JP6185353B2 - Circuit board and manufacturing method thereof - Google Patents

Description

  The present invention relates to a circuit board and a manufacturing method thereof.

Power module or switching module, eg IGBT (Insulated Gate)
As a circuit board used in an electronic device on which an electronic component such as a bipolar transistor is mounted, a ceramic board in which a metal plate made of, for example, copper or aluminum is joined with a brazing material containing Ag is used. The electronic component is mounted on a metal plate and is electrically connected to another metal plate by, for example, a bonding wire. As the metal plate, a foil mainly composed of copper or aluminum having a small electric resistance (resistivity) is used.

JP 2012-178513 JP

  However, in the prior art circuit board, when heat is generated from the electronic component mounted on the metal plate, the difference in thermal expansion coefficient between the insulating base and the metal plate joined to the main surface of the insulating base. There is a problem that the metal plate may be peeled off from the insulating substrate or a crack may be generated in the insulating substrate due to thermal stress caused by the above.

  In view of the above problems, an object of the present invention is to provide a highly reliable circuit board that reduces thermal stress between a metal plate and an insulating substrate and prevents peeling of the metal plate from the insulating substrate and cracking of the insulating substrate. Is to provide.

A circuit board according to one aspect of the present invention includes an insulating base, a metal plate formed by sintering copper particles, bonded to the main surface of the insulating base via a brazing material containing a silver component, In the metal plate, the grain boundaries of the copper particles are filled with the silver component diffused from the brazing material, and the particle size of the copper particles on the brazing material side is the metal It is smaller than the particle size of the copper particles on the surface layer side of the plate .

According to the circuit board according to one aspect of the present invention, in the metal plate, since the silver component diffused from the brazing material is filled in the grain boundaries of the copper particles, the silver component having a lower Young's modulus than the copper particles is a metal. Since it has an effect of lowering the Young's modulus of the entire plate, the thermal stress of the metal plate and the insulating base is easily relaxed. Also, in the metal plate, the Young's modulus can be reduced because the particle size of the copper particles is small and the amount of the silver component is large on the brazing material side where the greatest thermal stress is applied, and the thermal stress can be reduced.

It is sectional drawing which shows the circuit board of embodiment of this invention. It is an enlarged view of the A section of FIG. It is an enlarged view of the B section of FIG. It is an enlarged view of the C section of FIG.

  Hereinafter, a circuit board according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the circuit board is provided in a virtual xyz space and placed on the xy plane. In the present embodiment, the upper, upper, and upper portions indicate the positive direction of the virtual z axis, and the lower, lower surface, and lower portion indicate the negative direction of the virtual z axis.

  In the example shown in FIG. 1, the circuit board 10 includes an insulating base 11 and a metal plate 2. A metal plate 2 is joined to the main surface of the insulating base 11 with a brazing material 1.

  The insulating base 11 is made of an electrically insulating material, for example, ceramic such as aluminum oxide ceramics, mullite ceramics, silicon carbide ceramics, aluminum nitride ceramics, or silicon nitride ceramics. Among these ceramic materials, silicon carbide ceramics, aluminum nitride ceramics, or silicon nitride ceramics are preferred in terms of thermal conductivity that affects heat dissipation, and silicon nitride ceramics or silicon carbide ceramics in terms of strength. Is preferred.

  When the insulating base 11 is made of a ceramic material having a relatively high strength such as silicon nitride ceramics, the possibility of cracking in the insulating base 11 is reduced even if the metal plate 2 having a larger thickness is used. Thus, it is possible to realize a circuit board capable of allowing a larger current to flow while achieving the above.

The thinner insulating substrate 11 may be thin in terms of thermal conductivity, for example, about 0.1 mm to 1 mm, and may be selected according to the size of the circuit board 10 or the thermal conductivity or strength of the material used.

  If the insulating substrate 11 is made of, for example, silicon nitride ceramics, an appropriate organic binder, plasticizer, and solvent are added to and mixed with raw material powders such as silicon nitride, aluminum oxide, magnesium oxide, and yttrium oxide, and the slurry is mixed. A ceramic green sheet (ceramic raw sheet) is formed by adopting a conventionally known doctor blade method or calendar roll method, and then a suitable punching process is applied to the ceramic green sheet to obtain a predetermined shape. If necessary, a plurality of sheets are laminated to form a molded body, and then, this is manufactured by firing at a temperature of 1600 to 2000 ° C. in a non-oxidizing atmosphere such as a nitriding atmosphere.

  As shown in FIGS. 1 and 2, the metal plate 2 is joined to the main surface of the insulating base 11 via a brazing material 1 containing a silver component, and copper particles of a copper paste are sintered. The metal plate 2 is obtained by sequentially printing a brazing material paste to be the brazing material 1 and a copper paste to be the metal plate 2 on the main surface of the insulating base 11 and then firing the screen. Details of the manufacturing method will be described later. Since copper is used as the material of the metal plate 2, it is excellent in low electrical resistance and high thermal conductivity. In particular, with regard to high thermal conductivity, copper is excellent because its thermal conductivity is about 395 W / m · K.

