JP2021093482A - Manufacturing method of insulation circuit board - Google Patents

Abstract

To prevent the generation of stains due to soldering when a copper plate is formed into a circuit pattern by a wire cut discharge processing and jointed to a ceramic substrate.SOLUTION: A manufacturing method of a circuit board having a circuit layer formed in a circuit pattern on a front surface of a ceramic substrate, includes: a circuit layer copper plate formation step of cutting the copper plate made of copper or a copper alloy by wire cutting discharge processing to form the circuit layer copper plate of which a zinc concentration of a cutting end surface is 1.21 at% or less; and a joint step of forming the circuit layer by jointing the circuit layer copper plate with an active metal soldering to the ceramic substrate.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing an insulated circuit board such as a power module board.

As a substrate for a power module, one in which a circuit layer is formed on one surface of an insulating layer made of a ceramic substrate and a heat radiating layer is formed on the other surface is known. Further, when high power density is required due to miniaturization and high output of electronic components, copper or a copper alloy is used for the circuit layer in order to improve the heat dissipation of the circuit layer.
In Patent Document 1, a composite brazing material obtained by clad a thin plate of active metal brazing on a copper plate is punched or electric discharge machined to form a circuit pattern, and the composite brazing material on which this circuit pattern is formed is formed on the thin plate side of the active metal brazing plate. It is described that the joint portion of the circuit pattern of the composite brazing material is etched and removed after joining on a ceramic substrate.
In this case, as compared with the case where the copper plate is formed into a circuit pattern by punching, the case where the copper plate is formed into a circuit pattern by wire-cut electric discharge machining can shorten the delivery time because the production of the press die can be omitted.

Japanese Unexamined Patent Publication No. 6-177513

By the way, when a copper plate is joined to a ceramic substrate using an active metal brazing material, a surplus of the molten brazing material leaks from between the ceramic substrate and the copper plate, rises along the side surface of the copper plate, and crawls on the surface of the copper plate. The phenomenon of rising may occur. When the brazing material that crawls up on the surface of this copper plate solidifies as it is, it remains as a wax stain (called a wax stain) on the surface of the circuit layer. The wax stains are wet and spread in the surface direction from the peripheral edge of the circuit layer, and the surface of the circuit layer appears to be rough to the naked eye. If an electronic component is mounted in a state where the wax stain is formed, a bonding defect may occur during wire bonding or the like.

Compared with the case where the copper plate is punched out by the press punching described in Patent Document 1 to form the circuit pattern, the occurrence of wax stain becomes remarkable when the circuit pattern is formed by electric discharge machining (wire cut electric discharge machining). However, in the case of the circuit board described in Patent Document 1, since the connecting portion of the circuit pattern in the circuit layer is removed by etching after joining to the ceramic substrate, even if wax stains are formed after joining, etching is performed. Can be removed by
However, if etching is not performed, such as when a connecting portion is not formed in the circuit pattern, wax stains remain.

The present invention has been made in view of such circumstances, and a method for manufacturing an insulated circuit board capable of preventing the occurrence of wax stains when a copper plate is formed into a circuit pattern by wire-cut electric discharge machining and bonded to a ceramic substrate. The purpose is to provide.

The present inventor has earnestly studied measures to prevent wax stains and obtained the following findings.
The brazing material, which melts at the time of joining and becomes a liquid phase, leaks from the space between the ceramic substrate and the copper plate, then rises along the side surface of the copper plate, and crawls up from the side surface to the surface of the circuit layer. Form wax stains on the surface. Therefore, in order to prevent the occurrence of wax stains on the surface of the circuit layer, the molten brazing material leaks from between the ceramic substrate and the copper plate, rises on the side surface of the copper plate, and crawls up from the side surface to the surface. It is necessary to suppress one of the two forms.

