JP2018074147A - Circuit board and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board having high long term reliability for thermal stress.SOLUTION: A circuit board 20 includes a ceramic plate 1 having a first principal surface and a second principal surface, a metal circuit board 2 composed of a first metal material, and having third and fourth principal surfaces, where the fourth principal surface is arranged oppositely to the first principal surface, and having a cavity which is at least one of a groove 2a and a through hole 2b provided in the third principal surface along the outer boundary thereof, and a filler 3 composed of a material having a thermal expansion coefficient smaller than that of the first metal material, and placed in the cavity of the third principal surface. The inner part than the cavity and the outer part than the cavity of the metal circuit board 2 are connected integrally.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a circuit board having a metal plate and an electronic device.

2. Description of the Related Art Conventionally, as a circuit board used in an electronic device on which an electronic component such as an IGBT (Insulated Gate Bipolar Transistor) is mounted, for example, a circuit board in which a metal circuit board is bonded to the upper surface of a ceramic board is used.

  The metal circuit board forms a circuit for electrically connecting the electronic component to an external electric circuit. In such an electronic device, an electronic component and an external electric circuit are electrically connected to each other through a metal circuit board.

  In these circuit boards, in order to prevent a decrease in reliability such as destruction of a ceramic plate due to thermal stress due to the addition of a thermal cycle, for example, a groove or a through hole is formed in the outer peripheral edge of a metal circuit plate Is used (see Patent Document 1 and Patent Document 2).

JP-A-8-250823 JP-A-8-274423

  In the circuit board and the electronic device of the prior art described above, the concentration of thermal stress on the outer peripheral edge of the metal circuit board is reduced by the grooves or through holes provided in the outer peripheral edge of the metal circuit board. However, in recent years, in a circuit board and an electronic device including the circuit board, for example, in a vehicle-mounted application, further improvement in reliability is required.

  A circuit board according to one aspect of the present invention includes a ceramic plate having a first main surface and a second main surface opposite to the first main surface, a first metal material, and a third main surface and the third main surface. A fourth main surface opposite to the main surface, the fourth main surface being disposed opposite to the first main surface, and an outer periphery of the third main surface on the third main surface And a metal circuit board having a gap portion that is at least one of a groove and a through-hole provided along the surface, and a material having a smaller thermal expansion coefficient than the first metal material, and disposed in the gap portion of the third main surface. Filling. In the metal circuit board, an inner portion and an outer portion are integrally connected to the gap portion.

  An electronic device according to an aspect of the present invention includes a circuit board having the above-described configuration and an electronic component that is mounted on the metal circuit board and has terminals that are electrically connected to the metal circuit board.

According to the circuit board of one aspect of the present invention, because of the above configuration, it is possible to effectively suppress the destruction of the ceramic plate and the peeling of the metal circuit plate from the ceramic plate. That is, in the circuit board of this aspect, since the filler having a relatively small thermal expansion coefficient is disposed along the outer periphery of the metal circuit board, the apparent thermal expansion coefficient at the outer peripheral edge of the metal circuit board is reduced. . Therefore, the difference in thermal expansion coefficient between the metal circuit board and the ceramic board becomes smaller than before, and the generated thermal stress itself is effectively reduced. Therefore, mechanical destruction such as peeling of the metal circuit board from the ceramic plate due to thermal stress can be effectively suppressed.

  According to the electronic device of one aspect of the present invention, since the circuit board having the above-described configuration is included, it is possible to provide an electronic device effective for improving reliability such as long-term connection reliability of the metal circuit board to the ceramic board. it can.

(A) is a top view which shows the electronic device containing the circuit board of the 1st Embodiment of this invention, (b) is sectional drawing in the BB line of (a), (c) is from a lower surface. FIG. (A) is a top view which shows the modification of the circuit board of FIG. 1, (b) is sectional drawing in the BB line of (a), (c) is the top view seen from the lower surface. (A) is a top view which shows the electronic device containing the circuit board of the 2nd Embodiment of this invention, (b) is sectional drawing in the BB line of (a), (c) is from a lower surface. FIG. (A) is an enlarged view of the principal part of FIG.1 (b), (b) is an enlarged view of the principal part of FIG.2 (b), (c) is an expansion of the principal part of FIG.3 (b). FIG. It is an enlarged view of the principal part of Fig.3 (a). (A) is a top view which shows the principal part of the circuit board of the 3rd Embodiment of this invention, (b) is sectional drawing in the BB line of (a), (c) is (a). It is sectional drawing in CC line. (A) is a top view which shows the electronic device containing the circuit board of the 4th Embodiment of this invention, (b) is sectional drawing in the BB line of (a), (c) is from a lower surface. FIG. (A) is an enlarged view of the principal part of Fig.7 (a), (b) is sectional drawing in the BB line of (a). (A) is a top view which expands and shows the principal part of the other example of the circuit board of the 4th Embodiment of this invention, (b) is sectional drawing in the BB line of (a), (C) is sectional drawing in the CC line of (a). (A) is a top view which expands and shows the principal part of the other example of the circuit board of the 4th Embodiment of this invention, (b) is sectional drawing in the BB line of (a), (C) is sectional drawing in the CC line of (a).