Copper paste is a ball mill, three-roll mill, planetary mixer with copper powder as the main ingredient, organic binders such as acrylic resin and nitrocellulose resin, organic solvents such as terpineol and DBP, and dispersants as necessary. It adjusts by carrying out homogeneous mixing and kneading | mixing by kneading | mixing means. Since it is desirable that the binder can be removed in an atmosphere of 400 ° C. or lower in a vacuum furnace, an acrylic resin is usually used as a binder.

  The copper powder is preferably a fine powder made spherical by an atomization method in order to obtain a sintered body as dense as possible and to advance the sintering as quickly as possible, and a particle diameter of about 0.1 μm to 10 μm is preferably used. .

  Moreover, the kind and addition amount of the organic binder and the organic solvent may be reduced, and the viscosity may be adjusted to be higher than that of a general metallized paste for a wiring conductor layer. If the thickness of the metal plate 2 is about 5 to 300 μm, efficient heat dissipation is possible.

  As shown in FIGS. 1 and 2, a brazing material 1 is used for joining the metal plate 2 to the main surface of the insulating base 11. The brazing material 1 contains a silver component. As described above, the brazing material 1 is obtained by sequentially screen-printing the brazing material paste to be the brazing material 1 and the copper paste to be the metal plate 2 on the main surface of the insulating base 11 and then firing the same. During the firing, the copper particles are sintered to form the metal plate 2, and the silver component in the brazing paste that becomes the brazing material 1 diffuses to the copper paste side, and the metallic plate 2 passes through the brazing material 1. Bonded to the insulating substrate 11.

  Therefore, after firing, as shown in FIG. 3, the silver component 5 diffused from the brazing filler metal 1 is filled in the grain boundaries of the copper particles 3 in the metal plate 2. With this configuration, since the silver component 5 having a Young's modulus lower than that of the copper particles 3 has an effect of lowering the Young's modulus of the entire metal plate 2, the thermal stress of the metal plate 2 and the insulating base 11 is easily relaxed. Moreover, by filling the grain boundary of the copper particle 3 with the silver component 5, the thermal conductivity of the metal plate 2 can be improved and the generation of thermal stress can be suppressed.

  The silver powder contained in the brazing material paste used as the brazing material 1 is preferably a fine powder granulated by an atomizing method in order to facilitate diffusion, and the average particle size is preferably 0.1 μm to 10 μm.

The thickness of the brazing material 1 may be about 5 to 100 μm, for example. Moreover, in order to lower melting | fusing point other than a silver component, the brazing material 1 contains one or more types of tin and indium, for example, and contains the other metal material of about 1-20 mass%, or the component of the metal plate 2 It does not matter.

  The melting point of the brazing filler metal 1 is adjusted to, for example, about 520 to 650 ° C. or about 750 to 850 ° C. by adding tin and indium. Lowering the melting point of the brazing material 1 makes it easier for the silver component to diffuse from the brazing material 1 to the copper paste side during firing. As a result, the diffused silver component is filled in the interface of the copper particles.

  The brazing material 1 further contains at least one metal material of titanium, hafnium and zirconium. The brazing material 1 can firmly bond the metal plate 2 to the insulating substrate 11 by a metal material such as titanium which is an active metal material.

  As an example of the composition of the brazing filler metal 1, copper is 15 to 70 mass%, silver is 20 to 65 mass%, titanium is 1 to 20 mass%, and indium is about 1 to 5 mass%. More specific examples include 69% by mass of copper, 27% by mass of silver, 1% by mass of titanium, and 3% by mass of indium.

  The diffused silver component 5 may be mixed with tin and indium added to the paste of the brazing material 1. Even if the silver component 5 is mixed with tin and indium to form an alloy, the original Young's modulus of the silver component is not greatly changed.

  Moreover, it is preferable that the silver-copper alloy layer 6 is provided between the surface of the copper particle 3 and the silver component 5 with which the grain boundary of the copper particle 3 was filled like the example shown in FIG. . Since the silver-copper alloy layer 6 has a lower yield stress than the non-alloyed copper particles 3, the residual stress in the metal plate 2 is reduced during the thermal cycle, and the stress on the insulating substrate 11 by the metal plate 2 is also weakened.

  The metal plate 2 can be used not only as a circuit conductor but also as a metal member for mounting an electronic component mounted on the circuit board 10, a metal member for a ground conductor, a heat radiating plate, or the like. As described above, the metal plate 2 is used by being bonded to the insulating base 11 made of ceramics or the like as a conductive path for supplying a relatively large current of, for example, several tens of A or a heat dissipation material.

  Next, a method for manufacturing the circuit board 10 of the present invention will be described. Here, a method for manufacturing the circuit board 10 of the example shown in FIG. 1 will be described.

  (1) The insulating substrate 11 is manufactured by firing at a temperature of about 1600 to 2000 ° C. in a non-oxidizing atmosphere such as a nitriding atmosphere by the method described above.

