High strength, high ductility, and high reliability solder and its manufacturing method

Abstract

To provide a Sn-Ag-Cu solder having high strength and high ductility as well as high reliability and a method for producing the same, or more specifically, provide a Sn-Ag-Cu solder that achieves high strength, high ductility and high reliability through the addition of ceramic particles and an inexpensive and convenient production method therefor.SOLUTION: A high-strength high-ductility high-reliability solder includes Sn-Ag-Cu solder with ceramic particles dispersed therein, the ceramic particles being coated with NiO. The ceramic particles are preferably ZnO particles and / or ZrO2 particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a highly reliable solder that combines high strength and ductility, and to an efficient method for producing the same. [Background technology]

[0002] Currently, the mainstream general-purpose lead-free solder used in electronics products is Sn-3.0% by mass Ag-0.5% by mass Cu solder, which contains 3.0% by mass of Ag. However, this solder has problems with impact resistance, and due to the recent rise in the price of Ag, the use of low-Ag lead-free solder with a reduced Ag content is being considered.

[0003] Low Ag lead-free solder compositions include Sn-1.0 mass% Ag-0.5 mass% Cu, Sn-0.3 mass% Ag-0.7 mass% Cu, and Sn-0.1 mass% Ag-0.7 mass% Cu, but it is difficult to obtain sufficient tensile strength with these low Ag lead-free solders and they are said to have poor thermal fatigue properties.

[0004] Here, as a method for improving the heat resistance of solder, for example, Patent Document 1 (JP 2014-237170 A) proposes "a lead-free solder alloy for ultrasonic soldering, characterized by containing 5% by mass or more and 18% by mass or less of Sb, 0.5% by mass or more and 2% by mass or less of Cu, 0.001% by mass or more and 0.05% by mass or less of ceramic particles, with the remainder consisting of Sn and unavoidable impurities."

[0005] The lead-free solder alloy for ultrasonic soldering described in Patent Document 1 achieves excellent initial bondability and heat resistance by adding specific amounts of Sb, Cu, and ceramic particles, and it is stated that "if the amount of ceramic particles added is less than 0.001% by mass, the ceramic particles do not collide with the strong Al oxide film very often, and the Al oxide film cannot be easily removed, making it difficult to bond in a short time. On the other hand, if the amount of ceramic particles added is more than 0.05% by mass, although the initial bondability is good, the large amount of ceramic particles present in the solder alloy significantly deteriorates the solder alloy structure, resulting in a failure in a heat cycle test."

[0006] Furthermore, Patent Document 2 (JP Patent Publication No. 11-134933A) proposes the following hard conductive particles to be dispersed in solder: "Hard conductive particles with excellent solder dispersibility, characterized in that a ceramic powder having a particle size of 50 μm or less is coated by physical vapor deposition with a conductive metal layer of 0.1 to 5 μm thick made of Au, Ag, Cu, Al or an alloy thereof, and a solder reaction suppression layer of 0.05 to 0.5 μm thick made of Pt, Pd or an alloy thereof on top of that, and the outermost layer is coated with a 0.1 to 2 μm thick layer of Ni, Cu or an alloy thereof as a dispersion promotion layer into the solder, and the crystallite diameter of these three layers is 300 nm or less as calculated by Scherrer's formula from the half-width of X-ray diffraction."

[0007] Regarding the hard conductive particles described in Patent Document 2, it is stated that "when the crystallite diameter calculated from the half-width of the peak intensity of the X-ray diffraction of the coating layer using the Scherrer formula is 300 nm or less, the thermal stress generated in the coating layer due to the heat during coating or in the molten solder is alleviated, and hard conductive particles that are suppressed from peeling can be obtained." [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-237170 [Patent Document 2] Japanese Patent Application Publication No. 11-134933 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the lead-free solder alloy for ultrasonic soldering described in Patent Document 1, little consideration is given to the dispersibility of ceramic particles in the solder or the adhesion between the solder and the ceramic particles, and the amount of ceramic particles added is limited to an extremely small value (0.05 mass% or less). In other words, the effect of adding ceramic particles on improving the strength and reliability of the solder is limited, and the obtained effect is thought to vary greatly depending on the type of ceramic particles.

[0010] Furthermore, while the hard conductive particles described in Patent Document 2 have improved dispersibility in solder due to the coating layer, they require the formation of three layers with different compositions: a conductive metal layer, a reaction suppression layer, and an outermost layer. Furthermore, physical vapor deposition is required to form each layer, which is not suitable for mass production. Furthermore, when the particle shape is complex or the particles are nanoparticles, it is extremely difficult to form a uniform coating layer over the entire surface of the particles. In other words, the hard conductive particles described in Patent Document 2 are not suitable as an additive to solder, a general-purpose joining material, in terms of cost, quality, etc.

