JP2018152176A - Copper paste for bonding and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper paste for bonding that has excellent thermal conductivity and connection reliability, and enables a semiconductor element to be bonded to a semiconductor element mounting support member in a convenient process.SOLUTION: A copper paste for bonding contains copper particles, pyrolytic resin, and a solvent. The content of the copper particles is 65 mass% or more based on the total mass of the copper paste for bonding, and the content of the pyrolytic resin is 1 mass% or more based on the total mass of the copper particles and the pyrolytic resin.SELECTED DRAWING: None

Description

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

  When manufacturing a semiconductor device, as a method of adhering a semiconductor element and a lead frame (supporting 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 using silver paste). In this method, a paste adhesive is applied to a die pad of a lead frame using a dispenser, a printing machine, a stamping machine, etc., and then a semiconductor element is die-bonded and bonded by heat curing to obtain a semiconductor device.

  In recent years, as the speed and integration of semiconductor elements have increased, high heat dissipation characteristics are also required for adhesives in order to ensure the operational stability of semiconductor devices.

  So far, adhesives aimed at improving thermal conductivity have been proposed. For example, in the following Patent Documents 1 to 5, a die bonding paste (Patent Documents 1 and 2) highly filled with silver particles having high thermal conductivity, a conductive adhesive containing spherical silver powder having a specific particle size ( Patent Document 3), adhesive paste containing solder particles (Patent Document 4), metal powder having a specific particle diameter, and conductive adhesive containing metal ultrafine particles having a specific particle diameter (Patent Document 5) ) Is disclosed.

  In Patent Document 6 below, silver particles are sintered by heating a paste-like silver particle composition comprising non-spherical silver particles subjected to surface treatment and a volatile dispersion medium at 100 ° C. or more and 400 ° C. or less. There has been proposed a technique for forming 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. Thus, a technique for sintering copper particles to form solid copper is also introduced.

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

JP 2006-73811 A JP 2006-302834 A JP-A-11-66953 JP 2005-93996 A JP 2006-83377 A Japanese Patent No. 4353380 JP 2014-167145 A

  Although the method described in Patent Document 7 performs sintering without applying pressure, it is still not sufficient for practical use in the following points. That is, non-pressure joining using a joining material is performed well when the materials of the members to be joined are equal or close to each other, but the joining force is increased when the materials of the members to be joined are different. It is easy to drop greatly. According to the study by the present inventors, for example, when a copper plate having copper on the deposition surface and a copper block having nickel on the deposition surface are joined, a copper plate having copper on the deposition surface and nickel on the deposition surface In comparison with the case of bonding a silicon chip having a thickness, the bonding strength of the latter may be greatly reduced under pressureless sintering conditions. That is, when a member having a different coefficient of thermal expansion is bonded without pressure, such as a copper block and a silicon chip, a bonding failure may occur.

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

  The present invention provides a bonding copper paste that is excellent in thermal conductivity and connection reliability and can perform bonding between a semiconductor element and a semiconductor element mounting support member in a simple process, and a semiconductor device obtained using the same. The purpose is to provide.

  The present invention is a bonding copper paste containing copper particles, a thermally decomposable resin, and a solvent, and 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, wherein the content of the thermally decomposable resin is 1% by mass or more based on the total mass of the copper particles and the thermally decomposable resin.

  In the present invention, the thermally decomposable 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 size of 0.12 to 0.8 μm, and flaky micro-copper particles having a maximum diameter of 1 to 20 μm and an aspect ratio of 4 or more. The content of the flaky 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 semiconductor element mounting support member are bonded via the sintered copper paste for bonding.

  ADVANTAGE OF THE INVENTION According to this invention, the copper paste for joining which can join the semiconductor element and support member for mounting a semiconductor element which are excellent in thermal conductivity and connection reliability, and differ in a thermal expansion coefficient, and a semiconductor obtained by using it An apparatus 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 semiconductor element mounting support member are joined by the joining copper paste of the present invention.

