JP6848549B2 - Copper paste for bonding and semiconductor devices - Google Patents

Description

The present invention relates to a copper paste for bonding and a semiconductor device, and more specifically, a semiconductor element such as a power semiconductor, an LSI, or a light emitting diode (LED) is used as a lead frame, a ceramic wiring board, a glass epoxy wiring board, a polyimide wiring board, or the like. The present invention relates to a bonding copper paste suitable for bonding to a semiconductor mounting substrate and a semiconductor device obtained by using the bonding copper paste.

When manufacturing a semiconductor device, as a method of adhering a semiconductor element and a lead frame (support member), a paste-like adhesive in which a filler such as silver powder is dispersed in a resin such as an epoxy resin or a polyimide resin ( For example, there is a method of using silver paste). In this method, a paste-like adhesive is applied to a die pad of a lead frame using a dispenser, a printing machine, a stamping machine, or the like, and then a semiconductor element is die-bonded and bonded by heat curing to form a semiconductor device.

In recent years, as semiconductor elements have become faster and more integrated, adhesives are also required to have high heat dissipation characteristics in order to ensure the operational stability of semiconductor devices.

Adhesives for the purpose of improving thermal conductivity have been proposed so far. For example, Patent Documents 1 to 5 below include die bonding pastes (Patent Documents 1 and 2) highly filled with silver particles having high thermal conductivity, and conductive adhesives containing spherical silver powder having a specific particle size (Patent Documents 1 and 2). Patent Document 3), paste of adhesive containing solder particles (Patent Document 4), conductive adhesive containing metal powder having a specific particle size and ultrafine metal particles having a specific particle size (Patent Document 5). ) Is disclosed.

Further, in Patent Document 6 below, silver particles are baked by heating a paste-like silver particle composition composed of surface-treated non-spherical silver particles and a volatile dispersion medium at 100 ° C. or higher and 400 ° C. or lower. A technique has been proposed in which they are combined to form solid silver having a predetermined thermal conductivity.

Further, in Patent Document 7 below, a paste-like copper particle composition in which micro-sized copper particles and nano-sized copper particles are dispersed in a volatile dispersion medium is heated from 200 to 450 ° C. in nitrogen or hydrogen-mixed nitrogen. Similarly, a technique of sintering copper particles to form solid copper and joining them has been introduced.

The paste-like silver or copper particle composition described in Patent Documents 6 and 7 is considered to have superior thermal conductivity and connection reliability at high temperatures as compared with other methods because the metal particles form metal bonds. .. In particular, copper is considered to be highly effective in terms of cost.

Japanese Unexamined Patent Publication No. 2006-73811 Japanese Unexamined Patent Publication No. 2006-302834 Japanese Unexamined Patent Publication No. 11-66953 Japanese Unexamined Patent Publication No. 2005-93996 Japanese Unexamined Patent Publication No. 2006-8337 Japanese Patent No. 4353380 Japanese Unexamined Patent Publication No. 2014-167145

Although the method described in Patent Document 7 performs sintering without pressurization, it is not yet sufficient for practical use in the following points. That is, unpressurized joining using a joining material is performed well when the materials of the members to be joined are the same or close to each other, but when the materials of the members to be joined are different, the joining force is high. It tends to drop significantly. According to the studies by the present inventors, for example, a case where a copper plate having copper on the adherend surface and a copper block having nickel on the adherend surface are joined, and a case where the copper plate having copper on the adherend surface and nickel on the adherend surface are joined. Comparing with the case of bonding silicon chips having the above, the latter bonding strength may be significantly reduced under non-pressurized sintering conditions. That is, when members having different coefficients of thermal expansion, such as a copper block and a silicon chip, are joined without pressure, a joining defect may occur.

The inventor infers the reason for this as follows. That is, the paste-like copper particle composition composed of only the metal particles and the dispersion medium is insufficient in flexibility and adhesion when the dispersion medium is removed to form a sedimentary layer containing only the metal particles. Therefore, it is considered that the joint member is peeled off due to the displacement caused by the difference in the coefficient of thermal expansion between the joint members when the temperature is raised from room temperature to several hundred degrees, which is the firing temperature. Further, in such a paste-like copper particle composition, since the members to be joined are not sufficiently adhered to each other at the stage after coating / mounting the semiconductor element and before starting the firing step, transfer or the like is performed. It is also considered that the occurrence of defects due to vibration or impact is also an issue.

The present invention provides a bonding copper paste having excellent thermal conductivity and connection reliability and capable of bonding a semiconductor element and a semiconductor device mounting support member in a simple process, and a semiconductor device obtained by using the copper paste for bonding. The purpose is to provide.

The present invention is a bonding copper paste containing copper particles, a pyrolytic resin, and a solvent, wherein the content of the copper particles is 65% by mass or more based on the total mass of the bonding copper paste. Provided is a copper paste for bonding in which the content of the pyrolytic resin is 1% by mass or more based on the total mass of the copper particles and the pyrolytic resin.