  The circuit board and electronic device of the present invention will be described below with reference to the drawings. In addition, the distinction between the upper and lower sides in the following description is for convenience, and does not limit the upper and lower sides when the circuit board and the electronic device are actually used. Moreover, the thermal expansion coefficient in the following is a linear expansion coefficient unless otherwise specified.

  FIG. 1A is a plan view showing an electronic device 30 including a circuit board 20 according to the first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along the line AA of FIG. FIG. 1C is a plan view (bottom view) viewed from the bottom surface. 2A is a plan view showing a modification of the circuit board of FIG. 1, FIG. 2B is a cross-sectional view taken along the line AA of FIG. 2A, and FIG. It is the top view (bottom view) seen from. FIG. 3A is a plan view showing an electronic device including a circuit board according to the second embodiment of the present invention, and FIG. 3B is a cross-sectional view taken along the line AA in FIG. FIG.3 (c) is the top view (bottom view) seen from the lower surface. 4 (a) is an enlarged view of the main part (A part) of FIG. 1 (b), and FIG. 4 (b) is an enlarged view of the main part (B part) of FIG. 2 (b). FIG.4 (c) is an enlarged view of the principal part (C section) of FIG.3 (b). FIG. 5 is an enlarged view of a main part (A part) of FIG.

  The circuit board described below is for manufacturing the electronic device 30 by mounting electronic components. The electronic device is used by being electrically connected to an external electric circuit included in various electronic devices. The circuit board has a metal portion that constitutes a conductive path or the like that electrically connects the electronic component and the external electric circuit, and an insulator portion that holds the metal circuit board.

(First embodiment)
First, a circuit board according to a first embodiment of the present invention and an electronic device including the circuit board will be described with reference to FIGS. 1 and 4A.

  The circuit board 20 has a flat ceramic plate 1 as an insulator portion. Moreover, it has the metal circuit board 2 as a metal part. The ceramic plate 1 has a first main surface (upper surface in the example of FIG. 1) and a second main surface opposite to the first main surface (lower surface in the example of FIG. 1). The metal circuit board 2 is made of a first metal material (details will be described later), and has a third main surface (upper surface in the example of FIG. 1) and a fourth main surface opposite to the third main surface (lower surface in the example of FIG. 1). )have. In the following, for convenience, the first to fourth main surfaces may be referred to as an upper surface or a lower surface.

  The metal circuit board 2 is arranged such that the fourth main surface thereof faces the first main surface of the ceramic plate 1. In addition, the third main surface of the metal circuit board 2 is provided with a gap (not indicated as a gap) which is at least one of the groove 2a and the through hole 2b along the outer periphery of the third main surface. Yes. In the example of FIG. 1, a groove 2a is provided as a gap.

  A filler 3 made of a material having a smaller coefficient of thermal expansion than the first metal material is disposed in the gap. In other words, the metal circuit board 2 has a hole part or a groove part in which the filler 3 having a smaller coefficient of thermal expansion than the main body of the metal circuit board 2 is arranged on the outer periphery of the upper surface thereof. Therefore, the outer peripheral portion of the metal circuit board 2 has a smaller apparent thermal expansion coefficient in the outer peripheral portion including the filler 3 than in other portions. The filler 3 is a metal containing particles of an inorganic material having a smaller thermal expansion coefficient than that of the first metal material, such as a metal material (second metal material) having a smaller thermal expansion coefficient than that of the first metal material or a ceramic material. Material or glass material. Details of the second metal material and the filler 3 will be described later.

  A plurality of metal circuit boards 2 are arranged on the first main surface of the ceramic board 1. Among the plurality of metal circuit boards 2, the one arranged at the center of the first main surface is for mounting the electronic component 4. In addition, the six metal circuit boards 2 arranged on the outer peripheral portion of the first main surface with this interposed therebetween are electrically connected to the electronic component 4 to form a conductive path.

  The electronic component 4 is mounted on the third main surface of the metal circuit board 2 disposed in the center of the first main surface, and the other metal circuit board 2 and the electronic component 4 are electrically connected to each other via the bonding wires 5. The electronic device 30 of the embodiment is basically configured by being connected.

  The electronic component 4 is joined to the metal circuit board 2 by a so-called low melting point brazing material (no symbol) such as a tin-silver solder or a gold-silicon brazing material. A film or paste of a low melting point brazing material is disposed in advance on a predetermined portion of the upper surface of the metal circuit board 2, and the lower surface of the electronic component 4 is aligned and set in that portion, and is brazed by heating. Thus, the electronic component 4 is joined to the metal circuit board 2.

