JP5557698B2 - Sintered bonding agent, manufacturing method thereof and bonding method using the same - Google Patents

Description

  The present invention relates to a sintered bonding agent used for bonding electronic members and forming circuit wiring, and in particular, a highly heat-conductive sintered bonding agent mainly composed of copper oxide nanoparticles, a manufacturing method thereof, and the same The present invention relates to a joining method. In the present invention, semiconductor elements, circuit boards and the like are collectively referred to as electronic members.

  Metal nanoparticles (for example, particle size of 100 nm or less) are attracting attention as new functional materials because their surface area is larger than the volume of the particles, and their chemical activity is high and the sintering temperature is greatly reduced. Yes. For example, a paste containing metal nanoparticles is expected as a material used for joining electronic members in electronic equipment and forming circuit wiring. In general, metal nanoparticles having high thermal conductivity, electrical conductivity, and heat resistance (oxidation resistance) are preferred for use in such applications. For this reason, noble metal nanoparticles such as gold and silver are often used, and relatively inexpensive silver is often used.

  However, silver has a weak point that it tends to cause ion migration and easily cause a short circuit. For suppressing ion migration, it is effective to use copper nanoparticles. Copper has a thermal conductivity comparable to that of silver (silver: 430 W / m · K, copper 400 W / m · K), and is far more advantageous than silver in terms of cost.

  As a method for producing copper nanoparticles, for example, Non-Patent Document 1 reports a method of producing copper nanoparticles having a particle size of 100 nm or less using CTAB (Cetyl Trimethyl Ammonium Bromide) as a dispersant. However, it is necessary to wash the copper nanoparticles to remove excess CTAB before the sintering heat treatment.

  However, there is a problem that when copper nanoparticles are washed, metallic copper is oxidized and converted into cuprous oxide. Once metallic copper is oxidized to cuprous oxide, it becomes difficult to sinter in the atmosphere, and heating at 400 ° C or higher is required even in a reducing atmosphere such as hydrogen. Becomes difficult.

  On the other hand, as a technique for preventing the oxidation of copper nanoparticles, a method of coating the periphery of the nanoparticles with silicone oil at the time of preparing the copper nanoparticles (see, for example, Patent Document 1 and Patent Document 2), or a fine copper powder is produced. After that, a method of adding an additive to suppress copper oxidation (for example, see Patent Document 3), a method of adjusting the dispersibility and viscosity of copper nanoparticles and mixing with a resin to suppress oxidation (for example, Non-Patent Document 2) is disclosed.

  On the other hand, Patent Document 4 discloses a method of reducing and sintering cupric oxide nanoparticles in hydrogen. According to Patent Document 4, cupric oxide is reduced from around 200 ° C. in hydrogen, so that low temperature sintering is possible. In addition, since cupric oxide is stable at room temperature, there is no need to add viscosity modifiers or oxidation-resistant additives, and it is easier to handle than metallic copper nanoparticles and can be stored for a long time. Yes.

Japanese Patent Laying-Open No. 2005-60777 Japanese Patent Laid-Open No. 2005-60778 JP 2007-258123 A JP 2008-244242 A

Szu-Han Wu and Dong-Hwang Chen, Journal of Colloid and Interface Science 273 (2004) pp. 165-169. 14th Symposium on “Micro joining and Assembly Technology in Electronics” (2008) p. 191-194.

  The copper nanoparticles described in Patent Document 1 and Patent Document 2 seem to be excellent in terms of oxidation resistance, but in a narrow space such as a joint application between electronic members, Residues are likely to remain at the joints, and there is a concern that joint strength and thermal conductivity may be reduced. In addition, the method described in Non-Patent Document 2 is liable to cause residual resin during sintering heat treatment, which may impair sinterability. Furthermore, the additive coating method described in Patent Document 3 is a method in which an antioxidant is adsorbed on the surface of the produced copper fine powder using a ball mill or the like. In this method, the particle size is 100 nm or less. It is feared that it is difficult to uniformly coat the nanoparticles, and it is difficult to suppress the oxidation of the nanoparticles.

  On the other hand, bonding using cupric oxide nanoparticles described in Patent Document 4 is a very interesting technique from the viewpoint of particle stability, but in order to produce a paste for bonding agent, it is uniformly dispersed in a solvent. Low molecular, high molecular or oligomeric dispersants are used. However, in this case as well, there is a concern that the residue of the organic dispersant inhibits the sintering of the nanoparticles during the sintering heat treatment and causes a decrease in bonding strength.

  In addition, according to the investigations and studies by the present inventors, a paste was prepared by mixing cupric oxide powder (commercial product) with an average particle diameter of μm order with water using an organic dispersant (commercial product). As a result of a joining experiment between the members, it was found that the residue of the organic dispersant hindered the sintering of the powder and the joining was not successful. In addition, a paste was prepared by mixing cupric oxide nanoparticles (commercially available) having an average particle size of 50 nm or less with water without using a dispersant, and a bonding experiment between electronic members was conducted. It was found that the dispersibility was poor and spots were formed at the joint. Details of each will be described later.

