JP6608728B2 - Circuit board and electronic device - Google Patents

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 plate is bonded to an upper surface of an insulating substrate made of a ceramic sintered body or the like is used. ing.

  The metal plate of the circuit board forms a circuit for electrically connecting the electronic component to an external electric circuit. Electronic devices mounted on the circuit board are electrically connected to a metal plate to produce an electronic device. At this time, the electronic component is covered with a covering material such as a resin material. In such an electronic device, an electronic component and an external electric circuit are electrically connected to each other through a metal plate.

  In addition, a circuit board having a structure in which another metal plate and another insulating board are sequentially laminated on the lower surface of the insulating board is also used for improving heat dissipation to the outside (for example, patents). Reference 1). The lower metal plate is bonded and mounted on an external substrate for heat dissipation and the like, and heat is released to the outside.

JP 2003-86747 A

  In the conventional circuit board and electronic device, the entire circuit board tends to warp upward in a convex shape. This is because the area in plan view of the metal plate for heat dissipation is larger than the area in plan view of the metal plate on which the electronic component is mounted. That is, in a circuit board having an insulating substrate and a metal plate bonded to each other, between the insulating substrate having a small thermal expansion coefficient and the metal plate having a large thermal expansion coefficient while the temperature decreases from the bonding temperature to room temperature. Tends to be larger on the side of the metal plate for heat dissipation. Due to this difference in thermal stress, an upward convex warpage is likely to occur on the entire circuit board. When such warpage occurs, for example, the efficiency of thermal connection of the lower metal plate to an external substrate or the like may be reduced, and heat dissipation as a circuit board and an electronic device may be reduced.

The circuit board according to one aspect of the present invention includes a first ceramic plate and a second ceramic plate each having an upper surface and a lower surface, a first metal plate disposed on the upper surface of the first ceramic plate, and the second A second metal plate disposed on the lower surface of the ceramic plate and having an area larger than an area of the first metal plate in plan view; and the lower surface of the first ceramic plate and the upper surface of the second ceramic plate. A third metal plate disposed between them, and the third metal plate has a lower surface including a recess having a hollow inside , and the thickness of the third metal plate is It is larger than both the thickness of the first metal plate and the thickness of the second metal plate.

  An electronic device according to an aspect of the present invention integrally covers a circuit board, an electronic component mounted on the first metal plate or on the mounting portion, and from the electronic component to a side surface of the second ceramic plate. Mold resin.

  According to the circuit board of one aspect of the present invention, because of the above configuration, the thermal stress applied from the third metal plate to the second ceramic plate is relaxed by the recess. Therefore, the thermal stress difference due to the difference in area between the first metal plate and the second metal plate in plan view can be effectively reduced. Therefore, the stress applied to the second ceramic plate can be reduced below the stress applied to the first ceramic plate, and a circuit board in which upward convex warpage is suppressed can be provided. According to this circuit board, an electronic device with high heat dissipation can be easily manufactured.

  Moreover, 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 easy to effectively thermally connect to the external board, and the heat dissipation is improved. An effective electronic device can be provided.

(A) is a top view which shows the circuit board of the 1st Embodiment of this invention, (b) is sectional drawing which shows the electronic device of the 1st Embodiment of this invention. (A) is a top view which shows the 1st modification of the circuit board shown in FIG. 1, (b) is sectional drawing in the AA of (a). (A) is a top view which shows the 2nd modification of the circuit board shown in FIG. 1, (b) is sectional drawing in the AA of (a). (A) is a top view which shows the 3rd modification of the circuit board shown in FIG. 1, (b) is sectional drawing in the AA of (a). (A) is a top view which shows the 4th modification of the circuit board shown in FIG. 1, (b) is sectional drawing in the AA of (a). (A) is a top view which shows the circuit board of the 2nd Embodiment of this invention, (b) is sectional drawing in the AA of (a). (A) is a top view which shows the modification of the circuit board shown in FIG. 6, (b) is sectional drawing in the AA of (a). It is sectional drawing which shows the electronic device of the 2nd Embodiment of this invention.

  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. Similarly, for convenience of explanation, the circuit boards in the following examples are shown with electronic components mounted thereon.

(First embodiment)
A circuit board 20 and an electronic device 30 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1A is a sectional view showing a circuit board 20 according to the first embodiment of the present invention, and FIG. 1B is a sectional view showing an electronic device 30 according to the first embodiment of the present invention. The cross-sectional view of the circuit board 10 included in the electronic device 30 shown in FIG. 1B is, for example, a cross-sectional view taken along the line AA in FIG.

