Bonding paste, bonding layer, bonded body, and method for manufacturing bonded body

Abstract

The present invention has reduced strength inhibition. The paste for bonding (10) contains copper particles (12), a solvent (14), and an additive (16) consisting of a phosphate ester. In the paste for bonding (10), the content of the additive (16) is 0.5% or more and 3.0% or less in terms of mass ratio with respect to the total amount of the paste for bonding (10).

Description

TECHNICAL FIELD

[0001] The present application relates to a joining paste, a joining layer, a joined body, and a method for manufacturing a joined body. BACKGROUND

[0002] In joining two or more members, a joining material is generally used. For example, in Patent Literature 1, a solder is described as a joining material. Also, in recent years, heat resistance of non-joined bodies such as semiconductor elements has been improved, and for example, use in a high-temperature environment such as an engine compartment of an automobile has also been increasing, and thus, for example, as described in Patent Literature 2, a silver paste is sometimes used as a joining material. The silver paste can be sintered at a lower temperature, and the melting point of a joining layer formed after sintering is the same as that of silver. Therefore, the joining layer composed of the sintered body of the silver paste is excellent in heat resistance, and can be stably used in a high-temperature environment or in a large-current use. On the other hand, from the viewpoint of material cost, for example, as described in Patent Literature 3, a copper paste is sometimes used as a joining material.

[0003] Patent Literature 1: Japanese Patent Application Publication No. 2004-172378

[0004] Patent Literature 2: Japanese Patent No. 6531547

[0005] Patent Literature 3: Japanese Patent Application Publication No. 2019-67515

[0006] However, copper is easily oxidized, and the strength of a joining layer composed of a sintered body of copper can possibly be reduced. SUMMARY

[0007] The present application was completed in view of the above-described circumstances, and an object thereof is to provide a joining paste, a joining layer, a joined body, and a method for manufacturing a joined body, which can suppress reduction in strength.

[0008] To solve the above-described problem, the joining paste of the present disclosure contains a copper particle, a solvent, and an additive composed of a phosphate ester, wherein the content of the additive is 0.5% or more and 3.0% or less in terms of mass ratio with respect to the total amount of the joining paste.

[0009] To solve the above-described problem, in the method for manufacturing a joined body of the present disclosure, the joining paste is used as a joining layer, and a first member and a second member are joined to manufacture a joined body.

[0010] According to the present application, even in the case of joining under a non-reducing atmosphere, reduction in strength can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic view of the joining paste according to the first embodiment.

[0012] Figure 2 is a schematic view of a joint body according to the first embodiment.

[0013] Figure 3 is a schematic view of a joint material according to the second embodiment.

[0014] Figure 4 is a schematic view of a joint body according to the second embodiment. DETAILED DESCRIPTION

[0015] Hereinafter, the present application will be described in detail with reference to the drawings. In addition, the following modes for carrying out the present application (hereinafter, referred to as embodiments) do not limit the present application. Also, the constitutional elements in the following embodiments include elements that can be easily conceived by those skilled in the art, substantially identical elements, and elements in the so-called equivalent range. Furthermore, the constitutional elements disclosed in the following embodiments can be appropriately combined. Also, the numerical values include a range of rounding.

[0016] (First Embodiment)

[0017] Figure 1 is a schematic view of a joint material according to the first embodiment. The joint material according to the first embodiment is used for joining members to each other. As shown in Figure 1 , the joint material 10 according to the first embodiment contains copper particles 12, a solvent 14, and an additive 16. In addition, Figure 1 is a schematic view, and the shape of the actual joint material 10 is not limited to Figure 1 shown.

[0018] (Copper Particles)

[0019] The BET diameter of the copper particles 12 is preferably 50 nm or more and 300 nm or less. The BET diameter is a particle diameter calculated from the BET specific surface area and the true density of the copper particles 12 by treating the copper particles 12 as a regular sphere or a cube and by the BET method. Specifically, it can be obtained by the method described in the following examples.

[0020] When the BET diameter of the copper particles 12 is 50 nm or more, it is difficult to form a firm agglomerate. Therefore, the surface of the copper particles 12 can be uniformly covered by the solvent 14. On the other hand, when the BET diameter of the copper particles 12 is 300 nm or less, the reaction area becomes large, and the sintering property due to heating becomes high, so a firm joint layer can be formed. The BET diameter of the copper particles 12 is preferably in the range of 80 nm or more and 200 nm or less, and particularly preferably in the range of 80 nm or more and 170 nm or less.

[0021] The BET specific surface area of the copper particles 12 is preferably 2.0 m 2 / g or more and 8.0 m2 / g, more preferably in a range of 3.5 m 2 / g and 8.0 m 2 / g, more preferably in a range of 4.0 m 2 / g and 8.0 m 2 / g. Also, the shape of the copper particles 12 is not limited to a spherical shape, and can be a needle shape or a flat plate shape.

[0022] The surface of the copper particles 12 is preferably covered with an organic film, that is, an organic protective film. By being covered with the organic protective film, oxidation of the copper particles 12 can be suppressed, and reduction in sintering property due to oxidation of the copper particles 12 is less likely to occur. In addition, it can be said that the organic protective film covering the copper particles 12 is neither a film formed from the solvent 14 nor a film derived from the solvent 14. Also, it can be said that the organic protective film covering the copper particles 12 is not a film of copper oxide formed by oxidation of copper.

[0023] The case where the copper particles 12 are covered with the organic protective film can be confirmed by analyzing the surface of the copper particles 12 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Therefore, in the present embodiment, with respect to the copper particles 12, C3H3O3 - ions and the detected amount of Cu + ions are compared. The ratio of the detected amount of C3H3O3 - / Cu + is preferably 0.001 or more. The detected amount of C3H3O3 - / Cu + is further preferably in a range of 0.05 or more and 0.2 or less. Note that the surface of the copper particles 12 in the present analysis refers to the surface of the copper particles 12 including the organic protective film covering the same (that is, the surface of the organic protective film), and does not refer to the surface of the copper particles 12 when the organic protective film is removed from the copper particles 12.

[0024] With respect to the copper particles 12, C3H4O2 - ions and ions having a mass of 5 or more can be detected by analyzing the surface using time-of-flight secondary ion mass spectrometry. The detected amount of C3H4O2 - ions and the detected amount of Cu + ions are compared. The ratio of the detected amount of C3H4O2 - / Cu + is preferably 0.001 or more. Also, the ratio of the detected amount of ions having a mass of 5 or more to the detected amount of Cu + ions (ions having a mass of 5 or more / Cu + ions) is preferably less than 0.005.

[0025] C3H3O3 detected in time-of-flight secondary ion mass spectrometry - Ion, C3H4O2 - Ion and ions of C5 or more originate from an organic protective film covering the surface of the copper particles 12. Therefore, C3H3O3 - / Cu + Ratio and C3H4O2 - / Cu + When the ratio of each of C3H3O3 - / Cu + Ratio and C3H4O2 - / Cu + When the ratio of each of C3H3O3 - / Cu + Ratio and C3H4O2 - / Cu + The ratio of each of C3H3O3 + When the ratio of ions of C5 or more to Cu + is 0.005 times or more, since the organic protective film having a high desorption temperature exists in a large amount on the surface of the particles, as a result, the sinterability does not sufficiently appear and it is difficult to obtain a firm joining layer. The ratio of ions of C5 or more to Cu + is preferably less than 0.003 times.

