JP7778343B2 - High strength, high ductility, and high reliability solder and its manufacturing method - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies May 12, 2021 Published at Proceedings of 2021 International Conference on Electronics Packaging (ICEP 2021)

Article 30, Paragraph 2 of the Patent Act applies. June 9, 2021, Vacuum 191 (2021) 110370. Published at https://doi.org/10.1016/j.vacuum.2021.110370

Article 30, Paragraph 2 of the Patent Act applies August 10, 2021 Materials & Design 210 (2021) 110038 https://doi. org/10.1016/j. matdes. Published on 2021.110038

The present invention relates to a highly reliable solder that combines high strength and ductility, and an efficient method for manufacturing the same.

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.

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

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% to 18% by mass of Sb, 0.5% to 2% by mass of Cu, 0.001% to 0.05% by mass of ceramic particles, and the remainder consisting of Sn and unavoidable impurities."

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. It states, "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, making it difficult to remove the Al oxide film, 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, initial bondability is good, but 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."

Furthermore, Patent Document 2 (JP 11-134933 A) proposes hard conductive particles to be dispersed in solder, which are "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, and the outermost layer is coated with a 0.1 to 2 μm thick layer of Ni, Cu or an alloy thereof to promote dispersion into the solder, and the crystallite diameter of these three layers is 300 nm or less as calculated using the Scherrer formula from the half-width of X-ray diffraction."

The hard conductive particles described in Patent Document 2 above are described as follows: "When the crystallite diameter calculated using the Scherrer equation from the half-width of the X-ray diffraction peak intensity of the coating layer is 300 nm or less, the thermal stress generated in the coating layer due to the heat during coating or molten soldering is alleviated, resulting in hard conductive particles that are less susceptible to peeling."

JP 2014-237170 A Japanese Patent Application Publication No. 11-134933

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 ceramic particles, and the amount of ceramic particles added is limited to an extremely small value (0.05 mass% or less). In other words, not only is the effect of adding ceramic particles on improving the strength and reliability of the solder limited, but the obtained effect is also thought to vary greatly depending on the type of ceramic particles.

Furthermore, while the hard conductive particles described in Patent Document 2 have improved dispersibility in solder due to the coating layer, they still require the formation of three layers with different compositions: a conductive metal layer, a reaction suppression layer, and an outermost layer. In addition, physical vapor deposition must be used to form each layer, which is not only unsuitable for mass production, but also makes it extremely difficult to form a uniform coating layer over the entire surface of particles with complex shapes or in the case of nanoparticles, etc. 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.

In light of the above circumstances, the object of the present invention is to provide a highly reliable Sn-Ag-Cu solder that combines high strength and ductility, and a method for manufacturing the same. More specifically, the object is to provide a Sn-Ag-Cu solder that is endowed with high strength, ductility, and reliability by the addition of ceramic particles, and an inexpensive and simple method for manufacturing the same.

In order to achieve the above objective, the inventors conducted extensive research into surface treatment methods for ceramic particles to be dispersed in solder, as well as the shape, size, and amount of ceramic particles to be added. As a result, they discovered that coating the surfaces of ceramic particles with NiO is extremely effective in achieving the above objective, leading to the creation of the present invention.

In other words, the present invention provides a high-strength, high-ductility, and high-reliability solder characterized by ceramic particles dispersed in Sn-Ag-Cu solder, with the ceramic particles being coated with NiO.

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 suppresses 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).

In addition, by uniformly dispersing ceramic particles with a NiO coating in Sn-Ag-Cu solder, the ceramic particles become heterogeneous nucleation sites for the formation of the solder's microstructure, and the pinning effect of the ceramic particles suppresses coarsening of the solder's eutectic structure, thereby resulting in a finer solder structure. As a result, the solder layer can be endowed with excellent strength and ductility.