(2) After the paste-like brazing material 1 is printed on the insulating substrate 11, the copper paste is printed on the paste of the brazing material 1 with a desired patterning by screen printing. The printing masks for the brazing filler metal 1 and the copper paste have the same shape. As the brazing material 1 for joining the metal plate 2 and the insulating base 11, for example, a material having a melting point of about 600 ° C. is used. The melting point is adjusted by adjusting the amounts of tin and indium with respect to the amount of silver which is the main component of the brazing material 1. The suitable composition in that case is as described above.

  (3) Next, the insulating substrate 11, the paste of the brazing material 1, and the copper paste laminated are calcined in a vacuum furnace. Calcination is performed at 400 ° C. for 30 minutes to 4 hours, for example. The reason for using the vacuum furnace is to react and produce the active brazing material. When the active brazing material is not used, calcination is performed in a non-oxidizing atmosphere of hydrogen or nitrogen.

  (4) Next, the main calcination is performed in a vacuum furnace at a temperature higher than the melting point of the brazing filler metal 1 by about 0 ° C. to 100 ° C. for 1 minute to 3 hours. The firing time is adjusted by the thickness of the copper paste. When the active brazing material is not used, the main calcination is performed in a non-oxidizing atmosphere of hydrogen or nitrogen for the reasons described above.

  The brazing material 1 is preferably heated at a temperature about 50 ° C. higher than the melting point of the brazing material 1. When the heating temperature of the brazing material 1 is set near the melting point, the heat treatment time is set to 1 hour or more. It is good to set.

  Note that a metal having high conductivity and corrosion resistance and good wettability with the bonding material of the electronic component may be deposited on the surface of the metal plate 2 by a plating method. In this case, the metal plate 2 and the external electric circuit, the bonding material, and the like can be easily and firmly bonded. Further, the electrical connection between the metal plate 2 and the external electric circuit or the like can be made better.

  Examples of the plating metal include metal materials such as nickel, cobalt, copper, and gold, or alloy materials containing these metal materials as main components. For example, in the case of a nickel-phosphorus amorphous alloy plating layer containing 8 to 15% by mass of phosphorus inside, the surface oxidation of the nickel plating layer can be suppressed and the wettability of the bonding material 7 and the like can be maintained for a long time. It is preferable because it is possible. When the content of phosphorus with respect to nickel is about 8 to 15 masses, a nickel-phosphorus amorphous alloy is easily formed, and the adhesive strength of the bonding material 6 and the like to the plating layer can be improved. The thickness of this nickel plating layer should just be about 1.5-10 micrometers, for example.

  When the melting point of the brazing filler metal 1 is exceeded in the main firing, the diffusion of the silver component from the brazing filler paste to the copper paste starts, and the diffusion also ends when the sintering is finished.

  In addition, the metal plate of this invention is not limited to the example of the said embodiment, A various change is possible if it is in the range of the summary of this invention.

  For example, in the metal plate 2, the particle size of the copper particles 3 on the brazing material 1 side is preferably smaller than the particle size of the copper particles 3 on the surface layer side of the metal plate 2. The smaller the particle size of the copper particles 3, the larger the space of the grain boundaries 4, so the amount of the silver component 5 to be filled becomes larger. Therefore, in the metal plate 2, the Young's modulus can be reduced on the brazing filler metal 1 side where the greatest thermal stress is applied, and the thermal stress can be reduced.

  In order to obtain such a configuration, the silver content or the like in the paste used as the brazing material 1 may be adjusted to a predetermined value. When the firing of the paste is started, the copper component on the brazing material paste side is more likely to be alloyed as the silver component in the brazing material diffuses than the copper particles on the opposite side. Since the copper particles on the brazing filler metal 1 side are easily alloyed, the melting point is low, and since the sintering is completed early, the grains do not grow and the particle diameter tends to be small.

  For example, in the metal plate 2, it is preferable that the particle size of the copper particle 3 is uniform. In this case, since the space of the grain boundary 4 is increased, the amount of the silver component 5 to be filled is increased. Therefore, in the metal plate 2, the Young's modulus can be further reduced, and the thermal stress can be reduced.

DESCRIPTION OF SYMBOLS 1 ... Brazing material 2 ... Metal plate 3 ... Copper particle 4 ... Grain boundary 5 ... Silver component 6 ... Silver-copper alloy layer
10 ... Circuit board
11 ... Insulating substrate

Claims (2)

An insulating substrate;
A metal plate formed by sintering copper particles, which is bonded to the main surface of the insulating base via a brazing material containing a silver component;
In the metal plate, grain boundaries of the copper particles are filled with the silver component diffused from the brazing material, and the particle size of the copper particles on the brazing material side is the surface layer side of the metal plate. A circuit board smaller than the copper particle size .   The circuit board according to claim 1, wherein a silver-copper alloy layer is provided between a surface of the copper particles and the silver component filled in a grain boundary of the copper particles.

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