  The bonding wire 5 is, for example, a so-called gold wire or aluminum wire, and one end is connected to the electronic component 4 and the other end is connected to a predetermined portion of the metal circuit board 2.

  In the example shown in FIG. 1 and FIG. 4A, the metal plate 6 is disposed on the second main surface of the ceramic plate 1. The metal plate 6 has a heat radiation function of conducting or radiating heat generated in the electronic component 4 to the outside, for example.

  Further, in the example shown in FIG. 1 and FIG. 4A, a lower gap is provided along the outer periphery of the metal plate 6 also on the outer periphery of the metal plate 6. In the example of FIG. 1, a groove 6a is provided as a gap. In the groove 6a, a lower filling (no symbol) is arranged. The lower filling may have a smaller coefficient of thermal expansion than the metal plate 6. In this case, like the outer peripheral portion of the metal circuit board 2, the outer peripheral portion of the metal plate 6 can also have a smaller apparent thermal expansion coefficient than the other portions in the outer peripheral portion including the filler. it can.

  When the metal plate 6 functions as a heat dissipation material, for example, the lower surface of the metal plate 6 is joined to a heat dissipation material (not shown). Heat is conducted from the metal plate 6 to the heat dissipation material, and heat is effectively dissipated from the heat dissipation material to the outside. This heat is generated with the operation of the electronic component 4 mounted on the circuit board 20. Heat generated in the electronic component 4 is effectively dissipated to the outside through the metal circuit board 2, the ceramic board 1 and the metal board 6, and the heat dissipating material.

  The metal plate 6 can also function as a terminal for electrical connection to an external electric circuit. In this case, the lower surface of the metal plate 6 is joined to face a predetermined portion of the external electric circuit, and the circuit board 20 and the electronic device 30 are electrically connected to the external electric circuit via the metal plate 6. . This electrical connection is made, for example, to set the metal plate 6 to the ground potential.

  As described above, the circuit board 20 of the first embodiment is basically configured by the metal plate 6, the ceramic plate 1, and the metal circuit plate 2 that are sequentially stacked from the lower side. In addition, the electronic device 4 of the embodiment is basically configured by mounting the electronic component 4 on the circuit board 20.

  The ceramic plate 1 is made of a ceramic material such as aluminum oxide ceramics, mullite ceramics, silicon carbide ceramics, aluminum nitride ceramics, and silicon nitride ceramics. Among these ceramic materials, silicon carbide ceramics, aluminum nitride ceramics, and silicon nitride ceramics are higher in terms of thermal conductivity that affects heat dissipation. In terms of mechanical strength, silicon nitride ceramics and silicon carbide ceramics are higher.

The thickness of the ceramic plate 1 is, for example, about 0.1 mm to 1 mm, and may be appropriately set according to conditions such as predetermined external dimensions and mechanical strength of the circuit board 20 and the electronic device 30.

  If the ceramic plate 1 is made of, for example, silicon nitride ceramics, it can be manufactured by the following method. First, a suitable 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 to form a slurry. Next, the slurry is processed into a sheet shape by a molding method such as a doctor blade method or a calender roll method to produce a ceramic green sheet (ceramic green sheet). Next, the ceramic green sheet is subjected to an appropriate punching process or the like and formed into a predetermined shape, and a plurality of sheets are laminated as necessary to produce a laminate. Thereafter, this laminate (ceramic green sheet) is fired at a temperature of about 1600 to 2000 ° C. in a non-oxidizing atmosphere such as a nitrogen atmosphere. The ceramic plate 1 can be manufactured by the above process.

The metal circuit board 2 is formed of a metal material (first metal material) such as copper or aluminum. Moreover, the metal circuit board 2 may be formed of a metal material of an alloy whose main component is copper or aluminum. If the metal circuit board 2 is made of, for example, copper, by subjecting the copper plate material to metal processing such as cutting, rolling or etching, the metal circuit board 2 is processed into a predetermined shape and dimensions as the metal circuit board 2. Can be produced.

  The metal plate 6 can also be manufactured by the same method using the same material as the metal circuit board 2. In consideration of heat dissipation or stability of the ground potential, one metal plate 6 having a relatively large area in plan view is arranged as compared with the metal circuit plate 2 divided into a plurality of forms. It is desirable to be.

  The plurality of metal circuit boards 2 and the metal boards 6 are joined to the first main surface or the second main surface of the ceramic plate 1 via, for example, a silver (Ag) -copper (Cu) -based brazing material 7. The brazing material 7 may contain at least one active metal material of titanium, hafnium, and zirconium, for example, in order to be firmly bonded to the ceramic plate 1 by being wetted. Further, the brazing material 7 may have at least one metal material of indium and tin, for example. Since the melting point can be lowered with respect to the silver-copper brazing material, it is possible to reduce the residual stress due to the thermal stress generated when the circuit board 20 is manufactured. The brazing material 7 has a thickness of about 5 to 100 μm, for example.