[0011] In view of the above circumstances, an object of the present invention is to provide a Sn-Ag-Cu based solder that combines high strength and ductility with high reliability, and a method for producing the same. More specifically, an object of the present invention is to provide a Sn-Ag-Cu based solder that is endowed with high strength, high ductility, and high reliability by the addition of ceramic particles, and an inexpensive and simple method for producing the same. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the inventors have conducted extensive research into surface treatment methods for ceramic particles to be dispersed in solder, as well as the shape, size, and amount of added ceramic particles. As a result, they have found that coating the surfaces of ceramic particles with NiO is extremely effective in achieving the above-mentioned object, and have arrived at the present invention.

[0013] That is, the present invention provides a high-strength, high-ductility, and high-reliability solder characterized in that ceramic particles are dispersed in an Sn-Ag-Cu based solder, and the ceramic particles are coated with NiO.

[0014] The greatest feature of the high-strength, high-ductility, high-reliability solder of the present invention is that the surfaces of the dispersed ceramic particles are coated with NiO. The NiO coating improves the dispersibility of the ceramic particles in the solder, achieving uniform dispersion of the ceramic particles. In addition, the NiO coating improves the affinity between the ceramic particles and the solder, effectively strengthening the dispersion of the ceramic particles. In addition, the uniform dispersion of the ceramic particles can suppress the growth of intermetallic compounds at the bonding interface between the solder layer and the substrate (the material to be bonded), improving the high-temperature stability of the bonded body (strength and ductility are maintained even after exposure to high-temperature environments).

[0015] In addition, by uniformly dispersing the ceramic particles with NiO coating in the Sn-Ag-Cu solder, the ceramic particles become heterogeneous nucleation sites for the formation of the solder microstructure, and the pinning effect of the ceramic particles suppresses the coarsening of the eutectic structure of the solder, thereby resulting in a finer solder structure, which can impart excellent strength and ductility to the solder layer.

[0016] In the high-strength, high-ductility, and high-reliability solder of the present invention, the ceramic particles are preferably ZnO particles and / or ZrO2 particles. The density and thermal conductivity of the Sn-Ag-Cu based solder are 7.3 g / cm3, respectively. 3 and 25.0 x 10 -6 / K, by using ZnO particles or ZrO2 particles as ceramic particles, these values ​​can be made close to each other. Specifically, the density and thermal conductivity of ZnO are 5.6 g / cm3. 3 and 6.5 x 10 -6 / K, and the density and thermal conductivity of ZrO2 are 5.9 g / cm 3 and 9.6 x 10 -6 / K.

[0017] In addition, in the high-strength, high-ductility, high-reliability solder of the present invention, it is preferable that the ceramic particles are nanoparticles and / or tetrapod-type microparticles. Uniform dispersion of nanoparticles can improve the mechanical properties of the Sn-Ag-Cu solder evenly. Furthermore, due to the shape and size of the ceramic particles, the use of tetrapod-type microparticles can efficiently improve the mechanical properties of the entire solder layer with a small amount of addition, compared to the use of approximately spherical ceramic particles or nanoparticles.

[0018] In the high-strength, high-ductility, high-reliability solder of the present invention, the ceramic particles are preferably the ZnO particles and the ZrO2 particles, the ZnO particles being the tetrapod-shaped microparticles having an average particle size of 1 to 50 μm, and the ZrO2 particles being the nanoparticles having an average particle size of 10 to 500 nm. The combined addition of the tetrapod-shaped ZnO microparticles and ZrO2 nanoparticles can significantly improve the strength, ductility, and high-temperature reliability of the Sn-Ag-Cu solder compared to the case where each ceramic particle is added alone.

[0019] In the high-strength, high-ductility, high-reliability solder of the present invention, the ceramic particles are preferably the ZnO particles and the ZrO2 particles, the ZnO particles being nanoparticles with an average particle size of 10 to 500 nm, and the ZrO2 particles being tetrapod-type microparticles with an average particle size of 1 to 50 μm. The combined addition of the tetrapod-type ZrO2 microparticles and the ZnO nanoparticles can also very efficiently improve the strength, ductility, and high-temperature reliability of the Sn-Ag-Cu solder compared to the case where each ceramic particle is added alone.

[0020] In the high-strength, high-ductility, high-reliability solder of the present invention, the content of the ceramic particles is preferably 0.2 to 0.4 mass %. By adding the ceramic particles in an amount of 0.2 mass % or more, the strength, ductility, and high-temperature reliability of the Sn-Ag-Cu solder can be reliably improved, while by adding the ceramic particles in an amount of 0.4 mass % or less, the ceramic particles can be prevented from being unevenly dispersed due to aggregation, and a decrease in the strength and ductility of the Sn-Ag-Cu solder can be suppressed.