  The circuit board 20 has a flat plate-like first ceramic plate 1 and second ceramic plate 2 each having an upper surface and a lower surface as insulator portions. The first metal plate 3 is disposed with the lower surface superimposed on the upper surface of the first ceramic plate 1, and the second metal plate 4 is disposed with the upper surface superimposed on the lower surface of the second ceramic plate 2. A third metal plate 5 is disposed between the lower surface of the first ceramic plate 1 and the upper surface of the second ceramic plate 2. That is, the circuit board 20 of the embodiment is basically composed of the second metal plate 4, the second ceramic plate 2, the third metal plate 5, the first ceramic plate 1, and the first metal plate 3 that are sequentially stacked from the lower side. It is configured.

The first ceramic plate 1 and the second ceramic plate 2 are made of a ceramic material such as a silicon nitride sintered body, as will be described later. Moreover, the 1st metal plate 3, the 2nd metal plate 4, and the 3rd metal plate 5 consist of metal materials, such as copper, so that it may mention later.

  In addition, the electronic component 6 is mounted on the first metal plate 3 of the circuit board 20, and the electronic component 6 and the first metal plate 3 are electrically connected by a bonding wire 7 or the like. The electronic device 30 is manufactured by covering the side surface of the ceramic plate 2 with a mold resin 8 such as an epoxy resin. That is, the electronic device 30 according to the first embodiment of the present invention includes the circuit board 20 having the above configuration, the electronic component 6 mounted on the first metal plate 3, the electronic component 6 to the first metal plate 3, and the first metal plate 3. The upper surface of the first ceramic plate 1 and the mold resin 8 integrally covering the side surfaces of the second ceramic plate 2 beyond the side surfaces of the first ceramic plate 1 and the third metal plate 5 are basically constituted. .

  For example, after the electronic component 6 is mounted on the circuit board 20, the mold resin 8 is coated with a material for the mold resin 8 such as an uncured epoxy resin, and the uncured resin material is cured. Can be formed in position.

  In the example shown in FIG. 1B, the mold resin 8 covers the side surface of the second metal plate 4 beyond the side surface of the second ceramic plate 2. In other words, in the electronic device 30 of this embodiment, only the lower surface of the second metal plate 4 is not covered with the mold resin 8 and is exposed to the outside.

  The first metal plate 3 functions as a part of a conductive path that electrically connects the electronic component 6 mounted on the circuit board 20 to an external board (not shown). In the example shown in FIG. 1, a plurality of first metal plates 3 are joined to the upper surface of the first ceramic plate 1. Each first metal plate 3 forms, for example, an electrically independent circuit, and as described above, different electrodes (not shown) of the electronic component 6 are electrically connected by the bonding wires 7 or the like. Yes. Different electrodes of the electronic component 6 are, for example, electrodes for a large current and a control signal.

  The electronic component 6 is joined to the first metal plate 3 by a so-called low melting point brazing material (no symbol) such as a tin-silver solder or a gold-silicon brazing material. A low melting point brazing film or paste or the like is placed in advance on a predetermined portion of the upper surface of the first metal plate 3, and the lower surface of the electronic component 6 is aligned and set in that portion and brazed by heating. . Thus, the electronic component 6 is joined to the first metal plate 3. The electronic component 6 is electrically connected to the first metal plate 3 as described above, and the electronic component 6 is mounted on the circuit board 20.

  The bonding wire 7 is, for example, a so-called gold wire or aluminum wire, and one end portion is connected to the electronic component 6 and the other end portion is connected to a predetermined portion of the first metal plate 3.

  The second metal plate 4 functions as, for example, a heat dissipation material for radiating heat to the outside. For example, if the lower surface of the second metal plate 4 is joined to a heat dissipation material (not shown), heat is conducted from the second metal plate 4 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 6 mounted on the circuit board 20. Heat generated in the electronic component 6 is sequentially transmitted through the first metal plate 3, the first ceramic plate 1, the third metal plate 5, and the second ceramic plate 2 to be conducted to the second metal plate 4. That is, in this case, a heat transfer path is formed from the electronic component 6 (the first metal plate 3 on which the electronic component 6 is mounted) to the second metal plate 4 to dissipate the heat generated in the electronic component 6 to the outside. The

The second metal plate 4 can also function as a terminal for electrical connection to an external substrate (such as an electric circuit included in the external substrate). In this case, if the lower surface of the second metal plate 4 is joined so as to face a predetermined portion of the external electric circuit, the circuit board 20 and the electronic device 30 are electrically connected to the external electric circuit via the second metal plate 4. Connection is made. This electrical connection is made, for example, to set the second metal plate 4 to the ground potential.

