Adhesive structure and adhesive method

Abstract

To make it possible to strongly bond base materials of the same kind or different kinds to each other by improving an adhesive strength between a surface of the base material and an adhesive without roughening or deteriorating a surface of the base material with a chemical solution, even if the base material and the adhesive are difficult to adhere.SOLUTION: In an adhesive structure consisting of a first base material, a second base material, and an adhesive interposed between the base materials, a functional group is present on at least one surface of the first or second base material, and at least a portion of the functional group and the functional group of the adhesive are combined without reacting with each other.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an adhesive structure and an adhesive method for bonding different or the same substrates.

Background Art

[0002] For example, in the manufacturing processes of various products such as printed circuit boards, semiconductor substrates, touch panels, liquid crystal substrates, sports goods, stationery, etc., there is a process of bonding the same or different substrates, and an adhesive is sometimes used in such a process.

[0003] Incidentally, one of the reasons for using an adhesive is that when bonding different substrates, if these are directly bonded together, stress may occur due to the difference in the coefficient of thermal expansion, resulting in cracks or the like in the substrates. However, by interposing an adhesive between the substrates, the adhesive acts as a buffer material, and reasons such as being able to prevent the above-mentioned cracks and the like can be cited.

[0004] Here, if the substrate is of a difficult-to-adhere type such as Teflon or the like, or if the adhesive has a low dielectric constant or high heat resistance, the adhesive strength between the surface of the substrate and the adhesive is weak, and as a result, defects in the product formed by bonding the substrates may be caused.

[0005] Therefore, conventionally, when using the above-mentioned difficult-to-adhere substrates or difficult-to-adhere adhesives, pretreatment such as roughening or altering the substrate surface is performed in order to improve the adhesive strength between the substrate surface and the adhesive. For this pretreatment, for example, strong drugs or special chemical solutions such as metallic sodium ammonia water and permanganic acid are used.

[0006] However, the above-mentioned strong drugs and special chemical solutions have a large environmental burden due to their use and waste liquid, and it is expected that it will be difficult to continue using them in the future in view of various environmental conservation requirements in recent times.

[0007] On the other hand, as a method for bonding two substrates without using adhesive, for example, as shown in Patent Document 1, there is a method in which -OH groups are generated on the surface of a fluororesin sheet by plasma treatment, and the surface of this fluororesin sheet is bonded to a metal member.

[0008] However, the actual adhesive strength obtained through functional group reactions, such as dehydration condensation by -OH groups, is not particularly strong, and sufficient adhesive strength has not been achieved to date with difficult-to-adhere substrates such as Teflon. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 5152784 [Overview of the project] [Problems that the invention aims to solve]

[0010] Therefore, the present invention was made to solve the above-mentioned problems all at once, and its main objective is to improve the adhesive strength between the substrate surface and the adhesive without roughening or altering the substrate surface with a chemical solution, even if the substrate or adhesive is difficult to bond, and ultimately to enable strong bonding between substrates of the same or different types. [Means for solving the problem]

[0011] In other words, the adhesive structure according to the present invention is an adhesive structure comprising a first substrate, a second substrate, and an adhesive interposed between these substrates, characterized in that a functional group is present on at least one surface of the first substrate or the second substrate, and at least a portion of that functional group and the functional groups of the adhesive are bonded together without reacting with each other.

[0012] With this type of adhesive structure, at least some of the functional groups present on the surface of at least one of the first and second substrates and the functional groups of the adhesive are bonded together without reacting with each other, for example, by covalent bonds or molecular bonds. This improves the mechanical strength between the surface of at least one of the substrates and the adhesive. As a result, even if one of the first or second substrates is made of a material that is difficult to adhere to, such as Teflon, or if the adhesive is difficult to adhere to, the adhesive strength between the surface of one of the substrates and the adhesive can be improved without roughening or altering the substrate surface with the chemical solution, and consequently, the first and second substrates can be firmly bonded together.