  According to the circuit board 20 of the said form, destruction of the ceramic board 1 and peeling of the metal circuit board 2 from the ceramic board 1 etc. can be suppressed effectively. That is, in such a circuit board 20, since the filler 3 having a relatively small thermal expansion coefficient is disposed along the outer periphery of the metal circuit board 2 as described above, the outer peripheral edge portion of the metal circuit board 2 is disposed. The apparent thermal expansion coefficient is smaller than other parts such as the central part in plan view. Therefore, the difference in thermal expansion coefficient between the metal circuit board 2 and the ceramic board 1 can be effectively reduced. Thereby, the thermal stress itself generated between the ceramic plate 1 and the metal circuit board 2 is effectively reduced. Therefore, mechanical destruction such as peeling of the metal circuit board 2 from the ceramic board 1 due to thermal stress can be effectively suppressed.

  The metal circuit board 2 having the groove 2a (gap) and the filler 3 disposed in the gap can be manufactured, for example, by the following process. For example, first, an active brazing paste in which about 1 to 3% of an active metal is added to eutectic silver solder in a circuit shape is printed on the upper surface of a ceramic plate 1 made of aluminum oxide ceramics or the like. Also, copper is used as the first metal material, and a copper flat plate is placed on the active brazing paste and heated to bond to a wide range such as substantially the entire first main surface of the ceramic plate 1. Thereafter, when the metal circuit board 2 is formed by removing a part of the copper flat plate by etching, the groove 2a can be formed by adjusting the masking pattern as appropriate and performing etching.

Thereafter, a second brazing material having a lower temperature than the active brazing material is disposed in the groove 2a, and the filler 3 made of the second metal material having a smaller thermal expansion coefficient than the first metal material containing copper or aluminum is disposed. be able to. Thus, when the filler 3 is a second metal material different from the first metal material, the filler 3 and the metal circuit board 2 can be easily and firmly fixed by joining with a brazing material. Can do. The filler 3 is firmly fixed to the circuit board 20 in which the filler 3 is a second metal material different from the first metal material and the filler 3 and the metal circuit board 2 are joined by the brazing material. Therefore, even if repeated thermal stress is applied, the filling 3 is difficult to be detached from the metal circuit board 2, and the circuit board 20 with high reliability is obtained in which peeling of the metal circuit board 2 from the ceramic circuit board 1 is suppressed. The second metal material in this case is, for example, an iron-nickel alloy (so-called 42 alloy or the like), and its thermal expansion coefficient is about 4.2 × 10 ⁻⁶ / ° C. (30 to 300 ° C.), which is relatively small. This second metal material has a Young's modulus of, for example, about 135 GPa, and the circuit board 20 having the above-described configuration can be manufactured by embedding the thin wire as the filler 3 and heating and bonding.

Moreover, in the formation process of said metal circuit board 2, you may be as follows. That is, it is necessary to etch the groove 2a at a depth halfway in the thickness direction of the metal plate while simultaneously removing the metal plate into a predetermined shape of the metal circuit plate 2 by etching. At this time, etching may be performed in two steps. In this case, the etching may be performed in two portions from the surface (front surface) of the metal plate which is the third main surface of the metal circuit board 2.

  In addition, a part to be removed is half-etched on the surface (back surface) to be bonded to the first main surface of the ceramic plate 1 first, and then the metal plate is bonded to the first main surface of the ceramic plate 1. . After the joining, etching is performed from the main surface of the metal plate to a predetermined portion or the like that forms the groove 2a. In this way, when the groove 2a is formed by etching to the half-etching depth, the metal plate is removed in the entire thickness direction in the portion that has been half-etched on the back surface in advance, and divided into each metal circuit board 2 it can. Accordingly, the gap between the metal circuit boards 2 can be formed narrow, and a circuit composed of the plurality of metal circuit boards 2 can be formed with higher density. In addition, when etching is usually performed only from the front surface, the upper surface dimension of the metal circuit board is smaller than the dimension of the surface joined to the ceramic, but etching is performed from the front surface and the back surface in this way. When the groove 2a is formed by this method, the dimension of the upper surface of the metal circuit board 2 and the dimension of the surface joined to the ceramic are substantially close to each other. This wiring can be secured with a narrower wiring width (width of the surface joined to the ceramic plate).

  In the example shown in FIGS. 2 and 4B (modified example of FIG. 1), the groove 2a provided on the third main surface of the metal circuit board 3 is discontinuous. That is, discontinuous grooves 2a (2aa) are formed instead of the continuous grooves 2a as in the example shown in FIG. This form can also be regarded as a form in which a plurality of depressions are arranged at intervals along the outer periphery of the third main surface. Each of the plurality of depressions may have a circular shape or the like in a plan view as shown in FIG. 2, for example, and may have a linear shape (line segment shape), that is, a rectangular shape. Hereinafter, it is also simply referred to as the groove 2aa.