[0021] The present invention also provides a first step of coating the surfaces of the surface-enhanced ceramic particles with nickel acetate tetrahydrate to obtain nickel acetate tetrahydrate-coated ceramic particles; a second step of heating the nickel acetate tetrahydrate-coated ceramic particles to thermally decompose the nickel acetate tetrahydrate to obtain NiO-coated ceramic particles; a third step of dispersing the NiO-coated ceramic particles in molten Sn—Ag—Cu solder; Also provided is a method for producing high-strength, high-ductility, and high-reliability solder, characterized by:

[0022] The method for producing high-strength, high-ductility, and high-reliability solder of the present invention involves forming NiO coatings on the surfaces of ceramic particles in steps 1 and 2, and dispersing the NiO-coated ceramic particles in molten Sn-Ag-Cu solder in step 3 to obtain high-strength, high-ductility, and high-reliability solder.The presence of NiO coatings on the surfaces of the ceramic particles, which are compatible with the molten Sn-Ag-Cu solder, allows a relatively large amount of ceramic particles to be uniformly dispersed.

[0023] In the method for producing high-strength, high-ductility, high-reliability solder of the present invention, the pretreatment of the first step preferably includes a lattice strain introduction step in which lattice strain is introduced into the surfaces of the ceramic particles to obtain surface-enhanced ceramic particles. Furthermore, a ball mill is preferably used for the lattice strain introduction step. By using a ball mill, lattice strain can be introduced relatively uniformly into the surfaces of a large number of ceramic particles. The ball milling device and conditions used are not particularly limited as long as they do not impair the effects of the present invention, and can be optimized as appropriate while checking the lattice strain introduced into the surfaces of the ceramic particles. For example, a planetary ball mill can be used as the ball mill, and the lattice strain on the surfaces of the ceramic particles can be confirmed by XRD measurement.

[0024] In the method for producing high-strength, high-ductility, and high-reliability solder of the present invention, the ceramic particles are preferably ZnO particles and / or ZrO2 particles. ZnO particles and ZrO2 particles have a specific gravity similar to that of Sn-Ag-Cu solder, which makes it easy to achieve uniform dispersion in the solder in the third step.

[0025] Furthermore, in the method for producing high-strength, high-ductility, and high-reliability solder of the present invention, it is preferable that in the third step, the Sn-Ag-Cu solder to which the NiO-coated ceramic particles have been added is stirred while ultrasonic waves are applied. By stirring while ultrasonic waves are applied, aggregation of the NiO-coated ceramic particles is suppressed, and the NiO-coated ceramic particles can be uniformly dispersed very effectively. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a Sn-Ag-Cu based solder that has both high strength and ductility and high reliability, and a method for producing the same. More specifically, it is possible to provide a Sn-Ag-Cu based solder that is endowed with high strength, high ductility, and high reliability by the addition of ceramic particles, and an inexpensive and simple method for producing the same. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a process diagram of a method for producing a high-strength, high-ductility, high-reliability solder according to the present invention. [Figure 2] 1 is a TEM photograph of ZrO2 particles used in the examples. [Figure 3] 1 is a graph showing the change in half-value width of ZrO2 particles. [Figure 4] 1 shows the XRD pattern of NiO-coated ZrO2 particles. [Figure 5] TEM photograph of NiO-coated ZrO2 particles. [Figure 6] This is an HRTEM photograph of the surface of a NiO-coated ZrO2 particle. [Figure 7] This is the result of STEM-EDS mapping of NiO-coated ZrO2 particles. [Figure 8] 1 is a SEM photograph of ZnO microparticles used in the examples. [Figure 9] 1 is an SEM photograph of the surface of NiO-coated tetrapod-type ZnO microparticles. [Figure 10] 1 is an SEM photograph showing the microstructure of a high-strength, high-ductility, high-reliability solder. [Figure 11] 1 is a graph showing the tensile properties of solder (with only NiO-coated ZrO2 particles added). [Figure 12] 1 is a graph showing the tensile properties of solder (with only NiO-coated tetrapod-type ZnO microparticles added). [Figure 13] 1 is a graph showing the tensile properties of solder (combined addition). [Figure 14]1 shows SEM photographs of a cross section of a joint interface and a cross section of a solder layer of a high-strength, high-ductility, and high-reliability solder. [Figure 15] 10 is a graph showing the thickness of an intermetallic compound layer of a joined body. [Figure 16] 10 is a graph showing the shear strength of a bonded body. [Figure 17] 1 is an SEM photograph showing changes in an intermetallic compound layer and a solder layer after being held at high temperature (comparative solder material). [Figure 18] 1 is an SEM photograph showing the changes in the intermetallic compound layer and solder layer after being held at high temperature (high strength, high ductility, high reliability solder material). [Figure 19] 10 is a graph showing the shear strength of a bonded body after being held at a high temperature. DETAILED DESCRIPTION OF THE INVENTION

[0028] A preferred embodiment of the high-strength, high-ductility, high-reliability solder and its manufacturing method of the present invention will be described in detail below. Note that the following description merely illustrates one embodiment of the present invention, and the present invention is not limited thereto. Furthermore, redundant description may be omitted.

