JP2016032032A - Circuit board and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a circuit board and an electronic device, which can improve radiation efficiency while suppressing the occurrence of cracks and the like in an insulating substrate.SOLUTION: A circuit board has an insulating substrate 1, and a copper plate 3 provided on a principal surface of the insulating substrate via a silver-containing bonding material 2. A thickness of the bonding material at a central part of the copper plate is thicker than a thickness of the bonding material at a peripheral part of the copper plate. This can make heat generated at an electronic component 5 be favorably radiated to the insulating substrate 1 side at the central part of the copper plate 3. In addition, since the thickness of the bonding material 2 is thinner on the peripheral part than in the central part of the copper plate 3, diffusion of silver is not likely to occur and stress can be mitigated.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a circuit board 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) such as a power module or a switching module is mounted, for example, a copper plate is formed on a main surface of an insulating substrate via a bonding material. What was joined is used.

JP 2002-343911 A

  However, usually, the electronic component is disposed on the upper surface of the central portion of the copper plate, but the heat generated in the electronic component is not sufficiently dissipated to the insulating substrate via the bonding material.

  Further, when the copper plate is bonded to the insulating substrate by the bonding material containing silver, the silver diffuses inside the copper plate. Therefore, the hardness of the portion of the copper plate where silver has diffused increases. Further, if a thermal cycle is applied when the circuit board is used, stress tends to concentrate on the peripheral edge of the copper plate. Therefore, at the peripheral portion of the copper plate, the stress that tends to concentrate cannot be relieved due to the increased hardness, and cracks in the insulating substrate and peeling of the copper plate from the insulating substrate are likely to occur.

  In view of the above problems, an object of the present invention is to provide a circuit board and an electronic device that can improve heat dissipation efficiency while suppressing generation of cracks in an insulating substrate or peeling of a copper plate.

  A circuit board according to an aspect of the present invention includes an insulating substrate, and a copper plate provided on a main surface of the insulating substrate via a bonding material containing silver, and the circuit board in the central portion of the copper plate. The thickness of the bonding material is greater than the thickness of the bonding material at the peripheral edge of the copper plate.

  An electronic device according to one aspect of the present invention includes the above circuit board and an electronic component mounted on the circuit board.

  According to the circuit board of the present invention, the thickness of the bonding material at the central portion of the copper plate is thicker than the thickness of the bonding material at the peripheral portion of the copper plate. Usually, in a circuit board, electronic components are often arranged on the upper surface of the central portion of the copper plate, and therefore, in the bonding material having a large thickness in the central portion of the copper plate, the amount of silver having a higher thermal conductivity than copper is large. The heat generated in the electronic component can be radiated well to the insulating substrate side. Moreover, since the thickness of the bonding material at the peripheral portion of the copper plate is thinner than the thickness of the bonding material at the central portion of the copper plate, the amount of the bonding material is reduced at the peripheral portion, and from the bonding material to the copper plate from the central portion. Difficult to cause silver diffusion to Therefore, since the peripheral part of a copper plate does not become hard too much, when a thermal cycle is loaded at the time of use, stress can be relieved by the peripheral part where stress tends to concentrate.

  According to the electronic device of the present invention, since the above-described circuit board is included, it is possible to suppress the occurrence of cracks in the insulating substrate or the peeling of the copper plate and to improve the heat dissipation efficiency. it can.

(A) is a top view of the circuit board and electronic device of embodiment of this invention, (b) is sectional drawing in the AA of (a), (c) is a bottom view. (A)-(e) is sectional drawing explaining each process for manufacturing the circuit board of embodiment of this invention. It is sectional drawing which shows the other example of the circuit board of embodiment of this invention.

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

  In the example shown in FIG. 1, the circuit board 10 includes an insulating substrate 1, a bonding material 2, and a copper plate 3. In the example shown in FIG. 1, the electronic device 20 includes a circuit board 10 and an electronic component 5.

  The insulating substrate 1 is made of an electrically insulating material, for example, ceramics such as aluminum oxide ceramics, mullite ceramics, silicon carbide ceramics, aluminum nitride ceramics, or silicon nitride ceramics. Among these ceramic materials, silicon carbide ceramics, aluminum nitride ceramics, or silicon nitride ceramics are preferred in terms of thermal conductivity that affects heat dissipation, and silicon nitride ceramics or silicon carbide ceramics in terms of strength. Is preferred.

  When the insulating substrate 1 is made of a ceramic material having a relatively high strength such as silicon nitride ceramics, there is a possibility that the insulating substrate 1 may crack due to thermal stress caused by the difference in thermal expansion coefficient between the copper plate 3 and the insulating substrate 1. Therefore, it is possible to realize a circuit board capable of flowing a larger current while achieving downsizing.

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

  If the insulating substrate 1 is made of, for example, silicon nitride ceramics, an appropriate organic binder, plasticizer, and solvent are added to and mixed with raw material powders such as silicon nitride, aluminum oxide, magnesium oxide, and yttrium oxide, and then mixed with slurry. 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.