  The present invention has been made in view of the above circumstances, solves the problems of the prior art, and achieves both stable dispersibility and bondability in a sintered bonding agent using nanoparticles and suppresses ion migration. An object of the present invention is to provide a sintered bonding agent mainly comprising copper oxide nanoparticles that can be produced, a method for producing the same, and a bonding method using the same.

  In one embodiment of the present invention, in order to achieve the above object, a sintered bonding agent using cupric oxide nanoparticles, wherein the cupric oxide nanoparticles having a particle size of 2 nm to 50 nm are 1 A sintered bonding agent characterized in that the primary particles are aggregated to form secondary particles having a particle size of 3 nm or more and 1000 nm or less, and the secondary particles are dispersed in a solution. I will provide a.

  According to the present invention, in a sintered bonding agent using nanoparticles, a sintered bonding agent mainly composed of copper oxide nanoparticles that can suppress ion migration while achieving both stable dispersibility and bonding properties, The manufacturing method and the joining method using the same can be provided.

It is a flowchart which shows one example of the synthesis | combining method of the cupric oxide nanoparticle which concerns on this invention. It is a graph which shows the relationship between the major axis diameter of a primary particle, and a crystallite diameter. It is a graph which shows the relationship between an aggregate size and normalized bonding strength. It is a graph which shows the relationship between an aggregate aspect ratio and normalized bonding strength. It is a graph which shows the relationship between the frequency | count of washing | cleaning and normalized bonding strength, and the relationship between the frequency | count of washing | cleaning and the content rate of the cupric oxide cupric nanoparticle in dry powder. It is a cross-sectional schematic diagram which shows an example of the wiring board which mounts a semiconductor power module, and a pin fin cooling unit. It is the schematic diagram which showed the insulation type semiconductor device to which this invention is applied, (a) is a top view, (b) is AA sectional drawing of (a). It is the isometric view schematic diagram which showed the principal part of FIG. It is the cross-sectional schematic diagram which expanded and showed the semiconductor element mounting part of FIG. It is a cross-sectional schematic diagram of a capacitor built in a component built-in type multilayer wiring board. It is a cross-sectional schematic diagram of an LSI chip incorporated in a component built-in type multilayer wiring board. It is a cross-sectional schematic diagram of a core layer portion of a component built-in type multilayer wiring board. It is a cross-sectional schematic diagram which shows an example of the component built-in type multilayer wiring board to which this invention is applied. It is a cross-sectional schematic diagram which shows another example of the component-embedded multilayer wiring board to which the present invention is applied. It is a cross-sectional schematic diagram which shows another example of the multilayer wiring board with a built-in component to which the present invention is applied. It is a cross-sectional schematic diagram which shows an example of the laminated chip to which this invention is applied.

  As described above, the sintered bonding agent according to the present invention is a sintered bonding agent using cupric oxide nanoparticles, and the cupric oxide nanoparticles having a particle diameter of 2 nm to 50 nm are 1 Used as secondary particles, the primary particles aggregate to form secondary particles having a particle size of 3 nm or more and 1000 nm or less, and the secondary particles are dispersed in a solution.

Moreover, the present invention can add the following improvements and changes to the sintered bonding agent according to the above-described invention.
(1) The solution is water or a mixed solution of water and an alcohol solvent.
(2) The content of the cupric oxide nanoparticles is 90% by mass or more.
(3) The primary particles are composed of single crystallites.
(4) The primary particles are composed of a plurality of crystallites.
(5) A method for producing the sintered bonding agent, wherein after the step of dissolving the copper compound in the solution to produce copper ions, an alkaline solution is added to the solution while flowing an inert gas to oxidize the solution. Producing cupric colloid.
(6) In the method for producing a sintered bonding agent, the copper compound is at least one of copper nitrate hydrate, copper oxide, and carboxylic acid copper salt.
(7) A method for joining electronic members, the method including a step of applying a sintering heat treatment at 100 to 500 ° C. in a reducing atmosphere after the step of applying the above-described sintered bonding agent to the joining portion.
(8) In the method for joining electronic members, the reducing atmosphere is a hydrogen, formic acid, or ethanol atmosphere.
(9) In the joining method between the electronic members, the electronic member is a cooling fin and a metal support plate of a cooling unit, and the sintering is performed while pressurizing the cooling fin and the metal support plate in a joining direction. Apply heat treatment.
(10) In the bonding method of the electronic members, the electronic members are a chip and a wiring board of a semiconductor device, and the sintering heat treatment is performed while applying pressure in a direction in which the chip and the wiring board are bonded.

  Hereinafter, an embodiment of the present invention will be described along a manufacturing procedure of a sintered bonding agent with reference to the drawings. However, the present invention is not limited to the embodiments taken up here, and can be appropriately combined and improved without departing from the scope of the invention.

