Connection structure and method for manufacturing the same

Abstract

To provide a connection structure in which a connection defect of each substrate electrode is hard to occur and of which the reliability is high.SOLUTION: In an electrode connection of a first substrate 10 containing a first thermoplastic resin and a second substrate 20 containing a second thermoplastic resin, there are included: a conductive bonding material 30 bonding a first substrate electrode 11 (excluding the case of annular arrangement on a first principal surface 10a) and a second substrate electrode 21 (excluding the case of annular arrangement on a fourth principal surface 20d); and an insulation adhesive agent 40 performing an electrode adhesion between the first principal surface 10a other than a portion where the first substrate electrode 11 is arranged and the fourth principal surface 20d other than a portion where the second substrate electrode 21 is arranged. A bonding temperature of the bonding material 30 is lower than a fusion point or a glass transfer temperature of the first thermoplastic resin and lower than a fusion point or a glass transfer temperature of the second thermoplastic resin. An adhesion temperature of the adhesive agent 40 is lower than the fusion point or the glass transfer temperature of the first thermoplastic resin and lower than the fusion point or the glass transfer temperature of the second thermoplastic resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a connection structure and a method for manufacturing the connection structure. [Background technology]

[0002] In recent years, products have become smaller and more powerful in the fields of electrical equipment such as PCs and digital home appliances, as well as in the automotive industry. Accordingly, there is a demand for smaller and more densely packed motherboards, which are important electrical components in these products, and for miniaturization of the various components mounted on the motherboards. Among these various components are substrates for mounting electronic components such as IC chips. For example, multilayer substrates, in which multiple substrates are stacked, are used as such substrates.

[0003] Patent Document 1 discloses a composite wiring board structure in which a conductor portion is provided in an adhesive layer that bonds the substrates together in order to electrically connect surface conductors arranged on the substrates together. Specifically, Patent Document 1 discloses a composite wiring board structure comprising a first substrate having a first main surface and a second main surface, with an element mounting portion on the first main surface side to which a semiconductor circuit element can be connected, and a second substrate bonded to the second main surface side of the first substrate via an adhesive layer, wherein a first surface conductor that is electrically connected to a conductor portion of the first substrate and a second surface conductor that is electrically connected to a conductor portion of the second substrate are electrically connected to each other via the conductor portion in the adhesive layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-237233 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, liquid crystal polymer, thermoplastic polyimide, or polyether ether ketone is used as an adhesive layer for bonding the substrates together, and thermocompression bonding is performed to bond the substrates together.

[0006] However, when the substrates to be connected are flexible substrates containing thermoplastic resin and these substrates are bonded together by thermocompression bonding, the flexible substrates become soft due to the heat, and the wiring patterns and substrate electrodes arranged on the substrates become misaligned or sink, making it more likely that poor connections will occur.

[0007] The present invention has been made to solve the above problems, and aims to provide a connection structure that bonds each substrate and joins each substrate electrode arranged on each substrate, which is less likely to cause connection defects between each substrate electrode and is highly reliable. [Means for solving the problem]

[0008] a conductive bonding material bonding the first substrate electrode to the second substrate electrode; and an insulating adhesive bonding the first substrate electrode to the second substrate electrode except for the portion where the first substrate electrode is disposed, and the fourth substrate electrode to the first substrate electrode except for the portion where the second substrate electrode is disposed, wherein the bonding temperature of the bonding material is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin, and the bonding temperature of the adhesive is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin.

[0009] The method for manufacturing a connection structure of the present invention includes a first substrate preparation step of preparing a first substrate having a first main surface and a second main surface opposite to the first main surface, a first substrate electrode on the first main surface, and containing a first thermoplastic resin; a second substrate preparation step of preparing a second substrate having a third main surface and a fourth main surface opposite to the third main surface, a second substrate electrode on the fourth main surface, and containing a second thermoplastic resin; a bonding step of bonding the first substrate electrode and the second substrate electrode with a conductive bonding material; and a bonding step of bonding the first substrate electrode and the second substrate electrode to a substrate having a first thermoplastic resin. and a bonding step of bonding the first main surface other than the portion where the second substrate electrode is placed to the fourth main surface other than the portion where the second substrate electrode is placed with an insulating adhesive, wherein the joining step is performed at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin, and the bonding step is performed at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin. [Effects of the Invention]

[0010] According to the present invention, a connection structure can be provided that bonds each substrate and joins each substrate electrode arranged on each substrate, which is less likely to cause connection defects between each substrate electrode and is highly reliable. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an example of the connection structure of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of another embodiment of the connection structure of the present invention. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an example of another embodiment of the connection structure of the present invention. [Figure 4] FIG. 4 is a cross-sectional view that schematically shows an example of a first substrate preparing step and a second substrate preparing step in the method for manufacturing a connection structure of the present invention. [Figure 5] FIG. 5 is a cross-sectional view that schematically shows an example of a resist forming step in the method for manufacturing a connection structure of the present invention. [Figure 6]FIG. 6 is a cross-sectional view that schematically shows an example of a surface treatment step in the method for producing a connection structure of the present invention. [Figure 7A] FIG. 7A is a cross-sectional view that schematically shows an example of an adhesive supplying step in the manufacturing method of the connection structure of the present invention. [Figure 7B] FIG. 7B is a cross-sectional view that schematically shows an example of an adhesive supplying step in the manufacturing method of the connection structure of the present invention. [Figure 8] FIG. 8 is a cross-sectional view that schematically shows an example of a resist removal step in the method for manufacturing a connection structure of the present invention. [Figure 9] FIG. 9 is a cross-sectional view that schematically shows an example of a bonding material supplying step in the manufacturing method of the connection structure of the present invention. [Figure 10A] FIG. 10A is a cross-sectional view schematically showing an example of a joining step and a bonding step in the manufacturing method of the connection structure of the present invention. [Figure 10B] FIG. 10B is a cross-sectional view that schematically shows an example of the joining step and the bonding step in the manufacturing method of the connection structure of the present invention. [Figure 11] FIG. 11 is a cross-sectional view that schematically shows an example of a water-repellent coating formation step in the manufacturing method of the connection structure of the present invention. [Figure 12A] FIG. 12A is a cross-sectional view that schematically shows an example of an adhesive supplying step in the manufacturing method of the connection structure of the present invention. [Figure 12B] FIG. 12B is a cross-sectional view that schematically shows an example of an adhesive supplying step in the manufacturing method of the connection structure of the present invention. [Figure 13] FIG. 13 is a cross-sectional view that schematically shows an example of a laser processing step in the method for manufacturing a connection structure of the present invention. [Figure 14] FIG. 14 is a cross-sectional photograph of the first substrate of the laminate before heating and pressing. [Figure 15] FIG. 15 is a cross-sectional photograph of the first substrate of the connection structure according to Example 1. As shown in FIG. [Figure 16] FIG. 16 is a cross-sectional photograph of the first substrate of the connection structure according to Comparative Example 1. As shown in FIG. [Figure 17] FIG. 17 is a cross-sectional view schematically showing a method for testing peel strength. [Figure 18] FIG. 18 is a chart showing the results of the peel strength test. DETAILED DESCRIPTION OF THE INVENTION

[0012] The connection structure of the present invention will be described below. However, the present invention is not limited to the following configurations, and can be appropriately modified and applied within the scope of the present invention. Note that the present invention also includes a combination of two or more of the individual desirable configurations of the present invention described below.