[0013] It is preferable that functional groups are present on the surfaces of both the first and second substrates, and that at least some of these functional groups and the functional groups of the adhesive are bonded to each other without reacting. With this method, even if both the first and second substrates are difficult to adhere to, the adhesive strength between the surface of each substrate and the adhesive can be improved without roughening or altering the surface of both substrates with the chemical solution.

[0014] In one embodiment for obtaining sufficient adhesion to a substrate that is difficult to adhere to, it is preferable that the functional group present on at least one surface of the first or second substrate, or the functional group in the adhesive, is at least one of -H, -NHx, -COOH, -C=O, -OH, -F, or -CFx. Hereinafter, x is a natural number of 1 or more.

[0015] It is preferable that the functional group present on at least one surface of the first or second substrate is -NHx. This design offers particularly excellent functionality in improving the adhesion between difficult-to-bond substrates such as fluororesins and low-dielectric adhesives.

[0016] The effects of the present invention are more pronounced when the substrate is difficult to adhere to. Examples of such substrates include those in which one or both of the first and second substrates are made of PS (polystyrene), PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PEN (polyethylene naphthalate), PET (polyethylene terephthalate), or metal.

[0017] Furthermore, an embodiment in which the adhesive strength between the substrate and the adhesive is dramatically improved compared to conventional methods is one in which one of the first substrate and the second substrate is made of copper, ceramic, or gold, and the functional groups are formed on its surface by plasma treatment, and at least a portion of the functional groups and the functional groups contained in the epoxy adhesive or silicone adhesive are bonded together without reacting with each other.

[0018] Furthermore, the effects of the present invention are more pronounced when the dielectric constant of the adhesive is low or when the heat resistance of the adhesive is high. Examples of such adhesives include those with a relative permittivity Dk of 3.0 or less, or those with a glass transition temperature Tg of 250°C or higher.

[0019] Furthermore, the bonding method according to the present invention is characterized by generating functional groups on at least one surface of the first substrate or the second substrate by plasma treatment, bonding at least a portion of these functional groups with the functional groups of the adhesive without causing them to react with each other, and bonding the surface of the first substrate and the surface of the second substrate via the adhesive. Even with this type of bonding method, it is possible to achieve the same effects as the bonding structure described above. [Effects of the Invention]

[0020] According to the present invention configured in this manner, even if the substrate or adhesive is difficult to bond, the adhesive strength between the substrate surface and the adhesive can be improved without roughening or altering the substrate surface with the chemical solution, and consequently, the same or different types of substrates can be firmly bonded together. [Brief explanation of the drawing]

[0021] [Figure 1] A diagram schematically showing the configuration of the plasma processing apparatus according to the present embodiment. [Figure 2] A flowchart showing the procedure of the bonding method in the same embodiment. [Figure 3] A conceptual diagram showing the configuration of the bonding structure in the same embodiment. [Figure 4] A conceptual diagram showing the bonding mode of the functional group in the same embodiment. [Figure 5] Analysis result of X-ray analysis of the bonding structure in the same embodiment. [Figure 6] A conceptual diagram for evaluating the bonding strength of the bonding structure in the same embodiment. [Figure 7] Result of X-ray analysis of the PTFE film before imparting the functional group in the same embodiment. [Figure 8] Result of X-ray analysis of the PTFE film after imparting the functional group in the same embodiment. [Figure 9] A conceptual diagram showing the configuration of the bonding structure in other embodiments. [Embodiments for Carrying Out the Invention]

[0022] The bonding structure and the bonding method according to an embodiment of the present invention will be described with reference to the drawings.

[0023] [Device Configuration] First, the device for manufacturing the bonding structure will be described.

[0024] This apparatus is a plasma processing apparatus 100 for plasma treatment of the surface of a substrate. As shown in Figure 1, it comprises a vacuum chamber 1, a lower electrode 2 provided inside the vacuum chamber 1 to support the substrate W, an upper electrode 3 positioned opposite the substrate W inside the vacuum chamber 1, and a high-frequency power supply 4. The apparatus is configured to generate plasma P inside the vacuum chamber 1 by supplying high-frequency power of, for example, 13.50 MHz (1 kHz to 2.45 GHz) from the high-frequency power supply 4 to the lower electrode 2 and grounding the upper electrode 3. Furthermore, depending on the substrate material, the type of reaction gas, etc., this plasma processing apparatus 100 is configured to switch to a method in which the lower electrode 2 is grounded and high-frequency power is supplied to the upper electrode 3.

