JP5812882B2 - Wiring board and electronic device - Google Patents

Description

  The present invention relates to a wiring board on which electronic components are mounted and an electronic apparatus.

  A wiring board in which a metal plate is bonded to a ceramic base is used as a wiring board used in an electronic device in which an electronic component such as an IGBT (Insulated Gate Bipolar Transistor) such as a power module or a switching module is mounted. The metal plate is a clad material in which a plurality of metal layers made of, for example, copper (Cu) or molybdenum (Mo) are laminated and bonded in the thickness direction of the ceramic substrate (see, for example, Patent Document 1). . For example, a clad material having a three-layer structure of Cu-Mo-Cu is known, and a lower Cu layer located below Mo is bonded to a ceramic substrate, and an upper Cu layer located above Mo is formed. This is an area for mounting an electronic component or a wiring that is electrically connected to the electronic component.

Japanese Unexamined Patent Publication No. 2007-335795

In the above wiring board, for example, when a metal plate made of a clad material having a three-layer structure of Cu—Mo—Cu is heated or cooled, the amount of expansion or contraction of the Cu layer is larger than the amount of expansion or contraction of the Mo layer. The amount is large. Further, by lower Cu layer which is joined to the ceramic base body, because it is bound to the ceramic base body, it is towards the expansion amount or shrinkage of the upper Cu layer than expansion amount or shrinkage of the lower Cu layer larger . Therefore, when the upper Cu layer expands or contracts, an internal stress is generated in the metal plate such that the Mo layer and the lower Cu layer are pulled by the upper Cu layer, and the metal plate is deformed. When the metal plate is deformed, the wiring board is warped by warping the ceramic base so as to be pulled by the deformation of the metal plate.

Wiring board according to one aspect of the present invention, the ceramic substrate and is bonded to a ceramic substrate, a plurality of first metal which is provided between the plurality of first metal layers and a plurality of first metal layer and a metal plate having a small thermal expansion coefficient the second metal layer than the layer. The thickness of the upper metal layer of the plurality of first metal layer is lower thickness of the metal layer rather smaller than, and equal to or greater than the thickness of the second metal layer.

According to another aspect of the present invention, an electronic apparatus includes a wiring board having the above structure, the electronic components mounted on the metal plate of the wiring board.

Wiring board according to one aspect of the present invention, among the plurality of first metal layer, the thickness of the expansion or contraction tends upper metal layer as compared with the lower metal layer that is constrained by being bonded to the ceramic matrix body but rather smaller than the thickness of the lower metal layer and equal to or more than the thickness of the second metal layer. By adopting such a configuration, the difference between the amount of expansion or contraction of the upper metal layer and the amount of expansion or contraction of the lower metal layer is reduced, so that the inner portion where the lower metal layer is pulled by the upper metal layer is reduced. Stress is reduced. Therefore, the deformation of the metal plate accompanying the contraction or expansion of the upper metal layer is reduced, the warpage of the ceramic substrate is reduced, and the warpage of the wiring board can be reduced. In addition, when a metal material having a high thermal conductivity such as copper is used for the upper metal layer, the thermal conductivity of the metal plate can be improved, so that the heat dissipation of the wiring board can be improved.

According to another aspect of the present invention, an electronic device includes a wiring board having the above structure, since it is provided with a mounting electronic components to a metal plate of the wiring board, the bonding strength between the wiring board and the electronic component High and excellent long-term reliability.

It is sectional drawing of the electronic device in embodiment of the reference example of this invention. It is an enlarged view of the A section of FIG. It is a cross-sectional view of the metal plate of the electronic device in the implementation of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Embodiments of the present invention and exemplary embodiments will be described below with reference to the drawings.

( Reference embodiment)
An electronic device according to an embodiment of a reference example of the present invention will be described with reference to FIGS. The electronic device in the present embodiment includes a wiring board 1 and an electronic component 2 mounted on the wiring board 1. 1 and 2, the electronic device is provided in a virtual xyz space and is placed on the xy plane. In the present embodiment, the upward direction is the positive direction of the virtual z axis. Also shows an internal stress due to shrinkage of the metal plate when the wiring substrate 1 was cooled by the arrow in double dot chain line.

  The wiring board 1 includes a ceramic base 11 and a metal plate 12 provided on the ceramic base 11.