When a copper plate is punched out to form a circuit pattern by punching according to Patent Document 1, burrs are generated on the periphery of the circuit pattern, and these burrs hinder the movement of the brazing material between the front and back surfaces of the copper plate and the side surfaces. It is thought that it can be done. However, when the copper plate is formed into a circuit pattern by wire cut electric discharge machining, burrs do not occur. Therefore, among the above three forms, the brazing material leaks from between the ceramic substrate and the copper plate, and the copper plate is cut. It is difficult to suppress the creeping up from the end face (side surface) to the surface. Further, it is impossible to completely eliminate the leakage of the brazing material in order to obtain a good bond up to the peripheral edge of the circuit layer. Therefore, in the case of forming a copper plate by this wire-cut electric discharge machining, the occurrence of wax stains cannot be prevented unless the brazing material can be prevented from rising on the cut end surface (side surface) of the copper plate.

Therefore, in order to compare and investigate the state of the cut end face (side surface) of the copper plate cut by wire cut discharge processing and the punched end face (side surface) of the copper plate punched by the press, a scanning electron microscope (SEM) was used. When the side surfaces of the copper plate were analyzed for their components by the energy dispersive X-ray spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy) used, a large amount of carbon, oxygen, and zinc were confirmed in addition to copper. Then, based on this analysis result, a study was conducted on measures to prevent the brazing material from rising on the cut end face (side surface) of the copper plate by wire-cut electric discharge machining. As a result, when the zinc concentration on the cut end face was high, the brazing material rose along the cut end face. We found that it was easy, and concluded that by suppressing the zinc concentration to a predetermined value or less, it was possible to prevent the brazing material from rising on the cut end face and suppress the occurrence of wax stains on the surface.

That is, the present invention is a method for manufacturing an insulated circuit board having a circuit layer formed in a circuit pattern on the surface of a ceramics substrate, in which a copper plate made of copper or a copper alloy is cut into the circuit pattern by wire-cut discharge processing. Then, the circuit layer copper plate forming step of forming the circuit layer copper plate having a zinc concentration of 1.21 at% or less on the cut end face and the circuit layer copper plate are joined to the ceramics substrate with an active metal brazing material to form the circuit. It has a joining step of forming a layer.

When a copper plate is formed into a circuit pattern by wire-cut electric discharge machining, the zinc concentration on the cut end face tends to increase, and when the zinc concentration exceeds 1.21 at%, the copper plate is used as a ceramic substrate with an active metal brazing material. When joined, the molten brazing material leaking from between the ceramic substrate and the copper plate rises along the cut end face of the copper plate and crawls up to the surface, and wax stains are likely to occur in the circuit layer. By setting the zinc concentration to 1.21 at% or less, it is possible to suppress the phenomenon that the brazing material melted at the time of joining travels along the cut end face (side surface) of the copper plate and rises to the surface, and the occurrence of wax stains can be prevented.

As a preferred embodiment of this manufacturing method, the zinc concentration on the surface of the wire used as an electrode for wire cut electric discharge machining is preferably 20% by mass or less.

As the wire used as the electrode for wire cut discharge processing, brass (brass) which is an alloy of copper and zinc (however, the amount of zinc is 20% by mass or less), oxygen-free copper, tungsten and the like are used as materials. In addition, there are also those in which the outer peripheral surface of a wire such as brass is coated with zinc. Of these wires, if the zinc concentration on the surface of the wire that is discharged in close proximity to the copper plate during processing is high, the zinc concentration on the cut end face of the copper plate after processing is high. In order to suppress the zinc concentration on the cut end surface of the copper plate to 1.21 at% or less, the zinc concentration on the surface of the wire may be 20% by mass or less.

According to the present invention, it is possible to prevent the occurrence of wax stains when a copper plate is formed into a circuit pattern by wire-cut electric discharge machining and bonded to a ceramic substrate.