It is a schematic cross section showing an example of a joined body. It is a schematic cross section which shows another example of a joined body. It is a schematic cross section showing an example of a semiconductor device of the present invention. It is a schematic cross section which shows another example of the semiconductor device of this invention. It is a schematic cross section which shows another example of the semiconductor device of this invention.

<Copper paste for bonding>
The bonding copper paste of the present embodiment at least includes copper particles, a thermally decomposable resin, and a solvent. The copper particles are sintered by firing, and the adherend and the sinterable copper particles are bonded to each other by a metal bond and develop a function of joining. Thermally decomposable resin, after the adherend and the bonding copper paste are in contact with each other, temporarily adhere the adherends until they are joined by the copper particle sintered body, and both peel off due to thermal stress and vibration during the process. To prevent. It should be noted that by selecting a thermally decomposable resin that has a thermal decomposability below the sintering temperature and that does not leave decomposition residue, it does not hinder sintering, and connection strength and connection reliability after sintering. Can be improved. The solvent is used for dissolving the thermally decomposable resin and dispersing the copper particles to obtain a paste. By being a paste, it has an adhesion function to the 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, expresses functions to prevent oxidation and improve dispersibility in a solvent, and improves the content of copper particles in the paste, improves storage stability, and improves viscosity characteristics. The sintering aid expresses the function of promoting the sintering of the 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) are preferably composed mainly of copper from the viewpoints of thermal conductivity, sinterability, and connection reliability. Of the elements contained in the copper particles, the ratio of the elements occupied by copper, excluding hydrogen, carbon, and oxygen, is preferably 80 atomic% or more, more preferably 90 atomic% or more, and 95 atomic%. More preferably, it is the above. If the content rate of copper falls from this, the produced | generated copper sintered compact joining layer will become an alloy which has a property different from copper, and thermal conductivity and connection reliability will fall.

  In order to reduce the sintering temperature to a low temperature (for example, 300 ° C. or less), the copper particles are produced by sub-copper particles having a volume average particle size of 0.12 μm or more and 0.8 μm or less (fine particle size copper particles). It is preferable to contain at least 50% by mass or more based on the total mass. The sub-micro copper particles of this size start sintering at about 250 ° C. and can be joined at a low temperature. In addition, if a volume average particle diameter is 0.12 micrometer or more, it will become easy to acquire effects, such as suppression of the synthesis cost of submicro copper particles, favorable dispersibility, and suppression of the usage-amount of a surface treating agent. If the volume average particle size is 0.8 μm or less, the effect that the sinterability of the sub-micro copper particles is excellent is easily obtained. From the viewpoint of further exerting the above effects, the volume average particle diameter of the sub-micro copper particles may be 0.15 μm or more and 0.8 μm or less, 0.15 μm or more and 0.6 μm or less, and 0 It may be not less than 2 μm and not more than 0.5 μm, and may be not less than 0.3 μm and not more than 0.45 μm. In the present specification, the volume average particle diameter means 50% volume average particle diameter.

  In the sintering with the sub-micro copper particles as described above, 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 both the micro copper particles having a maximum diameter of 1 μm or more and 20 μm or less are included together with the sub micro copper particles. When micro copper particles are included, effects of reducing volume shrinkage during sintering and improving the strength of the bonding layer after sintering can be obtained. From the viewpoint of further achieving the above effects, 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.

  5 mass% or more is preferable, as for content of the micro copper particle in a copper particle, 10 mass% or more is more preferable, and 20 mass% or more is further more preferable. The upper limit of the content is preferably 50% by mass or less. When there is too much content of micro copper particles, the sinterability at 300 degrees C or less tends to fall, and there exists a tendency for joining strength to fall.

  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-like or flake-like copper particles having a large aspect ratio are used, a reinforcing effect and a density improving effect due to the orientation of the micro copper particles are obtained, which is preferable.

