Joint structure

Abstract

Provided is a joint structure in which an element member comprising a ceramic portion and an element electrode including a pair of inner electrodes and a pair of outer electrodes is electrically joined to a circuit board, the joint structure exhibiting stable electric characteristics under a high-humidity environment. A joint structure comprising: an element member in which a ceramic portion and an element electrode including a pair of inner electrodes and a pair of outer electrodes are formed on a first base material, wherein the ceramic portion is coated with a first protection layer, the pair of outer electrodes are exposed from the first protection layer, and the pair of inner electrodes are positioned inside the ceramic portion, the ceramic portion having a thickness of less than or equal to 40 μm; a circuit board having a pair of land electrodes formed on a second base material; and a joint portion electrically joining the pair of outer electrodes and the pair of land electrodes opposite each other, with the ceramic portion and the first protection layer disposed between the first base material and the second base material.

Description

[Technical field]

[0001] The present disclosure relates to a joint structure, and more particularly to a joint structure (which may also be referred to as a "mounting structure") in which an element member is electrically joined (or mounted) to a circuit board via a joint. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there is known a joint structure in which an electronic component, such as a chip component having a ceramic portion and a pair of external electrodes, is joined to a circuit board by a solder material (see Patent Documents 1 and 2).

[0003] In such a joint structure, measures against ion migration are an important issue. Patent Document 2 discloses that, in order to prevent ion migration that may occur between a pair of external electrodes of an electronic component, three of the four side surfaces of an approximately rectangular parallelepiped electronic component excluding the side surface facing the main surface of a circuit board (claim 1), or all four side surfaces of the approximately rectangular parallelepiped electronic component (claims 2 and 3) are covered with a coating resin layer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-157951 A [Patent Document 2] International Publication No. 2017 / 110136 [Patent Document 3] Patent Publication No. 2021-58894 [Patent Document 4] JP 2013-149774 A Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, chip components and the like have been used as electronic components electrically connected to circuit boards, but it is conceivable to use element members in which an element structure is formed on a separate substrate (base material) instead of chip components.

[0006] Patent Document 2, which relates to a bonded structure in which a chip component is electrically bonded to a circuit board, describes that ion migration is a phenomenon in which, between electrodes with a potential difference, the metal components of one electrode are ionized and move toward the other electrode, causing the deposited metal to reduce the insulation between the electrodes or cause a short circuit between the electrodes, and that this phenomenon is likely to occur under high humidity conditions.

[0007] In contrast, according to further research by the present inventors, in a bonded structure in which an element member, in which an element structure including a ceramic part and a pair of electrodes is formed on a substrate (base material), is electrically bonded to a circuit board, ion migration (hereinafter also simply referred to as "migration") occurs between electrodes with a potential difference, in which the metal component of one electrode is ionized and moves toward the other electrode, and the deposited metal reduces the insulation (in other words, resistance) between the electrodes, and in severe cases, the electrodes are shorted. In addition, it has been found that the metal component of one electrode is ionized and the one electrode is dissolved, increasing the resistance between the electrodes, and in severe cases, the one electrode is dissolved and penetrates (hereinafter referred to as "open"). Migration occurs depending on the magnitude of the electric field intensity, in other words, it occurs in proportion to the load voltage and inversely proportional to the distance between the electrodes. According to research by the present inventors, it has been found that when the above-mentioned element member includes element electrodes including a pair of internal electrodes and a pair of external electrodes, there is a problem in that the electrodes are dissolved first due to migration, resulting in high resistance. Conventionally, in the case of typical chip components, the problem of low resistance due to migration has been addressed, but because the electrodes are thick, high resistance due to migration has not actually been an issue.

[0008] In a high humidity environment, it is not preferable that the resistance of the bonded structure becomes significantly lower or higher than the initial value due to ion migration, since in either case the electrical characteristics of the bonded structure are impaired.

[0009] An object of the present disclosure is to provide a joint structure in which an element member having a ceramic part and an element electrode including a pair of internal electrodes and a pair of external electrodes is electrically joined to a circuit board, the joint structure exhibiting stable electrical characteristics even in a high-humidity environment. [Means for solving the problem]

[0010] [1] an element member in which a ceramic part and element electrodes including a pair of internal electrodes and a pair of external electrodes are formed on a first substrate, the ceramic part is covered with a first protective layer, the pair of external electrodes are exposed from the first protective layer, the pair of internal electrodes are located within the ceramic part, and the ceramic part has a thickness of 40 μm or less; a circuit board having a pair of land electrodes formed on a second base material; a joint portion that electrically joins the pair of external electrodes and the pair of land electrodes that face each other in a state in which the ceramic portion and the first protective layer are disposed between the first base material and the second base material; and A joint structure comprising:

[0011] [2] The joint structure described in [1] above, wherein a surface of the first protective layer opposite the first substrate protrudes toward the second substrate further than surfaces of the pair of external electrodes opposite the first substrate.

[0012] [3] The joint structure according to the above-mentioned [1] or [2], wherein the circuit board has a second protective layer disposed on the second base material, and the pair of land electrodes are exposed from the second protective layer.

[0013] [4] The joint structure described in [3] above, wherein a surface of the second protective layer opposite the second substrate protrudes toward the first substrate more than surfaces of the pair of land electrodes opposite the second substrate.

[0014] [5] The bonded structure according to any one of the above [1] to [4], wherein the first protective layer contains a first resin material.

[0015] [6] The bonded structure described in [5] above, wherein the first resin material includes at least one selected from the group consisting of polyimide-based resins, polyamideimide-based resins, epoxy-based resins, liquid crystal polymers, polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, polyester-based resins, polyurethane-based resins, polyamide-based resins, polyetherimide-based resins, and (meth)acrylic-based resins.

[0016] [7] The bonded structure described in [5] or [6] above, wherein the first protective layer further includes a first metal layer.

[0017] [8] The bonded structure according to any one of the above [1] to [7], wherein the first base material includes a second resin material and a second metal layer.

[0018] [9] The bonded structure according to any one of the above [1] to [8], wherein the second base material is a flexible substrate containing a third resin material.

[0019]

[10] The joint structure according to any one of the above [1] to [9], wherein the joint portion contains a solder material.

[0020]

[11] The joint structure according to

[10] above, wherein the area of ​​the joint region of the pair of land electrodes is three times or less the area of ​​the joint region of the pair of external electrodes.

[0021]

[12] The joint structure according to any one of the above [1] to

[11] , wherein the joint is covered with a cured resin material as a fourth resin material.

[0022]

[13] The joint structure according to any one of the above [1] to

[11] , wherein the joint is covered with a thermoplastic resin material as a fifth resin material.

[0023]

[14] The joint structure according to any one of the above [1] to [9], wherein the joint portion contains an anisotropic conductive material.

[0024]

[15] The joint structure according to any one of the above [1] to

[14] , wherein the ceramic portion is formed between the pair of external electrodes.

[0025]

[16] The joint structure according to any one of the above [1] to

[14] , wherein the ceramic portion is formed adjacent to the pair of external electrodes.

[0026]

[17] The bonded structure according to any one of the above [1] to

[16] , wherein the ceramic portion contains a thermistor material, and the bonded structure is a temperature sensor. Effect of the Invention