  Also in this example, the filler 3 is disposed in each of the grooves 2aa which are a plurality of depressions. These fillers 3 can be disposed in the groove 2aa as follows, for example. First, the second brazing material as described above is placed in the groove 2aa in the form of a paste or a preform, for example. Next, balls or metal pillars made using the second metal material are embedded in the grooves 2aa. Thereafter, the second brazing material is heated, and a ball or a metal column is joined to the inner surface of the recess 2aa. Through this process, the circuit board 20 of this form can be manufactured.

  Since the groove 2a and the discontinuous groove 2aa provided as the gap do not penetrate the metal circuit board 2 in the thickness direction, the inner part and the outer part of the gap are integrated without being separated from each other. linked. Therefore, good electrical conductivity as a circuit is ensured.

  Also in the circuit board 20 of this form, the coefficient of thermal expansion is higher than that of the first metal material forming the metal circuit board 2 at the outer peripheral edge (the part along the outer periphery of the third main surface) of the metal circuit board 2. A small filling 3 is embedded. As a result, the apparent thermal expansion coefficient at the outer peripheral edge of the metal circuit board 2 is reduced. Therefore, the difference in thermal expansion coefficient between the metal circuit board 2 and the ceramic board 1 can be made smaller than before, and the generated thermal stress itself can be effectively reduced. Therefore, mechanical destruction such as peeling of the metal circuit board 2 from the ceramic board 1 due to thermal stress can be effectively suppressed.

In this case, compressive stress is applied to the outer edge portion of the metal circuit board 2 due to the difference in thermal expansion coefficient with the filler 3 having a relatively small thermal expansion coefficient as the temperature decreases. As a result, the tensile stress applied to the ceramic plate 1 at a portion overlapping the outer peripheral edge portion of the metal circuit board 2 in a plan view is reduced. Therefore, it is difficult for the metal circuit board 2 to be peeled off from the ceramic board 1 even when temperature cycle stress is applied. That is, the highly reliable circuit board 20 is obtained. As described above, the ceramic material forming the ceramic plate 1 is not limited to the aluminum oxide ceramics, and the above various materials, that is, silicon nitride ceramics (having a thermal expansion coefficient of about 2.8 × 10 ⁻⁶ / ° C. ), Aluminum nitride ceramics (thermal expansion coefficient 4.6 × 10 ⁻⁶ / ° C.).

In addition, copper (so-called pure copper having a thermal expansion coefficient of about 16.7 × 10 ⁻⁶ / ° C. as the first metal material.
Instead of this, a copper alloy may be used. However, when pure copper is used, 300 ° C
In the above, since the residual stress falls within the range of 300 ° C. or less due to plastic deformation, the residual stress is reduced. Thermal stress generated by heating the metal circuit board 2 (and the metal board 6) to a temperature equal to or higher than the melting point of the brazing material and then cooling the metal circuit board 2 to the room temperature is present as residual stress in the circuit board 20. This residual stress is mainly generated when the metal circuit board 2 (and the metal plate 6) is elastically deformed. Here, pure copper undergoes plastic deformation at 300 ° C. or higher, and elastic deformation as residual stress occurs at less than 300 ° C. On the other hand, in a copper alloy, the temperature at which plastic deformation starts is generally higher than pure copper (higher than 300 ° C.). That is, the temperature range in which the copper alloy is elastically deformed is larger than that of pure copper, so that the residual stress is increased. That is, pure copper is suitable from the viewpoint of reducing residual stress. The thermal stress due to the thermal cycle (especially during cooling) is further added to this residual stress, making it easier to break the circuit board. However, the residual stress can be reduced to break the circuit board by adding thermal stress. Is reduced. Therefore, the circuit board 20 in which the first metal material is copper and the brazing material 7 has a melting point of 300 ° C. or higher is excellent in reliability.

As the second metal material, instead of 42 alloy (thermal expansion coefficient is about 4.2 × 10 ⁻⁶ / ° C (30-300 ° C), Young's modulus is about 135 GPa), Fe-Ni 36% (iron-nickel 36% alloy) (Thermal expansion coefficient is about 4.4 × 10 ⁻⁶ / ° C. (30-300 ° C.), Young's modulus is about 145 GPa), Tungsten (thermal expansion coefficient is about 4.5 × 10 ⁻⁶ / ° C. (30-300 ° C.), Young's modulus Is about 375 GPa), molybdenum (coefficient of thermal expansion is about 5.3 × 10 ⁻⁶ / ° C. (30 to 300 ° C.), Young's modulus is about 300 GPa), iron-nickel-cobalt alloy (coefficient of thermal expansion is 5.1 × 10 ⁻⁶ / ° C (30-300 ° C), Young's modulus is about 160 GPa, or the like may be used.

