Junction structure

Abstract

To provide a junction structure capable of improving a strength with respect to a bending stress.SOLUTION: A junction structure 100 comprises a first metal layer 21 containing Sn, and an intermetallic compound layer 22 consisting of an intermetallic compound containing Sn. In a case where such an intermetallic compound layer 22 is included, a strength with respect to a bending stress is higher in a structure where a brittle intermetallic compound and the soft first metal layer 21 of Sn are collected in comparison with a structure in which a brittle intermetallic compound is dispersed in the entire junction structure 100 (refer to e.g., Fig. 6). On the other hand, in the junction structure 100, a ratio of a value of a peripheral length of the first metal layer 21 on a cross section of the first metal layer 21 with respect to a value of a cross-sectional area of the cross section of the first metal layer 21 is smaller than 0.06. When the value is within this range, the soft first metal layer 21 of Sn can be disposed in a collected state in the junction structure 100.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a joint structure. [Background technology]

[0002] In recent years, advances in electronics have led to the development of technologies for mounting electronic components on substrates. For example, in the past, when assembling fine electronic components, gold was used for the terminals of the electronic components, and Sn was applied to the opposing wiring board by plating or thin film deposition, and the components were joined by soldering or diffusion bonding. When joining electronic components and wiring boards using Au and Sn plating, there was a tendency for an intermetallic compound of Au and Sn to form at the joining interface due to a eutectic reaction. One of the issues with Sn-Au solder is the brittleness of Sn-Au based intermetallic compounds. To overcome this brittleness, a technology has been disclosed in which the intermetallic compound is dispersed at a rate of 5 to 50% in terms of area fraction of the joint cross section (e.g., Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-286531 Summary of the Invention [Problem to be solved by the invention]

[0004] Because Sn has a low melting point, metallic elements tend to diffuse easily within alloys containing Sn. Therefore, in structures where intermetallic compounds are dispersed, elements that form intermetallic compounds with Sn diffuse into the alloy containing Sn, forming an intermetallic compound layer with Sn. However, intermetallic compound layers can be brittle. Therefore, there is a need to improve the strength of joint structures against bending stress.

[0005] An object of the present disclosure is to provide a joint structure that can improve strength against bending stress. [Means for solving the problem]

[0006] A joining structure according to one embodiment of the present disclosure is a joining structure joining an electronic component and a wiring board, comprising a first metal layer containing Sn and an intermetallic compound layer composed of an intermetallic compound containing Sn, wherein the ratio of the value of the perimeter of the first metal layer in a cross section of the first metal layer to the value of the cross-sectional area of ​​the cross section of the first metal layer is less than 0.06.

[0007] A joint structure according to one embodiment of the present disclosure includes a first metal layer containing Sn and an intermetallic compound layer composed of an intermetallic compound containing Sn. When such an intermetallic compound layer is included, a structure in which the brittle intermetallic compound and the soft Sn first metal layer are cohesively integrated has higher strength against bending stress than a structure in which the brittle intermetallic compound is dispersed throughout the joint structure. In contrast, in the joint structure according to the present disclosure, the ratio of the perimeter of the first metal layer in the cross section to the cross-sectional area of ​​the first metal layer is less than 0.06. When this ratio is within this range, the soft Sn first metal layer can be arranged in a cohesive state within the joint structure. As a result, the strength against bending stress of the joint structure can be improved.

[0008] The intermetallic compound layer may contain Au. Au is a metal element that easily forms an intermetallic compound with Sn and easily diffuses into a layer containing Sn, making the bonded structure brittle. In contrast, by adopting the bonded structure of the present disclosure, strength against bending stress can be improved even when Au is used.

[0009] The joint structure may include, in order from the electronic component side, a first intermetallic compound layer composed of an intermetallic compound containing Sn, a first metal layer, and a second intermetallic compound layer composed of an intermetallic compound containing Sn. In this case, the brittle intermetallic compound layer is disposed on the electronic component side and the wiring board side. Meanwhile, the soft Sn first metal layer is disposed on the center side of the joint structure where bending stress is more likely to act. This structure can improve the strength of the joint structure against bending stress.