(Method for producing sintered bonding agent)
FIG. 1 is a flowchart showing an example of a method for synthesizing cupric oxide nanoparticles according to the present invention. First, as a solvent for synthesizing cupric oxide nanoparticles, prepared is distilled water that has been subjected to inert gas bubbling for 30 minutes or more with stirring. The reason for performing inert gas bubbling is to remove dissolved oxygen in the solvent and prevent impurities other than cupric oxide from being generated during synthesis. The inert gas may be anything as long as it suppresses the reaction of copper ions in the solution to other than cupric oxide, and examples thereof include nitrogen gas, argon gas, and helium gas. The inert gas bubbling is preferably continued until the synthesis of cupric oxide is completed. Further, the flow rate of bubbling is not particularly limited, but for example, a range of 1 mL / min to 1000 mL / min is preferable.

  Next, while stirring the solvent whose temperature is controlled to be 5 ° C. or higher and 90 ° C. or lower, the copper compound powder as a raw material is dissolved to produce copper ions. The copper compound as a raw material is preferably a compound that can reduce the residue resulting from the anion at the time of dissolution, for example, copper nitrate trihydrate, copper chloride, copper hydroxide, copper carboxylate, etc. are preferred as copper acetate Used. Among these, copper nitrate trihydrate is particularly preferable because it produces a small amount of impurities during the synthesis of cupric oxide and does not hinder secondary particle formation (aggregate formation).

  The concentration of the copper compound solution is preferably such that the copper concentration is 0.001 to 1 mol / L, particularly preferably 0.010 mol / L. A concentration of less than 0.001 mol / L is not preferable because it is too dilute and the yield of cupric oxide decreases. A concentration of more than 1 mol / L is not preferable because formation of aggregates (secondary particles) is inhibited.

  The reason for setting the solvent temperature to 5 ° C. or higher and 90 ° C. or lower is as follows. Since this synthesis method uses a solvent mainly composed of water, when the solvent temperature (reaction temperature) exceeds 90 ° C., nanoparticles (primary particles) and aggregates (secondary particles) having a stable size and shape are obtained. It is not preferable because it cannot be obtained. Moreover, when the solvent temperature (reaction temperature) is less than 5 ° C., the desired cupric oxide is hardly produced, and the yield is unfavorable.

Next, a colloid of cupric oxide nanoparticles is generated by adding an alkaline solution. The alkaline solution to be added is not particularly limited. For example, potassium hydroxide (KOH), barium hydroxide (Ba (OH) ₂ ), sodium carbonate (Na ₂ CO ₃ ), calcium hydroxide (Ca (OH) ₂ ), Sodium hydroxide (NaOH) and the like are preferably used. Of these, NaOH and KOH are particularly preferred. This is because NaOH and KOH have a low content of impurities and hardly generate by-products and impurities during synthesis.

The amount of the alkaline solution to be added, the alkali ion content of the copper ion content [Cu ^2+] [OH ^-] molar ratio ^{([OH -] / [Cu} 2+]) be made to be 1.5 or more and less than 2.1 Is preferred. When “[OH ⁻ ] / [Cu ²⁺ ]” is 2.1 or more, the shape of the produced cupric oxide secondary particles deteriorates, and the bonding strength is lowered when the electronic members are bonded together. Further, when “[OH ⁻ ] / [Cu ²⁺ ]” is less than 1.5, cupric oxide itself is hardly generated. Details will be described later.

  As described above, although this synthesis method uses a solvent mainly composed of water, the reaction rate and the primary particle size can be controlled by mixing a polar organic solvent. Examples of polar organic solvents include alcohols (eg, ethanol, methanol, isopropyl alcohol, 2-ethylhexyl alcohol, ethylene glycol, triethylene glycol, ethylene glycol monobutyl ether), aldehydes (eg, acetaldehyde), polyols (For example, glycol etc.) can be suitably used. The mixing ratio of water and polar organic solvent can be arbitrary. In addition to polar machine solvents, nonpolar organic solvents (for example, ketones such as acetone, tetrahydrofuran, N, N-dimethylformamide, toluene, hexane, cyclohexane, xylene, benzene, etc.) may be added.

  The synthesis time is not particularly limited, but it is preferably performed in the range of 1 minute to 336 hours (14 days). When the time is less than 1 minute, the synthesis reaction is not completed, and the yield decreases. On the other hand, since the synthesis reaction is completed within 336 hours at the latest, a longer time is wasted.

  The nanoparticles synthesized above may be used as a sintered bonding agent as they are, but since unreacted products, by-products, anions, etc. remain during synthesis, centrifugal washing is performed 1 to 10 times after synthesis. Preferably it is done. Thereby, unreacted substances, by-products, anions and the like at the time of synthesis can be removed. As the cleaning liquid, the above-described water or polar organic solvent can be preferably used.