When a metal having a low thermal expansion coefficient below the Curie point, such as Fe-Ni 36%, is used as the second metal material, a 42 alloy having a similar thermal expansion coefficient at 30-300 ° C. The coefficient of thermal expansion on the low temperature side is smaller than that. Therefore, the effect of stress relaxation becomes higher on the low temperature side where the tensile stress applied to the ceramic plate becomes larger. Therefore, even when the stress of the temperature cycle is applied, the metal circuit board 2 becomes difficult to peel from the ceramic board 1.

  When the filler 3 is the second metal material as described above, it is advantageous in the following points. That is, in this case, the filler 3 is filled in the gaps in various forms according to the usage, environment, economy, and other conditions of the circuit board 20 and the electronic device 30 including the circuit board 20 (hereinafter also referred to as a product). Is easy to arrange. Specifically, in this case, the second metal material as the filler 3 is elastic. Therefore, even if the cross-sectional shape of the groove 2a as the gap or the through hole 2b in FIG. 3 described later has various shapes, the stress due to the shape is effectively absorbed by the deformation of the second metal material. can do. That is, it is possible to reduce the possibility that mechanical damage occurs in the filler 3 due to stress. Therefore, the degree of freedom in designing the circuit board 20 and the electronic device 30 can be effectively increased.

(Second Embodiment)
For example, as shown in FIG. 3 and FIG. 4C, the circuit board 20 and the electronic device 30 including the circuit board 20 according to the second embodiment of the present invention penetrate the metal circuit board 2 in the thickness direction as gaps, A through hole 2b having an opening in the third main surface and the fourth main surface is provided. A plurality of through holes 2b are provided, and the openings on the third main surface side thereof are arranged along the outer periphery of the third main surface.
That is, the gap portion may include a plurality of through holes 2b formed discontinuously on the outer peripheral edge portion of the third main surface of the metal circuit board.

  Further, the fillers 3 are also arranged in the through holes 2b. Further, the filler 3 in this example is directly bonded to the ceramic plate 1 at the opening on the fourth main surface side of the metal circuit board 2. In such a case, the filler 3 such as the second metal material directly joined to the ceramic plate 1 also functions as a so-called wedge that has entered the metal circuit plate 2. This adds an effect of relieving stress generated between the ceramic plate 1 and the metal circuit board 2. Therefore, the stress applied to the outer peripheral edge portion of the metal circuit board 2 becomes smaller. Therefore, even when a temperature cycle stress is applied, it is possible to effectively reduce the possibility of mechanical destruction such that the metal circuit board 2 is peeled off from the ceramic board 1.

  Even in the configuration in which a plurality of through-holes 2b are provided as the gaps, these through-holes 2b are discontinuous, and therefore, the inner part and the outer part from the gaps are integrated without being separated from each other. linked. Therefore, good electrical conductivity as a circuit is ensured.

Further, as described above, when the first metal material is copper (pure copper or the like), it is advantageous in the following points. In other words, Sn-Ag solder having a low melting point may be used as the second brazing material, but when a brazing material having a melting point lowered to about 600 ° C. by adding indium (In) to the Ag—Cu brazing material is used. To do. At this time, a compressive stress can be generated in advance on the outer peripheral edge of the metal circuit board 2 by using a cylindrical filling 3 having the same diameter (diameter) as the through hole 2b. . Thus, if the second brazing filler metal is heated to the melting point of the second brazing filler metal in the state including the compressive stress in advance, the stresses cancel each other, and the stress applied to the outer peripheral edge of the metal circuit board 2 is effective. Can be lowered.

The second metal material is connected to the metal circuit board 2 (first metal material) with a brazing material having a melting point of about 300 ° C. or more, for example. Therefore, when copper having high thermal conductivity is used for the metal circuit board 2, the effect of stress relaxation due to the small coefficient of thermal expansion of the second metal material can be exhibited in the entire temperature region where copper is not plastically deformed at 300 ° C. or lower. Therefore, the effect of stress relaxation becomes high, and the possibility that the metal circuit board 2 is peeled off from the ceramic board 1 can be effectively reduced even when a temperature cycle stress is applied.

As shown in FIG. 5, the circuit board 20 and the electronic device 30 according to the above-described embodiment are assumed to have a circular joining surface with the ceramic plate 1 made of a second metal material, and the through holes 2b adjacent to each other. The distance (adjacent spacing) between the fillers 3 between them is d, and the thermal expansion coefficients of the ceramic plate 1, the first metal material, and the second metal material at 300 ° C. or less are αc, α1, α, respectively.
2 and when the Young's moduli of the first metal material and the second metal material are E1 and E2, respectively, the relational expression of (α1 × E1 × φ + α2 × E2 × d) / (E1 × φ + E2 × d) ≦ αc It may satisfy.