[0026] The organic protective film is preferably derived from citric acid. A method for producing the copper particles 12 covered with the organic protective film derived from citric acid will be described later. The covering amount of the organic protective film with respect to 100 mass% of the copper particles 12 is preferably in the range of 0.5 mass% or more and 2.0 mass% or less, more preferably in the range of 0.8 mass% or more and 1.8 mass% or less, and further preferably in the range of 0.8 mass% or more and 1.5 mass% or less. By the covering amount of the organic protective film being 0.5 mass% or more, the copper particles 12 can be more uniformly covered with the organic protective film, and oxidation of the copper particles 12 can be more reliably suppressed. Also, by the covering amount of the organic protective film being 2.0 mass% or less, it is possible to suppress the occurrence of voids in the sintered body (joining layer) of the copper particles due to a gas generated by decomposition of the organic protective film caused by heating. The covering amount of the organic protective film can be measured using a commercially available device. For example, the covering amount can be measured using a differential thermal balance TG8120-SL (manufactured by Rigaku Corporation). At this time, for example, the sample is the copper particles from which moisture is removed by freeze drying. In order to suppress oxidation of the copper particles, the measurement is performed in a nitrogen atmosphere (G2 grade), the temperature increase rate is set to 10°C / min, and the weight reduction rate from 250°C to 300°C is defined as the covering amount of the organic protective film. That is, the covering amount = (weight of the sample after measurement) / (weight of the sample before measurement) x 100 (wt%). The measurement can be performed three times on the same batch of copper particles, and the arithmetic mean value is taken as the covering amount.

[0027] With respect to the copper particles 12, it is preferable that 50 mass% or more of the organic protective film decompose when heated at a temperature of 300°C for 30 minutes in a non-reactive gas atmosphere such as helium. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporation gas of acetone, and water vapor upon decomposition.

[0028] The copper particles 12 covered with the organic protective film derived from citric acid can be produced, for example, in the following manner. First, a copper citrate aqueous dispersion is prepared, and a pH adjuster is added to the copper citrate aqueous dispersion to adjust the pH to 2.0 or more and 7.5 or less. Next, a hydrazine compound that is a reducing agent capable of reducing copper ions is added to the pH-adjusted copper citrate aqueous dispersion in a non-reactive gas atmosphere in an amount of 1.0 equivalent or more and 1.2 equivalents or less, and mixed. The resulting mixture is heated to a temperature of 60°C or more and 80°C or less in a non-reactive gas atmosphere and held for 1.5 hours or more and 2.5 hours or less. Thus, the copper ions eluted from the copper citrate are reduced to generate the copper particles 12, and an organic protective film derived from citric acid is formed on the surface of the copper particles 12.

[0029] The copper citrate aqueous dispersion can be prepared by adding a powder of copper citrate to pure water such as distilled water, ion-exchanged water, or the like, at a concentration of 25 mass% or more and 40 mass% or less, and stirring with a stirring blade to uniformly disperse it. As the pH adjuster, triammonium citrate, ammonium hydrogen citrate, citric acid, or the like can be given. Among these, triammonium citrate is preferable in terms of easily adjusting the pH gently. The pH of the copper citrate aqueous dispersion is set to 2.0 or more in order to rapidly generate copper particles and obtain the desired fine copper particles 12 by accelerating the elution rate of copper ions eluted from the copper citrate. Further, the pH is set to 7.5 or less in order to improve the yield of the copper particles 12 by suppressing the eluted copper ions from becoming copper (II) hydroxide. Further, by setting the pH to 7.5 or less, it is possible to suppress the reducing power of the hydrazine compound from becoming too high, and easily obtain the desired copper particles 12. The pH of the copper citrate aqueous dispersion is preferably adjusted to a range of 4 or more and 6 or less.

[0030] The reduction of the copper citrate with the hydrazine compound is performed under a non-reactive gas atmosphere. This is in order to prevent oxidation of the copper ions eluted in the liquid. As examples of the non-reactive gas, nitrogen, helium, or the like can be given. The hydrazine compound has the advantages that no residue is generated after the reduction reaction, is highly safe, and is easy to handle when reducing the copper citrate in an acidic solution. As the hydrazine compound, hydrazine hydrate, anhydrous hydrazine, hydrazine hydrochloride, hydrazine sulfate, or the like can be given. Among these hydrazine compounds, hydrazine hydrate and anhydrous hydrazine, which do not contain components such as sulfur or chlorine that can become impurities, are preferable.

[0031] Generally, copper generated in an acidic solution with a pH of less than 7 dissolves. However, in the present embodiment, a hydrazine compound as a reducing agent is added to the acidic solution with a pH of less than 7 and mixed, and the copper particles 12 are generated in the obtained mixed solution. Therefore, since components derived from citric acid generated from the copper citrate rapidly cover the surface of the copper particles 12, it is possible to suppress the dissolution of the copper particles 12. With respect to the copper citrate aqueous dispersion after the pH adjustment, the temperature is preferably set to 50°C or more and 70°C or less in order to easily perform the reduction reaction.

[0032] The mixed solution in which the hydrazine compound is mixed under a non-active gas atmosphere is heated to a temperature of 60°C or higher and 80°C or lower and held for 1.5 hours or more and 2.5 hours or less in order to generate the copper particles 12 and form an organic protective film on the surface of the generated copper particles 12 to cover. The heating and holding under a non-active gas atmosphere is performed in order to prevent oxidation of the generated copper particles 12. The copper citrate as a starting material generally contains a copper component of about 35 mass%. By adding the hydrazine compound as a reducing agent to the copper citrate aqueous dispersion containing the copper component to this extent, and performing temperature elevation heating and holding at the above temperature for the above time, the generation of the copper particles 12 and the generation of the organic protective film on the surface of the copper particles 12 are performed in balance, whereby the copper particles 12 can be obtained in which the coverage amount of the organic protective film is in the range of 0.5 mass% or more and 2.0 mass% or less with respect to 100 mass% of the copper particles. In the case where the heating temperature is lower than 60°C and the holding time is less than 1.5 hours, it is possible that the copper citrate is not completely reduced, the generation speed of the copper particles 12 becomes too slow, and the amount of the organic protective film covering the copper particles 12 becomes too much. Also, in the case where the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, it is possible that the generation speed of the copper particles 12 becomes too fast, and the amount of the organic protective film covering the copper particles 12 becomes too little. The preferable heating temperature is 65°C or higher and 75°C or lower, and the preferable holding time is 2 hours or more and 2.5 hours or less.

[0033] The copper particles 12 generated in the mixed solution are solid-liquid separated from the mixed solution under a non-active gas atmosphere, for example, using a centrifugal separator, and dried by a freeze drying method, a reduced pressure drying method, to obtain the copper particles 12 whose surface is covered with the organic protective film. Since the surface of the copper particles 12 is covered with the organic protective film, oxidation does not easily occur even when stored in the atmosphere before use as the joining paste 10.

[0034] (Solvent)

[0035] The solvent 14 functions as a binder for the copper particles 12. The solvent 14 is an organic solvent. As the solvent 14, any substance can be used, and for example, an alcohol solvent, a glycol solvent, an acetate solvent, a hydrocarbon solvent, and an amine solvent can be cited. As specific examples of the alcohol solvent, a-terpineol, isopropyl alcohol can be cited. As specific examples of the glycol solvent, ethylene glycol, diethylene glycol, polyethylene glycol can be cited. As specific examples of the acetate solvent, diethylene glycol butyl ether acetate can be cited. As specific examples of the hydrocarbon solvent, decane, dodecane, tetradecane can be cited. As specific examples of the amine solvent, hexylamine, octylamine, dodecylamine can be cited.

[0036] (Additive)

[0037] The additive 16 is a phosphate ester. The ester obtained by dehydration condensation of phosphoric acid with an alcohol in an organic phosphoric compound is referred to as a phosphate ester. The average molecular weight of the phosphate ester used as the additive 16 is preferably 1,000 or more and 2,000 or less, more preferably 1,200 or more and 1,800 or less, and further preferably 1,400 or more and 1,600 or less. By the average molecular weight of the phosphate ester being 1,000 or more, decomposition at ordinary temperature is suppressed and storage stability is improved, and by the average molecular weight of the phosphate ester being 2,000 or less, decomposition and reaction can be performed at a desired heating temperature (around 200 to 350°C). The average molecular weight herein refers to a weight average molecular weight. The average molecular weight can be measured by, for example, size exclusion chromatography.

