JP2021174968A - Double-sided cooled semiconductor module, double-sided cooled semiconductor device and method for manufacturing double-sided cooled semiconductor module - Google Patents

Abstract

To provide a double-sided cooled semiconductor module with excellent reliability, a double-sided cooled semiconductor device, and a method for manufacturing a double-sided cooled semiconductor module.SOLUTION: A double-sided cooled semiconductor module 100 has a semiconductor device 1, a first substrate 11a provided on one main side of the semiconductor device, a second substrate 11b provided on the other main side of the semiconductor device, a first junction 2 consisting of a copper sintered body 31 that joins the semiconductor device and the first substrate, and a second junction 4 consisting of a copper sintered body 31 and a spacer 41 that joins the semiconductor device and the second substrate.SELECTED DRAWING: Figure 1

Description

The present invention relates to a double-sided cooling type semiconductor module, a double-sided cooling type semiconductor device, and a method for manufacturing a double-sided cooling type semiconductor module.

As a semiconductor device used for an inverter or the like, a semiconductor device including a semiconductor module and a cold heat source has been proposed. A substrate for energizing a semiconductor element is arranged inside the semiconductor module, and the semiconductor module is joined via a joining portion formed of a joining material or the like. The substrate and the cold heat source are joined by abutting or a joining material, and the heat generated from the semiconductor element at the time of energization is dissipated toward the cold heat source via the substrate.

In recent years, due to demands for miniaturization, high density, and high temperature operation of semiconductor devices, the current flowing through a substrate and a joint to be energized has increased, and the amount of heat generated by the semiconductor element has increased. Therefore, a double-sided cooling type semiconductor module and a semiconductor device in which substrates are arranged on both sides of a semiconductor element and a cooling heat source is connected to each substrate have been proposed (see, for example, Patent Document 1 below).

JP-A-2017-28040

Due to the recent increase in demand for high-temperature operation of semiconductor devices, the maximum temperature of semiconductor elements has risen, making it difficult to ensure reliability with conventional double-sided cooling semiconductor modules.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a double-sided cooling type semiconductor module, a double-sided cooling type semiconductor device, and a method for manufacturing a double-sided cooling type semiconductor module having excellent reliability.

In order to solve the above problems, one aspect of the present invention is a semiconductor element, a first substrate provided on one main surface side of the semiconductor element, and a second substrate provided on the other main surface side of the semiconductor element. The substrate, the first junction for joining the semiconductor element and the first substrate, and the second junction for joining the semiconductor element and the second substrate are provided, and the first junction and the first junction are provided. Provided is a double-sided cooled semiconductor module in which at least one of the joints of two contains a copper sintered body.

In the above-mentioned double-sided cooling type semiconductor module, since the joint portion contains the copper sintered body, the reliability of the joint portion with respect to the temperature cycle and the joint life can be improved. Further, since the joint portion contains the copper sintered body, it is possible to prevent the joint portion from causing an increase in thermal resistance and deteriorating the heat dissipation property in the heat dissipation path from the semiconductor element to the substrate. The generated heat can be efficiently dissipated to the cold heat source via the substrate. Therefore, the above-mentioned double-sided cooling type semiconductor module can have excellent reliability.

The double-sided cooling type semiconductor module may have two or more semiconductor elements.

By the way, in a double-sided cooling type semiconductor module, when a plurality of semiconductor elements having different heights are mounted, it is necessary to adjust the height by sandwiching a spacer between at least one semiconductor element and at least one substrate. Therefore, the accuracy required for each part in the height direction becomes strict. Further, if the position of the bonding surface of the semiconductor element with the substrate or the distance between the substrates varies due to the variation in the height of each semiconductor element, the surface pressure distribution becomes uneven when the substrate and the semiconductor element are sandwiched at the time of bonding. Since it occurs, the bondability tends to deteriorate. On the other hand, in the double-sided cooling type semiconductor module according to the present invention, since the joint portion contains the copper sintered body, the position (height) of the joint surface can be set even if the height of the semiconductor element varies. It is easy to adjust, and it may be easy to suppress an increase in manufacturing cost due to additional processing such as sorting work of semiconductor elements and processing for adjusting the position (height) of the joint surface.

The copper sintered body may be a sintered body of a bonding material containing copper particles.

In the double-sided cooling type semiconductor module, one or more of the first joint portion and the second joint portion may include a spacer.

Another aspect of the present invention is the double-sided cooling semiconductor module according to the present invention, and the first cold heat source and the first cold heat source connected to the first substrate and the second substrate of the double-sided cooling semiconductor module, respectively. Provided is a double-sided cooling type semiconductor device including the two cold heat sources.

By providing the double-sided cooling type semiconductor module according to the present invention, the above-mentioned double-sided cooling type semiconductor device is excellent in reliability and can be operated at a high temperature.

Another aspect of the present invention is the method for manufacturing a double-sided cooling semiconductor module according to the present invention, in which a bonding material containing copper particles provided between a first substrate and a semiconductor element is sintered. A method for manufacturing a double-sided cooled semiconductor module, comprising a first joining step of sintering and / or a second joining step of sintering a bonding material containing copper particles provided between a second substrate and a semiconductor element. I will provide a. When the first joining step and the second joining step are provided, the first joining step and the second joining step may be performed in this order, in the reverse order, or at the same time.

According to the above-mentioned manufacturing method of the double-sided cooling type semiconductor module, by providing the above-mentioned first joining step and / or the above-mentioned second joining step, even if the height of the semiconductor element varies, the joining surface It becomes easy to adjust the position (height) of the semiconductor element, and it is possible to suppress an increase in manufacturing cost due to additional processing such as sorting work of semiconductor elements and processing for adjusting the position (height) of the joint surface. ..

According to the present invention, it is possible to provide a double-sided cooling type semiconductor module, a double-sided cooling type semiconductor device, and a method for manufacturing a double-sided cooling type semiconductor module having excellent reliability.

The double-sided cooling type semiconductor module and the double-sided cooling type semiconductor device according to the present invention can operate in a high temperature environment where the semiconductor element temperature is 175 ° C. or higher, which is difficult in solder bonding. Further, the double-sided cooling type semiconductor module and the double-sided cooling type semiconductor device according to the present invention can have a long life and a small variation in failure timing. According to the method for manufacturing a double-sided cooling type semiconductor module according to the present invention, it is possible to obtain the above-mentioned double-sided cooling type semiconductor module and double-sided cooling type semiconductor device.

It is a schematic cross-sectional view which shows one Embodiment of a double-sided cooling type semiconductor device. It is a schematic cross-sectional view which shows the other embodiment of the double-sided cooling type semiconductor device. It is a cross-sectional enlarged view of the joint part.

Unless otherwise specified, the materials exemplified in the present specification may be used alone or in combination of two or more. The content of each component in the bonding material means the total amount of the plurality of substances present in the bonding material when a plurality of substances corresponding to each component are present in the bonding material, unless otherwise specified. The numerical range indicated by using "~" indicates a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value of the numerical range of one step may be replaced with the upper limit value or the lower limit value of the numerical range of another step. Further, in the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. The term "layer" includes a structure having a shape formed on the entire surface and a structure having a shape formed on a part of the structure when observed as a plan view.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

<Double-sided cooling type semiconductor module and double-sided cooling type semiconductor device>
The double-sided cooling type semiconductor module of the present embodiment includes a semiconductor element, a first substrate provided on one main surface side of the semiconductor element, and a second substrate provided on the other main surface side of the semiconductor element. A first junction for joining the semiconductor element and the first substrate, and a second junction for joining the semiconductor element and the second substrate are provided, and the first junction and the second junction are provided. At least one of the portions contains a copper sintered body.

The double-sided cooling type semiconductor module may have two or more semiconductor elements. Further, one or more of the first joint portion and the second joint portion may include a spacer.

The double-sided cooling semiconductor device of the present embodiment is a first substrate connected to the double-sided cooling semiconductor module according to the present embodiment and the first substrate and the second substrate of the double-sided cooling semiconductor module. It includes a cold heat source and a second cold heat source.

The double-sided cooling type refers to a type in which the direction of heat flow is directed from the semiconductor element to each of the substrates arranged on both main surfaces of the semiconductor element.

Hereinafter, the present embodiment will be described with reference to the drawings.

