JP2021188071A - Joint material, method for producing joint material and joining method - Google Patents

Abstract

To provide a joint material that can form a metal joint layer with very few voids by a non-pressure joining process.SOLUTION: A joint material contains metal particle powder and a solvent. When measured at 25°C and 0.157 s-1, the joint material has a viscosity of 1000 Pa s or less.SELECTED DRAWING: None

Description

The present invention relates to a joining material, a method for producing the joining material, and a joining method.

In recent years, in the field of power devices such as power LEDs, high-frequency devices, and inverters, the problem of heat generation of devices has become more serious with the miniaturization and higher output of devices, and the discussion of thermal management has become active. It's coming. Further, in other semiconductor devices as well, studies on changing from conventional silicon-based devices to compound semiconductor devices are progressing, and the junction temperature tends to increase.

Based on these technical backgrounds, heat dissipation and bonding reliability are required for materials for bonding various semiconductor devices and substrates. Recently, a bonding material using metal fine particle powder such as sintered silver has been attracting attention as a material capable of realizing this heat dissipation property and bonding reliability. Further, since such a bonding material is sintered at a low temperature to form a metal bonding layer, attention is also paid to the fact that a substrate having low heat resistance can be used.

As described above, the metal bonding layer formed from the bonding material is required to have bonding strength and bonding reliability. Reducing voids in the metal bonding layer is effective in increasing these.

Further, as a bonding method, a bonding material is applied on a substrate, a semiconductor element or the like is placed on the formed coating film, and the material is fired while being pressed with a strong force (for example, a pressure of 10 MPa) in the bonding material. There is a pressure-type bonding method for forming a metal bonding layer by sintering the metal fine particles of the above (see, for example, Patent Documents 1 and 2). According to this, it is possible to form a metal bonding layer having few voids.

However, when such a strong force is applied to a semiconductor element or the like and a substrate under the semiconductor element or the like, these are damaged, and there is a concern in terms of reliability of a product manufactured by joining them. Therefore, studies have been made on joining materials and joining methods for performing joining with a weak force even when pressed or without pressing (for example, Patent Documents 3 to 6).

Japanese Unexamined Patent Publication No. 2011-046770 Japanese Unexamined Patent Publication No. 2019-149529 Japanese Unexamined Patent Publication No. 2017-214609 Japanese Unexamined Patent Publication No. 2020-035721 Japanese Unexamined Patent Publication No. 2016-054098 Japanese Unexamined Patent Publication No. 2011-175871

The present inventor also examined a non-pressurized joining method because of the concern about damage caused by the above-mentioned pressurization. As a void formation location during bonding (firing), a gap between the metal bonding layer and the substrate or the like can be considered. In the case of pressure bonding, the coating film (which is being sintered to form a metal bonding layer) is pressed against the substrate or the like, and these gaps are crushed and disappear to form a metal bonding layer in which voids are suppressed. However, in the case of non-pressurized joining, such a thing cannot be expected, and voids actually occur.

Therefore, it is an object of the present invention to provide a bonding material capable of forming a metal bonding layer having very few voids by bonding without pressure.

As a result of diligent studies to solve the above problems, the present inventor measured the viscosity at a very low shear rate even between the bonding materials having the same viscosity measured at the shear rate in the region widely used in the viscosity measurement of the bonding material. When used for non-pressurized bonding (between the metal bonding layer and the substrate, etc.), a bonding material with a low viscosity measured at such a low shear rate may have different viscosities. We have found that it is possible to form a metal bonding layer with very few voids, and have completed the present invention.

That is, the present invention is as follows.
[1] A bonding material containing a metal particle powder and a solvent, which has a viscosity of 1000 Pa · s or less as measured at ^{0.157 s-1 at 25 ° C.}

[2] The bonding material according to [1], wherein a part of the metal particle powder is a metal fine particle powder having an average primary particle diameter of 150 nm or less.

[3] The bonding material according to [2], wherein the content of the metal fine particle powder in the bonding material is 2 to 45% by mass.

[4] The bonding material according to any one of [1] to [3], wherein the viscosity is 800 Pa · s or less.

[5] The bonding material according to any one of [1] to [4], wherein the viscosity is 500 Pa · s or less.

[6] A part of the metal particle powder has a filling rate of 65.0% or more, and a volume-based cumulative 50% particle diameter (D50) measured by a laser diffraction type particle size distribution measuring device is 0.8 to 3. The bonding material according to any one of [1] to [5], which is a large metal particle powder having a thickness of 2 μm.

[7] The bonding material according to [6], wherein the content of the large metal particle powder in the bonding material is 40 to 88% by mass.

[8] The bonding material according to [6] or [7], wherein the filling rate of the large metal particle powder is 66.5% or more.

[9] The bonding material according to any one of [1] to [8], wherein the metal is at least one selected from the group consisting of gold, silver and copper.

[10] The bonding material according to any one of [1] to [9], wherein the metal is silver.

[11] The joining material according to any one of [1] to [10], which is used for joining in a non-pressurized method.

[12] The bonding material according to any one of [1] to [11], wherein the content of the metal particle powder in the bonding material is 90 to 96% by mass.