In the high-strength, high-ductility, high-reliability solder of the present invention, the ceramic particles are preferably ZnO particles and/or _ZrO2 particles. The density and thermal conductivity of Sn-Ag-Cu solder are 7.3 g/ ^cm3 and 25.0 x ^10-6 /K, respectively, but by using ZnO particles or _ZrO2 particles as the ceramic particles, these values can be made close to these. Specifically, the density and thermal conductivity of ZnO are 5.6 g/ ^cm3 and 6.5 x ^10-6 /K, respectively, and the density and thermal conductivity of _ZrO2 are 5.9 g/ ^cm3 and 9.6 x ^10-6 /K, respectively.

Furthermore, 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.

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 tetrapod-type microparticles having an average particle size of 1 to 50 μm, and the _ZrO2 particles being nanoparticles having an average particle size of 10 to 500 nm. The combined addition of the tetrapod-type 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.

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 tetrapod-type ZrO2 microparticles and ZnO nanoparticles can also significantly improve the strength, ductility, and high-temperature reliability of Sn-Ag-Cu based solder compared to the case where each ceramic particle is added alone.

Furthermore, 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 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. 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.

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:

The method for producing high-strength, high-ductility, high-reliability solder of the present invention involves forming a NiO coating on the surface of ceramic particles in the first and second steps, and then dispersing the NiO-coated ceramic particles in molten Sn-Ag-Cu solder in the third step to obtain high-strength, high-ductility, high-reliability solder. Because the surface of the ceramic particles contains a NiO coating that is compatible with the molten Sn-Ag-Cu solder, a relatively large amount of ceramic particles can be uniformly dispersed.

In the method for producing high-strength, high-ductility, high-reliability solder of the present invention, the preliminary treatment 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 ceramic particles with high surface energy. 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 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 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.

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, making it easy to achieve uniform dispersion in the solder in the third step.

Furthermore, in the method for producing high-strength, high-ductility, high-reliability solder of the present invention, it is preferable that in the third step, the Sn-Ag-Cu-based 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 dispersed uniformly very effectively.

The present invention provides a highly reliable Sn-Ag-Cu solder that combines high strength and ductility, as well as a method for producing the same. More specifically, it provides a Sn-Ag-Cu solder that is endowed with high strength, ductility, and reliability through the addition of ceramic particles, as well as an inexpensive and simple method for producing the same.

1 is a process diagram of a method for producing a high-strength, high-ductility, high-reliability solder according to the present invention. 1 is a TEM photograph of _ZrO2 particles used in the examples. 1 is a graph showing the change in half-value width of _ZrO2 particles. FIG. 1 is an XRD pattern of NiO-coated _ZrO₂ particles. 1 is a TEM photograph of NiO-coated _ZrO2 particles. 1 is a HRTEM photograph of the surface of a NiO-coated _ZrO2 particle. 1 shows the STEM-EDS mapping results of NiO-coated _ZrO2 particles. 1 is a SEM photograph of ZnO microparticles used in the examples. 1 is an SEM photograph of the surface of NiO-coated tetrapod-type ZnO microparticles. 1 is a SEM photograph showing the microstructure of a high-strength, high-ductility, high-reliability solder. 1 is a graph showing the tensile properties of solder (with only NiO-coated _ZrO2 particles added); 1 is a graph showing the tensile properties of solder (with only NiO-coated tetrapod-type ZnO microparticles added). 1 is a graph showing the tensile properties of solder (composite addition). 1 is a SEM photograph of a cross section of a joint interface and a cross section of a solder layer of a high-strength, high-ductility, high-reliability solder. 10 is a graph showing the thickness of an intermetallic compound layer of a joined body. 10 is a graph showing the shear strength of a bonded body. 1 is a SEM photograph showing changes in an intermetallic compound layer and a solder layer after being held at high temperature (comparative solder material). 1 is a SEM photograph showing changes in an intermetallic compound layer and a solder layer after being held at high temperature (high strength, high ductility, high reliability solder material). 10 is a graph showing the shear strength of a bonded body after being held at a high temperature.

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 does not limit the present invention. Furthermore, redundant explanations may be omitted.