  In the electronic device 30 of the first embodiment, the lower surface of the second metal plate 4 is bonded and mounted on an external substrate or the like (not shown). As a result, the electronic device 30 is mounted on the external substrate, and heat is radiated from the electronic device 30 to the outside via the second metal plate 4. The external substrate may have a heat radiation function part (not shown) such as a heat radiation fin or a cooling pipe.

  The lower surface of the second metal plate 4 and the external substrate are joined by, for example, passing a screw or the like through the fixing hole 10 and screwing it to the external substrate or pressing the periphery of the circuit substrate 20 from above with a spring or the like. It is. The electronic device 30 is mechanically connected to the external substrate and thermally connected by this bonding. In order to enhance the effect of this thermal connection, it is preferable that there is no gap (that is, air having a low thermal conductivity) between the lower surface of the second metal plate 4 and the external substrate.

  The third metal plate 5 is interposed between the first ceramic plate 1 and the second ceramic plate 2 and functions as a heat transfer layer that effectively conducts heat between them. Therefore, the lower surface of the first ceramic plate 1 and the upper surface of the third metal plate 5 are joined, and the upper surface of the second ceramic plate 2 and the lower surface of the third metal plate 5 are joined.

  In the circuit board 20 of the embodiment, the third metal plate 5 is thicker than both the first metal plate 3 and the second metal plate 4. That is, the third metal plate 5 that is thicker than the first metal plate 3 and the second metal plate 4 and has relatively high rigidity is disposed between the first ceramic plate 1 and the second ceramic plate 2. For this reason, the rigidity of the circuit board 20 as a whole is enhanced as compared with the prior art. The relatively high rigidity of the third metal plate 5 is effective for suppressing the warp of the circuit board 20.

  Note that at least one of the second metal plate 4 and the third metal plate 5 may have a function as a grounding conductor. When such a grounding conductor is disposed, it is effective for electromagnetic shielding between the first metal plate 3 serving as a circuit board to which a signal such as a control signal is transmitted and the outside.

  In the circuit board 20 of the first embodiment, the lower surface of the third metal plate 5 has a recess 5a. Therefore, the thermal stress applied to the second ceramic plate 2 is relaxed by the recess 5a. This is because the stress generated when the third metal plate 5 contracts (when the temperature falls) is larger than that of the second ceramic plate 2 as compared with the case where there is no recess 5a. It can be reduced by.

  Therefore, the thermal stress difference due to the difference in area between the first metal plate 3 and the second metal plate 4 in plan view can be effectively reduced. Therefore, the stress applied to the second ceramic plate 2 can be reduced below the stress applied to the first ceramic plate 1, and the circuit board 20 in which the upward convex warpage is suppressed can be provided. According to this circuit board 20, it is possible to easily manufacture the electronic device 30 with high heat dissipation.

That is, if the entire circuit board 20 is warped upward, for example, when the lower surface of the second metal plate 4 of the circuit board 20 and the external board are connected by screws or the like using the fixing holes 10. In addition, since there is a possibility that an air layer (gap) is generated in the central portion of the lower surface of the bottom surface having the shortest heat path immediately below the electronic component 6, there is a relatively high possibility that the heat transmitted to the external substrate is blocked by the air layer. large. As a result, heat conduction to the external substrate is significantly reduced, and heat dissipation may be reduced. On the other hand, in the circuit board 20 of the first embodiment, since the upward convex warpage of the circuit board 20 is suppressed, the gap between the lower surface of the second metal plate 4 and the external board is suppressed. The possibility of an air layer (gap) occurring is effectively reduced.

  Further, although the thermal conductivity is small in the concave portion 5a, the position of the arrangement can be set to a position where the amount of heat transfer such as the outer peripheral portion of the third metal plate 5 is relatively small. The possibility of the resulting decrease in heat transfer can be effectively reduced. Moreover, the function as a heat-transfer layer of the 3rd metal plate 5 can also be ensured favorable by adjusting the number of the recessed parts 5a, the magnitude | size by planar view, etc. suitably.

  As the arrangement of the recesses 5a in consideration of the heat transfer as described above, a plurality of recesses 5a are spaced apart from each other at the peripheral edge (outer peripheral part) of the third metal plate 5 in a plan view as in the example shown in FIG. An example can be given in which

  In this case, you may make it form the some recessed part 5a in the part in which the 1st metal plate 3 is not formed by planar seeing. As a result, for example, stress (thermal stress) is suppressed from being biased up and down over the entire circuit board 20. Therefore, for example, deformation such as local warping of the circuit board 20 due to stress bias can be effectively suppressed.