[13] Metal fine particle powder having an average primary particle diameter of 150 nm or less, a filling rate of 65.0% or more, and a volume-based cumulative 50% particle diameter (D50) measured by a laser diffraction type particle size distribution measuring device are 0. A method for producing a bonding material, in which a large metal particle powder having a size of 0.8 to 3.2 μm and a solvent are mixed.

[14] The amount of the metal fine particle powder and the metal large particle powder used is such that the contents of the metal fine particle powder and the metal large particle powder in the bonding material are 2 to 45% by mass and 40 to 88% by mass, respectively. The method for producing a bonding material according to [13].

[15] The total amount of the metal fine particle powder and the metal large particle powder used is such that the total content of the metal fine particle powder and the metal large particle powder in the bonding material is 90 to 96% by mass. 13] or [14], the method for producing a bonding material.

[16] The method for producing a bonding material according to any one of [13] to [15], wherein the filling rate of the large metal particle powder is 66.5% or more.

[17] The method for producing a bonding material according to any one of [13] to [16], wherein the metal is at least one selected from the group consisting of gold, silver and copper.

[18] A joining method for joining two members to be joined, wherein the joining material according to any one of [1] to [12] or any of [13] to [17] is placed on one of the members to be joined. A step of applying a bonding material manufactured by the method for manufacturing a bonding material described in 1 to form a coating film, a step of placing the other member to be bonded on the coating film, and a step of placing the other member to be bonded on the coating film. A bonding method comprising a step of firing a coating film on which a member is placed at 160 to 350 ° C. to form a metal bonding layer from the coating film.

[19] The joining method according to [18], wherein no pressure is applied to the two members to be joined and the coating film when the coating film is fired to form a metal bonding layer.

[20] The joining method according to [18] or [19], wherein one of the members to be joined is a substrate and the other member to be joined is a semiconductor element.

According to the present invention, there is provided a bonding material capable of forming a metal bonding layer having very few voids by non-pressurizing bonding.

Hereinafter, embodiments of the present invention will be described in detail.
[Joining material]
The embodiment of the bonding material of the present invention contains a metal particle powder and a solvent, and has a viscosity measured at a very low shear rate (0.157s ^-1 , which will be described later, a viscosity measured under the condition of 25 ° C., hereinafter “ It is also characterized by low shear viscosity).

<Low shear viscosity>
The viscosity of the embodiment of the bonding material of the present invention ^{measured at a shear rate of 0.157 s -1} and a temperature of 25 ° C. is 1000 Pa · s or less. It is considered that such a very low shear rate substantially corresponds to the gravity applied to the coating film formed by applying the bonding material to the object to be bonded such as a substrate. If the viscosity at such a shearing force (corresponding shear rate) is low to some extent, it is considered that the coating film wets and spreads on the object to be joined due to its own weight. As a result, it is considered that a gap is not formed between the object to be joined (such as a substrate) and the coating film, and when the metal bonding layer is formed, the void derived from the gap is not formed.

From the viewpoint of void reduction, the low shear viscosity is preferably 800 Pa · s or less, more preferably 500 Pa · s or less, and particularly preferably 450 Pa · s or less. The low shear viscosity is preferably 10 Pa · s or more. The low shear viscosity shall be measured using an E-type rotary viscometer. As described above, the low shear viscosity is an index of the ease of flow when the bonding material is applied to a substrate or the like and then self-flows to follow the surface shape of the substrate or the like. Therefore, the shear rate is measured by a viscometer. It is necessary to be able to measure the viscosity stably in the low region. In the evaluation of low shear viscosity, the low shear viscosity is calculated from the shear stress 60 seconds after the start of rotation when the cone of the viscometer is rotated at a shear rate of 0.157 s- ^1. From the viewpoint of ensuring the reliability of the measured data, the shear rate is within ± 1% of ^{the set value of 0.157s -1 for 30 seconds from 30 seconds to 60 seconds after the start of rotation.} The measurement condition is that.

<Metal particle powder>
The embodiment of the bonding material of the present invention contains metal particle powder, which is basically sintered by firing to form a metal bonding layer.

The content of the metal particle powder in the bonding material is preferably 70 to 98% by mass, more preferably 80 to 97% by mass, and further preferably 90 to 96% by mass. When the content of the metal particle powder in the bonding material is high, other organic components (solvents, etc., which are volatilized or remain during firing, and the organic components are present in the bonding material) are present. Can be voids), which is advantageous in terms of void reduction.

The constituent metal of the metal particle powder is preferably gold, silver, copper or an alloy of two or more of these from the viewpoint of conductivity and thermal conductivity. Further, silver is particularly preferable from the viewpoint of cost and oxidation resistance. The same applies to the large metal particle powder and the fine metal particle powder described later.

The shape of the metal particle powder is not particularly limited. It may have any shape such as substantially spherical, flake-shaped, and amorphous, but substantially spherical metal particle powder is preferable from the viewpoint of packing properties of particles in the bonding material. The same applies to the large metal particle powder and the fine metal particle powder described later.

(Metallic large particle powder)
Some of the metal particle powders described above have a cumulative 50% particle diameter (D50) of 0.8 to 3.2 μm on a volume basis measured by a laser diffraction type particle size distribution measuring device, and a filling rate of 65.0%. It is preferable that the metal large particle powder described above is used.