(1) First Embodiment FIG. 1 is a schematic cross-sectional view showing an embodiment of a double-sided cooling type semiconductor device. The double-sided cooling type semiconductor device 101 shown in FIG. 1 is provided on the semiconductor element 1, the first substrate 11a provided on one main surface side of the semiconductor element 1, and the other main surface side of the semiconductor element. The second substrate 11b, the first junction 2 for joining the semiconductor element 1 and the first substrate 11a, and the second junction 4 for joining the semiconductor element 1 and the second substrate 11b are formed. It includes a double-sided cooling type semiconductor module 100, and a first cold heat source 21 and a second cold heat source 22 connected to the first substrate 11a and the second substrate 11b, respectively. In the double-sided cooling type semiconductor module 100 of the present embodiment, the first joint portion 2 is composed of a copper sintered body 31, and the second joint portion 4 is composed of a copper sintered body 31 and a spacer 41. The semiconductor element 1 is sealed by the resin member 61.

The semiconductor element 1 is configured as a power element such as a boost converter, a diode constituting an inverter or the like, an IGBT, or a MOSFET.

The resin member 61 that seals the semiconductor element 1 can be formed of a synthetic resin such as an epoxy resin.

Examples of the materials of the substrates 11a and 11b include copper, aluminum, nickel, molybdenum, titanium, stainless steel, gold, silver, platinum and the like from the viewpoint of thermal conductivity and conductivity. Further, depending on the substrate configuration, it is preferable that an insulating material having good thermal conductivity and heat resistance, such as ceramic, is formed inside the conductive substrate. The substrate may have a substrate bonded to the semiconductor element and a substrate extending outward, or may have an electric circuit formed by a wire 51 connecting these substrates. Examples of the material of the wire 51 include aluminum, copper, and gold. The wire diameter of the wire 51 is preferably φ0.04 to 0.4 mm. Busbars or clips may be applied instead of wires.

In the substrates 11a and 11b, it is preferable to provide a metallized layer on the joint surface with the joint portions 2 and 4. Examples of the material of the metallized layer include nickel, gold, silver, titanium, tungsten, molybdenum and the like. The metallized layer can be formed by, for example, a method such as plating, sputtering, or vapor deposition. The thickness of the metallized layer can be 0.05 μm to 500 μm.

When the insulating layers are provided on the substrates 11a and 11b, it is preferable that the coefficient of thermal expansion of the substrate is equal to or close to that of the semiconductor element 1. The coefficient of thermal expansion of the substrate may be, for example, 3.0 × ^{10-6 to} 9.0 × ^10-6 / K.

The copper sintered body 31 may be a sintered body of a bonding material (copper paste) containing copper particles. Details of the bonding material (copper paste) will be described later.

The spacer 41 can be provided as necessary for adjusting the height of the double-sided cooling type semiconductor module 100 or the double-sided cooling type semiconductor device 101. In the present embodiment, the spacer is provided at the second joint portion 4, but it may be provided at the first joint portion. Further, a plurality of spacers may be provided at each joint.

Examples of the material of the spacer 41 include copper, aluminum, nickel, molybdenum, titanium, stainless steel, gold, silver, platinum and the like from the viewpoint of thermal conductivity and conductivity.

In the spacer 41, it is preferable to provide a metallized layer on the joint surface with the copper sintered body 31. Examples of the material of the metallized layer include nickel, gold, silver, titanium, tungsten, molybdenum and the like. The metallized layer can be formed by, for example, a method such as plating, sputtering, or vapor deposition. The thickness of the metallized layer can be 0.05 μm to 500 μm.

The cold heat sources 21 and 22 are made of a material having good thermal conductivity, and known materials can be used. The cooling method of the cold heat source may be water cooling, air cooling, or Perche. From the viewpoint of cooling performance, the water cooling method is preferable.

The cold heat sources 21 and 22 and the substrates 11a and 11b may be in contact with each other, or may be joined by a joining material such as a solder, a sintered material, or a brazing material. When the substrates 11a and 11b do not have an insulating layer, it is preferable that an insulating layer is provided between the cold heat sources 21 and 22 and the substrates 11a and 11b.

(2) Second Embodiment FIG. 2 is a schematic cross-sectional view showing another embodiment of a double-sided cooling type semiconductor device. The double-sided cooling semiconductor device 101 shown in FIG. 2 has the same configuration as that in the first embodiment of the double-sided cooling semiconductor device, except that a plurality of semiconductor elements are provided.

In the double-sided cooling type semiconductor device according to the second embodiment, the height (length in the current direction) of the semiconductor element may vary (height difference or length difference).

<Manufacturing method of double-sided cooling type semiconductor module>
The double-sided cooling semiconductor module according to the present embodiment described above has a first bonding step of sintering a bonding material containing copper particles provided between a first substrate and a semiconductor element, and / or a second. It can be manufactured by a method including a second bonding step of sintering a bonding material containing copper particles provided between the substrate and the semiconductor element.

When the double-sided cooling type semiconductor module according to the first embodiment is manufactured, a bonding material is applied to the bonding position of the substrate 11a with the semiconductor element 1, and the coating film provided by drying as necessary is applied as necessary. The semiconductor element 1 is brought into contact with the semiconductor element 1 using a jig, the coating film (bonding layer) is fired (first bonding step), and a bonding material is applied to the bonding surface of the semiconductor element 1 with the spacer 41, which is necessary. If necessary, the spacer 41 is brought into contact with the coating film that has been dried and provided, and the bonding material is applied to the joint surface of the spacer 41 with the substrate, and if necessary, the spacer 41 is dried and provided. If necessary, the substrate 11b can be brought into contact with the coated coating film using a jig, and these coating films (bonding layers) can be fired (second bonding step). In the present embodiment, the firing of the coating film in the first joining step and the firing of the coating film in the second joining step may be performed at the same time.

As the bonding material, a copper paste containing copper particles and a dispersion medium can be used.

Examples of the copper particles include sub-micro copper particles and micro copper particles. The sub-micro copper particles refer to copper particles having a particle size of 0.01 μm or more and less than 1.00 μm. The micro copper particles refer to copper particles having a particle size of 1 μm or more and less than 50 μm.

The particle size of the copper particles can be determined by the following method. The particle size of the copper particles can be calculated from, for example, an SEM image. The powder of copper particles is placed on a carbon tape for SEM with a spatula to prepare a sample for SEM. This SEM sample is observed with an SEM device at a magnification of 5000. A quadrangle circumscribing the copper particles of this SEM image is drawn by image processing software, and one side thereof is used as the particle size of the particles.

(Sub-micro copper particles)
Examples of the sub-micro copper particles include copper particles having a particle size of 0.12 μm or more and 0.8 μm or less. For example, copper particles having a volume average particle size of 0.12 μm or more and 0.8 μm or less may be used. can. When the volume average particle size of the sub-micro copper particles is 0.12 μm or more, the effects of suppressing the synthesis cost of the sub-micro copper particles, good dispersibility, and suppressing the amount of the surface treatment agent used can be easily obtained. When the volume average particle size of the sub-micro copper particles is 0.8 μm or less, the effect of excellent sinterability of the sub-micro copper particles can be easily obtained. From the viewpoint of further exerting the above effect, the volume average particle size of the sub-micro copper particles may be 0.15 μm or more and 0.8 μm or less, 0.15 μm or more and 0.6 μm or less, and may be 0. It may be .2 μm or more and 0.5 μm or less, and may be 0.3 μm or more and 0.45 μm or less.

In the specification of the present application, the volume average particle diameter means a 50% volume average particle diameter. When determining the volume average particle size of copper particles, the particle size distribution is measured by the light scattering method, in which copper particles as a raw material or dried copper particles obtained by removing volatile components from a bonding material are dispersed in a dispersion medium using a dispersant. It can be obtained by a method of measuring with an apparatus (for example, a Shimadzu nanoparticle size distribution measuring apparatus (SALD-7500 nano, manufactured by Shimadzu Corporation)). When a light scattering particle size distribution measuring device is used, hexane, toluene, α-terpineol or the like can be used as the dispersion medium.

The sub-micro copper particles can contain 10% by mass or more of copper particles having a particle size of 0.12 μm or more and 0.8 μm or less. From the viewpoint of the sinterability of the bonding material, the sub-micro copper particles can contain 20% by mass or more of copper particles having a particle size of 0.12 μm or more and 0.8 μm or less, and can contain 30% by mass or more, 100. Can include% by mass. When the content ratio of the copper particles having a particle size of 0.12 μm or more and 0.8 μm or less in the sub-micro copper particles is 20% by mass or more, the dispersibility of the copper particles is further improved, the viscosity is increased, and the paste concentration is decreased. It can be more suppressed.