[0038] The phosphate ester used for the additive 16 can be any substance, and examples thereof include lauryl alcohol polyether-n phosphate ester, oleyl alcohol polyether-n phosphate ester, stearyl alcohol polyether-n phosphate ester (n is an integer), and the like. As the additive 16, one of these or two or more of these can be used.

[0039] (Binding paste)

[0040] In the present embodiment, with respect to the binding paste 10, it is preferable that no substance other than the copper particles 12, the solvent 14, and the additive 16 composed of a phosphate ester be included, except for inevitable impurities. However, the binding paste 10 can include an additive other than the copper particles 12, the solvent 14, and the additive 16 composed of a phosphate ester, without being limited thereto.

[0041] In the binding paste 10, the content of the additive 16 is 0.5% or more and 3.0% or less, preferably 0.5% or more and 2.0% or less, and further preferably 1.0% or more and 1.5% or less, in terms of mass ratio with respect to the total amount of the binding paste 10. By the content of the additive 16 being within this range, oxidation of the copper particles 12 is suppressed, and as a result, when the binding paste 10 is used to bind parts to each other in a non-reducing atmosphere, a decrease in the strength of the binding layer can be appropriately suppressed.

[0042] In the binding paste 10, the content of the solvent 14 is preferably 5% or more and 20% or less, more preferably 5% or more and 15% or less, and further preferably 8% or more and 13% or less, in terms of mass ratio with respect to the total amount of the binding paste 10. By the content of the solvent 14 being within this range, the copper particles 12 can be appropriately dispersed.

[0043] (Method for producing binding paste)

[0044] The joining paste 10 is manufactured by performing a mixing process of mixing the copper particles 12, the solvent 14, and the additive 16. In the mixing process, the copper particles 12, the solvent 14, and the additive 16 are mixed in such a manner that the content of the additive 16 is 0.5% or more and 3.0% or less in terms of mass ratio with respect to the total amount of the joining paste 10. Also, in the mixing process, the copper particles 12, the solvent 14, and the additive 16 are mixed in such a manner that the contents of the solvent 14 and the copper particles 12 are also within the above-mentioned ranges with respect to the total amount of the joining paste 10. Also, in the mixing process, the copper particles 12, the solvent 14, and the additive 16 can be mixed using a kneading device. As the kneading device, for example, a three-roll mill can be used.

[0045] (Method for manufacturing a joined body)

[0046] Figure 2 is a schematic view of a joined body according to the first embodiment. As shown in Figure 2 In the first embodiment, the joining paste 10 is used as the joining layer 20 to join the first member 21 and the second member 22 to manufacture the joined body 30. The first member 21 and the second member 22 can be arbitrary members, for example, one of the first member 21 and the second member 22 can be a substrate and the other can be an electronic element. That is, a semiconductor module in which a substrate and an electronic element are joined by the joining layer 20 can be manufactured as the joined body 30. As the substrate, there is no particular limitation, and for example, an oxygen-free copper plate, a copper-molybdenum plate, a highly heat-dissipating insulating substrate (for example, a DCB (Direct Copper Bond)), an LED (Light Emitting Diode) package, and the like can be mentioned as a substrate for mounting a semiconductor element. Also, as the electronic element, for example, an IGBT (Insulated Gate Bipolar Transistor), a diode, a Schottky diode, a MOS-FET (Metal Oxide Semiconductor Field Effect Transistor), a thyristor, a logic device, a sensor, an analog integrated circuit, an LED, a semiconductor laser, a dialer, and the like can be mentioned as a semiconductor element.

[0047] In the present production method, a coating layer forming step of applying the joining slurry 10 to the surface of at least one of the first member 21 and the second member 22 to form a coating layer is performed. The application method is not particularly limited, and examples thereof include a spin coating method, a metal mask method, a spray coating method, a dispenser coating method, a doctor blade coating method, a slit coating method, an inkjet coating method, a screen printing method, an offset printing method, a die coating method, and the like. Subsequently, a preheating step of 1 minute to 30 minutes at a temperature of 50°C to 150°C is performed in order to volatilize the solvent in the slurry. Subsequently, a lamination step of laminating the first member 21 and the second member 22 via the coating layer is performed.

[0048] Subsequently, a heating step of heating the first member 21 and the second member 22 laminated via the coating layer is performed. In the heating step, at least one of the laminated first member 21 and the second member 22 is heated at a prescribed temperature for a prescribed time while a prescribed pressure is applied thereto in a non-reducing atmosphere. By performing the heating step, the copper particles 12 in the coating layer are sintered to form the joining layer 20, and the joining body 30 in which the first member 21 and the second member 22 are joined by the joining layer 20 is produced.

[0049] The non-reducing atmosphere in the heating step refers to a state in which a non-reducing gas is filled, and can also be referred to as a non-active gas atmosphere in which a non-active gas is filled. As the non-reducing gas, a noble gas such as nitrogen or argon can be used. For example, in the present embodiment, the heating step can be performed in a nitrogen atmosphere in which the oxygen concentration is 1000 ppm. By performing the heating step in a non-reducing atmosphere, it is not necessary to use a reducing gas, and the heating step can be easily performed.

[0050] Further, the prescribed pressure applied to at least one of the first member 21 and the second member 22 is preferably 0.5 MPa or higher and 10 MPa or lower, more preferably 1 MPa or higher and 5 MPa or lower, and further preferably 2 MPa or higher and 5 MPa or lower. By setting the applied pressure to such a low range, the first member 21 and the second member 22 can be properly joined while the shape defect of the joining layer 20 is suppressed. Note that the pressure is applied in a direction in which the first member 21 and the second member 22 are pressed against each other via the coating layer.

[0051] Further, the prescribed temperature as the heating temperature in the heating step is preferably 200°C or higher and 300°C or lower, more preferably 230°C or higher and 300°C or lower, and further preferably 250°C or higher and 300°C or lower. By setting the heating temperature to such a low range, the copper particles 12 can be properly sintered while the shape defect of the joining layer 20 is suppressed.

[0052] Further, the prescribed time as the heating time in the heating step is preferably 1 minute or more and 10 minutes or less, more preferably 1 minute or more and 5 minutes or less, and further preferably 1 minute or more and 3 minutes or less. By setting the heating time to this range, the copper particles 12 can be appropriately sintered.

[0053] (Bonding layer)

[0054] As explained above, the bonding layer 20 in the present embodiment is a layer formed by heating the bonding paste 10 to sinter the copper particles 12. The bonding layer 20 is positioned between the first member 21 and the second member 22, and bonds the first member 21 and the second member 22. The bonding layer 20 can also be said to be a copper sintered body. Regarding the bonding layer 20, the sintering density of the copper particles is preferably 80% or more, more preferably 85% or more and 95% or less, and further preferably 85% or more and 90% or less. By having the sintering density within this range, the bonding layer 20 can ensure electrical conductivity and thermal conductivity. Note that the sintering density refers to the ratio of the volume of the bonding layer 20 excluding open pores and closed pores to the entire volume of the bonding layer 20 including open pores and closed pores. Regarding the sintering density, an image randomly obtained by observing a cross section of the bonding layer at a magnification of 30,000 times by SEM (Scanning Electron Microscope) is binarized using image processing software (ImageJ manufactured by National Institutes of Health), divided into a particle portion and a void portion, and the sintering density is calculated from the following formula.