[0010] The proportion of the cross-sectional area of ​​the first metal layer in the cross section of the joint structure may be greater than 50.00% and less than 99.99% of the sum of the cross-sectional areas of the first metal layer and the intermetallic compound layer. In this case, by increasing the first metal layer of Sn in the joint structure, the concentration gradient of metal elements that form intermetallic compounds with Sn, which acts as a driving force for diffusion, is reduced, and Kirkendall voids can be suppressed.

[0011] The intermetallic compound layer may contain a first metal element that forms an intermetallic compound with Sn, and the amount of the first metal element contained in the first metal layer may be 1.01% or less of the amount of the first metal element contained in the intermetallic compound layer. In this case, by reducing the amount of the first metal element (e.g., Au) that is easily diffused in the first metal layer, Kirkendall voids can be suppressed.

[0012] The terminal of the wiring board may have a conductive film containing Ni formed on the surface of the terminal. The conductive film containing Ni can suppress a reaction between the inside of the terminal of the wiring board and a metal element that forms an intermetallic compound with Sn. This can suppress the diffusion distance extension of the metal element that forms an intermetallic compound with Sn, and can suppress Kirkendall voids. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide a joint structure that can improve strength against bending stress. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view showing a mounting substrate including a joint structure according to an embodiment of the present disclosure. [Figure 2] 1 is a schematic cross-sectional view showing a wiring board to which a joining structure according to an embodiment of the present disclosure is applied; [Figure 3] FIG. 1(a) is a schematic cross-sectional view showing an example of a laminated structure of a bonded structure, and FIG. 1(b) is a schematic cross-sectional view showing a state before bonding. [Figure 4]FIG. 2 is an enlarged cross-sectional view showing an example of a detailed structure of the joining structure according to the present embodiment. [Figure 5] FIG. 2 is a diagram showing the shape of a joining structure. [Figure 6] FIG. 2 is an enlarged cross-sectional view of a joining structure according to liquid phase joining. [Figure 7] 1 is a table showing experimental conditions and measurement results. [Figure 8] FIG. 10 is a diagram showing the contents of a share test. DETAILED DESCRIPTION OF THE INVENTION

[0015] A junction structure 100 according to an embodiment of the present disclosure will be described with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing a mounting substrate 1 equipped with the junction structure 100 according to an embodiment of the present disclosure. Figure 2 is a schematic cross-sectional view showing a wiring substrate 3 to which the junction structure 100 according to an embodiment of the present disclosure is applied.

[0016] 1, the mounting board 1 includes an electronic component 2 and a wiring board 3. The mounting board 1 is configured by mounting the electronic component 2 on the wiring board 3 with a bonding layer 40 interposed therebetween.

[0017] The electronic component 2 includes a main body 6 and a pair of terminals 7. The main body 6 is a member for fulfilling the function of the electronic component 2. The terminals 7 are metal portions formed on the main surface of the main body 6. The terminals 7 are made of a material such as a metal containing Cu, Ti, Au, Ni, Sn, Bi, P, B, In, Ag, Zn, Pd, Mo, Pt, or Cr, or an alloy containing at least two of these elements. The electronic component 2 is formed, for example, by a micro LED. The micro LED is a component that emits light in response to input from the wiring substrate 3.

[0018] The wiring board 3 includes a base material 8, a wall 9, and a pair of terminals 5. The base material 8 is a flat body of the wiring board 3. The base material 8 has a main surface. The base material 8 may be a printed circuit board for mounting the conductor patterns and electronic components of the wiring board 3 on its main surface. Known resin materials and ceramic materials used for printed circuit boards may be used as the material for the base material 8. The wall 9 is a member formed of an insulator on the upper surface of the base material 8. Resin materials such as epoxy resin, acrylic resin, phenolic resin, melamine resin, urea resin, and alkyd resin are used as the material for the wall 9. Epoxy resin and acrylic resin are particularly preferred as the material for the wall 9. The terminal 5 includes a terminal body 10 and a conductive film 12. The terminal body 10 is a metal portion formed on the main surface of the base material 8. Examples of materials for the terminal body 10 include Ni, Cu, Ti, Cr, Al, Mo, Pt, Au, and alloys selected from at least two of these. The conductive film 12 is a layer that covers the surface of the terminal body 10. The conductive film 12 may be made of a material such as Ti, Cu, Ni, Al, Mo, Cr, or Ag, or a film made by mixing metal particles with a binder.