[0027] According to the present disclosure, there is provided a joint structure in which an element member having a ceramic part and an element electrode including a pair of internal electrodes and a pair of external electrodes is electrically joined to a circuit board, the joint structure exhibiting stable electrical characteristics even in a high-humidity environment. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a bonded structure according to one embodiment (embodiment 1) of the present disclosure. [Diagram 2]2A and 2B are diagrams illustrating a method for manufacturing the bonded structure in the embodiment of FIG. 1, and are schematic top views sequentially illustrating the steps of manufacturing the element member. [Diagram 3] FIG. 3 is a diagram for explaining a manufacturing method of the joined structure in the embodiment of FIG. 1, and shows an element member produced in a process subsequent to that of FIG. 2(b), where FIG. 3(a) is a schematic cross-sectional view of the element member, and FIG. 3(b) is a schematic top view of the element member (FIG. 3(a) is a schematic cross-sectional view as viewed along line AA in FIG. 3(b)). [Figure 4] 4A and 4B are diagrams illustrating a method for manufacturing a joint structure in the embodiment of FIG. 1, in which FIG. 4A is a schematic cross-sectional view of a circuit board, and FIG. 4B is a schematic top view of the circuit board (FIG. 4A is a schematic cross-sectional view as viewed along line BB in FIG. 4B). [Diagram 5] 5A and 5B are schematic enlarged cross-sectional views of the joint portion of the joint structure in the embodiment of FIG. 1, with FIG. 5A showing a case where L2 / L1 is 3 or less (e.g., 3), and FIG. 5B showing a case where L2 / L1 exceeds 3 (e.g., 3.5) (L1 is the length of the joint area of ​​the external electrode, and L2 is the length of the joint area of ​​the land electrode. FIG. 5 shows external electrode 4a, land electrode 14a, and joint 30a, but the same applies to external electrode 4b, land electrode 14b, and joint 30b). [Figure 6] FIG. 6 is a schematic cross-sectional view showing a joint structure according to another embodiment (embodiment 2) of the present disclosure. [Figure 7] 7A and 7B are diagrams illustrating a manufacturing method of the bonded structure in the embodiment of FIG. 6, in which FIG. 7A is a schematic cross-sectional view of an element member, and FIG. 7B is a schematic top view of the element member (FIG. 7A is a schematic cross-sectional view as viewed along line AA in FIG. 7B). [Figure 8] FIG. 8 is a schematic cross-sectional view showing a joint structure according to another embodiment (Embodiment 3) of the present disclosure. [Figure 9]FIG. 9 is a schematic cross-sectional view showing a joint structure according to another embodiment (embodiment 4) of the present disclosure. [Figure 10] 10A and 10B are diagrams illustrating a manufacturing method of the bonded structure in the embodiment of FIG. 9, in which FIG. 10A is a schematic cross-sectional view of an element member, and FIG. 10B is a schematic top view of the element member (FIG. 10A is a schematic cross-sectional view as viewed along line AA in FIG. 10B). [Figure 11] FIG. 11 is a schematic cross-sectional view showing a bonded structure in another embodiment (embodiment 5) of the present disclosure, where FIG. 11(a) shows a cross-section including a bonded portion and FIG. 11(b) shows a cross-section including a ceramic portion (FIG. 11(a) is a schematic cross-sectional view seen along line EE in FIG. 12(b) and FIG. 13(b), and FIG. 11(b) is a schematic cross-sectional view seen along line FF in FIG. 12(b) and FIG. 13(b)). [Figure 12] 12A and 12B are diagrams illustrating a manufacturing method of the joined structure in the embodiment of FIG. 11, in which FIG. 12A is a schematic cross-sectional view of an element member, and FIG. 12B is a schematic top view of the element member (FIG. 12A is a schematic cross-sectional view as viewed along line CC in FIG. 12B). [Figure 13] 13A and 13B are diagrams for explaining a manufacturing method of the joint structure in the embodiment of FIG. 11, in which FIG. 13A is a schematic cross-sectional view of a circuit board, and FIG. 13B is a schematic top view of the circuit board (FIG. 13A is a schematic cross-sectional view as viewed along line DD in FIG. 13B). [Figure 14] FIG. 14 is a schematic cross-sectional view showing a bonded structure of a comparative example in which a chip part is bonded to a circuit board. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Some embodiments of the present disclosure will be described in detail below with reference to the drawings, but the present disclosure is not limited to these embodiments. Note that similar components are given similar reference symbols, and similar descriptions may apply unless otherwise specified.

[0030] (Embodiment 1) 1 to 4, a joint structure 40 of the present embodiment includes: an element member 10 in which a pair of element electrodes 2a, 2b (hereinafter also referred to as element electrodes 2), each including a pair of internal electrodes 3a, 3b and a pair of external electrodes 4a, 4b, a ceramic portion 5, and a first protective layer 6 are formed on a first base material 1; a circuit board 20 having a pair of land electrodes 14a, 14b formed on a second base material 11; The ceramic part 5 and the first protective layer 6 are disposed between the first substrate 1 and the second substrate 11, and include joints 30a, 30b that electrically join a pair of opposing external electrodes 4a, 4b and a pair of land electrodes 14a, 14b, respectively.

[0031] The ceramic part 5 is covered with a first protective layer 6, the pair of external electrodes 4a, 4b are exposed from the first protective layer 6, the pair of internal electrodes 3a, 3b are located within the ceramic part 5, and the thickness t of the ceramic part 5 is 40 μm or less. According to this embodiment, such a configuration provides a joint structure that exhibits stable electrical characteristics even in a high-humidity environment.

[0032] The joint structure 40 of this embodiment will be described in detail below through its manufacturing method. Note that the explanations regarding each member and / or material can also be applied to the joint structure 40 that is finally obtained, unless otherwise specified.

[0033] ·Element materials 2(a), the element electrodes 2 are formed on the surface of the first base material 1. (Hereinafter, the surface of the first base material 1 on which the element electrodes 2 are formed is also referred to as the "principal surface" of the first base material 1.)

[0034] The first substrate 1 may be any suitable substrate (or substrate) as long as the surface portion on which the element electrodes 2 are formed is insulating. For example, the first substrate 1 may be a flexible substrate (base layer). The first substrate 1 may include any suitable resin material (second resin material), without any particular limitation. The resin material (second resin material) used for the first substrate 1 may include at least one selected from the group consisting of polyimide resin, polyester resin, glass-epoxy resin, liquid crystal polymer (LCP), and the like. The first substrate 1 may be made of the above-mentioned resin material, or may include other components in addition to the above-mentioned resin material in a relatively small amount (for example, less than 50 mass %, particularly 30 mass % or less, based on the entire first substrate 1). The other components preferably have lower moisture permeability than the above-mentioned resin material. However, the present embodiment is not limited thereto, and the first substrate 1 may be a rigid substrate. The rigid substrate may be a conventional rigid substrate (which may be made of glass-epoxy resin, paper-phenolic resin, paper-epoxy resin, and the like).

[0035] The thickness of the first substrate 1 can be appropriately selected, and can be, for example, 10 μm or more and 5 mm or less. When the first substrate 1 is a flexible substrate, the thickness of the first substrate 1 can be relatively thin, for example, 10 μm or more and 80 μm or less, particularly 60 μm or less, and more particularly 50 μm or less.

[0036] The method of forming the element electrode 2 on the surface of the first base material 1 is not particularly limited. For example, a metal foil (e.g., Cu foil) is adhered to the first base material 1 with an adhesive, the metal foil on the first base material 1 is patterned according to the shape of the element electrode 2 by photolithography, and the surface of the patterned metal (e.g., Cu base material) is appropriately subjected to electrolytic or electroless metal plating (e.g., a plating layer containing Ni and / or Au) to form the element electrode 2 (in other words, the internal electrodes 3a, 3b and the external electrodes 4a, 4b integrally) (Note that in this case, the adhesive layer may remain between the first base material 1 and the element electrode 2). According to this method, the element electrode 2 having a fine structure can be formed with high precision. However, the present embodiment is not limited thereto, and although less preferable, for example, the element electrode 2 may be formed by applying (e.g., printing) a conductive paste on the first base material 1 in a pattern according to the shape of the element electrode 2 and appropriately heating it. The heating may be performed simultaneously with the formation of the ceramic part 5 described later, or may be performed separately.

[0037] The element electrode 2 is formed using any suitable conductive material, and may be made of, for example, a metal. The Ag content in the element electrode 2 may be, for example, 20% by mass or less, particularly 10% by mass or less, and preferably substantially 0% by mass. In conventional general chip components, when a conductive paste containing Ag-containing particles (such as Ag particles or particles containing Ag and Pd) is used as the material for the internal electrodes and / or external electrodes, the ceramic material and the Ag-containing particles can be co-sintered when the ceramic body is formed, so that the internal electrodes and / or external electrodes often contain Ag. However, when such a chip component is joined to a circuit board with a solder material, and while the joined structure obtained by this is used under high humidity conditions, Ag is likely to precipitate between a pair of external electrodes and dendrites are likely to grow, which may cause a decrease in the resistance of the chip component and, in some cases, a short circuit. In contrast to this, in the present embodiment, by making the Ag content of the element electrode 2 small as described above, and preferably substantially free of Ag, the growth of dendrites between the external electrodes 4a, 4b due to migration can be reduced or prevented even when the finally obtained joint structure 40 is used under high humidity conditions (compared to a joint structure in which a chip component or joint member having a higher Ag content in the external electrodes is joined to a circuit board), and the reduction in resistance of the joint structure 40 (and in severe cases, short circuits) can be effectively reduced or prevented.

[0038] Although not limiting this embodiment, the element electrode 2 may be composed of a base material made of at least one metal selected from the group consisting of Cu, Al, Ni, Sn, Ti, Zn, Fe, etc., and a plating layer (which may be a single layer or multi-layer structure) made of at least one metal selected from the group consisting of Ni, Au, Sn, Zn, Cr, W, Pd, Pt, Cu, etc.

[0039] The thickness of the element electrode 2 is not particularly limited as long as it is smaller than the thickness of the ceramic part 5 described later, but may be, for example, 30 μm or less, particularly 20 μm or less, and may be, for example, 1 μm or more, but the lower limit is not particularly limited. Such a relatively thin element electrode 2 may be considered to be susceptible to the effect of dissolution due to migration, if it were not covered with the bonding parts 30a, 30b and the first protective layer 6 described later.

[0040] The shape of the element electrode 2 (including a pair of internal electrodes 3a, 3b and a pair of external electrodes 4a, 4b) can be appropriately selected depending on the electrical characteristics desired for the element member 10 and ultimately the joint structure 40, and the dimensions desired for the joint structure 40, etc.

[0041] Next, as shown in FIG. 2(b), a ceramic portion 5 is formed on a predetermined region of the first substrate 1 and the element electrode 2.

[0042] The ceramic portion 5 may be formed using any appropriate ceramic material depending on the function desired for the element member 10. For example, generally, a raw material mixture containing particles of a predetermined metal oxide (ceramic material) may be applied (e.g., printed) onto predetermined regions of the first substrate 1 and the element electrode 2 by any appropriate method, and then fired by heating, and optionally annealed and / or dried, to form the ceramic portion 5. The heating (including firing) temperature may be set depending on the ceramic material used, but it is preferable that the heating does not substantially cause deformation of the first substrate 1.

