JP2019013957A - Solder joint and bonding method - Google Patents

Abstract

To provide a solder joint in which βSn particles are oriented in a desired specific direction, and the βSn particle has a desired structure; and to provide a bonding method related to the solder joint.SOLUTION: In a solder joint in which at least two copper boards 2 are bonded by using a lead-free solder alloy containing Sn, a solder ball 1 related to the lead-free solder alloy contains one or a plurality of nucleation particles 4, and single grain βSn crystal-oriented in a specific direction to the copper boards 2 in the state where its [001] direction is parallel to a facet surface of the nucleation particles 4.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a solder joint in which at least two members to be joined are joined using a lead-free solder alloy containing Sn and a joining method.

  In electrical and electronic joining using soldering, βSn is the main phase. However, βSn is very anisotropic in its thermophysical properties. For example, the thermal expansion coefficient, rigidity, and solute diffusion coefficient vary greatly depending on the direction of βSn. Further, in research on the reliability of solder joints, it is known that the thermal cycle ability, shear fatigue life, and electron transfer ability depend on the orientation of βSn in the [001] direction with respect to the surface of the substrate on which soldering is performed. Yes.

  In the case of the electron transfer capability, the electron transfer is very good in the solder joint in which the [001] direction of the βSn particles is substantially parallel to the current direction, that is, the direction perpendicular to the plane of the substrate. This is because the diffusivity along the [001] direction (c-axis) of solute atoms such as Cu, Ni, Ag, or Au is high. In other words, electron movement can be minimized by making the [001] direction of βSn particles parallel to the surface of the substrate.

  The influence of βSn particle orientation on the heat cycle capability depends on factors including the stress state and shape of the solder joint. In shear fatigue, it has been reported that a solder joint having βSn having a [001] direction on the surface of the substrate and oriented at approximately 35 to 65 ° with respect to the shear direction is less susceptible to fatigue damage. Yes.

  On the other hand, in Patent Document 1, the annealing atmosphere in the manufacturing process or the pickling method after annealing is appropriately selected, and the crystal grain size measured in the direction perpendicular to the rolling direction on the surface is 30 μm or less. To obtain a Sn-containing copper alloy material having an excellent solderability, in which the Sn3d / Cu2p ratio of the peak area ratio of quantitative analysis when the surface is measured by X-ray photoelectron spectroscopy is 0.3 or less Is disclosed.

JP 2000-144285 A

  As described above, it is possible to control the orientation of βSn particles formed at the time of solder joining, and the βSn particles, although the orientation of βSn particles plays an important role in determining the characteristics of solder joints. It was not devised to control the structure. These are neither disclosed nor devised in the technology relating to the Sn-containing copper alloy material of Patent Document 1.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a solder joint in which βSn particles are oriented in a desired specific direction and the βSn particles have a desired structure, and the solder. It is providing the joining method which concerns on a coupling.

  The solder joint according to the present invention is a solder joint in which at least two members to be joined are joined using a lead-free solder alloy containing Sn, and the solder portion related to the lead-free solder alloy is formed during soldering. The intermetallic compound layer, the intermetallic compound nucleation particles bonded to the intermetallic compound layer, and the [100] or [010] direction intersects the thickness direction of the intermetallic compound layer, And a single grain βSn crystallized so that the direction is substantially parallel to the joining surface of the member to be joined.

  The solder joint according to the present invention is characterized in that the single grain βSn is oriented so that its [001] direction is substantially parallel to the surface of the member to be joined.

In the solder joint according to the present invention, the nucleation particles of the intermetallic compound include at least one of PtSn ₄ , PdSn ₄ , βIrSn _{4, and} αCoSn ₃ .

In the solder joint according to the present invention, for the αCoSn ₃ intermetallic compound, the minimum dimension of the nucleation particles is 25 μm in width (longest dimension in FIG. 1) and 0.2 μm in thickness (in the cross direction). is there. The maximum dimension must be smaller than the surface of the member to be joined (for example, the copper substrate in FIG. 2).