  It is preferable to dry the cupric oxide nanoparticles obtained by centrifugal washing, and then disperse them in an appropriate liquid (dispersion medium) to prepare a paste-like sintered bonding agent. At this time, the cupric oxide content in the sintered bonding agent is preferably 90% by mass or more from the viewpoint of improving the bonding strength. As the dispersion medium, water or the above-mentioned polar organic solvent (for example, alcohols, aldehydes, polyols) can be preferably used. Further, in addition to the polar machine solvent, the aforementioned nonpolar organic solvent may be added.

  In order to improve the dispersibility of the cupric oxide nanoparticles in the sintered bonding agent, a dispersant may be added. At this time, the dispersant is preferably one that has little influence during sintering joining (one with little residue). For example, sodium dodecyl sulfate, cetyltrimethylammonium chloride (CTAC), citric acid, ethylenediaminetetraacetic acid, sodium bis (2-ethylhexyl) sulfonate (AOT), cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone, polyacrylic acid , Polyvinyl alcohol, polyethylene glycol and the like. The dispersant may be mixed to such an extent that the dispersibility of the nanoparticles is improved, and 30 parts by mass or less of the dispersant is preferable with respect to 100 parts by mass of cupric oxide. If it is added more than that, a residue is likely to remain in the bonding layer, which causes a decrease in bonding strength.

(Properties of sintered bonding agent)
The primary particle size of the cupric oxide nanoparticles is preferably 2 to 50 nm, more preferably 8 to 18 nm. When the primary particle diameter is less than 2 nm, the chemical activity of the surface becomes too high, and it becomes difficult to control the secondary particles (aggregates). In addition, primary particles having a particle size of more than 50 nm are difficult to produce by the above-described synthesis method, and the chemical activity of the surface becomes too low to control secondary particles (aggregates). . When the primary particle diameter is 8 to 18 nm, more uniform secondary particles (aggregates) can be formed, and as a result, strong bonding can be obtained. The shape of the primary particles does not need to be a true sphere, and may be an elliptical sphere or a polyhedron. In addition, when the particle shape is an ellipsoidal shape or a polyhedral shape, the volume of the ellipsoidal sphere is obtained from the major axis diameter and minor axis diameter of the particle, and the diameter of the sphere having the same volume (converted diameter) (The length of the long axis x the square of the length of the short axis = the cube of the converted diameter). Further, the primary particle may be composed of a single crystallite or a plurality of crystallites.

  The sintered bonding agent according to the present invention is characterized in that the primary particles described above aggregate to form secondary particles (aggregates), and the aggregates are uniformly dispersed. Aggregates are defined as aggregates in which primary particles are fused or in contact with each other. When the arithmetic average of the major axis length and the minor axis length of the aggregate is defined as the aggregate size, the aggregate size is preferably 3 nm or more and 1000 nm or less. When the aggregate size exceeds 1000 nm, the dispersibility decreases and the stability as a sintered bonding agent deteriorates. The aspect ratio of the major axis length to the minor axis length of the aggregate is preferably 1 or more and 3 or less. When the aspect ratio of the aggregate is larger than 3, the denseness at the time of bonding deteriorates and the bonding strength is reduced. By agglomerating primary particles composed of nanoparticles as described above, it is possible to improve the denseness of the bonding layer as compared with a bonding agent in which single nanoparticles (primary particles) as in the prior art are dispersed. Thus, a stronger bonding strength can be obtained.

  When the primary particles are composed of single crystallites, the aggregate size is more preferably 50 nm or more and 800 nm or less. On the other hand, when the primary particles are composed of a plurality of crystallites, the aggregate size is more preferably 10 nm or more and 100 nm or less. Thus, although the mechanism by which a more preferable aggregate size differs is not yet elucidated, it is thought that the process in which copper oxide is reduced to metallic copper and sintered is related. In the sintering joining process, the copper oxide particles are once polycrystallized, then reduced to metallic copper, and then sintered. For this reason, primary particles composed of single crystallites (that is, particles having a large crystallite diameter) are reduced while rearranging to a plurality of crystallites, and thus more energy is considered to be required. On the other hand, primary particles composed of a plurality of crystallites (that is, particles having a small crystallite diameter) are considered to proceed with reduction with relatively little energy.

  Observation of primary particles and secondary particles can be performed using an electron microscope (for example, a transmission electron microscope). The crystallite diameter can be calculated from the peak obtained by the X-ray diffraction method using the Scherrer equation. When the measured crystallite diameter is not less than the major axis diameter of the observed primary particles, it can be determined that the primary particles are composed of single crystallites. On the other hand, when the measured crystallite diameter is less than the observed major axis diameter of the primary particles, it can be determined that the primary particles are composed of a plurality of single crystallites.

