Joining material and jointed structure using the joining material

Abstract

To provide a joint material that forms a fine junction.SOLUTION: A joint material includes a host phase having a melting point of 30°C or less and Cu nano-particles, where the host phase includes at least Ga, and the Cu nano-particles have an average particle diameter of 10-1000 nm, are dispersed in the host phase, and contained in the joint material in an amount of 10-75 mass%.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a bonding material capable of forming a joint portion that bonds between electrodes at a temperature of 100° C. or lower, and a joint structure formed using this bonding material. More specifically, for example, in a sensor device, an input / output device of a human interface, etc., it relates to a bonding material for bonding an electronic component and a circuit board, and a joint structure of a fine electronic circuit board bonded using the bonding material.

Background Art

[0002] In a sensor device, an electronic component is bonded to a circuit board using a solder material as a bonding material. When bonding a semiconductor package such as a CSP (Chip Scale Package) and a circuit board, generally, Sn-3 mass% Ag-0.5 mass% Cu having a melting point of 219° C. is used as the bonding material. FIG. 7 schematically shows a cross-sectional view of a state where a semiconductor package 1 is bonded to a circuit board 2.

[0003] In this specification, in order to describe the composition of an alloy, for example, an expression method of “A - x mass% B - y mass% C (where A, B, and C are metal elements, and x and y are percentage values)” is used. This means that when the alloy is composed of metal elements A, B, and C and the total alloy is 100 mass%, the metal element B is x mass%, the metal element C is y mass%, and the remainder is the mass% of the metal element A (= 100 - x - y).

[0004] First, using a solder paste printing device, for example, a solder material (e.g., Sn-3 mass% Ag-0.5 mass% Cu) having a melting point of 219° C. is processed into particles with a diameter of 10 to 25 μm and mixed with a flux, and the paste is transferred onto the circuit board electrode 3. Next, the semiconductor package 1 is mounted using an electronic component mounting device, and finally, after heating to a temperature above the solder melting point using a reflow heating device and then cooling, a joint portion 5 is formed.

[0005] With the increasing sophistication of sensor devices, human interface input / output devices, and other components, semiconductor packages are becoming more multi-electrode, smaller, and thinner. The number of electrodes in semiconductor packages, which was previously 400 or less, is expected to increase to over 1000 in the future. To achieve both increased terminal count and miniaturization, miniaturization of the semiconductor package line / space width is essential. The conventional line width of 10 μm / space width of 10 μm will narrow to 3 μm / space width or less. This narrowing of the line width also leads to miniaturization of the semiconductor package electrodes, requiring bonding materials capable of forming fine junctions. Furthermore, to form fine junctions, it is necessary to transfer only a small amount of bonding material to prevent short-circuit failures between electrodes. This transfer is difficult with conventional screen printing, making jet dispensing essential.

[0006] Furthermore, as semiconductor packages become thinner, they are more prone to warping, so it is desirable to keep the heating temperature during bonding by reflow heating low, around 100°C.

[0007] Therefore, an Ag nanoparticle paste, which is a mixture of metal nanoparticles and a dispersion medium, has been proposed as a first bonding material capable of forming fine joints (see, for example, Patent Document 1). The metal nanoparticles constituting this bonding material have a particle size of 1 to 100 nm or less, and by using metal nanoparticles with such a particle size, a fine bond can be formed.

[0008] Furthermore, a second joining material has been proposed that keeps the heating temperature during joining low (see, for example, Patent Document 2). This joining material is formed by creating a film on the ball surface of an alloy consisting of three types of metals: Sn-Bi-In. Since the melting point of the Sn-Bi-In ternary alloy is 60-100°C, using this joining material can lower the heating temperature during joining to around 100°C.

[0009] Furthermore, a third bonding material has been proposed that keeps the heating temperature during bonding low (see, for example, Patent Document 3). This bonding material is mainly composed of Ga, and by reacting it with Cu, which is the electrode material, an intermetallic compound of CuGa2 is produced to form a bond. By using this bonding material, the bond can be formed at a temperature of 30°C. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] WO2011 / 158659 [Patent Document 2] Japanese Patent Publication No. 2021-48392 [Patent Document 3] WO2020 / 100614 [Overview of the project] [Problems that the invention aims to solve]

[0011] The first bonding material described above has the problem that, since the bond is formed by solid-phase diffusion, it must be heated to a high temperature of 150°C to 200°C in the case of Sn, and 250°C to 350°C in the case of Ag or Cu.

[0012] The second bonding material mentioned above is a Sn-Bi-In ternary alloy, and while it can form a bond at temperatures around 100°C, it is difficult to produce nanoparticles of the ternary alloy. Therefore, there is a problem in that it is not possible to produce a paste with a viscosity of 10 Pa·s or less that can be used in jet dispensing.