When the cumulative 50% particle diameter (D50) of the large metal particle powder is 0.8 μm or more, the viscosity of the bonding material (not the low shear viscosity, but the shear rate corresponding to the shearing force at the time of printing of the bonding material is measured. If the cumulative 50% particle size (D50) is 3.2 μm or less, the large metal particle powder is given some shearability to improve the bonding strength. It is possible to form an excellent metal bonding layer. From the above viewpoint, the cumulative 50% particle diameter (D50) of the large metal particle powder is preferably 1.0 to 2.2 μm.

With respect to the filling rate of the large metal particle powder, the low shear viscosity of the embodiment of the bonding material of the present invention is defined in the present invention described above by appropriate selection of the type and amount of the metal particle powder, solvent and other components. However, if the large metal particle powder having a high filling rate (65.0% or more) is used, the low shear viscosity of the bonding material can be preferably adjusted to the above range. can.

The filling factor is the ratio of the tap density of the large metal particle powder to the bulk density (true density) of the metal (tap density ÷ bulk density × 100 (%)). When a large metal particle powder having a filling rate of 65.0% or more is added to the bonding material, its low shear viscosity can be 1000 Pa · s or less, preferably 800 Pa · s or less. When a large metal particle powder having a filling rate of 66.5% or more is added to the bonding material, the low shear viscosity can be set to a numerical value such as 500 Pa · s or less or 450 Pa · s or less, and the viewpoint of reducing voids in the metal bonding layer can be obtained. Is particularly preferable. The filling rate of the large metal particle powder is preferably 85.8% or less.

The filling rate of the powder is an index of the fluidity of the powder (affected by the smoothness of the particle surface, etc.). It is considered that the low shear viscosity of the material can be reduced.

Most of the known metal powders having a size of about the size of large metal particle powder have a filling factor of 64.0% or less, but some of them have a filling factor of more than 65.0%. In the present invention, as an example for achieving the low shear viscosity, a large metal particle powder having a high filling rate of 65.0% or more is selectively used. The details of the method for measuring the tap density for obtaining the filling rate will be described in the section of Examples.

The content of the large metal particle powder in the bonding material is preferably 40 to 88% by mass, more preferably 50 to 85% by mass, and further preferably more preferably, from the viewpoint of achieving a low shear viscosity of the bonding material. It is 60 to 82% by mass.

The large metal particle powder may be coated with an organic compound from the viewpoint of enhancing the dispersibility in the bonding material and thereby enhancing the filling property. As the organic compound, a known organic compound capable of covering the particle surface of a large metal particle powder can be used without particular limitation. Examples of the organic compound include organic compounds having 12 to 24 carbon atoms having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a thiol group and a disulfide group. The organic compound may have branches and may be saturated or unsaturated.

(Metal fine particle powder)
The embodiment of the bonding material of the present invention preferably contains metal fine particle powder having an average primary particle diameter of 150 nm or less as a part of the metal particle powder. As described above, the fine metal fine particle powder has excellent sinterability, and a metal bonding layer having excellent bonding strength is formed from the bonding material containing the fine metal particles.

The average primary particle size of the metal fine particle powder is preferably 130 nm or less, more preferably 100 nm or less, from the viewpoint of sinterability by firing at a low temperature. The average primary particle size of the metal fine particle powder is preferably 1 nm or more.

In the present specification, the average primary particle size is an average value of the primary particle size (average primary particle based on the number) obtained from a transmission electron micrograph (TEM image) or a scanning electron micrograph (SEM image) of the particles. Diameter). More specifically, the particles are predetermined by, for example, a transmission electron microscope (TEM) (JEM-1011 manufactured by Nippon Denshi Co., Ltd.) or a scanning electron microscope (SEM) (S-4700 manufactured by Hitachi High-Technologies Co., Ltd.). Average primary particles from the primary particle diameter of 100 or more, preferably 250 arbitrary particles (diameter of a circle having the same area as the particle (circle equivalent to the area)) on the image (SEM image or TEM image) observed at the magnification of The diameter can be calculated. The diameter of the circle corresponding to the area can be calculated by, for example, image analysis software (A image-kun (registered trademark) manufactured by Asahi Kasei Engineering Co., Ltd.).

The content of the metal fine particle powder in the bonding material is preferably 2 to 45% by mass, from the viewpoint of forming a metal bonding layer having excellent bonding strength and preventing the low shear viscosity of the bonding material from increasing. It is preferably 5 to 35% by mass, more preferably 8 to 30% by mass.

Since the metal fine particle powder has a small particle diameter, it tends to easily aggregate. In order to prevent this, it is preferable that the metal fine particle powder is coated with an organic compound. As the organic compound, a known organic compound capable of covering the particle surface of the metal fine particle powder can be used without particular limitation. Examples of the organic compound include organic compounds having 1 to 18 carbon atoms having at least one functional group selected from the group consisting of a hydroxyl group, a carboxyl group, an amino group, a thiol group and a disulfide group. The organic compound may have branches and may be saturated or unsaturated.

The organic compound preferably has 12 or less carbon atoms and has 2 carbon atoms so that it is sufficiently separated from the metal fine particle powder by firing at about 160 to 350 ° C. and does not hinder the saturation of the metal fine particle powder particles. Saturated fatty acids or unsaturated fatty acids of -8, saturated amines or unsaturated amines are more preferred.