  When the above formula is satisfied, the metal circuit board 2 and the second metal material are synthesized rather than the ceramic board 1 in the region connecting the central portions of the filler 3 (through hole 2b) made of the second metal material. The apparent thermal expansion coefficient is reduced. At this time, a compressive stress is applied to the ceramic plate 1 at the joining edge portion of the second metal material, that is, the filler 3 with the ceramic plate 1. Therefore, when the circuit board 20 is cooled, not only the stress reduction effect by the second metal material but also the effect of reducing the stress when the circuit board 20 is cooled is included. Therefore, the stress applied to the outer peripheral edge of the metal circuit board 2 is further relaxed, and the possibility that the metal circuit board 2 is peeled off from the ceramic board 1 even when the stress of the temperature cycle is applied is effective. Can be reduced.

As shown in FIGS. 2, 6 (b), 3, and 4 (c), in the configuration in which the discontinuous grooves 2 aa or the through holes 2 b are formed as the voids, the low melting glass is filled in the voids as the filler 3. You may make it fill with. In this case, for example, after discontinuous grooves 2aa or through-holes 2b are formed in the metal circuit board 2, bismuth glass (for example, Bi ₂ O ₃ as composition is 55 to 80% by mass, B ₂ O ₃ 5 to 5% 25% by mass, ZnO 5-25% by mass) and 20% by mass of zirconium phosphate (thermal expansion coefficient 1.7 × 10 ⁻⁶ / ° C. (30-300 ° C.)) as a low thermal expansion filler The discontinuous grooves 2aa or through holes 2b are filled. After that, the paste-like material is heated and melted so that the thermal expansion coefficient is about 4.8 × 10 ⁻⁶ / ° C. (30 to 300 ° C.).
The filler 3 made of glass is formed. The circuit board 20 can be manufactured as described above. Instead of bismuth glass, a low thermal expansion filler may be added to vanadium glass having a smaller thermal expansion coefficient of the glass itself.

  The filler 3 is a low-melting glass, and since the circular groove 2aa or the through hole 2b is formed discontinuously on the outer peripheral edge of the third main surface of the metal circuit board 2 in a top view, Below the solidification temperature, compressive stress is always applied to the surrounding metal circuit board. Therefore, as a result, the tensile stress applied to the ceramic plate 1 at the outer peripheral edge of the metal circuit board 2 is reduced. Therefore, even when a stress of a temperature cycle is applied, the possibility that the metal circuit board 2 is peeled off from the ceramic board 1 can be effectively reduced.

(Third embodiment)
FIG. 6A is a plan view showing an essential part of a circuit board according to a third embodiment of the present invention, and FIG. 6B is a cross-sectional view taken along line BB in FIG. 6 (c) is a cross-sectional view taken along line CC of FIG. 6 (a). As in the example illustrated in FIG. 6, the gap portion may be configured by the groove 2 a and the through hole 2 b. In this example, a groove 2 a is provided in the third main surface of the metal circuit board 2 along the outer periphery of the third main surface, and a through hole that penetrates from the bottom surface of the groove 2 a to the fourth main surface of the metal circuit board 2. 2b is provided. A plurality of through holes 2b are arranged in the length direction of the groove 2a with a space between each other. In other words, the through holes 2b are arranged along the outer periphery of the third main surface. The filler 3 at this time is disposed in the groove 2a, but is not disposed in the through-hole 2b, and the through-hole 2b can be left as a gap. With such a structure, the apparent thermal expansion coefficient is reduced by the filler 3 in the outer peripheral edge portion of the third main surface of the metal circuit board 2 and the through-hole 2b is a gap, so that the metal circuit board 2 The thermal stress applied to the outer edge portion from the inside is relaxed. Therefore, the thermal stress generated at the joint between the outer peripheral edge of the metal circuit board 2 and the ceramic board 1 is effectively reduced. Therefore, even when a stress of a temperature cycle is applied, the possibility that the metal circuit board 2 is peeled from the ceramic board 1 can be more effectively reduced.

(Fourth embodiment)
8A is an enlarged view of the main part (A part) of FIG. 7A, and FIG. 8B is a cross-sectional view taken along line BB of FIG. 8A. FIG. 9A is a plan view showing the main part of another example of the circuit board according to the fourth embodiment of the present invention, and FIG. 9B is a sectional view taken along line BB in FIG. 9A. FIG. 9C is a cross-sectional view taken along the line CC of FIG. 9A. FIG. 10A is a plan view showing the main part of another example of the circuit board according to the fourth embodiment of the present invention, and FIG. 10B is a cross-sectional view taken along the line BB of FIG. 10A. FIG.10 (c) is sectional drawing in the CC line | wire of Fig.10 (a).