[0043] The thickness t of the ceramic part 5 (see FIG. 1 and FIG. 3(a)) may be 40 μm or less. The thickness t of the ceramic part refers to the height from the surface (main surface) of the first substrate 1 to the surface of the ceramic part 5 opposite to the main surface. The lower limit of the thickness of the ceramic part 5 may be larger than the thickness of the element electrode 2, but may be, for example, 2 μm or more, particularly 5 μm or more, larger than the thickness of the element electrode 2. Although this embodiment is not bound by any theory, by making the thickness t of the ceramic part 5 so small, the adhesion interface of each layer of the finally obtained joint structure 40 is less uneven, improving the sealing property, and even when the joint structure 40 is used under high humidity conditions, migration can be suppressed, and the increase in resistance (open in severe cases) and / or the decrease in resistance (short in severe cases) of the joint structure 40 can be effectively reduced or prevented.

[0044] Thereafter, as shown in FIGS. 3(a) and 3(b), a first protective layer 6 that covers the ceramic portion 5 is formed.

[0045] The first protective layer 6 may contain any appropriate material as long as the portion in contact with the ceramic portion 5 and the element electrode 2 is insulating. For example, the first protective layer 6 may be flexible. Typically, the first protective layer 6 may contain any appropriate resin material (first resin material). The resin material (first resin material) used for the first protective layer 6 may contain at least one selected from the group consisting of polyimide resin, polyamideimide resin, epoxy resin, liquid crystal polymer (LCP), polyethylene resin, polypropylene resin, polystyrene resin, polyester resin, polyurethane resin, polyamide resin (including nylon), polyetherimide resin, and (meth)acrylic resin. Among them, LCP is preferable because it has a relatively low moisture permeability and is therefore more effective in suppressing migration. The first protective layer 6 may be made of the above-mentioned resin material, and may contain, in addition to the above-mentioned resin material, a relatively small amount of other components (for example, less than 50% by mass, particularly 30% by mass or less, based on the entire first protective layer 6). The other components preferably have lower moisture permeability than the above-mentioned resin material.

[0046] The method of forming the first protective layer 6 that covers the ceramic part 5 is not particularly limited. For example, the first protective layer 6 that covers the ceramic part 5 can be formed by using a first protective layer 6 having an area sufficiently larger than the ceramic part 5, disposing the first protective layer 6 including an adhesive layer on the ceramic part 5 (or disposing the first protective layer 6 via an adhesive), and then pressing the first protective layer 6. The adhesive may be one that can be bonded at room temperature or one that can be bonded by heating. In the latter case, heating for bonding the first protective layer 6 may be performed simultaneously with heating for forming a joint, which will be described later, or may be performed separately.

[0047] The first protective layer 6 may be a single layer or a multilayer, and in the latter case may include one or more adhesive layers as appropriate. The first protective layer 6 may or may not be a coverlay layer derived from a so-called coverlay. The surface of the first protective layer 6 may be water-repellent as it is and / or may be treated to be water-repellent as necessary.

[0048] The thickness of the first protective layer 6 can be appropriately selected depending on the moisture permeability of the first protective layer 6, and can be, for example, 10 μm or more, particularly 15 μm or more, and more particularly 20 μm or more. The upper limit of the thickness of the first protective layer 6 is not particularly limited, and the thickness can be, for example, 50 μm or less, particularly 40 μm or less, and more particularly 30 μm or less.

[0049] The first protective layer 6 may be formed on any appropriate region as long as it covers the ceramic portion 5 and exposes the pair of external electrodes 4a, 4b. For example, as shown in Fig. 3(a), the first protective layer 6 may be formed between the external electrodes 4a, 4b on the surface (principal surface) of the first substrate 1, and preferably may also be formed on the outer circumferential region of the surface (principal surface) of the first substrate 1, and more preferably may be formed so as to surround each of the external electrodes 4a, 4b, as shown in Fig. 3(b).

[0050] Of the element electrode 2, the portions located within the ceramic part 5 are the internal electrodes 3a, 3b, and the portions exposed from the first protective layer 6 are the external electrodes 4a, 4b. The element electrode 2 may further include portions located outside the ceramic part 5 but covered with the first protective layer 6 adjacent to the external electrodes 4a, 4b, and these portions may be considered to be included in the internal electrodes 3a, 3b (particularly when referring to dissolution resulting from migration).

[0051] The internal electrodes 3a, 3b may have a comb-like shape with teeth facing each other, for example, as shown in FIG. 3(b).

[0052] 3(b), the ceramic portion 5 may be formed between the external electrodes 4a, 4b so as to be as far apart as possible (in this case, as described above, the first protective layer 6 is formed between the external electrodes 4a, 4b, and when the second protective layer 16 described below is present on the circuit board 20, the second protective layer 16 is formed between the land electrodes 14a, 14b). (Also, for example, in some cases, the ceramic portion 5 may be formed adjacent to the external electrodes 4a, 4b, as described in detail in the fifth embodiment.)

[0053] However, the arrangement and / or shape of the internal electrodes 3a, 3b and the external electrodes 4a, 4b are not limited to this and can be selected appropriately depending on the electrical characteristics desired for the element member 10 and thus the joint structure 40, and the dimensions desired for the joint structure 40, etc.

[0054] According to this embodiment, by covering the ceramic part 5 with the first protective layer 6 and setting the thickness t of the ceramic part 5 (see Figures 1 and 3(a)) to 40 μm or less, even when the finally obtained joint structure 40 is used under high humidity conditions, dissolution of the internal electrodes 3a and / or 3b (for example, near the external electrodes 4a and / or 4b) due to migration can be reduced or prevented, and the increase in resistance of the joint structure 40 (or opening in severe cases) can be effectively reduced or prevented.

[0055] In this manner, the element member 10 can be produced.

[0056] Circuit Boards 4(a)-(b), a pair of land electrodes 14a, 14b and lead wires 15a, 15b extending from each of the land electrodes 14a, 14b are formed on the surface of the second substrate 11. (Hereinafter, the surface of the second substrate 1 on which the land electrodes 14a, 14b are formed is also referred to as the "principal surface" of the second substrate 11.)

[0057] The second substrate 11 may be any suitable substrate (or substrate) as long as the surface portion on which the land electrodes 14a, 14b and the lead wires 15a, 15b are formed is insulating. For example, the second substrate 11 may be a flexible substrate (base layer). Although not particularly limited, the second substrate 11 may include any suitable resin material (third resin material). The resin material (third resin material) used for the second substrate 11 may be the same as the resin material (second resin material) described above for the first substrate 1. The second substrate 11 may be made of the above-mentioned resin material, or may contain other components in addition to the above-mentioned resin material in a relatively small amount (for example, less than 50 mass %, particularly 30 mass % or less with respect to the entire second substrate 11). The other components preferably have lower moisture permeability than the above-mentioned resin material. However, the present embodiment is not limited thereto, and the second substrate 11 may be a rigid substrate. The rigid substrate may be the same as the rigid substrate described above for the first substrate 1.

[0058] The thickness of the second base material 11 can be appropriately selected, and can be, for example, 10 μm or more and 5 mm or less. When the second base material 11 is a flexible substrate, the thickness of the second base material 11 can be relatively thin, and can be, for example, 10 μm or more and 80 μm or less, particularly 60 μm or less, and more particularly 50 μm or less.

[0059] The method for forming the land electrodes 14a, 14b and the leads 15a, 15b is not particularly limited. For example, a metal foil (e.g., Cu foil) is adhered to the second base material 11 with an adhesive, the metal foil on the second base material 11 is patterned by photolithography according to the shapes of the land electrodes 14a, 14b and the leads 15a, 15b, and the land electrodes 14a, 14b and the leads 15a, 15b are integrally formed by electrolytically or non-electrolytically plating the surface of the patterned metal (e.g., Cu base material) appropriately (note that in this case, an adhesive layer may remain between the second base material 11 and the land electrodes 14a, 14b and the leads 15a, 15b). However, the present embodiment is not limited thereto. For example, a conductive paste may be applied (e.g., printed) onto the second substrate 11 in a pattern corresponding to the shapes of the land electrodes 14a, 14b and the lead wires 15a, 15b, and then heated appropriately to form the land electrodes 14a, 14b and the lead wires 15a, 15b.

[0060] The land electrodes 14a, 14b and the leads 15a, 15b may be formed using any suitable conductive material, and may be made of, for example, a metal. The Ag content in the land electrodes 14a, 14b and the leads 15a, 15b may be, for example, 20 mass % or less, particularly 10 mass % or less, and preferably substantially 0 mass %. In this embodiment, by making the Ag content in the land electrodes 14a, 14b small as described above, and preferably substantially free of Ag, even when the finally obtained joint structure 40 is used under high humidity conditions, it is possible to reduce or prevent the growth of dendrites between the land electrodes 14a, 14b due to migration (compared to a joint structure in which a chip component or a joint member is joined to a circuit board having a higher Ag content in the land electrodes), and it is possible to effectively reduce or prevent the decrease in resistance (and in severe cases, short circuit) of the joint structure 40.

[0061] Although not limiting this embodiment, the land electrodes 14a, 14b and the lead wires 15a, 15b may be composed of a base material made of at least one metal selected from the group consisting of Cu, Al, Ni, Sn, Ti, Zn, Fe, etc., and a plating layer (which may be a single layer or multi-layer structure) made of at least one metal selected from the group consisting of Ni, Au, Sn, Zn, Cr, W, Pd, Pt, Cu, etc.