In the present invention, the thermosetting resin is preferably at least one selected from the group consisting of polycarbonate, polymethacrylic acid, polymethacrylic acid ester and polyester.

In the present invention, the copper particles are sub-micro copper particles having a volume average particle diameter of 0.12 μm or more and 0.8 μm or less, and flake-shaped micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 or more. The content of the flake-shaped micro copper particles is preferably 50% by mass or less based on the total mass of the copper particles.

The present invention also provides a semiconductor device having a structure in which a semiconductor element and a support member for mounting a semiconductor element are bonded via the above-mentioned sintered body of copper paste for bonding.

According to the present invention, a copper paste for joining, which is excellent in thermal conductivity and connection reliability and can join a semiconductor element composed of members having different coefficients of thermal expansion and a support member for mounting the semiconductor element, and a semiconductor obtained by using the paste. Equipment can be provided. The semiconductor device can have excellent thermal conductivity and connection reliability by having a structure in which a semiconductor element and a support member for mounting a semiconductor element are bonded by the bonding copper paste of the present invention.

It is a schematic cross-sectional view which shows an example of a joined body. It is a schematic cross-sectional view which shows another example of a joined body. It is a schematic cross-sectional view which shows an example of the semiconductor device of this invention. It is a schematic cross-sectional view which shows another example of the semiconductor device of this invention. It is a schematic cross-sectional view which shows another example of the semiconductor device of this invention.

<Copper paste for joining>
The bonding copper paste of this embodiment requires at least copper particles, a pyrolytic resin and a solvent. The copper particles are sintered by firing, and the adherend and the sintered copper particles are bonded to each other by a metal bond to exhibit a function of joining. In the pyrolyzable resin, after the adherend and the copper paste for bonding come into contact with each other, the adherends are temporarily fixed to each other until they are joined by the copper particle sintered body, and both are peeled off by thermal stress or vibration during the process. Prevent from doing. By selecting a thermally decomposable resin that has thermal decomposability below the sintering temperature and does not leave any decomposition residue, it does not hinder sintering, and the connection strength and connection reliability after sintering. You can improve your sex. The solvent is used to dissolve the pyrolytic resin and disperse the copper particles to obtain a paste. Since it is a paste, it has a function of adhering to an adherend surface by coating, printing, and deformation.

The bonding copper paste of the present embodiment preferably further contains a dispersant, a sintering aid, and the like. The dispersant coats the surface of the copper particles to exhibit the functions of preventing oxidation and improving the dispersibility in the solvent, improving the content of the copper particles in the paste, improving the storage stability, and improving the viscosity characteristics. The sintering aid exhibits a function of promoting the sintering of copper particles during firing, reduces the sintering temperature, and improves the density of the sintered body. Hereinafter, each component will be described in detail.

<Copper particles>
The copper particles (sinterable copper particles) preferably contain copper as a main component from the viewpoint of thermal conductivity, sinterability, and connection reliability. Among the elements contained in the copper particles, the element ratio of copper in the element ratio excluding hydrogen, carbon, and oxygen is preferably 80 atomic% or more, more preferably 90 atomic% or more, and 95 atomic% or more. The above is more preferable. If the copper content is lower than this, the produced copper sintered body bonding layer becomes an alloy having properties different from those of copper, and the thermal conductivity and connection reliability are lowered.

For copper particles, in order to lower the sintering temperature (for example, 300 ° C. or lower), sub-micro copper particles (micro-particle size copper particles) having a volume average particle size of 0.12 μm or more and 0.8 μm or less are used as copper particles. It is preferable to contain at least 50% by mass or more based on the total mass. Sub-micro copper particles of this size start sintering at about 250 ° C. and can be bonded at a low temperature. When the volume average particle size 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 diameter is 0.8 μm or less, the effect of excellent sinterability of the submicro copper particles can be easily obtained. From the viewpoint of further exerting the above effect, the volume average particle size of the submicro 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, or 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.

In the above-mentioned sintering of the sub-micro copper particles alone, the volume shrinkage is large, and cracks on the sintered body, peeling from the adherend surface, and a decrease in the density of the sintered body are likely to occur. Therefore, it is preferable that the sub-micro copper particles and the micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less are contained together. When micro-copper particles are contained, the effect of reducing the volume shrinkage during sintering and improving the strength of the bonded layer after sintering can be obtained. From the viewpoint of further exerting the above effect, the maximum diameter of the micro copper particles may be 1 μm or more and 10 μm or less, or 3 μm or more and 10 μm or less.

The content of the micro copper particles in the copper particles is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 20% by mass or more. The upper limit of the content is preferably 50% by mass or less. If the content of the micro copper particles is too large, the sinterability at 300 ° C. or lower tends to decrease, and the bonding strength tends to decrease.

Examples of the shape of the micro copper particles include a spherical shape, a substantially spherical shape, a polyhedral shape, a needle shape, and a flake shape. In particular, when needle-shaped or flake-shaped copper particles having a large aspect ratio are used, the reinforcing effect and the density improving effect due to the orientation of the micro copper particles can be obtained, which is preferable.