[0013] The following embodiments are merely examples, and it goes without saying that partial substitution or combination of the configurations shown in different embodiments is possible. From the second embodiment onwards, descriptions of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0014] The drawings shown below are schematic, and the dimensions and aspect ratios may differ from the actual product.

[0015] [First embodiment] FIG. 1 is a cross-sectional view schematically showing an example of the connection structure of the present invention.

[0016] The connection structure 1 shown in Figure 1 includes a first substrate 10 having a first main surface 10a and a second main surface 10b opposite the first main surface 10a and containing a first thermoplastic resin, and a second substrate 20 having a third main surface 20c and a fourth main surface 20d opposite the third main surface 20c and facing the first main surface 10a and containing a second thermoplastic resin. In addition, a first substrate electrode 11 is disposed on the first major surface 10a, and a second substrate electrode 21 is disposed on the fourth major surface 20d.

[0017] The first substrate electrode 11 and the second substrate electrode 21 are joined by a conductive bonding material 30. In the connection structure 1, the first substrate electrode 11 and the second substrate electrode 21 have the same size, and are joined so that they coincide and overlap when viewed in the thickness direction.

[0018] Furthermore, the first main surface 10a other than the portion where the first substrate electrode 11 is arranged and the fourth main surface 20d other than the portion where the second substrate electrode 21 is arranged are bonded together with an insulating adhesive 40.

[0019] Furthermore, in the connection structure 1, the bonding temperature of the bonding material 30 is lower than the melting point or glass transition temperature of the first thermoplastic resin and is lower than the melting point or glass transition temperature of the second thermoplastic resin. Furthermore, in the connection structure 1, the bonding temperature of the adhesive 40 is lower than the melting point or glass transition temperature of the first thermoplastic resin and is lower than the melting point or glass transition temperature of the second thermoplastic resin.

[0020] When manufacturing the connection structure 1, a bonding material 30 is placed between the first substrate electrode 11 and the second substrate electrode 21, an adhesive 40 is placed between the first main surface 10a other than the portion where the first substrate electrode 11 is placed and the fourth main surface 20d other than the portion where the second substrate electrode 21 is placed, and heat is applied to the first substrate 10 and the second substrate 20 to connect them.

[0021] In the connection structure 1, the bonding temperature of the bonding material 30 is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin. Therefore, the first substrate electrode 11 and the second substrate electrode 21 can be bonded by the bonding material 30 at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin. In other words, the first substrate electrode 11 and the second substrate electrode 21 can be connected by the bonding material 30 before the first thermoplastic resin and the second thermoplastic resin melt or soften. As a result, the first substrate electrode 11 and the second substrate electrode 21 are less likely to deviate or sink from the positions where they are arranged on the first substrate 10 and the second substrate 20, respectively.

[0022] Furthermore, in the connection structure 1, the bonding temperature of the adhesive 40 is lower than the melting point or glass transition temperature of the first thermoplastic resin and is lower than the melting point or glass transition temperature of the second thermoplastic resin. Therefore, the first main surface 10a and the fourth main surface 20d can be bonded together with the adhesive 40 at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin. In other words, the first main surface 10a and the fourth main surface 20d can be bonded together before the first thermoplastic resin and the second thermoplastic resin melt or soften. As a result, the first substrate electrode 11 and the second substrate electrode 21 are less likely to deviate or sink from the positions where they are arranged on the first substrate 10 and the second substrate 20, respectively. That is, in the connection structure 1, the first substrate electrode 11 and the second substrate electrode 21 do not sink into the first substrate 10 and the second substrate 20, respectively, but maintain the same height as the surroundings.

[0023] Since the connection structure 1 has the above-mentioned configuration, poor connection of the first substrate electrode 11 and the second substrate electrode 21 caused by the first substrate electrode 11 and the second substrate electrode 21 shifting or sinking from their respective positions on the first substrate 10 and the second substrate 20 is unlikely to occur.

[0024] Each component of the connection structure 1 will be described in detail below.

[0025] (First substrate and second substrate) First substrate 10 may be any substrate as long as it can accommodate first substrate electrode 11 and contains the first thermoplastic resin, but is preferably a flexible substrate.

[0026] In this specification, the term "first thermoplastic resin" refers to a resin that has the property of melting or softening when heat is applied.

[0027] When the first thermoplastic resin melts by application of heat, its melting point is preferably 150°C or higher and 350°C or lower, and more preferably 200°C or higher and 350°C or lower. Furthermore, when the first thermoplastic resin softens by application of heat, its glass transition temperature is preferably 100°C or higher and 350°C or lower, and more preferably 150°C or higher and 350°C or lower.

[0028] In this specification, the melting point or glass transition temperature of the first thermoplastic resin refers to a value measured in accordance with differential scanning calorimetry (DSC) according to JIS K7121. Furthermore, when the first thermoplastic resin contains multiple resins, the "melting point or glass transition temperature of the first thermoplastic resin" means the melting point or glass transition temperature of the resin that has the largest mass proportion contained in the first thermoplastic resin. When there are multiple resins that have the largest mass proportion in the first thermoplastic resin, "the melting point or glass transition temperature of the first thermoplastic resin" means the average value of the melting points or glass transition temperatures of those resins. When the first thermoplastic resin contains multiple resins, the mass proportion and type of each resin can be measured by methods such as Fourier Transform Infrared Spectroscopy (FT-IR) and Gas Chromatography-Mass spectrometry (GC-MS).

[0029] The first thermoplastic resin is not particularly limited, and may be, for example, a liquid crystal polymer (melting point: approximately 240 to 320°C); a fluorine-based resin such as polytetrafluoroethylene (PTFE) (melting point: approximately 330°C) or perfluoroalkoxyalkane (PFA) (melting point: approximately 310°C); polyimide (PI) (glass transition temperature: approximately 250°C); polyphenylene ether (PPE) (glass transition temperature: approximately 200°C); cycloolefin polymer (COP) (melting point: approximately 230°C); etc. These resins are flexible at room temperature, and so by using these resins, the first substrate can be easily made into a flexible substrate. Furthermore, since these resins have low dielectric constants, first substrate 10 containing these resins can reduce transmission loss.

[0030] The dielectric constant of the first thermoplastic resin is preferably 3.5 or less, and more preferably 2.0 or more and 3.0 or less. In this specification, the dielectric constant is the relative dielectric constant (ε r ) means

[0031] The first thermoplastic resin contained in the first substrate 10 may be one type or two or more types.

[0032] Second substrate 20 may be any substrate as long as it can accommodate second substrate electrode 21 and contains the second thermoplastic resin, but is preferably a flexible substrate.

[0033] In this specification, the term "second thermoplastic resin" refers to a resin that has the property of melting or softening when heat is applied.