  When the micro copper particles are flaky (the flaky micro copper particles), the aspect ratio may be 4 or more, or 6 or more. If the aspect ratio is within the above range, the flaky 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. In this specification, “aspect ratio” indicates the long side / thickness of a particle. The measurement of the long side and thickness of the particle can be obtained, for example, from the SEM image of the particle.

  Micro copper particles and sub-micro copper particles may be treated with a surface treatment agent. However, the surface treatment agent is preferably one that can be removed in the sintering step. Examples of such a surface treatment agent 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 acid, cetyl alcohol, stearyl alcohol, isobornylcyclohexanol, aliphatic alcohol such as tetraethylene glycol, aromatic alcohol such as p-phenylphenol, alkylamine such as octylamine, dodecylamine, stearylamine, stearonitrile And an organic nitrile compound such as decanonitrile, and a polymer treating agent such as a thermally decomposable resin described later.

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

<Pyrolytic resin>
As the thermally decomposable resin, an amorphous polymer capable of exhibiting adhesiveness and tackiness is preferable for the purpose of temporarily fixing the adherend and the bonding copper paste from after application to firing. Moreover, it is preferable to have thermal decomposability that can be decomposed at the sintering temperature and decomposed without residue.

  The thermal decomposability temperature is the decomposition start temperature of the thermodegradable resin, and is a 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 not the oxidative atmosphere such as air but the decomposition start temperature in a reducing atmosphere containing hydrogen or formic acid.

  The residue after pyrolysis of the thermally decomposable resin is preferably as small as possible to prevent sintering of the copper particles, and is usually preferably 5% by mass or less and more preferably 2% by mass or less with respect to the resin mass before pyrolysis. The amount of residue after pyrolysis of the pyrolyzable resin is the weight after holding for only the sintering time at the sintering temperature with TG / DTA of the pyrolyzable resin in a hydrogen containing inert gas (nitrogen or argon). It can be measured as the amount of change. Note that TG / DTA measurement in air is not preferable because oxidative decomposition progresses and the amount of residue is reduced compared to the amount of residue in a reducing atmosphere.

  The thermally decomposable resin needs to be soluble in the solvent. Polycarbonate, polymethacrylic acid, polymethacrylic acid ester, polyester are mentioned as the heat-decomposable resin having the solubility and the desired properties.

<Solvent>
The solvent is required to have the function of obtaining copper paste for bonding by dispersing copper particles and dissolving the thermally decomposable resin, and it must be volatilized and removed during firing to remain in the sintered layer after sintering. Is required.

The dispersion medium that can disperse the copper particles and dissolve the thermally decomposable resin depends on the type of the surface treatment agent for the copper particles, the type of the dispersant added to the bonding copper paste, the type of the thermally decomposable resin, and the like. For example, a high-polarity solvent and a high-polarity heat-decomposable resin are preferred when a high-polarity solvent is selected, and a low-polarity dispersant and a low-polarity heat-decomposable resin are preferred. A polar solvent is preferred.
It can be inferred that it is preferable to select a combination of such a dispersant, a thermally decomposable resin, and a solvent having similar Hansen solubility parameters. The Hansen solubility parameter can be searched from, for example, the end document database of the following published document, or can be 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, and more preferably 370 ° C. or lower. If the boiling point of the solvent is higher than this temperature, it will be difficult to volatilize and remove by the sintering temperature, which will inhibit sintering, generate gas after sintering, and cause 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 and N, N-dimethylformamide, esters such as γ-butyrolactone, water Is mentioned.

  Examples of low-polar solvents include pentanol, hexanol, heptanol, octanol, decanol, ethylene glycol, butylene glycol, α-terpineol, bornylcyclohexanol (MTPH) and other higher alcohols and ethylene glycol butyl ether, ethylene glycol phenyl ether , Diethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, diethylene glycol isobutyl ether, diethylene glycol hexyl ether, triethylene glycol methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol butyl methyl ether, diethylene glycol Tylene glycol isopropyl methyl ether, triethylene glycol dimethyl 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 , Ethers such as tripropylene glycol methyl ether and tripropylene glycol dimethyl ether, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether Examples include esters such as ether acetate (DPMA), ethyl lactate, butyl lactate, and propylene carbonate, aliphatic hydrocarbons such as cyclohexanone, octane, nonane, decane, and undecane, and aromatic hydrocarbons such as benzene, toluene, and xylene.