When the micro-copper particles are flake-shaped (flake-shaped micro-copper particles), the aspect ratio may be 4 or more, or 6 or more. When the aspect ratio is within the above range, the flake-shaped micro copper particles in the bonding copper paste are oriented substantially parallel to the bonding surface, so that the volume shrinkage when the bonding copper paste is sintered is reduced. Easy to suppress. 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 microcopper particles and the submicrocopper particles may be treated with a surface treatment agent. However, it is preferable that the surface treatment agent can be removed in the sintering step. Examples of such surface treatment agents include aliphatic carboxylic acids such as acetic acid, lauric acid, palmitic acid, stearic acid, arachidic acid, terephthalic acid and oleic acid, and aromatics such as pyromellitic acid and o-phenoxybenzoic acid. Carboxylic acids, cetyl alcohols, stearyl alcohols, aliphatic alcohols such as isobornylcyclohexanol and tetraethyleneglycol, aromatic alcohols such as p-phenylphenol, alkylamines such as octylamine, dodecylamine and stearylamine, stearonitrile , Organic nitrile compounds such as decanitrile, and polymer treatment agents such as the thermally decomposable resin described below.

In the present specification, the sub-micro copper particles mean particles having a particle size of 0.1 μm or more and less than 1.0 μm, and the micro copper particles mean particles having a particle size of 1.0 μm or more and less than 20 μm. To do.

<Pyrolytic resin>
As the pyrolytic resin, a non-crystalline polymer capable of exhibiting adhesiveness and adhesiveness is preferable for the purpose of temporarily fixing the adherend and the copper paste for bonding from application to firing. Further, it is preferable to have a thermal decomposability that can be decomposed at the sintering temperature and decomposed without residue.

The pyrolyzable temperature is the decomposition start temperature of the pyrolyzable resin, and is set to the 5% weight loss temperature in the TG / DTA measurement. The decomposition start temperature needs to be lower than the sintering temperature, and is usually preferably 300 ° C. or lower, more preferably 250 ° C. or lower. However, this temperature is the decomposition start temperature in a reducing atmosphere containing hydrogen, formic acid, etc., not in an oxidizing atmosphere such as air.

The amount of the residue after thermal decomposition of the thermosetting resin is better because it hinders the sintering of copper particles, and is usually preferably 5% by mass or less, more preferably 2% by mass or less, based on the mass of the resin before thermal decomposition. The amount of residue after pyrolysis of the pyrolyzable resin is the weight after holding for the sintering time at the sintering temperature by the TG / DTA of the pyrolysis resin in an inert gas (nitrogen or argon) containing 3 to 5% by mass of hydrogen. It can be measured as the amount of change. It should be noted that the TG / DTA measurement in air is not preferable because the amount of residue in the reducing atmosphere is smaller than that in the reducing atmosphere because oxidative decomposition proceeds.

The pyrolytic resin needs to be soluble in a solvent. Examples of the thermosetting resin having solubility and the above desired properties include polycarbonate, polymethacrylic acid, polymethacrylic acid ester, and polyester.

<Solvent>
The solvent is required to have a function of dispersing copper particles and dissolving a thermally decomposable resin to obtain a copper paste for bonding, and is further volatilized and removed during firing so as not to remain in the sintered layer after sintering. Is required.

The dispersion medium capable of dispersing the copper particles and dissolving the pyrolytic resin depends on the type of the surface treatment agent for the copper particles, the type of the dispersant added to the copper paste for bonding, the type of the pyrolytic resin, and the like. For example, when a highly polar dispersant or a highly polar pyrolytic resin is selected, a highly polar solvent is suitable, and when a low polar dispersant or a low polar pyrolytic resin is selected, it is low. Polar solvents are preferred.
It is inferred that it is preferable to select a combination of such dispersants, pyrolytic resins, and solvents having similar Hansen solubility parameters. The Hansen solubility parameter can be searched, for example, from the database at the end of the following published literature, or searched / calculated by the database and simulation integrated software HSPiP.
Published literature: "HANSEN SOLUBILITY PARAMETERS: A USER'S HANDBOOK" (CRC Press, 1999)

The boiling point of the solvent is preferably 400 ° C. or lower, more preferably 370 ° C. or lower. If the boiling point of the solvent is higher than this temperature, it becomes difficult to volatilize and remove it by the sintering temperature, which causes sintering inhibition, gas generation after sintering, and corrosion.

Examples of highly polar solvents include carbonate esters such as 1,3-dioxolan-2-one and 4-methyl-1,3-dioxolan-2-one, lower alcohols such as methanol and ethanol, glycerin and diglycerin. , Polyhydric alcohols such as diethylene glycol and propylene glycol, amines, acid amides such as N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, esters such as γ-butyrolactone, water Can be mentioned.