[0034] The preferred melting point or glass transition temperature, preferred type, preferred dielectric constant, etc. of the second thermoplastic resin are the same as the preferred melting point or glass transition temperature, preferred type, preferred dielectric constant, etc. of the first thermoplastic resin. The second substrate 20 may contain one type of second thermoplastic resin, or two or more types of second thermoplastic resin.

[0035] In the connection structure 1, the first thermoplastic resin and the second thermoplastic resin may be the same type of resin or different types of resin.

[0036] The first substrate 10 may contain a silicon compound, a nitrogen compound, or the like in addition to the first thermoplastic resin. Furthermore, the second substrate 20 may contain a silicon compound, a nitrogen compound, or the like in addition to the second thermoplastic resin. The first substrate 10 and the second substrate 20 may have the same composition or different compositions.

[0037] In the connection structure 1, it is preferable that the first substrate 10 and the second substrate 20 are the same size and are stacked so that the first main surface 10a and the fourth main surface 20d coincide and overlap when viewed from the thickness direction. However, in the connection structure of the present invention, the first and second substrates may be joined so that they at least partially overlap when viewed in the thickness direction. Also, in the connection structure of the present invention, one substrate may be larger than the other substrate, and one substrate may be joined so that it entirely overlaps the other substrate when viewed in the thickness direction, or so that it at least partially overlaps.

[0038] (First substrate electrode and second substrate electrode) As long as the first substrate electrode 11 and the second substrate electrode 21 can be bonded to each other via the bonding material 30, they may be made of any material and may have any shape.

[0039] The first substrate electrode 11 and the second substrate electrode 21 are preferably formed from a conductive material containing a metal such as Au, Ag, or Cu. In the connection structure 1, the first substrate electrode 11 and the second substrate electrode 21 may be made of the same material or different materials.

[0040] A metal anticorrosive layer such as Zn / Cr or an organic anticorrosive layer such as a silane coupling agent may be formed on the surfaces of the first substrate electrode 11 and the second substrate electrode 21 that come into contact with the bonding material 30. The contact surface may be pre-fluxed or plated with Ni, Ni / Au, Ni / Ag, or the like.

[0041] The first substrate electrode 11 and the second substrate electrode 21 are preferably patterned by a method such as photolithography, printing, inkjet, or plating.

[0042] In the connection structure 1, the first substrate electrode 11 and the second substrate electrode 21 have the same size, and are joined so that they coincide and overlap when viewed in the thickness direction. However, in the connection structure of the present invention, the first and second substrate electrodes may be joined so as to overlap at least partially when viewed in the thickness direction. Also, in the connection structure of the present invention, one substrate electrode may be larger than the other substrate electrode, and one substrate electrode may be joined so as to overlap the entire other substrate electrode when viewed in the thickness direction, or may be joined so as to overlap at least partially.

[0043] (bonding material) The bonding material 30 is not particularly limited as long as it is conductive and can bond the first substrate electrode 11 and the second substrate electrode 21 at the bonding temperature, and may be, for example, a sintered body of a conductive paste containing metal nanoparticles, lead-free solder, a conductive adhesive containing conductive particles and a thermosetting resin, etc.

[0044] In this specification, the "bonding temperature of the bonding material" refers to the temperature at which the bonding material 30 undergoes a change in properties such as softening or hardening, and becomes able to bond the first substrate electrode 11 and the second substrate electrode 21 together.

[0045] When the bonding material 30 is a sintered body of a conductive paste containing metal nanoparticles, the "bonding temperature of the bonding material" means the sintering temperature of the metal nanoparticles. The sintering temperature of the metal nanoparticles is preferably 150°C or less, and more preferably 100°C or more and 150°C or less.

[0046] The metal nanoparticles are not particularly limited, and examples thereof include Ag nanoparticles, Au nanoparticles, Cu nanoparticles, and Ni nanoparticles.

[0047] When the bonding material 30 is a lead-free solder, the "bonding temperature of the bonding material" means the melting point of the lead-free solder. The melting point of the lead-free solder is preferably 150° C. or lower, and more preferably 140° C. or lower, and is preferably 100° C. or higher.

[0048] The lead-free solder is not particularly limited, but a lead-free solder consisting of two or more conductive metals is preferred, and Sn-Bi-Sb-Ni based lead-free solder (melting point: 140°C) and Sn-Bi based lead-free solder (melting point: 139°C) are more preferred.

[0049] When the bonding material 30 is a conductive adhesive containing conductive particles and a thermosetting resin, the "bonding temperature of the bonding material" means the thermosetting temperature of the thermosetting resin. The thermosetting temperature of the thermosetting resin is preferably 150°C or lower, and more preferably 100°C or higher and 150°C or lower.

[0050] Examples of conductive particles include metal particles such as Cu particles and Ag particles, and non-metal particles such as carbon particles. Examples of thermosetting resins include epoxy resins (curing temperature: 80 to 150°C) and silicone resins (curing temperature: 100 to 150°C).

[0051] The thickness of the bonding material 30 is not particularly limited, but is preferably 5 μm or more and 50 μm or less.

[0052] (glue) The composition of adhesive 40 is not particularly limited as long as it has insulating properties and can bond first main surface 10a and fourth main surface 20d together at the bonding temperature. For example, the adhesive 40 may be an adhesive containing a polyolefin resin. The polyolefin resin is preferably a polyolefin resin obtained by polymerizing an alkene having 2 to 4 carbon atoms, such as ethylene or propylene. The polyolefin resin may also be an acid-modified polyolefin resin that has been acid-modified with an unsaturated carboxylic acid component. The unsaturated carboxylic acid component is preferably acrylic acid or methacrylic acid, with methacrylic acid being more preferred. The adhesive 40 may contain one type of polyolefin resin, or may contain two or more types.

[0053] The adhesive 40 also functions as a part of the resist, and therefore also serves to prevent short circuits between the substrate electrodes.

[0054] The adhesive 40 may contain urethane resin, melamine resin, or the like in addition to polyolefin resin.

[0055] The proportion of polyolefin resin contained in adhesive 40 is preferably 50% by weight or more and 95% by weight or less.

[0056] The adhesive 40 may also be made of an underfill material such as epoxy resin.

[0057] In this specification, the "adhesive temperature of the adhesive" refers to the temperature at which adhesive 40 undergoes a change in properties such as softening or hardening, and becomes able to bond first main surface 10a and fourth main surface 20d together. For example, when the adhesive 40 is an adhesive containing a polyolefin resin, the "adhesive temperature of the adhesive" means the melting point or glass transition temperature of the polyolefin resin. The melting point or glass transition temperature of the resin is preferably 150°C or lower, and more preferably 80°C or higher and 150°C or lower. The melting point or glass transition temperature of the resin refers to a value measured in accordance with differential scanning calorimetry (DSC) according to JIS K7121. When the adhesive 40 contains a plurality of resins, the "adhesion temperature of the adhesive" means the melting point or glass transition temperature of the resin that is contained in the adhesive 40 at the largest mass ratio. When there are multiple types of resins that have the largest mass proportions in the adhesive 40, the "adhesion temperature of the adhesive" refers to the average value of the melting points or glass transition temperatures of those resins. When the adhesive 40 contains a plurality of resins, the mass proportion and type of each resin can be measured by a method such as FT-IR or GC-MS.