  The ceramic substrate 11 has a substantially square shape and functions as a support member that supports the metal plate 12. The ceramic substrate 11 is made of an electrically insulating material, for example, ceramic such as aluminum oxide ceramics, mullite ceramics, silicon carbide ceramics, aluminum nitride ceramics, or silicon nitride ceramics. Among these ceramic materials, silicon carbide ceramics, aluminum nitride ceramics, or silicon nitride ceramics are preferred in terms of thermal conductivity that affects heat dissipation, and silicon nitride ceramics or silicon carbide ceramics in terms of strength. Is preferred. When the ceramic substrate 11 is made of a relatively strong ceramic material such as silicon nitride ceramics, the possibility of cracks in the ceramic substrate 11 is reduced even if a thicker metal plate 12 is used. Thus, it is possible to realize the wiring board 1 capable of allowing a larger current to flow while reducing the size.

The thickness of the ceramic substrate 11 may be smaller in terms of thermal conductivity, for example, about 0.1 mm to 1 m.
m, and may be selected according to the size of the wiring substrate 1 or the thermal conductivity or strength of the material used.

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

The metal plate 12 includes a plurality of first metal layers 121 and a second metal layer 122 having a smaller thermal expansion coefficient than the plurality of first metal layers 121 provided between the plurality of first metal layers 121. Is included. In this embodiment, the metal plate 12 has a three-layer structure in which a second metal layer 122 is provided between two first metal layers 121. The first metal layer 121 and the second metal layer 122 are laminated in the thickness direction of the ceramic base 11, that is, the z-axis direction. As shown in FIG. 2, the first metal layer 121 is provided above the second metal layer 122 and below the second metal layer 122. The first metal layer 121 is provided on the ceramic base 11. And a lower metal layer 121b having surfaces to be joined. Lower metal layer 1
Since 21b is joined to the ceramic substrate 11, shrinkage or expansion is suppressed by the ceramic substrate 11. FIG. 2 shows the metal plate 12 provided on the upper surface of the ceramic substrate 11. However, the metal plate 12 provided on the lower surface is reversely configured in the vertical direction, and is thus bonded to the ceramic substrate 11. Becomes the lower metal layer 121b.

  The metal plate 12 is attached to at least one main surface (upper surface or lower surface) of the ceramic substrate 11 and functions as a heat radiating plate for radiating heat generated by the electronic component 2 mounted on the metal plate 12.

For the first metal layer 121 of the metal plate 12, a metal material having high thermal conductivity is used from the viewpoint of heat dissipation, and a metal material having high thermal conductivity such as copper is preferably used (heat conductivity of copper). : 395W / m
・ K). By applying a metal processing method such as mechanical processing such as rolling or punching or chemical processing such as etching to a copper ingot (lump), for example, a predetermined plate shape having a thickness of 10 to 300 μm Formed into a pattern.

The second metal layer 122 of the metal plate 12 is for suppressing the thermal expansion of the metal plate 12. For example, when the first metal layer 121 is copper, molybdenum having a smaller thermal expansion coefficient than copper. By using the same metal material as that of the first metal layer 121, a flat plate having a thickness of 20 to 300 μm is formed in a predetermined pattern.

The metal plate 12 is formed by overlapping a first metal layer 121 and a second metal layer 122. Specifically, after the second metal layer 122 is overlaid on the lower metal layer 121b of the first metal layer 121, the upper metal layer 121a of the first metal layer 121 is overlaid on the second metal layer 122. Are stacked to form a metal laminate. The metal laminate is formed into a predetermined pattern in a flat plate shape having a thickness of 0.05 to 1 mm, for example, by applying a metal processing method such as mechanical processing such as rolling or punching or chemical processing such as etching. The metal plate 12 is formed. The thickness D121a of the upper metal layer 121a is equal to the lower metal layer 121b.
If the thickness D121b of the lower metal layer 121b is 60 to 90 μm, the thickness D121a of the upper metal layer 121a is 20 to 40 μm. Further, when the metal plate 12 is provided on the lower surface of the ceramic substrate 11, the metal plate 12 is formed on almost the entire lower surface of the ceramic substrate 11 and mounted on the wiring board 1 as in the example shown in FIG. It is preferable to improve the heat dissipation of the electronic component 2.