[0029] 1.High strength, high ductility, and highly reliable solder The high-strength, high-ductility, and high-reliability solder of the present invention is characterized in that ceramic particles are dispersed in an Sn-Ag-Cu solder, and the ceramic particles are coated with NiO. The Sn-Ag-Cu solder and the NiO-coated ceramic particles that serve as the base material are described in detail below.

[0030] (1) Sn-Ag-Cu solder The Sn-Ag-Cu solder may be a Sn-Ag-Cu material having a composition generally used for soldering. For example, a solder material containing more than 0% by mass of Ag and not more than 4% by mass of Cu, with the remainder being Sn, may be used. Such a Sn-Ag-Cu material may have a melting point of about 215 to about 230°C.

[0031] From the viewpoints of reducing costs and improving impact properties, the Ag content is preferably more than 0 and not more than 3% by mass, more preferably more than 0 and not more than 2% by mass, and most preferably more than 0 and not more than 1% by mass. In the high-strength, high-ductility, high-reliability solder of the present invention, the dispersion of NiO-coated ceramic particles can suppress the deterioration of strength and thermal fatigue properties that accompanies a decrease in the Ag content.

[0032] Furthermore, the Sn—Ag—Cu based solder may further contain other components such as flux in addition to the NiO coated ceramic particles.

[0033] (2) NiO-coated ceramic particles (2-1) Ceramic particles NiO-coated ceramic particles are ceramic particles with a NiO coating formed on the surface. An intermediate layer may be included between the ceramic particles and the NiO coating, but it is preferable that the ceramic particles and the NiO coating are directly and firmly bonded to each other.

[0034] The material of the ceramic particles is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known ceramics can be used. Examples of the ceramics include ZnO, ZrO2, SiC, Si3N4, AlN, Al2O3, and SiO2, but ZnO or ZrO2 is preferred.

[0035] The density and thermal conductivity of Sn-Ag-Cu solder are 7.3 g / cm 3 and 25.0 x 10 -6 / K, by using ZnO particles or ZrO2 particles as ceramic particles, these values ​​can be made close to each other. Specifically, the density and thermal conductivity of ZnO are 5.6 g / cm 3 and 6.5 x 10 -6 / K, and the density and thermal conductivity of ZrO2 are 5.9 g / cm 3 and 9.6 x 10 -6 / K.

[0036] The shape and size of the ceramic particles are not particularly limited as long as they do not impair the effects of the present invention, and can be any of the shapes and sizes of various conventional ceramic particles used to strengthen metal materials, but nanoparticles or tetrapod-type microparticles are preferred, and a combination of nanoparticles and tetrapod-type microparticles is even more preferred. Here, tetrapod-type refers to a shape with four legs extending radially from the center of the particle.

[0037] Uniform dispersion of nanoparticles can improve the mechanical properties of Sn-Ag-Cu solders. Furthermore, the use of tetrapod-shaped microparticles, due to the shape and size of the ceramic particles, can efficiently improve the mechanical properties of the entire solder layer with a small amount of addition compared to the use of roughly spherical ceramic particles or nanoparticles.

[0038] The improvement in strength, ductility, and high-temperature reliability of Sn-Ag-Cu solder due to the addition of NiO-coated ceramic particles can be achieved by adding only one type of ceramic particle, but by adding a combination of nanoparticles and tetrapod-shaped microparticles, the effect is much more pronounced than when each type of ceramic particle is added alone.

[0039] Suitable combinations of ceramic particles include a combination of tetrapod-type ZnO microparticles with an average particle size of 1-50 μm and ZrO nanoparticles with an average particle size of 10-500 nm, and a combination of tetrapod-type ZrO microparticles with an average particle size of 1-50 μm and ZnO nanoparticles with an average particle size of 10-500 nm. The average particle size of the ceramic particles can be measured using a laser particle counter. It can also be measured from electron microscope photographs, or calculated from the electron microscope photographs using an image processing device.