[0058] By using such adhesive 40, the adhesive strength between first substrate 10 and second substrate 20 can be improved.

[0059] The thickness of the adhesive 40 is not particularly limited, but is preferably 30 μm or more and 80 μm or less.

[0060] In the connection structure 1, the dielectric constant of the adhesive 40 is preferably lower than the dielectric constant of the first thermoplastic resin and the dielectric constant of the second thermoplastic resin. The dielectric constant of the adhesive 40 is preferably 3.5 or less, and more preferably 2.0 or more and 3.0 or less. By using such an adhesive 40 with a low dielectric constant to bond the first main surface 10a and the fourth main surface 20d, the transmission loss in the entire connection structure 1 can be reduced.

[0061] In the connection structure 1, the water absorption rate of the adhesive 40 is preferably 1% or less, and more preferably 0.1% or less. When the first main surface 10a and the fourth main surface 20d are bonded using such an adhesive 40 with low water absorption, the adhesive 40 is less likely to absorb moisture in the air, which makes it possible to prevent a decrease in the reliability of the entire connection structure 1 due to moisture absorption.

[0062] In the connection structure 1, the structure and components of the adhesive 40 can be determined using Fourier transform infrared spectroscopy (FT-IR) and gas chromatography mass spectrometry (GC-MS).

[0063] In the connection structure 1, it is preferable that the ratio of the linear expansion coefficient of the first thermoplastic resin to the linear expansion coefficient of the first substrate electrode is linear expansion coefficient of the first thermoplastic resin / linear expansion coefficient of the first substrate electrode = 0.8 or more and 1.2 or less. Furthermore, it is preferable that the ratio of the linear expansion coefficient of the second thermoplastic resin to the linear expansion coefficient of the second substrate electrode (linear expansion coefficient of second thermoplastic resin / linear expansion coefficient of second substrate electrode) is 0.8 or more and 1.2 or less. When the ratio of the linear expansion coefficient of the thermoplastic resin contained in the substrate to the linear expansion coefficient of the substrate electrodes is close to 1.0, the substrate electrodes are less likely to shift due to thermal expansion when the first substrate and second substrate are heated, which reduces the likelihood of poor connection between the first substrate electrode 11 and the second substrate electrode 21.

[0064] In the connection structure 1, preferred combinations of materials for the first and second thermoplastic resins, the first and second substrate electrodes, the bonding material, and the adhesive are as follows. First thermoplastic resin and second thermoplastic resin: liquid crystal polymer (product name: MetroCirc, manufacturer: Murata Manufacturing Co., Ltd.) or polyimide First substrate electrode and second substrate electrode: Cu Joining material: Sn-Bi lead-free solder Adhesive: Polyolefin resin made by modifying ethylene-propylene copolymer with methacrylic acid

[0065] In this specification, the linear expansion coefficient refers to the linear expansion coefficient in the planar direction measured by thermomechanical analysis (TMA) in accordance with JIS C6481.

[0066] When the dielectric constant of the adhesive 40 is within the above range, the connection structure 1 is preferably used in electronic devices that transmit signals at 4G frequencies (3.5 GHz band), and more preferably used in electronic devices that transmit signals at 5G frequencies (sub6 (3.7 GHz, 4.5 GHz band)) and millimeter wave (28 GHz band) frequencies. Generally, transmission loss is likely to occur when transmitting high-frequency signals. However, in connection structure 1 having adhesive 40 with a dielectric constant within the above range, transmission loss is unlikely to occur. Therefore, even when connection structure 1 is used in electronic devices that transmit signals of the above frequencies, good transmission characteristics are achieved.

[0067] Next, another embodiment of the connection structure of the present invention will be described. FIG. 2 is a cross-sectional view schematically showing an example of another embodiment of the connection structure of the present invention. In the connection structure 101 shown in Figure 2, a first substrate block 110B in which multiple substrates 110 including a first substrate 10 are stacked is connected to a second substrate block 120B in which multiple substrates 120 including a second substrate 20 are stacked. The connection structure 101 has the same configuration as the above-mentioned connection structure 1, except that multiple substrates 110 are stacked on the second main surface 10b side of the first substrate 10, and multiple substrates 120 are stacked on the third main surface 20c side of the second substrate 20.

[0068] When conventional substrate blocks are multi-layered, if the substrates that make up the substrate blocks contain thermoplastic resin and the substrate blocks are connected to each other at a temperature above the melting point or glass transition temperature of the thermoplastic resin, the thermoplastic resin may melt or soften, which could result in poor connections due to misalignment of the substrate electrodes or wiring inside the substrate blocks.

[0069] However, when manufacturing connection structure 101, first substrate 10 is placed on the outermost portion of first substrate block 110B, and second substrate 20 is placed on the outermost portion of second substrate block 120B, and the first substrate 10 and second substrate 20 are connected together. At this time, before the first thermoplastic resin and the second thermoplastic resin melt or soften, first substrate electrode 11 and second substrate electrode 21 can be bonded together by bonding material 30, and first main surface 10a and fourth main surface 20d can be bonded together by adhesive 40. Therefore, in the manufactured connection structure 101, connection defects due to misalignment of wiring not only between the first substrate electrode 11 and the second substrate electrode 21 but also between the first substrate block 110B and the second substrate block 120B are unlikely to occur.

[0070] Furthermore, since the first substrate block 110B and the second substrate block 120B are connected, it is possible to suppress misalignment of the substrate electrodes and wiring positions throughout the entire connection structure 101 compared to connecting the substrate 110, the first substrate 10, the second substrate 20, and the substrate 120 one by one. Furthermore, by connecting the substrate blocks, the yield rate can be increased.

[0071] The substrate 110 included in the first substrate block 110B may be a flexible substrate or a rigid substrate, and may be a general substrate used in this field. Similarly, the substrate 120 included in the second substrate block 120B may be a flexible substrate or a rigid substrate, and these substrates may be general substrates used in this field. Furthermore, the first substrate block 110B and the second substrate block 120B may be composite substrates in which both flexible substrates and rigid substrates are stacked.

[0072] The first substrate block 110B and the second substrate block 120B can be connected together in the same manner as the method for connecting the first substrate 10 and the second substrate 20 in the connection structure 1 described above.

[0073] Next, another embodiment of the connection structure of the present invention will be described. FIG. 3 is a cross-sectional view schematically showing an example of another embodiment of the connection structure of the present invention. In the connection structure 201 shown in Figure 3, a first substrate block 110B is arranged on a motherboard M, and a first substrate 10 is arranged on the outermost side of the first substrate block 110B on the side not in contact with the motherboard M. In addition, a second substrate block 120B is connected to a portion of the first main surface 10a of the first substrate 10, and a third substrate block 210B consisting of a third substrate 210 that serves as a connecting substrate to the first substrate block 110B and a plurality of substrates 220 stacked on the third substrate 210 is connected to another portion.