The content of the sub-micro copper particles may be 20% by mass or more and 90% by mass or less, or 30% by mass or more and 90% by mass or less, based on the total mass of the metal particles contained in the bonding material. , 35% by mass or more and 85% by mass or less, or 40% by mass or more and 80% by mass or less. When the content of the sub-micro copper particles is within the above range, it becomes easy to form the joint portion according to the above-described embodiment.

When the bonding material of the present embodiment contains sub-micro copper particles and flake-shaped micro copper particles as copper particles, the content of the sub-micro copper particles is the mass of the sub-micro copper particles and the flake-shaped micro copper particles. Based on the total mass, it may be 20% by mass or more and 90% by mass or less. When the content of the sub-micro copper particles is 20% by mass or more, the space between the flake-shaped micro copper particles can be sufficiently filled, and the joint portion according to the present embodiment described above can be easily formed. .. When the content of the sub-micro copper particles is 90% by mass or less, the volume shrinkage when the bonding material is sintered can be sufficiently suppressed, so that it is easy to form the bonding portion according to the present embodiment described above. Become. From the viewpoint of further exerting the above effect, the content of the sub-micro copper particles is 30% by mass or more and 85% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the flake-shaped micro copper particles. It may be 35% by mass or more and 85% by mass or less, or 40% by mass or more and 80% by mass or less.

The shape of the sub-micro copper particles is not particularly limited. Examples of the shape of the sub-micro copper particles include a spherical shape, a lump shape, a needle shape, a flake shape, a substantially spherical shape, and an aggregate thereof. From the viewpoint of dispersibility and filling property, the shape of the submicro copper particles may be spherical, substantially spherical, or flake-shaped, and from the viewpoint of flammability, dispersibility, mixing with flake-shaped microparticles, and the like, the shape of the submicro copper particles may be spherical. Alternatively, it may be substantially spherical.

The sub-micro copper particles may have an aspect ratio of 5 or less or 3 or less from the viewpoint of dispersibility, filling property, and mixing property with flake-shaped micro particles. As used herein, the "aspect ratio" refers to the long side / thickness of the particles. The measurement of the long side and the thickness of the particle can be obtained from, for example, an SEM image of the particle.

The submicro copper particles may be treated with a specific surface treatment agent. Specific surface treatment agents include, for example, organic acids having 8 to 16 carbon atoms. Examples of organic acids having 8 to 16 carbon atoms include capric acid, methylheptanic acid, ethylhexanoic acid, propylpentanoic acid, pelargonic acid, methyloctanoic acid, ethylheptanoic acid, propylhexanoic acid, capric acid, methylnonanoic acid and ethyl. Octanoic acid, propylheptanic acid, butylhexanoic acid, undecanoic acid, methyldecanoic acid, ethylnonanoic acid, propyloctanoic acid, butylheptanic acid, lauric acid, methylundecanoic acid, ethyldecanoic acid, propylnonanoic acid, butyloctanoic acid, pentylheptanic acid, Tridecanoic acid, methyldodecanoic acid, ethylundecanoic acid, propyldecanoic acid, butylnonanoic acid, pentyloctanoic acid, myristic acid, methyltridecanoic acid, ethyldodecanoic acid, propylundecanoic acid, butyldecanoic acid, pentylnonanoic acid, hexyloctanoic acid, pentadecanoic acid , Methyltetradecanoic acid, ethyltridecanoic acid, propyldodecanoic acid, butylundecanoic acid, pentyldecanoic acid, hexylnonanoic acid, palmitic acid, methylpentadecanoic acid, ethyltetradecanoic acid, propyltridecanoic acid, butyldodecanoic acid, pentylundecanoic acid, hexyldecane Acids, heptylnonanoic acid, methylcyclohexanecarboxylic acid, ethylcyclohexanecarboxylic acid, propylcyclohexanecarboxylic acid, butylcyclohexanecarboxylic acid, pentylcyclohexanecarboxylic acid, hexylcyclohexanecarboxylic acid, heptylcyclohexanecarboxylic acid, octylcyclohexanecarboxylic acid, nonylcyclohexanecarboxylic acid, etc. Saturated fatty acids in Aromas such as acid, pyromellitic acid, o-phenoxy benzoic acid, methyl benzoic acid, ethyl benzoic acid, propyl benzoic acid, butyl benzoic acid, pentyl benzoic acid, hexyl benzoic acid, heptyl benzoic acid, octyl benzoic acid, nonyl benzoic acid, etc. Group carboxylic acids include. One type of organic acid may be used alone, or two or more types may be used in combination. By combining such an organic acid with the above-mentioned sub-micro copper particles, there is a tendency that both the dispersibility of the sub-micro copper particles and the desorption of the organic acid at the time of sintering can be achieved at the same time.

The treatment amount of the surface treatment agent may be an amount that adheres to the surface of the sub-micro copper particles in a single-layer to a triple-layer. This amount is the number of molecular layers (n) attached to the surface of the sub-micro copper particles, the specific surface area (Ap) (unit: m ² / g) of the sub-micro copper particles, and the molecular weight (Ms) (unit: g) of the surface treatment agent. / Mol), the minimum coating area (SS) of the surface treatment agent (unit: m ² / piece), and the Avogadro's number (NA) (6.02 × 10 ²³ pieces). Specifically, the treatment amount of the surface treatment agent is calculated according to the formula of the treatment amount (mass%) of the surface treatment agent = {(n ・ Ap ・ Ms) / (SS ・ NA + n ・ Ap ・ Ms)} × 100%. Will be done.

The specific surface area of the sub-micro copper particles can be calculated by measuring the dried sub-micro copper particles by the BET specific surface area measurement method. Minimum coverage of the surface treatment agent, if the surface treatment agent is a straight-chain saturated fatty acids, is 2.05 × ¹⁰ -19 ^m 2/1 molecule. In the case of other surface treatment agents, for example, calculation from a molecular model or "Chemistry and Education" (Akihiro Ueda, Sumio Inafuku, Iwao Mori, 40 (2), 1992, p114-117). It can be measured by the method described. An example of a method for quantifying a surface treatment agent is shown. The surface treatment agent can be identified by a heat desorption gas / gas chromatograph mass spectrometer of the dry powder obtained by removing the dispersion medium from the bonding material, whereby the carbon number and molecular weight of the surface treatment agent can be determined. The carbon content ratio of the surface treatment agent can be analyzed by carbon content analysis. Examples of the carbon content analysis method include a high-frequency induction heating furnace combustion / infrared absorption method. The amount of the surface treatment agent can be calculated from the carbon number, molecular weight and carbon content ratio of the identified surface treatment agent by the above formula.

The treatment amount of the surface treatment agent may be 0.07% by mass or more and 2.1% by mass or less, 0.10% by mass or more and 1.6% by mass or less, and 0.2% by mass. It may be 1.1% by mass or less.

As the submicro copper particles, commercially available ones can be used. Examples of commercially available sub-micro copper particles include CH-0200 (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 0.36 μm) and HT-14 (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 0. 41 μm), CT-500 (manufactured by Mitsui Metal Mining Co., Ltd., volume average particle size 0.72 μm), Tn-Cu100 (manufactured by Taiyo Nisshi Co., Ltd., volume average particle size 0.12 μm).

(Micro copper particles)
Examples of the micro copper particles include copper particles having a particle size of 1.0 μm or more and 50 μm or less. For example, copper particles having a volume average particle size of 1.0 μm or more and 50 μm or less can be used. The volume average particle size of the micro copper particles may be 2.0 μm or more and 20 μm or less, 2.0 μm or more and 10 μm or less, 3.0 μm or more and 20 μm or less, and 3.0 μm or more. It may be 10 μm or less.

Examples of the shape of the microcopper particles include a spherical shape, a lump shape, a needle shape, a flake shape, a substantially spherical shape, and an aggregate thereof. Of these, flakes are preferred. The flake shape includes a flat plate shape such as a plate shape or a scale shape.

Examples of the flake-shaped microcopper particles include copper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 or more. For example, an average maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 are included. The above copper particles can be used. When the average maximum diameter and aspect ratio of the flake-shaped microcopper particles are within the above ranges, the volume shrinkage when the bonding material is sintered can be sufficiently reduced, and the bonding portion according to the present embodiment described above can be formed. It will be easy. From the viewpoint of further exerting the above effect, the average maximum diameter of the flake-shaped microcopper particles may be 1 μm or more and 10 μm or less, or 3 μm or more and 10 μm or less. The measurement of the maximum diameter and the average maximum diameter of the flake-shaped microcopper particles can be obtained from, for example, an SEM image of the particles, and is obtained as the major axis X and the average value Xav of the major axis of the flake-shaped structure described later.