In the solder joint according to the present invention, the minimum dimension of the nucleation particles is 10 μm for the PtSn ₄ , PdSn ₄ , or βIrSn ₄ intermetallic compound, and the thickness is 0.1 μm. 2 μm (in the cross direction). The maximum dimension must be smaller than the surface of the member to be joined (for example, the copper substrate in FIG. 2).

  In the solder joint according to the present invention, the member to be joined has a plate shape, and the maximum size of the nucleation particles is the same as the size of the joining surface of the member to be joined.

  The solder joint according to the present invention is characterized in that the intermetallic compound layer is formed at a joint interface between any of the members to be joined and the solder portion.

  In the joining method according to the present invention, at least two to-be-joined members are soldered using a lead-free solder alloy containing Sn, and the two to-be-joined members are joined by a solder portion related to the lead-free solder alloy. In the joining method, an arrangement step of arranging an intermetallic compound crystal at a place where the solder portion is to be formed, and a soldering step of performing the soldering so that the solder portion includes the crystal of the intermetallic compound. It is characterized by including.

  In the bonding method according to the present invention, the arranging step includes a step of fixing the intermetallic compound crystal to any member to be bonded so that the largest facet surface of the intermetallic compound crystal is in a specific direction. It is characterized by including.

  In the joining method according to the present invention, the arranging step includes a step of performing Sn coating on a place where the crystal of the intermetallic compound is to be fixed in any of the members to be joined, and the crystal of the intermetallic compound is coated. It is fixed on Sn.

  The bonding method according to the present invention is characterized in that the crystals of the intermetallic compound are fixed on a portion covered with Sn by an excessive liquid phase bonding method.

  The joining method according to the present invention is characterized in that a reflow method is used in the soldering step.

  The bonding method according to the present invention is characterized in that the crystals of the intermetallic compound have a rectangular plate shape.

The bonding method according to the present invention is characterized in that the intermetallic compound includes at least one of PtSn ₄ , PdSn ₄ , βIrSn _{4, and} αCoSn ₃ .

  According to the present invention, if necessary, the βSn particles can be oriented in a specific direction, and a desired structure can be obtained in the βSn particles.

An example of the extracted nucleation particle is shown. It is explanatory drawing explaining the process of manufacturing the solder joint which concerns on this Embodiment using the joining method which concerns on this Embodiment. It is the enlarged photograph which expanded between the copper substrate and the nucleation particle in case soldering was performed to the copper substrate to which the nucleation particle was fixed. In the case of using the PtSn ₄ nucleation particles, a result of analysis by the reflection of the solder joints electron image and the electron backscatter diffraction (EBSD). PtSn ₄ as nucleating particles, in the case of using the BetaIrSn ₄ and ArufaCoSn _3, the results of the analysis of the solder joints by electron backscatter diffraction. An example of the solder joint according to the present embodiment manufactured by the joining method according to the present embodiment will be shown. It is the result of investigating the influence which the dimension of a nucleation particle has on the control of nucleation and crystal orientation of βSn. It is the result of investigating the influence which the number of soldering has on the control of nucleation and crystal orientation of βSn. It is the other result which investigated the influence which the number of soldering has on control of the nucleation of βSn, and crystal orientation. When αCoSn ₃ is used as the nucleation particles in the solder joint according to the present embodiment and Sn-3.5Ag alloy is used as the lead-free solder alloy, the result of analyzing the solder joint by the electron beam backscatter diffraction method is there. When αCoSn ₃ is used as the nucleation particles in the solder joint according to the present embodiment and Sn-0.7Cu-0.05Ni-Ge alloy is used as the lead-free solder alloy, the solder joint is subjected to electron beam backscatter diffraction. It is the result analyzed by the law.

  A crystal having relatively good lattice matching with βSn formed when soldering using a lead-free solder alloy containing Sn was expected to play an important role in crystal growth of βSn. . That is, it is considered that such a crystal becomes a so-called seed, on which a βSn crystal grows. The detailed mechanism is that the (100) plane of βSn nucleates in a specific orientation on the largest facet plane of these crystals. Here, the facet plane refers to a flat surface in the crystal.