The constituent metal of the metal fine particle powder is a single type of constituent metal of the metal bonding layer formed from the bonding material, and the thermal expansion coefficient can be substantially constant over the entire bonding layer to improve the bonding reliability. It is preferably the same as the constituent metal of the particle powder.

As described above, in the embodiment of the bonding material of the present invention, it is preferable to include the metal large particle powder as a part of the metal particle powder and the metal fine particle powder as a part of the metal particle powder. The total of the large metal particle powder and the fine metal particle powder in the total metal particle powder (100% by mass) is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. Yes, especially preferably 100% by mass.

<Solvent>
Embodiments of the bonding material of the present invention include a solvent. As the solvent, a solvent capable of dispersing the metal particle powder and having substantially no reactivity with the components in the bonding material can be widely used.

The content of the solvent in the bonding material is preferably 1.5 to 18% by mass, more preferably 2.5 to 16% by mass, and even more preferably 3 to 9.5% by mass. .. A polar solvent or a non-polar solvent can be used as this solvent, but it is preferable to use a polar solvent from the viewpoint of compatibility with other components in the bonding material and an environmental load.

An example of a polar solvent is water;
Tarpineol, texanol, phenoxypropanol, 1-octanol, 1-decanol, 1-dodecanol, 1-tetradecanol, Telsolve MTPH (manufactured by Nippon Terpen Chemical Co., Ltd.), dihydroterpinyloxyethanol (manufactured by Nippon Terpen Chemical Co., Ltd.) , Telsolve TOE-100 (manufactured by Nippon Telpen Chemical Co., Ltd.), Telsolve DTO-210 (manufactured by Nippon Telpen Chemical Co., Ltd.) and other monoalcohols;
3-Methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol (octanediol), hexyldiglycol, 2-ethylhexylglycol, dibutyldiglycol, glycerin, dihydroxytriol, 3-methylbutane-1, 2,3-Triol (Isoplentriol A (IPTL-A), manufactured by Nippon Telpen Chemical Co., Ltd.), 2-Methylbutane-1,2,4-Triol (Isoplentriol B (IPTL-B), manufactured by Nippon Telpen Chemical Co., Ltd.) ) And other polyols;
Ether compounds such as butyl carbitol, diethylene glycol monobutyl ether, turpinylmethyl ether (manufactured by Nippon Terpen Chemical Co., Ltd.), dihydroterpinyl methyl ether (manufactured by Nippon Terpen Chemical Co., Ltd.);
Glycol ether acetate such as butyl carbitol acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate;
Nitrogen-containing cyclic compounds such as 1-methylpyrrolidinone and pyridine;
γ-Butyrolactone, methoxybutyl acetate, methoxypropyl acetate, ethyl lactate, 3-hydroxy-3-methylbutyl acetate, dihydroterpinyl acetate, Telsolv IPG-2Ac (manufactured by Nippon Telpen Chemical Co., Ltd.), Telsolv THA-90 (Japan) Ester compounds such as Telpen Chemical Co., Ltd.) and Telsolve THA-70 (manufactured by Nippon Telpen Chemical Co., Ltd.);
Etc. can be used. These may be used alone or in combination of two or more.

<Other ingredients (additives)>
The embodiment of the bonding material of the present invention may contain additives known as other components. Specifically, as additives, dispersants such as acid-based dispersants and phosphoric acid ester-based dispersants, sintering accelerators such as glass frit, antioxidants, viscosity regulators, pH regulators, buffers, and defoamers. Examples include agents, leveling agents, and volatilization inhibitors. The content of the additive in the bonding material is preferably 2% by mass or less (when a plurality of types of additives are contained, the total content is 2% by mass or less) (when the bonding material contains an additive, the content thereof). The amount is preferably 0.005% by mass or more (when a plurality of types of additives are contained, the content of each is 0.005% by mass or more).

In addition, there is a type of bonding material in which a resin is mixed to function as a binder between metal particle powders, but such a resin remains in the metal bonding layer formed from the bonding material and has heat dissipation properties. It may adversely affect the conductivity. Further, since the resin has a coefficient of thermal expansion significantly different from that of the metal, stress is generated due to the above difference when the metal bonding layer undergoes a thermal cycle, which adversely affects the bonding reliability.

From the above, it is preferable that the resin is not substantially blended in the embodiment of the bonding material of the present invention. Specifically, the content of the resin in the bonding material is preferably 0.3% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0.05% by mass or less. preferable.

[Manufacturing method of joint material]
In the embodiment of the bonding material of the present invention, the metal particle powder (preferably including the metal large particle powder and the metal fine particle powder as described above), the solvent, and other optional components (additives and the like) described above are known. It can be manufactured by kneading by the method of. Regarding the amount of each component used, it is preferable that the content of each component in the bonding material is an amount calculated from the charged amount of each component and is the amount described above as a preferable content thereof. In particular, the total amount of the metal fine particle powder and the metal large particle powder used is such that the total content of the metal fine particle powder and the metal large particle powder in the bonding material is 90 to 96% by mass. Preferred from the point of view.

The kneading method is not particularly limited. For example, each component is prepared individually, and in any order, an ultrasonic disperser, a disper, a three-roll mill, a ball mill, a bead mill, a twin-screw kneader, a planetary mixer, etc. Alternatively, the bonded material can be manufactured by kneading with a revolving rotation type stirrer or the like.

