (III), chloroauric acid (III), gold(I) chloride, gold(III) trifluoride, gold(I) monofluoride, gold(I) monobromide, gold(III) tribromide, hydroxygold(III) oxide, gold(III) triiodide, gold(III) trisnitrate, gold(I) nitrate, gold(I) sulfite salts, and hydrates or salts thereof. Known reducing agents for electroless plating solutions include formaldehyde, hydrazine, ascorbic acid, thiourea, hydroquinone, dimethylamine borane, hypophosphite, hydrogen peroxide, formic acid, hypophosphite, boron hydride, thiosulfuric acid, hydroxylamine, and sodium erythorbate, with ascorbic acid, boron hydride, hydroquinone, and formaldehyde being preferred.

[0073] C-4 Post-heat treatment step (curing step) The electroless plating step described above forms a plating film on the primer layer, essentially completing the electroless plating method of the present invention. However, to ensure the adhesive strength between the plating film and the substrate, it is preferable to add a post-heat treatment step. This post-heat treatment step involves heating at a temperature above the glass transition temperature to fluidize the primer layer and embed the noble metal nanoparticles in the primer layer.

[0074] The heating temperature in the post-heat treatment step is preferably within ±50°C of the glass transition temperature (Tg) of the primer layer, and is preferably 200°C or higher and 300°C or lower. Within this range, the primer layer becomes fluidized, and the noble metal nanoparticles are incorporated into the primer layer, increasing the adhesion strength. This heat treatment can be performed in an air atmosphere, but can also be performed in a reduced pressure atmosphere or a non-oxidizing atmosphere. The heating time is preferably 0.1 hours or higher and 2 hours or lower.

[0075] The post-heat treatment step ensures adhesion between the plating film and the substrate (primer layer). After the post-heat treatment step, post-treatment such as plasma ashing may be performed as needed.

[0076] D Electroless Plated Structure According to the Present Invention An electroless plated structure can be obtained by the electroless plating substrate and electroless plating method according to the present invention described above. This electroless plated structure is composed of the above-mentioned substrate and primer layer, and at least one metal plating film formed on the primer layer. In this case, the plating film formed on the primer layer is a plating film formed by electroless plating. When a further plating film is formed on the electroless plating film, the plating film may be an electroless plating film or an electrolytic plating film. There are no particular limitations on the thickness of each plating film.

[0077] In addition, the electroless plated structure according to the present invention does not require the presence of noble metal nanoparticles applied to the substrate during the manufacturing process. When the same type of noble metal is used for the noble metal nanoparticles and the plating film (for example, when Au nanoparticles are used as catalytic nuclei and Au plating is performed on top of them), the noble metal nanoparticles are integrated with the plating film and do not form a separate structure. Furthermore, even if the noble metal nanoparticles and the plating film are made of different metals, if the noble metal nanoparticles are fine, they may diffuse into the metal of the plating film and not be recognized as a separate structure.

[0078] Furthermore, the electroless plated structure according to the present invention can be used to form multilayer electrodes and wirings on which thin films of wiring metals such as copper are formed. Furthermore, the multilayer electrodes and wirings formed using the electroless plated structure according to the present invention do not require a barrier layer made of a thin film of nickel, nickel-phosphorus, a noble metal, or the like. As described above, this is because, in the present invention, the primer layer suppresses attack of the resin substrate by diffusion of metal ions from the metal wiring.

[0079] As described above, by optimizing the configuration of the primer layer, the electroless plating substrate of the present invention can improve the initial adhesion strength of the plating film to a level higher than conventional levels, and suppress metal ion diffusion to avoid attacking the base material.

[0080] These effects enable the plating film to which the present invention is applied to have durability. Furthermore, the electroless plating substrate of the present invention eliminates the need for the barrier layer that has been commonly used in the manufacture of metal wiring consisting of multilayer metal films. This is expected to lead to improved performance, such as higher frequency bands and lower resistance, for metal wiring and, ultimately, semiconductor devices.

[0081] Graph showing the initial adhesion strength of the plating film after plating on electroless plating substrates having primer layers of Examples 1 to 4 produced according to the present embodiment, and the change in adhesion strength due to a durability test (72 h, 168 h). Graph showing the initial adhesion strength of the plating film after plating on electroless plating substrates having primer layers of Comparative Example, Reference Example, and Conventional Example produced according to the present embodiment, and the change in adhesion strength due to a durability test (72 h, 168 h). Cross-sectional SEM photographs of the electroless plating substrates of Example 1 and Reference Example 1 produced according to the present embodiment after a durability test (after 168 hours).