  Based on the above facts, in the present embodiment, an attempt was made to control βSn nucleation and orientation in a solder joint.

As a result of consideration based on lattice matching analysis, as described above, crystals used for nucleation and orientation of βSn (hereinafter referred to as nucleation particles) are PtSn ₄ , PdSn ₄ , βIrSn _{4, and} αCoSn ₃ . New intermetallic compounds were considered.

A method for producing nucleation particles of these intermetallic compounds will be described.
In a mold, a desired nucleation surface is grown as a facet by a series of processes for solidifying a hypereutectic Sn—Pt, Sn—Pd, Sn—Ir, or Sn—Co alloy. Next, nucleation particle single crystals of intermetallic compounds are extracted by removing βSn in a solution obtained by adding o-nitrophenol and sodium hydroxide to distilled water or in a solution of hydrochloric acid.

  FIG. 1 shows an example of extracted nucleation particles. Most of the nucleation particles grown by the above-described method are substantially rectangular, and the largest facet formed is the desired surface for nucleating βSn. As shown in FIG. 1, the nucleation particles have grown to a width of 1 μm to 200 μm.

  Hereinafter, a method for manufacturing the solder joint according to the present embodiment using the nucleation particles of the intermetallic compound described above will be described. For convenience, a case where two copper substrates are joined using a lead-free solder alloy containing Sn will be described as an example. For example, such a lead-free solder alloy is a Sn-3Ag-0.5Cu alloy. FIG. 2 is an explanatory diagram for explaining a process of manufacturing the solder joint 10 according to the present embodiment using the joining method according to the present embodiment.

  First, in any one of the copper substrates 2, a portion where soldering is to be performed, particularly a portion where the nucleation particles 4 are to be fixed, as described later, is covered with Sn. For example, the thickness of the Sn coating layer 3 is approximately 1 μm.

  At least any one nucleation particle 4 is fixed on the coated Sn. Specifically, the nucleation particles 4 are placed on the Sn coating layer 3 and fixed using an excessive liquid phase bonding method. The excessive liquid phase bonding method is performed at a temperature of 240 ° C. to 300 ° C. for 5 to 180 minutes.

  At this time, it is placed so that the largest faceted surface of the nucleation particles 4 of the intermetallic compound is parallel to the surface 21 (joint surface) to be soldered on the copper substrate 2. As a result, βSn generated during soldering is such that its [001] direction is parallel to the facet surface of the nucleation particle 4, in other words, a direction substantially parallel to the surface 21 of the copper substrate 2. Nucleated to grow crystals. That is, βSn nucleates and grows so that [100] or [010] intersects the thickness direction of the intermetallic compound layer (see FIG. 2).

  In the above, the case where the nucleation particle 4 is placed so that the facet surface of the nucleation particle 4 is parallel to the surface 21 of the copper substrate 2 has been described as an example, but the present embodiment is not limited to this. If necessary, that is, depending on the desired βSn nucleation and crystal growth directions, the arrangement of the facet planes of the nucleation particles 4 may be appropriately adjusted.

  Subsequently, soldering is performed on the surface 21 of the copper substrate 2 on which the nucleation particles 4 are fixed using an Sn-3Ag-0.5Cu alloy, and a solder ball (solder portion) 1 having a diameter of about 600 μm is formed. . At this time, the nucleation particles 4 are contained in the solder balls 1 and the solder balls 1 contain a βSn phase. Such soldering uses, for example, a reflow method.