The flake-shaped micro copper particles can contain 50% by mass or more of copper particles having a maximum diameter of 1 μm or more and 20 μm or less. From the viewpoint of orientation in the bonded body, reinforcing effect, and filling property of the bonded paste, the flake-shaped microcopper particles can contain 70% by mass or more of copper particles having a maximum diameter of 1 μm or more and 20 μm or less, and include 80% by mass or more. It can contain 100% by mass. From the viewpoint of suppressing bonding defects, the flake-shaped microcopper particles preferably do not contain particles having a size exceeding the bonding thickness, such as particles having a maximum diameter of more than 20 μm.

An example is a method of calculating the major axis X of flake-shaped microcopper particles from an SEM image. The powder of flake-shaped microcopper particles is placed on a carbon tape for SEM with a spatula to prepare a sample for SEM. This SEM sample is observed with an SEM device at a magnification of 5000. A rectangle circumscribing the flake-shaped microcopper particles of the SEM image is drawn by image processing software, and the long side of the rectangle is defined as the major axis X of the particles. Using a plurality of SEM images, this measurement is performed on 50 or more flake-shaped microcopper particles, and the average value Xav of the major axis is calculated.

The flake-shaped microcopper particles may have an aspect ratio of 4 or more, or 6 or more. When the aspect ratio is within the above range, the flake-shaped microcopper particles in the bonding material are oriented substantially parallel to the bonding surface to reduce the volume shrinkage when the bonding layer (bonding material) is sintered. It can be suppressed, and it becomes easy to form the joint portion according to the present embodiment described above.

The shape of the flake-shaped microcopper particles according to the present embodiment can also be specified by the parameters of major diameter (average maximum diameter) X, medium diameter (width) Y, and minor diameter (thickness) T. The major axis X is the distance between the two parallel planes circumscribing the flake-shaped microcopper particles in the three-dimensional shape of the flake-shaped microcopper particles, which is selected so that the distance between the two parallel planes is maximized. be. The medium diameter Y is selected so as to maximize the distance between the two parallel planes orthogonal to the parallel two planes giving the major axis X and circumscribing the flake-shaped microcopper particles. Distance. The minor axis T is orthogonal to the parallel two planes giving the major axis X and the parallel two planes giving the medium diameter Y, and the distance between the two parallel planes is the largest among the two parallel planes circumscribing the flake-shaped microcopper particles. Is the distance between two parallel planes chosen to be.

The average value Xav of the major axis may be 1 μm or more and 50.0 μm or less, 1 μm or more and 20 μm or less, or 3 μm or more and 10 μm or less. When Xav is within the above range, it is easy to form a sintered body of the joining material with an appropriate thickness in the joining body produced by sintering the joining material.

Xav / Tab, which is the ratio (aspect ratio) of the average value Xav of the major axis to the average value Tab of the minor axis, may be 4.0 or more, 6.0 or more, or 10.0 or more. There may be. When Xav / Tav is within the above range, the flake-shaped microcopper particles in the bonding material are likely to be oriented substantially parallel to the bonding surface, and the volume shrinkage when the bonding material is sintered can be suppressed. It becomes easy to secure the joining strength of the joined body manufactured by sintering the joining material.

Xav / Yav, which is the ratio of the average value Xav of the major axis to the average value Yav of the medium diameter, may be 2.0 or less, 1.7 or less, or 1.5 or less. .. When Xav / Yav is within the above range, the shape of the flake-shaped microcopper particles becomes flake-shaped particles having a certain area, and the flake-shaped microcopper particles in the bonding material are oriented substantially parallel to the bonding surface. This facilitates the suppression of volume shrinkage when the bonding material is sintered, and makes it easy to secure the bonding strength of the bonded body produced by sintering the bonding material. When Xav / Yav exceeds 2.0, it means that the shape of the flake-shaped microcopper particles approaches an elongated linear shape.

Yav / Tab, which is the ratio of the average value Yav of the medium diameter to the average value Tav of the minor diameter, may be 2.5 or more, 4.0 or more, or 8.0 or more. good. When Yav / Tav is within the above range, the flake-shaped microcopper particles in the bonding material are likely to be oriented substantially parallel to the bonding surface, and the volume shrinkage when the bonding material is sintered can be suppressed. It becomes easy to secure the joining strength of the joined body manufactured by sintering the joining material.

The content of the flake-shaped microcopper particles may be 1% by mass or more and 90% by mass or less, 10% by mass or more and 70% by mass or less, or 20% by mass, based on the total mass of the metal particles. It may be 50% by mass or less. When the content of the flake-shaped microcopper particles is within the above range, it becomes easy to form the joint portion according to the above-described embodiment.

When the bonding material of the present embodiment contains sub-micro copper particles and flake-shaped micro copper particles as copper particles, the total content of the sub-micro copper particles and the flake-shaped micro copper particles is the total of the metal particles. It may be 80% by mass or more based on the mass. When the total content of the sub-micro copper particles and the content of the flake-shaped micro copper particles is within the above range, it becomes easy to form the joint portion according to the above-described embodiment. From the viewpoint of further exerting the above effect, the total content of the sub-micro copper particles and the content of the flake-shaped micro copper particles may be 90% by mass or more based on the total mass of the metal particles, and may be 95. It may be 100% by mass or more, or 100% by mass.

In the flake-shaped microcopper particles, the presence or absence of treatment with the surface treatment agent is not particularly limited. From the viewpoint of dispersion stability and oxidation resistance, the flake-shaped microcopper particles may be treated with a surface treatment agent. The surface treatment agent may be one that is removed at the time of joining. Examples of such surface treatment agents include aliphatic carboxylic acids such as palmitic acid, stearic acid, arachidic acid, and oleic acid; aromatic carboxylic acids such as terephthalic acid, pyromellitic acid, and o-phenoxybenzoic acid; and cetyl alcohols. , Aliphatic alcohols such as stearyl alcohol, isobornylcyclohexanol, tetraethylene glycol; aromatic alcohols such as p-phenylphenol; alkylamines such as octylamine, dodecylamine, stearylamine; Aliphatic nitriles; silane coupling agents such as alkylalkoxysilanes; polymer-treated materials such as polyethylene glycols, polyvinyl alcohols, polyvinylpyrrolidones, and silicone oligomers. As the surface treatment agent, one type may be used alone, or two or more types may be used in combination.

The amount of the surface treatment agent to be treated may be one or more molecular layers on the surface of the particles. The treatment amount of such a surface treatment agent varies depending on the specific surface area of the flake-shaped microcopper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent. The treatment amount of the surface treatment agent is usually 0.001% by mass or more. The specific surface area of the flake-shaped microcopper particles, the molecular weight of the surface treatment agent, and the minimum coating area of the surface treatment agent can be calculated by the above-mentioned method.

By using the sub-micro copper particles and the flake-shaped micro copper particles together, the volume shrinkage when the bonding material is sintered is suppressed, and it becomes difficult to peel off from the adherend surface when the bonding material is sintered. Sufficient bondability and reliability can be easily obtained in the bonding of the above.

In the bonding material of the present embodiment, the content of the microcopper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of less than 2 contained in the metal particles has a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio. Based on the total amount of flake-shaped microcopper particles having a value of 4 or more, 50% by mass or less is preferable, 40% by mass or less is more preferable, and 30% by mass or less is further preferable. By limiting the content of microcopper particles having an average maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of less than 2, the flake-shaped microcopper particles in the bonding material are oriented substantially parallel to the bonding surface. This facilitates the process, and the volume shrinkage when the bonding material is sintered can be suppressed more effectively. This makes it easy to form the joint portion according to the present embodiment described above. In terms of making it easier to obtain such an effect, the content of microcopper particles having an average maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of less than 2 is such that the maximum diameter is 1 μm or more and 20 μm or less, and the aspect ratio. It may be 20% by mass or less, or 10% by mass or less, based on the total amount of flake-shaped microcopper particles having a value of 4 or more.

As the flake-shaped microcopper particles according to the present embodiment, commercially available ones can be used. Commercially available flake-shaped microcopper particles include, for example, MA-C025 (manufactured by Mitsui Mining & Smelting Co., Ltd., average maximum diameter 4.1 μm), 3L3 (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., maximum volume diameter 7.3 μm). ), 1110F (Mitsui Mining & Smelting Co., Ltd., average maximum diameter 5.8 μm), 2L3 (Fukuda Metal Foil Powder Industry Co., Ltd., average maximum diameter 9 μm) and the like.