[0013] The third bonding material mentioned above, being primarily composed of Ga, can form a bond at a temperature of 30°C. However, because Ga has a low viscosity of 0.003 Pa·s, it cannot maintain its shape when transferred to an electrode, causing the Ga to spread across the electrode. This results in a thinner bond and reduced bonding reliability.

[0014] Therefore, the present invention aims to provide a joining material that requires low heating, has low viscosity, and offers high reliability, in order to solve the problems associated with using the above-mentioned joining materials, namely high heating, high viscosity, and low reliability. [Means for solving the problem]

[0015] As a result of further consideration of the above issues, the bonding material according to this disclosure is a bonding material comprising a matrix with a melting point of 30°C or lower and Cu nanoparticles, wherein the matrix contains at least Ga, the Cu nanoparticles have an average particle size of 10 nm to 1000 nm, the Cu nanoparticles are dispersed in the matrix, and constitute 10% to 75% by mass of the bonding material.

[0016] Furthermore, the bonding structure according to this disclosure is a bonding structure comprising a bonding portion in which a substrate electrode and a component electrode are bonded, wherein the bonding portion is composed of a metal matrix and Cu nanoparticles, wherein Cu nanoparticles with an average particle diameter of 1 nm to 100 nm are dispersed in the metal matrix, and the metal matrix contains at least an intermetallic compound CuGa2 phase. [Effects of the Invention]

[0017] According to the bonding material of this disclosure, it is possible to form a bonded portion with a low viscosity of 10 Pa·s or less, which allows the bonding material to be transferred onto an electrode by jet dispensing at a low temperature of 100°C or less, and which allows the bonded portion to be formed with a viscosity of 1 Pa·s or more that allows the shape to be maintained after transfer, thereby enabling the construction of a highly reliable bonded structure. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic cross-sectional view illustrating the cross-sectional structure of a jointed structure having a joint formed using the joining material according to Embodiment 1. [Figure 2]Conceptually shows the process of forming a joint using the bonding material according to Embodiment 1. FIG. 2(a) is a schematic cross-sectional view showing the cross-sectional structure of the bonding material before heating. FIG. 2(b) is a schematic cross-sectional view showing the cross-sectional structure in a state where the matrix phase containing Ga is melted to generate a liquid phase upon heating. FIG. 2(c) is a schematic cross-sectional view showing the cross-sectional structure in a state where the bonding material is applied on the electrode. FIG. 2(d) is a schematic cross-sectional view showing the cross-sectional structure in a state where a semiconductor package is mounted and an intermetallic compound is being formed. FIG. 2(e) is a schematic cross-sectional view showing the cross-sectional structure of the joint after bonding by soldering. [Figure 3] It is a diagram showing a graph of the relationship between the median particle diameter of Cu nanoparticles contained in the bonding material, the viscosity of the bonding material, and the bonding strength of the formed joint. [Figure 4] It is a diagram showing a graph of the relationship between the content ratio of Cu nanoparticles contained in the bonding material, the viscosity of the bonding material, and the bonding strength of the formed joint. [Figure 5] Table 1 shows the results of the viscosity of the bonding material using the particle diameters and contents of various Cu nanoparticles and the bonding strength of the formed joint. [Figure 6] Table 2 shows the results of the viscosity of the bonding material using various matrix phases containing Ga, the particle diameters and contents of various Cu nanoparticles, and the bonding strength of the formed joint. [Figure 7] It is a schematic cross-sectional view schematically showing the cross-sectional structure in a state where a semiconductor package is bonded to a circuit board.

Embodiments for Carrying Out the Invention

[0019] The bonding material according to the first aspect is a bonding material containing a matrix phase with a melting point of 30°C or lower and Cu nanoparticles. The matrix phase contains at least Ga, the Cu nanoparticles have an average particle diameter of 10 nm to 1000 nm, and the Cu nanoparticles are dispersed in the matrix phase and are in the range of 10% to 75% by mass of the bonding material.

[0020] The bonding material according to the second aspect may have In or / and Sn present in the matrix phase in the first aspect.

[0021] The bonding structure according to the third embodiment is a bonding structure having a bonding portion in which a substrate electrode and a component electrode are bonded, wherein the bonding portion is composed of a metal matrix and Cu nanoparticles, wherein Cu nanoparticles with an average particle size of 1 nm to 100 nm are dispersed in the metal matrix, and the metal matrix contains at least an intermetallic compound CuGa2 phase.

[0022] The joint structure according to the fourth embodiment may include an intermetallic compound (Cu,Ni)Ga2 phase in the metal matrix, as in the third embodiment.

[0023] The following description will provide further details on the joining materials and joining structures using the joining materials according to embodiments of the present disclosure, with reference to the attached drawings. The following description is illustrative of specific forms for carrying out the present disclosure, and the present disclosure is not limited to such forms.