1. High-Strength, High-Ductility, High-Reliability Solder The high-strength, high-ductility, high-reliability solder of the present invention is characterized in that ceramic particles are dispersed in a Sn—Ag—Cu solder, and the ceramic particles are coated with NiO. The Sn—Ag—Cu solder and NiO-coated ceramic particles that serve as the base material are described in detail below.

(1) Sn—Ag—Cu-based solder For Sn—Ag—Cu-based solder, a Sn—Ag—Cu-based material having a composition generally suitable for soldering can be used. For example, a solder material containing more than 0% by mass and not more than 4% by mass of Ag, more than 0% by mass and not more than 1.0% by mass of Cu, and the remainder being Sn can be used. Such Sn—Ag—Cu-based materials can have a melting point of about 215 to about 230°C.

From the standpoint of reducing costs and improving impact properties, the Ag content is preferably greater than 0 and less than 3% by mass, more preferably greater than 0 and less than 2% by mass, and most preferably greater than 0 and less 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 in strength and thermal fatigue properties that accompanies a decrease in the Ag content.

In addition to the NiO-coated ceramic particles, the Sn-Ag-Cu solder may also contain other components such as flux.

(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.

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.

The density and thermal conductivity of Sn-Ag-Cu solder are 7.3 g/ ^cm3 and 25.0 x ^10-6 /K, respectively, but by using ZnO particles or _ZrO2 particles as the ceramic particles, these values can be made close to these. Specifically, the density and thermal conductivity of ZnO are 5.6 g/ ^cm3 and 6.5 x ^10-6 /K, respectively, and the density and thermal conductivity of _ZrO2 are 5.9 g/ ^cm3 and 9.6 x ^10-6 /K, respectively.

Furthermore, 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 various shapes and sizes of ceramic particles known in the art for strengthening metal materials. However, nanoparticles or tetrapod-type microparticles are preferred, and it is even more preferable to add a combination of nanoparticles and tetrapod-type microparticles. Here, tetrapod-type refers to a shape with four legs extending radially from the center of the particle.

By uniformly dispersing nanoparticles, the mechanical properties of Sn-Ag-Cu solder can be improved evenly. Furthermore, by using tetrapod-shaped microparticles, the mechanical properties of the entire solder layer can be improved more efficiently with a small amount added compared to when using roughly spherical ceramic particles or nanoparticles, due to the shape and size of the ceramic particles.

The improvement in strength, ductility, and high-temperature reliability of Sn-Ag-Cu solder achieved by adding NiO-coated ceramic particles can be achieved by adding only one type of ceramic particle. However, by adding a combination of nanoparticles and tetrapod-type microparticles, this effect is significantly more pronounced than when each type of ceramic particle is added alone.

Suitable combinations of ceramic particles include a combination of tetrapod-type ZnO microparticles with an average particle size of 1 to 50 μm and _ZrO2 nanoparticles with an average particle size of 10 to 500 nm, and a combination of tetrapod-type _ZrO2 microparticles with an average particle size of 1 to 50 μm and ZnO nanoparticles with an average particle size of 10 to 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.

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 a preferred amount is 0.2 to 0.4 mass%. Adding ceramic particles in an amount of 0.2 mass% or more reliably improves the strength, ductility, and high-temperature reliability of the Sn-Ag-Cu solder, while adding ceramic particles in an amount of 0.4 mass% or less prevents uneven dispersion of the ceramic particles due to aggregation, etc., and suppresses a decrease in the strength and ductility of the Sn-Ag-Cu solder. When different ceramic particles are added in combination, these values refer to the total amount added.

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

The formation of a NiO coating on the surface of ceramic particles can be confirmed using SEM-EDS, TEM-EDS, and STEM-EDS observations. The crystal structure can be confirmed using TEM observation, or more simply, by performing XRD measurements (powder method) on NiO-coated ceramic particles.

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

Although an intermediate layer may exist between the NiO coating and the surface of the ceramic particles, it is preferable that the NiO coating and the surface of the ceramic particles are directly and firmly bonded.

(3) Others One aspect of the high-strength, high-ductility, high-reliability solder of the present invention can be, for example, a mixture of a Sn—Ag—Cu-based solder base material, NiO-coated ceramic particles, and flux (or components of the flux). Such a high-strength, high-ductility, high-reliability solder can be used as a so-called solder paste (or cream solder).