The circuit board 20 of the fourth embodiment and the electronic device 30 including the same have a second gap portion on the inner side of the gap portion on the third main surface, as in the example shown in FIG. The filler 3 is not disposed in the gap 2. In the example shown in FIG. 8, the gap is a groove 2 a, and a filler 3 having a lower thermal expansion coefficient than the metal circuit board 2 is disposed in the groove 2 a. Moreover, it has the 2nd groove | channel 2c which is a 2nd space | gap part along the groove | channel 2a over the perimeter inside this space | gap part (groove 2a). And it is the structure where the filler is not arrange | positioned in the 2nd space | gap part (2nd groove | channel 2c). In the case of such a circuit board 20, the thermal stress applied to the outer edge portion from the inside of the metal circuit board 2 is relaxed by the second groove 2 c, so that the thermal stress between the ceramic board 1 and the metal circuit board 2 is reduced. Since it decreases more, it becomes a circuit board with more excellent temperature cycle reliability.

  In the configuration of the fourth embodiment, the gap is not limited to the groove. As in the example illustrated in FIG. 9, the gap portion may be the through hole 2 b described in the second embodiment. Alternatively, it may be a discontinuous groove 2aa as described in the first embodiment. In the example shown in FIG. 9, the width of the groove 6 a of the metal plate 6 is larger than the width of the groove 2 a of the metal circuit board 2. As described above, the groove 2 a of the metal circuit board 2 and the groove 6 a of the metal plate 6 may have different widths. By enlarging the groove 6 a provided in the metal plate 6, the effect of reducing thermal stress becomes more remarkable even in the large metal plate 6. The same applies to the relationship between the width of the second groove 2 c of the metal circuit board 2 and the width of the second groove 6 c of the metal plate 6. The same applies to the relationship between the diameter of the through hole 2b of the metal circuit board 2 and the diameter of the through hole 6b of the metal plate 6.

  Further, the second groove 2c can be provided only in the vicinity of the corner portion of the metal circuit board 2 where stress is likely to be increased as in the example shown in FIG. In such a case, for example, even when a plurality of bonding wires 5 are connected, it is easy to secure a bonding wire connection region. The second groove 2c is not limited to a continuous groove, and even when the second groove 2c is a discontinuous second groove 2c or a second through hole having the same shape as the discontinuous groove 2a or the through hole 2b. Similar stress relaxation effects can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Ceramic plate 2 ... Metal circuit board 2a ... Groove 2b ... Through-hole 2c ... Second groove 3 ... Filler 4 ... Electronic component 5 ... Bonding wire 6 ... Metal plate 6a ... Groove 6b ... Through hole 6c ... Second groove 7 ... Brazing material
20 ... Circuit board
30 ・ ・ ・ Electronic device

Claims (8)

A ceramic plate having a first main surface and a second main surface opposite to the first main surface;
It consists of a 1st metal material, has a 3rd main surface and the 4th main surface on the opposite side to this 3rd main surface, and this 4th main surface is arrange | positioned facing the said 1st main surface. And a metal circuit board having a void portion that is at least one of a groove and a through hole provided along the outer periphery of the third main surface on the third main surface;
A filler made of a material having a smaller coefficient of thermal expansion than the first metal material and disposed in the gap portion of the third main surface,
The circuit board according to claim 1, wherein an inner part and an outer part of the metal circuit board are integrally connected to the gap. 2. The circuit board according to claim 1, wherein the filler is a second metal material different from the first metal material, and the filler and the metal circuit board are joined by a brazing material. The void portion includes a plurality of through holes formed discontinuously on the outer peripheral edge portion of the third main surface of the metal circuit board, and the filler disposed in the through hole serves as the ceramic plate. The circuit board according to claim 2, wherein the circuit board is directly connected to the circuit board. The circuit board according to claim 2, wherein the first metal material is copper, and the brazing material has a melting point of 300 ° C. or higher. The thermal expansion coefficients of the ceramic plate, the first metal material, and the second metal material at 300 ° C. or lower are αc, α1, and α2, respectively, and the Young's moduli of the first metal material and the second metal material are E1. , E2, and the joint surface of the second metal material with the ceramic plate is circular with a diameter φ, and the distance between the fillers between the through holes adjacent to each other is d, 4. The circuit board according to claim 3, wherein (α1 × E1 × φ + α2 × E2 × d) / (E1 × φ + E2 × d) ≦ αc. 2. The circuit board according to claim 1, wherein the filler is low-melting glass, and the circular voids are discontinuously formed on the outer peripheral edge of the metal circuit board in a top view. 3. The first main surface has a second gap inside the gap, and no filler is disposed in the second gap. 7. The circuit board according to any one of 6. A circuit board according to any one of claims 1 to 7,
An electronic device comprising: an electronic component mounted on the metal circuit board and having a terminal electrically connected to the metal circuit board.

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