[0019] The Sn layer 20 is a layer containing Sn that bonds the terminal 7 of the electronic component 2 to the terminal 5 of the wiring board 3. Before assembly, the wiring board 3 includes a bonding material 4A disposed on the upper surface of the conductive film 12 (see FIG. 2). The bonding material 4A functions as solder. During assembly, the terminal body 10, the conductive film 12, the bonding material 4A, and the terminal 7 are stacked together, and then solder bonding is performed.

[0020] A recess 11 is formed in the wall 9. The recess 11 is formed by a through-hole that penetrates the wall 9 in the height direction. As a result, the top surface of the substrate 8 is exposed at the bottom side of the recess 11. The recess 11 is rectangular when viewed in the height direction. The terminal 7, the terminal main body 10, the conductive film 12, and the Sn layer 20 are disposed in the recess 11 formed in the wall 9, and are surrounded by the wall 9. Small gaps are formed between the terminal 7, the terminal main body 10, the conductive film 12, and the Sn layer 20 and the four inner surfaces of the recess 11 (i.e., the inner surfaces of the wall 9).

[0021] Within the recess 11, a constituent material 50 is disposed between the wall 9 and the electronic component 2 and Sn layer 20. This supports the electronic component 2 with the constituent material 50, making it less likely to peel off from the wiring board 3. Furthermore, the force applied to the electronic component 2, the Sn layer 20, and the terminals 7 and 10 is alleviated, improving reliability. The constituent material 50 may be made of, for example, epoxy resin, acrylic resin, phenolic resin, melamine resin, urea resin, alkyd resin, or a mixture thereof, or a mixture of any of the above resin materials with SiOx, ceramics, or the like. It is particularly preferable to use epoxy resin or acrylic resin as the material for the constituent material 50.

[0022] Next, with reference to Fig. 3, an outline of the layer configuration of the junction structure 100 according to this embodiment will be described in more detail. In the example of Fig. 3(a), the junction structure 100 includes a first metal layer 21 and an intermetallic compound layer 22 as the Sn layer 20. In addition, in this embodiment, the intermetallic compound layer 22 includes a first intermetallic compound layer 22A and a second intermetallic compound layer 22B. Therefore, the junction structure 100 includes, in order from the electronic component 2 side, the terminal 7, the first intermetallic compound layer 22A, the first metal layer 21, the second intermetallic compound layer 22B, and the terminal 5 (conductive film 12).

[0023] The first metal layer 21 is a layer containing Sn. Unlike the intermetallic compound layer 22, the first metal layer 21 contains Sn as a metal layer in a state where it is not an intermetallic compound. The thickness of the first metal layer 21 is not particularly limited, but may be set to 10 nm to 5000 nm. The thickness of the first metal layer 21 may be, for example, 100 nm to 4000 nm. The thickness of the first metal layer 21 may be, for example, 1000 nm to 3000 nm.

[0024] The intermetallic compound layer 22 is composed of an intermetallic compound containing Sn. The first intermetallic compound layer 22A and the second intermetallic compound layer 22B are composed of an intermetallic compound containing Sn. The intermetallic compound layer 22 (22A, 22B) contains a first metal element that forms an intermetallic compound with Sn. An example of the first metal element is Au. In this case, the intermetallic compound layer 22 contains Au. When the intermetallic compound layer 22 contains Au, the intermetallic compound layer 22 contains an AuSn-based intermetallic compound. Examples of AuSn-based intermetallic compounds include AuSn, AuSn2, and AuSn4. Alternatively, any of Cu, Ni, Ag, and Pd may be used as the first metal element. The intermetallic compound layer 22 may contain multiple metal elements. For example, even when the main metal element is Au, other metal elements may also be included. For example, if the terminals 7 and 5 contain Ni, the intermetallic compound layers 22A and 22B may contain a NiSn(+Au) intermetallic compound near the boundary with the terminals 7 and 5. The intermetallic compound layers 22A and 22B may be formed by solid-phase diffusion of a first metal element of the second metal layer 32 (described later) into Sn. The thickness of the intermetallic compound layers 22A and 22B is not particularly limited, but may be set to 5 nm to 2500 nm. The thickness of the intermetallic compound layers 22A and 22B may each independently be, for example, 20 nm to 1000 nm. The thickness of the intermetallic compound layers 22A and 22B may each independently be, for example, 30 nm to 200 nm.