In addition, high-strength, high-ductility, high-reliability solder can be used in any form, such as solder balls or solder wires, and is suitable for use as a joining material in the mounting process of electronic components.

The high-strength, high-ductility, high-reliability solder can also be used as a solder paste to fabricate electronic circuit boards using a reflow soldering process. Alternatively, the high-strength, high-ductility, high-reliability solder can also be used as a flow solder (or solder jet) to fabricate electronic circuit boards using a flow soldering process. Processes known in the art can be applied to the reflow or flow soldering process.

2. Manufacturing Method of High-Strength, High-Ductility, High-Reliability Solder Figure 1 shows a process diagram of the manufacturing method of high-strength, high-ductility, high-reliability solder of the present invention. The manufacturing method of high-strength, high-ductility, high-reliability solder of the present invention includes a first step (S01) of coating the surfaces of ceramic particles with nickel acetate tetrahydrate to obtain nickel acetate tetrahydrate-coated ceramic particles, a second step (S02) of heating the nickel acetate tetrahydrate-coated ceramic particles and thermally decomposing the nickel acetate tetrahydrate to obtain NiO-coated ceramic particles, and a third step (S03) of dispersing the NiO-coated ceramic particles in molten Sn—Ag—Cu-based solder. Furthermore, as a pretreatment for the first step (S01), a lattice strain introduction step (S00) is preferably performed to introduce lattice strain into the surfaces of the ceramic particles to obtain surface-enhanced ceramic particles. Each step is described in detail below.

(1) Lattice strain introduction step (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.

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

The method for introducing lattice strain into the surface of ceramic particles 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. Using a ball mill allows lattice strain to 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 surface of the ceramic particles. For example, a planetary ball mill can be used, and treatment can be carried out using appropriate media at a rotation speed of several hundred rpm for approximately 1 to 20 hours.

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

There are no particular limitations on the method for coating high-surface-energy ceramic particles with nickel acetate tetrahydrate, as long as it does not impair the effects of the present invention. For example, coating can be achieved by stirring and mixing high-surface-energy ceramic particles and nickel acetate tetrahydrate particles in ethanol while applying ultrasound, and then heating the resulting ethanol solution to approximately 70°C to evaporate all of the ethanol.

During the evaporation of ethanol, the dissolved nickel acetate tetrahydrate crystallizes on the surface of the high-energy ceramic particles, forming 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.

(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.

The NiO coating is formed by the self-assembly phenomenon of a nickel acetate tetrahydrate coating/surface-enhanced ceramic particle system due to 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 appropriate depending on the amount of nickel acetate tetrahydrate-coated ceramic particles to be treated and the formation of the NiO coating, but can be, for example, approximately 1 to 10 minutes.

(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.

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. However, 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, allowing for extremely effective uniform dispersion of the NiO-coated ceramic particles.

Furthermore, by using ZnO particles 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 the ZnO particles 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.

The above describes representative embodiments of the present invention, 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 in any way.

(1) NiO Coating on Ceramic Particles Commercially available _ZrO2 particles (HW NANO, China) were coated with NiO. The _ZrO2 particles were roughly spherical nanoparticles with diameters of 60 to 120 nm. A TEM photograph of the _ZrO2 particles is shown in Figure 2.

Using a planetary ball mill (Tencan XQM-0.4L, manufactured in China), the _ZrO2 particles were subjected to a lattice strain introduction process 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.

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 based on the change in the half-width of the peaks corresponding to the (-111) and (111) _ZrO2 . The 2θ of the peaks corresponding to the (-111) and (111) ZrO2 was 28.2° and 31.5°, respectively. The resulting changes in half-width are shown in Figure 3. The half-width increased with ball milling, confirming the introduction of lattice strain. Furthermore, the half-width increased with increasing treatment time, indicating that the amount of lattice strain on the ceramic particle surface can be controlled by the treatment time.