[0025] In this embodiment, the plasma processing apparatus 100 is used to generate functional groups on the surface of a substrate W, and a process gas G corresponding to the functional groups to be generated is supplied into the vacuum chamber 1 under reduced pressure of 0.1 to 10000 Pa.

[0026] <Adhesion method> Next, the procedure for bonding a first substrate and a second substrate of different or the same type using an adhesive, with reference to the flowchart in Figure 2 and the conceptual diagram in Figure 3, will be explained using the plasma processing apparatus described above.

[0027] The first and second substrates are, for example, flat plates, and specifically, they can be made of poorly bonded resins such as PS (polystyrene), PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PEN (polyethylene naphthalate), or PET (polyethylene terephthalate), or of metals such as copper, aluminum, or iron.

[0028] The following describes a method for bonding two different substrates, a first substrate and a second substrate, which are used, for example, as printed circuit boards with high-frequency characteristics of 60-80 GHz for 5G applications. The description will focus on the case where the first substrate is made of fluororesin and the second substrate is made of metal such as copper.

[0029] However, the applications and materials of the substrate are not limited to these; for example, the substrate may be used in the manufacturing processes of various products such as semiconductor substrates, touch panels, liquid crystal substrates, sporting goods, and stationery.

[0030] First, the first substrate (hereinafter also referred to as the resin substrate) is subjected to plasma treatment using the plasma processing apparatus described above, thereby forming a dangling bond on the surface of the resin substrate as shown in Figures 2 and 3 (S1).

[0031] Specifically, by plasma etching the resin substrate, F atoms are separated from the CF bonds on the surface, forming dangling bonds (unbonded bonds) of C atoms, thereby activating the reactivity of the resin substrate surface.

[0032] Next, as shown in Figures 2 and 3, a desired functional group (hereinafter also referred to as the first functional group) is attached to the dangling bond (S2).

[0033] Specifically, by selecting a gas species corresponding to the first functional group as the process gas mentioned above and supplying it into the vacuum chamber, the first functional group is plasma-activated and bonded to the dangling bond.

[0034] In this embodiment, an amino group, which is a hydrophilic functional group, is formed on the surface of the resin substrate as the first functional group, and the process gas is an amino group-containing gas such as ammonium gas.

[0035] More specifically, ammonium gas is supplied to a vacuum chamber at a flow rate of 1 sccm or more, and under an atmosphere where the process pressure is maintained at 0.1 to 10,000 Pa, a high frequency of 1 kHz to 2.45 GHz is applied at 0.01 to 3 W / cm². 2 High-frequency reduced-pressure plasma treatment is performed by applying power at this power density. Furthermore, the process gas may be a mixture of an amino group-containing gas and a noble gas or inert gas (He, Ne, Ar, Kr, Xe, N2).

[0036] As a result, the amino groups, such as -NH (secondary amino group) and -NH2 (primary amino group), are plasma-activated and bond with the dangling bond formed on the surface of the resin substrate. Note that the first functional group is not limited to the amino group -NHx; it may also be -H, -COOH, -C=O, -OH, -F, or -CFx, etc.

[0037] Here, the formation of the first functional group in S2 may be carried out together with the formation of the dangling bond in S1, or it may be carried out as a separate step from S1 after the formation of the dangling bond in S1, taking into consideration, for example, the material of the substrate and the type of the first functional group.

[0038] In other words, if a resin substrate is plasma-etched while supplying an amino group-containing gas into a vacuum chamber, the formation of dangling bonds and amino groups proceed simultaneously, so steps S1 and S2 proceed simultaneously as a single process.

[0039] On the other hand, if a resin substrate is plasma-etched while supplying a process gas other than an amino group-containing gas, such as a halogen gas, into a vacuum chamber, the process gas is switched from the halogen gas to the amino group-containing gas after the formation of dangling bonds, and the first functional group is formed, so that steps S1 and S2 proceed as separate processes.

