CONDUCTIVE JOINING MATERIAL AND CONDUCTIVE JOINING STRUCTURE WHICH USE METAL PARTICLES AND CONDUCTIVE MATERIAL PARTICLES

Abstract

A conductive joining material and conductive joined structure for joining two joining members by a joining layer using metal nanoparticles at the time of which even if there is a difference in the amounts of heat expansion due to a difference in linear thermal expansion coefficients between these two joining members and further use at a high temperature is sought, it is possible to adjust the amount of heat expansion of the joining layer to a suitable value between the two joining members to ease the thermal stress occurring at the joining layer and possible to sufficiently hold the joint strength between the two joining members are provided.

A conductive joining material containing metal nanoparticles, microparticles of a conductive material, and a solvent, wherein the conductive material forming the microparticles has a linear thermal expansion coefficient smaller than the linear thermal expansion coefficient of the metal forming the nanoparticles and the microparticles of conductive material have an average particle size of 0.5 to 10 m.

Claims

1-12. (canceled)

13. A conductive joining material containing metal nanoparticles, microparticles of a conductive material, and a solvent, wherein the conductive material forming said microparticles has a linear thermal expansion coefficient smaller than the linear thermal expansion coefficient of the metal forming said nanoparticles and the microparticles of conductive material have an average particle size of 0.5 to 10 m.

14. The conductive joining material according to claim 13, wherein said difference in linear thermal expansion coefficient between the metal forming the nanoparticles and the conductive material forming the microparticles is 510.sup.6/K or more.

15. The conductive joining material according to claim 13, wherein said metal nanoparticles are any one of Ag, Au, Cu, and Ni.

16. The conductive joining material according to claim 13, wherein said microparticles of conductive material are one or more of a metal or metal boride.

17. The conductive joining material according to claim 13, wherein said microparticles of conductive material are one or more of any of W, Mo, Cr, TiB.sub.2, and ZrB.sub.2.

18. The conductive joining material according to claim 13, wherein 10 to 80 vol % of the total of the metal nanoparticles and microparticles of conductive material contained in said conductive joining material is comprised of said microparticles of conductive material.

19. A joining method using a conductive joining material comprising placing a conductive joining material according to claim 13 between the first joining member and second joining member and heating it to 450 C. or less to join said first joining member and said second joining member.

20. A conductive joined structure obtained by using a conductive joining material according to claim 13 to join a first joining member and a second joining member, wherein 2 to 90 mass % of the conductive material derived from said microparticles and the metal derived from said metal nanoparticles in the cross-section in the joining direction is said conductive material.

21. The conductive joined structure according to claim 20, wherein a difference in linear thermal expansion coefficients of said metal and said conductive material is 510.sup.6/K or more.

22. The conductive joined structure according to claim 20, wherein said metal is any of Ag, Au, Cu, and Ni.

23. The conductive joined structure according to claim 20, wherein said conductive material is a conductive material of one or more of a metal or metal boride.

24. The conductive joined structure according to claim 20, wherein said conductive material is one or more of W, Mo, Cr, TiB.sub.2, and ZrB.sub.2.

25. The conductive joining material according to claim 14, wherein said metal nanoparticles are any one of Ag, Au, Cu, and Ni.

26. The conductive joining material according to claim 14, wherein said microparticles of conductive material are one or more of a metal or metal boride.

27. The conductive joining material according to claim 15, wherein said microparticles of conductive material are one or more of a metal or metal boride.

28. The conductive joining material according to claim 25, wherein said microparticles of conductive material are one or more of a metal or metal boride.

29. The conductive joining material according to claim 14, wherein said microparticles of conductive material are one or more of any of W, Mo, Cr, TiB.sub.2, and ZrB.sub.2.

30. The conductive joining material according to claim 15, wherein said microparticles of conductive material are one or more of any of W, Mo, Cr, TiB.sub.2, and ZrB.sub.2.

31. The conductive joining material according to claim 16, wherein said microparticles of conductive material are one or more of any of W, Mo, Cr, TiB.sub.2, and ZrB.sub.2.

32. The conductive joining material according to claim 25, wherein said microparticles of conductive material are one or more of any of W, Mo, Cr, TiB.sub.2, and ZrB.sub.2.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1 is a cross-sectional view showing an example of a conventional metal joined structure.