[0082] Hereinafter, an embodiment of the present invention will be described. In this embodiment, as a preliminary study, a substrate for electroless plating was manufactured by forming a primer layer on a base material based on the primer layer used in the prior art (Patent Document 1) while adjusting the content of the thermosetting resin serving as an adhesive component. Then, electroless plating of a gold plating film was performed, and the change in the adhesion of the gold plating film depending on the content of the thermosetting resin serving as an adhesive component was studied.

[0083] The primer layer was formed by dissolving a polyester resin (UPICACOAT GV-110, manufactured by Japan U-Pica Corporation) as resin I (main component), a melamine resin (CYMEL (registered trademark) 303LF, manufactured by Allnex) as resin II (crosslinking agent component), a bisphenol A-type epoxy resin (jER828, manufactured by Mitsubishi Chemical Corporation) as resin III (adhesion agent component), and a photoacid generator (CYCAT (registered trademark) 4040, manufactured by Allnex) in a cyclohexane solvent, and then coating and baking the primer liquid on the substrate.

[0084] In this embodiment, ten types of primer layers (primer layer A to primer layer J) were formed using ten types of primer liquids (primer liquid A to primer liquid J) with different compositions based on Resin I, Resin I, and Resin III. In addition, to compare this embodiment with the prior art, a primer liquid (primer liquid K) that did not contain bisphenol A-type epoxy resin, which is Resin III (adhesive agent component), was prepared and a primer layer (primer layer K) was formed. The resin compositions of the primer liquids evaluated in this embodiment are as shown in Table 1.

[0085]

[0086] To form a primer layer after applying the primer liquid, 4 mL of the primer liquid was applied to a glass substrate (dimensions: 10 cm x 10 cm) by spin coating. The substrate after applying the primer liquid was then prebaked to remove the solvent and form primer layers (primer layer A to primer layer K). The prebaking was performed by heating in an air atmosphere in a forced circulation oven at 260°C for 30 minutes. The composition of each formed primer layer was measured by combined analysis using gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy.

[0087] Next, a gold plating film was formed on the electroless plating substrate manufactured by the above process. In this embodiment, the surface of the primer layer was exposed to light in a predetermined pattern to partially deactivate the acceptors (amino groups). The exposure process used a photomask to form a linear pattern (L / S = 5 μm) with a width of 5 μm and an interval of 5 μm. A deep ultraviolet light exposure machine (Deep UV Multilight, manufactured by Ushio Inc.) was used to irradiate the surface with deep ultraviolet light at a wavelength of 254 nm at 800 mJ / cm. ２ Irradiated with.

[0088] Then, an Au nanoparticle dispersion (SEADCAT (registered trademark) CAT Au-10, manufactured by EEJA Corporation) was applied to the surface of the substrate (primer layer) after the exposure treatment as precious metal nanoparticles that would become catalytic nuclei. This Au nanoparticle dispersion was a dispersion of Au nanoparticles with a particle size of 16 nm. In the Au nanoparticle dispersion application treatment, the substrate was immersed in the dispersion at room temperature for 15 minutes and then dried in the atmosphere.

[0089] After the Au nanoparticles were fixed to the primer layer, an Au plating film was formed by electroless plating. An Au electroless plating solution (AC FAB (registered trademark) AU-ACG3000GX, manufactured by EEJA Corporation) was used as the electroless plating solution, and the Au plating film was formed at a plating temperature of 65°C for a plating time of 5 minutes. These plating conditions were intended to result in an Au plating film with a thickness of 50 nm.

[0090] After the formation of the Au plating film, a heat treatment (curing process) was performed to sink the Au nanoparticles into the primer layer. The curing process involved heating in air at 260°C for 30 minutes in a static oven. Through these processes, an Au plating film was formed on the electroless plating substrates of each Example, Conventional Example, and Comparative Example.

[0091] Finally, a Cu plating film was formed on the Au plating film formed above. The Cu plating was performed using a commercially available electrolytic Cu plating solution (MICROFAB (registered trademark) Cu250, manufactured by EEJA Corporation) at a current density of 3 A / dm ２ The copper foil was subjected to electrolytic plating treatment at 4000 kJ / min for 20 minutes to form a Cu plating film having a thickness of about 15 μm.

[0092] After the Cu plating film was formed, the adhesion (adhesion strength) of the plating film was evaluated. The evaluation of adhesion strength was based on the peel strength obtained by a peel test (test conditions: 90° tensile test according to JIS K 6854-1). The pass value in the cross-cut test evaluation in the prior art (Patent Document 1) is 0.2 to 0.3 N / mm when converted to the peel strength in the peel test employed in this embodiment. With reference to this, in this embodiment, samples with a peel strength of 0.4 N / mm or more were judged to pass. The evaluation results are shown in Table 2, along with the compositions of each primer layer (primer layer A to primer layer K).