Examples of low polar solvents include higher alcohols such as pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, butylene glycol, α-terpineol and bornylcyclohexanol (MTPH), ethylene glycol butyl ether and 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 butyl methyl ether, diethylene glycol isopropyl methyl ether, triethylene glycol. Diethyl ether, triethylene glycol butyl methyl ether, propylene glycol propyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol dimethyl ether, tripropylene glycol methyl ether, tripropylene Ethers such as 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), ethyl lactate, butyl lactate, esters such as propylene carbonate, etc. Examples thereof include aliphatic hydrocarbons such as cyclohexanone, octane, nonane, decane and undecane, and aromatic hydrocarbons such as benzene, toluene and xylene.

<Sintering aid>
The sintering aid exhibits a function of promoting the sintering of copper particles, and has the effects of reducing the starting temperature of sintering and improving the density of the sintered body. As such a sintering aid, there are dissimilar metal particles having a melting point lower than that of copper.

Dissimilar metal particles having a melting point lower than that of copper start sintering at a temperature lower than that of the copper particles from the contact point with copper, and the effect of reducing the sintering temperature can be obtained. Examples of such dissimilar metal species include zinc, tin, silver, gold, palladium, indium, gallium, aluminum and antimonide. These dissimilar metals may be used as a simple substance or as an alloy, or a plurality of types of dissimilar metal particles may be used at the same time.

The smaller the particle size of the dissimilar metal particles, the higher the effect, but with metal species other than gold, silver, and palladium, the effect tends to decrease due to surface oxidation when nanoparticles are used. Therefore, the 50% volume average particle size is preferably 0.1 μm or more. In particular, the 50% volume average particle size is more preferably 0.2 to 5 μm because of its availability.

The amount of the sintering aid added is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, and 0.1% by mass or more, based on the total mass of the copper particles. More preferably, it is 1% by mass or less. If it is less than this amount, it is difficult to obtain a sufficient effect, and if it is more than this amount, it is alloyed with copper to lower the thermal conductivity and electrical conductivity, or as a foreign substance that is not incorporated into the sintered body, the sintered body Reduces strength.

<Composition ratio of copper paste for bonding>
The content of the copper particles is preferably 65% by mass or more and 95% by mass or less, and more preferably 75% by mass or more and 94% by mass or less, based on the total mass of the copper paste for bonding. If it is less than this, the difference between the volume of the copper paste for bonding and the volume of the sintered body becomes large, which causes peeling and cracks. If it is more than this, the fluidity of the bonding copper paste is lost, and the coatability and adhesion are deteriorated.

The content of the pyrolytic resin is preferably 0.6% by mass or more and 15% by mass or less based on the total mass of the copper paste for bonding.

The content of the pyrolytic resin is preferably 1% by mass or more, preferably 1.5% by mass, based on the total mass of the copper particles and the pyrolytic resin (that is, the mass when the solvent is dried and removed). % Or more is more preferable. If the amount of the pyrolytic resin is less than this, peeling occurs due to thermal stress between the members before the start of sintering, resulting in poor bonding. The upper limit of the content is preferably 20% by mass or less based on the total mass of the copper particles and the thermally decomposable resin. If it is more than this, the difference between the volume of the copper paste for bonding and the volume of the sintered body becomes large, which causes a decrease in the density of the sintered body, peeling and cracks.

The content of the solvent can be, for example, the balance of the contents of the copper particles and the thermally decomposable resin. The content is preferably 4% by mass or more and 34% by mass or less, and more preferably 8% by mass or more and 20% by mass or less, based on the total mass of the copper paste for bonding. If it is less than this, the fluidity is lost and the coatability and adhesion are deteriorated. On the other hand, if it is more than this, the difference between the volume of the copper paste for bonding and the volume of the sintered body becomes large, which causes peeling and cracks.

<Preparation of copper paste for bonding>
The copper paste for bonding can be prepared by mixing the above-mentioned copper particles, pyrolytic resin, other metal particles and any additive with a solvent. For example, it can be prepared by dissolving a thermally decomposable resin in a solvent and then adding copper particles, other metal particles, a dispersant and an arbitrary additive to carry out a dispersion treatment. Alternatively, a solution obtained by mixing a pyrolytic resin in a solvent and dissolving it, and a dispersion liquid obtained by mixing sintered copper particles and a dispersant in a solvent and performing a dispersion treatment are mixed, and copper particles, other metal particles, and optionally. Can be prepared by adding the above additives.

The copper particles contain at least sub-micro copper particles and micro-copper particles, but a dispersant is added to a solvent or a thermally decomposable resin solution as necessary, and the sub-micro copper particles are first mixed and then dispersed. The dispersion treatment may be carried out by adding microcopper particles and other metal particles. The dispersion method and dispersion conditions suitable for dispersion may differ between the sub-micro copper particles and the micro copper particles. In general, sub-microcopper particles require stronger dispersion than microcopper particles, while microcopper particles are easy to disperse and low-strength dispersion is sufficient, and strong dispersion causes the microcopper particles to deform. Occurs. By performing such a procedure, the dispersibility is improved, and the performance of the copper paste for bonding can be further improved. The agglomerates may be removed by performing a classification operation on the dispersion liquid.

