Bonding paste, and method for producing bonded body

Abstract

To enable appropriate application to a member.SOLUTION: A bonding paste 10 includes copper particles 12, a solvent 14, and an additive 16, in which a viscosity change rate between one day after and thirty days after production of the bonding paste 10 is 20% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a bonding paste and a method for manufacturing a bonded body.

Background Art

[0002] In some cases, a bonding material is used to bond two or more components. In recent years, the use of a paste containing copper particles as a bonding material has been considered. Patent Document 1 describes that the first member and the second member are bonded by sintering a copper paste applied between the first member and the second member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in order to appropriately bond members to each other, it is required to appropriately apply a bonding paste to the members.

[0005] The present invention has been made in view of the above, and an object thereof is to provide a bonding paste that can be appropriately applied to a member and a method for manufacturing a bonded body.

Means for Solving the Problems

[0006] The bonding paste of the present disclosure is a bonding paste containing copper particles, a solvent, and an additive, and the rate of change in viscosity at 1 day and 30 days after preparing the bonding paste is 20% or less.

[0007] The additive is preferably a phosphate ester.

[0008] The average molecular weight of the additive is preferably 500 or more and 1400 or less.

[0009] The content of the additive is preferably 0.1% or more and 10% or less by mass ratio with respect to the whole of the paste for bonding.

[0010] The solvent is preferably a terpineol-based solvent.

[0011] The average molecular weight of the solvent is preferably 100 or more and 200 or less.

[0012] The method for manufacturing a bonded body of the present disclosure manufactures a bonded body by bonding a first member and a second member using the paste for bonding as a bonding layer.

Advantages of the Invention

[0013] According to the present invention, it is possible to obtain a paste for bonding that can be appropriately applied to a member and a method for manufacturing a bonded body.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic diagram of the paste for bonding according to the present embodiment. [Figure 2] FIG. 2 is a schematic diagram of the bonded body according to the present embodiment. [Figure 3] FIG. 3 is a table showing the pastes for bonding of each example.

Modes for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited by the following modes for carrying out the invention (hereinafter referred to as embodiments). In addition, the constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art, substantially the same ones, and those within the so-called equivalent range. Furthermore, the constituent elements disclosed in the following embodiments can be combined as appropriate. Also, the numerical values include the range of rounding.

[0016] FIG. 1 is a schematic diagram of a bonding paste according to this embodiment. The bonding paste according to this embodiment is used to bond components together. As shown in FIG. 1, a bonding paste 10 according to this embodiment contains copper particles 12, a solvent 14, and an additive 16. Note that FIG. 1 is a schematic diagram, and the shape of the actual bonding paste 10 is not limited to that shown in FIG. 1.

[0017] (copper particles) The copper particles 12 preferably have a BET diameter of 50 nm or more and 300 nm or less. The BET diameter is a particle diameter calculated from the BET specific surface area and true density of the copper particles determined by the BET method, assuming that the copper particles 12 are perfect spheres. Specifically, the BET diameter can be determined by the method described in the Examples below.

[0018] If the BET diameter of the copper particles 12 is 50 nm or more, strong agglomerates are unlikely to form. This allows the surfaces of the copper particles 12 to be uniformly coated with the solvent 14. On the other hand, if the BET diameter of the copper particles 12 is 300 nm or less, the reaction area is large and the sintering property by heating is high, making it possible to form a strong bonding layer. The BET diameter of the copper particles 12 is preferably in the range of 80 nm to 200 nm, and particularly preferably in the range of 80 nm to 170 nm.

[0019] The BET specific surface area of copper particles 12 is 2.0 m 2 / g or more 8.0m 2 / g or less, and 2 / g or more 8.0m 2 / g or less, and more preferably 4.0m 2 / g or more 8.0m 2 / g or less. The shape of the copper particles 12 is not limited to a spherical shape, but may be a needle shape or a flat plate shape.

[0020] The surfaces of the copper particles 12 are preferably coated with an organic protective film, which is a film of an organic substance. By being coated with the organic protective film, oxidation of the copper particles 12 is suppressed, and a decrease in sinterability due to oxidation of the copper particles 12 is further unlikely to occur. Note that the organic protective film coating the copper particles 12 is not formed by the solvent 14, and can be said to be not derived from the solvent 14. It can also be said that the organic protective film coating the copper particles 12 is not a copper oxide film formed by the oxidation of copper.