[0093]

[0094] Looking at Table 2 for the effect of the thermosetting resin (resin having a bisphenol skeleton) which is the adhesive agent component (resin III), the substrates having primer layers A to G have improved adhesion strength compared to the substrate having the conventional primer layer K. This suggests that the addition of the thermosetting resin having a bisphenol skeleton which is the adhesive agent component works favorably in the configuration of the primer layer.

[0095] However, it is also undesirable to add an excessive amount of the bisphenol skeleton resin, which is an adhesive agent component. This is because the primer layers of the electrolessly plated substrates having primer layers H to J contain an excess of adhesive agent components exceeding 48% by mass, resulting in lower adhesion strength than primer layer H, which does not contain an adhesive agent component. Furthermore, the results of primer layer J, which has extremely low adhesion strength, show that the thermoplastic resin (polyester resin), which is the main component (resin I), is essential for the primer layer.

[0096] [Confirmation of the effect of the reinforcing agent component (titanium element)] The above preliminary test confirmed the effect of the thermosetting resin having a bisphenol skeleton on improving initial adhesion strength. Therefore, as an embodiment of the electroless plating substrate according to the present invention, a primer layer containing titanium element as a reinforcing agent component was produced based on the composition of primer layer A in the above preliminary test.

[0097] In this embodiment, the titanium alkoxide tetra-tert-butyl titanate was added to the primer liquid as an organic titanium compound that serves as a precursor for the toughening agent component (Examples 1-4, Comparative Examples 1 and 2). In some examples, a primer liquid was prepared to which an imidazole compound (1-benzyl-2-methylimidazole) was added as a curing agent component (Example 1). In this embodiment, in addition to the primer layers containing these toughening agents, the same evaluation was also performed on primer layers made with the primer liquids (A, B, and K) examined in the preliminary test described above (these are referred to as Reference Examples 1 and 2 and the Conventional Example). The compositions of the primer liquids examined in this embodiment are shown in Table 3.

[0098]

[0099] Then, using the same conditions and steps as in the preliminary test, a primer solution was applied to a polyimide film substrate (Kapton 300H: dimensions 10 cm x 10 cm) and baked to form a primer layer, thereby producing a substrate for electroless plating. The composition of the primer layer formed in each of the Examples, Reference Examples, and Comparative Examples is shown in Table 4.

[0100]

[0101] After forming a primer layer to prepare a substrate for electroless plating, gold plating was performed in the same pattern as in the preliminary test, and then copper plating was performed on the gold plating. Copper plating was performed using an electrolytic copper plating solution (MICROFAB (registered trademark)-Cu250, manufactured by EEJA Co., Ltd.) at room temperature with a current density of 3 A / dm ２ The plating was carried out for 20 minutes (film thickness: about 15 μm).

[0102] After the copper plating film was formed, durability was evaluated by a heat resistance test. In the heat resistance test, the sample was exposed to an air atmosphere at 150°C for 72 hours (3 days) and 168 hours (7 days). After this heat resistance test, the adhesion strength was measured under the same conditions as the preliminary test. The results of these measurements are shown in Table 5. Graphs showing the change in adhesion strength between the initial stage and the durability test are shown in Figures 1 and 2.

[0103]

[0104] Referring to Table 5 and Figures 1 and 2, the durability improvement effect of titanium, a reinforcing agent, can be confirmed in the primer layers of Examples 1 to 4. The primer layer of Reference Example 1, which served as the base for the primer layers of each Example, had the highest initial adhesion strength (1.39 N / mm), but the adhesion strength after the heat resistance test was 0.29 N / mm, a decrease of approximately 80% or more compared to the initial adhesion strength. The primer layer of Example 1 had an initial adhesion strength slightly lower than that of Reference Example 1 (1.12 N / mm), but the adhesion strength after the heat resistance test was 0.91 N / mm, maintaining more than 70% of the initial adhesion strength. Examples 2 to 4 also maintained a high rate of high adhesion strength. Furthermore, the adhesion strength of each Example after the durability test (after 168 hours) clearly exceeded the adhesion strength (0.4 N / mm) that was the pass standard in the preliminary test described above.

[0105] FIG. 3 shows cross-sectional SEM photographs (magnification: 50,000 times) of samples of Example 1 and Reference Example 1 after the durability test (after 168 hours). In Example 1, no defects were observed at the interface between the copper plating layer and the gold plating layer or at the interface between the gold plating layer and the polyimide substrate. On the other hand, in Reference Example 1, void formation was confirmed at the interface between the copper plating layer and the gold plating layer, and discoloration due to copper diffusion was observed near the voids in the polyimide substrate. It is believed that these voids and copper diffusion caused the decrease in adhesion strength in Reference Example 1. The results of this cross-sectional observation also confirmed the effect of titanium, a reinforcing agent, on improving durability.