  In the example shown in FIG. 1, a copper plate 3 is provided on the main surface of the insulating substrate 1 with a bonding material 2 containing silver.

The copper plate 3 has a flat plate shape, and the thickness thereof is, for example, 20 to 600 μm. The copper plate 3 is preferable as a member constituting the circuit board 10 because it has low electrical resistance and high thermal conductivity.

  The copper plate 3 is, for example, oxygen-free copper. When oxygen-free copper is used as the copper plate 3, when the copper plate 3 and the insulating substrate 1 are joined, the surface of the copper plate 3 is reduced from being oxidized by oxygen present in the copper, and the joining material 2. Therefore, the bonding strength with the insulating substrate 1 is improved.

  Further, when the bonding material 2 has a copper component, a diffusion layer is formed by diffusing the copper component in each member at the bonding portion of both the bonding material 2 and the copper plate 3. 2 and the copper plate 3 are preferably joined firmly to each other.

  Further, in the example shown in FIG. 1A, an electronic component 5 is mounted on the upper surface of the central copper plate 3 via a bonding material 4, and the electronic component 5 is bonded to another copper plate 3 with a bonding wire. It is connected by a conductive connecting material such as 6. Thus, in the example shown in FIG. 1, the copper plate 3 functions as a circuit conductor. The copper plate 3 can also be used as a metal member for mounting the electronic component 5 mounted on the circuit board and a metal member for the ground conductor. Further, the copper plate 3 on the lower surface of the insulating substrate 1 shown in FIG. 1C is mainly used as a heat sink. Thus, the copper plate 3 is used by being joined to the insulating substrate 1 made of ceramics or the like as a conductive path for supplying a relatively large current of, for example, several tens of A.

The electronic component 5 is, for example, a transistor or an LS for a CPU (Central Processing Unit).
It is a semiconductor element such as I (Large Scale Integrated circuit), IGBT (Insulated Gate Bipolar Transistor), or MOS-FET (Metal Oxide Semiconductor-Field Effect Transistor).

  The bonding material 4 for bonding the electronic component 5 to the copper plate 3 is made of, for example, metal or conductive resin. The bonding material made of metal is, for example, solder, a gold-tin (Au—Sn) alloy, or a tin-silver-copper (Sn—Ag—Cu) alloy. The bonding material made of conductive resin is, for example, an adhesive with high thermal conductivity such as Ag epoxy resin.

  A plating film may be formed on the surface of the copper plate 3 by a plating method. According to this configuration, since the wettability with the bonding material 4 becomes good, the electronic component 5 can be firmly bonded to the surface of the copper plate 3. The plating film may be made of a metal having high conductivity and corrosion resistance, and examples thereof include nickel, cobalt, copper, gold, and alloy materials containing these metal materials as main components. The thickness of the plating film may be, for example, 1.5 to 10 μm.

  The plating film preferably contains phosphorus inside. For example, a nickel-phosphorus amorphous alloy plating film is preferable because surface oxidation of the nickel plating film can be suppressed and wettability of a bonding material or the like can be maintained for a long time. Further, when the content of phosphorus with respect to nickel is about 8 to 15% by mass, a nickel-phosphorus amorphous alloy is easily formed, and the adhesive strength of a bonding material or the like to the plating film can be further improved.

  In the example shown in FIG. 1, the copper plate 3 is provided on the main surface of the insulating substrate 1 with a bonding material 2 containing silver.

The copper plate 3 is bonded to the upper surface of the insulating substrate 1 via, for example, an Ag—Cu-based bonding material 2. The bonding material 2 contains, for example, at least one active metal material of titanium, hafnium, and zirconium in order to be firmly bonded to the insulating substrate 1 when wet. Moreover, this bonding material 2 may have at least one of In and Sn, for example. In addition, the thickness of this joining material 2 should just be about 5-100 micrometers, for example.

  As in the example shown in FIG. 1, the thickness of the bonding material 2 at the center of the copper plate 3 is thicker than the thickness of the bonding material 2 at the peripheral edge of the copper plate 3. Usually, in the circuit board 10, the electronic component 5 is often disposed on the upper surface of the central portion of the copper plate 3, and therefore, the bonding material 2 having a large thickness at the central portion of the copper plate 3 is made of silver having a higher thermal conductivity than copper. Since the amount is large, the heat generated in the electronic component 5 can be radiated well to the insulating substrate 1 side. Moreover, since the thickness of the bonding material 2 at the peripheral portion of the copper plate 3 is thinner than the thickness of the bonding material 2 at the central portion of the copper plate 3, the amount of the bonding material 2 is reduced at the peripheral portion, compared to the central portion, Silver diffusion from the bonding material 2 to the copper plate 3 hardly occurs. Therefore, since the peripheral part of the copper plate 3 does not become too hard, the stress can be relieved at the peripheral part where the stress tends to concentrate when a thermal cycle is applied during use.