In the bonding material of the present embodiment, the micro copper particles to be blended include flake-shaped micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less, an aspect ratio of 4 or more, and a maximum diameter of 1 μm or more and 20 μm or less. It is possible to use microcopper particles having an aspect ratio of less than 2 and having a content of microcopper particles of 50% by mass or less, preferably 30% by mass or less, based on the total amount of the flake-shaped microcopper particles. When commercially available flake-shaped microcopper particles are used, the maximum diameter is 1 μm or more and 20 μm or less, the flake-shaped microcopper particles having an aspect ratio of 4 or more are included, and the maximum diameter is 1 μm or more and 20 μm or less. The content of the microcopper particles having a ratio of less than 2 is 50% by mass or less, more preferably 40% by mass or less, still more preferably 30% by mass or less, based on the total amount of the flake-shaped microcopper particles. You may.

The bonding material may contain other metal particles other than copper particles. Examples of other metal particles include particles such as nickel, silver, gold, palladium, and platinum.

The volume average particle diameter of the other metal particles may be 0.01 μm or more and 10 μm or less, 0.01 μm or more and 5 μm or less, or 0.05 μm or more and 3 μm or less. When other metal particles are contained, the content thereof may be less than 20% by mass based on the total mass of the metal particles contained in the bonding material from the viewpoint of obtaining sufficient bondability. It may be mass% or less. Other metal particles may not be included. The shapes of the other metal particles are not particularly limited.

Since the bonding material of the present embodiment contains metal particles other than copper particles, a sintered metal layer in which a plurality of types of metals are solid-dissolved or dispersed can be obtained. Characteristics are improved, and connection reliability is likely to be improved. Further, by adding a plurality of types of metal particles, the formed joint portion tends to have improved joint strength and connection reliability with respect to an adherend such as a semiconductor element and a substrate.

(Dispersion medium)
The dispersion medium is not particularly limited and may be volatile. Examples of the volatile dispersion medium include monovalent and polyvalent and polyvalent such as pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, α-terpineol and isobornylcyclohexanol (MTPH). Valuable alcohols; ethylene glycol butyl ether, ethylene glycol phenyl ether, diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol Butylmethyl ether, diethylene glycol isopropylmethyl ether, triethylene glycol dimethyl ether, triethylene glycol butylmethyl ether, propylene glycol propyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, di Ethers such as propylene glycol dimethyl ether, tripropylene glycol methyl ether, tripropylene glycol dimethyl ether; ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether acetate (DPMA), lactic acid Ethers such as ethyl, butyl lactate, γ-butyrolactone, propylene carbonate; acid amides such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide; cyclohexane, octane, nonane, decane, Examples thereof include aliphatic hydrocarbons such as undecane; aromatic hydrocarbons such as benzene, toluene and xylene; mercaptans having an alkyl group having 1 to 18 carbon atoms; and mercaptans having a cycloalkyl group having 5 to 7 carbon atoms. Examples of mercaptans having an alkyl group having 1 to 18 carbon atoms include ethyl mercaptan, n-propyl mercaptan, i-propyl mercaptan, n-butyl mercaptan, i-butyl mercaptan, t-butyl mercaptan, pentyl mercaptan, and hexyl mercaptan. And dodecyl mercaptan. Examples of mercaptans having a cycloalkyl group having 5 to 7 carbon atoms include cyclopentyl mercaptan, cyclohexyl mercaptan and cycloheptyl mercaptan.

The content of the dispersion medium may be 5 to 50 parts by mass, where 100 parts by mass is the total mass of the metal particles contained in the bonding material. When the content of the dispersion medium is within the above range, the bonding material can be adjusted to a more appropriate viscosity, and the sintering of copper particles is less likely to be hindered.

In the present embodiment, the dispersion medium preferably contains a solvent having a boiling point of 300 ° C. or higher. As the boiling point of a solvent having a boiling point of 300 ° C. or higher, from the viewpoint that it does not interfere with sintering and densification during sintering of the coating film (bonding layer) and is rapidly evaporated and removed when the bonding temperature is reached. May be 300 ° C. or higher and 450 ° C. or lower, 305 ° C. or higher and 400 ° C. or lower, or 310 ° C. or higher and 380 ° C. or lower.

For a solvent having a boiling point of 300 ° C. or higher, it is preferable to select a structure having a high affinity with the surface of the metal particles in order to improve the dispersibility of the contained metal particles. When the metal particles are surface-treated with a surface treatment agent containing an alkyl group, it is preferable to select a solvent having an alkyl group. Examples of such a solvent having a boiling point of 300 ° C. or higher include isobornylcyclohexanol (MTPH, manufactured by Nippon Terpen Co., Ltd.), butyl stearate, Exepearl BS (manufactured by Kao Co., Ltd.), stearyl stearate, and Exepearl SS (manufactured by Kao Co., Ltd.). ), 2-Ethylhexyl stearate, Exepearl EH-S (manufactured by Kao), Isotridecyl stearate, Exepearl TD-S (manufactured by Kao), Isooctadecanol, Fineoxocol 180 (manufactured by Nissan Chemical Co., Ltd.), Fineoxo Cole 180T (manufactured by Nissan Chemical Co., Ltd.), 2-hexyldecanol, Fineoxocol 1600 (manufactured by Nissan Chemical Co., Ltd.), tributylin, tetraethylene glycol, heptadecane, octadecane, nonadecan, eikosan, heneikosan, docosan, methylheptadecane, tridecylcyclohexane, Tetradecylcyclohexane, pentadecylcyclohexane, hexadecylcyclohexane, undecylbenzene, dodecylbenzene, tetradecylbenzene, tridecylbenzene, pentadecylbenzene, hexadecylbenzene, heptadecylbenzene, nonylnaphthalene, diphenylpropane, octyl octanate, myristin Methyl acid, ethyl myristate, methyl linoleate, methyl stearate, triethylene glycolbis (2-ethylhexanoic acid), tributyl citrate, pentylphenol, dibutyl sevacinate, oleyl alcohol, cetyl alcohol, methoxyphenetyl alcohol, benzylphenol , Hexadecanenitrile, heptadecanenitrile, benzyl benzoate, symmethyrine and the like.

As the solvent having a boiling point of 300 ° C. or higher, it is preferable to select a solvent having a Hansen solubility parameter close to that of the surface treatment agent from the viewpoint of improving dispersibility. Since organic acids, organic amines, hydroxyl group-containing polymers, polyvinylpyrrolidone and the like are easy to handle as surface treatment agents, the solvent having a boiling point of 300 ° C. or higher is at least one from the group consisting of a hydroxy group, an ether group and an ester group. It preferably has a seed group. The Hansen solubility parameter can be searched, for example, from the database at the end of the handbook, or searched / calculated by the database and simulation integrated software HSPiP.

The content of the solvent having a boiling point of 300 ° C. or higher can be 2% by mass or more based on the total mass of the bonding material. The content of the solvent having a boiling point of 300 ° C. or higher may be 2.2% by mass or more, 2.3% by mass or more, or 2.4% by mass, based on the total mass of the bonding material. It may be% or more. When the content of the solvent having a boiling point of 300 ° C. or higher is within the above range, a certain amount of solvent can remain in the bonding layer when the coating film (bonding layer) of the present embodiment is sintered. , The flexibility and adhesiveness of the bonding material between the members are easily maintained, and even when the members used for bonding have different coefficients of thermal expansion, they tend to be bonded without peeling. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher is not particularly limited. From the viewpoint that the time until the dispersion medium is removed at the sintering temperature can be suppressed and the sintering time can be shortened, the total mass of the bonding material may be 9% by mass or less.

Further, in the bonding material of the present embodiment, the content of the solvent having a boiling point of 300 ° C. or higher may be 15% by volume or more, or 17% by volume or more, based on the total volume of the bonding material. It may be 23% by volume or more. When the content of the solvent having a boiling point of 300 ° C. or higher is within the above range, a certain amount of solvent remains in the coating film (bonding layer) when the coating film (bonding layer) of the present embodiment is sintered. The flexibility and adhesiveness of the bonding material between the members can be easily maintained, and even when the members used for bonding have different coefficients of thermal expansion, they tend to be bonded without peeling. The upper limit of the content of the solvent having a boiling point of 300 ° C. or higher is not particularly limited. From the viewpoint that the time until the dispersion medium is removed at the sintering temperature can be suppressed and the sintering time can be shortened, the total volume of the bonding material may be 60% by volume or less.