  The first ceramic plate 1 and the second ceramic plate 2 are made of an electrically insulating material. Examples of the electrical insulating material include ceramic materials 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.

  When the first ceramic plate 1 and the second ceramic plate 2 are made of a ceramic material having a relatively high mechanical strength such as silicon nitride ceramics, thermal expansion with the first metal plate 3 and the second metal plate 4 is performed. The possibility of mechanical destruction such as generation of cracks in the first ceramic plate 1 and the second ceramic plate 2 due to thermal stress caused by the coefficient difference is reduced.

The thicknesses of the first ceramic plate 1 and the second ceramic plate 2 are, for example, about 0.1 mm to 1 mm, and can be appropriately set according to conditions such as predetermined external dimensions and mechanical strength of the circuit board 20 and the electronic device 30. Good.

  If the first ceramic plate 1 and the second ceramic plate 2 are made of, for example, silicon nitride ceramics, they can be produced 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. Through the above steps, the first ceramic plate 1 and the second ceramic plate 2 can be manufactured.

  The first metal plate 3 is formed of a metal material such as copper or aluminum, for example. Moreover, the 1st metal plate 3 may be formed with the metal material of the alloy which has copper or aluminum as a main component. If the first metal plate 3 is made of, for example, copper, the copper plate material is subjected to metal processing such as cutting, rolling, or etching to be processed into a predetermined shape and dimensions as the first metal plate 3. Can be produced.

  The second metal plate 4 can also be manufactured in the same manner using the same material as the first metal plate 3. The second metal plate 4 has a relatively large area in plan view as compared with the first metal plate 3 in a plurality of divided forms in consideration of heat dissipation or ground potential stability. It is desirable to arrange.

  Similarly to the first metal plate 3 and the second metal plate 4, the third metal plate 5 is also a metal having a high thermal conductivity, such as copper or an alloy containing copper as a main component or aluminum or an alloy containing aluminum as a main component. It is made of material. Therefore, the heat generated in the electronic component 6 is efficiently conducted to the third metal plate 5 through the heat transfer path.

  As described above, the thermal conductivity between the first ceramic plate 1 and the first metal plate 3 and the second ceramic plate 2 and the second metal plate 4 is effectively increased. Thus, the circuit board 20 capable of manufacturing the electronic device 30 having excellent heat dissipation can be obtained, and by providing the circuit board 20, the electronic device 30 having excellent heat dissipation can be provided.

If the thickness of the 3rd metal plate 5 is a case where it consists of copper, for example, what is necessary is just to set to about 0.5-10 mm thicker than any of the thickness of the 1st metal plate 3 and the 2nd metal plate 4. FIG. The third metal plate 5 may be thicker than the combined thickness of the first metal plate 3 and the second metal plate 4. In this case, the apparent thermal expansion coefficient of the circuit board 20 of the embodiment is an apparent thermal expansion coefficient of a circuit board (not shown) when a single plate of a silicon nitride sintered body is used as an insulating substrate. Larger than the thermal expansion coefficient of the mold resin 8. That is, the stress resulting from the difference between the thermal expansion coefficients of the two becomes smaller.

  The third metal plate 5 can also be manufactured in the same manner using the same material as the first metal plate 3. As for the third metal plate 5, in consideration of ensuring heat dissipation and rigidity, one plate having a relatively large area in plan view is arranged as compared with the first metal plate 3 divided into a plurality of forms. It is desirable to have. In this case, the recess 5a can be formed by applying processing such as grinding or etching to the lower surface of the third metal plate 5 at a predetermined shape, size, and arrangement position of the recess 5a.

  The plurality of first metal plates 3 and second metal plates 4 are joined to the upper surface of the first ceramic plate 1 or the lower surface of the second ceramic plate 2 through, for example, an Ag—Cu brazing material (not shown). ing. This brazing material contains at least one active metal material of, for example, titanium, hafnium and zirconium in order to be firmly bonded to the first ceramic plate 1 and the second ceramic plate 2 by being wetted. May be. Moreover, this brazing material may have at least one metal material of indium and tin, for example. In addition, the thickness of this brazing material should just be about 5-100 micrometers, for example.