[0074] In the connection structure 201, mounted components 251 are arranged on the first main surface 10a of the first substrate 10 in areas where the second substrate block 120B and the third substrate block 210B are not bonded. Furthermore, mounted components 252 are arranged on the motherboard M in areas where the first substrate block 110B is not arranged.

[0075] The first substrate block 110B and the second substrate block 120B are connected by the same structure as the connection structure 101 described above.

[0076] Therefore, when manufacturing the connection structure 201, the first substrate block 110B and the second substrate block 120B are connected. The connection between the first substrate block 110B and the second substrate block 120B can be performed in the same manner as the method for connecting the first substrate 10 and the second substrate 20 in the connection structure 1 described above.

[0077] Next, the connection between the first substrate block 110B and the third substrate block 210B will be described. A third substrate 210 is disposed in the third substrate block 210B, and serves as a connection substrate for connecting to the first substrate block 110B. The third substrate 210 has a fifth main surface 210e and a sixth main surface 210f that faces the fifth main surface 210e and also faces the first main surface 10a. Furthermore, a third substrate electrode 211 is disposed on the sixth main surface 210f. The third substrate electrode 211 is bonded to the first substrate electrode 11 arranged on the first substrate 10 by a bonding material 230 having electrical conductivity. Furthermore, the sixth main surface 210f other than the portion where the third substrate electrode 211 is arranged and the first main surface 10a other than the portion where the first substrate electrode 11 is arranged are bonded together with an adhesive 240 having insulating properties. The third substrate 210 also includes a third thermoplastic resin.

[0078] The bonding temperature of the bonding material 230 is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the third thermoplastic resin, and the bonding temperature of the adhesive 240 is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the third thermoplastic resin.

[0079] When manufacturing the connection structure 201, a bonding material 230 is placed between the first substrate electrode 11 and the third substrate electrode 211, an adhesive 240 is placed between the first main surface 10a other than the portion where the first substrate electrode 11 is placed and the sixth main surface 210f other than the portion where the third substrate electrode 211 is placed, and heat is applied to the first substrate 10 and the third substrate 210 to connect them.

[0080] In the connection structure 201, the bonding temperature of the bonding material 230 is lower than the melting point or glass transition temperature of the first thermoplastic resin and is lower than the melting point or glass transition temperature of the third thermoplastic resin. Therefore, the first substrate electrode 11 and the third substrate electrode 211 can be bonded by the bonding material 230 at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the third thermoplastic resin. In other words, the first substrate electrode 11 and the third substrate electrode 211 can be connected by the bonding material 230 before the first thermoplastic resin and the third thermoplastic resin melt or soften. As a result, the first substrate electrode 11 and the third substrate electrode 211 are less likely to deviate or sink from the positions where they are arranged on the first substrate 10 and the third substrate 210, respectively.

[0081] Furthermore, in the connection structure 201, the bonding temperature of the adhesive 240 is lower than the melting point or glass transition temperature of the first thermoplastic resin and is lower than the melting point or glass transition temperature of the third thermoplastic resin. Therefore, the first main surface 10a and the sixth main surface 210f can be bonded together by the adhesive 240 at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the third thermoplastic resin. In other words, the first main surface 10a and the sixth main surface 210f can be bonded together before the first thermoplastic resin and the third thermoplastic resin melt or soften. As a result, the first substrate electrode 11 and the third substrate electrode 211 are less likely to deviate or sink from the positions where they are arranged on the first substrate 10 and the third substrate 210, respectively.

[0082] Since the connection structure 201 has the above configuration, poor connection between the first substrate electrode 11 and the third substrate electrode 211 is unlikely to occur.

[0083] The preferred aspects of the third substrate 210, the third substrate electrode 211, and the third thermoplastic resin are the same as the preferred aspects of the first substrate 10, the first substrate electrode 11, and the first thermoplastic resin. Furthermore, the substrate 220 may be a flexible substrate or a rigid substrate, and the third substrate block 210B may be a composite substrate in which both flexible substrates and rigid substrates are stacked.

[0084] The preferred embodiments of the bonding material 230 and the adhesive 240 are the same as the preferred embodiments of the bonding material 30 and the adhesive 40 described above.

[0085] When manufacturing the connection structure 201, the connection between the first substrate block 110B and the second substrate block 120B and the connection between the first substrate block 110B and the third substrate block 210B may be performed simultaneously. Alternatively, the second substrate block 120B and the third substrate block 210B may be connected at different times.

[0086] The motherboard M, the mounted components 251, and the mounted components 252 are not particularly limited, and ordinary components used in this field can be used.

[0087] In the above connection structure 201, the third substrate block 210B includes the third substrate 210, but as long as the first substrate block 110B and the third substrate block 210B are connected, the third substrate block 210B does not need to include the third substrate 210. The first substrate block 110B and the third substrate block 210B may be connected together using a common bonding material and adhesive used in this field.

[0088] 3, by connecting the first block 110B, the second substrate block 120B, and the third substrate block 210B so as not to cover the entire first main surface 10a of the first substrate 10 in the first substrate block 110B, a cavity portion can be formed in the first main surface 10a of the first substrate 10. Because the connection structure 201 has such a cavity portion, it becomes possible to place a mounted component 251 in the cavity portion. Furthermore, by providing a space for placing other mounted components 252 on the aggregate substrate, it is possible to prevent the wiring from being blocked by the mounted components 252, making it possible to route complex wiring.

[0089] [Second embodiment] Next, a method for manufacturing the connection structure of the present invention will be described. The method for manufacturing a connection structure of the present invention includes a first substrate preparation step of preparing a first substrate having a first main surface and a second main surface opposite the first main surface, a first substrate electrode on the first main surface, and containing a first thermoplastic resin; a second substrate preparation step of preparing a second substrate having a third main surface and a fourth main surface opposite the third main surface, a second substrate electrode on the fourth main surface, and containing a second thermoplastic resin; a bonding step of bonding the first substrate electrode and the second substrate electrode with a conductive bonding material; and a bonding step of bonding the first main surface other than the portion where the first substrate electrode is disposed and the second substrate electrode together with a conductive bonding material. and a bonding step of bonding the fourth main surface other than the portion where the second substrate electrode is arranged to an insulating adhesive, wherein the joining step is performed at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin, and the bonding step is performed at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin, and any other steps may be included as long as the connection structure of the present invention can be manufactured.

[0090] Three methods (Process 1 to Process 3) for producing the connection structure of the present invention will be explained below.

[0091] [Process 1] The manufacturing method of the connection structure of the present invention relating to Process 1 includes a first substrate preparation step, a second substrate preparation step, a resist formation step, a surface treatment step, an adhesive supply step, a resist removal step, a bonding material supply step, a bonding step, and an adhesion step. Each step will be explained below.