[0040] Next, as shown in Figure 3, the second substrate (hereinafter also referred to as the copper substrate) is subjected to plasma treatment using the plasma processing apparatus described above, thereby forming so-called microcracks on the surface of the copper substrate (S3). The microcracks referred to here include everything from minute anchors to atomic lattice defects.

[0041] Specifically, by plasma etching a copper substrate, defects ranging from a few nanometers to several hundred nanometers or smaller (microcracks, including everything from minute anchors to atomic lattice defects) are formed on the surface to serve as structures for bonding functional groups.

[0042] Next, as shown in Figure 3, a desired functional group (hereinafter also referred to as the second functional group) is bonded to a microcrack, which is a microstructure (S4). Specifically, by selecting a gas species corresponding to the second functional group as the process gas mentioned above and supplying it into the vacuum chamber, the second functional group is plasma-activated and bonded to microcracks.

[0043] In this embodiment, -H or -OH (hydroxyl group) is formed as a second functional group on the surface of the copper substrate, and the process gas used contains hydrogen gas, which may be hydrogen gas itself, or hydrogen gas mixed and diluted with a noble gas or inert gas.

[0044] More specifically, hydrogen gas is supplied to a vacuum chamber at a flow rate of 1 sccm or more, and under an atmosphere where the process pressure is maintained at 1 to 1,000 Pa, a high frequency of 1 to 100 MHz is applied at 0.01 to 3 W / cm². 2 High-frequency reduced-pressure plasma treatment is performed by applying power at this power density. Furthermore, the process gas may be a mixture of hydrogen gas and noble gases or inert gases (He, Ne, Ar, Kr, Xe, N2).

[0045] As a result, -H and -OH are plasma-activated and bond to microcracks formed on the surface of the copper substrate. The second functional group is not limited to -H and -OH, but may also be -NHx, -COOH, -C=O, --F, or -CFx, etc.

[0046] Here, similar to the formation of the first functional group in S2, the formation of the second functional group in S4 may be carried out together with the formation of microcracks in S3, or it may be carried out as a separate step from S3 after the formation of microcracks in S3, taking into consideration, for example, the material of the substrate and the type of second functional group.

[0047] In other words, if a copper substrate is plasma-etched while a mixed gas, such as hydrogen gas and argon gas, is supplied into a vacuum chamber, the formation of microcracks and the formation of functional groups such as -H and -OH proceed simultaneously, so steps S3 and S4 proceed simultaneously as a single process.

[0048] On the other hand, if a copper substrate is plasma-treated while supplying a process gas other than hydrogen gas, such as argon gas, into a vacuum chamber, microcracks can be formed on the copper substrate. Subsequently, by switching the process gas from argon gas to hydrogen gas or a mixture of hydrogen gas and a noble gas or inert gas, a second functional group can be formed, and steps S3 and S4 proceed as separate processes.

[0049] Through the steps S1 to S4 described above, the first and second functional groups are formed on the surfaces of the first and second substrates, respectively, with a thickness ranging from atomic level to several tens of nanometers.

[0050] In this embodiment, the first functional group is formed on the first substrate, a resin substrate, and then the second functional group is formed on the second substrate, a copper substrate. However, the order of these steps may be reversed, or they may be performed simultaneously using multiple plasma processing devices.

[0051] Then, as shown in Figures 2 and 3, the surface of the first resin substrate on which the first functional group is formed and the surface of the second copper substrate on which the second functional group is formed are placed facing each other, and these first and second substrates are bonded together via an adhesive (S5).

[0052] As shown in Figure 3, adhesives are organic substances having a functional group (hereinafter also referred to as a third functional group), and examples include epoxy adhesives and silicone adhesives. Examples of the third functional group include -H, -NHx, -COOH, -C=O, -OH, -F, or -CFx.