[0055] Sintering density (%) = (total area of particle portion / (total area of particle portion + total area of void portion)) x 100

[0056] Further, the bonding layer 20 contains phosphorus. The phosphorus here refers to phosphorus as an element, and includes not only elemental phosphorus but also phosphorus contained in any compound. In the bonding layer 20, the phosphorus content with respect to the total amount of the bonding layer 20 is preferably 10 ppm or more and 1,000 ppm or less, more preferably 50 ppm or more and 500 ppm or less, and further preferably 100 ppm or more and 500 ppm or less, in terms of mass ratio. By having the phosphorus content within this range, even if the bonding layer 20 is formed, for example, in a non-reducing atmosphere, a decrease in strength can be suppressed. Note that the phosphorus content can be measured by ICP-OES (Inductivity Coupled Plasma Optical Emission Spectrometer). In the present embodiment, the phosphorus contained in the bonding layer 20 originates from the phosphate contained in the bonding paste 10.

[0057] Further, the thickness of the joining layer 20 is preferably 10 μm or more and 200 μm or less, more preferably 20 μm or more and 150 μm or less, and further preferably 50 μm or more and 100 μm or less. By the thickness of the joining layer 20 being within this range, stress caused by differences in linear expansion coefficients between components based on temperature differences can be moderated and high heat dissipation can be maintained.

[0058] Thus, the joining layer 20 according to the present embodiment is a copper sintered body having a sintering density of 80% or more and containing phosphorus. Since the joining layer 20 according to the present embodiment has a sintering density of 80% or more, the strength can be suppressed from decreasing. Further, since oxidation of the copper particles 12 is suppressed by the substance derived from phosphorus (phosphate in the present embodiment) contained in the joining layer 20, the strength of the joining layer 20 containing phosphorus can be suppressed from decreasing. In addition, as described above, although the joining layer 20 in the present embodiment is a layer formed by heating the joining paste 10, the method of forming the joining layer 20 can be any method as long as the above-described characteristics are satisfied.

[0059] (EFFECTS)

[0060] As described above, the joining paste 10 according to the present embodiment contains the copper particles 12, the solvent 14, and the additive 16 composed of a phosphate, and the content of the additive 16 is 0.5% or more and 3.0% or less by mass relative to the total amount of the joining paste 10. The joining paste 10 according to the present embodiment, by adding a phosphate as an additive, can suppress oxidation of the copper particles 12, and as a result, even if components are joined to each other in a non-reducing atmosphere, the strength of the joining layer can be suppressed from decreasing.

[0061] Further, the method of manufacturing the joining paste 10 according to the present embodiment includes a step of mixing the copper particles 12, the solvent 14, and the additive 16 to manufacture the joining paste 10, with the content of the additive 16 being 0.5% or more and 3.0% or less by mass relative to the total amount of the joining paste 10. According to the present manufacturing method, by adding a phosphate as an additive, oxidation of the copper particles 12 can be suppressed, and as a result, even if components are joined to each other in a non-reducing atmosphere, the strength of the joining layer can be suppressed from decreasing.

[0062] Further, in the method of manufacturing the joined body according to the present embodiment, the joining paste 10 is used as the joining layer, and a first component and a second component are joined to manufacture the joined body. According to the present method, since the joining paste 10 is used as the joining layer, even if components are joined to each other in a non-reducing atmosphere, the strength of the joining layer can be suppressed from decreasing.

[0063] (EMBODIMENTS CORRESPONDING TO THE FIRST EMBODIMENT)

[0064] Next, embodiments will be described.

[0065] (Example 1)

[0066] In Example 1, copper particles having a BET diameter of 153 nm were prepared. As for the BET diameter, the nitrogen adsorption amount of the copper particles was measured using a specific surface area measuring device (QUANTACHROME AUTOSORB-1 manufactured by Quantachrome Instruments), and the specific surface area of the copper particles was obtained by the BET method. Using the obtained specific surface area S (m 2 / g) and the density p (g / cm 3 ) of the copper particles, the BET diameter was calculated from the following equation.

[0067] BET diameter (nm) = 6000 / (p (g / cm 3 ) x S (m 2 / g))

[0068] In Example 1, as the phosphate ester serving as an additive, oleyl polyether-10 phosphate was prepared, and as the solvent, ethylene glycol was prepared.

[0069] Then, in Example 1, the copper particles, the additive, and the solvent were mixed in such a manner that the content of the additive was 1 mass%, the content of the solvent was 10 mass%, and the remainder was the copper particles, and a paste for bonding was obtained.

[0070] (Examples 2 to 10)

[0071] In Examples 2 to 10, the BET diameter of the copper particles, the kind of the additive, the kind of the additive, the content of the additive, or the content of the solvent were set as shown in Table 1, and a paste for bonding was obtained in the same manner as in Example 1, except for this.

[0072] (Comparative Examples 1 to 3)

[0073] In Comparative Examples 1 to 3, the kind of the additive or the content of the additive was set as shown in Table 1, and a paste for bonding was obtained in the same manner as in Example 1, except for this.

[0074] (Evaluation)

[0075] Using the paste for bonding obtained in each example, a bonded body was manufactured. Specifically, after forming an opening of 3 mm on an oxygen-free copper plate, the paste for bonding of each example was printed using a metal mask having a thickness of 50 pm and a metal squeegee, and then dried at 90°C for 5 minutes using a hot plate, and a 2.5 mm x 2.5 mm silicon dummy chip on which gold was sputtered at a thickness of 100 nm was placed on the back surface, and bonding was performed by heating at 250°C for 3 minutes while pressurizing at 5 MPa in a nitrogen atmosphere.

[0076] In the evaluation, the shear strength of the obtained joint body (the jointed silicon dummy chip and the oxygen-free copper plate) was measured. The shear strength of 40 MPa was "excellent", 20 MPa or more and less than 40 MPa was "good", 10 MPa or more and less than 20 MPa was "pass", and less than 10 MPa was "fail", and "pass", "good", and "excellent" were qualified.

[0077] With respect to the shear strength, the shear strength of the obtained joint body was measured by a method in accordance with JIS Z 3198-7 (Test methods for lead-free solder - Part 7: Test method for solder joint shear of chip components). Specifically, the load applied to the silicon dummy chip was measured using a tool of a bond tester (SERIES 4000 manufactured by Nordson DAGE) when the silicon dummy chip was peeled from the copper joint layer (maximum shear load). The moving speed of the tool was set to 50 μm / sec, and the gap between the front end of the tool and the oxygen-free copper substrate was set to 50 μm. The value obtained by converting the obtained maximum shear load into Newton and dividing by the area of the copper joint layer (2.5 mm x 2.5 mm) was taken as the shear strength (unit: MPa). Seven joint bodies were produced, and the shear strength of each joint body was measured. The value shown in Table 1 is the average value of the shear strengths of the seven joint bodies.

[0078] [Table 1]

[0079]

[0080] Table 1 is a table showing the evaluation results of each example. As shown in Table 1, it was found that the shear strength was qualified in the examples, and by using the jointing paste containing the phosphate ester in an amount of 0.5% by mass or more and 3.0% by mass or less, the strength reduction could be suppressed even when joining under a non-reducing atmosphere. On the other hand, it was found that in Comparative Example 1 in which the phosphate ester was not used as an additive, the shear strength was not qualified, and the strength reduction could not be suppressed when joining under a non-reducing atmosphere. Also, it was found that in Comparative Examples 2 and 3 in which the content of the phosphate ester was outside the range of 0.5% or more and 3.0% or less, the shear strength was not qualified, and the strength reduction could not be suppressed when joining under a non-reducing atmosphere.

[0081] (Second Embodiment)

[0082] Figure 3 is a schematic view of the jointing paste according to the second embodiment. The jointing paste of the second embodiment is used to join members to each other. As shown in Figure 3 , the jointing paste 10 of the present embodiment contains copper particles 12, a solvent 14, and an additive 16. In addition, Figure 3 is a schematic view, and the shape of the actual jointing paste 10 is not limited to Figure 3 the shape shown in the drawing.

[0083] (Copper particles)

[0084] The BET diameter of the copper particles 12 is preferably 50 nm or more and 300 nm or less. The BET diameter is a particle diameter calculated from the BET specific surface area and the true density of the copper particles 12, assuming that the copper particles 12 are a regular sphere or a cube, and is obtained by the BET method. Specifically, it can be obtained by the method described in the Examples described later.