FIG. 3 is an enlarged photograph in which the space between the copper substrate 2 and the nucleation particles 4 is enlarged when the copper substrate 2 to which the nucleation particles 4 are fixed is soldered. Specifically, FIG. 3 is an enlarged photograph of the round dotted line portion of FIG. 3A, 3B, and 3C show cases where the nucleation particles 4 are αCoSn ₃ , PtSn _4, and βIrSn ₄ , respectively. As can be seen from FIGS. 2 and 3, a layer related to the nucleation particles 4 is formed at the bonding interface between the solder balls 1 (βSn) and the copper substrate 2. Further, a layer of intermetallic compounds of Cu ₃ Sn and Cu ₆ Sn ₅ is generated between the copper substrate 2 and the nucleation particles 4. The intermetallic compound layer of Cu ₃ Sn and Cu ₆ Sn ₅ is a layer of intermetallic compound produced during soldering.

  Thereafter, in order to join the other copper substrate 2 to the solder ball 1, soldering using the reflow method is performed again. Thus, the two copper substrates 2 are joined via the solder balls 1, and the solder joint according to the present embodiment is manufactured.

  In the above, the case where the excessive liquid phase bonding method is used for fixing the nucleation particles 4 and the reflow method is used for soldering has been described as an example. However, the present invention is not limited to this, and other methods may be used. .

The microstructure of the solder joint 10 manufactured in this way was observed. FIG. 4 shows the result of analyzing the solder joint 10 by the backscattered electron image and electron beam backscatter diffraction method (EBSD) when PtSn ₄ is used for the nucleation particles 4. (A) is a mapping image by EBSD, (b) to (d) show the fine structure of the solder ball 1, and (e) to (h) are βSn, PtSn ₄ , Cu ₆ Sn ₅ and copper, respectively. It is an IPF (Inverse Pole Figure) map of EBSD with respect to the Z direction of the board | substrate 2 (Cu).

FIG. 4 (a) shows the distribution of _four phases (βSn, PtSn ₄ , Cu ₆ Sn ₅ and Cu) in green, red, blue and yellow, respectively. 4B to 4D, a βSn dendrite phase is formed in the solder ball 1, and a eutectic mixture of βSn, Ag ₃ Sn, and Cu ₆ Sn ₅ is formed between the dendrite arms. . Also, (e) to (h) in FIG. 4 represent the crystal orientation in color.

  In FIG. 4 (e), the solder ball 1 shows a green single color, and βSn is a single crystal oriented in the <100> direction (that is, the direction perpendicular to the copper substrate 2) in the Z direction. ing. Accordingly, the [001] direction of βSn is parallel to the surface 21 of the copper substrate 2.

Also, from (e) to (f) of FIG. 4, the [100] direction of βSn and the [001] direction of PtSn ₄ are parallel (see □), and the [010] direction of βSn and the PtSn ₄ It can be seen that the [010] direction is parallel (see the circles), and the [001] direction of βSn and the [100] direction of PtSn ₄ are parallel (see the triangles). For this reason, βSn particles appear to inherit crystal orientation from PtSn ₄ crystals.

  Furthermore, such a structure has been reported as a structure that minimizes electron transfer damage.

In the case of using the BetaIrSn ₄ or ArufaCoSn ₃ not PtSn ₄ as nucleating particles 4, the same results as in FIG. 4 were obtained. FIG. 5 shows the result of analyzing the solder joint 10 including the solder ball 1 and the copper substrate 2 by the electron beam backscatter diffraction method when PtSn ₄ , βIrSn ₄ and αCoSn ₃ are used as the nucleation particles 4. Sn-3Ag-0.5Cu alloy is used as the lead-free solder alloy.

(A) to (c) in FIG. 5 are mapping images of βSn when the nucleation particles 4 are PtSn ₄ , βIrSn ₄ and αCoSn ₃ , respectively, and (d) in FIG. 5 quantifies the crystal orientation of βSn. Are summarized in

  5A to 5C, all the solder balls 1 represent one βSn crystal orientation (green). That is, βSn is oriented in the <100> direction along the Z direction.

  5D, all the solder balls 1 have the <001> direction on the XY plane, that is, the surface 21 of the copper substrate 2, and all the solder balls 1 are in the <100> direction. One direction exists in the Z direction, that is, in the direction perpendicular to the copper substrate 2.