<Sintering aid>
The sintering aid expresses the function of promoting the sintering of the copper particles, and the effect of reducing the sintering start temperature and improving the density of the sintered body can be obtained. 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 an effect of reducing the sintering temperature is obtained. Examples of such different metal species include zinc, tin, silver, gold, palladium, indium, gallium, aluminum, and antimony. These dissimilar metals may be used alone or as an alloy, and plural kinds of dissimilar metal particles may be used simultaneously.

  The smaller the particle size of the dissimilar metal particles, the higher the effect. However, in the case of 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 easy availability.

  The addition amount of the sintering aid 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 more preferably 0.1% by mass or more based on the total mass of the copper particles. 1% by mass or less is more preferable. When the amount is less than this amount, it is difficult to obtain a sufficient effect, and when the amount is large, it is alloyed with copper to reduce the thermal conductivity and electrical conductivity, or as a foreign matter that is not taken into the sintered body. Reduce 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 bonding copper paste. If it is less than this, the difference between the volume of the bonding copper paste and the volume of the sintered body becomes large, which causes peeling and cracking. Moreover, when it is more than this, the fluidity | liquidity of the copper paste for joining will be lost, and applicability | paintability and adhesiveness will worsen.

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

  The pyrolyzable resin content is preferably 1% by mass or more based on the total mass of the copper particles and the thermodegradable resin (that is, the mass when the solvent is removed by drying), and 1.5 mass. % Or more is more preferable. When the amount of the heat decomposable resin is smaller than this, peeling occurs due to the thermal stress between the members before the sintering starts, resulting in poor bonding. Moreover, it is preferable that the upper limit of the said content is 20 mass% or less on the basis of the total mass of a copper particle and a thermally decomposable resin. When the amount is larger than this, the difference between the volume of the bonding copper paste and the volume of the sintered body becomes large, resulting in a decrease in the density of the sintered body, peeling and cracking.

  The content of the solvent can be the remainder of the content of the copper particles and the thermally decomposable resin, for example. The content is preferably 4% by mass or more and 34% by mass or less, more preferably 8% by mass or more and 20% by mass or less, based on the total mass of the bonding copper paste. If it is less than this, the fluidity is lost, and the coating property and adhesion are deteriorated. Moreover, when it is more than this, the difference of the volume of the copper paste for joining and the volume of a sintered compact will become large, and will cause peeling and a crack.

<Preparation of copper paste for bonding>
The bonding copper paste can be prepared by mixing the above-described copper particles, thermally decomposable resin, other metal particles, and optional additives in a solvent. For example, it can be prepared by dissolving a thermally decomposable resin in a solvent and then adding a copper particle, other metal particles, a dispersant, and an optional additive to perform a dispersion treatment. Alternatively, a solution obtained by mixing a thermally decomposable resin in a solvent and a solution obtained by mixing a sintered copper particle and a dispersion obtained by mixing and dispersing a dispersant in a solvent are mixed to obtain a copper particle, other metal particles, and any It can be prepared by adding the additive.

  The copper particles include at least sub-micro copper particles and micro-copper particles, but if necessary, a dispersant is added to the solvent or the thermally decomposable resin solution, and after the sub-micro copper particles are mixed, the dispersion treatment is performed. The dispersion treatment may be performed by adding micro copper particles and other metal particles. The sub-micro copper particles and the micro copper particles may have different dispersion methods and dispersion conditions suitable for dispersion. In general, sub-micro copper particles require a stronger dispersion than micro-copper particles. On the other hand, micro-copper particles are not only dispersible, but a lower-strength dispersion is sufficient. Arise. By setting it as such a procedure, dispersibility becomes good and the performance of the copper paste for joining can be improved more. Aggregates may be removed by classifying the dispersion.