[0040] The amount of ceramic particles added is not particularly limited as long as it does not impair the effects of the present invention and can be adjusted appropriately depending on the composition of the Sn-Ag-Cu solder and the desired mechanical properties, but is preferably 0.2 to 0.4 mass%. By adding ceramic particles in an amount of 0.2 mass% or more, the strength, ductility, and high-temperature reliability of the Sn-Ag-Cu solder can be reliably improved, while by adding ceramic particles in an amount of 0.4 mass% or less, uneven dispersion of the ceramic particles due to aggregation, etc., can be prevented, and a decrease in the strength and ductility of the Sn-Ag-Cu solder can be suppressed. When different ceramic particles are added in combination, these values ​​refer to the total amount added.

[0041] (2-2)NiO coating It is preferable that the NiO coating be formed on the entire surface of the ceramic particles, but if at least 50% of the surface is coated, good dispersibility and adhesion to Sn-Ag-Cu solder can be obtained.

[0042] The formation of a NiO coating on the surface of ceramic particles can be confirmed using SEM-EDS observation, TEM-EDS observation, STEM-EDS observation, etc. The crystal structure can be confirmed using TEM observation, or simply by performing XRD measurement (powder method) on the NiO-coated ceramic particles.

[0043] The NiO coating may be formed on the surface of the ceramic particles as a film having a uniform thickness, or fine granular NiO may be aggregated to coat the surface of the ceramic particles.

[0044] An intermediate layer may exist between the NiO coating and the surface of the ceramic particle, but it is preferable that the NiO coating and the surface of the ceramic particle are directly and firmly bonded to each other.

[0045] (3) Other One embodiment of the high-strength, high-ductility, and high-reliability solder of the present invention can be, for example, a mixture of a Sn-Ag-Cu solder base material, NiO-coated ceramic particles, and a flux (or a component of the flux). Such a high-strength, high-ductility, and high-reliability solder can be used as a so-called solder paste (or cream solder).

[0046] Furthermore, the high-strength, high-ductility, high-reliability solder can be used in any form, such as solder balls or solder wires, and can be suitably used as a joining material in the mounting process of electronic components.

[0047] Furthermore, the high-strength, high-ductility, high-reliability solder can be used as a solder paste to fabricate an electronic circuit board by a reflow soldering process. Alternatively, the high-strength, high-ductility, high-reliability solder can be used as a flow solder (or solder jet) to fabricate an electronic circuit board by a flow soldering process. The reflow or flow soldering process can be performed using a process known in the art.

[0048] 2. Manufacturing method for high-strength, high-ductility, and highly reliable solder Figure 1 shows a process diagram of the method for producing high-strength, high-ductility, and high-reliability solder of the present invention. The method for producing high-strength, high-ductility, and high-reliability solder of the present invention includes a first step (S01) in which nickel acetate tetrahydrate is coated on the surfaces of ceramic particles to obtain nickel acetate tetrahydrate-coated ceramic particles; a second step (S02) in which the nickel acetate tetrahydrate-coated ceramic particles are heated to thermally decompose the nickel acetate tetrahydrate to obtain NiO-coated ceramic particles; and a third step (S03) in which the NiO-coated ceramic particles are dispersed in molten Sn-Ag-Cu solder. Furthermore, as a pretreatment for the first step (S01), a lattice strain introduction step (S00) is preferably performed in which lattice strain is introduced into the surfaces of the ceramic particles to obtain ceramic particles with high surface energy. Each step is described in detail below.

[0049] (1) Lattice strain introduction process (S00) The lattice strain introduction step (S00) is a step for introducing lattice strain into the surfaces of ceramic particles to obtain ceramic particles with high surface energy.

[0050] By increasing the energy of the surface of the ceramic particles by introducing lattice strain, it is possible to increase the bonding strength between the NiO coating formed in the second step (S02) and the ceramic particles, and also to form a NiO coating on the entire surface of the ceramic particles. On the other hand, if the ceramic particles are damaged by the lattice strain introduction step, this step may be omitted.

[0051] The method for introducing lattice strain into the ceramic particle surface is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known methods can be used, but it is preferable to use a ball mill. By using a ball mill, lattice strain can be introduced relatively uniformly into the surface of a large number of ceramic particles. The ball mill device and conditions used are not particularly limited as long as they do not impair the effects of the present invention, and can be optimized as appropriate while checking the lattice strain introduced into the ceramic particle surface. For example, a planetary ball mill can be used as the ball mill, and treatment can be performed using appropriate media at a rotation speed of several hundred rpm for approximately 1 to 20 hours.

[0052] (2) First step (S01: Nickel acetate tetrahydrate coating step) The first step (S01) is a step for coating the surface of the surface-enhanced ceramic particles obtained in the surface strain introduction step (S00) with nickel acetate tetrahydrate.