[0062] The thicknesses of the land electrodes 14a, 14b and the leads 15a, 15b are not particularly limited, but may be, for example, 30 μm or more, particularly 20 μm or more, and may be, for example, 50 μm or less, particularly 35 μm or less. Such relatively thin land electrodes 14a, 14b may be considered to be susceptible to dissolution due to migration if they were not covered with the bonding parts 30a, 30b (and the second protective layer 16, if present) described below.

[0063] The arrangement and shape of the land electrodes 14a, 14b may be appropriately selected depending on the arrangement and shape of the external electrodes 4a, 4b. The arrangement and shape of the lead wires 15a, 15b may be appropriately selected depending on the desired dimensions and terminal positions of the finally obtained joint structure 40.

[0064] Although not essential to this embodiment, the circuit board 20 may have a second protective layer 16 disposed on the second base material 11. The pair of land electrodes 14a, 14b are exposed from the second protective layer 16.

[0065] The second protective layer 16 may be formed on any appropriate region of the second substrate 11 as long as the pair of land electrodes 14a, 14b are exposed. For example, as shown in Fig. 4(a), the second protective layer 16 may be formed between the land electrodes 14a, 14b on the surface (main surface) of the second substrate 11, and preferably may also be formed on the outer circumferential region of the surface (main surface) of the second substrate 11, and more preferably may be formed so as to surround each of the land electrodes 14a, 14b, as shown in Fig. 4(b).

[0066] Additionally, the above description of the first protective layer 6 may be similarly applied to the second protective layer 16. The second protective layer 16 may or may not be a coverlay layer derived from a so-called coverlay. The surface of the second protective layer 16 may be water-repellent as it is, and / or may be subjected to a water-repellent treatment as necessary.

[0067] In this manner, the circuit board 20 can be produced.

[0068] ·Joint part The element member 10 and circuit board 20 prepared as described above are arranged such that the ceramic part 5 and the first protective layer 6 are present between the first substrate 1 and the second substrate 11, and the pair of opposing external electrodes 4a, 4b and the pair of land electrodes 14a, 14b are electrically joined at joints 30a, 30b.

[0069] The joints 30a, 30b are not particularly limited as long as they can electrically connect the external electrodes 4a, 4b and the land electrodes 14a, 14b, but may include, for example, a solder material. A lead-free solder material may be used as the solder material. The lead-free solder material may be, for example, Sn-Cu-based, Sn-Ag-based, Sn-Ag-Cu-based, Sn-Zn-based, Sn-Bi-based, etc. The Ag content in the solder material may be, for example, 20 mass % or less, particularly 10 mass % or less.

[0070] The method of forming the joints 30a, 30b is not particularly limited. Typically, a conductive paste containing particles of a solder material is applied (for example, printed) onto the land electrodes 14a, 14b, and then the element member 10 and the circuit board 20 are arranged so that the ceramic part 5 and the first protective layer 6 are present between the first base material 1 and the second base material 11, and the pair of external electrodes 4a, 4b are superimposed so that they are placed on the conductive paste on the pair of land electrodes 14a, 14b facing each other, and the joints 30a, 30b that electrically join the external electrodes 4a, 4b and the land electrodes 14a, 14b are formed by heating in a reflow furnace or the like in this superimposed state. The heating temperature can be set to be equal to or higher than the melting point of the solder material used, but it is preferable that the first base material 1, the second base material 11, the first protective layer 6, and the second protective layer 16, if present, are not substantially deformed by heating.

[0071] The thickness of the conductive paste containing particles of solder material applied (e.g., printed) onto the land electrodes 14a, 14b is greater than the sum of the maximum height h1 (see Figure 1) from the surface of the first base material 1 opposite the surface (main surface) of the external electrodes 4a, 4b to the surface of the first protective layer 6 opposite the element electrode 2, and the maximum height h2 (see Figure 1) from the surface of the second base material 11 opposite the surface (main surface) of the land electrodes 14a, 14b to the surface of the second protective layer 16 opposite the land electrodes 14a, 14b, and can preferably be appropriately set so that the solder material sufficiently wets and spreads over the exposed surfaces of the external electrodes 4a, 4b and the exposed surfaces of the land electrodes 14a, 14b when the element component 10 is joined to the circuit board 20, as described below.

[0072] The conductive paste containing the solder material particles may contain any other appropriate components in addition to the solder material particles as described above. Such other components may be a flux, a viscosity modifier, a solvent, etc. The flux is not particularly limited, and a known flux may be used. For example, the flux may be a flux composition containing a rosin modified substance as described in Patent Document 3. Such a flux composition is said to be capable of coating the solder material particles and suppressing migration. The rosin modified substance is a compound containing rosin or a rosin derivative and a compound represented by the following structural formula: NH 3-n (R-OH) n (n≦3) The rosin modified product may be a rosin modified product consisting of a reaction product with an alkanolamine represented by the structural formula (1) above. Such a rosin modified product can be obtained by reacting rosin or a rosin derivative with an organic acid and an alkanolamine. More specifically, such a rosin modified product may be a reaction product consisting of a reaction product with a COOH group of the rosin or rosin derivative and an NH 3-n or an ester bond obtained by condensing a COOH group of rosin or a rosin derivative with the OH group in the above structural formula (1).

[0073] The solder material melts during the heating, wets and spreads on the exposed surfaces of the pair of external electrodes 4a, 4b and the pair of land electrodes 14a, 14b, and then solidifies as the temperature drops to form joints 30a, 30b. In order to obtain sufficient conductivity and joint strength, it is preferable that the area of ​​the joint region of the land electrodes 14a, 14b is substantially equal to or greater than (i.e., at least one time) the area of ​​the joint region of the opposing external electrodes 4a, 4b. In addition, it is preferable that the area of ​​the joint region of the land electrodes 14a, 14b is three times or less the area of ​​the joint region of the opposing external electrodes 4a, 4b.

[0074] The bonding area of ​​the external electrodes 4a, 4b refers to the area of ​​the surface of the external electrodes 4a, 4b opposite to the first substrate 1. The exposed surface of the external electrodes 4a, 4b refers to the combination of the bonding area of ​​the external electrodes 4a, 4b and the side surface of the external electrodes 4a, 4b between the first substrate 1 and the bonding area. The bonding area of ​​the land electrodes 14a, 14b refers to the area of ​​the surface of the land electrodes 14a, 14b opposite to the second substrate 11. The exposed surface of the land electrodes 14a, 14b refers to the combination of the bonding area of ​​the land electrodes 14a, 14b and the side surface of the land electrodes 14a, 14b between the second substrate 11 and the bonding area.

[0075] By making the ratio of the area of ​​the bonding region of the land electrodes 14a, 14b to the area of ​​the bonding region of the external electrodes 4a, 4b 3 times or less, for example, when the width of the bonding region of the external electrodes 4a, 4b is the same as that of the land electrodes 14a, 14b, the ratio of the length L2 of the bonding region of the land electrodes 14a, 14b to the length L1 of the bonding region of the external electrodes 4a, 4b is 3 times or less (i.e., L2 / L1 is 3 or less) as shown in Fig. 5(a), so that the solder material can sufficiently wet and spread on the exposed surfaces (bonding regions and side surfaces) of the external electrodes 4a, 4b and the exposed surfaces (bonding regions and side surfaces) of the land electrodes 14a, 14b when the element member 10 is bonded to the circuit board 20. The bonded portions 30a, 30b formed thereby can sufficiently cover the external electrodes 4a, 4b and the land electrodes 14a, 14b (without substantially exposing them). The thus obtained joints 30a, 30b can reduce or prevent dissolution of the land electrodes 14a and / or 14b (at the portions exposed from the joints 30a, 30b) due to migration even when the finally obtained joint structure 40 is used under high humidity conditions, and can effectively reduce or prevent high resistance (open in severe cases) of the joint structure 40. Although this embodiment is not bound by any theory, even if migration occurs due to the use of the joint structure 40 under high humidity conditions, the external electrodes 4a, 4b and the land electrodes 14a, 14b are covered with the joints 30a, 30b (without being substantially exposed), so that the solder material of the joints 30a, 30b selectively dissolves, and dissolution of the external electrodes 4a, 4b and / or the land electrodes 14a, 14b, which are likely to affect the electrical characteristics of the joint structure 40, is reduced or prevented, and stable electrical characteristics are obtained.

[0076] On the other hand, when the ratio of the area of ​​the bonding area of ​​the land electrodes 14a, 14b to the area of ​​the bonding area of ​​the external electrodes 4a, 4b exceeds three times, for example, when the width of the bonding area of ​​the external electrodes 4a, 4b is the same as that of the land electrodes 14a, 14b, as shown in Fig. 5(b), if L2 / L1 exceeds 3, particularly 3.5 or more, when the element member 10 is bonded to the circuit board 20, the solder material does not sufficiently wet and spread on the exposed surfaces (bonding areas and side surfaces) of the external electrodes 4a, 4b and the exposed surfaces (bonding areas and side surfaces) of the land electrodes 14a, 14b, and a part of the land electrodes 14a, 14b may remain exposed without being covered by the bonding portions 30a, 30b. (Note that the exposed parts of the land electrodes 14a, 14b may be covered with a resin material as described later in, for example, embodiments 3 and 4, if necessary.)

[0077] In the manner described above, the joint structure 40 of the present embodiment can be produced.