[Joining method]
In the embodiment of the joining method of the present invention, two members to be joined are joined by using the joining material manufactured by the embodiment of the joining material of the present invention or the embodiment of the method of manufacturing the joining material of the present invention. How to do it. The embodiment of the bonding method of the present invention includes a coating film forming step, a mounting step, and a metal bonding layer forming step, and may also carry out a pre-drying step and the like. Hereinafter, each of these steps will be described.

<Coating film forming process>
In this step, the bonding material produced according to the embodiment of the bonding material of the present invention or the method of manufacturing the bonding material of the present invention is printed on one of the members to be bonded (for example, metal mask printing, screen printing). Apply by printing, pin transfer), etc. to form a coating film. Since the embodiment of the bonding material of the present invention has a low shear viscosity, it is considered that the coating film wets and spreads on one of the members to be bonded, and a gap is unlikely to be formed between them.

An example of the one of the members to be joined is a substrate. As the substrate, a metal substrate such as a copper substrate, an alloy substrate of copper and some metal (for example, W (tungsten) or Mo (molybdenum)), or a ceramic in which SiN (silicon nitride) or AlN (aluminum nitride) is sandwiched between copper plates. Examples thereof include a substrate, a plastic substrate such as a PET (polyethylene terephthalate) substrate, and a PCB substrate such as FR4. Further, a laminated substrate in which these are laminated can also be used in the joining method of the present invention.

The portion to which the joining material of one of the members to be joined is applied may be plated with metal. From the viewpoint of bonding compatibility with the metal particle powder in the coating film, it is preferable that the metal plating is the same metal plating as the constituent metal of the metal particle powder.

<Placement process>
Subsequently, the other member to be joined is placed on the coating film formed on the one member to be joined. Examples of the other member to be joined include semiconductor devices such as Si chips, SiC, and GaN chips, and the same substrate as mentioned as an example of one member to be joined. Since a metal bonding layer with reduced voids is formed from the coating film, the embodiment of the bonding method of the present invention is preferably used for bonding a substrate and a semiconductor element. That is, a semiconductor element is preferable as the other member to be joined.

Further, since the embodiment of the bonding material of the present invention (the coating film formed from) has a low shear viscosity, when the other member to be bonded is placed on the coating film, the coating film is coated on the other. It is considered that the joint member is deformed following the surface shape of the portion (bottom surface) in contact with the coating film, and it is difficult to form a gap between the coating film and the other member to be joined.

The portion (bottom surface) of the other member to be joined that comes into contact with the coating film may be plated with metal. From the viewpoint of the bonding compatibility with the metal particle powder in the coating film, it is preferable that the metal plating of the other member to be bonded is the same metal plating as the constituent metal of the metal particle powder. Further, when the other member to be joined is placed on the coating film, the pressure in the direction in which the coating film is compressed by the two members to be joined (for example, 0.03 to 0. It may or may not be applied with a pressure of about 2 MPa).

<Preliminary drying process>
In order to reduce voids in the metal bonding layer formed when the coating film on which the other bonded member is placed is fired to sinter the metal particle powder, the other bonded member is placed on the coating film. After mounting (after the mounting step), a pre-drying step of pre-drying the coating film may be performed. The pre-drying is intended to remove the solvent from the coating film, and is dried under conditions such that the solvent volatilizes and the metal particle powder does not substantially cause sintering. Therefore, pre-drying is preferably carried out by heating the coating film at 60 to 150 ° C. Drying by this heating may be performed under atmospheric pressure, or may be performed under reduced pressure or vacuum. Further, in the metal bonding layer forming step described below, if the rate of temperature rise to the firing temperature is about 7 ° C./min or less, the preliminary drying step can be carried out by raising the temperature to the firing temperature.

<Metal bonding layer forming process>
After carrying out the mounting step and, if necessary, the pre-drying step, the coating film sandwiched between the two members to be joined is calcined at 160 to 350 ° C. to obtain metal particle powder (particularly fine metal fine particle powder). ) Is sintered to form a metal bonding layer, and the two members to be bonded are bonded.

In the metal bonding layer forming step, the temperature is raised to the firing temperature of 160 to 350 ° C., and the temperature is maintained at the firing temperature for, for example, 1 minute to 2 hours to form the metal bonding layer from the coating film of the bonding material. The rate of temperature rise is not particularly limited, but can be, for example, 1.5 ° C./min to 12 ° C./min, preferably 2 ° C./min to 6 ° C./min.

The firing temperature is preferably 175 to 280 ° C. from the viewpoint of the bonding strength and cost of the formed metal bonding layer.

The time for holding at the firing temperature is preferably 10 to 90 minutes from the viewpoint of the bonding strength of the formed metal bonding layer and the heat cost. If the firing temperature is higher than the firing temperature range shown above, for example, the firing temperature is 280 ° C. or higher, a metal bonding layer may be formed before the temperature rises to the firing temperature. In such a case, the holding time at the firing temperature may be 0 minutes.