[0021] The fact that the copper particles 12 are coated with an 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 this embodiment, the copper particles 12 are coated with an organic protective film. + C3H3O3 vs. detected ion amount - Ratio of detected ions (C3H3O3 - / Cu + It is preferable that the ratio is 0.001 or more. - / Cu + The ratio is more preferably in the range of 0.05 to 0.2. Note that the surface of copper particles 12 in this analysis does not refer to the surface of copper particles 12 after the organic protective film has been removed from copper particles 12, but refers to the surface of copper particles 12 including the covering organic protective film (i.e., the surface of the organic protective film).

[0022] The copper particles 12 were analyzed by time-of-flight secondary ion mass spectrometry to determine that the copper particles were C3H4O2 - Cu ions and ions of C5 or higher may be detected. + C3H4O2 vs. detected ion amount - Ratio of detected ions (C3H4O2 - / Cu + The ratio is preferably 0.001 or more. + The ratio of the amount of ions detected above C5 to the amount of ions detected (ions above C5 / Cu + It is preferable that the ratio is less than 0.005.

[0023] C3H3O3 detected by time-of-flight secondary ion mass spectrometry - ions and C3H4O2 - ions and ions with 5 or more carbons are derived from the organic protective film covering the surface of the copper particles 12. Therefore, the C3H3O3 - / Cu + ratio and the C3H4O2 - / Cu + ratio, when each is 0.001 or more, makes the surface of the copper particles 12 less likely to oxidize and the copper particles 12 less likely to aggregate. Also, the C3H3O3 - / Cu + ratio and the C3H4O2 - / Cu + ratio, when they are 0.2 or less, can suppress the oxidation and aggregation of the copper particles 12 without excessively reducing the sinterability of the copper particles 12, and can further suppress the generation of decomposition gases of the organic protective film during heating. Therefore, a bonding layer with few voids can be formed. To further improve the oxidation resistance during storage of the copper particles 12 and further improve the sinterability at low temperatures, the C3H3O3 - / Cu + ratio and the C3H4O2 - / Cu + ratio are preferably in the range of 0.08 or more and 0.16 or less. Also, when the ratio of ions with 5 or more carbons / Cu + is 0.005 times or more, there are many organic protective films with relatively high desorption temperatures on the particle surface. As a result, the sinterability is not fully expressed and it is difficult to obtain a strong bonding layer. The ratio of ions with 5 or more carbons / Cu + is preferably less than 0.003 times.

[0024] The organic protective film is preferably derived from citric acid. A method for producing the copper particles 12 coated with the organic protective film derived from citric acid will be described later. The coating amount of the organic protective film on the copper particles 12 is preferably in the range of 0.5% by mass or more and 2.0% by mass or less, more preferably in the range of 0.8% by mass or more and 1.8% by mass or less, and even more preferably in the range of 0.8% by mass or more and 1.5% by mass or less with respect to 100% by mass of the copper particles. When the coating amount of the organic protective film is 0.5% by mass or more, the copper particles 12 can be uniformly coated with the organic protective film, and the oxidation of the copper particles 12 can be more reliably suppressed. Further, when the coating amount of the organic protective film is 2.0% by mass or less, it is possible to suppress the generation of voids in the sintered body (bonding layer) of the copper particles due to the gas generated by the decomposition of the organic protective film by heating. The coating amount of the organic protective film can be measured using a commercially available device. For example, the coating amount can be measured using a differential scanning calorimeter TG8120-SL (manufactured by RIGAKU). In this case, for example, as the sample, copper particles from which moisture has been removed by freeze-drying are used. The measurement is performed in a nitrogen (G2 grade) gas atmosphere to suppress the oxidation of the copper particles, the heating rate is set to 10 ° C / min, and the weight loss rate when heated from 250 ° C to 300 ° C can be defined as the coating amount of the organic protective film. That is, the coating amount = (sample weight after measurement) / (sample weight before measurement) × 100 (wt%). The measurement is performed three times for each of the copper particles of the same lot, and the arithmetic mean value may be used as the coating amount.

[0025] When the copper particles 12 are heated at a temperature of 300 ° C for 30 minutes in an inert gas atmosphere such as argon gas, it is preferable that 50% by mass or more of the organic protective film decomposes. The organic protective film derived from citric acid generates carbon dioxide gas, nitrogen gas, evaporation gas of acetone, and water vapor during decomposition.

[0026] The copper particles 12 coated with the organic protective film derived from citric acid can be produced, for example, as follows. First, a water dispersion of copper citrate is prepared, and a pH adjuster is added to this copper citrate water dispersion to adjust the pH to 2.0 or more and 7.5 or less. Next, in an inert gas atmosphere, a hydrazine compound in an amount of 1.0 to 1.2 times the equivalent amount capable of reducing copper ions is added as a reducing agent to the pH-adjusted copper citrate water dispersion and mixed. The obtained mixed solution is heated to a temperature of 60°C or more and 80°C or less and held for 1.5 hours or more and 2.5 hours or less in an inert gas atmosphere. Thereby, the copper ions eluted from copper citrate are reduced to generate copper particles 12, and an organic protective film derived from citric acid is formed on the surface of the copper particles 12.