  Next, a manufacturing method of the circuit board 10 according to the embodiment of the example shown in FIG. 1 of the present invention will be described with reference to FIG.

  (1) First, as a first step, as shown in FIG. 2A, the main surface of a copper plate base material 3 ′ to be the copper plate 3 is disposed on the main surface of the insulating substrate 1. In this step, before the copper plate base material is arranged, the bonding material 2 is applied in advance to a predetermined position on both main surfaces of the insulating substrate 1 in a predetermined shape by a method such as screen printing. As this bonding material 2, for example, a material containing silver and copper as main components, further containing Ti, and having a melting point adjusted to about 790 ° C. with In or Sn is used. In the printing application of the bonding material 2, the bonding material 2 is printed only in the formation region of the copper plate 3 as shown in FIG.

  (2) Next, as a second step, the thickness of the bonding material 2 is adjusted so that the thickness of the bonding material 2 at the center of the copper plate 3 is larger than the thickness of the bonding material 2 at the peripheral edge of the copper plate 3.

  Specifically, as shown in FIG. 2 (b), a frame jig 11 having a wall portion formed along a copper plate non-formation region that is removed by etching in a process described later is connected to a copper plate base material 3 '. Press against the insulating substrate 1 from the upper or lower surface. Thereby, as shown in FIG.2 (c), the copper plate base material 3 'deform | transforms in the vicinity of the copper plate non-formation area | region pressed by the wall part, and the thickness of the joining material 2 becomes small. On the other hand, since the copper plate base material 3 ′ is not deformed in the central portion of the copper plate forming region that is not pressed by the wall portion, the thickness of the bonding material 2 becomes relatively large.

  By this step, the thickness of the bonding material 2 at the center portion of the copper plate forming region becomes thicker than the thickness of the bonding material 2 at the peripheral portion of the copper plate forming region.

  In addition, when the high melting point metal particles are contained in the bonding material 2, when the copper plate base material 3 ′ is pressed by the frame jig 11, the center of the copper plate formation region that is not suppressed by the wall portion. In the portion, the bonding material hardly flows, and the thickness of the bonding material 2 is easily made thicker than the peripheral portion.

  (3) Next, as a third step, the copper plate base material 3 ′ is bonded to the insulating substrate 1 by heat treatment. In this step, the laminated body obtained in the second step is placed in a vacuum furnace, and heat treatment is performed at about 830 ° C. in a vacuum state. As a result, the bonding material 2 is melted and cooled to solidify the bonding material 2, and the copper plate base material 3 ′ is bonded to the insulating substrate 1.

  (4) Next, as a fourth step, the copper plate non-formation region in the copper plate base material 3 ′ is removed by etching, and the copper plate 3 is left.

Specifically, as shown in FIG. 2 (d), a resist 13 is formed in the copper plate formation region to be left as the copper plate 3, and etching is performed so that a plurality of copper plates 3 as in the example shown in FIG. 1 (a) remain. Do.
For example, ferric chloride may be used as the etching solution. Note that the resist 13 is removed after the etching. Through the above steps, the circuit board 10 can be obtained as shown in FIG.

  Next, an example of another embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view showing another example of the circuit board according to the embodiment of the present invention.

  In the example shown in FIG. 3, the thickness of the bonding material 2 at the center of the copper plate 3 is thicker than the thickness of the bonding material 2 at the peripheral portion of the copper plate 3 on the lower surface of the insulating substrate 1. Is curved to be convex downward. With this configuration, when the circuit board 10 is bonded to an external heat dissipation base or the like, the central portion of the copper plate 3 on the lower surface of the insulating substrate 1 is securely in contact with the heat dissipation base or the like. Therefore, the heat generated in the electronic component 5 can be efficiently radiated from the circuit board 10 to the external heat radiating base.

  In order to manufacture the circuit board of the example shown in FIG. 3, a copper plate base material 3 ′ whose copper plate formation region is curved in a convex shape is prepared in advance, and then the copper plate base material 3 ′ is joined to the insulating substrate 1. Like that. In order to curve the copper plate forming region in the copper plate base material 3 ′, the copper plate base material 3 ′ may be press-molded in advance.

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

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 2 ... Bonding material 3 ... Copper plate 3 '... Copper plate base material 4 ... Bonding material 5 ... Electronic component 6 ... Bonding wire
10 ... Circuit board
11 ... Frame jig
20 ... Electronic device

Claims (2)

An insulating substrate;
A copper plate provided on a main surface of the insulating substrate via a bonding material containing silver;
The circuit board, wherein a thickness of the bonding material in a central portion of the copper plate is thicker than a thickness of the bonding material in a peripheral portion of the copper plate. A circuit board according to claim 1;
And an electronic component mounted on the circuit board.

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