Next, surface-enhanced _ZrO2 particles and nickel acetate tetrahydrate particles (manufactured by 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 surfaces of the surface-enhanced _ZrO2 particles (first step).

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 coating (second step). The furnace temperature was increased at a rate of 20°C/min.

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.

Figure 5 shows a TEM image of the 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.

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. An SEM photograph of the ZnO microparticles is shown in Figure 8. A surface photograph 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.

(2) Dispersion of NiO-coated ceramic particles in Sn-Ag-Cu solder. Sn-1.0 wt% Ag-0.5 wt% Cu solder was heated to 380°C to melt, and NiO-coated ceramic particles were added. Next, the mixture was stirred with an 80 W ultrasonic wave 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 were as shown in Table 1. NiO-coated _ZrO2 particles alone, NiO-coated tetrapod-type ZnO microparticles alone, and a combination of these particles were used. Note that without the NiO coating, it was not possible to uniformly disperse _ZrO2 and/or ZnO particles in the solder in any case.

Figure 10 shows the microstructures (SEM photographs) of the high-strength, high-ductility, high-reliability solders obtained by adding only NiO-coated _ZrO2 particles. For comparison, the microstructures of the solders without NiO-coated _ZrO2 particles are also shown. Figure 10 shows that even with 0.3 mass% of NiO-coated _ZrO2 particles added, no significant defects were observed, indicating a good dispersion state.

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%.

When NiO-coated _ZrO2 particles were added alone, and when NiO-coated tetrapod-type ZnO microparticles were added alone, the addition of these particles improved the tensile properties of the solder, revealing 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% by mass, while when NiO-coated tetrapod-type ZnO microparticles were added alone, strength reached its maximum at 0.3% by mass and ductility reached its maximum at 0.1% by mass.

On the other hand, the combined addition of NiO-coated _ZrO2 particles and NiO-coated tetrapod-type ZnO microparticles can provide better tensile properties than when either is added alone. When 0.18% by mass of NiO-coated _ZrO2 particles and 0.12% by mass of NiO-coated tetrapod-type ZnO microparticles are combined, the strength and ductility are higher than when either is added alone.

(3) Bonding using high-strength, high-ductility, high-reliability solders. Each of the obtained high-strength, high-ductility, high-reliability solders was rolled and punched to form solder materials with a diameter of 4 mm and a thickness of 100 μm. Next, the solder materials were placed between a 10 mm diameter disk-shaped copper material and a 3 mm diameter disk-shaped copper material, and the copper materials were bonded together at a bonding temperature of 260° C. for a bonding time of 50 seconds.

Figure 14 shows SEM photographs of the cross section of the joint interface and solder layer for a solder material (comparative solder material) without the addition of NiO-coated ceramic particles and a solder material (high-strength, high-ductility, high-reliability solder material of the present invention) with a composite addition of 0.18 mass% NiO-coated ZrO2 _particles and 0.12 mass% NiO-coated tetrapod-type ZnO microparticles. In the comparative solder material, a thick intermetallic compound layer was formed at the joint interface, resulting in coarsening of the solder structure. In contrast, in the high-strength, high-ductility, high-reliability solder of the present invention, it can be seen that the formation of the intermetallic compound layer and the coarsening of the solder structure were suppressed.

Furthermore, to evaluate the bond strength of the bonded bodies, a shear test was performed using a joint strength testing machine (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 maximum load at break was divided by the area of the bonded part to determine the bond strength. The bond strength of four bonded bodies was measured for each treatment condition, and the average was taken as the bond strength for that treatment condition.

The thickness and shear strength of the intermetallic compound layer of the joint 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 was increased by 15%.

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 high-temperature stability. The holding time was 128 to 1008 hours. Figures 17 and 18 show 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, respectively.

When the comparative solder material was used, the thickness of the intermetallic compound layer increased with increasing holding time, and microcracks appeared 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 changes were observed in the microstructure of the solder layer.

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

Claims (5)

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 ZrO2 _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 ZrO2 _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. 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 ZrO2 _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 ZrO2 _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. 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: 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: 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: