Bonding paste composition, method for producing bonded structure, method for temporarily fixing to-be-bonded body, and bonded structure

Abstract

Provided is a bonding paste composition with which it is possible to improve tackiness between a coating film and a to-be-bonded body and to obtain, by using a simple method, a bonded structure having high bonding strength. Also provided are: a method for producing a bonded structure in which the aforementioned bonding paste composition is used; and method for temporarily fixing a to-be-bonded body. This bonding paste composition contains a copper powder, a solvent, and an additive. The solvent contains a glycol-based solvent, and the additive contains at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms. The organic component content in the bonding paste composition is 0.4-10 mass%.

Description

Bonding paste composition, method for producing bonded structure, temporary fixing method for objects to be bonded, and bonded structure

[0001] The present invention relates to a bonding paste composition, a method for producing a bonded structure, a temporary fixing method for objects to be bonded, and a bonded structure.

[0002] In recent years, semiconductor elements (semiconductor chips) called power devices have been widely used as power conversion and control devices such as inverters. During mounting, a semiconductor element is bonded to a substrate such as a circuit board, a ceramic substrate, or a wiring body such as a lead frame. On the other hand, solder has conventionally been frequently used for mounting semiconductor elements. Further, with the increasing environmental awareness in recent years, there is a demand for the use of lead-free solder that does not contain lead.

[0003] However, due to the nature of power devices that control high currents, they generate a large amount of heat during operation. In contrast, lead-free solder has low heat resistance, which poses the problem of being insufficient for power device mounting.

[0004] Accordingly, it has been proposed to use a paste-like composition containing metal powder such as copper powder (bonding paste composition) instead of solder. When bonding a set of objects to be bonded consisting of a substrate and a semiconductor element using a bonding paste composition, for example, the bonding paste composition is applied to one surface of one object to be bonded (substrate) and dried to form a coating film, then the other object to be bonded (semiconductor element) is mounted on the obtained coating film to produce a laminate. Thereafter, when the laminate is heated, the metal powder in the paste composition sinters to form a bonding layer made of a sintered body, and the objects to be bonded are bonded to each other via this bonding layer.

[0005] It has also been proposed that the heat treatment of the laminate is performed under pressure when bonding objects to be bonded. Performing heat treatment under pressure increases the sintering driving force of the metal powder and further promotes sintering, which has the advantage of further increasing the bonding strength of the bonded structure.

[0006] Patent documents 1 and 2 disclose pressure bonding using bonding paste compositions. Patent document 1 discloses bonding a first conductor and a second conductor using a bonding composition containing copper powder, a liquid medium and a reducing agent, and when firing under pressure, applying a pressure of 0.001 MPa to 20 MPa to assist in the sintering of copper particles (claims 1 to 7 and

[0045] ). Patent document 2 discloses bonding a substrate and an object to be bonded using a paste containing metal fine particles and an organic solvent on a substrate, and applying pressure using a pressurizing member during heating (paragraphs

[0042] to

[0048] ).

[0007] International Publication No. 2020 / 032161, International Publication No. 2021 / 193150

[0008] Although pressure bonding techniques using bonding paste compositions containing metal powders such as copper powder have been known for some time, there was room for improvement in these conventional techniques.

[0009] In other words, when joining a pair of objects to be joined by pressure, as described above, a laminate is created consisting of one object to be joined, a coating film formed from a joining paste composition, and the other object to be joined. Then, this laminate is heated under pressure to join the objects to be joined together.

[0010] The process of fabricating the laminate and the bonding process of heating the laminate are usually carried out using separate equipment. Therefore, it is necessary to transport the laminate between the two processes, and external forces such as vibration may be applied to the laminate during this process. External forces are also applied to the laminate during the bonding process. However, in the laminate, one of the components to be bonded (semiconductor elements) is only mounted on the coating and is not sufficiently fixed. Therefore, external forces applied during transport and bonding may cause displacement of the mounted components (chip rotation) or even cause the components to detach (see Figure 1). If displacement or detachment of components occurs, pressure bonding in subsequent processes becomes difficult, which leads to a decrease in productivity.

[0011] To avoid these problems, one possible approach is to lower the drying temperature during coating formation to leave solvent in the coating. If solvent remains in the coating, the tackiness (adhesion) between the coating and the object to be bonded will improve when the object to be bonded is mounted on the coating, which is expected to help prevent misalignment and detachment.

[0012] However, if a large amount of low-viscosity solvent remains in the coating, the coating may become too soft, reducing its shape retention. Specifically, it may not be able to maintain its shape during pressure bonding, and a phenomenon called squeeze-out may occur where the coating squeezes out from between the bonded parts. When squeeze-out occurs, it becomes impossible to form a high-strength bond layer. Furthermore, even if a bond layer is formed, the large amount of solvent present may cause pores (voids, cavities) in the bond layer, which may lead to a decrease in the strength of the bond and bond failure. Bonding structures used for mounting devices with high heat generation, such as power devices, are subjected to repeated thermal stress caused by device heat generation, so excellent bond reliability is required. Therefore, bond failure is undesirable. In addition, residual solvent may induce substrate contamination.

[0013] Another possible method involves applying a temporary fixing agent (tacking agent) to the coating before mounting the objects to be joined in order to prevent misalignment or detachment of the objects. For example, Patent Document 2 proposes a method for manufacturing a joined structure using a temporary fixing composition, which is said to effectively prevent misalignment between the joined objects (paragraphs

[0045] and

[0046] ). However, while the method using a temporary fixing agent (temporary fixing composition) is effective in preventing misalignment, it requires a separate step of applying the temporary fixing agent, which increases the amount of equipment needed, complicates the manufacturing process, and worsens productivity.

[0014] Thus, there is a trade-off relationship between improving tackiness and improving joint strength, making it difficult to simultaneously increase both (tackiness and joint strength) while maintaining high productivity using simple methods.

[0015] In view of these problems, the inventors conducted thorough research. As a result, they developed a bonding paste composition containing a predetermined amount of a specific organic component in addition to copper powder, as well as a specific solvent. They found that by using this bonding paste composition to bond objects, the tackiness between the coating film and the objects to be bonded is improved, and a bonded structure with high bonding strength can be obtained by a simple method.

[0016] The present invention was completed based on such findings, and aims to provide a bonding paste composition that improves the tackiness between the coating film and the object to be bonded, and that allows for the acquisition of a bonded structure with high bonding strength by a simple method. Furthermore, the present invention also aims to provide a method for manufacturing a bonded structure using the bonding paste composition, a method for temporarily fixing the object to be bonded, and a bonded structure.

[0017] The present invention encompasses the following embodiments (1) to (16). In this specification, the expression "~" includes the numerical values ​​at both ends. That is, "X~Y" is synonymous with "X or more and Y or less".

[0018] (1) A bonding paste composition comprising copper powder, a solvent, and an additive, wherein the solvent comprises a glycol-based solvent, the additive comprises at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms, and the content of the organic component in the bonding paste composition is 0.4% by mass or more and 10% by mass or less.

[0019] (2) The bonding paste composition according to (1), wherein the content of copper powder in the bonding paste composition is 60% by mass or more and 85% by mass or less.

[0020] (3) The bonding paste composition according to (1) or (2) above, wherein the content of the solvent in the bonding paste composition is 10% by mass or more and 40% by mass or less.

[0021] (4) The bonding paste composition according to any of (1) to (3) above, wherein the boiling point of the glycol-based solvent is 160°C or higher and 290°C or lower.

[0022] (5) Any of the bonding paste compositions described in (1) to (4) above, wherein the content of the organic component in the bonding paste composition is 0.5% by mass or more and 7% by mass or less.

[0023] (6) A bonding paste composition according to any of (1) to (5) above, wherein the number of carbon atoms in the organic component is 12 or more and 30 or less.

[0024] (7) The bonding paste composition according to any of (1) to (6) above, wherein the organic component comprises at least one aliphatic alcohol selected from the group consisting of 1-decanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, 12-hydroxystearyl alcohol, ricinoleyl alcohol, and oleyl alcohol.

[0025] (8) The bonding paste composition according to any of (1) to (7) above, wherein the organic component comprises at least one fatty acid ester selected from the group consisting of glyceryl octanoate, glyceryl laurate, glyceryl decanoate, dibutyl sebacate, methyl laurate, methyl palmitate, methyl stearate, methyl 12-hydroxystearate, methyl ricinoleate, and glyceryl stearate citrate.

[0026] (9) A method for manufacturing a bonded structure in which a first body to be joined and a second body to be joined via a bonding layer, comprising the steps of: applying a bonding paste composition of any of (1) to (8) above to one surface of the first body to be joined to form a wet film; removing at least a portion of the solvent from the wet film to obtain a coating film; temporarily fixing the second body to be joined to the coating film by pressurizing to obtain a laminate in which the first body to be joined, the coating film and the second body to be joined are stacked in this order; and heating the laminate under pressurizing to sinter the copper powder in the coating film, thereby joining the first body to be joined and the second body to be joined via a bonding layer formed thereby.

[0027] (10) A method for temporarily fixing a first object to be joined and a second object to be joined, comprising the steps of: applying a bonding paste composition according to any of (1) to (8) above to one surface of the first object to be joined to form a wet film; removing at least a portion of the solvent from the wet film to obtain a coating film; and temporarily fixing the second object to be joined to the coating film by pressurization.

[0028] (11) A bonding structure in which a first bonded body and a second bonded body are bonded via a bonding layer, wherein the bonding layer is composed of a copper sintered body, and a peak based on at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms is detected by gas chromatography-mass spectrometry (GC(MS) analysis).

[0029] (12) The bonding structure according to (11), wherein the bonding layer has a mass loss rate of 0.1% by mass or more and 5% by mass or less in the temperature range of 40°C to 500°C as measured by thermogravimetric analysis.

[0030] (13) The bonding structure according to (11) or (12), wherein the organic component comprises at least one aliphatic alcohol selected from the group consisting of 1-decanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, 12-hydroxystearyl alcohol, ricinoleyl alcohol, and oleyl alcohol.

[0031] (14) Any of the above (11) to (13) bonding structures, wherein the organic component comprises at least one fatty acid ester selected from the group consisting of glyceryl octanoate, glyceryl laurate, glyceryl decanoate, dibutyl sebacate, methyl laurate, methyl palmitate, methyl stearate, methyl 12-hydroxystearate, methyl ricinoleate, and glyceryl stearate citrate, 12-hydroxyoctadecanoate, and methyl octadecenoate.

[0032] (15) Any of the bonding structures described in (11) to (14) above, wherein the thickness of the bonding layer is 5 μm or more and 200 μm or less.

[0033] (16) Any of the above (11) to (15) joint structures, wherein the bonding strength in the bonding layer is 30 MPa or more.

[0034] The present invention provides a bonding paste composition that improves the tackiness between the coating film and the object to be bonded, and enables the acquisition of a bonded structure with high bonding strength by a simple method. Furthermore, the present invention provides a method for manufacturing a bonded structure using the bonding paste composition, a method for temporarily fixing the object to be bonded, and a bonded structure.

[0035] This figure shows the manufacturing process of a conventional bonded structure. This figure shows the manufacturing process of the bonded structure according to this embodiment. The GC (MS) analysis results (gas chromatogram) obtained for the bonded layer of the bonded structure are shown (Example 3). The GC (MS) analysis results (gas chromatogram) obtained for the bonded layer of the bonded structure are shown (Example 5). The GC (MS) analysis results (gas chromatogram) obtained for the bonded layer of the bonded structure are shown (Example 6).

[0036] Specific embodiments of the present invention (hereinafter referred to as "these embodiments") are described below. However, the present invention is not limited to the following embodiments, and various modifications are possible as long as they do not alter the essence of the invention. Furthermore, in this specification, any combination of preferred embodiments can be adopted as long as technical consistency can be maintained. For example, one of the preferred numerical ranges can be arbitrarily combined with the other.

[0037] <<1. Bonding Paste Composition>> The bonding paste composition of this embodiment (hereinafter sometimes simply referred to as "paste composition" or "composition") contains copper powder, a solvent, and an additive. The solvent includes a glycol-based solvent. The additive contains at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms. The content of the organic component in the bonding paste composition is 0.4% by mass or more and 10% by mass or less. With such a composition, it is possible to improve the tackiness between the coating film and the object to be bonded, and to obtain a bonded structure with high bonding strength by a simple method.

[0038] [1] Copper Powder The paste composition of this embodiment contains copper powder. The copper powder is a powder mainly composed of copper and is a constituent material of the bonding layer (bonding part) obtained by firing the composition. That is, the sintered body of the copper powder contained in the composition constitutes the bonding layer. In this specification, powder or powder is an aggregate of many particles. It can also be said that many particles constitute powder or powder.

[0039] Copper powder may contain copper elements and have a composition consisting of unavoidable impurities. These unavoidable impurities may be, for example, oxides inevitably formed on the surface of the copper particles constituting the copper powder. Typically, the content of elements other than copper in copper powder is 5% by mass or less. Alternatively, copper powder may contain copper at a ratio of 50% by mass or more, with other elements making up the remainder. Copper alloy powder is an example of such copper powder. From the viewpoint of improving conductivity, the copper content in copper powder is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The content of each element in copper powder can be measured, for example, by ICP emission spectrometry or inert gas fusion / non-dispersive infrared absorption spectroscopy.

[0040] The shape of the copper particles constituting the copper powder is not particularly limited. For example, they may have various shapes such as spherical, flattened, flake-like, polyhedral, dendritic, or columnar. Flattened refers to a flat shape with few irregularities, and includes flake-like particles. From the viewpoint of increasing particle packing and forming a bonding layer with high strength (bonding strength), it is preferable for the copper powder to contain spherical copper particles, and more preferably to contain both spherical and flattened copper particles. Whether or not the copper particles are spherical can be determined from the particle's circularity coefficient. Specifically, the copper powder is observed using a scanning electron microscope (SEM), and the area S and perimeter L of randomly selected copper particles are measured, from which the circularity coefficient 4πS / L is obtained. ２ To determine this, we calculate the circularity coefficient for multiple copper particles and then calculate its average value. A copper particle is defined as spherical if its arithmetic mean of the circularity coefficient is 0.85 or greater.

[0041] The content of copper powder in the paste composition is preferably 60% by mass or more and 85% by mass or less, more preferably 65% by mass or more and 80% by mass or less. By appropriately increasing the content of copper powder, the conductivity and strength of the bonding layer are further enhanced. In addition, by appropriately suppressing the content of copper powder, aggregation of copper particles in the composition is suppressed, and the coatability of the composition is improved. The content referred to herein is the total amount of copper powder contained in the composition. That is, as described later, when the copper powder includes a first copper powder and a second copper powder, the total amount of the first copper powder and the second copper powder corresponds to the content.

[0042] The average particle diameter (D50) of the copper powder is preferably 0.03 µm or more, more preferably 0.05 µm or more. By appropriately increasing the particle diameter of the copper powder, aggregation of particles in the paste composition can be prevented, and particle dispersibility can be improved. On the other hand, the average particle diameter (D50) of the copper powder is preferably 20 µm or less, more preferably 10 µm or less. By appropriately reducing the particle diameter of the copper powder, the sinterability of the copper powder can be improved. From the viewpoint of achieving both dispersibility and sinterability, D50 is preferably 0.03 µm or more and 20 µm or less, and more preferably 0.05 µm or more and 10 µm or less.

[0043] The average particle diameter (D50) of copper powder can be determined as follows. First, an organic solvent such as 2-propanol in an amount 10 times the mass of the paste composition is added, followed by sufficient stirring, and then a washing operation of removing only the supernatant while leaving a solid content (cake) is repeated. The obtained cake is left to stand at room temperature and sufficiently dried, and the obtained dried product (copper powder) is observed by SEM. During SEM observation, an SEM image at a magnification of 1000 to 100000 times is obtained. Then, in this SEM image, 50 or more particles whose outlines can be observed are randomly selected, and the particle diameter (Heywood diameter) is measured. The particle volume when the particle is a true sphere is calculated from the Heywood diameter, and the volume-based particle size distribution is obtained from the obtained data. Next, in the obtained particle size distribution, the particle diameter at which the cumulative volume from the side of smaller particle diameters reaches 50% by volume (50% cumulative volume diameter) is calculated, and this is defined as the average particle diameter (D50).

[0044] The average particle diameter (D50) of the copper powder may be determined by measuring the particle diameter of the copper powder used when preparing the paste composition. When the copper particles constituting the copper powder are spherical, D50 is determined by scanning electron microscope (SEM) observation. Specifically, the copper powder is observed by SEM, 50 particles are randomly selected from the SEM image at a magnification of 1000 to 100,000 times, and the particle diameter (Heywood diameter) of each particle is obtained. Then, assuming that the copper particles are true spheres, the volume is calculated from the obtained particle diameters. A volume-based particle size distribution is obtained from the particle diameters of the 50 particles, and the diameter at which the cumulative volume reaches 50% (50% volume cumulative particle diameter) is defined as D50.

[0045] More preferably, the copper powder comprises a first copper powder having a 50% cumulative volume diameter (D50) of 0.05 µm or more and less than 1 µm in a region of less than 1 µm in the particle size distribution measured by SEM observation, and a second copper powder having a 50% cumulative volume diameter (D50) of 1 µm or more and 10 µm or less in a region of 1 µm or more in the particle size distribution. When the copper particles constituting the copper powder have a shape other than spherical, that is, when they have a flat shape, a flake (scale-like) shape, a polyhedral shape, a dendritic shape, or a columnar shape, the particle diameter D50 is determined by laser diffraction scattering type particle size distribution measurement. Specifically, 0.1 g of a measurement sample is mixed with a dispersant dispersion, and the mixture is dispersed for 1 minute with an ultrasonic homogenizer. As the ultrasonic homogenizer, for example, US-300T manufactured by Nippon Seiki Seisakusho Co., Ltd. or an equivalent product thereof is used. Thereafter, a volume-based particle size distribution is obtained using a laser diffraction scattering type particle size distribution analyzer, and the diameter at which the cumulative volume reaches 50% (50% volume cumulative particle diameter) is defined as D50. As the laser diffraction scattering type particle size distribution analyzer, MT-3300EXII manufactured by MicrotracBEL or an equivalent product thereof is used.

[0046] The D50 of the first copper powder is preferably 0.05 μm or larger from the viewpoint of preventing aggregation in the paste composition and obtaining good particle dispersibility. The D50 of the first copper powder is preferably less than 1 μm, more preferably 0.8 μm or smaller, and even more preferably 0.6 μm or smaller from the viewpoint of ensuring sufficient sinterability of the copper powder. The D50 of the second copper powder is preferably 1 μm or larger from the viewpoint of improving the strength of the bonding layer obtained by sintering the copper powder. The D50 of the second copper powder is preferably 10 μm or smaller, more preferably 8 μm or smaller, and even more preferably 6 μm or smaller from the viewpoint of improving the coatability of the composition.

[0047] The ratio of the first copper powder to the total mass of the first and second copper powders in the paste composition is preferably 10% to 95% by mass, more preferably 15% to 90% by mass, and even more preferably 20% to 80% by mass. The ratio of the second copper powder to the total mass of the first and second copper powders is preferably 5% to 90% by mass, more preferably 10% to 85% by mass, and even more preferably 20% to 80% by mass. By setting the blending ratio within the above ranges, it is possible to improve the particle packing and sufficiently increase the strength of the bonding layer.

[0048] The copper powder may be untreated (unsurface-treated copper powder). Alternatively, it may be surface-treated (surface-treated copper powder) to the extent that it does not impair the effects of this embodiment. Examples of surface-treated copper powder include copper powder on which a surface treatment layer consisting of fatty acids, fatty acid copper salts, aliphatic amines, silane coupling agents, titanate coupling agents, aluminate coupling agents, etc., is provided on the surface of the copper powder.

[0049] [2] Solvent The paste composition of this embodiment contains a solvent. The solvent provides the composition with appropriate viscosity and good coatability. It also helps to ensure good conductivity and strength of the bonded layer obtained by firing the composition by uniformly dispersing the copper particles in the composition.

[0050] The solvent includes glycol-based solvents. Glycol-based solvents have high solubility for additives (aliphatic alcohols, fatty acid esters). Furthermore, using glycol-based solvents ensures the coatability and volatility of the composition during the manufacturing of the bonded structure. The boiling point (at 1 atmosphere) of the glycol-based solvent is preferably between 160°C and 290°C. Examples of such glycol-based solvents, though not limited to these, include propylene glycol (boiling point: 188°C), ethylene glycol (boiling point: 197°C), hexylene glycol (boiling point: 197°C), octylene glycol (boiling point: 244°C), diethylene glycol (boiling point: 245°C), 1,3-butanediol (boiling point: 207°C), 1,4-butanediol (boiling point: 228°C), dipropylene glycol (boiling point: 231°C), tripropylene glycol (boiling point: 273°C), and 3-methyl-1,5-pentanediol (boiling point: 250°C). As a solvent, one type of solvent may be used alone, or a combination of multiple types of solvents may be used.

[0051] The amount of solvent in the paste composition is not limited. However, from the viewpoint of balancing the applicability of the composition, the tackiness of the coating film, and the shape retention, the solvent content in the composition is preferably 15% by mass or more and 40% by mass or less, more preferably 20% by mass or more and 35% by mass or less. When the solvent consists only of a glycol-based solvent, the amount of glycol-based solvent is the amount of solvent; when the solvent contains other solvents, the total amount of the glycol-based solvent and the other solvent is the amount of solvent.

[0052] The solvent may contain solvents other than glycol-based solvents. However, from the viewpoint of utilizing the effects based on glycol-based solvents, it is preferable that the proportion of glycol-based solvent in the solvent be higher than that of other solvents. The proportion of glycol-based solvent in the solvent is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The content of solvents other than glycol-based solvents in the solvent may be less than or equal to the amount of impurities contained in the glycol-based solvent (for example, 1.0% by mass relative to the glycol-based solvent). However, in this embodiment, the content of solvents other than glycol-based solvents is not limited to less than or equal to the amount of impurities. Needless to say, it includes cases where the content is greater than the amount of impurities.

[0053] [3] Additives The paste composition of this embodiment contains at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms as an additive component. Aliphatic alcohols having 10 or more carbon atoms and fatty acid esters have the function of improving the tackiness between the coating film and the object to be bonded when manufacturing the bonded structure. That is, aliphatic alcohols and fatty acid esters having 10 or more carbon atoms have relatively high melting and boiling points. Therefore, they tend to remain as stable solids in the coating film formed by applying and drying the bonding composition. It is presumed that the aliphatic alcohols and fatty acid esters remaining in a solid state act as adhesives, increasing the tackiness of the object to be bonded. It is also thought that they enhance the bonding between copper powders and contribute to improving the stability of the coating film. Furthermore, by using aliphatic alcohols and fatty acid esters having 10 or more carbon atoms, it is possible to increase the bonding strength of the obtained bonded structure. This is because when aliphatic alcohols and fatty acid esters having 10 or more carbon atoms are used, they are adsorbed onto the surface of the copper particles, preventing aggregation between copper particles in the paste composition and maintaining a good dispersion state of the paste. This smooths the surface where the paste composition and the object to be bonded come into contact, allowing more copper particles to come into contact with the object. Therefore, it is presumed that bonding occurs at more contact points during the bonding process, resulting in higher bonding strength.

[0054] In contrast, compositions that do not contain aliphatic alcohols and fatty acid esters may have difficulty in achieving improved tackiness and bonding strength. When organic components other than aliphatic alcohols and fatty acid esters are used, not only tackiness and bonding strength but also paste properties such as applicability may decrease. For example, when organic components with strong acidity are used, copper powder tends to aggregate in the composition, making it difficult to obtain a composition with excellent paste properties. Furthermore, even if a composition contains aliphatic alcohols and fatty acid esters, if their carbon number is less than 10, it may still cause problems in terms of tackiness, bonding strength, and / or paste properties.

[0055] The number of carbon atoms in the organic components (aliphatic alcohols and fatty acid esters) contained in the paste composition is not particularly limited, as long as it is 10 or more. However, generally, organic components with a large number of carbon atoms have high melting and boiling points. Compositions containing organic components with an excessively large number of carbon atoms may result in a large amount of organic components remaining in the coating film and bonding layer (bonding area) formed therefrom, which may lead to bonding failure. From the viewpoint of further improving tackiness and bonding strength and suppressing the occurrence of problems such as bonding failure, the number of carbon atoms in the organic components (aliphatic alcohols and / or fatty acid esters) is preferably 12 to 30, and more preferably 15 to 27. Furthermore, the organic components (aliphatic alcohols and / or fatty acid esters) are preferably in a solid state at 25°C and 1 atm, and their melting point (at 1 atm) is preferably 30°C or higher.

[0056] The paste composition may contain at least one of an aliphatic alcohol and a fatty acid ester. It may contain only one of the aliphatic alcohol and / or a fatty acid ester, or both. If the composition contains an aliphatic alcohol as an organic component, it is preferable that the organic component is at least one selected from the group consisting of 1-decanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, 12-hydroxystearyl alcohol, ricinoleyl alcohol, and oleyl alcohol. If the composition contains a fatty acid ester as an organic component, it is preferable that the organic component is at least one selected from the group consisting of glyceryl octanoate, glyceryl laurate, glyceryl decanoate, dibutyl sebacate, methyl laurate, methyl palmitate, methyl stearate, 12-hydroxystearate, methyl ricinoleate, and glyceryl stearate citrate. Furthermore, the composition may contain one organic component (aliphatic alcohol, fatty acid ester) alone, or a combination of multiple organic components.

[0057] The organic components included in the paste composition are not limited to the specific examples of aliphatic alcohols and fatty acid esters described above. When the composition contains an aliphatic alcohol as an organic component, the organic component (aliphatic alcohol) may be at least one selected from the group consisting of 1-pentadecanol, 1-heptadecanol, elaidyl alcohol, 1-eicosanol, 1-heneicosanol, behenyl alcohol, erucyl alcohol, lignoceryl alcohol, ceryl alcohol, 1-octacosanol, 1-triacontanol, etc. When the composition contains a fatty acid ester as an organic component, the organic component (fatty acid ester) may be at least one selected from the group consisting of myristyl myristate, stearyl stearate, sorbitan monostearate, sorbitan tristearate, sorbitan monopalmitate, succinate stearate monoglyceride, stearate monoglyceride, oleate monoglyceride, oleate diglyceride, etc. Furthermore, the composition may contain one organic component (aliphatic alcohol, fatty acid ester) alone, or it may contain a combination of multiple organic components.

[0058] In the paste composition of this embodiment, the content of organic components in the composition is 0.4% by mass or more and 10% by mass or less. If the content is less than 0.4% by mass, the effects based on the organic components will not be fully exhibited. As a result, there is a risk that the tackiness and bonding strength will decrease. If the content exceeds 10% by mass, a large amount of organic components will remain in the coating film or bonding layer (bonding area) formed from the composition, which may lead to bonding failure. In addition, there is a risk that the viscosity of the composition will become so high that it will be difficult to form into a paste. From the viewpoint of further improving tackiness and bonding strength and suppressing the occurrence of problems such as bonding failure, the content of organic components in the composition is preferably 0.5% by mass or more and 7% by mass or less, and more preferably 0.7% by mass or more and 5% by mass or less.

[0059] [4] Other Components The paste composition may contain other components besides copper powder, solvent (glycol-based solvent), and additives (aliphatic alcohol, fatty acid ester), as long as it does not impair the effects of this embodiment. Examples of other components include reducing agents, binder components, surface tension modifiers, defoaming agents, and viscosity modifiers. More specifically, examples include terpene-based compositions such as isobornylcyclohexanol, fatty acid components, components such as bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane (Bis-Tris) which act as a reducing agent for copper particles, gelling agents to enhance thixotropy, and copper carboxylates to further enhance bonding strength. The amount of other components is preferably 15% by mass or less relative to the copper powder. The amount of other components may be 0% by mass. In particular, the composition may not substantially contain organic polymer components (binder resin). The composition of this embodiment makes it possible to obtain a bonded structure with improved tack between the coating film and the bonded object and high bonding strength by a simple method, even without containing other components.

[0060] The paste composition of this embodiment is a bonding composition. That is, it is used to create a bonded structure by joining a set of objects to be joined. This composition is particularly suitable for joining objects under pressure. In other words, the composition is preferably a pressure bonding composition.

[0061] The paste composition of this embodiment is characterized by containing a predetermined amount of a specific organic component in addition to copper powder, as well as a specific solvent. With such a composition, it is possible to improve the tackiness between the coating film and the object to be bonded, and to obtain a bonded structure with high bonding strength by a simple method.

[0062] <<2. Method for Manufacturing the Bonding Paste Composition>> The manufacturing method of the bonding paste composition of this embodiment is not limited as long as the above requirements are satisfied. However, preferably, it is manufactured by mixing copper powder, a solvent, an additive, and other components as needed. Copper powder can be manufactured by various methods such as wet reduction, atomization, and electrolytic reduction. Spherical particles are easily obtained when using wet reduction or atomization. Dendritic or columnar particles are easily obtained when using electrolytic reduction. Flake particles can be obtained by applying mechanical force to spherical particles and causing plastic deformation. When using copper powder containing fine primary copper powder and coarse secondary copper powder, the primary and secondary copper powders can be prepared separately and mixed. A glycol-based solvent is used as at least part of the solvent. At least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms is used as at least part of the additive. The amount of organic components is adjusted so that the organic component content in the composition is between 0.4% by mass and 10% by mass. Mixing can be carried out using a known mixing device such as a roll mill.

[0063] <<3. Method for Manufacturing a Joined Structure>> The method for manufacturing a joined structure according to this embodiment comprises the following steps: applying the above-described joining paste composition to one surface of the first object to be joined to form a wet film (coating step); removing at least a portion of the solvent from the wet film to obtain a coating film (solvent removal step); temporarily fixing the second object to be joined to the coating film by pressurizing to obtain a laminate in which the first object to be joined, the coating film, and the second object to be joined are stacked in this order (stacking step); and heating the laminate under pressurizing to sinter the copper powder in the coating film, thereby joining the first object to be joined and the second object to be joined via the joining layer formed thereby (joining step). The joined structure is formed by joining the first object to be joined and the second object to be joined via the joining layer. An example of the manufacturing process according to this embodiment is schematically shown in Figure 2.

[0064] <Joining Structure> The joining structure consists of a first object to be joined, a second object to be joined, and a joining layer placed between the first and second objects to be joined to join them. Here, the objects to be joined (first object to be joined, second object to be joined) are objects to be joined, and examples include conductive materials such as spacers and heat sinks made of various conductive metals such as gold, silver, or copper, metal wires, substrates having metal wires on their surface, or semiconductor elements (semiconductor chips). More specifically, examples include semiconductor elements such as power modules, oscillators, amplifiers, and LED modules, lead frames, ceramic substrates with metal plates attached, substrates for mounting semiconductor elements, metal wiring, block bodies, power supply members, heat sinks, water cooling plates, and metal clips. Furthermore, there are no limitations on the combination of the first object to be joined and the second object to be joined. The first object to be joined and the second object to be joined may be made of the same type of material, or they may be made of different types of materials.

[0065] Specific examples of bonding structures include, for instance, a semiconductor device in which a substrate for mounting a semiconductor element is used as the first object to be bonded, a semiconductor element is used as the second object to be bonded, and the two are bonded together with a sintered body of a paste composition. Other examples include a bonded body in which a heat sink is used as the first object to be bonded, a substrate for mounting a semiconductor element is used as the second object to be bonded, and the two are bonded together with a sintered body of a paste composition, or a bonded body in which a semiconductor element is used as the first object to be bonded, a metal clip is used as the second object to be bonded, and the two are bonded together with a sintered body of a paste composition.

[0066] <Coating Process> In the coating process, the paste composition is applied to one surface of the first workpiece to form a wet film. The coating can be performed by known means such as screen printing, dispense printing, gravure printing, offset printing, reverse coating method, or doctor blade method. The wet film may be applied to the entire surface of the first workpiece, or it may be applied discontinuously to a part of the surface. From the viewpoint of more reliably ensuring high bonding strength, the wet film may be applied not only to the first workpiece but also to one surface of the second workpiece.

[0067] From the viewpoint of increasing the strength of the bonding layer, it is preferable that the thickness of the wet film be relatively large. On the other hand, from the viewpoint of preventing cracking in the coating after solvent removal, it is preferable that the thickness of the wet film be relatively small. From the viewpoint of improving bonding strength and preventing coating cracking, the average thickness of the wet film is preferably 20 μm or more and 500 μm or less, more preferably 30 μm or more and 450 μm or less, and even more preferably 35 μm or more and 400 μm or less. Note that the above thickness refers to the thickness of the wet film when a wet film is formed only on the first object to be bonded, and the total thickness of both wet films when a wet film is formed on both the first object to be bonded and the second object to be bonded.

[0068] <Solvent Removal Process> In the solvent removal process, at least a portion of the solvent is removed from the wet film to obtain the coating. By removing a portion of the solvent and reducing the amount of solvent, the shape retention of the coating is improved, and as a result, deformation of the coating can be suppressed even when pressure is applied to the coating in the subsequent bonding process. Furthermore, if the coating to be used in the bonding process contains an excessive amount of solvent, pores may be formed during the heating process of bonding, which may reduce the strength of the bonded layer. By removing a portion of the solvent in advance, the problem of reduced bond strength can be prevented. Solvent removal can be carried out by means of natural drying utilizing solvent volatilization, hot air drying, infrared irradiation, hot plate drying, etc. However, it is preferable to heat dry the wet film in order to promote the volatilization removal of the solvent.

[0069] When heating and drying a wet film, it is desirable to adjust the heating temperature and heating time to fall within an appropriate range. By controlling the heating temperature and heating time, it is possible to prevent an excessive amount of solvent from remaining in the coating film, thereby improving the shape retention of the coating film and preventing a decrease in bonding strength due to pore formation.

[0070] From the viewpoint of achieving a good balance of tackiness, shape retention, and bonding strength, the heating and drying temperature is preferably 100°C to 200°C, more preferably 105°C to 190°C, even more preferably 110°C to 180°C, and particularly preferably 110°C to 160°C. From the same viewpoint, the heating time is preferably 10 minutes to 60 minutes, more preferably 15 minutes to 50 minutes, and even more preferably 20 minutes to 40 minutes. Heating can be carried out in an inert gas atmosphere such as nitrogen gas and argon gas, an atmospheric atmosphere, and a reduced pressure atmosphere.

[0071] <Lamination Process> In the lamination process (tack process), the second object to be bonded is temporarily fixed to the coating film by pressurization, thereby obtaining a laminate in which the first object to be bonded, the coating film, and the second object to be bonded are laminated in this order. The paste composition used in the manufacturing method of this embodiment has the effect of improving tackiness (adhesion). Therefore, by placing the second object to be bonded in contact with the coating film and applying a small amount of pressure, the second object to be bonded can be temporarily fixed to the coating film without causing displacement or detachment.

[0072] When applying pressure, it is preferable to apply pressure so that the second object to be joined is in close contact with the coating film. For example, pressure is applied from a direction perpendicular to the coating film surface. From the viewpoint of properly fixing the object temporarily and increasing the joint strength, it is preferable that the pressure be somewhat high. On the other hand, from the viewpoint of preventing the object from breaking, it is preferable that the pressure be somewhat low. The pressure is preferably 0.1 MPa to 5.0 MPa, more preferably 0.2 MPa to 4.5 MPa, and even more preferably 0.21 MPa to 4.4 MPa. The pressurizing time is preferably 0.01 seconds or more, and more preferably 0.1 seconds or more. There is no upper limit to the pressurizing time, but it can be, for example, 5 seconds or less.

[0073] Temporary fixing may be performed at room temperature or while heating. The heating temperature for the first workpiece and the coating film is preferably 15°C to 270°C, more preferably 18°C ​​to 260°C, and even more preferably 20°C to 250°C. The heating temperature for the second workpiece is preferably 15°C to 300°C, more preferably 18°C ​​to 250°C, and even more preferably 20°C to 200°C.

[0074] <Joining Process> In the joining process, the laminate is heated under pressure to sinter the copper powder in the coating, and the first object to be joined and the second object to be joined are joined via the joining layer formed thereby. The joining layer is composed of a sintered body in which the copper particles constituting the copper powder are firmly bonded, and therefore has high conductivity and strength. In this specification, "pressure" means applying force from outside the laminate. That is, it does not include the force generated by the weight of the laminate or the components constituting the laminate (first object to be joined, second object to be joined, etc.).

[0075] From the viewpoint of increasing the strength of the bonded layer, the heating temperature during bonding is preferably 180°C to 450°C, and more preferably 200°C to 400°C. From the same viewpoint, the heating time is preferably 1 minute to 30 minutes, and more preferably 2 minutes to 25 minutes. The pressure applied during bonding is preferably 1 MPa to 35 MPa, more preferably 2 MPa to 32 MPa, and even more preferably 3 MPa to 30 MPa. Bonding may be carried out, for example, in an atmospheric atmosphere, an inert gas atmosphere, or a reducing atmosphere, and is preferably carried out in an inert gas atmosphere or a reducing atmosphere.

[0076] A bonded structure can be obtained in this way. The bonded structure of this embodiment has high bonded layer strength. A bonded structure having such features is suitable for use in various electronic circuits, especially electronic circuits used in high-temperature environments, such as automotive electronic circuits and electronic circuits on which power devices are mounted.

[0077] <<4. Method for Temporarily Fixing the Joined Objects>> This embodiment also covers a method for temporarily fixing the first and second joined objects. This method comprises the following steps: applying the above-described bonding paste composition to one surface of the first joined object to form a wet film (coating step); removing at least a portion of the solvent from the wet film to obtain a coating film (solvent removal step); and temporarily fixing the first and second joined objects via the coating film by pressurizing (temporary fixing step). Details of the coating step, solvent removal step, and temporary fixing step are as described in the method for manufacturing the bonded structure.

[0078] According to the temporary fixing method of this embodiment, the tackiness between the coating film and the object to be joined can be improved. Furthermore, a joined structure with high bonding strength can be obtained using a simple method.

[0079] <<5. Bonding Structure>> This embodiment also applies to a bonding structure comprising a first bonded body, a second bonded body, and a bonding layer. In this bonding structure, the first bonded body and the second bonded body are bonded via a bonding layer. The bonding layer is composed of a copper sintered body, and a peak based on at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms is detected by gas chromatography-mass spectrometry (GC (MS) analysis). Note that "a peak is detected" means that a peak based on a predetermined organic component is observed in the gas chromatogram obtained by GC (MS) analysis. In other words, it means that the bonding layer contains a predetermined organic component.

[0080] Furthermore, GC (MS) analysis is performed by taking an analytical sample from near the center of the bonding layer (copper sintered body). That is, the joined bodies (first joined body, second joined body) are removed from the bonded structure to extract only the bonding layer, an analytical sample is taken from near the center of the obtained bonding layer, and the collected analytical sample is analyzed. Alternatively, the bonded structure may be processed to expose the cross-section, and the analysis may be performed near the center of the cross-section of the bonding layer. In addition to these, predetermined jigs may be used as the first joined body and the second joined body, respectively, and the bonding layer may be placed between these jigs. In this case, the jigs may be peeled off from the bonding layer, only the bonding layer may be taken, and the collected analytical sample may be analyzed. The analytical conditions may be those of the examples described later or similar conditions.

[0081] The bonded structure of this embodiment is characterized by high bonding strength because the bonding layer contains the specific organic components described above. Furthermore, the organic components described above are derived from the components contained in the bonding paste composition used in the manufacture of the bonded structure. By using a bonding paste composition containing the organic components described above, the bonding strength in the bonding layer of the resulting bonded structure is increased. This is because aliphatic alcohols and fatty acid esters with 10 or more carbon atoms maintain a good dispersion state in the paste.

[0082] The number of carbon atoms in the organic component (aliphatic alcohol or fatty acid ester) contained in the bonding layer is not particularly limited, as long as it is 10 or more. However, from the viewpoint of further increasing the bonding strength and suppressing problems such as bonding defects, the number of carbon atoms in the organic component (aliphatic alcohol and / or fatty acid ester) is preferably 12 to 30, and more preferably 15 to 27. Furthermore, the organic component (aliphatic alcohol and / or fatty acid ester) is preferably in a solid state at 25°C and 1 atmosphere, and its melting point (at 1 atmosphere) is preferably 30°C or higher.

[0083] If the bonding layer contains an aliphatic alcohol as an organic component, it is preferable that the organic component contains at least one aliphatic alcohol selected from the group consisting of 1-decanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, 12-hydroxystearyl alcohol, ricinoleyl alcohol, and oleyl alcohol. If the bonding layer contains a fatty acid ester as an organic component, it is preferable that the organic component contains at least one fatty acid ester selected from the group consisting of glyceryl octanoate, glyceryl laurate, glyceryl decanoate, dibutyl sebacate, methyl laurate, methyl palmitate, methyl stearate, methyl 12-hydroxystearate, methyl ricinoleate, and glyceryl stearate citrate, 12-hydroxyoctadecanoic acid, and methyl octadecenoate.

[0084] Preferably, the bonding layer has a mass loss rate of 0.1% to 5% by mass in the thermogravimetric measurement range of 40°C to 500°C. The mass loss in thermogravimetric measurement is mainly due to the decomposition and volatilization of organic components. If the mass loss rate is 0.1% by mass or more, the amount of organic components in the bonding layer is sufficient. Since the effects based on the organic components are fully exerted, the bonding strength is higher. Also, if the mass loss rate is 5% by mass or less, the excessive residue of organic components is suppressed. Therefore, it becomes possible to prevent the occurrence of bonding defects. From the viewpoint of improving bonding strength and preventing bonding defects, a mass loss rate of 0.3% to 3% by mass is more preferable, and 0.5% to 2.5% by mass is even more preferable.

[0085] Preferably, the thickness of the bonding layer is 5 μm or more and 200 μm or less. A thickness of 5 μm or more increases the bonding strength in the bonding layer. Also, a thickness of 200 μm or less makes it possible to prevent cracking of the coating film during the manufacturing of the bonded structure. From the viewpoint of improving bonding strength and preventing cracking of the coating film, the thickness of the bonding layer is preferably 10 μm or more and 150 μm or less, more preferably 15 μm or more and 50 μm or less.

[0086] The joint structure of this embodiment is characterized by the high joint strength of its joint layer. The joint strength is preferably 30 MPa or more, more preferably 35 MPa or more, even more preferably 40 MPa or more, and particularly preferably 45 MPa or more. There is no particular upper limit to the joint strength. Although not limited, it may be, for example, 60 MPa or less.

[0087] The method for manufacturing the bonded structure of this embodiment is not particularly limited. However, it is preferable that the structure is obtained by the manufacturing method described above, that is, the following steps: applying the above-described bonding paste composition to one surface of the first body to be bonded to form a wet film (coating step); removing at least a portion of the solvent from the wet film to obtain a coating film (solvent removal step); temporarily fixing the second body to be bonded to the coating film by pressurization to obtain a laminate in which the first body to be bonded, the coating film, and the second body to be bonded are stacked in this order (stacking step); and heating the laminate under pressurization to sinter the copper powder in the coating film, thereby joining the first body to be bonded and the second body to be bonded via the bonding layer formed thereby (bonding step).

[0088] The present invention will be described in more detail using the following examples. However, the present invention is not limited to the following examples.

[0089] [Example 1 (Example)] (1) Preparation of bonding paste composition As copper powder, a mixture of copper powder consisting of spherical copper particles with an average particle size (D50) of 0.16 μm (spherical copper powder) and copper powder consisting of flat copper particles with an average particle size (D50) of 4.5 μm (flat copper powder) was prepared in a mass ratio of spherical copper powder:flat copper powder = 70:30. In addition, hexylene glycol was prepared as the solvent and myristyl alcohol was prepared as an additive. Myristyl alcohol is a C14 aliphatic alcohol that is solid at 25°C and 1 atm, as shown in Table 1 below.

[0090] Next, copper powder (spherical copper powder and flattened copper powder), solvent (hexylene glycol), and additive (myristyl alcohol) were weighed in the proportions shown in Table 2 below. The weighed raw materials (copper powder, solvent, and additive) were then mixed, and the resulting mixture was pre-kneaded with a spatula before being pasteurized using a rotating / revolving vacuum mixer (Sinky Co., Ltd., ARE-500). During pasteurization, two cycles were performed, each consisting of a stirring mode (1000 rpm x 1 minute) and a defoaming mode (2000 rpm x 30 seconds). Next, the resulting paste was dispersed and mixed using a three-roll mill to prepare a bonding paste composition.

[0091] (2) Fabrication of the bonded structure A substrate (20 mm x 20 mm, 2 mm thick) made by laminating copper and ceramics in the thickness direction was prepared as the first object to be bonded. A bonding paste composition was printed onto the copper side of this substrate using a metal mask (6 mm x 6 mm, 100 μm thick) to form a rectangular wet film (coating step). The wet film was then oxygenated (O ２ The coating film was obtained by drying in a nitrogen atmosphere with a concentration of 3% or less at 120°C for 30 minutes to partially remove the solvent (solvent removal step).

[0092] As the second substrate to be bonded, a model component of a semiconductor power device was assumed, and an Ag-plated SiC chip (5 mm x 5 mm x 0.2 mm) was prepared. Next, the SiC chip was adsorbed onto an adsorption collet heated to 170°C in a chip mounter. Then, while maintaining that temperature (170°C), the SiC chip was placed in the center of the coating film so that the Ag-plated surface was in contact with the coating film, and at the same time, the SiC chip was pressed into the coating film. During pressing, a force of 6 kgf (equivalent to a pressure of approximately 2.4 MPa) was applied to the side of the SiC chip opposite the Ag side for 0.5 seconds. In this way, the SiC chip was temporarily fixed to the coating film, and a laminate was fabricated (lamination process).

[0093] Next, the obtained laminate was transported to a firing furnace, pressurized to 25 MPa under a nitrogen atmosphere, heated to 270°C, and held at that temperature (270°C) for 5 minutes to fire the coating film and form a bonding layer, thereby obtaining a bonded structure (bonding process).

[0094] [Example 2 (Example)] In Example 2, octylene glycol was used as the solvent and myristyl alcohol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (myristyl alcohol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0095] [Example 3 (Example)] In Example 3, hexylene glycol was used as the solvent and palmityl alcohol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (hexylene glycol), and additive (palmityl alcohol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Palmityl alcohol is a C16 aliphatic alcohol that is solid at 25°C and 1 atm, as shown in Table 1 below.

[0096] [Example 4 (Example)] In Example 4, octylene glycol was used as the solvent and glyceryl stearate citrate was used as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (glyceryl stearate citrate) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Glyceryl stearate citrate is a C27 ​​fatty acid ester that becomes solid at 25°C and 1 atm, as shown in Table 1 below.

[0097] [Example 5 (Example)] In Example 5, hexylene glycol was used as the solvent and methyl stearate was used as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (hexylene glycol), and additive (methyl stearate) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Methyl stearate is a C19 fatty acid ester that becomes solid at 25°C and 1 atm, as shown in Table 1 below.

[0098] [Example 6 (Example)] In Example 6, octylene glycol was used as the solvent and methyl 12-hydroxystearate was used as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (methyl 12-hydroxystearate) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Methyl 12-hydroxystearate is a C19 fatty acid ester that becomes solid at 25°C and 1 atm, as shown in Table 1 below.

[0099] [Example 7 (Example)] In Example 7, octylene glycol was used as the solvent and glyceryl laurate was used as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (glyceryl laurate) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Glyceryl laurate is a C15 fatty acid ester that becomes solid at 25°C and 1 atm, as shown in Table 1 below.

[0100] [Example 8 (Comparative Example)] In Example 8, hexylene glycol was used as the solvent, but no additives were added to the paste composition. Also, copper powder (spherical copper powder and flattened copper powder) and solvent (hexylene glycol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0101] [Example 9 (Comparative Example)] In Example 9, octylene glycol was used as the solvent, but no additives were added to the paste composition. Also, copper powder (spherical copper powder and flattened copper powder) and solvent (octylene glycol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0102] [Example 10 (Comparative Example)] In Example 10, hexylene glycol was used as the solvent and ethylene glycol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (hexylene glycol), and additive (ethylene glycol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Ethylene glycol is a carbon-2 alcohol that becomes liquid at 25°C and 1 atmosphere, as shown in Table 1 below.

[0103] [Example 11 (Comparative Example)] In Example 11, octylene glycol was used as the solvent and octanol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (octanol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1. Octanol is a carbon-8 aliphatic alcohol that is liquid at 25°C and 1 atmosphere, as shown in Table 1 below.

[0104] [Example 12 (Comparative Example)] In Example 12, hexylene glycol was used as the solvent and octanol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (hexylene glycol), and additive (octanol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0105] [Example 13 (Comparative Example)] In Example 13, hexylene glycol was used as the solvent and myristyl alcohol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (hexylene glycol), and additive (myristyl alcohol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0106] [Example 14 (Example)] In Example 14, octylene glycol was used as the solvent and palmityl alcohol as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (palmityl alcohol) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0107] [Example 15 (Example)] In Example 15, octylene glycol was used as the solvent and glyceryl stearate citrate was used as the additive. Copper powder (spherical copper powder and flattened copper powder), solvent (octylene glycol), and additive (glyceryl stearate citrate) were weighed in the proportions shown in Table 2 below. Otherwise, the bonding paste composition and bonding structure were prepared using the same procedure as in Example 1.

[0108]

[0109]

[0110] (3) The samples obtained in Evaluation Examples 1 to 15 were evaluated for various characteristics as follows.

[0111] <Tack Strength> The tack strength of the laminates obtained in the lamination process was evaluated. Specifically, the tack strength was measured for five laminates made from the same paste composition, and the minimum, maximum, and average values ​​were determined. Tack strength (kPa) is defined as: breaking load (N) / bottom area (mm²) of the SiC chip. ２ This is the value defined by ). The measurement was performed under the following conditions.

[0112] - Measuring device: Condor Sigma, XYZTEC - Load cell: 10 kgf - Shear tool: 6.0 mm width, 2.0 mm thickness, 1 / 4 inch shaft (model number TOS 663060) - Shear speed: 10 μm / sec - Shear height: 0.02 mm (The zero point was defined as a 6 mm square printed coating area.)

[0113] Furthermore, based on the obtained tack strength (average value), the samples were graded according to the following criteria.

[0114] ○ (Pass): Tack strength of 4.0 kPa or higher × (Fail): Tack strength of less than 4.0 kPa

[0115] <Bonding Strength> To confirm the bonding strength, the shear strength of the bonded structures was measured. Specifically, the shear strength was measured for five bonded structures made from the same paste composition, and the minimum, maximum, and average values ​​were determined. Shear strength (MPa) is calculated as: Breaking load (N) / Bottom area (mm²) of the SiC chip. ２ This is the value defined by ). The measurement was performed under the following conditions.

[0116] - Measuring device: Condor Sigma, manufactured by XYZTEC - Load cell: 200 kgf - Shear tool: 6.0 mm wide, 2.0 mm thick, 1 / 4 inch shaft (model number TOS663060) - Shear speed: 50 μm / sec - Shear height: 0.02 mm (The zero point was defined as a 6 mm square printed coating area.)

[0117] Furthermore, based on the obtained joint strength (average value of shear strength), the samples were graded according to the following criteria.

[0118] ○ (Pass): Joint strength of 30 MPa or higher × (Fail): Joint strength of less than 30 MPa

[0119] <GC (MS) Analysis> (1) Preparation of Analysis Samples A copper substrate (20 mm x 20 mm, 2 mm thick) plated with Al was prepared as the first substrate to be bonded. On the copper side of this substrate, a bonding paste composition (Examples 3, 5, 6, Comparative Example 13) was printed using a metal mask (6 mm x 6 mm, 100 μm thick) to form a rectangular wet film (coating step). The wet film was then subjected to oxygen (O ２ The coating film was obtained by drying in a nitrogen atmosphere with a concentration of 3% or less at 120°C for 30 minutes to partially remove the solvent (solvent removal step).

[0120] Next, an Al block (6 mm × 6 mm × 4.5 mm) was prepared as the second substrate to be bonded, assuming a model component of a semiconductor power device. This was laminated onto the dried coating of the first substrate to obtain a laminate.

[0121] The resulting laminate was transported to a firing furnace, pressurized to 25 MPa under a nitrogen atmosphere, heated to 270°C, and held at that temperature (270°C) for 5 minutes to sinter the coating film to form a bonding layer and obtain a sintered film.

[0122] (2) Analytical method The central portion of the obtained sintered body (sintered film) was taken and gas chromatography-mass spectrometry (GC (MS) analysis) was performed. The GC (MS) analysis was performed according to the following procedure.

[0123] In this embodiment, the bonded structure exhibits a peak based on at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms, as detected by gas chromatography-mass spectrometry under the following measurement conditions. The lower limit of the detected peak height is not particularly limited and may be above the detection limit.

[0124] [Analytical Instruments] - Gas chromatograph-mass spectrometer: JMS-Q1500GC (JEOL Ltd.) - Pyrolysis sample introduction device: PY-3030D (Frontier Lab Co., Ltd.)

[0125] [Gas Chromatography Conditions] - Carrier gas: He 1.5 mL / min - Column: Ultra ALLOY ±5 (0.25 mm I.D. x 30 m, df 0.25 μm) - Heating desorption temperature: 350 °C - Gas chromatograph inlet temperature: 300 °C - Split ratio: 20:1 - Column oven temperature: The heating conditions are shown in Table 3 below.

[0126]

[0127] [Mass Spectrometry Conditions] - Ionization Method: Electron Ionization - Mass Spectrometer Interface Temperature: 250°C - Scan Range: m / z 28–500 - Sample Weight: 0.05–2.5 mg

[0128] Furthermore, based on the analysis results obtained, the samples were graded according to the following criteria.

[0129] ○ (Pass): A peak based on at least one organic component selected from the group consisting of aliphatic alcohols with 10 or more carbon atoms and fatty acid esters with 10 or more carbon atoms is detected in the gas chromatogram. × (Fail): No peak based on the above organic component is detected.

[0130] <Thermogravimetric Analysis> A sintered body (sintered film) was obtained using the same method as for GC (MS). Next, thermogravimetric analysis was performed using this sintered body as the measurement sample. During the measurement, the measurement sample set in the measuring apparatus was heated from 25°C (room temperature) to 40°C at a rate of 2°C / min under a nitrogen atmosphere, held at that temperature (40°C) for 20 minutes, and then heated to 500°C at a rate of 10°C / min. The measurement conditions were as follows.

[0131] - Measuring device: TG-DTA: TG-GTA8122 (Rigaku Corporation) - Sample mass: 7 mg

[0132] Based on the obtained measurement results, the mass loss rate in the temperature range of 40°C to 500°C was determined.

[0133] (4) Evaluation Results The evaluation results obtained for the samples from Example 1 to Example 15 are summarized in Table 4 below.

[0134] As shown in Table 3, in the example samples (Examples 1 to 7, 14 and 15) which contained a glycol-based solvent as a solvent and also contained 0.4% by mass or more of an aliphatic alcohol or fatty acid ester having 10 or more carbon atoms, both the tack strength and bonding strength were relatively high (tack strength: 4.0 kPa or higher, bonding strength: 30 MPa or higher).

[0135] In contrast, comparative examples (Examples 8-10) that did not contain either aliphatic alcohols or fatty acid esters showed relatively low bonding strength (less than 30 MPa). Comparative examples (Examples 11 and 12) that contained aliphatic alcohols but had fewer than 10 carbon atoms also showed relatively low bonding strength (less than 30 MPa). Furthermore, comparative example (Example 13) that contained aliphatic alcohols with 10 or more carbon atoms but had a content of less than 0.4% by mass showed relatively low tack strength (less than 4.0 kPa).

[0136]

[0137] Table 5 below shows the GC (MS) analysis results (presence or absence of organic component detection) obtained for the bonding layers of the samples in Examples 3, 5, 6, and 13, as well as the mass reduction rate of the bonding layer of the sample in Example 3. Figures 3 to 5 show the GC (MS) analysis results (gas chromatograms) obtained for the bonding layers of the bonding structures in Examples 3, 5, and 6, respectively.

[0138] In the bonding layers of the example samples (Examples 3, 5, and 6), peaks of the same organic components (palmityl alcohol (Example 3), methyl stearate (Example 5), and methyl 12-hydroxystearate (Example 6)) as those contained in the bonding paste composition were detected. In contrast, no peaks of organic components were detected in the bonding layer of the comparative example sample (Example 13).

[0139]

[0140] From the results described above, it is understood that this embodiment provides a bonding paste composition that improves the tackiness between the coating film and the object to be bonded, and allows for the acquisition of a bonded structure with high bonding strength by a simple method.

Claims

1. A bonding paste composition comprising copper powder, a solvent, and an additive, wherein the solvent comprises a glycol-based solvent, the additive comprises at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms, and the content of the organic component in the bonding paste composition is 0.4% by mass or more and 10% by mass or less.

2. The bonding paste composition according to claim 1, wherein the content of copper powder in the bonding paste composition is 60% by mass or more and 85% by mass or less.

3. The bonding paste composition according to claim 1 or 2, wherein the content of the solvent in the bonding paste composition is 15% by mass or more and 40% by mass or less.

4. The bonding paste composition according to claim 1 or 2, wherein the boiling point of the glycol-based solvent is 160°C or higher and 290°C or lower.

5. The bonding paste composition according to claim 1 or 2, wherein the content of the organic component in the bonding paste composition is 0.5% by mass or more and 7% by mass or less.

6. The bonding paste composition according to claim 1 or 2, wherein the number of carbon atoms in the organic component is 12 or more and 30 or less.

7. The bonding paste composition according to claim 1 or 2, wherein the organic component comprises at least one aliphatic alcohol selected from the group consisting of 1-decanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, 12-hydroxystearyl alcohol, ricinoleyl alcohol, and oleyl alcohol.

8. The bonding paste composition according to claim 1 or 2, wherein the organic component comprises at least one fatty acid ester selected from the group consisting of glyceryl octanoate, glyceryl laurate, glyceryl decanoate, dibutyl sebacate, methyl laurate, methyl palmitate, methyl stearate, methyl 12-hydroxystearate, methyl ricinoleate, and glyceryl stearate citrate.

9. A method for manufacturing a bonded structure in which a first body to be bonded and a second body to be bonded are bonded via a bonding layer, comprising the steps of: applying a bonding paste composition according to claim 1 or 2 to one surface of the first body to be bonded to form a wet film; removing at least a portion of the solvent from the wet film to obtain a coating film; temporarily fixing the second body to be bonded to the coating film by pressurization to obtain a laminate in which the first body to be bonded, the coating film, and the second body to be bonded are stacked in this order; and heating the laminate under pressurization to sinter the copper powder in the coating film, thereby bonding the first body to be bonded and the second body to be bonded via the bonding layer formed thereby.

10. A method for temporarily fixing a first object to be joined and a second object to be joined, comprising the steps of: applying a bonding paste composition according to claim 1 or 2 to one surface of the first object to be joined to form a wet film; removing at least a portion of the solvent from the wet film to obtain a coating film; and temporarily fixing the second object to be joined to the coating film by pressurization.

11. A bonding structure in which a first bonded body and a second bonded body are bonded via a bonding layer, wherein the bonding layer is composed of a copper sintered body, and a peak based on at least one organic component selected from the group consisting of aliphatic alcohols having 10 or more carbon atoms and fatty acid esters having 10 or more carbon atoms is detected by gas chromatography-mass spectrometry (GC(MS) analysis).

12. The bonding structure according to claim 11, wherein the bonding layer has a mass loss rate of 0.1% by mass or more and 5% by mass or less in the temperature range of 40°C to 500°C as measured by thermogravimetric analysis.

13. The bonding structure according to claim 11 or 12, wherein the organic component comprises at least one aliphatic alcohol selected from the group consisting of 1-decanol, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, 12-hydroxystearyl alcohol, ricinoleyl alcohol, and oleyl alcohol.

14. The bonding structure according to claim 11 or 12, wherein the organic component comprises at least one fatty acid ester selected from the group consisting of glyceryl octanoate, glyceryl laurate, glyceryl decanoate, dibutyl sebacate, methyl laurate, methyl palmitate, methyl stearate, methyl 12-hydroxystearate, methyl ricinoleate, and glyceryl stearate citrate, 12-hydroxyoctadecanoate, and methyl octadecenoate.

15. The bonding structure according to claim 11 or 12, wherein the thickness of the bonding layer is 5 μm or more and 200 μm or less.

16. The bonding structure according to claim 11 or 12, wherein the bonding strength in the bonding layer is 30 MPa or more.

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