[0078] In the joint structure 40 of this embodiment, the surface of the first protective layer 6 opposite to the first substrate 1 (main surface) protrudes toward the second substrate 11 more than the surfaces of the pair of external electrodes 4a, 4b opposite to the first substrate 1 (main surface). In this case, the path between the external electrodes 4a and 4b is not linear due to the protrusion located therebetween, and the larger the protrusion, the more difficult it is for water to penetrate. With this configuration, even when the finally obtained joint structure 40 is used under high humidity conditions, it is possible to suppress or inhibit the penetration of water (compared to a case where there is no protrusion or the protrusion is smaller), and the growth of dendrites between the external electrodes 4a, 4b due to migration can be reduced or prevented, and the reduction in resistance of the joint structure 40 (short circuit in severe cases) can be effectively reduced or prevented. The size of the protrusion is, for example, 5 μm or more, particularly 10 μm or more, and the upper limit can be determined by the contact of the first protective layer 6 with the circuit board 20 (more specifically, the second protective layer 16, if present).

[0079] In addition, in the joint structure 40 of this embodiment, when the second protective layer 16 is present, the surface of the second protective layer 16 opposite to the second substrate 11 (main surface) protrudes toward the first substrate 1 more than the surfaces of the pair of land electrodes 14a, 14b opposite to the second substrate 11 (main surface). In this case, the path between the land electrodes 14a and 14b is not linear due to the protrusion located therebetween, and the larger the protrusion, the more difficult it is for water to penetrate. With this configuration, even when the finally obtained joint structure 40 is used under high humidity conditions, it is possible to suppress or inhibit the penetration of water (compared to a case where there is no protrusion or the protrusion is smaller), and it is possible to reduce or prevent the growth of dendrites between the land electrodes 14a, 14b due to migration, and it is possible to effectively reduce or prevent the decrease in resistance of the joint structure 40 (short circuit in severe cases). The size of the protrusion is, for example, 5 μm or more, particularly 10 μm or more, and the upper limit can be determined by the contact of the second protective layer 16 with the element member 10 (more specifically, the first protective layer 6).

[0080] Unlike Patent Document 1, the joint structure 40 of this embodiment does not require covering the entire element member 10 with a protective film made of a resin material from the surface of the element member 10 opposite the circuit board 20. With such a joint structure 40, it is easy to check whether the element member 10 is properly electrically joined to the circuit board 20, and the element member 10 can be replaced if a failure occurs. In addition, when multiple element members 10 are joined to one circuit board 20, if a defect is found in one element member 10, only that element member 10 can be replaced.

[0081] As can be understood from the above description, the present embodiment provides a joint structure 40 that exhibits stable electrical characteristics even in a high-humidity environment. The joint structure 40 of the present embodiment can exhibit stable electrical characteristics and can be drip-proof or waterproof even when used in contact with a liquid containing ions (water, body fluids, etc.).

[0082] In the joint structure 40 of this embodiment, the ceramic part 5 may include a thermistor material (for example, an NTC thermistor material). Such a joint structure 40 may be used as a temperature sensor having moisture resistance (or drip-proof or waterproof, the same applies below), and may preferably be a thin and flexible temperature sensor having moisture resistance (for example, an NTC thermistor). A thin and flexible temperature sensor having moisture resistance may be suitably used, for example, in-vehicle applications and healthcare applications. When the temperature sensor is expected to be used in a temperature range of, for example, -55°C to 150°C, condensation occurs when the temperature changes from a low temperature to a high temperature. In addition, in healthcare applications, it may be expected that the temperature sensor will come into direct contact with body fluids. The joint structure 40 of this embodiment can exhibit stable electrical characteristics even when used as a temperature sensor exposed to such condensation or body fluids. As described above, the joint structure 40 of this embodiment has excellent sealing properties, and since there are no exposed metal areas on the outer surfaces of the joint structure 40 (more specifically, on both the surface opposite the main surface of the first substrate 1 and the surface opposite the main surface of the second substrate 11), the joint structure 40 exhibits high insulation against the external environment, and can prevent the occurrence of electric shock, short circuits, noise, and the like not only when the joint structure 40 comes into contact with liquid, but also when the human body or other conductive bodies come into contact with the joint structure 40.

[0083] (Embodiment 2) This embodiment is a modification of the first embodiment, and relates to an embodiment in which one or both of the first protective layer and the first base material include a metal layer. In this embodiment, the differences from the above-mentioned first embodiment will be mainly described, and unless otherwise specified, the same description as in the first embodiment may be applied.

[0084] In the joint structure 41 of this embodiment, at least one of the first protective layer 6 and the first base material 1 includes a metal layer. More specifically, with reference to Figs. 6 to 7, the first protective layer 6 further includes a first metal layer 7 in addition to the first resin material described above in the first embodiment. The first base material 1 further includes a second metal layer 8 in addition to the second resin material described above in the first embodiment. The first metal layer 7 may be provided on the first protective layer 6 in any appropriate manner as long as it is not in direct contact with the ceramic part 5. The second metal layer 8 may be provided on the first base material 1 in any appropriate manner as long as it is not in direct contact with the element electrode 2 (including the internal electrodes 3a, 3b and the external electrodes 4a, 4b). (Note that Figs. 6 and 7 correspond to Figs. 1 and 3, respectively, referred to in the first embodiment.)

[0085] The first metal layer 7 and the second metal layer 8 may comprise any suitable metal, for example, may be made of a metal. Such a metal may be, but is not limited to, at least one selected from the group consisting of Cu, Al, Ni, Au, etc. The first metal layer 7 and the second metal layer 8 may be made of the same material (including a metal) or different materials (including a metal).

[0086] The thickness of the first metal layer 7 and the second metal layer 8 may be, for example, 1 μm to 30 μm. The first metal layer 7 and the second metal layer 8 may have the same or different thicknesses.

[0087] The method of producing the first protective layer 6 and the first base material 1, each including the first metal layer 7 and the second metal layer 8, is not particularly limited. For example, the first protective layer 6 can be formed by sandwiching a metal foil between two films made of a predetermined resin material (with an adhesive interposed between them as appropriate) and bonding them together at room temperature or under heat. The first base material 1 can be formed in a similar manner.

[0088] The metal layer has lower moisture permeability than the resin material. On the other hand, the resin material has excellent processability, insulating properties, and the like, and can be flexible. Therefore, by combining the metal layer and the resin material, it is possible to realize the element structure 41 including the first protective layer 6 and the first base material 1 having low moisture permeability without adversely affecting the electrical characteristics and flexibility of the element structure 41.

[0089] Therefore, according to this embodiment, compared to the bonded structure of embodiment 1, the first protective layer 6 and the first substrate 1 have low moisture permeability, which can further suppress migration, thereby providing a bonded structure 41 that exhibits more stable electrical characteristics even in a high-humidity environment.

[0090] In the embodiment shown in Figures 6 to 7, an example is shown in which both the first protective layer 6 and the first base material 1 contain a metal layer, but this embodiment is not limited to this, and although less preferred, only one of the first protective layer 6 and the first base material 1 may contain a metal layer.

[0091] (Embodiment 3) This embodiment is a modification of the first and second embodiments, and relates to an embodiment in which the joint is covered with a cured resin material. In this embodiment, the differences from the first and second embodiments will be mainly described, and unless otherwise specified, the same description as in the first and second embodiments may be applied.

[0092] As shown in Fig. 8, in a joint structure 42 of this embodiment, joints 30a, 30b are covered with a cured resin material (cured resin material, fourth resin material) 31. (Note that Fig. 8 is a view corresponding to Fig. 6 referred to in the second embodiment.)

[0093] The curable resin material 31 may be any suitable resin material (fourth resin material) cured by moisture, heat and / or radiation (including light, ultraviolet light, etc.) as long as it has insulating properties, and may typically be a cured product of a moisture-curable (so-called room temperature curable), radiation (e.g. ultraviolet light) curable, and / or thermosetting resin material. Such a curable resin material may be, for example, a silicone-based resin, an acrylic-based resin, an epoxy-based resin, etc.

[0094] The cured resin material 31 covers at least a part, preferably substantially all, of the surfaces of the joints 30a, 30b that are not in contact with the external electrodes 4a, 4b and the land electrodes 14a, 14b. When there are parts of the external electrodes 4a, 4b and / or the land electrodes 14a, 14b that are not covered by the joints 30a, 30b, the cured resin material 31 can also cover such parts. The cured resin material 31 may or may not fill substantially the entire space between the element member 10 and the circuit board 20 other than the joints 30a, 30b.

[0095] The method of producing the cured resin material 31 that covers the joints 30a, 30b is not particularly limited. For example, after producing the joint structure of embodiment 1 or 2, an uncured resin material is supplied around the joints 30a, 30b (preferably so as to cover substantially the entire surface that is not in contact with the external electrodes 4a, 4b and the land electrodes 14a, 14b), and then cured by an appropriate method depending on the uncured resin material used. The cured resin material 31 that is cured and formed after supplying the uncured resin material can be tightly adhered to and coated on the joints 30a, 30b (and preferably the external electrodes 4a, 4b and the land electrodes 14a, 14b) to seal them.

[0096] By covering the bonding portions 30a and 30b (including the solder material) with the cured resin material 31, migration can be suppressed also in the bonding portions 30a and 30b.