In the metal plate 12, the thickness D121a of the upper metal layer 121a that is easily expanded or contracted is smaller than the thickness D121b of the lower metal layer 121b, as compared with the lower metal layer 121b bonded and restrained to the ceramic substrate 11. Because of such a configuration, the difference between the amount of contraction or expansion of the upper metal layer 121a and the amount of contraction or expansion of the lower metal layer 121b is reduced, so that the upper metal layer 121a contracts or expands. The difference between the internal stress F121a and the internal stress F121b due to contraction or expansion of the lower metal layer 121b is reduced. For example, the upper metal layer 121a and the lower metal layer 121
2b, the difference between the internal stress F121a caused by the shrinkage of the upper metal layer 121a and the internal stress F121b caused by the shrinkage of the lower metal layer 121b is reduced as in the example shown in FIG. . Therefore, the internal stress that causes the lower metal layer 121b to be pulled by the upper metal layer 121a is reduced, and the deformation of the metal plate 12 can be reduced.

In the present embodiment, when the thickness D121a of the upper metal layer 121a is smaller than the thickness D122 of the second metal layer 122 , deformation of the second metal layer 122 due to the internal stress F121a of the upper metal layer 121a can be reduced. In particular, when the thickness D121a of the upper metal layer 121a is smaller than the thickness D122 of the second metal layer 122, the deformation of the second metal layer 122 due to the internal stress F121a caused by the shrinkage or expansion of the upper metal layer 121a is further reduced. Thus, the deformation of the metal plate 12 can be further reduced.

When the material of the first metal layer 121 is copper, the copper used for the lower metal layer 121b is preferably oxygen-free copper. When oxygen-free copper is used, when the metal plate 12 and the ceramic substrate 11 are joined, the copper surface is reduced from being oxidized by oxygen present in the copper, and the wettability with the joining material 3 is reduced. since the better, it increases the bonding strength between the metal plate 12 and the ceramic substrate 11.

The metal plate 12 may have a five-layer structure of copper-molybdenum-copper-molybdenum-copper or a seven-layer structure of copper-molybdenum-copper-molybdenum-copper-molybdenum-copper. Thus, when the metal plate 12 has a five-layer structure or a seven-layer structure, the upper metal layer 121a is positioned at the uppermost position of the metal plate 12 .

When the metal plate 12 is processed into a predetermined pattern shape of the metal plate 12 by etching after the metal plate 12 is bonded to the ceramic base 11, for example, the processing is performed as follows. An etching resist ink is printed and applied in a predetermined pattern shape on the surface of the metal plate 12 bonded on the ceramic substrate 11 using a technique such as a screen printing method to form a resist film, and then, for example, phosphoric acid, acetic acid, nitric acid , hydrogen peroxide, sulfuric acid, hydrofluoric acid, ferric chloride, or by immersing the second copper solution and the like chloride alone or mixed etching solution, and or spraying an etching solution, other than the predetermined pattern of the metal plate 12 What is necessary is just to remove a part and to remove a resist film after that.

If a metal having high conductivity, corrosion resistance and good wettability with the brazing material is deposited on the metal plate 12 bonded to the ceramic substrate 11 by a plating method, the metal plate 12 and an external electric circuit ( It is possible to improve the electrical connection with the device (not shown). In this case, if an amorphous alloy of nickel-phosphorus is prepared by containing phosphorus in an amount of 8 to 15% by mass, the surface oxidation of the plating layer made of nickel is suppressed and the wettability with the brazing material is maintained for a long time. Is preferable. When the phosphorus content relative to nickel is 8% by mass or more and 15% by mass or less, it is easy to form an amorphous alloy of nickel-phosphorus, and the adhesive strength of the solder to the plating layer can be improved. If the plating layer made of nickel has a thickness of 1.5 μm or more, the exposed surface of the metal plate 12 can be easily covered, and oxidative corrosion of the metal plate 12 can be suppressed. Further, when the thickness is 10 μm or less, particularly when the thickness of the ceramic substrate 11 is less than 300 μm, the internal stress existing in the plating layer can be reduced, and the warpage generated in the metal plate 12 is reduced. Further, warping or cracking of the ceramic substrate 11 caused thereby can be suppressed.

  The metal plate 12 is bonded to the ceramic base 11 via a bonding material such as a bonding metal layer. The brazing paste for the bonding material is, for example, a silver brazing material (for example, silver: 72% by mass—copper: 28% by mass) made of silver and copper powder, silver-copper alloy powder, or a mixed powder thereof, and titanium. , Hafnium, zirconium or a hydride thereof is added to and mixed with 2 to 5% by mass of the silver brazing material, an appropriate binder, an organic solvent and a solvent are added and mixed, and then kneaded. The joining temperature of the silver brazing material is 780 ° C. to 900 ° C., and indium (In) or tin (Sn) may be added in an amount of about 1 to 10% by mass for the purpose of reducing the joining temperature or the hardness of the joining material 3.