  You may perform a stirring process after mixing of each component. The bonding copper paste may adjust the maximum particle size of the dispersion by classification operation. At this time, the maximum particle size of the dispersion liquid can be 20 μm or less, and can also be 10 μm or less.

  The dispersion treatment can be performed using a disperser or a stirrer. For example, Ishikawa-type stirrer, Silverson stirrer, cavitation stirrer, rotation / revolution type stirrer, ultra-thin film high-speed rotary disperser, ultrasonic disperser, reiki machine, twin-screw kneader, bead mill, ball mill, three roll mill, homomixer , Planetary mixers, ultra-high pressure type dispersers, and thin layer shear dispersers.

  The stirring treatment can be performed using a stirrer. Examples thereof include an Ishikawa stirrer, a rotation / revolution stirrer, a reika machine, a twin-screw kneader, a three-roll mill, and a planetary mixer.

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

  You may adjust the copper paste for joining to the viscosity suitable for each printing and application | coating method. The viscosity of the bonding copper paste may be, for example, a Casson viscosity at 25 ° C. of 0.05 Pa · s to 2.0 Pa · s, and 0.06 Pa · s to 1.0 Pa · s. Also good.

<Joint and semiconductor device>
Hereinafter, preferred embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

  FIG. 1 is a schematic cross-sectional view showing an example of a joined body manufactured using the joining copper paste of the present embodiment. The joined body 100 of the present embodiment is the first member 2, the second member 3 having a coefficient of thermal expansion different from that of the first member, and the above-described joint for joining the first member and the second member. And a sintered body 1 of the copper paste for use. In addition, as shown in FIG. 2, the joined body of this embodiment includes a plurality of first members 2a and 2b, a second member 3 having a different coefficient of thermal expansion from the first member, and a first member The joined body 110 provided with the sintered body 1 of the said copper paste for joining which joins a member and a 2nd member may be sufficient.

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

  As the first member 2 and the second member 3, for example, semiconductor elements such as IGBT, diode, Schottky barrier diode, MOS-FET, thyristor, logic, sensor, analog integrated circuit, LED, semiconductor laser, transmitter, etc. , A lead frame, a ceramic substrate with a metal plate (for example, DBC), a substrate for mounting a semiconductor element such as an LED package, a power supply member such as a copper ribbon, a metal block, and a terminal, a radiator plate, and a water-cooled plate.

  The 1st member 2 and the 2nd member 3 may contain the metal in the surfaces 4a and 4b which contact the sintered compact of the copper paste for joining. Examples of the metal include copper, nickel, silver, gold, palladium, platinum, lead, tin, and cobalt. A metal may be used individually by 1 type and may be used in combination of 2 or more type. 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, and molybdenum in addition to the above metals. Examples of the member containing metal on the surface in contact with the sintered body include, for example, 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. Or the lead frame which consists of various metals, a copper plate, and copper foil are 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, or 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 bonding copper paste.

  The difference in 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 joined body using the joining copper paste of the present embodiment will be described. The manufacturing method of the joined body using the bonding copper paste of the present embodiment is different from the bonding copper paste and the first member on the first member, the direction in which the weight of the first member works. Prepare a laminate in which the second member having the thermal expansion coefficient is laminated in this order, and apply the bonding copper paste to the weight of the first member or the weight of the first member and the pressure of 0.01 MPa or less. And a step of sintering in a heated state. 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 on a necessary portion of the second member and then placing the first member on the bonding copper paste.

  As a method of providing the bonding copper paste of the present embodiment on a necessary portion of the second member, any method can be used as long as the bonding copper paste can be deposited. Examples of such methods include screen printing, transfer printing, offset printing, jet printing, dispenser, jet dispenser, needle dispenser, comma coater, slit coater, die coater, gravure coater, slit coat, letterpress printing, intaglio printing, gravure printing. Printing, stencil printing, soft lithography, 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, or 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 for arranging the first member on the bonding copper paste include a chip mounter, a flip chip bonder, a positioning jig made of carbon or ceramics.