[0085] When the BET diameter of the copper particles 12 is 50 nm or more, it is difficult to form a firm agglomerate. Therefore, the surface of the copper particles 12 can be uniformly covered with the solvent 14. On the other hand, when the BET diameter of the copper particles 12 is 300 nm or less, the reaction area becomes large and the sintering property due to heating becomes high, and thus a firm joint layer can be formed. The BET diameter of the copper particles 12 is preferably in the range of 80 nm or more and 200 nm or less, and particularly preferably in the range of 80 nm or more and 170 nm or less.

[0086] The BET specific surface area of the copper particles 12 is preferably in the range of 2.0 m 2 / g or more and 8.0 m 2 / g or less, more preferably in the range of 3.5 m 2 / g or more and 8.0 m 2 / g or less, and particularly preferably in the range of 4.0 m 2 / g or more and 8.0 m 2 / g or less. Furthermore, the shape of the copper particles 12 is not limited to a spherical shape, and can be a needle shape or a flat plate shape.

[0087] The surface of the copper particles 12 is preferably covered with an organic film, that is, an organic protective film. By being covered with the organic protective film, oxidation of the copper particles 12 can be suppressed, and reduction in the sintering property due to oxidation of the copper particles 12 is less likely to occur. In addition, it can be said that the organic protective film covering the copper particles 12 is neither a film formed from the solvent 14 nor a film derived from the solvent 14. Furthermore, it can be said that the organic protective film covering the copper particles 12 is not a film of copper oxide formed by oxidation of copper.

[0088] The case where the copper particles 12 are covered with the organic protective film can be confirmed by analyzing the surface of the copper particles 12 using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Therefore, in the present embodiment, with respect to the copper particles 12, the ratio of the detected amount of C3H3O3 - ions to the detected amount of Cu + ions (C3H3O3 - / Cu + ) detected by analyzing the surface using time-of-flight secondary ion mass spectrometry is preferably 0.001 or more. The ratio of the detected amount of C3H3O3 - / Cu + The ratio is further preferably in the range of 0.05 or more and 0.2 or less. In addition, the surface of the copper particles 12 in the present analysis means the surface of the copper particles 12 including the organic protective film covering the same (i.e., the surface of the organic protective film), and does not mean the surface of the copper particles 12 from which the organic protective film is removed.

[0089] As for the copper particles 12, C3H4O2 - ions can be detected by analyzing the surface using time-of-flight secondary ion mass spectrometry. - The ratio of the detection amount of C3H4O2 + ions to the detection amount of Cu - The ratio (C3H4O2 + / Cu + The ratio (C5 or more ions / Cu + The ratio (C5 or more ions / Cu

[0090] C3H3O3 - ions, C3H4O2 - ions, and C5 or more ions detected in time-of-flight secondary ion mass spectrometry originate from the organic protective film covering the surface of the copper particles 12. Therefore, when the ratio of the detection amount of C3H3O3 - / Cu + and the ratio of the detection amount of C3H4O2 - / Cu + are each 0.001 or more, the surface of the copper particles 12 is less likely to be oxidized and the copper particles 12 are less likely to be aggregated. Also, when the ratio of the detection amount of C3H3O3 - / Cu + and the ratio of the detection amount of C3H4O2 - / Cu + are each 0.2 or less, the sinterability of the copper particles 12 does not excessively decrease, and oxidation and aggregation of the copper particles 12 can be suppressed, and decomposition gas of the organic protective film at the time of heating can be suppressed, so that a joining layer having few voids can be formed. In order to further improve the oxidation resistance of the copper particles 12 in storage and further improve the sinterability at low temperatures, it is preferable that the ratio of the detection amount of C3H3O3 - / Cu + and the ratio of the detection amount of C3H4O2 - / Cu + are in the range of 0.08 or more and 0.16 or less. Also, when the ratio of C5 or more ions to Cu + is 0.005 times or more, since the organic protective film having a high desorption temperature exists in a large amount on the surface of the particles, as a result, the sinterability does not sufficiently appear, and it is difficult to obtain a firm joining layer. When the ratio of C5 or more ions to Cu +The ratio is preferably less than 0.003 times.

[0091] The organic protective film is preferably derived from citric acid. A method for producing the copper particles 12 covered with the organic protective film derived from citric acid will be described later. The covering amount of the organic protective film with respect to 100 mass% of the copper particles 12 is preferably in the range of 0.5 mass% or more and 2.0 mass% or less, more preferably in the range of 0.8 mass% or more and 1.8 mass% or less, and further preferably in the range of 0.8 mass% or more and 1.5 mass% or less. By the covering amount of the organic protective film being 0.5 mass% or more, the copper particles 12 can be more uniformly covered with the organic protective film, and oxidation of the copper particles 12 can be more reliably suppressed. Also, by the covering amount of the organic protective film being 2.0 mass% or less, it is possible to suppress the occurrence of voids in the sintered body (joining layer) of the copper particles due to a gas generated by decomposition of the organic protective film caused by heating. The covering amount of the organic protective film can be measured using a commercially available device. For example, the covering amount can be measured using a differential thermal balance TG8120-SL (manufactured by Rigaku Corporation). At this time, for example, the sample is the copper particles from which moisture is removed by freeze drying. In order to suppress oxidation of the copper particles, the measurement is performed in a nitrogen atmosphere (G2 grade), the temperature increase rate is set to 10°C / min, and the weight reduction rate from 250°C to 300°C is defined as the covering amount of the organic protective film. That is, the covering amount = (weight of the sample after measurement) / (weight of the sample before measurement) x 100 (wt%). The measurement can be performed three times using the same batch of copper particles, and the arithmetic mean value is used as the covering amount.

[0092] With respect to the copper particles 12, it is preferable that 50 mass% or more of the organic protective film decompose when heated at a temperature of 300°C for 30 minutes in a non-active gas atmosphere such as helium. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporation gas of acetone, and water vapor upon decomposition.

[0093] The copper particles 12 covered with the organic protective film derived from citric acid can be produced, for example, in the following manner. First, a copper citrate aqueous dispersion liquid is prepared, and a pH adjusting agent is added to the copper citrate aqueous dispersion liquid to adjust the pH to 2.0 or more and 7.5 or less. Next, a hydrazine compound that is a reducing agent capable of reducing copper ions is added to the pH-adjusted copper citrate aqueous dispersion liquid in a non-active gas atmosphere in an amount of 1.0 times or more and 1.2 times or less of the equivalent amount, and mixed. The obtained mixture is heated to a temperature of 60°C or more and 80°C or less in a non-active gas atmosphere and held for 1.5 hours or more and 2.5 hours or less. Thus, the copper ions dissolved from the copper citrate are reduced to generate the copper particles 12, and the organic protective film derived from citric acid is formed on the surface of the copper particles 12.

[0094] The copper citrate aqueous dispersion can be prepared by adding the powder form of copper citrate to pure water such as distilled water, ion exchanged water, etc. in a concentration of 25 mass% or more and 40 mass% or less, stirring with a stirring blade, and uniformly dispersing it. As the pH adjuster, triammonium citrate, ammonium hydrogen citrate, citric acid, etc. can be given. Among these, triammonium citrate is preferable in terms of easily and gently adjusting the pH. The pH of the copper citrate aqueous dispersion is set to 2.0 or more in order to rapidly generate copper particles and obtain the desired fine copper particles 12 by accelerating the dissolution rate of the copper ions dissolved from the copper citrate. Further, the pH is set to 7.5 or less in order to improve the yield of the copper particles 12 by suppressing the dissolved copper ions from becoming copper (II) hydroxide. Further, by setting the pH to 7.5 or less, it is possible to suppress the reducing power of the hydrazine compound from becoming too high, and it is easy to obtain the desired copper particles 12. The pH of the copper citrate aqueous dispersion is preferably adjusted to a range of 4 or more and 6 or less.