[0019] FIG. 2 is a cross-sectional view showing an example of a metal joined structure of the present invention.

[0020] FIG. 3 is a cross-sectional view showing another example of a metal joined structure of the present invention.

DESCRIPTION OF EMBODIMENTS

[0021] The present invention provides a conductive joined structure comprised of a first joining member and a second joining member between which is provided a joining layer comprised of a sintered conductor containing microparticles of a conductive material and formed by sintering metal nanoparticles, wherein the conductive material forming the microparticles is comprised of a conductive material with a linear thermal expansion coefficient smaller than the linear thermal expansion coefficient of the metal forming the nanoparticles and has an average particle size of 0.5 to 10 m.

[0022] In the present invention, the metal nanoparticles means metal fine particles with an average particle size of less than 1 m, preferably 500 nm or less, preferably 5 nm or more, more preferably 100 nm or less. By using a sintered metal comprised of such metal fine particles sintered together as the joining layer of the joined structure, the metal fine particles are sintered together at a far lower temperature than the melting point of the melt (bulk metal) forming the metal nanoparticles, the first joining member and the second joining member can be joined, and the joint strength at the obtained joined structure can be maintained up to near the melting point of the metal. If the metal nanoparticles have an average particle size of 500 nm or less, the fluidity of the particles increases, so this is preferable. If 100 nm or less, the sinterability at a low temperature increases, so this is more preferable. Conversely, if smaller than 5 nm, the ratio of the oxides and organic shells at the surface of the metal nanoparticles becomes larger and the sinterability is liable to deteriorate and the joinability is liable to fall. Note that, the average particle size of the metal nanoparticles can be measured by the next method.

[0023] Method of Measurement of Particle Size of Metal Nanoparticles

[0024] A slurry obtained by dispersing the particles in ethanol, water, or another solvent at a high degree was coated on a sample stage and fully dried by vacuum drying or another method to prepare a sample for observation by a high resolution SEM (scanning electron microscope) or TEM (transmission electron microscope). The thus prepared observation sample was observed in a range of field of the diameter of particlesabout 10 (for example, SEM image of field of 1270 nm950 nm) to obtain an SEM image or TEM image. The obtained image was printed on paper and the length of the scale bar in the image and the diameters of the particles were measured by a ruler. The scale bar was used to convert the particle sizes to the actual sizes. These were arithmetically averaged to calculate the average particle size of the particles.

[0025] The element of the metal nanoparticles used in the present invention can be suitably selected in accordance with the materials of the two joining members to be joined together by the joining layer, but when preparing a power semiconductor module, one of Ag, Au, Cu, and Ni is suitable. These are often used for the joining layer of semiconductor devices not only because of the required excellent electrical conductivity and thermal conductivity, but also the correlation with the electrode structure at the back side of the semiconductor device. Therefore, depending on the electrode structure of the back side of the semiconductor device, it is also possible to use other elements. Further, the Ag, Au, Cu, and Ni metal nanoparticles may contain alloy ingredients other than those elements.

[0026] In the present invention, as shown in FIG. 2, between the joining surface 1a of the first joining member 1 (first joining surface) and the joining surface 2a of the second joining member 2 (second joining surface), a joining layer 3 is formed containing microparticles of conductive material 5 and comprising a metal nanoparticle phase 4 obtained by sintering metal nanoparticles. The inventors succeeded in solving the above problem by making the conductive material forming the microparticles 5 by a material with a smaller linear thermal expansion coefficient than the metal forming the nanoparticles. If a difference occurs between the amounts of heat expansion of the first joining member 1 and the second joining member 2, the amount of heat expansion of the joining layer 3 can be adjusted by the ratio of the volume of the conductive microparticles 5 with respect to the total of the metal nanoparticles and microparticles of conductive material 5, the difference of the amount of heat expansion between the first joining member 1 and second joining member 2 can be eased, and thereby a drop in the joint strength between the first joining member 1 and the second joining member 2 can be prevented in advance. Further, since the amount of heat expansion of the joining layer 3 can be adjusted to a suitable value between the amounts of heat expansion of the first joining member 1 and the second joining member 2, it is possible to reduce the difference in the amounts of heat expansion between the first joining member 1 and the second joining member 2 even with the extent of heat deformation of the low ductility joining layer comprised of a sintered metal of metal nanoparticles and prevent a drop in the initial joint strength between the first joining layer and the second joining layer.