  Further, FIG. 5D shows that all the solder balls 1 have the [001] direction within 15 ° with respect to the XY plane, that is, the plane 21 of the copper substrate 2.

  From the above, it can be seen that nucleation and crystal orientation of βSn generated during soldering are performed along the largest facet plane of the nucleation particles 4. In other words, βSn nucleation and crystal orientation can be controlled by controlling the arrangement of the facet surfaces of the nucleation particles 4. In addition, βSn can be selectively made into a single crystal or a polycrystal.

  As a result, since the nucleation and crystal orientation of βSn can be controlled, the characteristics (for example, thermal cycle capability, shear fatigue life, electron transfer capability, etc.) of the solder joint can be controlled according to the application.

FIG. 6 shows an example of the solder joint 10 according to the present embodiment manufactured by the joining method according to the present embodiment. In such a solder joint 10, αCoSn ₃ is used as the nucleation particle 4, and βSn nucleation and crystal orientation are controlled in accordance with the application. Moreover, Sn-3Ag-0.5Cu alloy is used as a lead-free solder alloy.

  FIG. 6A shows a state in which the nucleation particles 4 are fixed on the four copper substrates 2. FIG. 6B shows the microstructure of the four solder joints 10 after soldering. FIG. 6C shows the result of analyzing the four solder joints 10 by electron beam backscatter diffraction, and is a mapping image of βSn in the X and Y directions. Furthermore, (d) of FIG. 6 is a crystal orientation map corresponding to (c).

  In the joining method (solder joint) of the present embodiment according to FIG. 6, each nucleation particle 4 has each c / b axis on the XY plane and at about 45 ° with respect to the X direction. It is fixed so as to be positioned (see FIG. 6A).

  As a result, as can be seen from FIGS. 6C and 6D, in all four solder joints 10 (solder balls 1), βSn has a c-axis ([001] direction) on the surface 21 of the copper substrate 2. It is located about 45 ° above and with respect to the main shear direction (X direction). Such a structure has been reported as a structure that provides the longest shear fatigue life (see the red region in FIG. 6D).

  That is, by controlling the arrangement of the nucleation particles 4 (facet surfaces), the [001] direction of βSn can be controlled, and the solder joint 10 (solder ball 1) can be provided with the longest shear fatigue life. did it.

  In FIG. 2, although the case where the nucleation particle | grains 4 are fixed to the lower copper substrate 2 among the two copper substrates 2 is mentioned as an example, this Embodiment is not restricted to this. Needless to say, the same effect can be obtained even if the nucleation particles 4 are fixed to the upper copper substrate 2.

The influence of the size of the nucleation particles 4 on the control of nucleation and crystal orientation of βSn was investigated. FIG. 7 shows the results of examining the influence of the size of the nucleation particles 4 on the control of βSn nucleation and crystal orientation. 7A to 7D show a state where the nucleation particles 4 are fixed on the copper substrate 2 when αCoSn ₃ is used as the nucleation particles 4. Moreover, (e)-(h) of FIG. 7 is the result of having analyzed the solder joint 10 which concerns on (a)-(d) by the electron beam backscattering diffraction method, and is a mapping image of (beta) Sn in a Z direction. Sn-3Ag-0.5Cu alloy is used as the lead-free solder alloy.

When αCoSn ₃ was used as the nucleation particle 4, it was found that if the size of the nucleation particle 4 was 25 μm or less in width (the longest dimension), βSn nucleation and crystal orientation could not be controlled (FIG. 7 (d) and (h)).

More specifically, when αCoSn _{3 is} used as the nucleation particle 4, the minimum dimension of the nucleation particle 4 is 25 μm in width (longest dimension in the direction along the surface 21 of the copper substrate 2) and 0.2 μm in thickness (crossing). In the direction) (see FIG. 1). At this time, the maximum size of the nucleation particles 4 is the same as the size of the surface 21 of the copper substrate 2.