[0095] The reduction of the copper citrate with the hydrazine compound is performed under a non-reactive gas atmosphere. This is in order to prevent oxidation of the copper ions dissolved in the liquid. As examples of the non-reactive gas, nitrogen, helium, etc. can be given. When the hydrazine compound reduces the copper citrate in an acidic state, it has the advantages that no residue is generated after the reduction reaction, it is highly safe, and it is easy to handle. As the hydrazine compound, hydrazine hydrate, anhydrous hydrazine, hydrazine hydrochloride, hydrazine sulfate, etc. can be given. Among these hydrazine compounds, hydrazine hydrate and anhydrous hydrazine, which do not contain components such as sulfur or chlorine that can become impurities, are preferable.

[0096] Generally, copper generated in an acidic liquid with a pH of less than 7 dissolves. However, in the present embodiment, the hydrazine compound as the reducing agent is added to the acidic liquid with a pH of less than 7 and mixed, and the copper particles 12 are generated in the obtained mixed liquid. Therefore, since the components derived from the citric acid generated from the copper citrate rapidly cover the surface of the copper particles 12, it is possible to suppress the dissolution of the copper particles 12. With respect to the copper citrate aqueous dispersion after the pH adjustment, the temperature is preferably set to 50°C or more and 70°C or less in order to easily perform the reduction reaction.

[0097] The mixed solution in which the hydrazine compound is mixed under a non-active gas atmosphere is heated to a temperature of 60°C or higher and 80°C or lower and held for 1.5 hours or more and 2.5 hours or less in order to generate the copper particles 12 and form an organic protective film on the surface of the generated copper particles 12 to cover. The heating and holding under a non-active gas atmosphere is performed in order to prevent oxidation of the generated copper particles 12. The copper citrate as a starting material generally contains a copper component of about 35 mass%. By adding the hydrazine compound as a reducing agent to the copper citrate aqueous dispersion containing the copper component to this extent, and performing temperature elevation heating and holding at the above temperature for the above time, the generation of the copper particles 12 and the generation of the organic protective film on the surface of the copper particles 12 are performed in balance, whereby the copper particles 12 can be obtained in which the coverage amount of the organic protective film is in the range of 0.5 mass% or more and 2.0 mass% or less with respect to 100 mass% of the copper particles. In the case where the heating temperature is lower than 60°C and the holding time is less than 1.5 hours, it is possible that the copper citrate is not completely reduced, the generation speed of the copper particles 12 becomes too slow, and the amount of the organic protective film covering the copper particles 12 becomes too much. Also, in the case where the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, it is possible that the generation speed of the copper particles 12 becomes too fast, and the amount of the organic protective film covering the copper particles 12 becomes too little. The preferable heating temperature is 65°C or higher and 75°C or lower, and the preferable holding time is 2 hours or more and 2.5 hours or less.

[0098] The copper particles 12 generated in the mixed solution are solid-liquid separated from the mixed solution under a non-active gas atmosphere, for example, using a centrifugal separator, and dried by a freeze drying method, a reduced pressure drying method, to obtain the copper particles 12 whose surface is covered with the organic protective film. Since the surface of the copper particles 12 is covered with the organic protective film, oxidation does not easily occur in storage in the atmosphere before use as the joining paste 10.

[0099] (Solvent)

[0100] The solvent 14 functions as a binder for the copper particles 12. The solvent 14 is an organic solvent. As the solvent 14, any substance can be used, and for example, an alcohol solvent, a glycol solvent, an acetate solvent, a hydrocarbon solvent, and an amine solvent can be cited. As specific examples of the alcohol solvent, α-terpineol, isopropyl alcohol can be cited. As specific examples of the glycol solvent, ethylene glycol, diethylene glycol, polyethylene glycol can be cited. As specific examples of the acetate solvent, diethylene glycol butyl ether acetate can be cited. As specific examples of the hydrocarbon solvent, decane, dodecane, tetradecane can be cited. As specific examples of the amine solvent, hexylamine, octylamine, dodecylamine can be cited.

[0101] (Additive)

[0102] The additive 16 is a phosphate ester. The ester obtained by dehydration condensation of phosphoric acid with an alcohol in an organic phosphoric compound is referred to as a phosphate ester. The average molecular weight of the phosphate ester used as the additive 16 is preferably 1,000 or more and 2,000 or less, more preferably 1,200 or more and 1,800 or less, and further preferably 1,400 or more and 1,600 or less. By the average molecular weight of the phosphate ester being 1,000 or more, decomposition at ordinary temperature is suppressed and storage stability is improved, and by the average molecular weight of the phosphate ester being 2,000 or less, decomposition and reaction can be performed at a desired heating temperature (around 200 to 350°C). The average molecular weight herein refers to a weight average molecular weight. The average molecular weight can be measured by, for example, size exclusion chromatography.

[0103] The phosphate ester used for the additive 16 can be any substance, and examples thereof include lauryl alcohol polyether-n phosphate ester, oleyl alcohol polyether-n phosphate ester, stearyl alcohol polyether-n phosphate ester (n is an integer), and the like. As the additive 16, one of these or two or more of these can be used.

[0104] (Binding paste)

[0105] In the present embodiment, with respect to the binding paste 10, it is preferable that no substance other than the copper particles 12, the solvent 14, and the additive 16 composed of a phosphate ester be included, except for inevitable impurities. However, the binding paste 10 can include an additive other than the copper particles 12, the solvent 14, and the additive 16 composed of a phosphate ester, without being limited thereto.

[0106] In the binding paste 10, the content of the additive 16 is 0.5% or more and 3.0% or less, preferably 0.5% or more and 2.0% or less, and further preferably 1.0% or more and 1.5% or less, in terms of mass ratio with respect to the total amount of the binding paste 10. By the content of the additive 16 being within this range, oxidation of the copper particles 12 is suppressed, and as a result, when the binding paste 10 is used to bind parts to each other in a non-reducing atmosphere, a decrease in the strength of the binding layer can be appropriately suppressed.

[0107] In the binding paste 10, the content of the solvent 14 is preferably 5% or more and 20% or less, more preferably 5% or more and 15% or less, and further preferably 8% or more and 13% or less, in terms of mass ratio with respect to the total amount of the binding paste 10. By the content of the solvent 14 being within this range, the copper particles 12 can be appropriately dispersed.

[0108] (Method for producing binding paste)

[0109] The joining paste 10 is manufactured by performing a mixing process of mixing the copper particles 12, the solvent 14, and the additive 16. In the mixing process, the copper particles 12, the solvent 14, and the additive 16 are mixed in such a manner that the content of the additive 16 is 0.5% or more and 3.0% or less in mass ratio with respect to the total amount of the joining paste 10. Also, in the mixing process, the copper particles 12, the solvent 14, and the additive 16 are mixed in such a manner that the contents of the solvent 14 and the copper particles 12 are also within the above-mentioned ranges with respect to the total amount of the joining paste 10. Also, in the mixing process, the copper particles 12, the solvent 14, and the additive 16 can be mixed using a kneading device. As the kneading device, for example, a three-roll mill can be used.

[0110] (Method for manufacturing a joined body)

[0111] Figure 4 is a schematic view of a joined body according to the second embodiment. As shown in Figure 4 In the present embodiment, the joining paste 10 is used as the joining layer 20, and the first member 21 and the second member 22 are joined to manufacture the joined body 30. The first member 21 and the second member 22 can be arbitrary members, for example, one of the first member 21 and the second member 22 can be a substrate and the other can be an electronic element. That is, a semiconductor module in which a substrate and an electronic element are joined by the joining layer 20 can be manufactured as the joined body 30. As the substrate, there is no particular limitation, and for example, an oxygen-free copper plate, a copper-molybdenum plate, a high-heat-dissipation insulating substrate (for example, a DCB (Direct Copper Bond)), an LED (Light Emitting Diode) package, and the like can be mentioned as a substrate for mounting a semiconductor element. Also, as the electronic element, for example, an IGBT (Insulated Gate Bipolar Transistor), a diode, a Schottky diode, a MOS-FET (Metal Oxide Semiconductor Field Effect Transistor), a thyristor, a logic device, a sensor, an analog integrated circuit, an LED, a semiconductor laser, a dialer, and the like can be mentioned as a semiconductor element.