[0027] In the present invention, microparticles of conductive material means conductive particles of an average particle size of 0.5 m to 10 m, preferably 1 m to 3 m. By dispersing such microparticles of conductive material in a joining layer of a joined structure comprised of sintered metal nanoparticles, it is possible to reduce the heat expansion/contraction compared with a joining layer obtained by sintering only metal nanoparticles and possible to maintain the joint strength of the joined structure at a strength giving sufficient reliability. If the average particle size of the microparticles of conductive material exceeds 10 m, there is the problem that the particles deteriorate in fluidity. Further, if made 3 m or less, the particles become densified and sinterability increases, so this is further preferred. On the other hand, if the average particle size of the microparticles of conductive material becomes smaller than 0.5 m, the effect of reduction of the heat expansion/contraction becomes smaller. Further, the thermal conductivity and the electrical conductivity are liable to fall. Further, the microparticles of conductive material used in the present invention secure uniformity of heat conduction and electrical conduction, so to facilitate control for improving the filling rate of particles, the distribution of particle size should be narrower. Specifically, the distribution of particle size is preferably one with a standard deviation, calculated from all of the particle sizes measured by the following Method of Measurement of Particle Size of Conductive Microparticles, of 5 m or less. Further, the average particle size of the conductive microparticles can be found by using an SEM or TEM to directly observe the metal microparticles. Further, the conductive microparticles may be shaped not only as spherical shapes, but also as cube shapes, flat shapes, elliptical shapes, etc. In these cases, the longest side is defined as the particle size.

[0028] Method of Measurement of Particle Size of Conductive Microparticles

[0029] A slurry obtained by dispersing the conductive particles in ethanol, water, or another solvent at a high degree was coated on a sample stage and fully dried by vacuum drying or another method to prepare a sample for observation by an SEM or TEM. The thus prepared observation sample was observed in a range of field of the diameter of particles about 10 (for example, SEM image of field of 16.5 m12.4 m) to obtain an SEM image or TEM image. The obtained image was printed on paper and the length of the scale bar in the image and the diameters of the particles were measured by a ruler. The scale bar was used to convert the particle sizes to the actual sizes. These were arithmetically averaged to calculate the average particle size of the particles.

[0030] As the conductive material forming the microparticles of conductive material used in the present invention, it is possible to suitably select one from conductive materials having a linear thermal expansion coefficient smaller than the linear thermal expansion coefficient of the metal forming the nanoparticles in accordance with the type of the metal nanoparticles and the materials of the two joining members to be joined together by the joining layer etc., but to effectively ease the thermal stress occurring at the joining layer, it is preferably a metal having a difference from the linear thermal expansion coefficient of the metal forming the nanoparticles of 510.sup.6/K or more, more preferably 810.sup.6/K or more. For example, when preparing the power semiconductor module, it is preferably one or more types of materials selected from metals such as W (linear thermal expansion coefficient=about 4.510.sup.6/K, electrical resistance (20 C.)=about 5.510.sup.8 .Math.m), Mo (linear thermal expansion coefficient=about 4.810.sup.6/K, electrical resistance (20 C.)=about 5.710.sup.8 .Math.m), and Cr (linear thermal expansion coefficient=about 4.910.sup.6/K, electrical resistance (20 C.)=about 1310.sup.8 .Math.m) and metal borides such as TiB.sub.2 (linear thermal expansion coefficient=about (6.2 to 7.2)10.sup.6/K, electrical resistance (20 C.)=about 910.sup.8 .Math.m) and ZrB.sub.2 (linear thermal expansion coefficient=about (6.8 to 7.9)10.sup.6/K, electrical resistance (20 C.)=about 1010.sup.8 .Math.m). These are materials with a smaller linear thermal expansion coefficient than the metal in the temperature range from room temperature to the firing temperature of 450 C. Further, these microparticles of conductive material may be used suitably combined so as to give an amount of heat expansion of the joining layer easy to control considering the linear thermal expansion coefficients, average particle sizes, and ratios of content or may be used alone. Note that, even if elements other than these, if particles comprised of a material with a smaller linear thermal expansion coefficient compared with the metal forming the nanoparticles, an effect of reduction of the heat expansion/contraction can be expected. Further, the W, Mo, and Cr forming the microparticles of conductive material mean ones of contents of the elements in the particles (purity) of 99.5 mass % or more. If less than 0.5 mass %, unspecified unavoidable impurities may also be present. Further, the TiB.sub.2 and ZrB.sub.2 forming the microparticles of conductive material mean ones of contents of metal borides in the particles of 95 mass % or more. If less than 5 mass %, unspecified unavoidable impurities may also be present.