(Sintering heat treatment)
As the sintering heat treatment for the sintered bonding agent according to the present invention, it is preferable to perform the heat treatment at a temperature of 100 to 500 ° C. in a reducing atmosphere. Further, the reducing atmosphere is not particularly limited, but for example, a hydrogen atmosphere, a formic acid atmosphere, an ethanol atmosphere, or the like is preferable.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these descriptions.

(Preparation of copper oxide nanoparticles)
Cu (NO ₃ ) ₂ .3H ₂ O powder was used as a raw material copper compound, water was used as a solvent, and NaOH was used as a precipitant for cupric oxide nanoparticles. Add Cu (NO ₃ ) ₂ 3H ₂ O powder so that the copper ion concentration becomes 0.01 mol / L to 985 mL of distilled water that has been bubbled with nitrogen for 30 minutes in a beaker with a volume of 1000 mL. It was dissolved uniformly in a water bath at 80 ° C. Then, cupric oxide nanoparticle colloid was synthesize | combined by dripping 1.0 mol / mL NaOH aqueous solution (15 mL).

  After stirring at room temperature for 24 hours, the synthesized cupric oxide particles were subjected to centrifugal separation (centrifugal washing machine: Tommy Seiko Co., Ltd., Suprema 21) and washing operations three times each. Thereafter, the cupric oxide particles were taken out and dried to obtain 0.085 g of cupric oxide particles (samples 1 to 7).

(Investigation of properties of copper oxide nanoparticles)
With respect to the produced cupric oxide particles (Samples 1 to 7), the primary particle size and the aggregate size were observed and measured using a transmission electron microscope (JEM-2000FX II, manufactured by JEOL Ltd.). Moreover, the crystallite diameter which comprises a primary particle was measured using the X-ray-diffraction apparatus (Rigaku Corporation make, RU200B) (scanning speed = 2deg / min). The crystallite diameter was calculated using the Scherrer equation from the peaks of the (002) plane and the (-111) plane of cupric oxide in the XRD diffraction pattern. The properties of the primary particles and aggregates in Samples 1 to 7 are summarized in Table 1, and the relationship between the major axis diameter of the primary particles and the crystallite diameter is shown in FIG.

  As shown in Table 1 and FIG. 2, Samples 1 to 4 (particles synthesized at 20 to 50 ° C.) have a crystallite diameter equal to or greater than the major axis diameter of the primary particles, and the primary particles are formed from a single crystallite. It turns out that it is composed. On the other hand, Samples 5 to 7 (particles synthesized at 60 to 80 ° C.) had a crystallite diameter shorter than the major axis diameter of the primary particles, and the primary particles were composed of a plurality of crystallites. .

(Dispersibility investigation of copper oxide nanoparticles)
The dispersibility of the produced cupric oxide particles (samples 1 to 7) was investigated. For comparison, commercially available cupric oxide nanoparticles (manufactured by Sigma Aldrich Japan, product number 544868-25G, particle size of 50 nm or less) were used as comparative sample 1. Also, a dispersant (dispervic) is added to commercially available cupric oxide particles having a particle size of μm order (product number 036-14792 manufactured by Wako Pure Chemical Industries, Ltd.) according to the technique described in Patent Document 4. This was used as Comparative Sample 2. In the test method, water was used as a dispersion medium, and the particles were put into the dispersion medium and stirred well, and then allowed to stand to visually observe the state of dispersion. The results are shown in Table 2.

  As shown in Table 2, Comparative Sample 1 almost precipitated in 5 minutes after standing. Further, Comparative Sample 2 had good dispersibility, and no precipitation was observed even after 1 day after standing, but this was considered to be an effect of adding a dispersant. On the other hand, the produced cupric oxide particles (Samples 1 to 7) maintained a good dispersion state even after one day after standing, although no dispersant was added. This indicates that the dispersibility is improved by the cupric oxide particles of the present invention being an aggregate of nanoparticles. That is, it was confirmed that the particles obtained in the present invention were excellent in dispersibility in a dispersion medium without using a dispersant as in the prior art.

(Joint strength test of sintered bonding agent)
A joining strength test was conducted by simulating joining between electronic members. The test method is as follows. Each sintered bonding agent was prepared in a state in which each of Samples 1 to 7 and Comparative Samples 1 and 2 described above was poured into water so that the content was 90% by mass and well stirred. As a copper test piece used for the measurement, a lower test piece having a diameter of 10 mm and a thickness of 5 mm and an upper test piece having a diameter of 5 mm and a thickness of 2 mm were used. After applying the prepared sintered binder on the lower test piece and drying under reduced pressure at 80 ° C for 1 hour, the upper test piece was placed on the dried sintered bond, and the temperature was increased to 400 ° C in hydrogen. A sintering heat treatment was performed for a minute. At this time, a load having a surface pressure of 1.2 MPa was simultaneously applied. Using a shear tester (made by Seishin Shoji Co., Ltd., Bond Tester SS-100KP, maximum load 100 kg), the bonded specimen was subjected to shear stress (shear rate 30 mm / min), and the maximum load at break Was measured. The bonding strength was determined by dividing the maximum load by the bonding area. Furthermore, it normalized with the joint strength of the comparative sample 1, and calculated the normalization joint strength of each sintering joining agent.