[0053] Specifically, the adhesive used here is one with a low dielectric constant and high high-frequency characteristics, such as a relative permittivity Dk of 3.0 or less, making it difficult to bond. However, other adhesives that are difficult to bond include those with high heat resistance, such as those with a glass transition temperature (Tg) of 250°C or higher. Furthermore, adhesives are not necessarily limited to those that are difficult to bond; they may also be those with high adhesion, and the dielectric constant (Dk) and glass transition temperature (Tg) are not necessarily limited to the numerical ranges mentioned above.

[0054] This bonding process S5 is a process of applying a load to the first and second substrates in order to make the surfaces of the first and second substrates as flat as possible and bring them as close together as possible. Specifically, pressure is applied to bring these surfaces closer together, for example, to a few nanometers, and in this case, the load applied to the first and second substrates is 0.5 kg / cm². 2 That is what they say. Furthermore, the method for bringing the surface of the first substrate and the surface of the second substrate into close contact is not limited to pressurization; other methods such as vacuuming may be used, and these may be changed as appropriate.

[0055] In this way, when the surfaces of the first substrate and the second substrate become as flat as possible, for example, approaching a distance of a few nanometers, an attractive force is generated between the first functional group and the third functional group, as well as an attractive force is generated between the second functional group and the third functional group.

[0056] As a result, the first substrate and the second substrate are bonded together by covalent bonds, hydrogen bonds, or molecular bonds between the first functional group and the third functional group, and by covalent bonds, hydrogen bonds, or molecular bonds between the second functional group and the third functional group.

[0057] <Adhesive structure> The surfaces of the first substrate and the second substrate, which are bonded in this manner, are not roughened or altered, and possess extremely high flatness.

[0058] Furthermore, the adhesive structure, comprising a first substrate, a second substrate, and an adhesive interposed between these substrates, is characterized in that at least some of the functional groups present on the surface of at least one of the first or second substrates and the functional groups of the adhesive are bonded together without reacting with each other.

[0059] In this embodiment, functional groups are present on the surfaces of both the first and second substrates, and at least some of these functional groups are bonded to the functional groups of the adhesive without reacting with each other.

[0060] Specifically, in the example shown in Figure 4(a), an attractive force is generated between the terminal functional groups present on one surface of the first and second substrates and the -H atoms present on the other surface of the first and second substrates due to their differing polarities. This force causes at least some of the functional groups present on the surfaces of the first and second substrates to be bonded together by covalent or hydrogen bonds.

[0061] Furthermore, in the example shown in Figure 4(b), an attractive force is generated by the polarity caused by the uneven distribution of electrons within the molecule, and this force causes the functional groups present on the surfaces of the first and second substrates to be bonded together by intermolecular forces (van der Waals forces).

[0062] The spectrum shown in Figure 5 is the result of X-ray analysis of the adhesive structure of this embodiment. Specifically, in order to confirm the covalent bond, an amino group was added as the first functional group to the surface of a resin substrate (specifically a fluororesin) by plasma treatment to form a plasma-modified layer (NH3-treated layer), and an epoxy adhesive was applied to this layer as an adhesive to create an adhesive structure. This adhesive structure was then analyzed by XPS while etching it, for example, in increments of a few nanometers. The plasma surface treatment device used to impart functional groups to the first substrate was a plasma device manufactured by Denshi Giken Co., Ltd., and the XPS used for analysis was an AXIS ULTRA manufactured by Shimadzu Corporation and owned by the Osaka Institute of Industrial Technology.

[0063] As can be seen from these analysis results, the aforementioned adhesive structure is composed of three layers with different chemical bonding states: an adhesive, a plasma-modified layer (NH3-treated layer), and a resin substrate, and it was confirmed that each of these layers exists as a separate layer.

[0064] This is evidence that functional groups are present on the surface of the first substrate, and that at least some of these functional groups and the functional groups of the adhesive are bonded together without reacting with each other. [Examples]

[0065] The present invention will be described in more detail below with reference to examples. The present invention is not limited by the following examples, and it is certainly possible to implement it with appropriate modifications to the extent that it is in line with the spirit of the invention, and all such modifications are included within the technical scope of the present invention.