The type of dispersion medium contained in the bonding material can be analyzed by, for example, gas chromatography-mass spectrometry of high-temperature desorbed gas and TOF-SIMS. As another analysis method, the supernatant obtained by separating the particle components by centrifugation may be identified by ordinary organic analysis, for example, FT-IR, NMR, liquid chromatograph, or a combination thereof. The ratio of the types of dispersion medium can be quantified by liquid chromatograph, NMR or the like.

(Additive)
If necessary, a wetting improver such as a nonionic surfactant or a fluorine-based surfactant; a defoaming agent such as silicone oil; an ion trap agent such as an inorganic ion exchanger is appropriately added to the bonding material. May be good.

(Preparation of bonding material)
The bonding material may be prepared by mixing the above-mentioned sub-microcopper particles, microcopper particles, other metal particles and any additive with a dispersion medium. After mixing each component, stirring treatment may be performed. For the bonding material, the maximum particle size of the dispersion liquid may be adjusted by a classification operation.

As the bonding material, the sub-micro copper particles, the surface treatment agent, and the dispersion medium are mixed in advance, and the dispersion treatment is performed to prepare a dispersion liquid of the sub-micro copper particles, and further, the micro copper particles, other metal particles, and any addition are added. The agents may be mixed and prepared. By performing such a procedure, the dispersibility of the sub-micro copper particles is improved, the mixing property with the micro-copper particles is improved, and the performance of the bonding material is further improved. Agglomerates may be removed by classifying the dispersion of submicro copper particles.

As a method of applying the bonding material, stencil printing, dispenser, screen printing, transfer printing, offset printing, jet printing method, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, concave plate Printing, gravure printing, soft lithograph, bar coat, applicator, particle deposition method, spray coater, spin coater, dip coater, electrodeposition coating and the like can be used.

The thickness of the coating film may be 1 μm or more and 1000 μm or less, 10 μm or more and 1000 μm or less, 10 μm or more and 500 μm or less, 50 μm or more and 200 μm or less, or 10 μm or more and 3000 μm or less. It may be 15 μm or more and 500 μm or less, 20 μm or more and 300 μm or less, 5 μm or more and 500 μm or less, 10 μm or more and 250 μm or less, and 15 μm or more and 150 μm or less. It may be.

From the viewpoint of the effect of absorbing the height variation of the semiconductor element or the variation of the distance between the substrates and the printing accuracy, it is preferably 10 μm or more and 1000 μm or less. When the thickness of the coating film is 10 μm or more, it becomes easy to obtain the absorption result with height variation, and when it is 1000 μm or less, it becomes easy to secure the printing accuracy.

The method for drying the coating film may be drying by leaving it at room temperature, heat drying, or vacuum drying. For heat drying or vacuum drying, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic wave. A heating device, a heater heating device, a steam heating furnace, a hot plate pressing device, or the like can be used. The drying temperature and time may be appropriately adjusted according to the type and amount of the dispersion medium used. As the drying temperature and time, for example, it may be dried at 50 ° C. or higher and 180 ° C. or lower for 1 minute or longer and 120 minutes or shorter.

The coating film (bonding layer) can be sintered by heat treatment. For heat treatment, for example, a hot plate, a hot air dryer, a hot air heating furnace, a nitrogen dryer, an infrared dryer, an infrared heating furnace, a far infrared heating furnace, a microwave heating device, a laser heating device, an electromagnetic heating device, etc. A heater heating device, a steam heating furnace, or the like can be used.

The gas atmosphere at the time of sintering may be an oxygen-free atmosphere from the viewpoint of suppressing oxidation. The gas atmosphere at the time of sintering may be a reducing atmosphere from the viewpoint of removing surface oxides of copper particles. Examples of the anoxic atmosphere include the introduction of an oxygen-free gas such as nitrogen and a rare gas, or under vacuum. Examples of the reducing atmosphere include pure hydrogen gas, a mixed gas of hydrogen and nitrogen typified by a forming gas, nitrogen containing formic acid gas, a mixed gas of hydrogen and rare gas, and a rare gas containing formic acid gas. Can be mentioned.

The maximum temperature reached during the heat treatment may be 250 ° C. or higher and 450 ° C. or lower, and 250 ° C. or higher and 400 ° C. or higher, from the viewpoint of reducing heat damage to the members constituting the power card or the double-sided cooling module and improving the yield. It may be ℃ or less, and may be 250 ℃ or more and 350 ℃ or less. When the maximum ultimate temperature is 200 ° C. or higher, sintering tends to proceed sufficiently when the maximum ultimate temperature holding time is 60 minutes or less.

The maximum temperature retention time may be 1 minute or more and 60 minutes or less, or 1 minute or more and less than 40 minutes, from the viewpoint of volatilizing all the dispersion medium and improving the yield. It may be more than 30 minutes.

In the present embodiment, from the viewpoint of reducing the reducing property of the bonding material containing copper particles as a main component and reducing the thermal stress generated between the substrate and the semiconductor element, heating is performed at 350 ° C. or lower in hydrogen having a concentration of 1% or more. Is preferable.

Further, the coating film (bonding layer) can be sintered under a load of 0 to 100 MPa. In addition, in this embodiment, it is possible to join without pressure. As used herein, the term "no pressure" means the weight of the members to be joined, or a state in which a pressure of 0.01 MPa or less is applied in addition to the weight thereof.

The bonding material (copper paste) contains copper particles and a dispersion medium, and the copper particles are submicro copper particles having a volume average particle diameter of 0.01 μm or more and 0.8 μm or less, and a volume average particle diameter of 2.0 μm. The total content of the sub-micro copper particles and the micro-copper particles is 80% by mass or more based on the total mass of the metal particles contained in the bonding material, including the micro-copper particles having a size of 50 μm or more. , The content of the sub-micro copper particles is 30% by mass or more and 90% by mass or less based on the total of the mass of the sub-micro copper particles and the mass of the micro copper particles, and the content of the micro copper particles is the bonding material. When the total mass of the contained metal particles is 10% by mass or more and 50% by mass or less, sufficient bonding strength can be obtained even when bonding is performed without pressure.

The above reason is caused by the surface protective agent or the dispersion medium while maintaining sufficient sinterability by containing the sub-micro copper particles and the micro-copper particles contained in the bonding material in a specific ratio. It is considered that the volume shrinkage at the time of sintering can be sufficiently suppressed, the strength of the sintered body is secured, and the bonding force with the adherend surface is improved.

Further, since the above-mentioned bonding material can obtain the above-mentioned effect by the sub-micro copper particles and the micro copper particles, it is cheaper and more stable than the bonding material containing expensive copper nanoparticles as a main component. It has the advantage of being able to supply.

Further, the microcopper particles are preferably in the form of flakes. The use of flake-shaped microcopper particles makes it even easier to reduce the thermal stress generated between the semiconductor element and the substrate. The reason why such an effect can be obtained is that the microcopper particles in the bonding material are oriented substantially parallel to the bonding surface, so that the volume shrinkage when the bonding material is sintered can be suppressed, and the flakes. It is conceivable that the bonding force is improved by increasing the overlapping area of the shaped micro copper particles, and that the flake-shaped micro copper particles align the sub micro copper particles to obtain a reinforcing effect.

The joining material (copper paste) after joining becomes a sintered body (porous body) of copper.

FIG. 3 is an enlarged cross-sectional view of the joint portion according to the present embodiment. A copper sintered body for bonding a substrate and a semiconductor element or a semiconductor element and a spacer contains copper particles and a dispersion medium, and the copper particles are a bonding layer formed from a bonding material containing submicro copper particles and micro copper particles. The structure 31 (a) derived from the sub-micro copper particles, the structure 31 (b) derived from the copper particles of the flake-shaped micro copper particles as the micro copper particles, and the pores 31 (c). It is a porous body containing.

In the present embodiment, the bonding layer formed from the bonding material of the present embodiment described above is heated at 350 ° C. or lower in hydrogen having a concentration of 1% or more, and the volume resistivity, thermal conductivity, and adhesive strength are each increased. It is possible to form a sintered body having a thickness of 1, 1 × ^10-5 Ω · cm or less, 50 W · m ^-1 · K ^-1 or more, and 20 MPa or more, and by including such a sintered body in the joint portion, it is possible to form a sintered body. It is possible to realize a double-sided cooling type semiconductor module having excellent reliability.