[0025] The Sn layer 20 may contain, in addition to Sn, an element that lowers the melting point of Sn, such as Bi.

[0026] FIG. 3(b) is a diagram showing the state of the terminals 7, 5 before bonding, i.e., before the bonding structure 100 is formed. As shown in FIG. 3(b), a bonding material 4A is placed on the conductive film 12 of the terminal 5 on the wiring substrate 3 side. The bonding material 4A contains Sn in a state that is not an intermetallic compound, similar to the first metal layer 21. The terminal 7 on the electronic component 2 side before bonding has a terminal main body 31 and a second metal layer 32. The terminal main body 31 is the portion that remains as the terminal 7 after bonding. The material of the terminal main body 31 is the same as the material of the terminal 7 exemplified with reference to FIG. 1. The second metal layer 32 contains the first metal element described above. Unlike the intermetallic compound layer 22, the second metal layer 32 contains the first metal element as a metal layer in a state that is not an intermetallic compound. After bonding, almost all of the Au contained in the second metal layer 32 is used to form an intermetallic compound, and no part of the first metal element, such as Au, remains as a metal layer. The thickness of the bonding material 4A is not particularly limited, but may be set to 10 nm to 10,000 nm. The thickness of the second metal layer 32 is not particularly limited, but may be set to 5 nm to 2,500 nm.

[0027] During bonding, the terminals 7 of the electronic component 2 are placed on the bonding material 4A of the wiring board 3. If heating is performed for a long time (several minutes) at a temperature above the melting point of Sn, the entire structure will form a eutectic structure, making it difficult for the intermetallic compound layer 22 of the bonding structure 100 to become layered. Therefore, solid-phase diffusion, which does not produce a liquid phase, may be used to form the bonding structure 100 by controlling the processing temperature, processing time, and pressure. For example, a heating plate is placed on the electronic component 2 side and a cooling plate is placed on the wiring board 3 side, and only the contact area between the second metal layer 32 containing the first metal element and the bonding material 4A is melted. Furthermore, by lowering the heating temperature and raising the cooling temperature, the melted area gradually moves toward the wiring board 3, resulting in a layered structure rather than a eutectic structure.

[0028] The junction structure 100 will now be described in more detail with reference to FIGS. 4 and 5. FIG. 4 is an enlarged cross-sectional view showing an example of the detailed structure of the junction structure 100 according to this embodiment. In the example of FIG. 4, Sn is used as the material for the first metal layer 21, Ni is used as the material for the terminal 5, Ni is used as the material for the terminal body 31 of the terminal 7, and Au is used as the material for the second metal layer 32 of the terminal 7. As a result, SnAu is formed as the intermetallic compound of the intermetallic compound layers 22A and 22B. As shown in FIG. 4, the intermetallic compound layer 22 may be continuous, with the first intermetallic compound layer 22A and the second intermetallic compound layer 22B connected to each other at a portion in the thickness direction (portion C1 in the figure).

[0029] Here, the cross-sectional area of ​​the cross section of the first metal layer 21 is defined as the "cross-sectional area S." That is, a cross section is cut at a reference position of the junction structure 100, and the cross-sectional area of ​​the first metal layer 21 in this reference cross section is defined as the cross-sectional area S. The reference cross section of the junction structure 100 includes cross sections of the first metal layer 21, the intermetallic compound layers 22A and 22B, the terminal 5, and the terminal 7. If the first metal layer 21 has multiple regions separated from each other in the reference cross section, the cross-sectional area S is the sum of the cross-sectional areas of all the regions of the first metal layer 21. For example, in the example shown in FIG. 4, the first metal layer 21 has three regions E1, E2, and E3. In this case, the cross-sectional area S of the first metal layer 21 is the sum of the cross-sectional areas of the region E1, the region E2, and the region E3. This cross-sectional area S can be obtained by acquiring an image of the cross section using an electron microscope such as an SEM and measuring the area of ​​the cross section in the image by image analysis or the like.