  The third metal plate 5 is also joined to the first ceramic plate 1 and the second ceramic plate 2 by, for example, the same brazing material as described above. That is, the upper surface of the third metal plate 5 and the lower surface of the first ceramic plate 1 are joined via the brazing material, and the lower surface of the third metal plate 5 and the upper surface of the second ceramic plate 2 are made of the brazing material. Are joined through. The joining of the first ceramic plate 1 and the second ceramic plate 2 to the first metal plate 3, the second metal plate 4 and the third metal plate 5 with the brazing material, for example, adjusts these members to a predetermined positional relationship. It can be performed by temporarily fixing with a jig or the like and heating to a predetermined temperature in the furnace. The joining of each member may be performed in a lump, or may be performed sequentially in several steps.

Note that a plating layer of nickel, gold, or the like may be applied to the exposed surfaces of the first metal plate 3 and the second metal plate 4. The plating layer is constituted by, for example, a nickel plating layer and a gold plating layer that are sequentially deposited from the exposed surfaces of the first metal plate 3 and the second metal plate 4, and the first metal plate 3 and the second metal plate 4. Each of the exposed surfaces is entirely covered. By applying this plating layer, the mounting of the electronic component 6 and the connection to an external electric circuit as described above can be made easier and stronger.

(Modification of the first embodiment)
Various modifications of the circuit board 20 and the electronic device 30 of the above embodiment will be described below. In the following description, description of the same points as those of the circuit board 20 and the electronic device 30 of the embodiment will be omitted.

  2A is a plan view showing a first modification of the circuit board 20 shown in FIG. 1, and FIG. 2B is a cross-sectional view taken along the line AA in FIG. 2A. In FIG. 2, the same parts as those in FIG. In the example shown in FIG. 2, the thickness of the first ceramic plate 1 is larger than the thickness of the second ceramic plate 2.

  As described above, when the thickness of the first ceramic plate 1 is relatively large, the first metal plate 3 on the first ceramic plate 1, the second metal plate 4 below the first ceramic plate 1, and the third metal plate 3. The distance between each of the metal plates 5 can be further increased. In addition, the length of the insulating material (ceramic material) interposed therebetween can be further increased.

  Therefore, in this case, the dielectric breakdown voltage between the first metal plate 3 and each of the second metal plate 4 and the third metal plate 5 can be increased. In other words, in addition to the improvement in heat dissipation, the insulation between the metal circuit (first metal plate 3) through which the signal is transmitted and the metal plate on the ground side (second metal plate 4 and third metal plate 5). The circuit board 20 that is also effective in improving the breakdown voltage can be obtained.

  FIG. 3A is a plan view showing a second modification of the circuit board 20 shown in FIG. 1, and FIG. 3B is a cross-sectional view taken along the line AA in FIG. In FIG. 3, the same parts as those in FIG. In the example shown in FIG. 3, a plate body 9 having a smaller coefficient of thermal expansion than the third metal plate 5 is disposed in the recess 5 a of the third metal plate 5. The plate body 9 is joined to the third metal plate 5.

  When a plate body 9 having a relatively small thermal expansion coefficient (low thermal expansion) is disposed in the recess 5a on the lower surface of the third metal plate 5 and joined to the third metal plate 5, the second ceramic The stress applied to the plate 2 is reduced. That is, the apparent thermal expansion coefficient of the third metal plate 5 is reduced by the arrangement of the plate body 9 having a relatively small thermal expansion coefficient. Therefore, the thermal stress itself due to the difference in thermal expansion coefficient between the second ceramic plate 2 and the third metal plate 5 is reduced.

  Further, the plate body 9 may be bonded not only to the third metal plate 5 but also to the second ceramic plate 2, or may be bonded only to the second ceramic plate 2. If the plate body 9 is bonded to the second ceramic plate 2, the rigidity of the second ceramic plate 2 is increased, and the possibility that the entire circuit board 20 is warped is effectively reduced. Thereby, the second metal plate 4 side of the circuit board 20 can be brought close to flat. Further, as described above, if the concave portion 5a is provided in the outer peripheral portion of the third metal plate 5, expansion and contraction due to heat of the second metal plate 4 is relatively large inside the concave portion 5a in a plan view, The circuit board 20 tends to be convex downward. Therefore, the thermal connection to the external board becomes effective particularly directly under the electronic component 6. Therefore, the circuit board 20 can be easily improved in heat dissipation.

Examples of the material for forming the plate 9 include ceramic materials having a low thermal expansion coefficient such as mullite ceramics, silicon carbide ceramics, aluminum nitride ceramics and silicon nitride ceramics, metal materials having a low thermal expansion coefficient such as tungsten and molybdenum, and the like. Examples include various alloy materials exhibiting a low thermal expansion coefficient at 300 ° C. or lower. As this alloy material,
Examples thereof include iron-nickel alloys such as 42 alloy and Invar, which exhibit a low thermal expansion coefficient at 300 ° C. or lower. By subjecting such a material to processing selected from laser cutting, punching, and cutting, the plate body 9 can be manufactured.