7 (i) and (j) are the results of analyzing the solder joint 10 by the electron beam backscatter diffraction method when PtSn ₄ is used as the nucleation particles 4, and are mapping images of βSn. At this time, the dimension of PtSn ₄ was 10 to 20 μm in width (longest dimension), and βSn nucleation and control of crystal orientation could be effectively performed.

More specifically, when PtSn ₄ , PdSn ₄ , or βIrSn ₄ is used as the nucleation particle 4, the minimum dimension of the nucleation particle 4 is 10 μm in width (longest dimension in the direction along the surface 21 of the copper substrate 2). The thickness is 0.2 μm (in the crossing direction) (see FIG. 1). At this time, the maximum size of the nucleation particles 4 is the same as the size of the surface 21 of the copper substrate 2.

αCoSn ₃ reacts with copper and the liquid phase at the fastest rate among the nucleation particles 4 to form (Cu, Co) ₆ Sn ₅ . In addition, the (Cu, Co) ₆ Sn ₅ layer near αCoSn ₃ prevents contact between αCoSn ₃ and the liquid phase. Therefore, when αCoSn ₃ is used as the nucleation particles 4, the number of soldering (reflow methods) may affect the control of nucleation and crystal orientation of βSn.

FIG. 8 shows the results of examining the influence of the number of soldering on the control of βSn nucleation and crystal orientation. ΑCoSn ₃ was used as the nucleation particles 4 and soldering was performed by a reflow method. 8 (a) and 8 (b) and FIGS. 8 (c) and 8 (d) show the solder joint 10 when the soldering is performed twice and five times, respectively, by the electron beam backscatter diffraction method. It is the result of analysis, and is a mapping image of βSn in the Z direction. Also, (e) in FIG. 8 summarizes (a) to (d). Sn-3Ag-0.5Cu alloy is used as the lead-free solder alloy.

When αCoSn ₃ was used as the nucleation particle 4, the control of βSn nucleation and crystal orientation was 100% effective in the case of soldering by two reflow methods ((a), ( b), see (e)). However, in the case of soldering by the reflow method 5 times, the nucleation of βSn and the control of the crystal orientation could be controlled only by 50% (see (c), (d), and (e) of FIG. 8).

On the other hand, when PtSn ₄ or βIrSn ₄ is used as the nucleation particle 4, as shown in FIG. 9, control of βSn nucleation and crystal orientation even in the case of soldering by the reflow method 10 times or more. Was 100% effective. In FIG. 9, Sn-3Ag-0.5Cu alloy is used as the lead-free solder alloy.

  Further, when the soldering by the reflow method is performed while the copper substrate 2 is stopped, and when the soldering by the reflow method is performed while moving the copper substrate 2 in the convection oven, βSn There was no difference in the control of nucleation and crystal orientation.

  In the above, the case where the Sn-3Ag-0.5Cu alloy is used as the lead-free solder alloy has been described as an example, but the present embodiment is not limited to this. For example, the lead-free solder alloy may be a Sn-3.5Ag alloy or a Sn-0.7Cu-0.05Ni-Ge alloy.

10 and 11 show that αCoSn ₃ is used as the nucleation particle 4 in the solder joint 10 according to the present embodiment, and Sn-3.5Ag alloy and Sn-0.7Cu-0.05Ni- are used as lead-free solder alloys, respectively. When Ge alloy is used, it is the result of analyzing the solder joint 10 by the electron beam backscattering diffraction method, and is a mapping image of βSn in the Z direction.

  10 and 11, it can be seen that βSn nucleation and control of crystal orientation are effectively performed.

In the above description, the case where one of PtSn ₄ , PdSn ₄ , βIrSn _{4, and} αCoSn ₃ is fixed to one place of the copper substrate 2 as an example of the nucleation particle 4 has been described. Is not limited to this.

  For example, two or more identical nucleation particles 4 may be fixed to a plurality of locations on the copper substrate 2. Further, a plurality of different nucleation particles 4 may be fixed to a plurality of locations of the copper substrate 2. In this case, βSn nucleation and crystal orientation can be partially controlled.