[0030] The perimeter of the first metal layer 21 in the reference cross section of the junction structure 100 is defined as the "perimeter L." The perimeter L is the total length of a line SL that indicates the outline of the region corresponding to the first metal layer 21 in the reference cross section shown in FIG. 4. When the first metal layer 21 has multiple regions that are separated from each other in the reference cross section, the perimeter L is the sum of the perimeters of all the regions. For example, in the example shown in FIG. 4, the first metal layer 21 has three regions E1, E2, and E3. The total length of the line SL1 that indicates the outline of region E1 is the perimeter L1 of region E1. The total length of the line SL2 that indicates the outline of region E2 is the perimeter L2 of region E2. The total length of the line SL3 that indicates the outline of region E3 is the perimeter L31 of region E3. In this case, the perimeter L of the first metal layer 21 is the sum of the perimeter L1 of region E1, the perimeter L2 of region E2, and the perimeter L3 of region E3. The perimeter L can be obtained by obtaining an image of the cross section using an electron microscope such as an SEM, identifying the first metal layer 21 in the image, and measuring the perimeter. The boundary between the first metal layer 21 and the intermetallic compound layer 22 can be clearly grasped by identifying the composition using an SEM.

[0031] After obtaining the cross-sectional area S and the perimeter L of the first metal layer 21 as described above, the ratio of the perimeter L of the first metal layer 21 in the reference cross section to the cross-sectional area S of the reference cross section is obtained. This ratio is calculated by "value of perimeter L / value of cross-sectional area S." In this case, the ratio may be smaller than 0.06, and more preferably 0.05 or less. The lower limit of the ratio is not particularly limited, but the ratio may be 0.01 or more, and more preferably 0.02 or more. However, the lower limit does not have to be particularly set.

[0032] Here, with reference to FIG. 5, a method for setting a reference cross section that serves as a reference for obtaining the cross-sectional area S and perimeter L as described above will be described. FIG. 5 shows an enlarged view of the junction structure 100 as viewed from a horizontal direction (second direction D2) perpendicular to the direction (first direction D1) in which the pair of terminals 5, 5 face each other. As shown in FIG. 5, unlike the schematic diagram in FIG. 1, the Sn layer 20 may have a non-uniform shape. For the terminal 5 of such a junction structure 100, a reference line STL1 is set at one end in the first direction D1, and a reference line STL2 is set at the other end. A center line CL is set at the center position in the first direction D1 between the reference lines STL1 and STL2 set in this way. The junction structure 100 is cut at the position of the center line CL set in this way, and the cross section when viewed from the second direction is defined as the reference cross section.

[0033] 4, the proportion of the cross-sectional area of ​​the first metal layer 21 in the reference cross section of the joint structure 100 may be greater than 50.00%, and more preferably greater than 60%, of the total cross-sectional area of ​​the first metal layer 21 and the intermetallic compound layer 22. The upper limit of this proportion is not particularly limited, but may be 99.99% or less.

[0034] The amount of the first metal element contained in the first metal layer 21 may be 1.01% or less, and more preferably 0.11% or less, of the amount of the first metal element contained in the intermetallic compound layer 22. The lower limit of this amount does not need to be particularly set, and may be 0%.

[0035] As described above, in order to make the ratio of "perimeter length L / cross-sectional area S" smaller than 0.06, the joining of Sn and the first metal element such as Au can be performed by solid-phase diffusion bonding rather than liquid-phase bonding.