[0097] Therefore, according to this embodiment, compared to the joint structures of embodiments 1 and 2, an additional step is required to cover joints 30a, 30b with cured resin material 31, but migration can be further suppressed by cured resin material 31 covering joints 30a, 30b (including the solder material), and a joint structure 42 is provided that exhibits even more stable electrical properties even in a high-humidity environment.

[0098] 8 shows a modified example of the second embodiment in which the bonding portions 30a, 30b are coated with the cured resin material 31 in the bonded structure 42 in which both the first protective layer 6 and the first base material 1 contain metal layers, but the present embodiment is not limited thereto, and either the first protective layer 6 or the first base material 1 may contain a metal layer. Alternatively, as a modified example of the first embodiment, the bonding portions 30a, 30b may be coated with the cured resin material 31 in the bonded structure including the first protective layer 6 and the first base material 1 that do not contain a metal layer.

[0099] (Embodiment 4) This embodiment is a modification of the first and second embodiments, and relates to an embodiment in which the joint is covered with a thermoplastic resin material. In this embodiment, the differences from the first and second embodiments will be mainly described, and unless otherwise specified, the same description as in the first and second embodiments may be applied.

[0100] As shown in Fig. 9, in a joint structure 43 of this embodiment, joints 30a and 30b are covered with a thermoplastic resin material (fifth resin material) 32. (Note that Fig. 9 is a view corresponding to Fig. 6 referred to in the second embodiment.)

[0101] The thermoplastic resin material 32 may be any appropriate thermoplastic resin material (a thermoplastic resin material that has been heated and melted, a fifth resin material) as long as it has insulating properties. Such a thermoplastic resin material may be, for example, a polyester-based resin, a polyethylene-based resin, a polypropylene-based resin, a polystyrene-based resin, a polyurethane-based resin, a nylon-based resin, a polyetherimide-based resin, or the like.

[0102] The thermoplastic resin material 32 covers at least a part, preferably substantially all, of the surfaces of the bonding portions 30a, 30b that are not in contact with the external electrodes 4a, 4b and the land electrodes 14a, 14b. When there are parts of the external electrodes 4a, 4b and / or the land electrodes 14a, 14b that are not covered by the bonding portions 30a, 30b, the thermoplastic resin material 32 may also cover such parts. The thermoplastic resin material 32 may or may not fill substantially the entire space between the element member 10 and the circuit board 20 other than the bonding portions 30a, 30b.

[0103] The method of producing the thermoplastic resin material 32 covering the joints 30a, 30b is not particularly limited. For example, when producing the joint structure of the first or second embodiment, as shown in FIG. 10, after forming the first protective layer 6, the thermoplastic resin material 32' is applied (for example, printed) on the first protective layer 6 (and / or the first base material 1) so as to surround the external electrodes 4a, 4b, to produce the element member 10. (Note that FIG. 10 is a view corresponding to FIG. 7 referred to in the second embodiment.) After that, when the element member 10 is used to join the joints 30a, 30b (including a solder material) to the circuit board 20 in the same manner as in the first or second embodiment, the thermoplastic resin material 32' is also heated and melted when the solder material is heated and melted. The thermoplastic resin material 32, which is formed by once heating and melting the thermoplastic resin material 32' and then solidifying after being naturally deformed, can be adhered to and covered with the joints 30a, 30b (and preferably the external electrodes 4a, 4b and the land electrodes 14a, 14b) to seal them.

[0104] By covering the bonding portions 30a, 30b (including the solder material) with the thermoplastic resin material 32, migration can also be suppressed in the bonding portions 30a, 30b.

[0105] Therefore, according to this embodiment, compared to the joint structures of embodiments 1 and 2, an additional step is required to cover joints 30a, 30b with thermoplastic resin material 32, but migration can be further suppressed by the thermoplastic resin material 32 covering joints 30a, 30b (including the solder material), and a joint structure 43 is provided that exhibits even more stable electrical properties even in a high-humidity environment.

[0106] 9 and 10 show a modified example of the second embodiment in which the bonding portions 30a, 30b are coated with the thermoplastic resin material 32 in the bonded structure 43 in which both the first protective layer 6 and the first base material 1 contain metal layers, but the present embodiment is not limited thereto, and either the first protective layer 6 or the first base material 1 may contain a metal layer. Alternatively, as a modified example of the first embodiment, the bonding portions 30a, 30b may be coated with the thermoplastic resin material 32 in the bonded structure including the first protective layer 6 and the first base material 1 that do not contain a metal layer.

[0107] (Embodiment 5) This embodiment is a modification of the first and second embodiments, and relates to an embodiment in which the joint includes an anisotropic conductive material. In this embodiment, the differences from the first and second embodiments will be mainly described, and unless otherwise specified, the same description as in the first and second embodiments may be applied.

[0108] As shown in FIGS. 11 to 13, particularly FIG. 11(a), in a joint structure 44 of the present embodiment, a joint 30' includes an anisotropic conductive material.

[0109] The anisotropic conductive material constituting the joint 30' may be obtained by dispersing a plurality of conductive particles 33, at least the surface of which is conductive, in any appropriate resin material (binder resin, sixth resin material) 34. As long as such resin material (sixth resin material) has insulating properties, it may be a cured resin material, a thermoplastic resin material, or a mixture thereof, and typically may be a cured product of a thermosetting and / or radiation (including, for example, light, ultraviolet light, etc.) curable resin material.

[0110] The anisotropic conductive material constituting the joint 30' is not particularly limited and may be obtained using any suitable anisotropic conductive material, for example, a film-like or paste-like anisotropic conductive material (anisotropic conductive film (ACF) or anisotropic conductive paste (ACP)).

[0111] The anisotropic conductive material as a raw material before forming the joint 30' is a composition containing conductive particles 33 and a resin material (a sixth resin material or its precursor), and may contain other components (e.g., a curing agent, a filler, a solvent, etc.) as appropriate.

[0112] The resin material constituting the composition (the sixth resin material or its precursor) may be any suitable resin material that can be cured by moisture, heat and / or radiation (including light, ultraviolet light, etc.), or a thermoplastic resin material, or a mixture thereof. The resin material constituting the composition may be, for example, a thermosetting and / or radiation curing resin material, and may be cured by heating and / or radiation exposure when forming the joint 30'. The resin material constituting the composition may typically be a thermosetting resin material, and may include, but is not limited to, at least one selected from the group consisting of epoxy resins, (meth)acrylic resins, silicone resins, and the like.

[0113] The conductive particles 33 may be any particles that exhibit conductivity when the joint 30' is formed and can electrically connect the external electrodes 4a', 4b' and the land electrodes 14a', 14b'. The conductive particles 33 may be, for example, particles made of a conductive material, particles having an insulating coating formed on a core made of a conductive material, or particles having a core made of any appropriate resin material, a layer made of a conductive material, and an insulating coating formed on the core. The average particle size of the conductive particles 33 may be, for example, 20 μm or less, particularly 15 μm or less, and the lower limit is not particularly limited, but may be, for example, 1 μm or more, particularly 5 μm or more. The average particle size means a median diameter, and may be measured, for example, using a laser diffraction type particle size distribution measuring device.

[0114] The conductive material constituting the conductive particles may be a metal or a metal-containing material. When the resin material is a thermosetting resin material, the metal is preferably not melted at the heating temperature at which the joint 30' is formed. The metal may include, but is not limited to, at least one selected from the group consisting of Au, Ni, Pd and Cu. When present, the thickness of the layer made of the conductive material may be, for example, 0.1 μm or more, particularly 0.5 μm or more, more particularly 1 μm or more, with the upper limit being determined by the particle size of the conductive particles.

[0115] When present, the insulating coating may be made of any suitable resin material, etc. The thickness of the insulating coating is made relatively thin so that it can be broken by pressure between the external electrodes 4a', 4b' and the land electrodes 14a', 14b' when forming the joint 30', and can electrically connect them, and can be, for example, 50 μm or less, particularly 25 μm or less, and the lower limit can be set appropriately, but can be, for example, 1 μm or more.

[0116] The anisotropic conductive material may be a composition including conductive particles having a metal with a melting point of 400° C. or more on the conductive surface, a curable compound that can be cured by heating, a heat curing agent, and a flux, as described in Patent Document 4, for example. Examples of the metal having a melting point of 400° C. or more include gold, silver, copper, platinum, palladium, zinc, lead, aluminum, cobalt, indium, nickel, chromium, titanium, antimony, bismuth, germanium, and cadmium, as well as alloys thereof. In addition, tin-doped indium oxide (ITO) may be used as the metal. Only one of the above metals may be used, or two or more of them may be used in combination. The conductive particles preferably have a nickel layer, a palladium layer, a copper layer, or a gold layer on the outer surface. The curable compound is not particularly limited, and examples thereof include a curable compound having an unsaturated double bond and a curable compound having an epoxy group or a thiirane group, and preferably includes a curable compound having a (meth)acryloyl group. Examples of the heat curing agent include imidazole curing agent, amine curing agent, phenol curing agent, polythiol curing agent, acid anhydride, and thermal radical generator, etc. Examples of the flux include, but are not limited to, zinc chloride, a mixture of zinc chloride and an inorganic halide, a mixture of zinc chloride and an inorganic acid, a molten salt, phosphoric acid, a derivative of phosphoric acid, an organic halide, hydrazine, an organic acid, and rosin.