  The bonding copper paste disposed between the first member and the second member may be appropriately dried from the viewpoint of suppressing flow and void generation during sintering. The gas atmosphere at the time of drying may be air, an oxygen-free atmosphere such as nitrogen or a rare gas, or a reducing atmosphere such as hydrogen or formic acid. The drying method may be drying at room temperature, drying by heating, or drying under reduced pressure. For heat drying or reduced pressure drying, for example, hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic A heating device, a heater heating device, a steam heating furnace, a hot plate press 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, the drying may be performed at 50 ° C. or higher and 180 ° C. or lower for 1 minute or longer and 120 minutes or shorter.

  By sintering the laminated body, the bonding copper paste is sintered. For the heat treatment, for example, hot plate, hot air dryer, hot air heating furnace, nitrogen dryer, infrared dryer, infrared heating furnace, far infrared heating furnace, microwave heating device, laser heating device, electromagnetic heating device, 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 the surface oxides of the copper particles of the bonding copper paste. Examples of the oxygen-free atmosphere include introduction of oxygen-free gas such as nitrogen and rare gas, or under vacuum. Examples of the reducing atmosphere include pure hydrogen gas, hydrogen and nitrogen mixed gas typified by forming gas, nitrogen containing formic acid gas, hydrogen and rare gas mixed gas, and 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, from the viewpoint of reducing thermal damage to the first member and the second member and improving the yield, and may be 250 ° C. or higher and 400 ° C. or lower. Or 250 ° C. or more and 350 ° C. or less. If the ultimate temperature is 200 ° C. or higher, the sintering tends to proceed sufficiently when the ultimate temperature holding time is 60 minutes or less.

  The maximum temperature holding time may be from 1 minute to 60 minutes or from 1 minute to less than 40 minutes from the viewpoint of sufficiently removing the thermally decomposable resin and solvent and improving the yield. 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 without pressure is performed when the laminate is sintered. That is, sufficient bonding strength in a state in which only the own weight of the first member laminated on the bonding copper paste or the pressure of 0.01 MPa or less, preferably 0.005 MPa or less, in addition to the own weight of the first member. Can be obtained. If the pressure applied during the sintering is within the above range, a special pressurizing device is not required, and the void reduction, die shear strength and connection reliability can be further improved without impairing the yield. Examples of the method for receiving the pressure of the bonding copper paste of 0.01 MPa or less include a method of placing a weight on the first member.

  In the joined body, at least one of the first member and the second member may be a semiconductor element. Examples of the semiconductor element include a power module 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, a transmitter, an amplifier, and an LED module. In such a case, the joined body is 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 aspect of the joined body will be described. The semiconductor device of the present embodiment has a structure in which a semiconductor element and a semiconductor element mounting support member are joined via the sintered body of the joining copper paste.

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

  FIG. 4 is a schematic cross-sectional view showing an example of a semiconductor device manufactured using the bonding copper paste of this embodiment. The semiconductor device 210 has a semiconductor element 23 connected to the electrode 22 provided on the insulating substrate 21 via the sintered body 1 of the bonding copper paste of this embodiment, and the upper electrode of the semiconductor element 23 is Furthermore, it connects with the copper strip 25 through the sintered compact 1 of the copper paste for joining of this embodiment. The other end of the copper strip 25 is connected to the electrode 24 provided on the insulating substrate 21 through the sintered body 1 of the bonding copper paste of this embodiment. The semiconductor element 23 is connected to the electrode 26 through 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 opposite to the surface on which the electrodes and the like of the insulating substrate 21 are mounted.

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

  As a semiconductor device manufactured using the bonding copper paste of this embodiment, for example, a power composed of a diode, a rectifier, a thyristor, a MOS gate driver, a power switch, a power MOSFET, an IGBT, a Schottky diode, a fast recovery diode, and the like. Examples include modules, transmitters, amplifiers, high-intensity LED modules, semiconductor laser modules, logic, sensors, and the like.