[0024] (Embodiment 1) <Joining material> Figures 2(a) to 2(e) are a series of schematic cross-sectional views conceptually illustrating the process of forming a joint using the bonding material according to Embodiment 1. Figure 2(a) is a schematic cross-sectional view showing the cross-sectional structure of the bonding material before heating. Figure 2(b) is a schematic cross-sectional view showing the cross-sectional structure when the Ga-containing matrix melts and a liquid phase is formed after heating. Figure 2(c) is a schematic cross-sectional view showing the cross-sectional structure when the bonding material is applied to the electrode. Figure 2(d) is a schematic cross-sectional view showing the cross-sectional structure when the semiconductor package is mounted and an intermetallic compound is being formed. Figure 2(e) is a schematic cross-sectional view showing the cross-sectional structure of the joint after soldering. The bonding material according to Embodiment 1 comprises a matrix 108 containing Ga and Cu nanoparticles 109. The Cu nanoparticles 109 have an average particle size of 10 nm to 1000 nm, and are dispersed in the matrix, making up 10% to 75% by mass of the bonding material. This bonding material 110 is prepared by mixing a Ga-containing matrix 108 and Cu nanoparticles 109 in a predetermined ratio (i.e., content ratio). The preparation process is carried out by heating the Ga-containing matrix 108 to a temperature above its melting point, for example, 40°C, while the Ga-containing matrix 108 is in the liquid phase.

[0025] The Ga-containing matrix 108 is, for example, 100% by mass Ga (melting point 30°C), and the Ga-containing matrix may also contain In or Sn. The median particle size of the Cu nanoparticles 109 (melting point 1085°C) is, for example, an average of 100 nm. Other components that are inevitably included in the manufacturing of the material may also be included. In any case, these may be included to the extent that they do not cause unacceptable adverse effects on the issues of this disclosure.

[0026] The total mass of the Ga-containing matrix 108 and the Cu nanoparticles 109, that is, the mass ratio of the Cu nanoparticles 109 to the mass of the bonding material 110, i.e., the content ratio, is, for example, 65% by mass.

[0027] <Effects> When forming a joint by soldering using the bonding material according to Embodiment 1, the bonding material is heated until the Ga-containing matrix phase melts. Cu nanoparticles dissolve and diffuse into the resulting low-viscosity liquid phase and react, forming at least one intermetallic compound between Cu and Ga. Subsequently, the joint is formed upon cooling. As shown in Figure 1, in this joint, the formed intermetallic compound forms a matrix structure (or three-dimensional network structure) 106 (corresponding to the first metallic phase described later), and this structure contains a second metallic phase 107 derived from Cu nanoparticles (when Cu nanoparticles remain without participating in the formation of the intermetallic compound). The first metallic phase 105 mainly contains Ga, but may also contain Ni. The second metallic phase 107 mainly contains Cu. The intermetallic compound forms a three-dimensional network structure, which allows the second metallic phase to be retained within the network structure.

[0028] Furthermore, by changing the composition of the Ga-containing matrix and Cu nanoparticles in the bonding material that can form an intermetallic network structure, it becomes possible to control the heat resistance temperature and bonding strength of the bonded area. Specifically, by appropriately selecting the median particle size of the Cu nanoparticles, the Cu nanoparticle content ratio, etc., it is possible to achieve the desired paste viscosity (which corresponds to the coating thickness of the bonded area) and bonding strength.

[0029] As a result, even when the bonding material of the present invention is used to bond multi-electrode, narrow-pitch semiconductor packages such as sensor devices, crack formation at the joint is less likely to occur, and a decrease in the reliability of the bonded structure is suppressed. Furthermore, when soldering using the bonding material according to this embodiment 1 with a heating device, the Ga-containing matrix melts at a temperature of 30°C or lower. Therefore, soldering becomes possible at a low temperature of 100°C or lower, making it possible to assemble thin semiconductor packages without causing warping during the assembly process of bonding sensor devices.

[0030] <Joined structure> Figure 1 is a schematic cross-sectional view illustrating the cross-sectional structure of a bonded structure having a bonded portion 103 formed using the bonding material according to this embodiment 1. Figure 1 shows, as an example, an embodiment in which the external electrode 102 of a semiconductor package 101, as one object, is bonded to the electrode 105 of an insulating circuit board 104, as the other object, by the bonded portion 103. The bonded portion 103 shown is formed using a bonding material comprising a matrix phase containing Ga and Cu nanoparticles.

[0031] The joint 103 consists of a first metallic phase 106 mainly composed of Ga and a second metallic phase 107 mainly composed of Cu derived from Cu nanoparticles. As shown in the figure, the second metallic phase 107 is surrounded by the first metallic phase 106, which is the matrix. The first metallic phase 106 has a three-dimensional network structure and, as shown in the figure, has the second metallic phase 107 inside, joining the external electrode 102 and the electrode 105. Such a first metallic phase 106 has a melting point corresponding to the melting point of the intermetallic compound formed, for example, a melting point of 200°C or higher. As a result, even if the joint is heated to a high temperature of 200°C or higher, for example close to 250°C, the network structure is maintained without melting. Therefore, the joint 103 does not break and has excellent heat resistance.