Further, as described above, since the embodiment of the bonding material of the present invention (the coating film formed from) has a low shear viscosity, the formation of a gap between the coating film and one of the members to be joined is suppressed. it is conceivable that. Therefore, in this metal bonding layer forming step, even if no pressure is applied between the members to be bonded (in the direction in which the coating film being sintered to form the metal bonding layer is compressed by the two members to be bonded) ( Voids starting from the interface between the coating film (which is forming the metal bonding layer) and one of the members to be bonded are extremely difficult to form.

Applying pressure between the members to be joined, that is, to the two members to be joined and the coating film, may damage them as described in [Background Art]. For example, the joining can be carried out by suppressing the generation of voids without applying the above-mentioned pressurization. Further, when applying pressure, considering that a large number of joints are simultaneously performed from the viewpoint of the productivity of the joints, the same direction is applied to the sandwich structure of a large number of members to be joined-coating film-members to be joined. However, it is not easy to apply the same pressure at the same time, and there is a concern about the uniformity of the quality of the obtained product when a large number of pressure joints are performed at the same time. If the joint is not pressurized, there is no such concern. From the above, in the present invention, in principle, a non-pressurized bonding method is performed in which a metal bonding layer forming step is performed without pressurization to form a metal bonding layer.

The metal bonding layer forming step may be carried out in an atmospheric atmosphere or an inert atmosphere such as a nitrogen atmosphere, but it is preferably carried out in an inert atmosphere from the viewpoint of preventing oxidation. Further, from the viewpoint of cost, it is more preferable to carry out this step in a nitrogen atmosphere.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[Silver fine particle powder and silver large particle powder 1-4]
The physical characteristics of the silver fine particle powder and the silver large particle powders 1 to 4 used in the examples and comparative examples described below are as shown in Table 1 below.

The method for measuring various physical properties is as follows.

<Average primary particle size>
Primary particle diameter of 250 arbitrary particles on an image obtained by observing particles with a transmission electron microscope (TEM) (JEM-1011 manufactured by Nippon Denshi Co., Ltd.) at a magnification of 50,000 times (a circle with the same area as the particles (equivalent to the area)) The average primary particle diameter was calculated from the diameter of the circle). The diameter of the circle equivalent to the area was calculated by image analysis software (A-kun (registered trademark) manufactured by Asahi Kasei Engineering Co., Ltd.). At this time, the particle shape was also observed. The shapes of the silver large particle powders 1 to 4 were observed with a field emission scanning electron microscope (JSM-7200M, manufactured by JEOL Ltd.) at a magnification of 20000 times.

<Particle size distribution>
For the particle size distribution, use a laser diffraction type particle size distribution measuring device (SIMPATEC's Heros particle size distribution measuring device (HELOS & RODOS (air flow type dispersion module))), a dispersion pressure of 5 bar, and a lens with a focal length of 20 mm. By obtaining the volume-based particle size distribution of the sample powder, the cumulative 10% particle size (D10), the cumulative 50% particle size (D50), and the cumulative 90% particle size (D90) were obtained.

<Tap density>
The tap density is the same as the method described in JP-A-2007-263860, and the sample powder is filled in a bottomed cylindrical die having an inner diameter of 6 mm and a height of 11.9 mm up to 80% of the volume to form a powder layer. ^{After forming, a pressure of 0.160 N / m 2} is uniformly applied to the upper surface of the powder layer, the powder layer is compressed until the powder is no longer densely packed at this pressure, and then the height of the powder layer is measured. Then, the density of the powder was obtained from the measured value of the height of the powder layer and the weight of the filled sample powder, and this was used as the tap density of the powder.

<Filling rate (%)>
It was determined by calculating the percentage of the determined tap density to the bulk density of silver (10.49 g / cm ^3).

<Specific surface area>
For the specific surface area, a BET specific surface area measuring instrument (Macsorb manufactured by Mountech Co., Ltd.) was used to flow nitrogen gas into the measuring instrument at 105 ° C. for 20 minutes to remove substances adhering to the particle surface of the sample powder. It was measured by the BET 1-point method while flowing a mixed gas of nitrogen and helium (N2: 30% by volume, He: 70% by volume).

[Comparative example (preparation of bonding material)]
17.2% by mass of silver fine particle powder, 75.8% by mass of silver large particle powder 1, 0.2% by mass of SOLPLUSD-540 manufactured by Lubrizol as a dispersant, and Fuji Film Wako Junyaku Co., Ltd. as a solvent. Silver is kneaded with 2.35% by mass of Decanol manufactured by the company, 0.6% by mass of Telsolv IPTL-A manufactured by Nippon Telpen Chemical Co., Ltd., and 2.35 mass% of TOE-100 manufactured by Nippon Telpen Chemical Co., Ltd. A paste was prepared.

In order to adjust the viscosity of this silver paste to be suitable for printing, 0.75 wt% of each of decanol and TOE-100 was added and diluted to obtain a bonding material of Comparative Example. The silver concentration in the obtained bonded material was determined by the ignition loss method and found to be 93.0% by mass.

[Examples 1 to 4 (preparation of bonding material)]
<Example 1>
16.3% by mass of silver fine particle powder, 76.8% by mass of silver large particle powder 2, 0.2% by mass of SOLPLUSD-540 manufactured by Lubrizol as a dispersant, and Fuji Film Wako Junyaku Co., Ltd. as a solvent. Silver is kneaded with 2.35% by mass of Decanol manufactured by the company, 0.6% by mass of Telsolv IPTL-A manufactured by Nippon Telpen Chemical Co., Ltd., and 2.35 mass% of TOE-100 manufactured by Nippon Telpen Chemical Co., Ltd. A paste was prepared.