After mixing each component, stirring treatment may be performed. For the bonding copper paste, the maximum particle size of the dispersion may be adjusted by a classification operation. At this time, the maximum particle size of the dispersion liquid can be 20 μm or less, and can be 10 μm or less.

The dispersion treatment can be performed using a disperser or a stirrer. For example, Ishikawa stirrer, Silberson stirrer, cavitation stirrer, rotation and revolution type stirrer, ultra-thin high-speed rotary disperser, ultrasonic disperser, Raikai machine, twin-screw kneader, bead mill, ball mill, triple roll mill, homo mixer , Planetary mixer, ultra-high pressure type disperser, thin layer shear disperser.

The stirring process can be performed using a stirrer. For example, an Ishikawa type stirrer, a rotation / revolution type stirrer, a Raikai machine, a twin-screw kneader, a three-roll mill, and a planetary mixer can be mentioned.

The classification operation can be performed using, for example, filtration, natural sedimentation, and centrifugation. Examples of the filter for filtration include a water comb, a metal mesh, a metal filter, and a nylon mesh.

The bonding copper paste may be adjusted to a viscosity suitable for each printing / coating method. As the viscosity of the copper paste for bonding, for example, the Casson viscosity at 25 ° C. may be 0.05 Pa · s or more and 2.0 Pa · s or less, and 0.06 Pa · s or more and 1.0 Pa · s or less. May be good.

<Joints and semiconductor devices>
Hereinafter, preferred embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted. Moreover, the dimensional ratio of the drawing is not limited to the ratio shown in the drawing.

FIG. 1 is a schematic cross-sectional view showing an example of a bonded body manufactured by using the bonding copper paste of the present embodiment. The bonded body 100 of the present embodiment is the above-mentioned joint that joins the first member 2, the second member 3 having a coefficient of thermal expansion different from that of the first member, and the first member and the second member. A sintered body 1 of a copper paste for use is provided. As shown in FIG. 2, the bonded body of the present embodiment includes a plurality of first members 2a and 2b, a second member 3 having a coefficient of thermal expansion different from that of the first member, and a first member. The bonded body 110 may include the sintered body 1 of the copper paste for bonding that joins the member and the second member.

In such a configuration, when the temperature is raised from room temperature to the firing temperature during firing, the heat that causes the bonding copper paste before sintering to be peeled off from the difference in the coefficient of thermal expansion between the first member 2 and the second member 3. Stress works. In particular, since the thermal stress becomes stronger as the first member 2 becomes larger, the copper paste for bonding of the present embodiment, which can be temporarily fixed with a pyrolytic resin, can be preferably used.

Examples of the first member 2 and the second member 3 include semiconductor elements such as IGBTs, diodes, Schottky barrier diodes, MOS-FETs, thyristors, logics, sensors, analog integrated circuits, LEDs, semiconductor lasers, and transmitters. , Lead frame, ceramic substrate with metal plate attached (for example, DBC), base material for mounting semiconductor elements such as LED package, power supply member such as copper ribbon, metal block, terminal, heat radiating plate, water cooling plate and the like.

The first member 2 and the second member 3 may contain metal on the surfaces 4a and 4b in contact with the sintered body of the copper paste for joining. Examples of the metal include copper, nickel, silver, gold, palladium, platinum, lead, tin, cobalt and the like. As the metal, one type may be used alone, or two or more types may be used in combination. Further, the surface in contact with the sintered body may be an alloy containing the above metal. Examples of the metal used for the alloy include zinc, manganese, aluminum, beryllium, titanium, chromium, iron, molybdenum and the like in addition to the above metals. Examples of the member containing metal on the surface in contact with the sintered body include a member having various metal plating, a wire, a chip having metal plating, a heat spreader, a ceramic substrate to which a metal plate is attached, and a lead frame having various metal plating. Alternatively, a lead frame made of various metals, a copper plate, and a copper foil can be mentioned.

The die shear strength of the joined body may be 15 MPa or more, 20 MPa or more, or 30 MPa or more from the viewpoint of sufficiently joining the first member and the second member. The die shear strength can be measured using a universal bond tester (4000 series, manufactured by DAGE) or the like.

The thermal conductivity of the sintered body of the copper paste for bonding may be 100 W / (m · K) or more, and 120 W / (m · K) or more from the viewpoint of heat dissipation and connection reliability at high temperatures. It may be 150 W / (m · K) or more. The thermal conductivity can be calculated from the thermal diffusivity, specific heat capacity, and density of the sintered body of the copper paste for bonding.

The difference in the coefficient of thermal expansion between the first member and the second member may be 2 ppm to 30 ppm, 3 ppm to 23 ppm, or 5 ppm to 15 ppm.

Next, a method for manufacturing a bonded body using the bonding copper paste of the present embodiment will be described. The method for producing a bonded body using the bonding copper paste of the present embodiment is different from that of the first member, the bonding copper paste, and the first member on the side in which the weight of the first member acts. A laminate in which the second member having a coefficient of thermal expansion is laminated in this order is prepared, and the copper paste for joining is subjected to the own weight of the first member or the own weight of the first member and a pressure of 0.01 MPa or less. It is provided with a step of sintering in a state of being bent. The direction in which the weight of the first member works can also be said to be the direction in which gravity works.