[0032] The objects to be connected by the bonding material according to this embodiment 1 may be any suitable electronic component, electrical component, etc., that is to be electrically and physically bonded, that is, to ensure electrical conductivity and to be mechanically bonded. Specifically, examples include electrodes of semiconductor packages, insulating substrates, lead frames, circuit boards, and electrodes of various other electrical and electronic components. As an example of such an object to be connected, the case of a semiconductor package will be described.

[0033] <First metallic phase> The first metallic phase comprises a matrix phase 108 containing Ga and an intermetallic compound CuGa2 phase consisting of Cu derived from Cu nanoparticles 109. It may also further contain an intermetallic compound (Cu,Ni)Ga2 phase. The Ni in the (Cu,Ni)Ga2 phase may be Ni contained in the external electrode 102 and / or electrode 105.

[0034] <Second metallic phase> The second metallic phase originates from Cu nanoparticles 109, but when the Ga-containing matrix phase 108 becomes a liquid phase, the Cu nanoparticles 109 dissolve into the Ga-containing matrix phase 108 through liquid-phase diffusion. As a result, the size of the second metallic phase 107 becomes smaller compared to the particle size of the original Cu nanoparticles 109, for example, to about 1 / 10 of the original size. Note that 1 / 10 is an example and is not limited to this.

[0035] <Semiconductor Packages> A semiconductor package is an electronic component that packages semiconductor elements in resin or metal and has electrodes on its outer perimeter or bottom. Packages with electrodes on the outer perimeter include SOP (Small Outline Package), SOJ (Small Outline J-leaded), and QFP (Quad Flat Package), while packages with electrodes on the bottom include BGA (Ball Grid Array), LGA (Land Grid Array), and CSP (Chip Scale Package).

[0036] The semiconductor package may have any suitable dimensions, and depending on its function, larger dimensions such as 37mm x 37mm or 25mm x 25mm may be used, or smaller dimensions such as 10mm x 10mm or 5mm x 5mm may be used. The semiconductor package may have any suitable thickness, and depending on the dimensions of the semiconductor element, it may have a thickness of 0.4mm, 0.3mm, 0.2mm, 0.15mm, etc. The semiconductor package may have any suitable electrode pitch, and a pitch of 0.4mm, 0.3mm, or even 0.25mm or less may be used.

[0037] <Insulating substrate> The insulating substrate is generally made of glass epoxy, and to ensure adhesion with the bonding material, an electrode layer may be formed on the bonding material side of the insulating substrate, for example, by electroplating with a thickness of 35 μm, and a pattern may be formed by etching. The electrode layer may also be made of a metal that has good adhesion with the bonding material, such as Ni, Ag, Sn, or Pd. The thickness should be 10 μm or more to account for variations in the thickness of the deposited film, and the film deposition method is not limited to electroplating; vapor deposition, electroless plating, etc., may also be used.

[0038] Accordingly, the bonding structure according to this embodiment 1 has a bonding portion 103 between the semiconductor package 101 and the insulating substrate 104, which are the objects to be bonded. Furthermore, the bonding portion 103 is formed by placing the bonding material according to this embodiment 1 between these objects and having the first metal phase 106 and the second metal phase 107 described above.

[0039] <Joining method> Figure 2 schematically illustrates the process of forming a joint structure according to this embodiment 1 by forming a joint portion 103 between objects using the joining material according to this embodiment 1. (1) The bonding material 110 prepared as described above is supplied by a dispenser onto the electrodes of an insulating substrate (not shown), a semiconductor package (not shown) is placed on top of the bonding material 110, and then these are heated to a predetermined temperature to form a bond. Figure 2(a) is a schematic cross-sectional view illustrating the cross-sectional structure of the bonding material 110 before heating. Cu nanoparticles 109 are present within the Ga-containing matrix 108, and since the melting point is below that of the Ga-containing matrix 108, the bonding material 110 is solid.

[0040] (2) When applying the bonding material 110 onto the electrode 105, the bonding material 110 is heated to a temperature above the melting point of the Ga-containing matrix (solid phase) 108, for example, 40°C. Figure 2(b) is a schematic cross-sectional view showing the cross-sectional structure of the bonding material 112 when the Ga-containing matrix 111 is heated to 40°C and becomes a liquid phase. The Ga-containing matrix 111 becomes liquid, and the viscosity of the bonding material 112 becomes 4.1 Pa·s. When the viscosity of the bonding material 112 becomes 10 Pa·s or less, it can be applied with a jet dispenser.

[0041] (3) Figure 2(c) shows the bonding material 112 applied to the electrode 105. When the Ga-containing matrix 111 is in a liquid state, the reaction between the Ga-containing matrix 111 and the Cu nanoparticles 109 accelerates and the state changes. Therefore, it is desirable to quickly convert the Ga-containing matrix (liquid phase) 111 into a solid matrix (solid phase) 108 after application. For example, the material may be applied while the insulating substrate (not shown) is placed on a support stand at a temperature of 20°C, which is below the melting point of Ga.