[0027] The water dispersion of copper citrate can be prepared by adding powdery copper citrate to pure water such as distilled water or ion-exchanged water so that the concentration becomes 25% by mass or more and 40% by mass or less, and stirring with a stirring blade to uniformly disperse it. Examples of the pH adjuster include ammonium citrate tribasic, ammonium hydrogen citrate, and citric acid. Among these, ammonium citrate tribasic is preferable because it is easy to adjust the pH mildly. The reason for setting the pH of the copper citrate water dispersion to 2.0 or more is to increase the elution rate of the copper ions eluted from copper citrate and to allow the production of copper particles to proceed promptly so as to obtain the target fine copper particles 12. Also, the reason for setting the pH to 7.5 or less is to suppress the eluted copper ions from becoming copper(II) hydroxide and to increase the yield of the copper particles 12. Further, by setting the pH to 7.5 or less, it is possible to suppress the reducing power of the hydrazine compound from becoming excessively high, and the target copper particles 12 can be easily obtained. The pH of the copper citrate water dispersion is preferably adjusted within the range of 4 or more and 6 or less.

[0028] The reduction of copper citrate with a hydrazine compound is carried out under an inert gas atmosphere. This is to prevent the oxidation of copper ions eluted in the solution. Examples of the inert gas include nitrogen gas, argon gas, etc. The hydrazine compound has advantages such as not producing residues after the reduction reaction, relatively high safety, and easy handling when reducing copper citrate under acidic conditions. Examples of this hydrazine compound include hydrazine monohydrate, anhydrous hydrazine, hydrazine hydrochloride, hydrazine sulfate, etc. Among these hydrazine compounds, hydrazine monohydrate and anhydrous hydrazine that do not contain components that can become impurities such as sulfur and chlorine are preferred.

[0029] Generally, copper generated in an acidic solution with a pH less than 7 will dissolve. However, in this embodiment, a hydrazine compound as a reducing agent is added and mixed into an acidic solution with a pH less than 7 to generate copper particles 12 in the resulting mixed solution. Therefore, the components derived from citric acid generated from copper citrate quickly coat the surface of the copper particles 12, suppressing the dissolution of the copper particles 12. The aqueous dispersion of copper citrate after adjusting the pH is preferably set at a temperature of 50°C or higher and 70°C or lower to facilitate the progress of the reduction reaction.

[0030] Mixing the hydrazine compound in an inert gas atmosphere and heating the resulting mixture to a temperature of 60°C or higher and 80°C or lower, then holding for 1.5 hours or longer and 2.5 hours or shorter, is to generate copper particles 12 and form and coat an organic protective film on the surface of the generated copper particles 12. Heating and holding in an inert gas atmosphere is to prevent oxidation of the generated copper particles 12. Copper citrate as the starting material usually contains about 35% by mass of copper component. By adding a hydrazine compound as a reducing agent to a copper citrate aqueous dispersion containing this amount of copper component, heating with temperature increase at the above temperature, and holding for the above time, the generation of copper particles 12 and the generation of the organic protective film on the surface of copper particles 12 proceed in a well-balanced manner. Thus, copper particles 12 with the coating amount of the organic protective film in the range of 0.5% by mass or more and 2.0% by mass or less with respect to 100% by mass of copper particles can be obtained. If the heating temperature is less than 60°C and the holding time is less than 1.5 hours, copper citrate is not completely reduced, the generation rate of copper particles 12 becomes too slow, and the amount of the organic protective film coating copper particles 12 may become excessive. Also, if the heating temperature exceeds 80°C and the holding time exceeds 2.5 hours, the generation rate of copper particles 12 becomes too fast, and the amount of the organic protective film coating copper particles 12 may be too small. The preferred heating temperature is 65°C or higher and 75°C or lower, and the preferred holding time is 2 hours or longer and 2.5 hours or shorter.

[0031] The copper particles 12 generated in the mixture are separated from the mixture in an inert gas atmosphere, for example, using a centrifuge for solid-liquid separation, and then dried by freeze-drying or vacuum drying to obtain copper particles 12 with the surface coated with an organic protective film. Since the surface of these copper particles 12 is coated with an organic protective film, they are less likely to oxidize even when stored in the air until used as the bonding paste 10.