In order to adjust the viscosity of this silver paste to be suitable for printing, 0.70 wt% of each of decanol and TOE-100 was added and diluted to obtain the bonding material of Example 1. The silver concentration in the obtained bonded material was determined by the ignition loss method and found to be 93.1% by mass.

<Example 2>
17.6% by mass of silver fine particle powder, 75.5% by mass of silver large particle powder 2, 0.2% by mass of SOLPLUSD-540 manufactured by Lubrizol as a dispersant, and Fuji Film Wako Junyaku Co., Ltd. as a solvent. Silver is kneaded with 2.35% by mass of Decanol manufactured by the company, 0.6% by mass of Telsolv IPTL-A manufactured by Nippon Telpen Chemical Co., Ltd., and 2.35 mass% of TOE-100 manufactured by Nippon Telpen Chemical Co., Ltd. A paste was prepared.

In order to adjust the viscosity of this silver paste to be suitable for printing, 0.70 wt% of each of decanol and TOE-100 was added and diluted to obtain the bonding material of Example 2. The silver concentration in the obtained bonded material was determined by the ignition loss method and found to be 93.1% by mass.

<Example 3>
16.7% by mass of silver fine particle powder, 76.4% by mass of silver large particle powder 3, 0.2% by mass of SOLPLUSD-540 manufactured by Lubrizol as a dispersant, and Fuji Film Wako Junyaku Co., Ltd. as a solvent. Silver is kneaded with 2.35% by mass of Decanol manufactured by the company, 0.6% by mass of Telsolv IPTL-A manufactured by Nippon Telpen Chemical Co., Ltd., and 2.35 mass% of TOE-100 manufactured by Nippon Telpen Chemical Co., Ltd. A paste was prepared.

In order to adjust the viscosity of this silver paste to be suitable for printing, 0.70 wt% of each of decanol and TOE-100 was added and diluted to obtain the bonding material of Example 3. The silver concentration in the obtained bonded material was determined by the ignition loss method and found to be 93.1% by mass.

<Example 4>
17.2% by mass of silver fine particle powder, 75.8% by mass of silver large particle powder 4, 0.2% by mass of SOLPLUSD-540 manufactured by Lubrizol as a dispersant, and 0.2% by mass of SOLPLUSD-540 manufactured by Nippon Terupen Chemical Co., Ltd. as a solvent. Silver by kneading Telsolv IPTL-A with 0.6% by mass, Fuji Film Wako Pure Chemical Co., Ltd. with 2.35% by mass, and Nippon Telpen Chemical Co., Ltd. with TOE-100 with 2.35% by mass. A paste was prepared.

In order to adjust the viscosity of this silver paste to be suitable for printing, 0.70 wt% of each of decanol and TOE-100 was added and diluted to obtain the bonding material of Example 4. The silver concentration in the obtained bonded material was determined by the ignition loss method and found to be 93.0% by mass.

As described above, the component compositions of the prepared bonding materials of Comparative Examples 1 and Examples 1 to 4 are shown in Table 2 below.

[Viscosity measurement]
<Low shear viscosity>
For the joint materials of Comparative Examples and Examples 1 to 4, a rheometer (rotary dynamic viscometer) (HAAKE RheoStress 600 manufactured by Thermo), which is an E-type rotary viscometer, has a cone diameter of 35 mm and a cone angle of 2. The viscosity (low shear viscosity) was evaluated under the conditions of 25 ° C. and a shear rate of 0.157s ^{-1 using a ° cone).} The viscosity was measured as follows. The low shear viscosity was calculated from the shear stress 60 seconds after the start of rotation when the bonding material was injected into the gap between the stage and the cone and the cone ^{was rotated at 0.157s-1.} After confirming that the shear rate at that time is within ± 1% of ^{the set value of 0.157s -1} for 30 seconds from 30 seconds to 60 seconds after the start of rotation. Then, a low shear viscosity was obtained.

<Viscosity at 1 rpm and 5 rpm>
Moreover for the bonding material of Comparative Example and Examples 1-4, using the above and similar rheometer at 25 ° C., the rotational speed 1rpm (3.1s ^-1), and at 5rpm (15.7s ^-1) Viscosity and thixotropy (viscosity at 1 rpm / viscosity at 5 rpm) were determined.

The results of the above viscosity measurements are summarized in Table 3 below.

As shown in Table 3, it was confirmed that the bonding materials of Comparative Examples and Examples 1 to 4 differed greatly in low shear viscosity, although they did not change much in 1 rpm viscosity, 5 rpm viscosity and thixotropic ratio.

<Joining test (void evaluation)>
A DBC substrate (SiN (nitriding) having a size of 30 mm × 36.6 mm × 2.32 mm (Cu / SiN / Cu = 1.0 mm / 0.32 mm / 1.0 mm) degreased with ethanol and then treated with 10 mass% sulfuric acid. A ceramic substrate (silicon) sandwiched between copper plates) and a semiconductor element having a size of 8 mm × 8 mm × 0.1 mm with Ag plating on the joint surface (entire surface of the bottom surface) were prepared.