[0066] First, the schematic diagram shown in Figure 6 is a conceptual diagram for evaluating the adhesive strength to assess the effects of the present invention. Specifically, samples S (some with functional groups imparted to the surface of the substrate by plasma treatment, and others untreated) were placed on the front and back surfaces of the fluororesin F, adhesive X was applied to these samples S, and they were attached to a tensile jig at Z. The adhesive strength was evaluated by measuring the maximum point stress when pulled at a speed of 0.5 mm / min.

[0067] [Evaluation of adhesive strength between copper and epoxy adhesive] When functional groups were imparted to the copper surface using the plasma treatment conditions described in Table 1, and an epoxy adhesive was used as the adhesive, the adhesive strength was approximately four times greater than that of the untreated material (where the adhesive was applied without imparting functional groups to the substrate), as shown in Table 2, demonstrating a significant improvement in adhesion.

[0068] [Table 1] As anyone skilled in the art would understand, a high-frequency power of 500 [W] is equivalent to a power density of 0.13 [W / cm²]. 2 ]

[0069] [Table 2]

[0070] [Evaluation of adhesive strength between gold and silicone-based adhesive] When functional groups were imparted to the surface of gold using the plasma treatment conditions described in Table 3, and a silicone-based adhesive was used as the adhesive, the adhesive strength was approximately four times greater than that of the untreated material (where the adhesive was applied without imparting functional groups to the substrate), as shown in Table 4, demonstrating a significant improvement in adhesion.

[0071] [Table 3]

[0072] [Table 4]

[0073] [Evaluation of adhesive strength between ceramics and silicone-based adhesives] When functional groups were imparted to the surface of ceramics using the plasma treatment conditions described in Table 5, and a silicone-based adhesive was used as the adhesive, the adhesive strength was approximately four times greater than that of the untreated material (where the adhesive was applied without imparting functional groups to the substrate), as shown in Table 6, demonstrating a significant improvement in adhesion.

[0074] [Table 5]

[0075] [Table 6]

[0076] [Evaluation of adhesive strength between PTFE and epoxy adhesive] When functional groups were imparted to the surface of PTFE using the plasma treatment conditions described in Table 7, and an epoxy adhesive was used as the adhesive, as shown in Table 8, an improvement in adhesive strength was observed compared to the untreated material (where the adhesive was applied without imparting functional groups to the substrate), demonstrating a significant improvement in adhesion.

[0077] [Table 7]

[0078] [Table 8]

[0079] [Evaluation of adhesive strength between polyimide and epoxy adhesives] As shown in Table 9, functional groups were imparted to the surface of polyimide using the two-step plasma treatment conditions, and an epoxy adhesive was used as the adhesive. The result was approximately four times stronger than the untreated material (where the adhesive was applied without imparting functional groups to the substrate), demonstrating a significant improvement in adhesion.

[0080] [Table 9]

[0081] [Table 10]

[0082] Here, as representative of the examples described above, Figures 7 and 8 show the results of X-ray analysis of the PTFE film of sample 2 in Table 8. Figure 7 shows the film before the addition of functional groups, and Figure 8 shows the film after the addition of functional groups.

[0083] In the spectrum before the addition of functional groups (Figure 7), focusing on C reveals peaks of film-induced CF bonding, while focusing on O and N reveals no peaks of bonding originating from these elements.

[0084] In contrast, in the spectrum after the addition of functional groups (Figure 8), focusing on C reveals a peak distinct from the CF bond, and focusing on O and N also reveals peaks originating from these elements, indicating that functional groups have been added. The peak appearing at O ​​is presumed to be due to the surface becoming hydrophilic after plasma treatment of the PTFE film.

[0085] As described above, according to the adhesive structure and adhesive method of this embodiment, even if one of the first or second substrates is made of a material that is difficult to adhere to, such as Teflon, or if the adhesive is difficult to adhere to, the adhesive strength between the surface of one of the substrates and the adhesive can be improved without roughening or altering the substrate surface with the chemical solution, and consequently, the first and second substrates can be firmly bonded together. This makes it possible to manufacture printed circuit boards with high high-frequency characteristics while reducing environmental impact, which can contribute to technologies such as high-speed communication.