[0032] (Solvent) The solvent 14 acts as a binder for the copper particles 12. The solvent 14 is an organic solvent. Any substance may be used as the solvent 14, and examples thereof include at least one of an alcohol-based solvent, a glycol-based solvent, an acetate-based solvent, a hydrocarbon-based solvent, and an amine-based solvent. Further, the solvent 14 is preferably an alcohol-based solvent, and more preferably a terpineol-based solvent. Examples of the terpineol-based solvent used for the solvent 14 include at least one of dihydroterpineol, α-terpineol, and menthol, and dihydroterpineol is particularly preferred. As the alcohol-based solvent, isopropyl alcohol may be used. Specific examples of the glycol-based solvent include ethylene glycol, diethylene glycol, and polyethylene glycol. Specific examples of the acetate-based solvent include butyl acetate carbitol. Specific examples of the hydrocarbon-based solvent include decane, dodecane, and tetradecane. Specific examples of the amine-based solvent include hexylamine, octylamine, and dodecylamine.

[0033] The solvent 14 preferably has an average molecular weight of 100 or more and 200 or less. By the average molecular weight of the solvent 14 being within this range, the rate of change of the viscosity after producing the bonding paste 10 can be reduced, and the viscosity does not become too high over time, enabling the bonding paste 10 to be appropriately applied to the member. The average molecular weight here refers to the weight average molecular weight. The average molecular weight can be measured, for example, by size exclusion chromatography.

[0034] (Additive) The additive 16 is an additive added to the bonding paste 10. The additive 16 may have at least one function, such as reducing the rate of change of the viscosity after producing the bonding paste 10 and suppressing the oxidation of the copper particles 12.

[0035] The additive 16 may be any substance, but is preferably a phosphate ester. Among organic phosphoric acid compounds, an ester formed by dehydration condensation of phosphoric acid and alcohol may be called a phosphate ester. The phosphate ester used for additive 16 may be any, and examples thereof include laureth-n phosphate, oleth-n phosphate, steareth-n phosphate (n is an integer), polyoxyethylene tridecyl ether phosphate, polyoxyethylene oleyl ether phosphate, etc. One or more of these may be used as additive 16. It is also preferable to use a phosphate ester other than polyoxyethylene (10) ether phosphate as additive 16. It is more preferable to use at least one of polyoxyethylene tridecyl ether phosphate and polyoxyethylene oleyl ether phosphate as the additive 16. By using such a material as the additive 16, it is possible to reduce the rate of change in viscosity after preparing the bonding paste 10, and it is possible to properly apply the bonding paste 10 to a component. In addition, by using a phosphate ester as the additive 16, it is possible to suppress oxidation of the copper particles 12.

[0036] The additive 16 preferably has an average molecular weight of 500 or more and 1400 or less, more preferably 800 or more and 1400 or less, and even more preferably 1000 or more and 1400 or less. When the average molecular weight of the additive 16 is within this range, the rate of change in viscosity after preparation of the bonding paste 10 can be reduced, making it possible to properly apply the bonding paste 10 to components. The average molecular weight here refers to a weight average molecular weight. The average molecular weight can be measured, for example, by size exclusion chromatography.

[0037] (Composition ratio of bonding paste) In this embodiment, the bonding paste 10 preferably does not contain any substances other than the copper particles 12, the solvent 14, and the additive 16, except for unavoidable impurities. However, the bonding paste 10 is not limited thereto, and may contain additives other than the copper particles 12, the solvent 14, and the additive 16.

[0038] The content of the additive 16 in the bonding paste 10 is preferably 0.1% to 10% by mass, more preferably 0.5% to 5% by mass, and even more preferably 1% to 3% by mass, relative to the total mass of the bonding paste 10. When the content of the additive 16 falls within this range, the rate of change in viscosity after preparation of the bonding paste 10 can be reduced, and the bonding paste 10 can be appropriately applied to components.

[0039] The content of the solvent 14 in the bonding paste 10 is preferably 1% to 20% by mass, more preferably 5% to 15%, and even more preferably 5% to 10% by mass, relative to the total mass of the bonding paste 10. When the content of the solvent 14 falls within this range, the rate of change in viscosity after the bonding paste 10 is produced can be reduced, and the bonding paste 10 can be appropriately applied to components.

[0040] The content of copper particles 12 in bonding paste 10 is preferably 70% to 99%, more preferably 80% to 95%, and even more preferably 85% to 90%, by mass ratio relative to the entire bonding paste 10. When the content of copper particles 12 is within this range, members can be properly bonded.