[0053] The method for coating the surface-enhanced ceramic particles with nickel acetate tetrahydrate is not particularly limited as long as it does not impair the effects of the present invention. For example, the coating can be achieved by mixing the surface-enhanced ceramic particles and nickel acetate tetrahydrate particles in ethanol under ultrasonic irradiation, and then heating the resulting ethanol solution to approximately 70°C to evaporate all of the ethanol.

[0054] During the evaporation of ethanol, the dissolved nickel acetate tetrahydrate crystallizes on the surface of the energized ceramic particles to form nickel acetate tetrahydrate. The introduction of lattice strain on the surface of the ceramic particles makes the surface of the ceramic particles a good nucleation site, allowing for the formation of a good nickel acetate tetrahydrate coating.

[0055] (3) Second step (S02: thermal decomposition step) The second step (S02) is a step for obtaining NiO-coated ceramic particles by thermally decomposing the nickel acetate tetrahydrate coating formed on the surface of the surface-enhanced ceramic particles.

[0056] The NiO coating is formed by the self-assembly of a nickel acetate tetrahydrate coating / surface-enhanced ceramic particle system via thermal decomposition. Specifically, the nickel acetate tetrahydrate-coated ceramic particles are heated to approximately 500°C in a furnace in a nitrogen atmosphere and then cooled. The holding time at approximately 500°C can be adjusted as needed depending on the amount of nickel acetate tetrahydrate-coated ceramic particles to be treated and the state of the NiO coating formation, but can be set to approximately 1 to 10 minutes, for example.

[0057] (4) Third step (S03: NiO-coated ceramic particle dispersion step) The third step (S03) is a step for obtaining the high-strength, high-ductility, and high-reliability solder of the present invention by dispersing NiO-coated ceramic particles in molten Sn—Ag—Cu-based solder.

[0058] Although there are no particular limitations on the method for dispersing NiO-coated ceramic particles in molten Sn-Ag-Cu solder as long as it does not impair the effects of the present invention, it is preferable to stir the molten Sn-Ag-Cu solder to which the NiO-coated ceramic particles have been added while applying ultrasonic waves. By stirring while applying ultrasonic waves, aggregation of the NiO-coated ceramic particles is suppressed, and the NiO-coated ceramic particles can be dispersed uniformly very effectively.

[0059] Furthermore, by using ZnO and / or ZrO2 particles as the ceramic particles, it is possible to easily and efficiently achieve uniform dispersion of the ceramic particles in the Sn-Ag-Cu solder. Because ZnO and ZrO2 particles have a specific gravity similar to that of the Sn-Ag-Cu solder, precipitation and aggregation during the dispersion process can be suppressed.

[0060] Representative embodiments of the present invention have been described above, but the present invention is not limited to these. Furthermore, the high-strength, high-ductility, high-reliability solder and its manufacturing method of the present invention will be further described in the following examples, but the present invention is not limited to these examples. [Example]

[0061] (1) NiO coating on ceramic particles Commercially available ZrO2 particles (HW NANO, manufactured in China) were coated with NiO. The ZrO2 particles are roughly spherical nanoparticles with diameters of 60 to 120 nm. Figure 2 shows a TEM image of the ZrO2 particles.

[0062] Using a planetary ball mill (Tencan XQM-0.4L, manufactured in China), the ZrO2 particles were subjected to a lattice strain introduction treatment at 400 rpm for 1 to 20 hours (surface strain introduction process). 50 g of ZrO2 particles and 50 g of ZrO2 media were placed in the planetary ball mill. The ZrO2 media had a diameter of 1 to 5 mm.

[0063] XRD measurements were performed on the ZrO2 particles before ball milling and on the ZrO2 particles obtained after each treatment time. The amount of lattice strain introduced was evaluated by measuring the change in the half-width of the peaks corresponding to the (-111) and (111) ZrO2. The 2θ angles of the peaks corresponding to the (-111) and (111) ZrO2 are 28.2° and 31.5°, respectively. The changes in the half-width obtained are shown in Figure 3. The half-width increases with ball milling, confirming the introduction of lattice strain. Furthermore, the half-width increases with increasing treatment time, indicating that the amount of lattice strain on the ceramic particle surface can be controlled by adjusting the treatment time.

[0064] Next, surface-enhanced ZrO2 particles and nickel acetate tetrahydrate particles (Wako Pure Chemical Industries, Ltd.) were added to ethanol under ultrasonic irradiation at a molar ratio of Ni / Zr = 10%. The ethanol containing the surface-enhanced ZrO2 particles and nickel acetate tetrahydrate particles was heated to 70°C and held until the ethanol was completely evaporated, forming nickel acetate tetrahydrate on the surface of the surface-enhanced ZrO2 particles (first step).