[0036] For comparison, the cross-sectional structure of a joint structure 200 using liquid phase bonding will be described with reference to FIG. 6 . The joint structure 200 in FIG. 6 is obtained by heating the pre-bonding state shown in FIG. 3( b ) at a temperature above the melting point of Sn and performing liquid phase bonding. Liquid phase bonding involves phase growth and the generation of a liquid phase, followed by solidification. Therefore, the shape of each part of the joint structure 200 using liquid phase bonding differs from the joint structure using solid phase bonding shown in FIG. 4 . Specifically, as shown in FIG. 6 , in the joint structure 200, the first metal layer 21 is disposed on the wiring substrate 3 side and the electronic component 2 side, and the intermetallic compound layer 22 is disposed toward the center in the height direction. Furthermore, the intermetallic compound layer 22 has a needle-like or block-like shape, rather than the layer-like shape shown in FIG. 4 . Therefore, the perimeter of the first metal layer 21, i.e., the total length of the boundary line SL between the first metal layer 21 and the intermetallic compound layer 22, is longer than that of the joint structure 100 according to this embodiment.

[0037] Next, the functions and effects of the joint structure 100 according to this embodiment will be described.

[0038] The junction structure 100 of this embodiment is a junction structure that joins an electronic component and a wiring board, and comprises a first metal layer 21 containing Sn and an intermetallic compound layer 22 composed of an intermetallic compound containing Sn, and the ratio of the value of the perimeter of the first metal layer 21 in the cross section of the first metal layer 21 to the value of the cross-sectional area of ​​the cross section of the first metal layer 21 is less than 0.06.

[0039] The joint structure 100 according to this embodiment includes a first metal layer 21 containing Sn and an intermetallic compound layer 22 composed of an intermetallic compound containing Sn. When such an intermetallic compound layer 22 is included, a structure in which the brittle intermetallic compound and the soft Sn first metal layer 21 are concentrated together has higher strength against bending stress than a structure in which the brittle intermetallic compound is dispersed throughout the joint structure 100 (see, for example, FIG. 6 ). For example, in the joint structure 200 according to the comparative example shown in FIG. 6 , the intermetallic compound layer 22 is dispersed throughout the joint structure 100, and the brittle intermetallic compound layer 22 is present in large amounts at the center in the height direction where bending stress is most likely to act, increasing the likelihood of fracture at that location. In contrast, in the joint structure 100 according to this embodiment, the ratio of the perimeter of the first metal layer 21 in the cross section of the first metal layer 21 to the cross-sectional area of ​​the first metal layer 21 is less than 0.06. When the thickness is within this range, the first metal layer 21 made of soft Sn can be arranged in a cohesive state within the junction structure 100. As a result, the strength of the junction structure 100 against bending stress can be improved.

[0040] The intermetallic compound layer 22 may contain Au. Au is a metal element that easily forms an intermetallic compound with Sn and easily diffuses into a layer containing Sn, making the bonded structure brittle. In contrast, by employing the bonded structure 100 of this embodiment, strength against bending stress can be improved even when Au is used.

[0041] The junction structure 100 may include, in order from the electronic component 2 side, a first intermetallic compound layer 22A made of an intermetallic compound containing Sn, a first metal layer 21, and a second intermetallic compound layer 22B made of an intermetallic compound containing Sn. In this case, the brittle intermetallic compound layers 22A and 22B are arranged on the electronic component 2 side and the wiring board 3 side. On the other hand, the soft Sn first metal layer 21 is arranged on the center side in the height direction of the junction structure 100 where bending stress is likely to act. With such a structure, the strength of the junction structure 100 against bending stress can be improved.

[0042] The proportion of the cross-sectional area of ​​the first metal layer 21 in the cross section of the joint structure 100 may be greater than 50.00% and not more than 99.99% of the total cross-sectional area of ​​the first metal layer 21 and the intermetallic compound layer 22. In this case, by increasing the amount of the first metal layer 21 of Sn in the joint structure 100, the concentration gradient of metal elements that form intermetallic compounds with Sn, which acts as a driving force for diffusion, can be reduced, and Kirkendall voids can be suppressed.