The volume resistivity is calculated by the following formula.
ρ = A ・ R / L
Here, ρ is the electrical resistivity per unit volume (volume resistivity) (Ω · m), R is the resistance of the sintered body (Ω), A is the cross-sectional area of the sintered body (m ² ), and L is baked. The thickness (m) of the body is shown.

The thermal conductivity can be calculated from the thermal diffusivity, specific heat capacity, and density of the joint. For example, the thermal diffusivity of the joint is measured by a laser flash method (LFA467, manufactured by Netch Co., Ltd.), and the thermal diffusivity, the specific heat capacity obtained by the differential scanning calorimetry device (DSC8500, manufactured by Perkin Elmer), and The thermal conductivity [W / (m · K)] of the joint at 25 ° C. can be calculated from the product with the density obtained in the same manner as above.

The bond strength can be measured using a universal bond tester (4000 series, manufactured by DAGE) or the like.

The joint includes a structure 31 (b) derived from flaky copper particles oriented substantially parallel to the interface with the electrode, and the copper content in the joint is based on the volume of the joint. It may be 65% by volume or more.

The structure derived from the copper particles of the flake-shaped microcopper particles according to the present embodiment, that is, the flake-shaped structure in the sintered copper having the flake-shaped structure may have a ratio of the major axis to the thickness of 5 or more. The number average diameter of the major axis of the flake-shaped structure may be 2 μm or more, 3 μm or more, or 4 μm or more. When the shape of the flake-shaped structure is within this range, the reinforcing effect of the flake-shaped structure contained in the joint is improved, and the double-sided cooling type semiconductor module becomes more reliable.

The major axis and thickness of the flake-like structure can be obtained from, for example, an SEM image of a bonded body (copper sintered body and semiconductor element or substrate). The method of measuring the major axis and the thickness of the flake-like structure from the SEM image will be illustrated below. The conjugate is poured with epoxy cast resin so that the entire sample is filled and cured. Cut the cast sample near the cross section you want to observe, grind the cross section by polishing, and perform CP (cross section polisher) processing. The cross section of the sample is observed with an SEM device at a magnification of 5000. A cross-sectional image (for example, 5000 times) of the joint is acquired, and it is a dense continuous part, which is a linear, rectangular parallelepiped, or elliptical part, and is the longest of the straight lines contained in this part. The length of the major axis is 1 μm or more and the ratio of the major axis / thickness is 4 or more, when the one with the major axis is defined as the major axis and the one with the longest length among the straight lines included in this portion orthogonal to the major axis is defined as the thickness. Something is regarded as a flake-shaped structure, and the major axis and thickness of the flake-shaped structure can be measured by image processing software having a length measuring function. The average value thereof can be obtained by calculating the number average with 20 points or more randomly selected.

The major axis of the flake-like structure is given as the distance between the parallel straight lines circumscribing the flake-like structure, which is selected so that the distance between the parallel straight lines is maximized. The thickness of the flake-like structure is defined as the distance between the two parallel planes that are orthogonal to the parallel two straight lines that give the major axis and are selected so that the distance between the two parallel planes is the largest among the two parallel planes that circumscribe the flake-like structure. Given.

The image processing software is not particularly limited, and for example, Microsoft PowerPoint (manufactured by Microsoft) and ImageJ (manufactured by the National Institutes of Health) can be used.

For the content ratio of the flake-like structure to the entire structure, the cross-sectional area of the flake-like structure is obtained from the SEM image of the joint body, and the cross-sectional area of the flake-like structure is obtained from the major axis and thickness of the flake-like structure measured by the above method. Can be calculated by dividing the total cross-sectional area of the flake-shaped structure by the cross-sectional area of the joined body. In the joint portion according to the present embodiment, the content ratio of the flake-like structure to the entire structure obtained by the above method may be 10 to 40%, 15 to 35%, or 20 to 30. May be%.

The copper content (volume ratio) at the joint can be 65% by volume or more based on the volume of the joint. When the copper content in the joint portion is within the above range, it is possible to prevent the formation of large pores inside the joint portion and the sparseness of the sintered copper connecting the flake-like structures. Therefore, if the copper content in the bonded portion is within the above range, sufficient thermal conductivity can be obtained, the bonding strength between the copper sintered body and the semiconductor element or the substrate is improved, and the bonded body has improved connection reliability. It will be excellent. The copper content in the joint may be 67% by volume or more, or 70% by volume or more, based on the volume of the joint. The copper content in the joint may be 90% by volume or less based on the volume of the joint from the viewpoint of easiness of the manufacturing process.

When the composition of the material constituting the joint is known, for example, the copper content in the joint can be determined by the following procedure. First, the joint portion is cut into a rectangular parallelepiped, the length and width of the joint portion are measured with a caliper or an external shape measuring device, and the thickness is measured with a film thickness meter to calculate the volume of the joint portion. _{The apparent density M 1} (g / cm ³ ) is obtained from the volume of the cut-out joint and the weight of the joint measured by a precision balance. Using the obtained M1 and the copper density of 8.96 g / cm ³ , the copper content (volume%) at the joint can be determined from the following formula (2).
Copper content (% by volume) at the joint = [(M ₁ ) /8.96] × 100 ... (2)

In the present embodiment, after the first and second joining steps, an electric circuit can be formed by striking a wire on the substrate, and then sealing with a resin member can be performed.

After that, the cold heat sources 21 and 22 may be joined to the substrates 11a and 11b by abutting or a joining material to manufacture a double-sided cooling type semiconductor device.

Further, in the method for manufacturing a double-sided cooled semiconductor module according to the present embodiment, after performing a joining step of preliminarily joining one of the substrates and the semiconductor element and the other of the substrates and the spacer, two members are prepared. After applying the bonding material to the bonding surface of the semiconductor element of one member or the bonding position of the spacer of the other member with the semiconductor element, both members are brought into contact with each other and the coating film (bonding layer) of the bonding material is fired. It may include a third joining step.

For example, in the case of manufacturing the double-sided cooling type semiconductor module according to the second embodiment, in the third joining step, the semiconductor element and the spacer are brought into contact with each other while being pressurized in a direction approaching each other, and / or. It is preferable to fire the coating film (bonding layer) of the bonding material while applying pressure in the direction in which the semiconductor element and the spacer approach each other. By performing these pressurizations, even if the heights of the plurality of semiconductor elements 1 vary, the respective semiconductor elements 1 are bonded to the substrate 11 and the spacer 41 by the bonding layer having shape-following property. Sufficient sex can be obtained. Further, it is possible to reduce the variation in the thickness of the double-sided cooling type semiconductor module after joining.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following examples.

In this example, in order to evaluate the reliability of the joint portion in the joint, a joint between the lead frame and the Si chip was prepared, and a power cycle test was conducted using this joint.

The following materials were prepared to prepare the joint material.
[Metal particles]
3L3N (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., shape: flakes, 50% volume average particle size: 6.1 μm)
CH-0200 (manufactured by Mitsui Metal Mining Co., Ltd., shape: pseudo-spherical, surface treatment agent: lauric acid (dodecanoic acid), surface treatment amount: 0.973% by mass (based on the total mass of CH-0200), 50% volume average Particle size: 0.36 μm, content of copper particles having a particle size of 0.1 μm or more and less than 1 μm: 100% by mass, content of copper particles having a particle size of 0.12 μm or more and 0.8 μm or less: 100% by mass )
Zinc flakes (manufactured by Aifa Aesar, 325 mesh, trade name Zinc Flake)
AgC239 (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., shape: flakes, 50% volume average particle size: 7 μm)
[Dispersion medium]
Hydroterpineol (manufactured by Nippon Terpine Chemical Co., Ltd.)
Tributyrin (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.)
Isobornylcyclohexanol (manufactured by Nippon Terpen Chemical Co., Ltd., trade name: Telsolv MTPH)
Butyl stearate (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.)

(Joint body 1)
Add 1.215 g of dihydroterpineol, 0.18 g of tributyrin, 2.067 g of CH-0200, 1.531 g of 3L3N, and 0.5 g of zinc flakes to an agate mortar, and knead until there is no dry powder. Was transferred to a plastic bottle. ^{The sealed plastic bottle was stirred at 2000 min -1} (2000 rpm) for 2 minutes using a rotating and revolving stirrer (Planetary Vacuum Mixer ARV-310, manufactured by Shinky Co., Ltd.). The obtained paste-like mixture (metal paste) was used as the bonding material 1. The concentration of the bonding material 1 (the ratio of the total content of CH-0200, 3L3N and zinc flakes to the total amount of the bonding material 1) was 88% by mass.