  These semiconductor devices can be manufactured in the same manner as the above-described manufacturing method of the joined body. That is, the method for manufacturing a semiconductor device uses a semiconductor element as at least one of the first member and the second member, and the first member and the copper paste for bonding on the side in which the weight of the first member acts. And a laminated body in which the second member is laminated in this order, and the bonding copper paste is subjected to the weight of the first member or the weight of the first member and the pressure of 0.01 MPa or less. A step of sintering. For example, FIG. 3 includes a step of providing a bonding copper paste on the lead frame 10a, and further placing and heating the semiconductor element 11. The obtained semiconductor device can have sufficient die shear strength and connection reliability even when bonding is performed without applying pressure. The semiconductor device of this embodiment has a sufficient die-shear strength (for example, 15 MPa or more) by providing a copper sintered body having a sufficient bonding force and a high thermal conductivity and a high melting point. In addition to being excellent, it can also be 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 of copper paste for bonding)
CH-0200: Sub-micro copper particles (manufactured by Mitsui Kinzoku Mining Co., Ltd., product name “CH-0200”, 50% volume average particle size 0.3 μm).
MA-025KFD: Micro copper particles (Mitsui Metal Mining Co., Ltd., product name “MA-025KFD”, flakes, 50% volume average particle size 4 μm).
2L3N / A: Micro copper particles (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., product name “2L3N / A”, flaky, 50% volume average particle size 9 μm).
Poly (propylene carbonate): Thermally decomposable resin (manufactured by Sigma-Aldrich)
KFA-2000: Dihydroterpineol solution of thermally decomposable resin (acrylic, solution concentration 33.6% by mass, manufactured by Kyoyo Chemical Industry)
Propylene carbonate: solvent (manufactured by Wako Pure Chemical Industries, product name “4-methyl-1,3-dioxolan-2-one”)
Terpineol: (S)-(−)-α-terpineol (manufactured by Wako Pure Chemical Industries)

Example 1
2.40 g of propylene carbonate as a dispersion medium and 2.06 g of poly (propylene carbonate) as a thermally decomposable resin were mixed in a plastic bottle, sealed, and allowed to stand to dissolve. To this solution, 11.72 g of CH-0200 as submicro copper particles was added and stirred with a spatula until there was no dry powder. Furthermore, it processed 15 times using the 3 roll mill (M-50, the product made by EXAKT). Take 8.09 g of this dispersion treatment liquid, add 2.50 g of micro copper particles MA-025KFD, stir until dry powder disappears with a spatula, seal tightly, and rotate and revolve type stirring device (Planetary Vacuum Mixer ARV-310, sinky) The product was stirred at 2000 rpm for 1 minute, and further treated 5 times with a 3 roll mill to obtain a bonding copper paste. The copper paste for bonding was stored at room temperature, and was used after stirring for 1 minute at 2000 rpm using a rotation and revolution type stirring device before use.

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

(Die shear strength measurement method)
The copper paste for joining of each Example and Comparative Example was stencil-printed using a 75 μm-thick stainless steel mask and a squeegee having nine 3 mm × 3 mm square openings on a copper substrate 30 mm × 25 mm × 3 mm. On the printed copper paste for bonding, a Si chip (coated nickel) with titanium / nickel sputtered in this order on the entire bonding surface of size 3 mm × 3 mm and thickness 400 μm, and the nickel surface as the bonding copper paste The chip was placed in contact, and the chip was lightly pressed with tweezers to adhere the nickel surface and the bonding copper paste. The obtained sample was placed in a tube oven (manufactured by Ave Sea Co., Ltd.) capable of controlling the atmosphere, and treated in hydrogen under the conditions of a temperature increase of 15 minutes and a temperature of 300 ° C. for 1 hour to obtain a copper paste bonded sample for bonding.