  Further, the plate body 9 is, for example, silver having the same composition as the brazing material joining the first ceramic plate 1, the second ceramic plate 2 and the first metal plate 3, the second metal plate 4, and the third metal plate 5. It can be joined to the third metal plate 5 or the second ceramic plate 2 by a brazing material (not shown) such as brazing. The brazing material may contain at least one active metal material of titanium, hafnium and zirconium.

  In addition, the depth of the recess 5 a is formed deeper than the thickness of the plate body 9 by the thickness of the brazing material, and the upper and lower main surfaces of the plate body 9 are connected to the third metal plate 5 and the second ceramic plate 2. In this case, the range of the recess 5a is thermally conducted through the plate body 9. In this case, the plate 9 is made of a high thermal conductivity ceramic such as aluminum nitride ceramic or silicon carbide ceramic or a high thermal conductivity metal such as tungsten or molybdenum, which is very good. In such a case, the thermal conductivity is relatively high even in the range of the recess 5a. Thereby, the circuit board 20 having higher thermal conductivity (heat dissipation) can be obtained.

  4A is a plan view showing a third modification of the circuit board 20 shown in FIG. 1, and FIG. 4B is a cross-sectional view taken along line AA in FIG. 4, parts similar to those in FIG. 1 are denoted by the same reference numerals. In the example shown in FIG. 4, the 1st ceramic board 1 has the thin part 1a. Further, the thickness of the first ceramic plate 1 is larger than the thickness of the second ceramic plate 2.

  The thin portion 1a is a portion where the thickness of the first ceramic plate 1 is partially thinner than the others, for example, a portion where a recess or a groove is provided on the upper surface of the first ceramic plate 1. When such a thin portion 1a is present on the first ceramic plate 1, the rigidity of the thin portion 1a is low because the thickness is small, so the rigidity of the first ceramic plate 1 is lowered. Therefore, if the substrate thicknesses are the same, the rigidity of the first ceramic plate 1 is smaller than the rigidity of the second ceramic plate 2. In other words, the rigidity of the first ceramic plate 1 with relatively small thermal stress generated between the first metal plate 3 having a smaller area in plan view is relatively smaller than that of the second ceramic plate 2. As a result, the difference in deformation due to the difference in thermal stress accompanying the difference in area between the first metal plate 3 and the second metal plate 4 in plan view is also reduced. Therefore, the convex deformation of the entire circuit board 20 can be effectively suppressed.

  Moreover, when the 1st ceramic board 1 has the thin part 1a, even if it makes the thickness of the 1st ceramic board 1 comparatively large as mentioned above, the 1st ceramic board 1 which arises by the increase in the thickness And the increase in the difference in deformation due to the difference in thermal stress between the second ceramic plate 2 can be suppressed. That is, the possibility that the second metal plate 4 tends to warp upward is effectively reduced. Therefore, the circuit board 20 can increase the dielectric breakdown voltage between the first metal plate 3 and each of the second metal plate 4 and the third metal plate 5 and can also improve heat dissipation. Can do.

  For example, when the first ceramic plate 1 is formed by laminating two ceramic green sheets, the thin-walled portion 1a is formed by mechanical punching or laser at a predetermined portion of the upper ceramic green sheet that becomes the first ceramic plate 1. It can be formed by forming a hole to be the thin-walled portion 1a by processing or the like, bringing it into close contact with the ceramic green sheet on the lower side and firing and integrating it.

FIG. 5A is a plan view showing a fourth modification of the circuit board 20 shown in FIG. 1, and FIG. 5B is a cross-sectional view taken along the line AA in FIG. 5, parts similar to those in FIG. 1 are denoted by the same reference numerals. In the example shown in FIG. 5, the first ceramic plate 1 has a through hole 1 b that penetrates the first ceramic plate 1 in the thickness direction.

  The through hole 1b has the same function as the thin portion 1a in the third modification. That is, for example, even when the thickness of the first ceramic plate 1 is larger than that of the second ceramic plate 2, an increase in the difference in deformation due to the thermal stress difference between the first ceramic plate 1 and the second ceramic plate 2 is suppressed by the through holes 1b. Thus, deformation of the entire circuit board 20 (being convex in the upward direction) can be suppressed.