[0042] (4) Figure 2(d) shows the state in which the semiconductor package is mounted and an intermetallic compound is being formed. By mounting the semiconductor package and heating it to a temperature above the melting point of the Ga-containing matrix phase (solid phase) 108, the Cu nanoparticles 109 diffuse into the Ga-containing matrix phase (liquid phase) 111, which has become a liquid phase, and an intermetallic compound is formed. With the semiconductor package mounted in this state, soldering is performed by heating it to a temperature higher than the melting point of the Ga-containing matrix phase (solid phase) 108, for example, 100°C, in a nitrogen atmosphere with an oxygen concentration of 200 ppm.

[0043] (5) As the heating and holding time progresses, the amount of intermetallic compound formed increases, and as shown in Figure 2(e), Cu nanoparticles 109 diffuse into the Ga-containing matrix phase (liquid phase) 108 to form the first metallic phase 106, creating a network structure. The remaining Cu nanoparticles 109 become the second metallic phase 107. After cooling to room temperature, a junction is formed. In this junction, the second metallic phase 107, derived from the Cu nanoparticles 109, exists within the network structure of the first metallic phase 106.

[0044] As described above, the bonding material 110 capable of forming a joint is prepared by mixing a matrix phase (solid phase) 108 containing Ga with a melting point of 30°C or lower (for example, 100% by mass Ga, melting point 30°C) and metal nanoparticles having a higher melting point than the intermetallic compound to be formed (for example, Cu nanoparticles, melting point 1085°C). Therefore, by simply heating this bonding material to, for example, 100°C, the matrix phase containing Ga melts, and in a short time, Cu dissolves into the molten Ga and diffuses there to form an intermetallic compound with the Ga in the liquid phase. Thus, a joint, and therefore a bonded structure, can be formed in a short time.

[0045] Therefore, the method for forming a joint or the joining method according to Embodiment 1 includes a step of supplying the joining material according to Embodiment 1 to one of two objects to be joined, a step of placing the other object on the supplied joining material to dispose the joining material between the two objects, a step of heating the joining material and the objects to a temperature higher than the melting point of the matrix phase containing Ga, preferably a temperature 20°C higher, for example, heating to 100°C, holding the heating state for a predetermined time (for example, 20 seconds to 10 minutes, preferably 1 minute or more), and then cooling.

[0046] <Matrix phase containing Ga> The matrix phase 108 containing Ga is, for example, 100% by mass of Ga (melting point 30°C). The matrix phase 108 containing Ga is not limited to elemental Ga, and elements having a eutectic point with Ga may be mixed. Such an element may be one of In or Sn, or a ternary alloy in which two of In and Sn are mixed. In order to keep the melting point of the matrix phase 108 containing Ga at 30°C or lower, it is desirable that the content of In is 23% by mass or less and the content of Sn is 10% by mass or less.

[0047] <Cu nanoparticles> In the joining material according to Embodiment 1, the Cu nanoparticles 109 have a granular form and are usually composed of only Cu. The granular form includes so-called "granular" forms such as spherical, substantially spherical, ellipsoidal, polyhedral, and core-shell, and combinations of at least two of these shapes. It may also contain other components that will inevitably be included when manufacturing the material.

[0048] <Particle diameter of Cu nanoparticles> Regarding the size of the Cu nanoparticles, the concept of "median particle diameter" is used. This median particle diameter means the 50% diameter, so-called Dv50, of the volume-based particle diameter distribution obtained by measuring the particle diameter by the dynamic light scattering method. This median particle diameter is calculated by measuring the fluctuation of the scattered light when irradiated with laser light.

[0049] The median diameter of the Cu nanoparticles referred to herein was measured using a dynamic light scattering particle size distribution analyzer (Malvern Panalytical, product number: Zetasizer Nano ZS), commonly used for measuring submicron-sized particle size distributions, with pure water as the dispersion medium.

[0050] Figure 3 shows the preparation of bonding materials in which the median particle size of Cu nanoparticles 109 contained in the bonding material was varied, and the shear rate s was measured when heated at 40°C. -1 The graph shows the measured viscosity and the resulting joint strength of the joint formed using that viscosity.

[0051] A matrix containing 100% Ga was used. The mass ratio of Cu nanoparticles to the total mass of the Ga matrix and Cu nanoparticles, i.e., the content ratio, was 65% by mass. The bonding material was applied to a Cu plate (20 mm × 10 mm) to a thickness of 20 μm using a jet dispenser, a Cu test piece (1 mm × 1 mm) was placed on top, and the material was heated at 100°C for 1 minute and then cooled to room temperature to obtain a bonded structure with a bonded joint.