[0092] (First substrate preparation process and second substrate preparation process) FIG. 4 is a cross-sectional view that schematically shows an example of a first substrate preparing step and a second substrate preparing step in the method for manufacturing a connection structure of the present invention. As shown in Figure 4, in the first substrate preparation process, a first substrate 10 is prepared, which has a first main surface 10a and a second main surface 10b opposite to the first main surface 10a, has a first substrate electrode 11 on the first main surface 10a, and contains a first thermoplastic resin. Similarly, in the second substrate preparation process, a second substrate 20 is prepared, which has a third main surface 20c and a fourth main surface 20d opposite to the third main surface 20c, has a second substrate electrode 21 on the fourth main surface 20d, and contains a second thermoplastic resin. Preferred embodiments of the first substrate 10, the first thermoplastic resin, and the first substrate electrode 11, as well as preferred embodiments of the second substrate 20, the second thermoplastic resin, and the second substrate electrode 21 have already been described, so further description will be omitted here.

[0093] (Resist formation process) FIG. 5 is a cross-sectional view that schematically shows an example of a resist forming step in the method for manufacturing a connection structure of the present invention. Next, as shown in FIG. 5, a resist 50 is formed on the surface 11a of the first substrate electrode 11 and the surface 21a of the second substrate electrode 21. The resist 50 may be made of any material as long as it can protect the first substrate electrode 11 and the second substrate electrode 21 in the surface treatment step described below.

[0094] (Surface treatment process) FIG. 6 is a cross-sectional view that schematically shows an example of a surface treatment step in the method for producing a connection structure of the present invention. Next, as shown in FIG. 6, the first main surface 10a of the first substrate 10 and the fourth main surface 20d of the second substrate 20 are subjected to a surface treatment. Examples of the surface treatment include surface modification treatments such as plasma treatment, UV treatment, and flame treatment. By performing the surface modification treatment, the adhesion between the first substrate 10 and the adhesive 40, and the adhesion between the second substrate 20 and the adhesive 40 can be improved.

[0095] The plasma treatment is not particularly limited, but examples thereof include a method using vacuum plasma with oxygen gas, nitrogen gas, or argon gas, and atmospheric pressure plasma.

[0096] The UV treatment is not particularly limited, but examples thereof include methods using a rare gas excimer lamp, a rare gas halogen excimer lamp, and a low-pressure mercury lamp.

[0097] The flame treatment is not particularly limited, but examples thereof include a method using only a flame or a flame mixed with an organic compound or an inorganic compound.

[0098] (Adhesive supply process) 7A and 7B are cross-sectional views that schematically show an example of an adhesive supplying step in the manufacturing method of the connection structure of the present invention. Next, as shown in FIG. 7A, adhesive 40 is supplied to the first main surface 10a and the fourth main surface 20d. The adhesive 40 may be supplied by printing or dispensing. Thereafter, as shown in FIG. 7B, adhesive 40 is coated by a method such as spin coating or bar coating, and then dried. The drying conditions are preferably 100° C. or higher and 150° C. or lower, and for 30 seconds or longer and 60 seconds or shorter.

[0099] (resist removal process) FIG. 8 is a cross-sectional view that schematically shows an example of a resist removal step in the method for manufacturing a connection structure of the present invention. 8, the resist 50 is removed to expose the first substrate electrode 11 and the second substrate electrode 21. The method for removing the resist 50 is preferably determined appropriately depending on the type of resist 50.

[0100] (Joining material supply process) FIG. 9 is a cross-sectional view that schematically shows an example of a bonding material supplying step in the manufacturing method of the connection structure of the present invention. Next, as shown in FIG. 9, bonding material 30 is supplied to surface 11a of first substrate electrode 11 and surface 21a of second substrate electrode 21. Examples of the supplying method include a method of supplying the bonding material 30 by a printing method, a dispensing method, a plating method, or the like. As described above in the connection structure according to the first embodiment of the present invention, a lead-free solder, a conductive adhesive containing conductive particles and a thermosetting resin, or the like can be used as the bonding material 30. Alternatively, a conductive paste containing metal nanoparticles before sintering can also be used.

[0101] (Joining process and adhesion process) 10A and 10B are cross-sectional views that schematically show an example of a joining step and an adhering step in the manufacturing method of the connection structure of the present invention. Next, as shown in FIG. 10A, the second substrate 20 is turned over 180 degrees, and the second substrate 20 is laminated on the first substrate 10 so that the first main surface 10a and the fourth main surface 20d face each other, thereby producing a laminate. At this time, the bonding material 30 arranged on the first substrate electrode 11 and the bonding material 30 arranged on the second substrate electrode 21 are brought into contact with each other.

[0102] Then, as shown in FIG. 10B, the first substrate 10 and the second substrate 20 are heated and pressurized from above and below, and the first substrate electrode 11 and the second substrate electrode 21 are bonded with a bonding material 30, and the first main surface 10a and the fourth main surface 20d are bonded with an adhesive 40. In this case, the joining step and the bonding step are carried out simultaneously. By simultaneously performing the joining step and the adhesion step, the history of heating and pressurization can be reduced, and therefore damage to the substrates and internal components due to heating and pressurization can be reduced.

[0103] The conditions for heating and pressing are not particularly limited as long as the temperature is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin, and is higher than the bonding temperature of the bonding material 30 and higher than the bonding temperature of the adhesive 40. However, the following conditions are preferred.

[0104] The heating temperature is preferably 100°C or higher and 150°C or lower, and more preferably 120°C or higher and 150°C or lower. The pressure to be applied is preferably 0.1 MPa or more and 5.0 MPa or less, and more preferably 0.1 MPa or more and 1.0 MPa or less. The heating and pressing time is preferably 10 seconds or more and 1800 seconds or less, and more preferably 60 seconds or more and 1800 seconds or less.

[0105] In particular, when the bonding material 30 is a conductive paste containing metal nanoparticles, the heating temperature is preferably 80°C or higher and 150°C or lower, and more preferably 100°C or higher and 150°C or lower. Furthermore, when the bonding material 30 is lead-free solder, the heating temperature is preferably 100°C or higher and 150°C or lower, and more preferably 130°C or higher and 150°C or lower. Furthermore, when the bonding material 30 is a conductive adhesive containing conductive particles and a thermosetting resin, the heating temperature is preferably 100°C or higher and 150°C or lower, and more preferably 120°C or higher and 150°C or lower.

[0106] Furthermore, when the adhesive 40 is an adhesive containing a polyolefin resin, the heating temperature is preferably 80°C or higher and 150°C or lower, and more preferably 100°C or higher and 150°C or lower.

[0107] Through the above steps, the connection structure 1 shown in FIG. 1 can be manufactured.

[0108] In the manufacturing method of the connection structure of the present invention relating to Process 1, the bonding material 30 and the adhesive 40 are supplied to both the first substrate 10 and the second substrate 20, but in the manufacturing method of the connection structure of the present invention, the bonding material and the adhesive may be supplied to only one of the substrates.