[0117] As shown in Figure 11(a), in the joint structure 44 of this embodiment, in the joint 30', the conductive particles 33 are sandwiched between the external electrodes 4a', 4b' and the land electrodes 14a', 14b', thereby electrically joining them, and the resin material (sixth resin material) 34 covers the conductive particles 33, the external electrodes 4a', 4b' and the land electrodes 14a', 14b'.

[0118] In the joint structure 44 of this embodiment shown in Figures 11 to 13, referring to Figure 12, a pair of internal electrodes 14', 14b', a ceramic part 5' and a first protective layer 6' are formed adjacent to a pair of external electrodes 4a', 4b'.

[0119] The method for producing the joint 30' is not particularly limited. For example, the element member 10' shown in Fig. 12 and the circuit board 20' shown in Fig. 13 are produced, the element member 10' and the circuit board 20' are arranged such that the ceramic part 5' and the first protective layer 6' are present between the first base material 1' and the second base material 11', an anisotropic conductive material is sandwiched between the pair of external electrodes 4a', 4b' and the pair of land electrodes 14a', 14b' facing each other, and they can be electrically joined at the joint 30' by applying pressure while appropriately heating.

[0120] By including an anisotropic conductive material in the joint 30', migration can be suppressed at once by the resin material 34 in the external electrodes 4a', 4b', the land electrodes 14a', 14b', and the conductive particles 33 therebetween.

[0121] Therefore, according to this embodiment, compared to the joint structures of embodiments 1 and 2, a pressurizing step is required to form joint 30', but migration can be suppressed at once by the resin material 34 of joint 30', and a joint structure 44 is provided that exhibits stable electrical characteristics even in a high-humidity environment.

[0122] 11 to 13, in a bonded structure 44 in which both the first protective layer 6' and the first base material 1' include metal layers, the bonded portion 30' includes an anisotropic conductive material, but the present embodiment is not limited thereto, and either the first protective layer 6' or the first base material 1' may include a metal layer. Alternatively, in a bonded structure including the first protective layer 6' and the first base material 11' that do not include a metal layer, the bonded portion 30' may include an anisotropic conductive material, as a modified example of the first embodiment. EXAMPLES

[0123] Example 1 Example 1 relates to the joint structure described above in the first embodiment.

[0124] -Element materials (thermistor samples) Manganese acetylacetonate was added at a rate of 10 mass% (relative to the total mass of the metal oxide particles) to metal oxide particles with an average particle size of about 0.2 μm, containing Mn:Ni:Co in a ratio of 3:1:2 (atomic ratio), and ethanol was added as a solvent and mixed for 16 hours to obtain a raw material mixture in the form of a slurry. A Cu layer with a thickness of 12 μm was patterned into a predetermined shape by photolithography on a first substrate (base layer) that was a polyimide film with a thickness of 25 μm, and then a Ni plating layer and an Au plating layer were sequentially formed electrolessly on the surface of the patterned Cu base material. The total thickness of these plating layers was 3 μm. As a result, a Cu / Ni / Au element electrode (thickness 15 μm) was produced, as a portion corresponding to a pair of internal electrodes, a pair of comb-shaped opposing electrodes with a comb-tooth electrode spacing of 1.0 mm (d, see FIG. 2(a)), and a rectangular portion corresponding to a pair of external electrodes on both sides of the comb-shaped pair of opposing electrodes with a width (W1) of 0.4 mm and a length (L1) of 0.2 mm. The raw material mixture obtained above was supplied in the form of a sheet with a thickness of 20 μm by a doctor blade method onto the element electrode and the exposed surface of the first substrate to obtain a precursor laminate. This precursor laminate was dried at 100° C. for 10 hours, and then heated at 270° C. for 30 minutes under a pressure of 100 MPa using a heating press machine, and then annealed at 250° C. for 10 hours to remove any unnecessary organic matter that may remain, forming a ceramic part with a thickness (t) of 20 μm. A 25 μm thick coverlay (consisting of an epoxy resin (EP) adhesive layer and a polyimide resin (PI) cover layer) was pressed onto the ceramic part and the outer peripheral region of the first base material as a first protective layer so as to cover the obtained ceramic part and expose the pair of external electrodes.Then, it was cut with a dicing saw to obtain a thermistor sample (NTC thermistor) as an element member, with dimensions as viewed from above of 0.8 mm wide and 1.6 mm long, and a total thickness of approximately 50 μm.

[0125] Circuit Boards A 12 μm thick Cu layer was patterned into a predetermined shape by photolithography on the second substrate (base layer) which was a 25 μm thick polyimide film, and then a Ni plating layer and an Au plating layer were electrolessly formed in sequence on the surface of the patterned Cu base material. The total thickness of these plating layers was 3 μm. As a result, a pair of land electrodes made of Cu / Ni / Au (thickness 15 μm) was produced in a rectangle with a width (W2) of 0.4 mm and a length (L2) of 0.2 mm, together with a pair of lead wires. A 25 μm thick coverlay (made of an adhesive layer of epoxy resin (EP) and a cover layer of polyimide resin (PI)) was pressed as a second protective layer on the area including the space between the pair of land electrodes of the second substrate (including the area near the land electrodes of the pair of lead wires) so as to expose the obtained pair of land electrodes and cover the other surfaces. As a result, a circuit board with a total thickness of about 50 μm was obtained.

[0126] ·Joint part A conductive paste mainly composed of SnAgCu solder material (3 mass % Ag, 0.5 mass % Cu, and the remainder Sn) was printed to a thickness of 60 μm on a pair of land electrodes of the circuit board, and the thermistor sample prepared above was placed on the circuit board as an element member so that the pair of land electrodes and the pair of external electrodes faced each other, and the thermistor sample was mounted on the circuit board by reflowing at 240° C. for 10 seconds. This resulted in the joint structure of Example 1.

[0127] (Examples 2 to 3 and Comparative Example 1) Examples 2 and 3 relate to the joint structure described above in the first embodiment.

[0128] A bonded structure was obtained in the same manner as in Example 1, except that the thickness (t) of the ceramic part was 30 μm (Example 2), 40 μm (Example 3), or 50 μm (Comparative Example 1) (total thickness of the thermistor sample was approximately 50 μm).

[0129] Example 4 Example 4 relates to an embodiment in which the first protective layer and the first base material do not include a metal film in the bonded structure described above in Embodiment 3 (that is, a modified example of Embodiment 1).

[0130] After forming the joints, a room temperature curing silicone resin was supplied around the pair of joints between the element member (thermistor sample) and the circuit board, and left to stand for an appropriate period of time to fill the space around the joints and in the vicinity thereof with cured silicone resin, thereby obtaining a joint structure in the same manner as in Example 1.

[0131] Example 5 Example 5 relates to an embodiment in which the first protective layer and the first base material do not include a metal film in the bonded structure described above in Embodiment 3 (that is, a modified example of Embodiment 1).

[0132] A bonded structure was obtained in the same manner as in Example 1, except that (i) a 25 μm thick liquid crystal polymer (LCP) film was placed as the first protective layer instead of the 25 μm thick coverlay (total thickness of the thermistor sample was approximately 50 μm), and (ii) after the bonded portions were formed, room temperature curing silicone resin was supplied around the pair of bonded portions between the element member (thermistor sample) and the circuit board and left to stand for an appropriate period of time, filling the space around the bonded portions and in the vicinity thereof with cured silicone resin.

[0133] Example 6 Example 6 relates to an embodiment of the bonded structure described above in Embodiment 3, in which the first protective layer and the first base material include metal films (that is, a modified example of Embodiment 2).

[0134] A bonded structure was obtained in the same manner as in Example 1, except that (i) as the first substrate, a laminate was used in which a Cu foil (12 μm thick) of the same dimensions as the ceramic part was sandwiched between 12 μm thick LCP (having the same dimensions as the base layer) on the underside (surface opposite to the main surface) of a 25 μm thick polyimide film (base layer); (ii) as the first protective layer, a 25 μm thick liquid crystal polymer (LCP) film was placed, on which a Cu foil (12 μm thick) of the same dimensions as the ceramic part was placed, and on which a 12 μm thick liquid crystal polymer (LCP) film was placed (total thickness of the thermistor sample was approximately 100 μm); and (iii) after the bonding parts were formed, a room temperature curing silicone resin was supplied around the pair of bonding parts between the element member (thermistor sample) and the circuit board, and left to stand for an appropriate period of time to fill the space around and near the bonding parts with the cured silicone resin.

[0135] Example 7 Example 7 relates to an embodiment of the bonded structure described above in Embodiment 4, in which the first protective layer and the first base material include metal films (that is, a modified example of Embodiment 2).

[0136] (i) A laminate in which a Cu foil (thickness 12 μm) of the same dimensions as the ceramic part is sandwiched between 12 μm-thick LCP (having the same dimensions as the base layer) on the lower surface side (surface opposite to the main surface) of a 25 μm-thick polyimide film (base layer) was used as the first base material, (ii) a liquid crystal polymer (LCP) film of 25 μm in thickness was placed as the first protective layer, a Cu foil (thickness 12 μm) of the same dimensions as the ceramic part was placed thereon, and a liquid crystal polymer (LCP) film of 12 μm in thickness was placed on top of that (total thickness of the thermistor sample is about 100 μm), and (iii) a polyethylene (PE) film was pressed around the pair of land electrodes before printing the conductive paste. Except for this, a joint structure was obtained in the same manner as in Example 1. PE is a thermoplastic resin that melts once during heating (reflow) when joining with a solder material, naturally deforms, and then hardens to cover the periphery of the joint.