[0065] Next, the nickel acetate tetrahydrate-coated surface-enhanced ZrO2 particles were placed in a furnace with a nitrogen atmosphere, held at 500°C for 5 minutes, and then cooled to thermally decompose the nickel acetate tetrahydrate coating and form a NiO film (second step). The furnace temperature was increased at a rate of 20°C / min.

[0066] As a representative example, the XRD pattern of NiO-coated ZrO2 particles after 10 hours of ball milling is shown in Figure 4. In addition to the diffraction peaks attributable to ZrO2, diffraction peaks attributable to NiO can also be confirmed.

[0067] Figure 5 shows a TEM image of NiO-coated ZrO2 particles after 10 hours of ball milling, and Figure 6 shows an HRTEM image of the surface of the NiO-coated ZrO2 particles. Figure 7 also shows STEM-EDS mapping of the NiO-coated ZrO2 particles. These results confirm that the entire surface of the ZrO2 particles is coated with fine NiO particles.

[0068] Commercially available tetrapod-shaped ZnO microparticles (particle size: 5-20 μm) were also coated with NiO in the same manner as ZrO2 nanoparticles, except that the surface strain introduction process was not performed. SEM images of the ZnO microparticles are shown in Figure 8. Also, a surface image of the NiO-coated tetrapod-shaped ZnO microparticles is shown in Figure 9. It can be seen in Figure 9 that the surfaces of the ZnO microparticles are coated with white, fine NiO particles. Furthermore, because the surface strain introduction process was not performed, the tetrapod shape is maintained.

[0069] (2) Dispersion of NiO-coated ceramic particles in Sn-Ag-Cu solder Sn-1.0% by mass Ag-0.5% by mass Cu solder was heated to 380°C to melt, and NiO-coated ceramic particles were added. Next, the mixture was stirred while applying ultrasonic waves at an output of 80 W and then cooled to obtain the high-strength, high-ductility, and high-reliability solder of the present invention (third step). The types and amounts of NiO-coated ceramic particles added are shown in Table 1. NiO-coated ZrO2 particles alone, NiO-coated tetrapod-type ZnO microparticles alone, and both particles were added in combination. When NiO coating was not applied, it was not possible to uniformly disperse the ZrO2 and / or ZnO particles in the solder in any case.

[0070] [Table 1]

[0071] The microstructures (SEM photographs) of the high-strength, high-ductility, high-reliability solders obtained with the sole addition of NiO-coated ZrO2 particles are shown in Figure 10. For comparison, the microstructures of the solders without NiO-coated ZrO2 particles are also shown. In Figure 10, no significant defects were observed, even with the addition of 0.3 mass% NiO-coated ZrO2 particles, indicating that a good dispersion state was obtained.

[0072] Figure 11 shows the relationship between the amount of NiO-coated ZrO2 particles added alone and the tensile properties of the solder. Figure 12 shows the relationship between the amount of NiO-coated tetrapod-type ZnO microparticles added alone and the tensile properties of the solder. Figure 13 shows the relationship between the amount of ZnO microparticles added and the tensile properties of the solder when NiO-coated ZrO2 particles and NiO-coated tetrapod-type ZnO microparticles are added together. In the case of combined addition, the total amount added is standardized to 0.3 mass%.

[0073] When NiO-coated ZrO2 particles were added alone, and when NiO-coated tetrapod-type ZnO microparticles were added alone, the tensile properties of the solder were improved, and it was found that both strength and ductility could be improved. Here, when NiO-coated ZrO2 particles were added alone, both strength and ductility reached their maximum values ​​at 0.3 mass%, while when NiO-coated tetrapod-type ZnO microparticles were added alone, strength reached its maximum at 0.3 mass%, and ductility reached its maximum at 0.1 mass%.

[0074] On the other hand, by adding both NiO-coated ZrO2 particles and NiO-coated tetrapod-type ZnO microparticles in combination, better tensile properties of the solder can be obtained than when either is added alone. When 0.18 mass% of NiO-coated ZrO2 particles and 0.12 mass% of NiO-coated tetrapod-type ZnO microparticles are added in combination, the strength and ductility are higher than when either is added alone.

[0075] (3) Joining using high-strength, high-ductility, and highly reliable solder The resulting high-strength, high-ductility, high-reliability solders were rolled and punched to produce solder materials with a diameter of 4 mm and a thickness of 100 μm. Next, the solder materials were placed between two copper disks with a diameter of 10 mm and 3 mm, and the copper disks were joined at a temperature of 260°C for a time of 50 seconds.