[0041] (Rate of change in viscosity) The viscosity change rate Δη of the bonding paste 10 one day and 30 days after the production of the bonding paste 10 is 20% or less, preferably 10% or less, and more preferably 5% or more. The viscosity change rate Δη is preferably 5% or more and 20% or less, and more preferably 5% or more and 10% or less. By setting the viscosity change rate Δη within this range, the increase in viscosity over time is suppressed, and the bonding paste 10 can be appropriately applied to the member even after the passage of time since its production.

[0042] The viscosity change rate Δη of the bonding paste 10 one day and 30 days after the production of the bonding paste 10 is calculated as shown in the following formula (1).

[0043] Δη (%) = |η 30 - η1| / η1 × 100 ··· (1)

[0044] In formula (1), η1 is the viscosity (Pa·s) of the bonding paste 10 one day after the production of the bonding paste 10, and η 30 is the viscosity (Pa·s) of the bonding paste 30 days after the production of the bonding paste 10. That is, in the present embodiment, the viscosity change rate Δη indicates the viscosity change rate of the bonding paste 10 from one day after the production to 30 days after the production.

[0045] One day after the production of the bonding paste 10 may refer to the time point when 23 hours or more and 25 hours or less have elapsed after storing the bonding paste 10 in an air atmosphere and at room temperature (25°C) from the time when the copper particles 12, the solvent 14, and the additive 16 are mixed to produce the bonding paste 10. Thirty days after the production of the bonding paste 10 may refer to the time point when 719 hours or more and 721 hours or less have elapsed after storing the bonding paste 10 in an air atmosphere and at room temperature (25°C) from the time when the copper particles 12, the solvent 14, and the additive 16 are mixed to produce the bonding paste 10.

[0046] Also, the viscosity of the bonding paste 10 refers to the viscosity at 25°C. That is, η1 is the viscosity of the bonding paste 10 at 25°C after one day has passed since its preparation, and η 30 is the viscosity of the bonding paste 10 at 25°C after 30 days have passed since its preparation. The viscosity can be measured by a micro spiral viscometer (PCU-02V) manufactured by Malcolm Co., Ltd.

[0047] Note that, as described above, the change rate Δη of the viscosity refers to the change rate of the viscosity one day and 30 days after preparation, but it may also refer to the change rate of the viscosity 30 days after obtaining the prepared bonding paste 10. That is, η1 in formula (1) may be the viscosity after storing the prepared bonding paste 10 at 25°C for one day (for example, 23 hours or more and 25 hours or less), and η1 in formula (1) may be the viscosity after storing the prepared bonding paste 10 at 25°C for 30 days (for example, 719 hours or more and 721 hours or less).

[0048] The means for making the change rate Δη of the viscosity within the above range may be arbitrary. That is, for example, even if the types and mixing ratios of the solvent 14 and the additive 16 are arbitrary, as long as the change rate Δη of the viscosity is within the above range, the bonding paste 10 can be appropriately applied to the member even after a certain period of time has passed since its preparation. However, it is preferable to set at least one of the type of the solvent 14, the mixing ratio of the solvent 14, the type of the additive 16, and the mixing ratio of the additive 16 to those defined in the present embodiment, so that the change rate Δη of the viscosity can be appropriately within the above range.

[0049] The viscosity η 30 may be a value equal to or greater than the viscosity η1. The viscosity η 30is preferably 1 Pa·s or more and 200 Pa·s or less, more preferably 10 Pa·s or more and 200 Pa·s or less, and even more preferably 50 Pa·s or more and 200 Pa·s or less. Furthermore, the viscosity η1 is preferably 1 Pa·s or more and 200 Pa·s or less, more preferably 10 Pa·s or more and 200 Pa·s or less, and even more preferably 50 Pa·s or more and 200 Pa·s or less. When the viscosity is within this range, the bonding paste 10 can be appropriately applied to the member.

[0050] (Method of manufacturing bonding paste) The bonding paste 10 is produced by performing a mixing step of mixing copper particles 12, a solvent 14, and an additive 16. In this mixing step, the copper particles 12, the solvent 14, and the additive 16 are preferably mixed so that the content of the additive 16, the content of the solvent 14, and the content of the copper particles 12 are within the above-mentioned ranges. In the mixing step, the copper particles 12, the solvent 14, and the additive 16 may be mixed using a kneading device. As the kneading device, for example, a three-roll mill is used.