  The through hole 1b can be formed, for example, by subjecting a predetermined portion of the ceramic green sheet to be the first ceramic plate 1 or the first ceramic plate 1 to mechanical punching or laser processing.

  The positions of the thin-walled portion 1a and the through-hole 1b are such that the electrical insulation between the first metal plate 3 and the third metal plate 5 and the effective heat transfer path from the electronic component 6 to the second metal plate 4 are ensured. It is desirable to adjust appropriately considering the above. For example, if the thin portion 1a is formed to be separated from the first metal plate 3 to which a large potential difference is applied by the depth of the recess of the thin portion 1a or more than the thickness of the first ceramic plate 1, the mold resin 8 is thin after resin molding. Even when the portion 1a and the through hole 1b are not filled, the insulating property can be secured by the mold resin 8 on the first ceramic plate 1.

(Second Embodiment)
6A is a cross-sectional view showing a circuit board 20 according to the second embodiment of the present invention, and FIG. 6B is a cross-sectional view taken along the line AA of FIG. 6A. 5, parts similar to those in FIG. 1 are denoted by the same reference numerals.

  In the circuit board 20 of the second embodiment, the first ceramic plate 1 has an opening 1c that penetrates the first ceramic plate 1 in the thickness direction. In addition, the third metal plate 5 has a convex portion 5c protruding upward in the opening 1c. The circuit board 20 of the second embodiment is different from the circuit board 20 of the first embodiment in these points, and the other points are the same as those in the first embodiment. Explanation of these similar points is omitted.

  In the circuit board 20 of the present embodiment, the electronic component 6 is mounted on the upper surface of the convex portion 5c. The electronic component 6 to be mounted is electrically connected to the first metal plate 3, that is, a signal transmission path or the like via a bonding wire 7 or the like as in the case of the first embodiment.

  Since the electronic component 6 is mounted on the convex portion 5 c of the third metal plate 5 in the circuit board 20 of the present embodiment, heat is easily transmitted from the electronic component 6 to the third metal plate 5. Therefore, the thermal conductivity of the entire heat transfer path from the electronic component 6 through the third metal plate 5 to the second metal plate 4 can be increased.

  Also in this embodiment, the third metal plate 5 has a recess 5a on the lower surface. Therefore, it is effectively suppressed that the entire circuit board 20 becomes convex. Therefore, it is possible to provide the circuit board 20 that is excellent in heat dissipation to the outside in addition to the improvement in heat transfer from the electronic component 6 to the third metal plate 5.

In the first embodiment, the opening 1c is formed in the portion of the first ceramic plate 1 where the electronic component 6 is mounted. In the present embodiment, the opening 1c is formed in a portion overlapping the opening 1c in plan view. The ceramic plate 1 does not exist. In this portion, the second metal plate 4 is bonded to the lower surface of the second ceramic plate 2, and the third metal plate 5 thicker than the second metal plate 4 is bonded to the upper surface. For this reason, the second ceramic plate 2 is subjected to a large shrinking thermal stress on the upper surface, so that the circuit board 20 tends to have a downwardly convex shape immediately below the mounting portion of the electronic component 6. For this reason, if the circuit board 20 of the present embodiment is convex downward (not shown), it is immediately below the shortest heat path from the heat generating electronic component 6 to the external board (the lower surface of the second metal plate 4). The possibility that an air layer (gap) is generated between the external substrate and the external substrate can be reduced. For this purpose, for example, by passing a screw or the like through the fixing hole 10 and screwing it to the external board, or pressing the periphery of the circuit board 20 with a spring or the like from above, the electronic device 30 is mechanically connected to the external board. When thermally connected, heat can be released to the outside more efficiently.

  The opening 1c of the first ceramic plate 1 is provided in such a size that the convex portion 5c of the third metal plate 5 on which the electronic component 6 is mounted can be accommodated on the upper surface in plan view. In other words, the first ceramic plate 1 is formed with an opening 1 c having a size that includes the mounting area of the electronic component 6 on the circuit board 20. Note that if the opening 1c is too large in plan view, the mechanical strength of the first ceramic plate 1 may be reduced. For this reason, the corner of the opening 1c is not an acute angle, but is formed in a shape in which stress is not concentrated by taking R.

  The convex portion 5c is not only formed by processing the third metal plate 5, but a metal such as copper or molybdenum having a good thermal conductivity is used as a brazing material for the electronic component 6 mounting portion of the flat third metal plate 5. It may be formed by bonding. In the case where the low thermal expansion molybdenum plate is used as the convex portion 5c, the shape may be a convex shape directly below the mounting portion of the electronic component 6 as long as it is less than 50% of the area of the opening 1c in plan view. .