  The results of the normalized bonding strength in Samples 1 to 7 are also shown in Table 1, and the relationship between the aggregate size and the normalized bonding strength is shown in FIG. As shown in FIG. 3, it was found that the bonding strength of the sintered bonding agent of the present invention increases as the aggregate of cupric oxide nanoparticles increases. It is considered that by dispersing nanoparticle aggregates as a sintered bonding agent, the denseness in the bonding layer is easily improved and the bonding strength is improved. In addition, in Samples 1, 2, and 5, it was confirmed that a bonding strength higher than that of Comparative Sample 1 was obtained in addition to good dispersibility.

(Relationship between aggregate aspect ratio and bonding strength)
The molar ratio of ^- alkali ion content of the copper ion content [Cu ^2+] in the synthesis of cupric oxide nanoparticles ^{[OH] ([OH -]} / [Cu 2+]) to change the by aggregates obtained The relationship with the bonding strength was investigated by changing the aspect ratio. The synthesis and properties of cupric oxide nanoparticles were examined in the same manner as in Example 1, and the bonding strength test was conducted in the same manner as in Example 3. The synthesis temperature was 20 ° C. The properties of the produced samples 8 to 15 are summarized in Table 3, and the relationship between the aggregate aspect ratio and the normalized bonding strength is shown in FIG.

  As shown in Table 3 and FIG. 4, a standardized bonding strength higher than “1” was obtained in the range of the aggregate aspect ratio of “1.5 to 3.0”, but the aggregate aspect ratio was “3.0” or more. As a result, a decrease in normalized bonding strength was observed. This is thought to be because the denseness of the bonding layer tends to decrease as the aggregate aspect ratio increases. From the above results, it was found that better bonding is obtained when the aggregate aspect ratio of cupric oxide nanoparticles is lower than 3.0.

(Relationship between cleaning frequency and bonding strength during copper oxide nanoparticle synthesis)
The relationship between the number of washings after centrifugation during the synthesis of copper oxide nanoparticles and the bonding strength was investigated. The synthesis of the copper oxide nanoparticles was performed in the same manner as in Example 1 (synthesis temperature 20 ° C.), and the bonding strength test was performed in the same manner as in Example 3. FIG. 5 is a graph showing the relationship between the number of cleanings and the normalized bonding strength, and the relationship between the number of cleanings and the content of cupric oxide cupric nanoparticles in the dry powder. As shown in FIG. 5, the normalized bonding strength was improved by increasing the number of times of centrifugal cleaning, and the content of cupric oxide nanoparticles in the dry powder increased. In particular, when the content of cupric oxide nanoparticles was 90% by mass or more, the normalized bonding strength exceeded “1”. This was thought to be because impurities during the synthesis of copper oxide nanoparticles were removed by centrifugal washing. From the above results, in order to improve the bonding strength, it is preferable to perform centrifugal cleaning at the time of copper oxide nanoparticle synthesis, and the content of cupric oxide nanoparticles in the dry powder may be 90% by mass or more. It was confirmed that it was preferable.

(Application to cooling unit)
The example which applies this invention to the pin connection of the pin fin cooling unit of a semiconductor power module is shown. In recent years, semiconductor power modules have a tendency to increase the amount of heat generated, and therefore, technology for efficiently dissipating heat generated during operation to the outside of the module has become increasingly important. FIG. 6 is a schematic cross-sectional view showing an example of a wiring board on which a semiconductor power module is mounted and a pin fin cooling unit. As shown in FIG. 6, the wiring substrate 14 includes a circuit wiring 11 connected to the semiconductor chip, an insulating substrate 12 for electrically insulating the semiconductor chip and the circuit wiring 11 inside the module, A metallization layer 13 for soldering the pin fin cooling unit 111 to the metal support plate 101 is laminated. The pin fin cooling unit 111 has a structure in which a large number of pin fins 201 are bonded to the metal support plate 101 via the bonding layer 100. The heat generated in the semiconductor power module is transferred in the thickness direction of the wiring board 14, and the final heat dissipation is performed via the pin fins 201 attached to the metal support plate 101.

  The metal support plate 101 and the pin fin 201 of the pin fin cooling unit 111 are usually made of copper. Conventionally, the joining of the metal support plate 101 and the pin fins 201 has been performed at a temperature of 800 ° C. or higher using a silver brazing material. Therefore, the metal support plate 101 and the pin fins 201 are softened, and there is a problem that the mechanical strength is reduced and the metal support plate 101 and the pin fins 201 are easily deformed. Therefore, the metal support plate 101 and the pin fin 201 were joined using a sintered joining agent in which the sample 1 of Example 1 was dispersed in water. The sintering heat treatment was performed at a temperature of 400 ° C. in hydrogen while applying a pressure of 1.2 MPa. Bonding at a temperature lower than the softening temperature of copper becomes possible, and the problem of copper softening can be solved.