[0052] In Figure 3, the horizontal axis represents the median particle size of Cu particles, and the vertical axis represents the viscosity of the bonding material measured with a parallel plate viscometer (● in Figure 3) and the bonding strength of a 1 mm × 1 mm Cu test piece measured with a bond tester (〇 in Figure 3).

[0053] As can be seen from Figure 3, when the median particle size of the Cu nanoparticles is 10 nm, the viscosity of the bonding material is 9.5 Pa·s, and when it is 5 nm, it is 17 Pa·s. Therefore, it is thought that when the median particle size of the Cu nanoparticles is less than 10 nm, the viscosity exceeds 10 Pa·s. This is thought to be because as the median particle size decreases, the specific surface area of ​​the Cu nanoparticles increases, and as a result, the contact resistance between the solid and liquid increases. In a particularly preferred embodiment, considering the viewpoint that it is especially desirable for the viscosity to be 8 Pa·s or less, it is more preferable for the median particle size of the Cu nanoparticles to be 30 nm or more.

[0054] In addition, when the median particle diameter of the Cu nanoparticles exceeds 1000 nm and becomes large, the bonding strength suddenly decreases. This is presumably because the specific surface area of the Cu nanoparticles becomes small, and as a result, the amount of dissolution / diffusion into the liquid phase derived from the melting of the Cu nanoparticles decreases, suppressing the formation of intermetallic compounds. Considering the viewpoint that it is particularly desirable for the bonding strength to be 11 MPa or more in a particularly preferred embodiment, it is more preferable that the median particle diameter of the Cu nanoparticles is 300 nm or less.

[0055] In a preferred embodiment of the first embodiment, the median particle diameter of the Cu nanoparticles constituting the bonding material is 10 nm to 1000 nm, and in a more preferred embodiment, it is 30 nm to 300 nm. By having the Cu nanoparticles have a median particle diameter within this range, coating with a jet dispenser becomes possible, and a bonded structure having sufficient bonding strength can be obtained.

[0056] <Mixing ratio of matrix phase containing Ga and Cu nanoparticles> The bonding material according to the first embodiment includes a matrix phase containing Ga and Cu nanoparticles. Since the matrix phase containing Ga and the Cu nanoparticles react to form an intermetallic compound, the mixing ratio of the matrix phase containing Ga and the Cu nanoparticles is an important factor for the performance of the formed joint portion.

[0057] In FIG. 4, bonding materials in which the ratio (mass basis) of the content of Cu nanoparticles to the total amount of the matrix phase containing Ga and Cu nanoparticles, that is, the content ratio of Cu nanoparticles, were variously changed were prepared. A graph showing the results of measuring the viscosity measured at a shear rate s -1 in a state of heating this to 40°C, and the bonding strength of the joint portion formed using this is shown.

[0058] As the matrix phase containing Ga, 100% by mass of Ga was used, and for the Cu nanoparticles, particles having a median diameter of 100 nm were used. The bonding material was applied onto a Cu plate (20 mm × 10 mm) to a thickness of 20 μm using a jet dispenser, a Cu test piece (1 mm × 1 mm) was placed thereon, heated at 100°C for 1 minute, and then cooled to room temperature to obtain a bonded structure in which a joint portion was formed.

[0059] In Figure 4, the horizontal axis represents the Cu particle content ratio, and the vertical axis represents the viscosity of the bonding material measured with a parallel plate viscometer (● in Figure 4) and the bonding strength of a 1 mm × 1 mm Cu test piece measured with a bond tester (〇 in Figure 4).

[0060] As is clear from the graph in Figure 4, the Cu nanoparticle content required to reduce the viscosity to 10 Pa·s or less is 75% by mass or less. A viscosity of 8 Pa·s or less is more preferable, in which case the required Cu nanoparticle content is 65% by mass or less.

[0061] Furthermore, if the Cu nanoparticle content decreases to less than 10% by mass, the amount of Cu necessary to form the intermetallic compound becomes insufficient. As a result, it is thought that the bonding strength decreases because the matrix phase containing unreacted Ga remains. Since a bonding strength of 11 MPa or higher is particularly desirable, in that case, it is preferable that the Cu nanoparticle content be 55% by mass or higher.

[0062] As can be seen from the graph in Figure 4, if the Cu nanoparticle content is 10-75% by mass, the viscosity of the bonding material is 10 Pa·s or less, making it possible to apply it with a jet dispenser. If the Cu nanoparticle content is 55% by mass or more, the bonding strength is 11 MPa or more, which is more preferable. Furthermore, if the Cu nanoparticle content is 65% by mass or less, the viscosity becomes 8 MPa·s or less, which is even more preferable.

[0063] <Examples and Comparative Examples> In forming joints in bonded structures, it is necessary to balance the viscosity of the bonding material when heated to 40°C with the bonding strength of the joint formed using that material. To further investigate this balance, bonding materials were prepared by varying the median particle size and content ratio of Cu nanoparticles, and experiments were conducted to measure viscosity and bonding strength in the same manner as before. The results are shown in Table 1 of Figure 5.