[0051] (Method of manufacturing a bonded body) 2 is a schematic diagram of a bonded body according to this embodiment. As shown in FIG. 2, in this embodiment, a bonded body 30 is produced by bonding a first member 21 and a second member 22 using a bonding paste 10 as a bonding layer 20. The first member 21 and the second member 22 may be any members. For example, one of the first member 21 and the second base member may be a substrate, and the other may be an electronic component. That is, a semiconductor module in which a substrate and an electronic component are bonded by the bonding layer 20 may be produced as the bonded body 30. The substrate is not particularly limited, but examples thereof include an oxygen-free copper plate, a copper-molybdenum plate, a high-heat-dissipation insulating substrate (e.g., DCB (Direct Copper Bond)), and a substrate for mounting a semiconductor element such as an LED (Light Emitting Diode) package. Examples of electronic components include semiconductor elements such as IGBTs (Insulated Gate Bipolar Transistors), diodes, Schottky barrier diodes, MOS-FETs (Metal Oxide Semiconductor Field Effect Transistors), thyristors, logic, sensors, analog integrated circuits, LEDs, semiconductor lasers, and oscillators.

[0052] In this manufacturing method, a coating layer forming step is performed in which bonding paste 10 is applied to at least one surface of a first member 21 or a second member 22 to form a coating layer. The application method is not particularly limited, but examples include spin coating, metal masking, spray coating, dispenser coating, knife coating, slit coating, inkjet coating, screen printing, offset printing, and die coating. Next, a preheating step is performed at a temperature of 50°C to 150°C for 1 minute to 30 minutes to volatilize the solvent in the paste. Next, a superposition step is performed in which the first member 21 and the second member 22 are superposed with the coating layer interposed therebetween.

[0053] Next, a heating step is performed in which the first member 21 and the second member 22, which are stacked together with the coating layer interposed therebetween, are heated. In the heating step, the stacked first member 21 and the second member 22 are heated at a predetermined temperature for a predetermined time in a non-reducing atmosphere while a predetermined pressure is applied to at least one of the stacked first member 21 and the second member 22. By performing the heating step, the copper particles 12 in the coating layer are sintered to form a bonding layer 20, and a bonded body 30 in which the first member 21 and the second member 22 are bonded together with the bonding layer 20 is produced.

[0054] 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 an inert gas atmosphere in which an inert gas is filled. Examples of non-reducing gases include nitrogen and rare gases such as argon. For example, in this embodiment, the heating step may be performed in a nitrogen atmosphere with an oxygen concentration of 1000 ppm. By performing the heating step in a non-reducing atmosphere, there is no need to use a reducing gas, and the heating step can be easily performed.

[0055] Furthermore, the predetermined pressure applied to at least one of the first member 21 and the second member 22 is preferably 0.5 MPa or more and 10 MPa or less, more preferably 1 MPa or more and 5 MPa or less, and even more preferably 2 MPa or more and 5 MPa or less. By applying a pressure in such a relatively low range, it is possible to appropriately bond the first member 21 and the second member 22 while suppressing defects in the shape of the bonding layer 20. Note that the pressure is applied in a direction such that the first member 21 and the second member 22 are pressed against each other relatively via the coating layer.

[0056] Furthermore, the predetermined temperature, which is 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 even more preferably 250° C. or higher and 300° C. or lower. By setting the heating temperature in such a relatively low range, copper particles 12 can be appropriately sintered while preventing defects in the shape of bonding layer 20.

[0057] Furthermore, the predetermined time, which is the heating time in the heating step, is preferably from 1 minute to 10 minutes, more preferably from 1 minute to 5 minutes, and even more preferably from 1 minute to 3 minutes. By setting the heating time within this range, copper particles 12 can be appropriately sintered.

[0058] (Joining layer) As described above, the bonding layer 20 in this embodiment is formed by heating the bonding paste 10 and sintering the copper particles 12. The bonding layer 20 is located 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 considered a sintered body of copper. The sintered density of the copper particles in the bonding layer 20 is preferably 80% or more, more preferably 85% to 95%, and even more preferably 85% to 90%. When the sintered density is within this range, the bonding layer 20 can ensure electrical conductivity and thermal conductivity. The sintered density refers to the ratio of the volume of the bonding layer 20 excluding the open and closed pores to the total volume of the bonding layer 20 including the open and closed pores. The sintered density was calculated by binarizing images of the cross section of the bonding layer taken at random at a magnification of 30,000 times using an SEM (Scanning Electron Microscope) and dividing the images into particle and pore portions using image processing software (ImageJ, manufactured by the National Institutes of Health, USA). Sintered density (%) = (total area of particle parts / (total area of particle parts + total area of void parts)) x 100

[0059] Further, the bonding layer 20 may contain phosphorus. The phosphorus here refers to phosphorus as an element, including not only elemental phosphorus but also phosphorus contained in any compound. It is preferable that the phosphorus content in the entire bonding layer 20 is 10 ppm or more and 1000 ppm or less, more preferably 50 ppm or more and 500 ppm or less, and even more preferably 100 ppm or more and 500 ppm or less, by mass ratio. When the phosphorus content is within this range, the bonding layer 20 can suppress a decrease in strength even when formed, for example, in a non-reducing atmosphere. The phosphorus content can be measured by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer). In this embodiment, the phosphorus contained in the bonding layer 20 is derived from the phosphate ester contained in the bonding paste 10.