(Application to semiconductor devices)
7A and 7B are schematic views showing an insulating semiconductor device to which the present invention is applied, in which FIG. 7A is a plan view and FIG. 7B is a cross-sectional view taken along line AA of FIG. FIG. 8 is a schematic perspective view showing the main part of FIG. FIG. 9 is an enlarged schematic cross-sectional view showing the semiconductor element mounting portion of FIG. This will be described with reference to FIGS. A wiring board composed of the ceramic insulating substrate 303 and the wiring layer 302 is bonded to the support member 310 via the solder layer 309. The wiring layer 302 is obtained by applying nickel plating to a copper wiring. The collector electrode 307 of the semiconductor element 301 and the wiring layer 302 on the ceramic insulating substrate 303 are joined via a joining layer 305 (pure copper layer after joining) formed by the sintered joining agent according to the present invention. . In addition, the copper oxide particle-using bonding material 305 (pure copper layered after bonding) produced in Example 1 at 20 ° C. has the emitter electrode 306 of the semiconductor element 301 and the connection terminal 401 in a sintered bonding according to the present invention. Bonding is performed via a bonding layer 305 (pure copper layering after bonding) formed by an agent. Furthermore, the connection terminal 401 and the wiring layer 304 on the ceramic insulating substrate 303 are joined via a joining layer 305 (after joining, pure copper layer) formed by the sintered joining agent according to the present invention. The bonding layer 305 has a thickness of 80 μm. Nickel plating is applied to the surfaces of the collector electrode 307 and the emitter electrode 306. The connection terminal 401 is made of Cu or a Cu alloy. 7 denote the case 311, the external terminal 312, the bonding wire 313, and the sealing material 314, respectively.

  The bonding layer 305 is formed by, for example, applying a sintered bonding agent containing 90% by mass of the cupric oxide nanoparticle aggregate and 10% by mass of water according to the present invention to the bonding surface of the member to be bonded. This is possible by drying at 80 ° C. for 1 hour and then subjecting it to a sintering heat treatment at 350 ° C. for 1 minute in hydrogen while applying a pressure of 1.0 MPa. In joining, ultrasonic vibration may be applied. Further, the bonding layer 305 may be formed individually or simultaneously.

(Application to multilayer wiring board)
In this embodiment, application to a component-embedded multilayer wiring board will be described. FIG. 10A is a schematic cross-sectional view of a capacitor incorporated in a component-embedded multilayer wiring board. In the capacitor 803, a metallized layer 802 is formed as an electrode, and a copper plating layer 801 is formed on the outer layer of the metallized layer 802. FIG. 10B is a schematic cross-sectional view of an LSI chip embedded in a component-embedded multilayer wiring board. In the LSI chip 804, bumps 805 are provided on the electrodes, and a copper plating layer 806 is formed on the outer layer of the bumps 805. FIG. 10C is a schematic cross-sectional view of a core layer portion of a component-embedded multilayer wiring board. Conduction in the thickness direction of the core 807 is performed by the surface wiring 809 of the through hole 808. Conduction in the thickness direction of the prepreg 810 is performed by a bump-like 812 having a copper plating layer 811 on the surface. Further, a copper plating layer 811 may be provided on the surface wiring 809.

  FIG. 11 is a schematic cross-sectional view showing an example of a component built-in multilayer wiring board to which the present invention is applied. FIG. 12 is a schematic cross-sectional view showing another example of a component built-in multilayer wiring board to which the present invention is applied. FIG. 13 is a schematic cross-sectional view showing still another example of a component built-in multilayer wiring board to which the present invention is applied. Each of the capacitors 803, the LSI chip 804, the through wiring 812, and the surface wiring 809 is bonded to the copper plating layers 801, 806, 811 by applying the sintered bonding agent according to the present invention, and then dried in a formic acid atmosphere. This is done through a sintered copper layer 813 formed by the sintering heat treatment. It should be noted that the sintered copper layer 814 other than the respective joint portions is in close contact with the prepreg 810. Also, in the component built-in type multilayer wiring board to which the present invention is applied, an electronic component (for example, a capacitor 803) is connected in the vertical direction as shown in FIG. 12, or is connected in the horizontal direction as shown in FIG. Thus, the projected area of the multilayer wiring board can be minimized or the thickness can be minimized, and the degree of freedom in design is high. Furthermore, since the sintered copper layer 813 formed using the sintered bonding agent according to the present invention is thin, it is possible to perform bonding while suppressing delay of the electric signal.