The laminate can be prepared, for example, by providing the bonding copper paste of the present embodiment at a required portion of the second member and then arranging the first member on the bonding copper paste.

As a method of providing the bonding copper paste of the present embodiment at a required portion of the second member, any method may be used as long as the bonding copper paste can be deposited. Examples of such a method include screen printing, transfer printing, offset printing, jet printing method, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, concave printing, and gravure. Printing, stencil printing, soft lithograph, bar coating, applicator, particle deposition method, spray coater, spin coater, dip coater, electrodeposition coating and the like can be used. The thickness of the bonding copper paste may be 1 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, 10 μm or more and 3000 μm or less, and 15 μm or more. It may be 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, or 15 μm or more and 150 μm or less.

Examples of the method of arranging the first member on the bonding copper paste include a chip mounter, a flip chip bonder, and a positioning jig made of carbon or ceramics.

The bonding copper paste arranged between the first member and the second member may be appropriately dried from the viewpoint of suppressing flow and generation of voids during sintering. The gas atmosphere at the time of drying may be in the atmosphere, in an oxygen-free atmosphere such as nitrogen or rare gas, or in a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying by leaving 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 more and 120 minutes or less.

By heat-treating the laminate, the copper paste for bonding is sintered. 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 of the sintered body, the first member and the second member. The gas atmosphere at the time of sintering may be a reducing atmosphere from the viewpoint of removing surface oxides of copper particles of the copper paste for bonding. 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. from the viewpoint of reducing thermal damage to the first member and the second member and improving the yield. It may be 250 ° C. or higher and 350 ° C. or lower. 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 from the viewpoint of sufficiently removing the pyrolytic resin, the solvent, etc. and improving the yield, and is 1 minute or more and less than 40 minutes. It may be 1 minute or more and less than 30 minutes.

By using the bonding copper paste of the present embodiment, the bonded body can have sufficient bonding strength even when bonding is performed without pressure when sintering the laminated body. That is, sufficient bonding strength is obtained when only the weight of the first member laminated on the copper paste for bonding is applied, or when a pressure of 0.01 MPa or less, preferably 0.005 MPa or less is applied in addition to the weight of the first member. Can be obtained. When the pressure received during sintering is within the above range, void reduction, die shear strength and connection reliability can be further improved without impairing the yield because a special pressurizing device is not required. Examples of the method in which the bonding copper paste receives a pressure of 0.01 MPa or less include a method of placing a weight on the first member.

In the above-mentioned joint, at least one of the first member and the second member may be a semiconductor element. Examples of semiconductor elements include power modules including diodes, rectifiers, thyristors, MOS gate drivers, power switches, power MOSFETs, IGBTs, shotkey diodes, fast recovery diodes, transmitters, amplifiers, LED modules, and the like. In such a case, the bonded body becomes a semiconductor device. The obtained semiconductor device can have sufficient die shear strength and connection reliability.

Next, a semiconductor device, which is a more specific embodiment of the bonded body, will be described. The semiconductor device of the present embodiment has a structure in which a semiconductor element and a support member for mounting a semiconductor element are bonded via the above-mentioned sintered body of the copper paste for bonding.

FIG. 3 is a schematic cross-sectional view showing an example of a semiconductor device manufactured by using the bonding copper paste of the present embodiment. The semiconductor device 200 shown in FIG. 3 comprises a semiconductor element 11 connected to the lead frame 10a via the sintered body 1 of the bonding copper paste of the present embodiment, and a mold resin 13 for molding the semiconductor elements 11. The semiconductor element 11 is connected to the lead frame 10b via a wire 12.

FIG. 4 is a schematic cross-sectional view showing an example of a semiconductor device manufactured by using the bonding copper paste of the present embodiment. The semiconductor device 210 has a semiconductor element 23 connected to an electrode 22 provided on an insulating substrate 21 via a sintered body 1 of the copper paste for bonding of the present embodiment, and the upper electrode of the semiconductor element 23 is Further, it is connected to the copper strip 25 via the sintered body 1 of the bonding copper paste of the present embodiment. The other end of the copper strip 25 is connected to the electrode 24 provided on the insulating substrate 21 via the sintered body 1 of the copper paste for bonding of the present embodiment. The semiconductor element 23 is connected to the electrode 26 via a wire 27. These structures are covered with an insulating resin composition 29. The semiconductor device 210 includes a metal plate 28 on the side of the insulating substrate 21 opposite to the surface on which the electrodes and the like are mounted.