[0064] In addition, in the viscosity column of Table 1 in Figure 5, the guideline for viscosity is 10 Pa·s or less. A circle (○) indicates a good evaluation, a double circle (◎) indicates a sufficiently good evaluation of 8 MPa·s or less, and an X (×) indicates an evaluation that does not meet the specified viscosity.

[0065] Furthermore, in the "Joint Strength" column of Table 1 in Figure 5, the target joint strength is set at 10 MPa. A circle (○) indicates a good evaluation, a double circle (◎) indicates a sufficiently good evaluation of 11 MPa·s or higher, and an "X" (×) indicates an evaluation that does not meet the specified joint strength. Experimental examples that received a ○ or ◎ evaluation for both viscosity and joint strength are designated as "Examples," while experimental examples that received an × evaluation for either are designated as "Comparative Examples."

[0066] [Example 1] The viscosity of bonding material 110, prepared using Cu nanoparticles as shown in Table 1 of Figure 5, was measured using a parallel plate viscometer and found to be 4.1 Pa·s. This indicates a sufficiently good viscosity for application with a jet dispenser. Furthermore, bonding material 110 was applied to a Cu plate (20 mm × 10 mm) to a thickness of 20 μm, a Cu test specimen (1 mm × 1 mm) was placed on top, and the bonded structure was formed by heating at 100°C for 1 minute. The bonding strength of this Cu test specimen was measured using a bond tester and found to be 11.3 MPa, which is a sufficiently good bonding strength.

[0067] [Examples 2-5 and Comparative Examples 1-4] Using the Cu nanoparticles shown in Table 1 of Figure 5, a bonding material was prepared with a Cu nanoparticle content ratio of 65% by mass, and the viscosity and bonding strength were measured in the same manner as in Example 1.

[0068] As can be seen from Table 1 in Figure 5, if the size of the Cu nanoparticles (median particle diameter) is 10 nm or larger, the viscosity is 10 Pa·s or less, and it can be applied with a jet dispenser. However, if the size of the Cu nanoparticles exceeds 1000 nm, the bonding strength decreases to less than 10 MPa, which is not necessarily sufficient. From these results, the median particle diameter of Cu nanoparticles required to obtain a viscosity that can be applied with a jet dispenser and sufficient bonding strength is 10 nm to 1000 nm. Furthermore, to obtain a viscosity of 8 Pa·s or less and a bonding strength of 11 MPa or more, it is preferable to set the median diameter of the Cu particles to 30 to 300 nm.

[0069] [Examples 6-11 and Comparative Examples 5-6] Similar to the examples and comparative examples described above, bonding materials were prepared by varying the median diameter and content ratio of Cu nanoparticles shown in Table 1 of Figure 5. Bonding portions were then formed in the same manner as before, and experiments were conducted to measure their viscosity and bonding strength. The distinction between examples and comparative examples in the table, as well as their evaluation, is the same as described above.

[0070] In Example 6, a bonding material was prepared with a Cu nanoparticle content of 75% by mass. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonded structure was measured.

[0071] The viscosity of this bonding material is 9.9 Pa·s, indicating that it is suitable for application using a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 11.6 MPa, demonstrating good bonding strength.

[0072] In Example 7, a bonding material was prepared with a Cu nanoparticle content of 55% by mass. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured. The viscosity of this bonding material is 3.0 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 11.1 MPa, which is a good bonding strength.

[0073] In Example 8, a bonding material was prepared with a Cu nanoparticle content of 45% by mass. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured. The viscosity of this bonding material is 2.4 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 10.9 MPa, which is sufficient bonding strength.

[0074] In Example 9, a bonding material was prepared with a Cu nanoparticle content of 30% by mass. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured. The viscosity of this bonding material is 1.9 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 10.9 MPa, which is sufficient bonding strength.

[0075] In Example 10, a bonding material was prepared with a Cu nanoparticle content of 20% by mass. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured. The viscosity of this bonding material is 1.8 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 10.6 MPa, which is sufficient bonding strength.

[0076] In Example 11, a bonding material was prepared with a Cu nanoparticle content of 10% by mass. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured. The viscosity of this bonding material is 1.6 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 10.2 MPa, which is sufficient bonding strength.

[0077] [Examples 12-18] Similar to the examples and comparative examples described above, bonding materials were prepared by varying the median diameter and content ratio of the Ga-containing matrix and Cu nanoparticles. Bonding sections were then formed in the same manner as before, and experiments were conducted to measure their viscosity and bonding strength. The results are shown in Table 2 of Figure 6. The distinction between examples and comparative examples in Table 2, and their evaluations, are the same as in Table 1 of Figure 5 described above.

[0078] In Example 12, a bonding material was prepared using a Ga-8 mass%In matrix and Cu nanoparticles with a median diameter of 100 nm, resulting in a Cu nanoparticle content of 65 mass%. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured. The viscosity of this bonding material is 5.1 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 10.1 MPa, which is sufficient bonding strength.