(Application to multilayer chip)
In this embodiment, application to a multilayer chip will be described. FIG. 14 is a schematic cross-sectional view showing an example of a laminated chip to which the present invention is applied. A through electrode 903 is formed in the semiconductor element 901 with an insulating layer 902 interposed therebetween. A copper metallized layer 904 is provided on one surface of the through electrode 903, and the sintered bonding agent according to the present invention is applied and dried on this surface, and then sintered by heat treatment at 300 ° C. in hydrogen. A plurality of semiconductor elements are stacked via a bonding layer 905 made of copper.

  When the material of the through electrode is not copper (for example, in the case of aluminum), a nickel plating layer is formed on the through electrode, and the copper plating layer is formed thereon, thereby using the sintered bonding agent according to the present invention. Joining is possible. The semiconductor element 906 has a Cu metallized layer 907 formed on both sides of the through electrode with such a configuration, and the bonding layer 905 using the sintered bonding agent according to the present invention formed on the Cu metallized layer 907 is formed. Via the electrode 909 of the interposer 908. The joining with the interposer 908 may be brazing or pressure bonding. Further, the present invention may be applied to the bonding between the bump 910 provided on the interposer 908 and the circuit board, or a conventional bonding method may be applied.

11 ... circuit wiring, 12 ... insulating substrate, 13 ... metallized layer, 14 ... wiring substrate, 100 ... bonding layer,
101 ... Metal support plate, 111 ... Pin fin cooling unit, 201 ... Pin fin,
301 ... Semiconductor element, 302, 304 ... wiring layer, 303 ... ceramic insulating substrate,
305 ... Junction layer, 306 ... Emitter electrode, 307 ... Collector electrode, 309 ... Solder layer,
310 ... support member, 311 ... case, 312 ... external terminal, 313 ... bonding wire,
314 ... Sealing material, 401 ... Connection terminal,
801, 806, 811 ... copper plating layer, 802 ... metallized layer, 803 ... capacitor,
804 ... LSI chip, 805 ... Bump, 807 ... Core, 808 ... Through hole,
809 ... surface wiring, 810 ... prepreg, 812 ... through electrode, 813,814 ... sintered copper layer,
901, 906 ... Semiconductor element, 902 ... Insulating layer, 903 ... Through electrode,
904, 907 ... copper metallized layer, 905 ... bonding layer, 908 ... interposer, 909 ... electrode,
910 ... Bump.

Claims (11)

A sintered bonding agent for joining electronic members ,
The sintered binder is mainly composed of cupric oxide nanoparticles,
Using the cupric oxide nanoparticles having a particle diameter of 2 nm to 50 nm as primary particles,
The primary particles aggregate to form secondary particles;
The secondary particles have a particle size of 3 nm or more and 1000 nm or less, and an aspect ratio of a major axis length to a uniaxial length is 1.5 or more and less than 3.
A sintered bonding agent characterized in that the secondary particles are dispersed in a solution. In the sintered bonding agent according to claim 1,
The sintered bonding agent, wherein the solution is water or a mixed solution of water and an alcohol solvent. In the sintered bonding agent according to claim 1 or 2,
A sintered bonding agent, wherein the content of the cupric oxide nanoparticles is 90% by mass or more. In the sintered bonding agent according to any one of claims 1 to 3,
A sintered bonding agent, wherein the primary particles are composed of single crystallites. In the sintered bonding agent according to any one of claims 1 to 3,
A sintered bonding agent, wherein the primary particles are composed of a plurality of crystallites. A method for producing a sintered bonding agent for joining electronic members ,
The sintered binder is composed of cupric oxide nanoparticles as a main material, and the cupric oxide nanoparticles having a particle size of 2 nm to 50 nm are used as primary particles. A sintered binder comprising secondary particles having a diameter of 3 nm or more and 1000 nm or less, wherein the secondary particles are dispersed in a solution;
After the step of dissolving the copper compound in the solution to generate copper ions,
A method for producing a sintered binder, comprising a step of adding an alkaline solution while flowing an inert gas into the solution to produce a cupric oxide colloid. In the manufacturing method of the sintered joining agent of Claim 6,
The copper compound is at least one of copper nitrate hydrate, copper oxide, and carboxylic acid copper salt. A method for joining electronic members,
After the step of applying the sintered bonding agent according to any one of claims 1 to 5 to a bonding portion,
A method for joining electronic members, comprising a step of performing a sintering heat treatment at 100 to 500 ° C. in a reducing atmosphere. In the joining method of the electronic members of Claim 8,
The method for bonding electronic members, wherein the reducing atmosphere is a hydrogen, formic acid, or ethanol atmosphere. In the joining method of the electronic members of Claim 8 or Claim 9,
The electronic member is a cooling fin and a metal support plate of a cooling unit,
A method for joining electronic members, wherein the sintering heat treatment is performed while pressurizing the cooling fin and the metal support plate in a joining direction. In the joining method of the electronic members of Claim 8 or Claim 9,
The electronic member is a chip of a semiconductor device and a wiring board,
A method for joining electronic members, wherein the sintering heat treatment is performed while pressurizing the chip and the wiring board in a joining direction.

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