  In the above, the case where the copper substrate 2 is used has been described as an example, but the present embodiment is not limited to this. Instead of copper, a transition metal substrate such as copper may be used.

1 Solder ball (solder part)
2 Copper substrate (members to be joined)
3 coating layer 4 nucleation particle 10 solder joint 21 (copper substrate) surface

At this time, it is placed so that the largest faceted surface of the nucleation particles 4 of the intermetallic compound is parallel to the surface 21 (joint surface) to be soldered on the copper substrate 2. As a result, βSn generated during soldering is such that its [001] direction is parallel to the facet surface of the nucleation particle 4, in other words, a direction substantially parallel to the surface 21 of the copper substrate 2. Nucleated to grow crystals. That is, βSn is nucleated and crystal grows so that the [100] direction or [010] direction intersects the thickness direction of the intermetallic compound layer (see FIG. 2).

Claims (14)

In a solder joint in which at least two members to be joined are joined using a lead-free solder alloy containing Sn,
The solder portion related to the lead-free solder alloy is:
An intermetallic compound layer formed during bonding;
[100] or [010] single grain βSn crystallized so as to intersect the thickness direction of the intermetallic compound layer;
A solder joint, comprising nucleation particles that are interposed between the intermetallic compound layer and the single-grain βSn and are related to the crystal orientation of the single-grain βSn.   2. The solder joint according to claim 1, wherein the single grains βSn are oriented so that a [001] direction is along a joining surface of the members to be joined. _3. The solder joint according to claim 2, wherein the nucleation particles include at least one of PtSn ₄ , PdSn ₄ , βIrSn _{4, and} αCoSn ₃ . The longest dimension of the αCoSn ₃ nucleation particles in a direction along the joining surface of the member to be joined is 25 μm or more, and a dimension in a direction intersecting with the direction is 0.2 μm or more. 3. The solder joint according to 3. The nucleation particles of PtSn ₄ , PdSn ₄ , or βIrSn _{4 have} a longest dimension in the direction along the joining surface of the member to be joined of 10 μm or more, and a dimension in a direction intersecting with the direction is 0.2 μm or more. The solder joint according to claim 3. The member to be joined has a plate shape,
The solder joint according to any one of claims 2 to 5, wherein the maximum size of the nucleation particles is the same as the size of the joining surface of the member to be joined.   The solder joint according to any one of claims 1 to 6, wherein the intermetallic compound layer is formed at a joining interface between any of the members to be joined and the solder portion. In a joining method in which at least two members to be joined are soldered using a lead-free solder alloy containing Sn, and the two members to be joined are joined by a solder portion related to the lead-free solder alloy,
An arrangement step of disposing at least one nucleation particle of an intermetallic compound related to crystal orientation of the solder portion at a position where the solder portion is to be formed;
And a soldering step of performing the soldering so that the solder portion includes nucleation particles of the intermetallic compound. The placing step includes
9. The method according to claim 8, further comprising the step of fixing the intermetallic compound nucleation particles to any member to be bonded so that the largest facet surface of the intermetallic compound nucleation particles is in a specific direction. The joining method described in 1. The arranging step includes a step of performing Sn coating on a portion where the nucleation particles of the intermetallic compound are to be fixed in any of the bonded members,
The joining method according to claim 9, wherein the nucleation particles of the intermetallic compound are fixed on a portion covered with Sn.   The bonding method according to claim 10, wherein the nucleation particles of the intermetallic compound are fixed on the coated Sn by an excessive liquid phase bonding method.   The joining method according to any one of claims 8 to 11, wherein a reflow method is used in the soldering step.   The joining method according to any one of claims 8 to 12, wherein the nucleation particles of the intermetallic compound have a rectangular plate shape. The bonding method according to claim 8, wherein the intermetallic compound includes at least one of PtSn ₄ , PdSn ₄ , βIrSn _{4, and} αCoSn ₃ .