[0043] The intermetallic compound layer 22 contains a first metal element that forms an intermetallic compound with Sn, and the amount of the first metal element contained in the first metal layer 21 may be 1.01% or less of the amount of the first metal element contained in the intermetallic compound layer 22. In this case, Kirkendall voids can be suppressed by reducing the amount of the first metal element (such as Au) that is easily diffused in the first metal layer.

[0044] Terminal 5 of wiring board 3 may have conductive film 12 containing Ni formed on the surface of terminal 5. Conductive film 12 containing Ni can suppress a reaction between the inside of terminal 5 of wiring board 3 and a metal element (such as Au) that forms an intermetallic compound with Sn. This can suppress the extension of the diffusion distance of the metal element that forms an intermetallic compound with Sn, and can suppress Kirkendall voids.

[0045] The present disclosure is not limited to the above-described embodiments.

[0046] The arrangement, size, and number of layers of the joining structure are not particularly limited, and may be changed as appropriate within the scope of the present disclosure.

[0047] [Example] [First experiment] The thickness of the bonding material 4A before bonding was 3000 nm, and the thickness of the second metal layer 32 containing Au was 200 nm. Measurement results of the ratio of "perimeter L / cross-sectional area S" are described below for solid-phase diffusion bonding and liquid-phase bonding. To achieve solid-phase diffusion bonding, the heating temperature during bonding was set below the melting point of Sn, and pressure heating press was performed. Four measurement results were obtained by a bonding strength (shear strength) test. The measurement results of "perimeter L / cross-sectional area S" were "0.039," "0.042," "0.042," and "0.052," respectively. To achieve liquid-phase bonding, the heating temperature during bonding was set to 260°C, and the heating time was 1 minute. Four measurement results were obtained by a bonding strength (shear strength) test. The measurement results of "perimeter L / cross-sectional area S" were "0.060," "0.068," "0.074," and "0.066," respectively. [Second experiment] Experimental results regarding the strength of the bonded structures against bending stress will be described with reference to FIGS. 7 and 8. Samples 1 to 6 were prepared, in which the thickness of the second metal layer 32 before bonding, as shown in FIG. 3(b), was set to 0 nm, 30 nm, 50 nm, 70 nm, 90 nm, or 200 nm. The thickness of the bonding material 4A in each sample was set to 3000 nm. Au was used as the first metal element of the second metal layer 32. However, as shown in FIG. 8, the electronic component 2 was set to the size of one bonding structure 100. The dimensions of the terminals 5 and 7 in plan view were set to 0.05 mm × 0.05 mm. With the second metal layer 32 of the electronic component 2 and the Sn bonding material 4A of the wiring board 3 in contact, the bonding structure was formed by pressurizing and heating at a temperature below the melting point of Sn. SEM images of the reference cross section of each of the obtained samples 1 to 6 were taken and measured using image analysis software to obtain various values ​​as shown in FIG. 7. The "perimeter length L / cross-sectional area S" is the ratio of the value of the perimeter length L of the first metal layer 21 in the reference cross section to the value of the cross-sectional area S of the reference cross section. The "Sn cross-sectional area ratio" is the ratio (%) of the cross-sectional area of ​​the first metal layer 21 to the sum of the cross-sectional areas of the first metal layer 21 and the intermetallic compound layer 22 in the reference cross section. The "IMC cross-sectional area ratio" is the ratio (%) of the cross-sectional area of ​​the intermetallic compound layer 22 to the sum of the cross-sectional areas of the first metal layer 21 and the intermetallic compound layer 22 in the reference cross section. The "Au cross-sectional area ratio" is the ratio (%) of the amount of the first metal element contained in the first metal layer 21 to the amount of the first metal element contained in the intermetallic compound layer 22. For Samples 3, 5, and 6, the ratio of "perimeter length L / cross-sectional area S" was smaller than 0.06. For Sample 3, the "Sn cross-sectional area ratio" was greater than 50.00%. For samples 3, 5, and 6, the "Au cross-sectional area ratio" was 1.01% or less.