[0031] In the present invention, for example, to reduce the heat expansion/contraction ability of the joining layer and make it close to that (heat expansion/contraction ability) of the semiconductor device, it is sufficient to raise the ratio by volume of the microparticles of conductive material in the total volume of the metal nanoparticles and microparticles of conductive material contained in the conductive joining material of the present invention containing the metal nanoparticles and microparticles of conductive material. Further, it is sufficient to raise the ratio of content of the volume of the conductive material derived from the microparticles of conductive material to the metal derived from the metal nanoparticles in the sintered conductor obtained by sintering the conductive joining material and forming the joining layer, in other words, the ratio by volume of the microparticles of conductive material in the total volume of the metal nanoparticles and microparticles of conductive material forming the joining layer. Here, due to the firing, bonds are formed between the metal nanoparticles and other metal nanoparticles or between the metal nanoparticles and conductive microparticles, in particular metal bonds, and excellent joint strength is exhibited, but in general bonds are not formed between microparticles of conductive material and microparticles of conductive material at the 450 C. or less used for the firing temperature of metal nanoparticles. For this reason, the ratio of the microparticles of conductive material in the total volume of the metal nanoparticles and microparticles of conductive material contained in the conductive joining material has to be 80 vol % or less to obtain sufficient joint strength and reliability. Conversely, if the ratio of the microparticles of conductive material in the conductive joining material is less than 10 vol %, the heat expansion/contraction of the joining layer is liable to not be sufficiently reduced. Therefore, when the microparticles of the microparticles of conductive material contained in the conductive joining material are 10 vol % to 80 vol % of the total volume of the metal nanoparticles and microparticles of conductive material contained in the conductive joining material, preferably 30 vol % or more, still preferably 70 vol % or less, even with a material used in a high temperature and material used in an environment of a repeated temperature cycle of a high temperature and low temperature, a good joint strength can be maintained. Note that, the vol % of the microparticles in the conductive joining material can be found by the following method.

[0032] Method of Measurement of Vol % of Microparticles of Conductive Material with Respect to Total of Metal Nanoparticles and Microparticles of Conductive Material Contained in Conductive Joining Material

[0033] The density n of the metal forming the nanoparticles, the density m of the conductive material forming the microparticles, and the density y of the solvent are known. Here, the organic shells covering the nanoparticles are slight, so are ignored. The total mass Mn of the nanoparticles contained in the conductive material, the total mass Mm of the microparticles, and the mass My of the solvent are calculated by volume Vn of nanoparticles Vn=mass Mndensity n, volume Vm of microparticles=mass Mmdensity m, and volume Vy of solvent=mass Mydensity y. The total volume of the metal nanoparticles and microparticles of conductive material is Vn+Vm. The ratio of the microparticles of conductive material to the total volume is defined as Vm+(Vn+Vm). Further, the ratio of volume of the microparticles of conductive material in the total volume of the metal nanoparticles and microparticles of conductive material forming the joining layer (joined structure) cannot be directly measured, so instead a cross-section in the joining direction is obtained and the mass % of the conductive material to the total of the conductive material and metal material in that cross-section is measured.

[0034] Method of Measurement of Mass % of Conductive Material to Total of Conductive Material and Metal Material in Cross-Section in Joining Direction

[0035] First, the conductive joined structure is buried in a curable epoxy resin or other resin, the resin is cured, then this was cut vertical to the stacking direction from the first joining member through the joining layer to the second joining member to obtain a test piece. The cross-sectional surface is polished and in accordance with need processed by a CP (cross-section polisher) to prepare a test piece for SEM observation for observation of the cross-sectional surface.