The obtained bonding material 1 is mounted on a lead frame (joint size: 19 × 25 × 3 mm) subjected to electrolytic Ni plating by stencil printing using a metal squeegee, and has an area of the same size as the chip (5. It was applied to 7 mm × 5.7 mm) with a printing thickness of 200 μm. Next, a Si chip (Schottky barrier diode manufactured by infineon, SIDC32D170H) was mounted directly above the bonding material 1 applied to the lead frame so that the side opposite to the surface on which the plating film was applied was in contact with the applied bonding material 1. Next, this was set in a tube furnace (manufactured by ABC Co., Ltd.), and argon gas was flowed at 1 L / min to replace the air with argon gas. After that, the temperature is raised to 300 ° C. over 30 minutes while flowing hydrogen gas at 500 mL / min, and sintering treatment is performed at 300 ° C. for 60 minutes to form a sintered copper layer between the lead frame and the Si chip. It was formed as a joint. Then, the argon gas was changed to 0.3 L / min and cooled, and the sample was taken out into the air at 50 ° C. or lower. Next, in order to prevent the sintered copper layer from being oxidized during the test, a polyimide resin (HIMAL (HL-1210) manufactured by Hitachi Kasei Co., Ltd.) was brushed on the sintered copper protruding from the outer periphery of the Si chip. applying Te, the sample was placed on a hot plate, then capped with a Buchner funnel, N ₂ gas blowing while 50 ° C., the mixture was allowed to provisionally dried at 10 minutes condition, 200 ° C., the dried 60 min conditions Was given. In this way, a sample of the bonded body 1 was prepared.

(Joint body 2)
1.26 g of butyl stearate and 0.54 g of isobornyl cyclohexanol were placed in a plastic bottle and stirred with a mix rotor for 60 minutes to prepare a mixture 1. Next, 18.2 g of AgC239 and the mixed solution 1 were added to the agate mortar, kneaded until the dry powder was exhausted, and transferred to a new plastic bottle. ^{The sealed plastic bottle was stirred at 2000 min -1} (2000 rpm) for 1 minute using a rotating and revolving stirrer (Planetary Vacuum Mixer ARV-310, manufactured by Shinky Co., Ltd.). The obtained paste-like mixture (metal paste) was used as the bonding material 2. The concentration of the bonding material 2 (ratio of the content of AgC239 to the total amount of the bonding material 2) was 91% by mass.

The obtained bonding material 2 is mounted on a lead frame (joint size: 19 × 25 × 3 mm) subjected to electrolytic Ag plating by stencil printing using a metal squeegee, and has the same area as the chip (5. It was applied to 7 mm × 5.7 mm) with a printing thickness of 100 μm. Next, a Si chip (Schottky barrier diode manufactured by infineon, SIDC32D170H) was mounted directly above the bonding material 2 applied to the lead frame so that the side opposite to the surface on which the plating film was applied was in contact with the applied bonding material 2. Next, this was dried on a hot plate at 180 ° C. for 20 minutes, set in a thermocompression bonding device (manufactured by Ayumi Kogyo Co., Ltd.), heated in the air for 1 minute, and heated at 300 ° C. for 5 minutes. Sintering was performed under the condition of 20 MPa to form a sintered silver layer as a joint between the lead frame and the Si chip. Then, the load was removed and the sample was taken out at 50 ° C. or lower. In this way, a sample of the bonded body 2 was prepared.

(Joint body 3)
A sheet-shaped lead solder (manufactured by Senju Metal Industry Co., Ltd., Pb Ag1.5 Sn0.5, thickness 100 μm) is cut out into an area (5.7 mm × 5.7 mm) of the same size as the chip to be mounted, and a lead frame (joining) is performed. Part size: 19 x 25 x 3 mm) mounted on top. Next, a Si chip (Schottky barrier diode manufactured by infinion, SIDC32D170H) was mounted directly above the mounted sheet-shaped lead solder so that the side opposite to the surface on which the plating film was applied was in contact with the mounted sheet-shaped lead solder. It was then set to the thermocompression bonding device (manufactured by Ayumi Industries, Ltd.), 250 ° C. C. in formic acid, the reduction processing on for 15 minutes condition, in subsequent N _2, and heated until reaching 380 ° C. After confirming that the temperature was reached and the solder melted, vacuum replacement was performed to remove voids in the melted solder. _{Then, N 2} gas replacement was performed while slowly cooling, and a solder layer was formed as a joint between the lead frame and the Si chip. Then, the sample was taken out at 50 ° C. or lower. In this way, a sample of the bonded body 3 was prepared.

<Reliability evaluation of joints>
The following power cycle test was performed on the bonded product obtained above.
[Power cycle test]
The prepared sample is sandwiched by a spring jig with a load of 0.3 MPa, set in a power cycle test device (custom-made product), and the maximum value (junction temperature, Tj) of the chip heat generation temperature (junction temperature, Tj) estimated from the diode characteristics is set. By _{energizing the sample so that Tj max} ) becomes 175 ° C. and stopping energization until the chip temperature reaches 100 ° C. (Tj _min ), the condition that a temperature difference (ΔTj) occurs at the joint is derived in a short time. bottom. The energizing current and time at this time were used as test conditions, and this was repeated until the sample failed. Regarding the failure determination, when the same current as at the start was applied to the sample, the failure was determined when the junction temperature Tj changed by ± 10% or more, and the number of cycles at this time was defined as the number of failure cycles. This test was performed on n = 10 samples, and the Weibull distribution analysis was performed on the obtained number of failure cycles. By this Weibull distribution analysis, the relationship between the number of failure cycles and the cumulative failure rate was derived, and the power cycle life of each joint was evaluated. The cumulative failure rate means the ratio of failed samples in a certain number of cycles among all samples having the same configuration.

Table 1 summarizes the results of Weibull distribution analysis for the power cycle test. The evaluation items in the table have the following meanings.
Mean time between cycles: Mean time between failures when many passer cycle tests are performed (n = 10 or more for each sample).
Shape parameter m: An index for estimating a failure-causing factor. When m <1, it means an accidental failure, and when m ≧ 1, it means a failure due to deterioration.
Scale parameter η: Number of failure cycles at a cumulative failure rate of 63.2%.
Characteristic life (paired body 3) (times): Magnification when the scale parameter η of the bonded body 3 is 1.

It was confirmed that the bonded body 1 was joined under no pressure by a copper sintered body having excellent heat dissipation characteristics, but exhibited a characteristic life of 14.2 times that of the bonded body 3 using solder. rice field. Further, since the joint body 1 has a larger magnification of the characteristic life and a larger value of the shape parameter m than the joint body 2 joined by sintered silver, it can be seen that the joint body 1 has a long life and a small variation in failure timing. ..

According to the double-sided cooling type semiconductor module and the double-sided cooling type semiconductor device according to the present invention, reliability can be improved by applying a copper sintered body to the joint portion between the semiconductor element and the substrate.

1 ... Semiconductor element (power device), 11a, 11b ... Substrate (lead frame), 21,22 ... Cold heat source, 31 ... Copper sintered body, 41 ... Spacer, 51 ... Wire, 61 ... Resin member, 100,100' ... Double-sided cooling type semiconductor module (power card), 101 ... Double-sided cooling type semiconductor device.

Claims (6)

A semiconductor element, a first substrate provided on one main surface side of the semiconductor element, a second substrate provided on the other main surface side of the semiconductor element, the semiconductor element, and the first A first joining portion for joining the substrate and a second joining portion for joining the semiconductor element and the second substrate are provided.
A double-sided cooling semiconductor module in which at least one of the first joint and the second joint contains a copper sintered body. The double-sided cooling type semiconductor module according to claim 1, which has two or more of the semiconductor elements. The double-sided cooling type semiconductor module according to claim 1 or 2, wherein the copper sintered body is a sintered body of a bonding material containing copper particles. The double-sided cooling type semiconductor module according to any one of claims 1 to 3, wherein one or more of the first joint and the second joint include a spacer. The double-sided cooling semiconductor module according to any one of claims 1 to 4, and a first cooling heat source and a second cooling heat source connected to the first substrate and the second substrate of the double-sided cooling semiconductor module, respectively. A double-sided cooling semiconductor device equipped with a cold heat source. The method for manufacturing a double-sided cooling type semiconductor module according to any one of claims 1 to 4.
A first bonding step of sintering a bonding material containing copper particles provided between the first substrate and the semiconductor element, and / or provided between the second substrate and the semiconductor element. A method for manufacturing a double-sided cooling semiconductor module, comprising a second bonding step of sintering a bonding material containing the copper particles.

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