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

(Observation of cross-sectional morphology)
The copper paste joint sample for Example 1 was fixed in the cup with a sample clip (Sampleklip I, manufactured by Buehler), and an epoxy casting resin (Epomount, manufactured by Refinetech) was poured into the cup until the entire sample was filled. Then, it was left in a vacuum desiccator and degassed by reducing the pressure for 1 minute. Then, after leaving at room temperature (25 ° C.) for 10 hours, the epoxy casting resin was cured for 2 hours with a 60 ° C. thermostat. A refined soxel (made by Refine Tech) equipped with a resinoid cutting wheel was used to cut the cast sample near the cross section to be observed. The cross section was shaved with a polishing apparatus (Refine Polisher HV, manufactured by Refinetech) equipped with water-resistant abrasive paper (Carbo Mac paper, manufactured by Refinetech) to give a silicon chip with no cracks. Excess casting resin was scraped off in the same manner. Thereafter, the cross-section was smoothed with a polishing apparatus in which a buffing cloth dyed with a buffing abrasive was set, and a sample for SEM was obtained. The SEM sample (ESEM XL30, manufactured by Philips) was used to observe the cross section of the bonding copper paste bonding sample at an applied voltage of 10 kV and various magnifications. The particles were sintered and fused and joined to the adherend surface, so that they were in a good joined state. Other examples had similar results.

(Example 5)
A copper paste for bonding was prepared using an acrylic heat-decomposable resin (KFA-2000, Mutual Chemistry) as the heat-decomposable resin. KFA-2000 (terpineol solution, resin concentration 66.4 mass%) 11.51 g which is a thermally decomposable resin solution, and CH-0200 as fine copper particles are mixed in a 47.93 g plastic bottle and treated with a three roll mill five times. Thus, a mixed slurry of a thermally decomposable resin and copper particles was obtained. Using this slurry of thermal decomposable resin and copper particles, weigh out the sub-micro copper particles, micro-copper particles, and solvent in the proportions shown in Table 3 and stir them with a spatula until there is no dry powder. Then, using a rotation and revolution type stirrer (Planetry Vacuum Mixer ARV-310, manufactured by Sinky Corporation), the mixture was stirred at 2000 rpm for 1 minute and treated with a three roll mill five times to obtain a copper paste for bonding.

(Other examples and comparative examples)
A joining copper paste 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 of each example and comparative example was evaluated by die shear strength in the same manner as described above. The results are shown in Table 4.

DESCRIPTION OF SYMBOLS 1 ... Sintered body of copper paste for joining, 2, 2a, 2b ... 1st member, 3 ... 2nd member, 4a, 4b ... Surface in contact with sintered body of copper paste for joining, 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 Reference numeral 29: Insulating resin composition, 31: Mold resin, 32 ... Metal plate, 33 ... Metal plate, 34 ... Metal electrode, 35 ... Wire, 100, 110 ... Assembly, 200, 210, 220 ... Semiconductor device.

Claims (4)

A copper paste for bonding containing copper particles, a thermally decomposable resin, and a solvent,
The content of the copper particles is 65% by mass or more based on the total mass of the bonding copper paste,
The copper paste for joining whose content of the said thermally decomposable resin is 1 mass% or more on the basis of the total mass of the said copper particle and the said thermally decomposable resin.   The bonding copper paste according to claim 1, wherein the thermally decomposable resin is at least one selected from the group consisting of polycarbonate, polymethacrylic acid, polymethacrylic acid ester, and polyester.   The copper particles are sub-micro copper particles having a volume average particle size of 0.12 μm to 0.8 μm, and flaky micro copper particles having a maximum diameter of 1 μm to 20 μm and an aspect ratio of 4 or more. The copper paste for joining according to claim 1 or 2, wherein the content of the flaky micro copper particles is 50% by mass or less based on the total mass of the copper particles. A semiconductor device having a structure in which a semiconductor element and a semiconductor element mounting support member are bonded via the sintered body of the bonding copper paste according to claim 1.

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