[0036] Next, the prepared test piece is set on an SEM sample stage. The cross-sectional surface is observed under 5000 power. An image of the cross-sectional surface is obtained and is analyzed for assay of the elements by an EDX (energy dispersive X-ray spectroscope) attached to the SEM apparatus. If designating the mass % of the metal element A obtained by the quantitative analysis as M.sub.a, the mass % of the metal element B of the conductive material (for example, in the case of TiB.sub.2, indicating Ti) as M.sub.b, and the mass % of the element C other than the metal of the conductive material (for example, in the case of TiB.sub.2, indicating B) as M.sub.c the mass % of the conductive material with respect to the total of the conductive material and metal material is defined as (M.sub.b+M.sub.c)/(M.sub.a+M.sub.b+M.sub.c). These operations are performed for three to 10 cross-sectional surfaces. The mass % is found by the arithmetic average.

[0037] In the present invention, the joining layer gives an overall joining power due to the bonds between the metal, so it is not necessary to make the joining layer contain a component other than the metal. As explained above, when forming the joining layer of the present invention, for example, the conductive joining material of the present invention, that is, the conductive particle paste, is coated on the joining surface of the first joining member and/or second joining member, these members are superposed, then the assembly is fired at 200 C. or more to sinter the metal nanoparticles and realize a joint. This conductive particle paste is comprised of metal nanoparticles and microparticles of conductive material made to disperse in an ether etc. In general, metal nanoparticles are covered by organic shells comprised of an organic substance. Therefore, the joining layer before firing contains a solvent component and components of the organic shells in the conductive particle paste. When fired at 200 C. or more, these solvent component and components of the organic shells break down. Parts vaporize and separate from the joining layer, while the remainders carbonize and remain in the joining layer, but these components which carbonize and remain do not contribute to the joining power of the joining layer. Therefore, even if the joining layer contains components other than the metal, the total volume derived from the metal nanoparticles and microparticles of conductive material contained in the joining layer need only be 50 vol % of the joining layer (when there are cavities or voids, excluding these parts) or more, preferably 70 vol % or more. Due to this, the effects of the present invention can be sufficiently exhibited. Note that, the thickness of the joining layer of the present invention is preferably 10 m or more in the sintered conductor after firing, preferably 300 m or less, more preferably 20 m or more, still more preferably 150 m or less.

[0038] When the conductive joined structure of the present invention forms for example a power semiconductor module, it is possible to arrange a first joining member comprised of a semiconductor device, further arrange a second joining member comprised of a metal board, resin board, or ceramic board, coat the conductive joining material of the present invention on the joining surfaces of these first joining member and/or second joining member and overlay the same, and heat the first joining member and/or second joining member and the conductive joining material together to fire the conductive joining material and sinter it to obtain the joining layer. As the metal board of the second joining member, an aluminum board, iron board, copper base board, stainless steel board, etc. may be mentioned. As the resin board of the second joining member, an epoxy resin board, phenol resin board, etc. may be mentioned. As the ceramic board of the second joining member, an alumina board, silicon carbide board, nitride-based board, etc. may be mentioned. A ceramic board may also be formed with a circuit comprised of copper or aluminum interconnects.

[0039] Note that, for example, when the second joining member is Cu and the metal nanoparticles are Au or Ni, since the linear thermal expansion coefficient is smaller in Au or Ni compared with Cu, if arranging the microparticles of conductive material to reduce the heat expansion/contraction of the joining layer, the difference in heat expansion between the second joining surface and the joining layer conversely becomes larger. For this reason, for example, as shown in FIG. 3, it is possible to coat the joining surface of the second joining member 2 (second joining surface) 2a with a joining material containing only metal nanoparticles, cause it to sinter to form a joining layer 3a comprised of a sintered metal, coat the joining layer 3a and/or the joining surface 1a of the first joining member 1 (first joining surface) with the conductive joining material of the present invention containing metal nanoparticles and microparticles of conductive material, and overlay and fire the members to form a joining layer 3 of the present invention comprised of a sintered conductor so as to join the first joining member 1 and the second joining member 2 by the joining layer 3a and joining layer 3. Due to this, as shown in FIG. 3, it is possible to mainly reduce the heat expansion of the first joining member 1 side of the joining layer 3.