FIG. 5 is a schematic cross-sectional view showing an example of a semiconductor device manufactured by using the bonding copper paste of the present embodiment. The semiconductor device 220 has a semiconductor element 23 connected on a metal plate 32 via a sintered body 1 of the bonding copper paste of the present embodiment, and the other of the semiconductor elements 23 is the bonding copper paste of the present embodiment. The metal block 30 is connected to the metal block 30 via the sintered body 1 of the above, and the metal block 30 and the metal plate 33 are further joined via the sintered body 1 of the copper paste for bonding of the present embodiment. The semiconductor element 23 is connected to the metal electrode 34 via a wire 35. These structures are covered with a mold resin 31.

Examples of the semiconductor device manufactured by using the bonding copper paste of the present embodiment include a power including a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a Schottky diode, and a fast recovery diode. Examples include modules, transmitters, amplifiers, high-brightness LED modules, semiconductor laser modules, logics, sensors and the like.

These semiconductor devices can be manufactured in the same manner as the above-described method for manufacturing a bonded body. That is, in the method for manufacturing a semiconductor device, a semiconductor element is used for at least one of the first member and the second member, and the copper paste for bonding is placed on the side in the direction in which the weight of the first member and the first member acts. , And a laminate in which the second member is laminated in this order are prepared, and the bonding copper paste is subjected to the own weight of the first member or the own weight of the first member and a pressure of 0.01 MPa or less. It is provided with a step of sintering. For example, in FIG. 3, a step of providing a bonding copper paste on the lead frame 10a, further arranging the semiconductor element 11 and heating the lead frame 10a can be mentioned. The obtained semiconductor device can have sufficient die shear strength and connection reliability even when bonding is performed without pressurization. The semiconductor device of the present embodiment has sufficient bonding strength, and by providing a copper sintered body having high thermal conductivity and melting point, it has sufficient die shear strength (for example, 15 MPa or more), and the connection reliability is improved. It can be excellent as well as excellent in power cycle resistance.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

(Material for bonding copper paste)
CH-0200: Sub-micro copper particles (manufactured by Mitsui Mining & Smelting Co., Ltd., product name "CH-0200", 50% volume average particle size 0.3 μm).
MA-025KFD: Micro copper particles (manufactured by Mitsui Mining & Smelting Co., Ltd., product name "MA-025KFD", flake-shaped, 50% volume average particle size 4 μm).
2L3N / A: Micro copper particles (manufactured by Fukuda Metal Leaf Powder Industry Co., Ltd., product name "2L3N / A", flake-shaped, 50% volume average particle size 9 μm).
Poly (propylene carbonate): Thermosetting resin (manufactured by Sigma-Aldrich)
KFA-2000: Thermosetting resin dihydroterpineol solution (acrylic, solution concentration 33.6% by mass, manufactured by GOO CHEMICAL CO., LTD.)
Propylene carbonate: Solvent (manufactured by Wako Pure Chemical Industries, Ltd., product name "4-methyl-1,3-dioxolane-2-one")
Terpineol: (S)-(-)-α-terpineol (manufactured by Wako Pure Chemical Industries, Ltd.)

(Example 1)
2.40 g of propylene carbonate as a dispersion medium and 2.06 g of poly (propylene carbonate) as a thermosetting resin were mixed in a plastic bottle, sealed, and allowed to stand to dissolve. To this solution, 11.72 g of CH-0200 as submicrocopper particles was added, and the mixture was stirred with a spatula until the dry powder disappeared. Further, the treatment was carried out 15 times using a 3-roll mill (M-50, manufactured by EXAKT). Take 8.09 g of this dispersion treatment liquid, add 2.50 g of micro copper particles MA-025KFD, stir with a spatula until the dry powder disappears, close the stopper, and rotate / revolve type agitator (Planetry Vacuum Mixer ARV-310, Shinky). The mixture was stirred at 2000 rpm for 1 minute and further treated 5 times with a 3-roll mill to obtain a copper paste for bonding. The copper paste for bonding was stored at room temperature, stirred at 2000 rpm for 1 minute using a rotation / revolution type stirrer before use, and then used.

(Other Examples and Comparative Examples)
A copper paste for bonding was obtained in the same manner as in Example 1 except that the composition was changed as shown in Table 1.

(Measurement method of die shear strength)
Using a stainless mask with a thickness of 75 μm and a squeegee having nine 3 mm × 3 mm square openings on a copper substrate 30 mm × 25 mm × 3 mm, the bonding copper pastes of each Example and Comparative Example were stencil-printed. A Si chip (nickel on the adherend surface) in which titanium / nickel is sputtered on the entire surface of the bonding surface having a size of 3 mm × 3 mm and a thickness of 400 μm on the printed matter of the copper paste for bonding is used as the copper paste for bonding on the nickel surface. Placed in contact, the tip was lightly pressed with tweezers to bring the nickel surface into close contact with the bonding copper paste. The obtained sample was placed in an atmosphere-controllable tube oven (manufactured by ABC) and treated in hydrogen under the conditions of a temperature rise of 15 minutes and a holding temperature of 300 ° C. for 1 hour to obtain a copper paste bonding sample for bonding.