Next, the bonding materials of Comparative Examples and Examples 1 to 4 were applied onto the DBC substrate by metal mask printing, respectively. On the bonding material coated on the DBC substrate, the Ag-plated portion of the above-mentioned semiconductor element was arranged so as to be in contact with the bonding material. After applying a load of 5N (pressure of about 0.08 MPa) by pushing the entire upper surface of the device between the bonding material and the semiconductor device, 25 in a nitrogen atmosphere (oxygen concentration of 500 ppm or less) by a hot air circulation firing furnace. The temperature was raised from ° C. to 250 ° C. at a heating rate of 3 ° C./min and fired at 250 ° C. for 60 minutes to form a silver bonding layer, and the semiconductor element was bonded to the DBC substrate by this silver bonding layer.

The obtained DBC substrate-silver junction layer-semiconductor element junction was subjected to an ultrasonic flaw detection inspection device (C-SAM: D9500 manufactured by SONOSCAN) from the top surface of the semiconductor element to the junction (semiconductor element-silver junction layer from above). -The laminated part of the DBC substrate) was observed. From the obtained image (C-SAM image), the presence or absence of voids at the interface with the silver bonding layer of the DBC substrate was observed. In addition, using the analysis software attached to the device, the ratio (percentage) of the void points to all observation sites was calculated, and this was defined as the void rate. The void portion is a portion that appears white in the C-SAM image, and the entire observation portion is a square region of 8 mm × 8 mm corresponding to the joint surface of the semiconductor element.

The evaluation results of the void rate are shown in Table 4 below. Table 4 also shows the low shear viscosity of the bonding material and the tap density and filling rate of the silver large particle powder in the bonding material.

As shown in Table 4, in the comparative example using the bonding material having a large low shear viscosity, the void ratio was 1.24%, whereas in Examples 1 to 4, the low shear viscosity was 1000 Pa · s. It was confirmed that by using the following bonding material, the void ratio can be suppressed to 0.77% or less, which is lower than that of the comparative example, and the void can be reduced. It was also confirmed that the smaller the low shear viscosity, the lower the void ratio. In this way, by reducing the low shear viscosity of the bonding material, voids can be reduced.

Claims (20)

A bonding material containing metal particle powder and a solvent, having a viscosity of 1000 Pa · s or less measured at ^{0.157s-1 at 25 ° C.} The bonding material according to claim 1, wherein a part of the metal particle powder is a metal fine particle powder having an average primary particle diameter of 150 nm or less. The bonding material according to claim 2, wherein the content of the metal fine particle powder in the bonding material is 2 to 45% by mass. The bonding material according to any one of claims 1 to 3, wherein the viscosity is 800 Pa · s or less. The bonding material according to any one of claims 1 to 4, wherein the viscosity is 500 Pa · s or less. A part of the metal particle powder has a filling rate of 65.0% or more, and a volume-based cumulative 50% particle diameter (D50) measured by a laser diffraction type particle size distribution measuring device is 0.8 to 3.2 μm. The bonding material according to any one of claims 1 to 5, which is a large metal particle powder. The bonding material according to claim 6, wherein the content of the large metal particle powder in the bonding material is 40 to 88% by mass. The bonding material according to claim 6 or 7, wherein the filling rate of the large metal particle powder is 66.5% or more. The bonding material according to any one of claims 1 to 8, wherein the metal is at least one selected from the group consisting of gold, silver and copper. The bonding material according to any one of claims 1 to 9, wherein the metal is silver. The joining material according to any one of claims 1 to 10, which is used for joining in a non-pressurized method. The bonding material according to any one of claims 1 to 11, wherein the content of the metal particle powder in the bonding material is 90 to 96% by mass. Metallic fine particle powder with an average primary particle size of 150 nm or less, a filling rate of 65.0% or more, and a volume-based cumulative 50% particle size (D50) measured by a laser diffraction type particle size distribution measuring device are 0.8 to. A method for producing a bonding material, in which a large metal particle powder having a size of 3.2 μm and a solvent are mixed. The amount of the metal fine particle powder and the metal large particle powder used is such that the contents of the metal fine particle powder and the metal large particle powder in the bonding material are 2 to 45% by mass and 40 to 88% by mass, respectively. The method for producing a bonding material according to claim 13. 13. 14. The method for producing a bonding material according to 14. The method for producing a bonding material according to any one of claims 13 to 15, wherein the filling rate of the large metal particle powder is 66.5% or more. The method for producing a bonding material according to any one of claims 13 to 16, wherein the metal is at least one selected from the group consisting of gold, silver and copper. A joining method for joining two members to be joined, wherein the joining material according to any one of claims 1 to 12 or the joining material according to any one of claims 13 to 17 is placed on one of the members to be joined. The step of applying the bonding material manufactured by the manufacturing method to form a coating film, the step of placing the other member to be joined on the coating film, and the coating on which the other member to be joined is placed. A bonding method comprising a step of firing a film at 160 to 350 ° C. to form a metal bonding layer from the coating film. The joining method according to claim 18, wherein no pressure is applied to the two members to be joined and the coating film when the coating film is fired to form a metal bonding layer. The joining method according to claim 18 or 19, wherein one of the members to be joined is a substrate and the other member to be joined is a semiconductor element.