[0040] In the present invention, the conductive joining material for forming the joining layer between the first joining member and second joining member includes the above metal nanoparticles, microparticles of conductive material, a solvent for dispersing these metal nanoparticles and microparticles of conductive material, and a protective agent for forming organic shells on the surfaces of the metal nanoparticles to prevent aggregation of metal nanoparticles. Further, as the solvent, one is selected from alcohol-based or ether-based solvents in accordance with the type of metal nanoparticles. Further, as the protective agent, one is selected from amine-based agents, carboxylic acid-based agents, and polymer-based agents. Further, in accordance with need, as the dispersant, one is selected from an amine-based one, carboxylic acid-based one, and alcohol-based one is selected. Further, in accordance with need, in these conductive joining materials, a dispersion aid may be selected and added from various conventionally known anion-based ones, cation-based ones, and nonionic-based ones. It is possible to give the conductive joining material the desired fluidity etc. The solvent content in this conductive joining material is usually 30 vol % to 90 vol %, preferably 50 vol % or more, more preferably 70 vol % or less.

[0041] The thus prepared conductive joining material of the present invention may be a slurry form, paste form, grease form, wax form, etc. For example, an air spray coater, roll coater, electrostatic spray coater, the squeegee method, mask printing, etc. may be used to coat the joining surface of the first joining member and/or second joining member with this in a layer, then fire this to remove the solvent etc. in the conductive joining material and further sinter the metal nanoparticles whereby a joining layer is formed where 2 to 90 mass % of the total of the conductive material derived from the microparticles and the metal derived from the metal nanoparticles at the cross-section in the joining direction is the conductive material.

[0042] Here, the conductive joining material is, for example, coated by an air spray coater, roll coater, electrostatic spray coater, the squeegee method, mask printing, etc. on the joining surface of the first joining member and/or second joining member in a layer form. Further, the conductive joining material coated on the joining surface of the first joining member and/or second joining member is fired by heating it to usually 200 C. to 450 C., preferably 250 C. to 400 C. If the heating temperature at the time of firing is less than 200 C., sometimes a sufficient joint strength cannot be obtained, while conversely, if the heating temperature is over 450 C., damage to the semiconductor device or resin board etc. is a concern. Further, when firing this conductive joining material to form a joining layer, a suitable pressure, preferably 0.1 MPa to 50 MPa, more preferably 2 MPa to 10 MPa, may be applied between the first joining member, conductive joining material, and second joining member at the same time as heating.

EXAMPLES

Examples 1 to 8 and Comparative Examples 1 to 3

[0043] Using the metal nanoparticles of the average particle sizes shown in Table 1 and the microparticles of conductive material of the average particle sizes shown in Table 1 and, further, using a solvent comprised of a terpene-based alcohol, metal nanoparticles and microparticles of conductive material were mixed in the ratios shown in Table 1 to prepare conductive joining materials with total ratios of these metal nanoparticles and microparticles of conductive material of 50 vol %. Note that, in Table 1, the components other than the metal nanoparticles and microparticles of conductive material were the above solvent and organic shells covering the metal nanoparticles.

[0044] Next, as the first joining member, a thickness 0.45 mmvertical 3 mmhorizontal 3 mm size Si semiconductor device was used. One surface of this was formed with a total thickness 1.1 m Ti/Ni/Au film by the sputtering method to form the first joining surface. Further, as the second joining member, a circuit board comprised of a thickness 0.32 mmvertical 20 mmhorizontal 20 mm size alumina ceramic board on which a thickness 0.25 mm copper circuit layer was provided was used. On this copper circuit layer, a total thickness 5 m Ni/Au plating layer was formed to form the second joining surface.

[0045] The above joining surface of the first joining member (first joining surface) was coated with the conductive joining material shown in Table 1 by the squeegee method, then the joining surface of the second joining member (second joining surface) was overlaid so as to sandwich the conductive joining layer coated on the first joining surface of the first joining member, the assembly was heated under conditions of the temperature, pressure, holding time, and firing atmosphere shown in Table 1, the metal nanoparticles in the conductive joining material were fired to sinter them, and thereby a joining layer was formed between the first joining member and the second joining member to obtain the conductive joined structure of each of the examples and comparative examples. The conductive joined structures of the examples were as shown in FIG. 2. Further, the conductive joined structures of the comparative examples were as shown in FIG. 1.