[0137] (Examples 8 to 10) Examples 8 to 10 relate to the joint structure described above in the first embodiment.

[0138] A joint structure was obtained in the same manner as in Example 1, except that (i) the dimensions of a pair of external electrodes of the element member (thermistor sample) were rectangular with a width (W1) of 0.4 mm and a length (L1) of 0.1 mm, and (ii) the dimensions of a pair of land electrodes of the circuit board were rectangular with a width (W2) of 0.4 mm and a length (L2) of 0.2 mm (Example 8), 0.3 mm (Example 9), or 0.35 mm (Example 10).

[0139] Example 11 Example 11 relates to an embodiment of the bonded structure described above in Embodiment 5, in which the first protective layer and the first base material include metal films (that is, a modified example of Embodiment 2).

[0140] A bonded structure was obtained in the same manner as in Example 1, except that (i) as the first substrate, a laminate was used in which a Cu foil (12 μm thick) of the same dimensions as the ceramic part was sandwiched between 12 μm thick LCP (having the same dimensions as the base layer) on the underside (surface opposite to the main surface) of a 25 μm thick polyimide film (base layer), (ii) a ceramic part was formed adjacent to a pair of external electrodes, (iii) as the first protective layer, a 25 μm thick liquid crystal polymer (LCP) film was placed on top of which a Cu foil (12 μm thick) of the same dimensions as the ceramic part was placed, and a 12 μm thick liquid crystal polymer (LCP) film was placed on top of that (total thickness of the thermistor sample was about 100 μm), and (iii) the element member and the circuit board were (pressure-bonded) using a 25 μm thick anisotropic conductive film (ACF) containing Au-coated resin particles with an average particle size of 10 μm and an average thickness of 0.1 μm in an epoxy resin.

[0141] Comparative Example 2 Comparative Example 2 relates to a joint structure in which a conventional chip component is joined to a circuit board.

[0142] A bonded structure (see FIG. 14) was obtained in the same manner as in Example 1, except that a commercially available chip component was used instead of the element member (an NTC thermistor manufactured by Murata Manufacturing Co., Ltd.; see chip component 50 shown in FIG. 14. The pair of internal electrodes 43a, 43b and the pair of external electrodes 44a, 44b were made of Ag-Pd, the ceramic part 45 had a thickness (t) of 0.8 mm, an overall length of 1.6 mm and an overall width of 0.8 mm, and the dimensions of the bonding area of ​​the external electrodes were a rectangle with a width (W1) of 0.4 mm and a length (L1) of 0.2 mm).

[0143] Comparative Example 3 Comparative Example 3 relates to a joint structure in which a conventional chip component is joined to a circuit board.

[0144] After forming the joints, a room temperature curing silicone resin was supplied around the pair of joints between the chip component and the circuit board, and left to stand for an appropriate period of time to fill the space around the joints and in the vicinity thereof with cured silicone resin, thereby obtaining a joint structure in the same manner as in Comparative Example 2.

[0145] (evaluation) The joint structures produced in Examples 1 to 11 and Comparative Examples 1 to 3 were subjected to a water immersion test to examine the change in resistance value (average time until migration occurs) and evaluate their stability.

[0146] Three bonded structures were prepared in the same manner for each of the examples and comparative examples, and the average resistance value when a voltage of 5 V was applied to them (without immersion in pure water) was measured and set as the initial value. A voltage of 5 V was applied to these structures while they were immersed in pure water, and the average time until the resistance value changed by 3% or more from the initial value was measured. If the resistance value changed by 3% or more even after 500 hours from the start of immersion and voltage application, it was examined whether the resistance value changed by 3% or more at 1000 hours after 500 hours. The results are shown in Table 1. (In Table 1, ">500hr" means that the resistance value did not change by 3% or more at 500 hours, but changed by 3% or more at 1000 hours, and ">1000hr" means that the resistance value changed by 3% or more even at 1000 hours.)

[0147] [Table 1] * 1st base material: LCP+Cu+PI approximately 50μm ** Chip parts

[0148] The bonded structures in which migration had occurred were subjected to visual observation and elemental analysis by EDX. In Examples 1 to 3 and Comparative Example 1, the resistance increased due to migration caused by dissolution of the internal electrode near the external electrode. In particular, in Comparative Example 1, obvious areas of insufficient adhesion of the first protective layer were observed. However, in Examples 1 to 3, it was confirmed that the time until migration occurred was longer than in Comparative Example 1, and a higher stability of the resistance value was shown. In Example 4, Cu dendrites were observed and resistance decreased after 500 hours, while in Examples 5 and 6, a change in resistance of 3% or more was not observed even after 1000 hours. These results confirmed that it is preferable to cover the solder joints with silicone resin rather than leaving them as they are, and that it is preferable for the first protective layer to be LCP or LCP with Cu foil sandwiched therebetween rather than a coverlay layer (epoxy resin and polyimide resin). In Examples 8 and 9, the external electrodes and land electrodes were covered with the solder joints, but in Example 10, the solder joints did not sufficiently cover the land electrodes, causing the land electrodes to melt and increase in resistance. In Example 11, migration resistance of 1000 hours or more, similar to Examples 5 to 7, was confirmed. In Comparative Examples 2 and 3, Ag dendrites were observed and the resistance was reduced. [Industrial Applicability]

[0149] The joint structure of the present disclosure is suitably used in electronic devices that may be used in high humidity environments, but is not limited to such applications.

[0150] This application claims priority to Patent Application No. 2021-114406, filed in Japan on July 9, 2021, the entire contents of which are incorporated herein by reference. [Explanation of symbols]

[0151] 1, 1' 1st base material 2, 2a, 2b Element electrodes 3a, 3b, 3a', 3b' internal electrodes 4a, 4b, 4a', 4b' external electrode 5, 5' Ceramic section 6, 6' 1st protective layer 7, 7' 1st metal layer 8, 8' second metal layer 10, 10' Element member 11, 11' 2nd base material 14a, 14b, 14a', 14b' Land electrodes 15a, 15b, 15a', 15b' Lead wire 16, 16' 2nd protective layer 20, 20' circuit board 30a, 30b Joint (solder material) 30' Joint (anisotropic conductive material) 31 Cured resin material 32, 32' Thermoplastic resin material 33 Conductive particles 34 Resin materials 40, 41, 42, 43, 44 Jointed structure 43a, 43b Internal electrode 44a, 44b external electrode 45 Ceramic Section 50 Chip parts 60 Jointed structure

Claims

1. an element member in which a ceramic part and element electrodes including a pair of internal electrodes and a pair of external electrodes are formed on a first substrate, the ceramic part is covered with a first protective layer, the pair of external electrodes are exposed from the first protective layer, the pair of internal electrodes are located within the ceramic part, and the ceramic part has a thickness of 40 μm or less; a circuit board having a pair of land electrodes formed on a second substrate; a joint portion that electrically joins the pair of external electrodes and the pair of land electrodes that face each other in a state in which the ceramic portion and the first protective layer are disposed between the first base material and the second base material; and Including, a surface of the first protective layer opposite to the first base material protrudes toward the second base material beyond surfaces of the pair of external electrodes opposite to the first base material, the circuit board has a second protective layer disposed on the second base material, the pair of land electrodes being exposed from the second protective layer, a surface of the second protective layer opposite to the second substrate protrudes toward the first substrate beyond surfaces of the pair of land electrodes opposite to the second substrate, the first protective layer is disposed so as to surround the pair of external electrodes, and a part of the joint portion is present between the first protective layer and the pair of external electrodes; the second protective layer is disposed so as to surround the pair of land electrodes, and a part of the joint portion is present between the second protective layer and the pair of land electrodes. bonded structure.

2. The bonded structure according to claim 1 , wherein the first protective layer comprises a first resin material.

3. 3. The bonded structure according to claim 2, wherein the first resin material includes at least one selected from the group consisting of polyimide-based resins, polyamideimide-based resins, epoxy-based resins, liquid crystal polymers, polyethylene-based resins, polypropylene-based resins, polystyrene-based resins, polyester-based resins, polyurethane-based resins, polyamide-based resins, polyetherimide-based resins, and (meth)acrylic-based resins.

4. The bonded structure according to any one of claims 1 to 3, wherein the first base material includes a second resin material and a second metal layer.

5. The bonded structure according to any one of claims 1 to 4, wherein the second base material is a flexible substrate containing a third resin material.

6. The joint structure according to any one of claims 1 to 5, wherein the joint portion comprises a solder material.

7. The joint structure according to claim 6 , wherein an area of ​​the joint region of the pair of land electrodes is three times or less an area of ​​the joint region of the pair of external electrodes.

8. The joint structure according to any one of claims 1 to 7, wherein the joint portion is covered with a cured resin material as a fourth resin material.

9. The joint structure according to any one of claims 1 to 7, wherein the joint portion is covered with a thermoplastic resin material as a fifth resin material.

10. The joint structure according to claim 1 , wherein the joint portion comprises an anisotropic conductive material.

11. The joint structure according to any one of claims 1 to 10, wherein the ceramic portion is formed between the pair of external electrodes.

12. The joint structure according to any one of claims 1 to 10, wherein the ceramic portion is formed adjacent to the pair of external electrodes.

13. The bonded structure according to any one of claims 1 to 12, wherein the ceramic portion includes a thermistor material, and the bonded structure is a temperature sensor.

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