[0106] From the above results, it can be said that adding a reinforcing agent to the primer layer is effective in improving the durability of adhesion strength, taking into account the diffusion of metal ions (copper ions). However, adding an excessive amount of the reinforcing agent will not produce desirable results. The primer layers of Comparative Examples 1 and 2, in which the titanium content in the primer layer exceeded 3.0 mass%, not only exhibited poor initial adhesion strength, but also showed a significant decrease in adhesion strength in durability tests.

[0107] Furthermore, when comparing the primer layers of Examples 1 and 2, which have the same basic composition, the primer layer of Example 1, which contains a curing agent component (imidazole compound), has higher adhesion strength. However, when compared with a primer layer of a different composition, such as Example 3, it is found that the same adhesion and durability as Example 1 is exhibited even without the curing agent component. This also confirms that the imidazole compound, which is a curing agent component, is not essential.

[0108] From the above-described study results of this embodiment, it was confirmed that, in order to improve the adhesion strength of the plating film, a thermosetting resin having a bisphenol skeleton, which is an adhesion agent component, is effective in improving the initial adhesion strength, and that the addition of an organotitanium compound, which is a reinforcing agent component, is necessary to impart durability that can maintain the increased adhesion strength.

[0109] The electroless plating substrate of the present invention has a primer layer made of a three-component system (resins I, II, and III), with resin III being a predetermined thermosetting resin. Furthermore, in the present invention, the primer layer made of the three-component resin contains titanium or zirconium as a reinforcing agent. Due to these characteristics, the electroless plating substrate provided with the primer layer of the present invention improves the initial adhesion strength of the plating film and exhibits durability.

[0110] The durability of the adhesion strength of a plating film is largely affected by the diffusion of metal ions such as copper, but the present invention reduces the effect of these metal ions. Therefore, the electroless plating substrate of the present invention makes it possible to eliminate the need for a barrier layer below the wiring metal layer, which has been used until now. This contributes to improving the manufacturing efficiency and reducing the manufacturing cost of various wiring substrates, and can also contribute to reducing the height and improving the performance of circuits.

Claims

1. A substrate for electroless plating comprising a base material and a primer layer formed on one or both sides of the base material, the primer layer containing a thermoplastic resin I as a main component and a resin II as a crosslinking agent component, wherein the primer layer contains, in addition to resins I and II, a thermosetting resin III having a bisphenol skeleton as an adhesion agent component, and a titanium element or zirconium element as a reinforcing agent component, the content of resin III in the primer layer being 10% by mass or more and 48% by mass or less based on the mass of the entire primer layer, and the content of titanium element or zirconium element converted to metal being 0.5% by mass or more and 3.0% by mass or less based on the mass of the entire primer layer.

2. The substrate for electroless plating according to claim 1, wherein the primer layer further contains an imidazole compound as a curing agent component in an amount of 2.0% by mass or less based on the mass of the entire primer layer.

3. The substrate for electroless plating according to claim 1, wherein resin I is a polyester resin, a polyimide resin, an LCP resin, or a polyethylene terephthalate resin, and resin II is a resin containing an amino group.

4. The substrate for electroless plating according to claim 1 or 2, wherein the ratio of the content of resin I to the content of resin III is 1 or more and 7 or less.

5. A method for producing a substrate for electroless plating according to claim 1 or 2, comprising the steps of: applying a primer liquid onto a substrate, the primer liquid containing resin I as a main component, resin II as a crosslinking agent component, resin III as an adhesive component, and an organic titanium compound consisting of at least one of titanium alkoxide and titanium chelate, or an organic zirconium compound consisting of at least one of zirconium alkoxide and zirconium chelate, as a reinforcing agent component; and baking the applied primer liquid at a temperature of 150°C to 260°C to form a primer layer.

6. The method for producing a substrate for electroless plating according to claim 5, wherein the primer liquid further contains an imidazole compound as a curing agent component.

7. An electroless plating method for forming a metal plating film on a substrate by electroless plating, comprising the steps of: applying a primer liquid onto the substrate, the primer liquid containing resin I as a main component, resin II as a crosslinking agent component, resin III as an adhesion agent component, and a reinforcing agent component, an organic titanium compound composed of at least one of titanium alkoxide and titanium chelate, or an organic zirconium compound composed of at least one of zirconium alkoxide and zirconium chelate; baking the applied primer liquid at 150°C or higher and 260°C or lower to form a primer layer; dispersing a noble metal nanoparticle catalyst composed of a noble metal with a particle size of 1 nm or higher and 100 nm or lower on the surface of the primer layer; and forming a plating film on the surface of the primer layer using an electroless plating liquid.

8. The electroless plating method according to claim 7, wherein the primer liquid further contains an imidazole compound as a curing agent component.

9. An electroless plating structure comprising a substrate for electroless plating according to claim 1 or 2, and at least one layer of a metal plating film formed on the surface of the primer layer of the substrate for electroless plating.

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