[0046] In the joining layers of the conductive joined structures of the examples and comparative examples prepared in the above way, the majority of the content other than the metal material and the conductive material is the residue after carbonization by heating of the solvent and organic shells of the metal nanoparticles or the buried resin.

[0047] Measurement of Shear Strength

[0048] The conductive joined structures of the examples and comparative examples right after finishing being joined and prepared were cooled down to ordinary temperature, then measured for the shear strengths (n=10) of the Si semiconductor devices by the die shear mode using a bond tester (Series 4000 made by Dage). The results are shown in Table 1. In the examples of the present invention, in each case, the value was 10 MPa or more. As opposed to this, in the comparative examples, the shear strength was a low value of 10 MPa or less. As a result, in the conductive joined structures of the examples of the present invention, it was learned that the coefficient of thermal expansion of the joining layer is reduced and a good shear strength after joining is expressed.

[0049] Temperature Cycle Test

[0050] The conductive joined structures of the examples and comparative examples right after the joining operation is ended were subjected to a temperature cycle test using a gas phase type thermal shock tester (TSA-ES72-W made by Espec) and holding the structures at 40 C. and 250 C. for 30 minutes each. During this temperature cycle test, the conductive joined structures were taken out after the elapse of every 100 cycles and investigated for the states of peeling between the first joining member and the joining layer and between the joining layer and the second joining member using an ultrasonic video apparatus (FineSAT made by Hitachi Power Solutions). The structures were evaluated as Good when the rate of increase of peeling area after 1000 cycles was less than 20% based on the initial state and further as Poor when the rate of increase of peeling area was 20% or more. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Metal joining material Metal Microparticles of Joining Evaluation of nanoparticles conductive material layer conductive Average Average Ratio of Firing conditions at time of joining Thickness joined structure particle particle total Atmosphere after Shear size size particles Temperature Pressure Time at time of joining strength Temperature Type (nm) Type (m) (vol %) ( C.) (MPa) (min) firing (m) (MPa) cycle test Ex. 1 Ag 12 W 8 60 220 0 60 Air 45 >10 Good 2 Cu 60 W 3 55 280 1 30 3% H.sub.2N.sub.2 60 >10 Good 3 Ni 90 W 3 40 320 0 60 3% H.sub.2N.sub.2 120 >10 Good 4 Ag 12 Mo 10 10 230 5 60 Air 35 >10 Good 5 Cu 60 Mo 4 50 300 5 30 3% H.sub.2N.sub.2 55 >10 Good 6 Ni 90 Mo 4 30 320 5 60 3% H.sub.2N.sub.2 150 >10 Good 7 Au 8 Cr 1 55 250 0 60 Air 15 >10 Good 8 Ni 90 W 8 25 320 1 60 3% H.sub.2N.sub.2 100 >10 Good Mo 4 10 9 Ni 80 TiB.sub.2 2 80 300 0 60 3% H.sub.2N 130 >10 Good 10 Ni 80 ZrB.sub.2 2.5 80 300 0 60 3% H.sub.2N 130 >10 Good 11 Ni 80 TiB.sub.2 2 35 300 0 60 3% H.sub.2N 130 >10 Good ZrB.sub.2 2.5 35 12 Ni 80 W 3 35 300 0 60 3% H.sub.2N 130 >10 Good ZrB.sub.2 2.5 35 Comp. 1 Ag 12 220 0 60 Air 40 7 Poor ex. 2 Cu 60 280 1 30 3% H.sub.2N.sub.2 55 3 Poor 3 Ni 90 300 0 60 3% H.sub.2N.sub.2 100 5 Poor

[0051] In the comparative examples, the Si chips and joining layers completely peeled apart at the interface before 400 cycles, while in the examples of the present invention, no increase in peeling could be recognized up to 1000 cycles compared with the initial state.

REFERENCE SIGNS LIST

[0052] 1 . . . first joining member, 1a . . . first joining surface, 2 . . . second joining member, 2a . . . second joining surface, 3, 3a . . . joining layer, 4 . . . metal nanoparticle phase, 5 . . . metal microparticles.