The adhesive strength of the copper paste bonding sample for bonding was evaluated by the die shear strength. Using a universal bond tester (4000 series, manufactured by DAGE) equipped with a DS-100 load cell, push the Si chip horizontally at a measurement speed of 5 mm / min and a measurement height of 50 μm to increase the die shear strength of the copper paste bonding sample for bonding. It was measured. The average value of the measured values of eight Si chips was taken as the die shear strength. The results are shown in Table 2.

(Observation of cross-sectional morphology)
The copper paste bonding sample for bonding of Example 1 is fixed in a cup with a sample clip (Samplklip I, manufactured by Buehler), and an epoxy casting resin (Epomount, manufactured by Refine Tech) is poured around the sample until the entire sample is filled. , The mixture was allowed to stand in a vacuum desiccator and defoamed under reduced pressure for 1 minute. Then, after leaving it at room temperature (25 ° C.) for 10 hours, the epoxy casting resin was cured in a thermostat at 60 ° C. for 2 hours. Using Refine Saw Excel (manufactured by Refine Tech) equipped with a resinoid cutting wheel, the cast sample was cut near the cross section to be observed. The cross section was scraped with a polishing device (Refine Polisher HV, manufactured by Refine Tech) equipped with water resistant polishing paper (Carbomac Paper, manufactured by Refine Tech) to obtain a crack-free cross section on the silicon chip. The excess casting resin was scraped off in the same manner. Then, the cross section was smoothed with a polishing apparatus set with a buffing polishing cloth dyed with a buffing agent to prepare a sample for SEM. The cross section of the copper paste bonding sample for bonding was observed with an SEM device (ESEM XL30, manufactured by Philips) at an applied voltage of 10 kV and various magnifications. The particles were sintered and fused and bonded to the adherend surface, and were in a good bonding state. Similar results were obtained in other examples.

(Example 5)
A copper paste for bonding was prepared using an acrylic pyrolytic resin (KFA-2000, reciprocal chemistry) as the pyrolytic resin. 11.51 g of KFA-2000 (terpineol solution, resin concentration 66.4% by mass), which is a thermosetting resin solution, and CH-0200 as fine copper particles are mixed in a 47.93 g plastic bottle and treated 5 times with a 3-roll mill. A mixed slurry of a thermosetting resin and copper particles was obtained. Using this mixed slurry of thermally decomposable resin and copper particles, weigh the sub-micro copper particles, micro copper particles, and solvent in a plastic bottle at the ratio shown in Table 3, stir with a spatula until the dry powder is gone, and seal the stopper. Using a rotating and revolving stirrer (Plantery Particle Mixer ARV-310, manufactured by Shinky Co., Ltd.), the mixture was stirred at 2000 rpm for 1 minute and treated 5 times with a 3-roll mill to obtain a copper paste for bonding.

(Other Examples and Comparative Examples)
A copper paste for bonding was obtained in the same manner as in Example 5 except that the composition was changed as shown in Table 3.

The adhesive strength of the copper paste bonding samples for bonding in each example and comparative example was evaluated by the die shear strength in the same manner as described above. The results are shown in Table 4.

1 ... Sintered body of copper paste for bonding, 2, 2a, 2b ... First member, 3 ... Second member, 4a, 4b ... Surface in contact with sintered body of copper paste for bonding, 10a, 10b ... Lead Frame, 11 ... semiconductor element, 12 ... wire, 13 ... mold resin, 21 ... insulating substrate, 22 ... electrode, 23 ... semiconductor element, 24 ... electrode, 25 ... copper strip, 26 ... electrode, 27 ... wire, 28 ... metal Plate, 29 ... Insulating resin composition, 31 ... Mold resin, 32 ... Metal plate, 33 ... Metal plate, 34 ... Metal electrode, 35 ... Wire, 100, 110 ... Joined body, 200, 210, 220 ... Semiconductor device.

Claims (5)

A copper paste for joining a semiconductor element and a support member for mounting the semiconductor element.
And copper particles, a heat decomposable resin, and a solvent seen including,
The content of the copper particles is 65% by mass or more based on the total mass of the copper paste for bonding.
A copper paste for bonding in which the content of the pyrolytic resin is 1% by mass or more based on the total mass of the copper particles and the pyrolytic resin. The copper paste for bonding according to claim 1, wherein the thermosetting resin is at least one selected from the group consisting of polycarbonate, polymethacrylic acid, polymethacrylic acid ester, and polyester. The copper particles include submicro copper particles having a volume average particle diameter of 0.12 μm or more and 0.8 μm or less, and flake-shaped micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less and an aspect ratio of 4 or more. The copper paste for bonding according to claim 1 or 2, wherein the content of the flake-shaped micro copper particles is 50% by mass or less based on the total mass of the copper particles. The copper paste for bonding according to any one of claims 1 to 3, wherein the decomposition start temperature of the thermally decomposable resin in a reducing atmosphere is 250 ° C. or less. A semiconductor device having a structure in which a semiconductor element and a support member for mounting a semiconductor element are bonded via a sintered body of the copper paste for bonding according to any one of claims 1 to 4.

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