[0109] Furthermore, in the above-described manufacturing method of the connection structure of the present invention relating to Process 1, the bonding material 30 and the adhesive 40 are supplied to each substrate, and then the bonding step and the adhesion step are carried out simultaneously, but in the manufacturing method of the connection structure of the present invention, after the first substrate electrode and the second substrate electrode are bonded with the bonding material, an adhesive may be supplied between the first substrate and the second substrate, and the first main surface and the fourth main surface may be bonded with the adhesive. In other words, the bonding step and the adhesion step may be carried out separately.

[0110] [Process 2] The manufacturing method of the connection structure of the present invention relating to Process 2 is the same as the manufacturing method of the connection structure of Process 1 above, except that the following water-repellent coating formation process is performed instead of the resist formation process, and the water-repellent coating removal process is performed instead of the resist removal process. The water-repellent coating forming step and the water-repellent coating removing step will be described below.

[0111] (Water-repellent coating process) FIG. 11 is a cross-sectional view that schematically shows an example of a water-repellent coating formation step in the manufacturing method of the connection structure of the present invention. In the water-repellent coating formation step, a water-repellent treatment is performed on the surface 11a of the first substrate electrode 11 and the surface 21a of the second substrate electrode 21, and a water-repellent coating is formed. Examples of the water-repellent coating include a coating of a silane coupling-based water-repellent treatment agent, preflux, and the like. By forming a water-repellent coating on the surface 11a of the first substrate electrode 11 and the surface 21a of the second substrate electrode 21, it is possible to prevent a decrease in insulation resistance between the substrate electrodes due to the influence of moisture, impurities, etc. in the atmosphere.

[0112] (Water-repellent coating removal process) After the adhesive supplying step is performed, the water-repellent coating is removed to expose the surface 11a of the first substrate electrode 11 and the surface 21a of the second substrate electrode 21 (not shown). The method for removing the water-repellent coating is preferably determined appropriately depending on the type of water-repellent coating.

[0113] [Process 3] The manufacturing method of the connection structure of the present invention relating to Process 3 is the same as the manufacturing method of the connection structure of the present invention relating to Process 1, except that the resist formation step, surface treatment step, adhesive supply step, and resist removal step of Process 1 are replaced with the adhesive supply step and laser treatment step described below. The adhesive supplying step and the laser treatment step will be described below.

[0114] (Adhesive supply process) 12A and 12B are cross-sectional views that schematically show an example of an adhesive supplying step in the manufacturing method of the connection structure of the present invention. After the first substrate preparation step and the second substrate preparation step, adhesive 40 is supplied to the first main surface 10a of the first substrate 10 and the fourth main surface 20d of the second substrate 20, as shown in FIG. 12A. At this time, the first substrate electrode 11 and the second substrate electrode 21 are also covered with the adhesive 40. The adhesive 40 may be supplied by printing or dispensing. Thereafter, as shown in FIG. 12B, adhesive 40 is coated by a method such as spin coating or bar coating, and then dried. The drying conditions are preferably 100° C. or higher and 150° C. or lower, and for 30 seconds or longer and 60 seconds or shorter.

[0115] (Laser treatment process) FIG. 13 is a cross-sectional view that schematically shows an example of a laser processing step in the method for manufacturing a connection structure of the present invention. After the adhesive supplying step, as shown in FIG. 13, the adhesive 40 is removed by irradiating the first substrate electrode 11 and the second substrate electrode 21 with a laser L so as to expose them. The laser treatment is not particularly limited, but examples thereof include methods using a CO2 laser and a UV laser. [Example]

[0116] EXAMPLES Hereinafter, examples will be given that more specifically disclose the connection structure and the manufacturing method of the connection structure of the present invention, but the present invention is not limited to these examples.

[0117] Example 1 (First substrate preparation process and second substrate preparation process) A first substrate having a first main surface and a second main surface was prepared, which contained a liquid crystal polymer (LCP) (melting point: 250°C, dielectric constant: 3.0) obtained by polymerizing parahydroxybenzoic acid (PHB) and 6-hydroxy-2-naphthoic acid (HNA) in a 50:50 molar ratio as a first thermoplastic resin. The first substrate was a flexible substrate. Thereafter, a first substrate electrode was formed from Cu foil on the surface of the first main surface of the first substrate.

[0118] A second substrate containing LCP (melting point: 250° C., dielectric constant: 3.0) as a second thermoplastic resin and having a third main surface and a fourth main surface was prepared. The second substrate was a flexible substrate. Thereafter, a second substrate electrode was formed from Cu foil on the fourth main surface of the second substrate.

[0119] (Resist formation process) Next, a resist (product name: SL-1825, manufacturer: Showa Denko Materials) was formed on the first substrate electrode and the second substrate electrode.

[0120] (Surface treatment process) Next, the first main surface of the first substrate and the fourth main surface of the second substrate were subjected to plasma treatment, surface treatment using PC-300 (oxygen gas, RF: 150 W, Flow: 12 sccm, Time: 1 min).

[0121] (Adhesive supply process) As an insulating adhesive, we prepared a polyolefin resin (product name: Arrowbase, manufacturer: Unitika Ltd., melting point: 100°C, dielectric constant: 2.4) made by acid-modifying ethylene-propylene copolymer with methacrylic acid. Next, the prepared adhesive was dispensed onto the first main surface of the first substrate and the fourth main surface of the second substrate by a dispenser method, coated with the adhesive by a bar coat method, and dried at 100°C for 60 seconds.

[0122] (resist removal process) Next, the resist was removed with an alkaline solution to expose the first substrate electrode and the second substrate electrode.

[0123] (Joining material supply process) Next, Sn-Bi solder (product name: L20-BLT5-T7F, manufacturer: Senju Metal Industry Co., Ltd.) with a melting point of 140°C was prepared and placed on the exposed surfaces of the first substrate electrode and the second substrate electrode by mask printing.

[0124] (Joining process and adhesion process) Next, a second substrate was laminated on the first substrate so that the first main surface of the first substrate faced the second main surface of the second substrate, and the bonding material disposed on the first substrate electrode and the bonding material disposed on the second substrate electrode were in contact with each other to produce a laminate. Thereafter, the first and second substrates were heated and pressed from above and below under conditions of 150° C., 1 MPa, and 120 seconds. Through the above steps, the connection structure according to Example 1 was manufactured.

[0125] (Comparative Example 1) A connection structure according to Comparative Example 1 was produced in the same manner as in Example 1, except that the heating and pressurizing conditions in the joining and bonding steps were 260° C., 8 MPa, and 300 seconds.

[0126] (Evaluation of substrate electrode position) A laminate of a first substrate and a second substrate was prepared before heating and pressurizing in the joining and adhesion steps of manufacturing the connection structure according to Example 1. The laminate was cut perpendicular to the first main surface, so that the first substrate electrode was also cut. The cross section was observed with a scanning electron microscope (SEM), and the results are shown in FIG. The connection structure according to Example 1 and the connection structure according to Comparative Example 1 were cut perpendicular to the first main surface, so that the first substrate electrode was also cut. Each cross section was observed with an SEM. The results are shown in FIGS. 15 and 16. FIG. 14 is a cross-sectional photograph of the first substrate of the laminate before heating and pressing. FIG. 15 is a cross-sectional photograph of the first substrate of the connection structure according to Example 1. As shown in FIG. FIG. 16 is a cross-sectional photograph of the first substrate of the connection structure according to Comparative Example 1. As shown in FIG.