[0060] Also, the bonding layer 20 preferably has a thickness of 10 μm or more and 200 μm or less, more preferably 20 μm or more and 150 μm or less, and even more preferably 50 μm or more and 100 μm or less. When the thickness of the bonding layer 20 is within this range, it is possible to maintain high heat dissipation while relaxing the stress due to the difference in the linear expansion coefficient between members caused by the temperature difference.

[0061] Thus, the bonding layer 20 according to this embodiment is a copper sintered body having a sintering density of 80% or more and containing phosphorus. Since the bonding layer 20 according to this embodiment has a sintering density of 80% or more, a decrease in strength is suppressed. Furthermore, since the oxidation of the copper particles 12 is suppressed by the origin of phosphorus (phosphate ester in this embodiment) contained in the bonding layer 20, as a result, the bonding layer 20 containing phosphorus suppresses a decrease in strength. In this embodiment, the bonding layer 20 is formed by heating the bonding paste 10 as described above, but the formation method of the bonding layer 20 may be arbitrary as long as it satisfies the above characteristics.

[0062] (Effect) As described above, the bonding paste 10 according to this embodiment contains copper particles 12, a solvent 14, and an additive 16, and the rate of change in viscosity Δη is 20% or less 1 day and 30 days after the bonding paste 10 is prepared. According to this embodiment, since the rate of change in viscosity Δη is within this range, an increase in viscosity over time is suppressed (the viscosity is less likely to increase), and the bonding paste 10 can be appropriately applied to components even after a long time has passed since its preparation.

[0063] Additive 16 is preferably a phosphate ester. By using a phosphate ester as additive 16, oxidation of copper particles 12 can be suppressed.

[0064] The average molecular weight of the additive 16 is preferably not less than 500 and not more than 1400. By using a substance (preferably a phosphate ester) with an average molecular weight within this range as the additive 16, an increase in viscosity over time can be suppressed, and the bonding paste 10 can be appropriately applied to the component.

[0065] The content of the additive 16 is preferably 0.1% to 10% by mass with respect to the entire bonding paste 10. By setting the content of the additive 16 within this range, an increase in viscosity over time can be suppressed, and the bonding paste 10 can be appropriately applied to components.

[0066] A terpineol-based solvent is preferably used as the solvent 14. By using a terpineol-based solvent as the solvent 14, an increase in viscosity over time can be suppressed, and the bonding paste 10 can be appropriately applied to the member.

[0067] The average molecular weight of the solvent 14 is preferably between 100 and 200. By using a solvent 14 having an average molecular weight within this range (preferably a terpineol-based solvent), an increase in viscosity over time can be suppressed, and the bonding paste 10 can be appropriately applied to the component.

[0068] In the method for manufacturing a bonded body according to this embodiment, a first member 21 and a second member 22 are bonded together using the bonding paste 10 as the bonding layer 20 to manufacture a bonded body 30. According to this embodiment, the bonding paste 10 can be appropriately applied to the first member 21 and the second member 22, and the bonded body 30 can be appropriately manufactured.

[0069] (Example) Next, examples will be described. Figure 3 is a table showing the bonding pastes of the examples.

[0070] Example 1 In Example 1, copper particles with a BET diameter of 153 nm were prepared. The BET diameter was determined by measuring the amount of nitrogen gas adsorbed by the copper particles using a specific surface area measuring device (Quantachrome Instruments, QUANTACHROME AUTOSORB-1), and then calculating the specific surface area of the copper particles by the BET method. The obtained specific surface area S (m 2 / g) and the density of copper particles ρ (g / cm 3 ) and the BET diameter was calculated using the following formula. BET diameter (nm) = 6000 / (ρ(g / cm 3 )×S(m 2 / g)) In Example 1, polyoxyethylene tridecyl ether phosphate, which is a phosphoric acid ester, was prepared as the additive, and dihydroterpineol, which is a terpineol-based solvent, was prepared as the solvent. In Example 1, copper particles, additives, and a solvent were mixed so that the additive content was 2 mass %, the solvent content was 10 mass %, and the remainder was copper particles, to obtain a bonding paste.