[0086] However, the present invention is not limited to the embodiments described above.

[0087] For example, although the above embodiment described the case of bonding a resin substrate and a copper substrate, similar substrates, such as two copper substrates or two resin substrates, may also be bonded together using an adhesive. For example, when bonding two resin substrates together, as shown in Figure 9, at least one functional group of -H, -NHx, -COOH, -C=O, -OH, -F, or -CFx is formed on the surface of one substrate, and at least one functional group of -H, -NHx, -COOH, -C=O, -OH, -F, or -CFx is formed on the surface of the other substrate, and then adhesive is applied to one or both of these substrates to bond them together.

[0088] Furthermore, if either the first or second base material is made of resin or metal, the other material may be made of a different material, such as ceramic or wood.

[0089] Furthermore, although a copper substrate was described as the second substrate in the above embodiment, an aluminum substrate or a steel substrate may also be used. In this case, at least one functional group of -H, -NHx, -COOH, -C=O, -OH, -F, or -CFx should be formed on the surface of the aluminum substrate or steel substrate.

[0090] Furthermore, although the above embodiment described the case of bonding two substrates, the adhesive structure and bonding method according to the present invention may also be applied when bonding three or more substrates of different or the same type via an adhesive.

[0091] Furthermore, various modifications and combinations of the embodiments are permitted, as long as they do not contradict the spirit of the present invention. [Explanation of symbols]

[0092] X... Plasma processing equipment P...Plasma 1. Vacuum Chamber 2 ···Lower electrode 3...Top electrode 4...High frequency power supply

Claims

1. An adhesive structure comprising a first substrate, a second substrate, and an adhesive interposed between these substrates, One or both of the first substrate and the second substrate are poorly bonded materials consisting of PS (polystyrene), PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PEN (polyethylene naphthalate), PET (polyethylene terephthalate), or metal. A first functional group is present bonded to a dangling bond formed on the surface of the first substrate. A second functional group is present bonded to microcracks formed on the surface of the second substrate. The adhesive has a third functional group, With the third functional group interposed between the first and second functional groups, at least a portion of the first and second functional groups are bonded by covalent bonds or hydrogen bonds, so that at least a portion of the first or second functional group and the third functional group are bonded to each other without reacting. An adhesive structure characterized in that the first functional group and the second functional group are -NHx.

2. The adhesive structure according to Claim 1, characterized in that the third functional group is at least one of -H, -NHx, -COOH, -C=O, -OH, -F, or -CFx.

3. The adhesive structure according to claim 1 or 2, wherein one of the first substrate and the second substrate is made of copper, ceramic, or gold, and the functional groups are formed on its surface by plasma treatment, and at least a portion of the functional groups and the functional groups contained in the epoxy adhesive or silicone adhesive are bonded to each other without reacting.

4. The adhesive structure according to any one of claims 1 to 3, wherein the adhesive has a relative permittivity Dk of 3.0 or less.

5. The adhesive structure according to any one of claims 1 to 4, wherein the adhesive has a glass transition temperature Tg of 250°C or higher.

6. A bonding method for bonding a first substrate and a second substrate by interposing an adhesive between them, One or both of the first and second substrates are made of poorly bondable materials such as PS (polystyrene), PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PEN (polyethylene naphthalate), PET (polyethylene terephthalate), or metal. Plasma treatment is used to form a dangling bond on the surface of the first substrate, and the first functional group is bonded to the dangling bond. Microcracks are formed on the surface of the second substrate by plasma treatment, and the second functional group is bonded to the microcracks. The third functional group of the adhesive is interposed between the first functional group and the second functional group. By bonding at least a portion of the first functional group and the second functional group by covalent bonds or hydrogen bonds, at least a portion of the first functional group or the second functional group and the third functional group are bonded together without reacting with each other, and the surfaces of the first substrate and the second substrate are bonded together via the adhesive. A bonding method characterized in that the first functional group and the second functional group are -NHx.

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