An electronic component 2 is mounted on the upper surface of such a wiring board 1 via a die bonding material 4, and the electronic component 2 is electrically connected to a metal plate 12 by a plurality of bonding wires 5 to constitute an electronic device. . The die bond material 4 is made of, for example, a metal bonding material or a conductive resin. Such a metal bonding material is, for example, solder, a gold-tin (Au—Sn) alloy, a tin-silver-copper (Sn—Ag—Cu) alloy, or the like. The electronic component 2 is, for example, a transistor, an LSI (Large Scale Integrated circuit) for a CPU (Central Processing Unit), an IGBT (Insulated Gate Bipolar Transistor), or a MOS-FET (Metal O).
xide Semiconductor-Field Effect Transistor).

Wiring board 1 of this embodiment includes a ceramic substrate 11 is joined to the ceramic base 11, a plurality of first provided between the plurality of first metal layer 121 and a plurality of first metal layer 121 And a metal plate 12 having a second metal layer 122 having a smaller coefficient of thermal expansion than the metal layer 121. Among the plurality of first metal layer 121, the thickness D121a of expansion or contraction tends upper metal layer 121a than the lower metal layer 121b constrained by being joined to the ceramic base body 11 of the lower metal layer 121b It is smaller than the thickness D121b. With such a configuration, the difference between the expansion amount or contraction amount of the upper metal layer 121a and the expansion amount or contraction amount of the lower metal layer 121b is reduced, so that the lower metal layer 121b is pulled to the upper metal layer 121a. The internal stress is reduced. Therefore, the deformation of the metal plate 12 due to the contraction or expansion of the upper metal layer 121a is reduced, the warp of the ceramic base 11 is reduced, and the warp of the wiring board 1 can be reduced.

In the wiring board 1 of the present embodiment, when the thickness D121a of the upper metal layer 121a is smaller than the thickness D122 of the second metal layer 122, the second metal layer 122 due to the internal stress F121a of the upper metal layer 121a. Can be reduced. In particular, when the thickness D121a of the upper metal layer 121a is smaller than the thickness D122 of the second metal layer 122, the second metal layer 121a is contracted or expanded due to the second metal layer 121a.
Since the deformation of the metal layer 122 is further reduced, the deformation of the metal plate 12 is further reduced.

  Since the electronic device according to the present embodiment includes the wiring board 1 having the above-described configuration and the electronic component 2 mounted on the metal plate 12 of the wiring board 1, the bonding strength between the wiring board 1 and the electronic component 2 is high. High and long-term reliability.

(Embodiment of the present invention )
Next, it will be described with reference to FIG. 3 for an electronic device according to the implementation embodiments of the present invention.

The electronic device in the implementation form of the present invention is different from the electronic apparatus of an embodiment of the reference example described above, as in the example shown in FIG. 3, the thickness D121a of the upper metal layer 121a and the second metal layer This is the point that the thickness D122 is 122 or more. The thickness of the metal plate 12 is the same as that of the electronic device according to the embodiment of the reference example described above. The wiring board 1 of this embodiment can improve the thermal conductivity of the metal plate 12 when a metal material having a high thermal conductivity such as copper is used for the upper metal layer 121a. It can be improved.

1 ... Wiring board
11. ・ Ceramic substrate
12 ... Metal plate
121 ・ ・ ・ First metal layer
121a ..Upper metal layer
121b ..Lower metal layer
122 ... 2nd metal layer 2 ... Electronic parts 3 ... Bonding material 4 ... Die bonding material 5 ... Bonding wire

Claims (2)

A ceramic substrate;
It is bonded to the ceramic substrate, a small second metal of said plurality of coefficient of thermal expansion than the first metallic layer provided between the plurality of first metal layer and the plurality of first metal layers And a metal plate having a layer,
Wiring board, wherein the thickness of the top metal layer of the plurality of first metal layer is rather smaller than the thickness of the lower metal layer and equal to or more than the thickness of the second metal layer.   An electronic device comprising: the wiring board according to claim 1; and an electronic component mounted on the metal plate of the wiring board.

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