[0079] In Example 13, a bonding material was prepared using a Ga-23 mass%In matrix and Cu nanoparticles with a median diameter of 10 nm, resulting in a Cu nanoparticle content of 10 mass%. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured.

[0080] The viscosity of this bonding material is 9.1 Pa·s, indicating that it is suitable for application using a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 11.4 MPa, demonstrating good bonding strength.

[0081] In Example 14, a bonding material was prepared using a Ga-2 mass%Sn matrix and Cu nanoparticles with a median diameter of 1000 nm, resulting in a Cu nanoparticle content of 65 mass%. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured.

[0082] The viscosity of this bonding material is 3.1 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 10.2 MPa, which is sufficient bonding strength.

[0083] In Example 15, a bonding material was prepared using a Ga-10 mass%Sn matrix and Cu nanoparticles with a median diameter of 300 nm, resulting in a Cu nanoparticle content of 35 mass%. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured.

[0084] The viscosity of this bonding material is 7.9 Pa·s, indicating good performance that allows it to be applied with a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 11.3 MPa, which is also good bonding strength.

[0085] In Example 16, a bonding material was prepared using a Ga-10 mass%In-5 mass%Sn matrix and Cu nanoparticles with a median diameter of 30 nm, resulting in a Cu nanoparticle content of 55 mass%. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured.

[0086] The viscosity of this bonding material is 8.2 Pa·s, indicating that it is suitable for application using a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 11.2 MPa, demonstrating good bonding strength.

[0087] In Example 17, a bonding material was prepared using a Ga-20 mass%In-10 mass%Sn matrix and Cu nanoparticles with a median diameter of 100 nm, resulting in a Cu nanoparticle content of 65 mass%. The viscosity was measured in the same manner as in the experiment described above, and the bonding strength of the bonded portion of the formed bonding structure was measured.

[0088] The viscosity of this bonding material is 8.7 Pa·s, indicating that it is suitable for application using a jet dispenser. Furthermore, the bonding strength measured with a bond tester was 11.5 MPa, demonstrating good bonding strength.

[0089] These results indicate that the bonding material, a mixture of a matrix mainly composed of Ga and Cu nanoparticles, has a viscosity of 10 Pa·s or less when applied with a jet dispenser, and this bonding material is used to form the joint. As a result, the joint consists of a first metallic phase mainly composed of Ga and a second metallic phase derived from Cu nanoparticles, with the first metallic phase containing the second metallic phase, forming a bonded structure that joins the electrodes of the semiconductor package and the electrodes of the insulating substrate. Due to the presence of a matrix phase containing Ga with a low melting point, the joint can be formed at a low temperature of 100°C or less, and the joint has sufficient bonding strength due to the network structure of the intermetallic compounds formed. [Industrial applicability]

[0090] The bonding material of this disclosure has a viscosity of 10 Pa·s or less, allowing it to be applied to an electrode with a jet dispenser and retain its shape. Furthermore, since the Ga-containing matrix becomes liquid at 30°C or higher, the bond can be formed by low-temperature heating at 100°C. In addition, the formed bond has sufficient bonding strength because it has a network structure of intermetallic compounds of the Ga-containing matrix and Cu nanoparticles. For this reason, it can be used to bond semiconductor packages and circuit boards in sensor devices, human interface input / output devices, and the like. [Explanation of symbols]

[0091] 1. Semiconductor package 2 Circuit boards 3 Circuit board electrodes 4. Semiconductor package electrodes 5 Joint 101 Semiconductor Packages 102 External electrode 103 Joint 104 Insulating substrate 105 Electrode 106 First metallic phase 107 Second metallic phase Matrix (solid phase) containing 10⁸ Ga 10⁹Cu nanoparticles 110 Bonding material (solid phase) Matrix (liquid phase) containing 111 Ga 112 Bonding materials (liquid phase)

Claims

1. A bonding material comprising a matrix with a melting point of 30°C or lower and Cu nanoparticles, The matrix phase includes at least Ga, The Cu nanoparticles have an average particle size of 10 nm to 300 nm, and the Cu nanoparticles are dispersed in the matrix phase, with the bonding material comprising 10% to 65% by mass.

2. The bonding material according to claim 1, wherein the matrix phase contains In and / or Sn.

3. A bonding structure having a bonding portion in which a substrate electrode and a component electrode are joined, The junction is composed of a metal matrix and Cu nanoparticles, wherein Cu nanoparticles with an average particle size of 1 nm to 100 nm are dispersed in the metal matrix, and the metal matrix contains at least an intermetallic compound CuGa ２ Including the aspect, The bonded structure comprises Cu nanoparticles in the range of 10% to 65% by mass of the bonded portion.

4. The metal matrix contains the intermetallic compound (Cu, Ni)Ga ２ The joint structure according to claim 3, including a phase.

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