[0112] In the present production method, a coating layer forming step of applying the joining slurry 10 to the surface of at least one of the first member 21 and the second member 22 to form a coating layer is performed. The application method is not particularly limited, and examples thereof include a spin coating method, a metal mask method, a spray coating method, a dispenser coating method, a doctor blade coating method, a slit coating method, an inkjet coating method, a screen printing method, an offset printing method, a die coating method, and the like. Subsequently, in order to volatilize the solvent in the slurry, a preheating step of 1 minute to 30 minutes at a temperature of 50°C to 150°C is performed. Subsequently, a lamination step of laminating the first member 21 and the second member 22 via the coating layer is performed.

[0113] Subsequently, a heating step of heating the first member 21 and the second member 22 laminated via the coating layer is performed. In the heating step, at least one of the laminated first member 21 and the second member 22 is heated at a prescribed temperature for a prescribed time while a prescribed pressure is applied thereto in a non-reducing atmosphere. By performing the heating step, the copper particles 12 in the coating layer are sintered to form the joining layer 20, and the joining body 30 in which the first member 21 and the second member 22 are joined by the joining layer 20 is produced.

[0114] The non-reducing atmosphere in the heating step refers to a state in which a non-reducing gas is filled, and can also be referred to as a non-active gas atmosphere in which a non-active gas is filled. As the non-reducing gas, a noble gas such as nitrogen or argon can be used. For example, in the present embodiment, the heating step can be performed in a nitrogen atmosphere in which the oxygen concentration is 1000 ppm. By performing the heating step in a non-reducing atmosphere, it is not necessary to use a reducing gas, and the heating step can be easily performed.

[0115] Further, the prescribed pressure applied to at least one of the first member 21 and the second member 22 is preferably 0.5 MPa or higher and 10 MPa or lower, more preferably 1 MPa or higher and 5 MPa or lower, and further preferably 2 MPa or higher and 5 MPa or lower. By setting the applied pressure to such a low range, the first member 21 and the second member 22 can be properly joined while the shape defect of the joining layer 20 is suppressed. Note that the pressure is applied in a direction in which the first member 21 and the second member 22 are pressed against each other via the coating layer.

[0116] Further, the prescribed temperature as the heating temperature in the heating step is preferably 200°C or higher and 300°C or lower, more preferably 230°C or higher and 300°C or lower, and further preferably 250°C or higher and 300°C or lower. By setting the heating temperature to such a low range, the copper particles 12 can be properly sintered while the shape defect of the joining layer 20 is suppressed.

[0117] Further, the prescribed time as the heating time in the heating step is preferably 1 minute or more and 10 minutes or less, more preferably 1 minute or more and 5 minutes or less, and further preferably 1 minute or more and 3 minutes or less. By setting the heating time to this range, the copper particles 12 can be appropriately sintered.

[0118] (bonding layer)

[0119] As explained above, the bonding layer 20 in the present embodiment is a layer formed by heating the bonding paste 10 to sinter the copper particles 12. The bonding layer 20 is positioned between the first member 21 and the second member 22, and bonds the first member 21 and the second member 22. The bonding layer 20 can also be said to be a copper sintered body. Regarding the bonding layer 20, the sintering density of the copper particles is preferably 80% or more, more preferably 85% or more and 95% or less, and further preferably 85% or more and 90% or less. By having the sintering density within this range, the bonding layer 20 can ensure electrical conductivity and thermal conductivity. Note that the sintering density refers to the ratio of the volume of the bonding layer 20 excluding open pores and closed pores to the entire volume of the bonding layer 20 including open pores and closed pores. Regarding the sintering density, an image randomly obtained by observing a cross section of the bonding layer at a magnification of 50,000 times by SEM (Scanning Electron Microscope) is binarized using image processing software (ImageJ manufactured by National Institutes of Health), divided into a particle portion and a void portion, and the sintering density is calculated from the following equation.

[0120] Sintering density (%) = (total area of particle portion / (total area of particle portion + total area of void portion)) x 100

[0121] Further, the bonding layer 20 contains phosphorus. The phosphorus here refers to phosphorus as an element, and includes not only elemental phosphorus but also phosphorus contained in any compound. In the bonding layer 20, the phosphorus content with respect to the total amount of the bonding layer 20 is preferably 100 ppm or more and 1,000 ppm or less, more preferably 100 ppm or more and 500 ppm or less, and further preferably 200 ppm or more and 500 ppm or less, in terms of mass ratio. By having the phosphorus content within this range, even if the bonding layer 20 is formed, for example, in a non-reducing atmosphere, a decrease in strength can be suppressed. Note that the phosphorus content can be measured by ICP-OES (Inductivity Coupled Plasma Optical Emission Spectrometer). In the present embodiment, the phosphorus contained in the bonding layer 20 originates from the phosphate contained in the bonding paste 10.

[0122] Further, the thickness of the joining layer 20 is preferably 10 μm or more and 200 μm or less, more preferably 20 μm or more and 150 μm or less, and further preferably 50 μm or more and 100 μm or less. By the thickness of the joining layer 20 being within this range, stress caused by differences in linear expansion coefficients between the members based on temperature differences can be moderated and high heat dissipation can be maintained.

[0123] Thus, the joining layer 20 according to the present embodiment is a copper sintered body having a sintering density of 80% or more and containing phosphorus. Since the joining layer 20 according to the present embodiment has a sintering density of 80% or more, a decrease in strength can be suppressed. Further, since oxidation of the copper particles 12 is suppressed by the substance derived from phosphorus (phosphate in the present embodiment) contained in the joining layer 20, a decrease in strength of the joining layer 20 containing phosphorus can be suppressed. In addition, as described above, although the joining layer 20 in the present embodiment is a layer formed by heating the joining paste 10, the method of forming the joining layer 20 can be any method as long as the above-described characteristics are satisfied.

[0124] (EFFECTS)

[0125] As described above, the joining layer 20 according to the present embodiment is a copper sintered body joining members to each other and has a sintering density of 80% or more and contains phosphorus. With the joining layer 20 according to the present embodiment, the sintering density is 80% or more and oxidation of the copper particles 12 is suppressed by the substance derived from phosphorus (phosphate in the present embodiment), and thus a decrease in strength can be suppressed.

[0126] Further, the method of manufacturing the joined body 30 according to the present embodiment includes a coating layer forming step, a lamination step, and a heating step. In the coating layer forming step, a coating layer is formed by applying the joining paste 10 to the surface of at least one of the first member 21 and the second member 22, the joining paste 10 containing the copper particles 12, the solvent 14, and the additive 16 composed of phosphate and having a content of the additive 16 of 0.5% or more and 3.0% or less by mass ratio. In the lamination step, the first member 21 and the second member 22 are laminated via the coating layer. In the heating step, the first member 21 and the second member 22 laminated via the coating layer are heated to form the joined body 30. In the heating step, at least one of the first member 21 and the second member 22 is heated at a temperature of 200°C or more and 300°C or less under a non-reducing atmosphere while a pressure of 0.5 MPa or more and 10 MPa or less is applied. According to the present manufacturing method, by using the joining paste 10 to which phosphate as an additive is added, oxidation of the copper particles 12 is suppressed, and as a result, even when the members are joined to each other under a non-reducing atmosphere, a decrease in strength of the joining layer 20 can be suppressed.

[0127] (Examples corresponding to the second embodiment)

[0128] Next, the examples are described.