[0071] The obtained bonding paste was stored under atmospheric pressure at 25°C for one day (24 hours), and the viscosity η1 (Pa·s) was measured one day after the preparation of the bonding paste 10. The obtained bonding paste was also stored under atmospheric pressure at 25°C for 30 days (720 hours), and the viscosity η1 was measured 30 days after the preparation of the bonding paste 10. 30The viscosity (Pa s) was measured. Then, using formula (1) of the above embodiment, the rate of change in viscosity Δη (%) was calculated 1 day and 30 days after preparation. The viscosity was measured at 25°C using a Malcom micro spiral viscometer (PCU-02V). The rotation speed was 10 rpm. The measurement results are shown in Figure 3.

[0072] (Example 2, Comparative Example 1) In Example 2 and Comparative Example 1, a bonding paste was obtained in the same manner as in Example 1, except that the BET diameter of the copper particles, the type of additive, the content of the additive, the type of solvent, and the content of the solvent were as shown in FIG. 3, and the viscosity η1 and viscosity η 30、 The rate of change in viscosity, Δη (%), was measured, and the results are shown in Figure 3.

[0073] (evaluation) The bonding properties of the bonding paste obtained in each example were evaluated.

[0074] For the evaluation of bondability, a bonded body was manufactured using the bonding paste obtained in each example (bonding paste 30 days after preparation). Specifically, a 3 mm opening was formed in an oxygen-free copper plate, and the bonding paste of each example was printed using a 50 μm-thick metal mask and a metal squeegee. The plate was then dried at 90°C for 5 minutes on a hot plate, and a 2.5 mm × 2.5 mm silicon dummy chip with 100 nm-thick gold sputtered on its backside was placed on the plate. The plate was then heated at 250°C for 3 minutes under a nitrogen atmosphere while applying a pressure of 5 MPa to bond the plate. In the evaluation, the shear strength of the resulting bonded body (bonded silicon dummy chip and oxygen-free copper plate) was measured, and a shear strength of 10 MPa or more was evaluated as ◯, and a shear strength of less than 10 MPa was evaluated as ×. The shear strength was measured by a method conforming to JIS Z 3198-7 (Lead-free solder test method - Part 7: Solder joint shear test method for chip components). Specifically, a load was applied to a silicon dummy chip using a tool of a bond tester (manufactured by Nordson DAGE, SERIES 4000), and the load (maximum shear load) at the time when the silicon dummy chip was peeled off from the copper bonding layer was measured. The moving speed of the tool was set to 50 μm / sec, and the gap between the tip of the tool and the oxygen-free copper substrate was set to 50 μm. The obtained maximum shear load was converted to newtons and divided by the area of the copper bonding layer (2.5 mm × 2.5 mm), and the value thus obtained was defined as the shear strength (unit: MPa). Seven bonded bodies were fabricated, and the shear strength of each bonded body was measured. The shear strength used for evaluating the bondability was the average of the shear strengths of the seven bonded bodies. As shown in Fig. 3, in Examples 1 and 2 where the change rate of viscosity Δη (%) is 20% or less, the evaluation of the bondability is ○, and it can be seen that the bonding paste can be appropriately applied even after the passage of time. On the other hand, in Comparative Example 1 where the change rate of viscosity Δη (%) is not 20% or less, the evaluation of the bondability is ×, and it can be seen that the viscosity becomes high when time has passed and the bonding paste cannot be appropriately applied.

[0075] As described above, the embodiments of the present invention have been explained, but the embodiments are not limited by the contents of these embodiments. Further, the above-described components include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those within the so-called equivalent range. Furthermore, the above-described components can be combined as appropriate. Moreover, various omissions, substitutions, or changes of the components can be made without departing from the gist of the above-described embodiments.

Explanation of Reference Numerals

[0076] 10 Bonding paste 12 Copper particles 14 Solvent 16 Additive 20 Bonding layer 21 First member 22 Second member 30 Conjugate

Claims

1. A paste for bonding, comprising copper particles, a solvent, and an additive, wherein the rate of change of viscosity after 1 day and 30 days from the preparation of the paste for bonding is 20% or less. Paste for bonding.

2. The paste for bonding according to claim 1, wherein the additive is a phosphate ester.

3. The paste for bonding according to claim 2, wherein the average molecular weight of the additive is 500 or more and 1400 or less.

4. The paste for bonding according to any one of claims 1 to 3, wherein the content of the additive is 0.1% or more and 10% or less by mass ratio with respect to the whole of the paste for bonding.

5. The paste for bonding according to any one of claims 1 to 3, wherein the solvent is a terpineol-based solvent.

6. The paste for bonding according to claim 4, wherein the average molecular weight of the solvent is 100 or more and 200 or less.

7. A method for manufacturing a bonded body, wherein the first member and the second member are bonded using the paste for bonding according to any one of claims 1 to 3 as a bonding layer to manufacture a bonded body.

Images