[0076] Figure 14 shows SEM photographs of the cross section of the joint interface and solder layer for a solder material without NiO-coated ceramic particles (comparative solder material) and a solder material with a composite of 0.18 mass% NiO-coated ZrO particles and 0.12 mass% NiO-coated tetrapod-type ZnO microparticles (high-strength, high-ductility, high-reliability solder material of the present invention). With the comparative solder material, a thick intermetallic compound layer forms at the joint interface, and the solder structure is coarse. In contrast, with the high-strength, high-ductility, high-reliability solder of the present invention, the formation of the intermetallic compound layer and the coarsening of the solder structure are suppressed.

[0077] Furthermore, to evaluate the bond strength of the bonded bodies, a shear test was performed using a joint strength tester (STR-1001, manufactured by Rhesca Corporation). The bonded bodies were placed on a stage, and a shear load was applied to the top of the bonded bodies at a shear rate of 1.0 mm / min and a shear height of 200 μm. The bond strength was calculated by dividing the maximum load at break by the area of ​​the bonded part. The bond strength of four bonded bodies was measured for each treatment condition, and the average was used as the bond strength for that treatment condition.

[0078] The thickness of the intermetallic compound layer and the shear strength of the joints obtained using the comparative solder material shown in Figure 14 and the high-strength, high-ductility, high-reliability solder material of the present invention are shown in Figures 15 and 16, respectively. When the high-strength, high-ductility, high-reliability solder material of the present invention was used, the thickness of the intermetallic compound layer was reduced to about half of that when the comparative solder material was used, and the shear strength increased by 15%.

[0079] The joints obtained using the comparative solder material shown in Figure 14 and the high-strength, high-ductility, high-reliability solder material of the present invention were held at 150°C to evaluate their high-temperature stability. The holding time was 128 to 1008 hours. The changes in the intermetallic compound layer and solder layer (SEM photographs of the joint interface cross section and solder layer cross section) when the comparative solder material and the high-strength, high-ductility, high-reliability solder material of the present invention were used are shown in Figures 17 and 18, respectively.

[0080] When the comparative solder material was used, the thickness of the intermetallic compound layer increased with increasing holding time, and microcracks were generated in the intermetallic compound layer. In contrast, when the high-strength, high-ductility, high-reliability solder material of the present invention was used, the growth of the intermetallic compound layer was suppressed, and no significant change in the microstructure of the solder layer was observed.

[0081] The shear strength of the joints after holding at 150°C for various times is shown in Figure 19. For comparison, Figure 19 also shows the value for Sn-3.0 mass% Ag-0.5 mass% Cu solder, which has an increased Ag content. Joints using the high-strength, high-ductility, high-reliability solder material of the present invention have excellent high-temperature stability, and almost no decrease in strength due to high-temperature holding is observed. In particular, the shear strength after holding for 1008 hours is higher than that when Sn-3.0 mass% Ag-0.5 mass% Cu solder is used.

Claims

1. Ceramic particles are dispersed in the Sn-Ag-Cu solder. the ceramic particles are coated with NiO; the ceramic particles are ZnO particles and / or ZrO 2 particles, the ceramic particles are nanoparticles and / or tetrapod-type microparticles, the ZnO particles are tetrapod-type microparticles having an average particle size of 5 to 20 μm, the ZrO 2 particles are nanoparticles having an average particle size of 60 to 120 nm; The content of the ceramic particles is 0.2 to 0.4 mass %; High strength, high ductility and high reliability solder.

2. a first step of coating the surfaces of ceramic particles with nickel acetate tetrahydrate to obtain nickel acetate tetrahydrate-coated ceramic particles; a second step of heating the nickel acetate tetrahydrate-coated ceramic particles to thermally decompose the nickel acetate tetrahydrate to obtain NiO-coated ceramic particles; a third step of dispersing the NiO-coated ceramic particles in molten Sn—Ag—Cu solder; the ceramic particles are ZnO particles and / or ZrO 2 particles, the ceramic particles are nanoparticles and / or tetrapod-type microparticles, the ZnO particles are tetrapod-type microparticles having an average particle size of 5 to 20 μm, the ZrO 2 particles are nanoparticles having an average particle size of 60 to 120 nm; The content of the ceramic particles is 0.2 to 0.4 mass %; A method for manufacturing high-strength, high-ductility, and highly reliable solder characterized by the above.

3. a lattice strain introduction step for introducing lattice strain into the surfaces of the ceramic particles to obtain ceramic particles with high surface energy as a pretreatment for the first step; 3. The method for producing high-strength, high-ductility, high-reliability solder according to claim 2, wherein:

4. using a ball mill in the lattice strain introduction step; 4. The method for producing high-strength, high-ductility, high-reliability solder according to claim 3, wherein:

5. In the third step, the Sn—Ag—Cu-based solder to which the NiO-coated ceramic particles have been added is stirred while applying ultrasonic waves; 5. The method for producing high-strength, high-ductility, high-reliability solder according to claim 2, wherein:

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