[0129] (Example 11)

[0130] In Example 11, copper particles having a BET diameter of 400 nm were prepared. With respect to the BET diameter, the nitrogen adsorption amount of the copper particles was measured using a specific surface area measuring device (QUANTACHROME AUTOSORB-1 manufactured by Quantachrome Instruments), and the specific surface area of the copper particles was obtained by the BET method. Using the obtained specific surface area S (m 2 / g) and the density p (g / cm 3 ) of the copper particles, the BET diameter was calculated from the following equation.

[0131] BET diameter (nm) = 6000 / (p (g / cm 3 ) x S (m 2 / g))

[0132] In Example 11, as the phosphate ester serving as an additive, oleyl polyether-10 phosphate ester was prepared, and as the solvent, ethylene glycol was prepared.

[0133] Then, in Example 11, the copper particles, the additive, and the solvent were mixed at 1% by mass of the additive, 10% by mass of the solvent, and the remainder of the copper particles, and a paste for bonding was obtained.

[0134] In Example 11, using the obtained paste for bonding, a bonded body was manufactured. Specifically, an opening of 3 mm was formed on a copper plate, and after the paste for bonding of each example was printed using a metal mask having a thickness of 50 pm and a metal squeegee, it was dried for 5 minutes at 90°C using a hot plate, and a 2.5 mm x 2.5 mm silicon dummy chip on which gold was sputtered at a thickness of 100 nm was placed on the back surface, and the paste for bonding was heated to form a bonding layer, and a bonded body was obtained by heating at 250°C for 3 minutes while pressurizing at 5 MPa in a nitrogen atmosphere.

[0135] In Example 11, it was confirmed that the bonding layer contained phosphorus. The presence of phosphorus was confirmed by ICP-OES.

[0136] Also, in Example 11, the sintered density of the bonding layer was 91%. The sintered density was measured in the following manner.

[0137] After sealing the interface layer with an epoxy resin, the interface layer was cut in a direction horizontal with respect to the thickness direction of the interface layer. By performing mechanical polishing and cloth polishing on the cut surface of the interface layer, a cross section of the interface layer was exposed. Next, the cut surface of the interface layer was observed at 50,000 times using an SEM (scanning electron microscope). The SEM image obtained was binarized into a particle portion and a void portion using image processing software (ImageJ manufactured by National Institutes of Health), and the sintering density was calculated from the following equation.

[0138] Sintering density (%) = (total area of particle portion / (total area of particle portion + total area of void portion)) x 100

[0139] The sintering density was measured for the SEM images of 10 sites randomly taken. The value shown in Table 2 is the average of the sintering densities calculated from the SEM images of the 10 sites.

[0140] (Examples 12 to 17)

[0141] In Examples 12 to 17, the paste for bonding and the test conditions were set as shown in Table 2, and otherwise, the bonded body was obtained in the same manner as in Example 11.

[0142] (Comparative Example 2)

[0143] In Comparative Example 2, the paste for bonding was set as shown in Table 2, and otherwise, the bonded body was obtained in the same manner as in Example 11. The bonded body of Comparative Example 2 did not contain phosphorus, and the sintering density was 76%.

[0144] (Evaluation)

[0145] In the evaluation, the shear strength of the obtained bonded body (the bonded silicon dummy chip and the oxygen-free copper plate) was measured. When the shear strength was 40 MPa, it was "excellent", when it was 20 MPa or more and less than 40 MPa, it was "good", when it was 10 MPa or more and less than 20 MPa, it was "pass", and when it was less than 10 MPa, it was "fail". "Pass", "good", and "excellent" were qualified.

[0146] As for the shear strength, the shear strength of the obtained joint was measured by a method in accordance with JIS Z 3198-7 (Test methods for lead-free solders - Part 7: Test method for solder joint shear test of chip components). Specifically, the load at which the silicon dummy chip peeled from the copper joint layer was measured by applying a load to the silicon dummy chip using a tool of a bond tester (SERIES 4000 manufactured by Nordson DAGE). The moving speed of the tool was set to 50 μm / sec, and the gap between the front end of the tool and the oxygen-free copper substrate was set to 50 μm. The value obtained by converting the maximum shear load obtained into Newton and dividing by the area of the copper joint layer (2.5 mm x 2.5 mm) was taken as the shear strength (unit: MPa). Seven joints were produced, and the shear strength of each joint was measured. The value shown in Table 2 is the average value of the shear strengths of the seven joints.

[0147] [Table 2]

[0148]

[0149] Table 2 is a table showing the evaluation results of each example. As shown in Table 2, it was found that the shear strength in the examples was acceptable, and that the decrease in strength could be suppressed by using a joint containing phosphorus and having a sintered density of 80% or more. On the other hand, it was found that in Comparative Example 2, a joint not containing phosphorus and having a sintered density of less than 80% was used, and the decrease in strength could not be suppressed.

[0150] The above describes an embodiment of the present application, but the content of the embodiment is not limited to the embodiment. Also, the aforementioned constituent elements include elements that can be easily conceived by those skilled in the art, substantially identical elements, and elements in the so-called equivalent range. Furthermore, the aforementioned constituent elements can be appropriately combined. Furthermore, various omissions, substitutions, or changes of the constituent elements can be made within the scope of the gist of the aforementioned embodiment.

[0151] Symbol Explanation

[0152] 10 Jointing paste

[0153] 12 Copper particles

[0154] 14 Solvent

[0155] 16 Additive

[0156] 20 Joint layer

[0157] 21 First member

[0158] 22 Second member

[0159] 30 Joint

Claims

1. A bonding slurry comprising copper particles, a solvent, and an additive composed of a phosphate ester, wherein, The content of the additive relative to the total amount of the bonding slurry is 0.5% or more and 3.0% or less by mass. The additive comprises one or more of lauryl ether-n phosphate, oleyl ether-n phosphate, and stearyl ether-n phosphate, wherein n is an integer.

2. The bonding slurry according to claim 1, wherein, The average molecular weight of the phosphate ester is above 1000 and below 2000.

3. The bonding slurry according to claim 1 or 2, wherein, The content of the solvent relative to the total amount of the bonding slurry is 5% or more and 20% or less by mass.

4. The bonding slurry according to any one of claims 1 to 3, wherein, Regarding the copper particles, the surface of the copper particles is covered with an organic protective film derived from citric acid.

5. The bonding slurry according to any one of claims 1 to 4, wherein, The BET diameter of the copper particles is greater than 50 nm and less than 300 nm.

6. A method for manufacturing a joint, wherein, Using the bonding slurry as described in any one of claims 1 to 5 as a bonding layer, a joint body is manufactured by bonding the first component and the second component.

7. A bonding layer, which is a copper sintered body for joining components together, and is a layer formed by heating the bonding slurry according to any one of claims 1 to 5 to sinter the copper particles, the bonding layer having a sintering density of 80% or more and containing phosphorus.

8. The bonding layer according to claim 7, wherein, The phosphorus content relative to the total amount of the bonding layer is 100 ppm or more and 1000 ppm or less by mass.

9. The bonding layer according to claim 7 or 8, wherein, The thickness of the bonding layer is more than 10 μm and less than 200 μm.

10. A joint comprising a first component, a second component, and a joint layer disposed between the first component and the second component, as described in any one of claims 7 to 9.

11. The joint according to claim 10, wherein, The first component is a substrate, the second component is an electronic component, and the junction constitutes a semiconductor module.

12. A method for manufacturing a joint, comprising: The coating forming process involves applying the bonding slurry according to any one of claims 1 to 5 to the surface of at least one of the first component and the second component to form a coating. The lamination process involves laminating the first component and the second component via the coating; and The heating process involves heating the first and second components, which are laminated through the coating, to form a joint. In the heating process, under a non-reducing atmosphere, at least one of the first component and the second component is subjected to a pressure of 0.5 MPa or more and 10 MPa or less, while being heated at a temperature of 200°C or more and 300°C or less for 1 minute or more and 10 minutes.

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