[0048] For each sample, strength against bending stress was measured. Shear strength was measured as the strength against bending stress. A shear test such as that shown in Figure 8 was performed to measure shear strength. The tool 70 was brought into contact with the electronic component 2 from a horizontal direction, and the peak value at which the joint structure 100 broke was measured as the shear strength. Three specimens were prepared for each sample, and the shear strength of the three specimens for each sample was measured. The measurement results are shown in Figure 7. The average shear strength value for each sample is also shown in Figure 7. However, test results in which normal measurements could not be performed, such as when the tool 70 did not contact the electronic component 2 properly, are marked as "measurable."

[0049] It was confirmed that when the "Au thickness" was 30 to 50 nm, the shear strength was particularly high due to the reduction in brittle intermetallic compounds compared to other ranges. When the "Au thickness" was 0 nm, there was too little Au, so the bonding was incomplete, resulting in low shear strength. Compared to the "Au thickness" of 0 nm, the other "Au thicknesses" all had higher shear strength. Furthermore, although the Au thickness before bonding affects the thickness of the intermetallic compounds, it is estimated that it does not significantly change the shape, and therefore it is estimated that the "cross-sectional area S / perimeter L" of samples 2 and 4 will also be roughly the same as the other samples.

[0050] [Form 1] A joining structure in which an electronic component and a wiring board are joined, a first metal layer containing Sn; an intermetallic compound layer composed of an intermetallic compound containing Sn, A junction structure, wherein a ratio of a perimeter value of the first metal layer in a cross section of the first metal layer to a cross-sectional area value of the cross section of the first metal layer is smaller than 0.06. [Form 2] 2. The joint structure according to claim 1, wherein the intermetallic compound layer contains Au. [Form 3] In order from the electronic component side, a first intermetallic compound layer composed of an intermetallic compound containing Sn; the first metal layer; a second intermetallic compound layer made of an intermetallic compound containing Sn. [Form 4] The joining structure according to any one of the first to third aspects, wherein the proportion of the cross-sectional area of ​​the first metal layer in the cross section of the joining structure is greater than 50.00% and less than 99.99% of the sum of the cross-sectional area of ​​the first metal layer and the cross-sectional area of ​​the intermetallic compound layer. [Form 5] the intermetallic compound layer contains a first metal element that forms an intermetallic compound with Sn, The joining structure according to any one of the first to fourth aspects, wherein the amount of the first metal element contained in the first metal layer is 1.01% or less of the amount of the first metal element contained in the intermetallic compound layer. [Form 6] 6. The junction structure according to any one of embodiments 1 to 5, wherein the terminal of the wiring board has a conductive film containing Ni formed on a surface of the terminal. [Explanation of symbols]

[0051] 2...electronic component, 3...wiring board, 12...conductive film, 21...first metal layer, 22...intermetallic compound layer, 22A...first intermetallic compound layer, 22B...second intermetallic compound layer, 100...junction structure.

Claims

1. A joining structure in which an electronic component and a wiring board are joined, a first metal layer containing Sn; an intermetallic compound layer composed of an intermetallic compound containing Sn, A junction structure, wherein a ratio of a perimeter value of the first metal layer in a cross section of the first metal layer to a cross-sectional area value of the cross section of the first metal layer is smaller than 0.

06.

2. The joint structure according to claim 1 , wherein the intermetallic compound layer contains Au.

3. In order from the electronic component side, a first intermetallic compound layer composed of an intermetallic compound containing Sn; the first metal layer; The joint structure according to claim 1 , further comprising: a second intermetallic compound layer composed of an intermetallic compound containing Sn.

4. 2. The joint structure according to claim 1, wherein a proportion of a cross-sectional area of ​​the first metal layer in a cross section of the joint structure is greater than 50.00% and less than or equal to 99.99% of a sum of a cross-sectional area of ​​the first metal layer and a cross-sectional area of ​​the intermetallic compound layer.

5. the intermetallic compound layer contains a first metal element that forms an intermetallic compound with Sn, The joint structure according to claim 1 , wherein the amount of the first metal element contained in the first metal layer is 1.01% or less of the amount of the first metal element contained in the intermetallic compound layer.

6. The junction structure according to claim 1 , wherein the terminal of the wiring board has a conductive film containing Ni formed on a surface of the terminal.

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