[0127] Comparing FIG. 14 and FIG. 15, in the connection structure according to Example 1, no sinking of the first substrate electrode was observed. This is thought to be because the heating temperature was above the melting point of the bonding material and the melting point of the adhesive, but below the melting point of the first thermoplastic resin and the melting point of the second thermoplastic resin, and therefore the first substrate and the second substrate did not soften when the first substrate electrode and the second substrate electrode were joined, and when the first main surface of the first substrate and the fourth main surface of the second substrate were bonded. From this result, it can be said that in the connection structure according to Example 1, the first substrate electrode and the second substrate electrode are firmly joined by the joining material without misalignment. Therefore, in the connection structure according to Example 1, it is believed that poor connection between the first substrate electrode and the second substrate electrode is unlikely to occur.

[0128] Comparing FIG. 14 and FIG. 16, in the connection structure according to Comparative Example 1, sinking of the first substrate electrode was observed. This is thought to be because the heating temperature was above the melting point of the first thermoplastic resin and the melting point of the second thermoplastic resin, and therefore the first substrate and the second substrate softened when the first substrate electrode and the second substrate electrode were joined and when the first main surface of the first substrate and the fourth main surface of the second substrate were bonded.

[0129] (Peel strength test) Next, for the connection structure according to Example 1, the adhesive strength between the first substrate and the second substrate was measured by the following method. FIG. 17 is a cross-sectional view schematically showing a method for testing peel strength. As shown in Figure 17, double-sided tape was attached to the top surface of an FR-1 substrate 62, which served as a printed circuit board, placed on a stage 61, and the connection structure 1 was adhered onto the tape so that the second main surface 10b of the first substrate 10 was in contact with the tape. Next, the edge of the second substrate 20 was peeled off, and an upward force was applied so that the peeled portion of the second substrate 20 was perpendicular to the first main surface 10a of the first substrate 10, and the peel strength was measured. Peel strength was measured using a tensile tester (device name: TENSILON, manufacturer: A&D) under the following measurement conditions: load cell: 5 kg, tensile speed: 5 mm / min. Measurements were performed twice. The results are shown in Figure 18. FIG. 18 is a chart showing the results of the peel strength test (n=2).

[0130] 18, it was found that sufficient peel strength could be ensured in the connection structure according to Example 1. Because such peel strength could be ensured, poor conductivity and poor connection could be prevented. [Explanation of symbols]

[0131] 1, 101, 201 Connection structure 10 First board 10a First principal surface 10b Second principal surface 11 1st substrate electrode 11a: Surface of first substrate electrode 20 Second board 20c 3rd principal surface 20d Fourth principal surface 21 2nd substrate electrode 21a: Surface of second substrate electrode 30, 230 Bonding material 40, 240 adhesive 50 Resist 61 Stages 62 FR-1 board 110, 120, 220, board 110B First board block 120B Second board block 210 Third board 210B 3rd board block 210e 5th principal surface 210f 6th main surface 211 3rd substrate electrode 251 Mounted Parts 252 Mounting parts L Laser M motherboard

Claims

1. a first substrate having a first main surface and a second main surface opposite to the first main surface, the first substrate including a first thermoplastic resin; a first substrate electrode disposed on the first main surface (excluding the case where the first substrate electrode is disposed in a ring shape on the first main surface); a second substrate including a third main surface and a fourth main surface opposite the third main surface and facing the first main surface, the second substrate including a second thermoplastic resin; a second substrate electrode disposed on the fourth main surface (excluding the case where the second substrate electrode is disposed in a ring shape on the fourth main surface); a conductive bonding material that bonds the first substrate electrode and the second substrate electrode; an insulating adhesive that bonds the first main surface other than a portion where the first substrate electrode is disposed and the fourth main surface other than a portion where the second substrate electrode is disposed; a bonding temperature of the bonding material is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin; the adhesive has a bonding temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin; A connection structure, wherein the adhesive does not contain conductive particles.

2. The connection structure according to claim 1 , wherein the adhesive contains a polyolefin resin.

3. The connection structure according to claim 1 or 2, wherein the adhesive has a lower dielectric constant than the first thermoplastic resin and the second thermoplastic resin.

4. 4. The connection structure according to claim 1, wherein the bonding material is a sintered body of a conductive paste containing metal nanoparticles, and the bonding temperature of the bonding material is the sintering temperature of the metal nanoparticles.

5. 4. The connection structure according to claim 1, wherein the bonding material is a lead-free solder, and the bonding temperature of the bonding material is the melting point of the lead-free solder.

6. A connection structure according to any one of claims 1 to 3, wherein the bonding material is a conductive adhesive containing conductive particles and a thermosetting resin, and the bonding temperature of the bonding material is the thermosetting temperature of the thermosetting resin.

7. A connection structure according to any one of claims 1 to 6, wherein a first substrate block in which a plurality of substrates including the first substrate are stacked is connected to a second substrate block in which a plurality of substrates including the second substrate are stacked.

8. The connection structure according to claim 7 , wherein a third substrate block, in which a plurality of substrates are stacked, is further connected to the first substrate of the first substrate block.

9. the third substrate block has a fifth main surface and a sixth main surface that faces the fifth main surface and also faces the first main surface, and includes a third substrate containing a third thermoplastic resin, and a third substrate electrode disposed on the sixth main surface; the first substrate electrode and the third substrate electrode are bonded together by the bonding material, the first main surface other than the portion where the first substrate electrode is disposed and the sixth main surface other than the portion where the third substrate electrode is disposed are bonded together by the adhesive, a bonding temperature of the bonding material is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the third thermoplastic resin; 9. The connection structure according to claim 8, wherein the adhesive temperature is lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the third thermoplastic resin.

10. a first substrate preparation step of preparing a first substrate having a first main surface and a second main surface opposite to the first main surface, a first substrate electrode on the first main surface, and containing a first thermoplastic resin (excluding the case where the first substrate electrode is arranged in a ring shape on the first main surface); a second substrate preparation step of preparing a second substrate having a third main surface and a fourth main surface opposite the third main surface, a second substrate electrode on the fourth main surface, and containing a second thermoplastic resin (excluding the case where the second substrate electrode is arranged in a ring shape on the fourth main surface); a bonding step of bonding the first substrate electrode and the second substrate electrode with a conductive bonding material; a bonding step of bonding the first main surface other than a portion where the first substrate electrode is disposed and the fourth main surface other than a portion where the second substrate electrode is disposed, using an insulating adhesive; the joining step is carried out at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin; the bonding step is carried out at a temperature lower than the melting point or glass transition temperature of the first thermoplastic resin and lower than the melting point or glass transition temperature of the second thermoplastic resin; The method for manufacturing a connection structure, wherein the adhesive does not contain conductive particles.

11. The method for manufacturing a connection structure according to claim 10 , wherein the joining step and the bonding step are carried out simultaneously.

Images