  FIG. 7A is a plan view showing a modification of the circuit board 20 shown in FIG. 6, and FIG. 7B is a cross-sectional view taken along the line AA in FIG. 7A. 5, parts similar to those in FIG. 1 are denoted by the same reference numerals.

  In the example shown in FIG. 7, the third metal plate 5 has a concave portion 5 b on the upper surface side at a portion surrounding the opening 1 c of the first ceramic plate 1. In other words, the third metal plate 5 is stepped around the convex portion 5c and has a lower upper surface than the other portions, and the thickness is reduced accordingly. In this case, the circuit board 20 has the same convex shape as that in FIG. Since the upper surface side concave portion 5b is formed on the upper surface of the third metal plate 5, the thermal stress applied to the first ceramic plate 1 from the third metal plate 5 is relieved, so that the size of the opening 1c is reduced. As a result, the possibility that the mechanical strength of the first ceramic plate 1 is lowered is reduced, so that the degree of freedom in designing the opening 1c is increased. In addition, since the concave portion 5b on the upper surface side is formed in the opening portion 1c, the distance between the bonding wire 7 in the opening portion 1c portion and the surface of the third metal plate 5 can be increased by the depth of the concave portion 5b on the upper surface side. Therefore, higher insulation can be secured.

FIG. 8 is a sectional view showing an electronic device 30 according to the second embodiment of the present invention. In FIG.
The same code | symbol is attached | subjected to the site | part similar to. The electronic device 30 of the second embodiment is manufactured by mounting the electronic component 6 on the circuit board 20 of the second embodiment. Other points are the same as those of the electronic device 30 of the first embodiment.

  According to the electronic device 30 of the present embodiment, since the electronic component is directly mounted on the third metal plate 5 (convex portion 5c) as described above, the electronic device 30 is advantageous in terms of improving heat dissipation to the outside. Can be provided.

  In addition, in 1st and 2nd embodiment and each modification, joining to the convex part 5c of the electronic component 6 on the 1st ceramic plate 1 or the 3rd metal plate 5 is solder and gold-tin, for example Various bonding materials such as alloys can be used.

DESCRIPTION OF SYMBOLS 1 ... 1st ceramic plate 1a ... Thin part 1b ... Through-hole 1c ... Opening part 2 ... 2nd ceramic plate 3 ... 1st metal plate 4 ... 2nd metal plate 5 ... 3rd metal plate 5a ... Concave portion 5b ... Concave portion 5c on the upper surface side ... Convex portion 6 ... Electronic component 7 ... Bonding wire 8 ... Mold resin 9 ... Plate body
10 ... Hole for fixing
20 ... Circuit board
30 ・ ・ ・ Electronic device

Claims (8)

A first ceramic plate and a second ceramic plate each having an upper surface and a lower surface;
A first metal plate disposed on the upper surface of the first ceramic plate;
A second metal plate disposed on the lower surface of the second ceramic plate and having an area larger than the area of the first metal plate in plan view ;
A third metal plate disposed between the lower surface of the first ceramic plate and the upper surface of the second ceramic plate,
The third metal plate has a lower surface including a recess having a hollow inside , and the thickness of the third metal plate is larger than both the thickness of the first metal plate and the thickness of the second metal plate. A circuit board characterized by that. The circuit board according to claim 1, wherein a thickness of the first ceramic plate is larger than a thickness of the second ceramic plate. A plate body having a smaller coefficient of thermal expansion than the third metal plate is disposed in the recess, and the plate body is joined to at least one of the third metal plate and the second ceramic plate. The circuit board according to claim 1, wherein the circuit board is characterized by the following. The circuit board according to claim 1, wherein the first ceramic plate has a thin portion. The circuit board according to claim 1, wherein the first ceramic plate has a through-hole penetrating the first ceramic plate in a thickness direction. The first ceramic plate has an opening that penetrates the first ceramic plate in the thickness direction, and the third metal plate has a convex portion protruding upward in the opening. The circuit board according to any one of claims 1 to 5, characterized in that: The circuit board according to any one of claims 1 to 5,
An electronic component mounted on the first metal plate;
An electronic apparatus comprising: a mold resin integrally covering the electronic component and a side surface of the second ceramic plate. A circuit board according to claim 6;
An electronic component mounted on the upper surface of the convex portion;
An electronic apparatus comprising: a mold resin integrally covering the electronic component and a side surface of the second ceramic plate.