It is a front view of the insulation circuit board which concerns on one Embodiment of this invention. It is a top view of the insulation circuit board shown in FIG. It is a schematic diagram which shows the state which the copper plate for a circuit layer of the insulation circuit board shown in FIG. 1 is wire-cut electric discharge machining. It is a figure which shows the state before joining of the insulation circuit board shown in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Structure of insulated circuit board]
The insulating circuit board 1 includes a ceramics substrate 11, a circuit layer 12 formed on one surface of the ceramics substrate 11, and a heat radiating layer 13 formed on the other surface of the ceramics substrate 11.

The ceramic substrate 11 is a rectangular plate-shaped insulating substrate that prevents electrical connection between the circuit layer 12 and the heat dissipation layer 13, and is, for example, silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), or aluminum oxide. It is formed of (Al ₂ O ₃ ) or the like, and its thickness is, for example, 0.2 mm to 1.2 mm. When both the circuit layer 12 and the metal layer 13 formed on both sides of the ceramic substrate 11 are made of copper or a copper alloy, it is preferable that the ceramic substrate is made of silicon nitride.

The plane size of the ceramic substrate 11 is not particularly limited, but is set to, for example, (40 mm to 140 mm) × (40 mm to 100 mm).

The circuit layer 12 is formed on the upper surface (one surface) of the ceramic substrate 11, and copper or a copper alloy having a purity of 99% by mass or more is used, and the thickness thereof is, for example, 0.2 mm or more and 2.0 mm or less.

The plane size of the circuit layer 12 is smaller than that of the ceramic substrate 11, and is not particularly limited, but is set to, for example, (36 mm to 136 mm) × (36 mm to 96 mm). Further, as shown in FIG. 2, a plurality of small circuit layers 121 and 122 are arranged at predetermined intervals to form one circuit layer 12, and the plane size of the circuit layer 12 is determined by these small circuits. It is the total size including the gap between the layers 121 and 122 and the small circuit layers 121 and 122. The circuit layer 12 may be a so-called solid circuit layer composed of a single metal plate.

The heat radiating layer 13 is formed on the lower surface (the other surface) of the ceramic substrate 11, and copper or a copper alloy having a purity of 99% by mass or more can be used. Its thickness is, for example, 0.2 mm or more and 2.0 mm or less.

The plane size of the heat radiating layer 13 is smaller than that of the ceramic substrate 11, and is not particularly limited, but is set to, for example, the same (36 mm to 136 mm) × (36 mm to 96 mm) as the circuit layer 12. Although the heat radiating layer 13 is composed of one metal plate in the illustrated example, it may be composed of a plurality of metal plates as in the case of the small circuit layers 121 and 122 of the circuit layer 12, for example.

The circuit layer 12 and the heat radiating layer 13 may have the same composition as copper or a copper alloy, but may have different compositions. The thickness and size of the circuit layer 12 and the heat radiating layer 13 may be the same, but may be different.

[Manufacturing method of insulated circuit board]
Next, a method of manufacturing the insulated circuit board 1 of the present embodiment will be described.

(Metal plate forming step used for circuit layer 12 and heat radiating layer 13 (Copper plate forming step for circuit layer))
A flat copper plate made of copper or a copper alloy is cut by wire-cut electric discharge machining to form a copper plate for a circuit layer and a copper plate for a heat dissipation layer. FIG. 3 shows a case where the copper plates 151 and 152 for the small circuit layer are formed from the flat plate-shaped copper plate 150.
In the wire cut discharge processing, for example, a pulse current is passed through a wire (electrode wire) 20 having a diameter of about 0.2 mm to 0.3 mm to generate a discharge phenomenon with the work (copper plate 150), for example, FIG. The work (copper plate 150) is moved to the wire 20 by running the wire 20 as shown by the arrow A and moving the work (copper plate 150) in the direction orthogonal to the length direction of the wire 20 as shown by the arrow B. It is cut while locally melting and removing at the facing portion. In this case, in order to cool the wire 20 and the work (copper plate 150), remove processing powder, and the like, the entire cut portion is processed in a state of being immersed in a processing liquid such as water.

When the copper plate 150 is cut by this wire cut electric discharge machining, the wire 20 and the copper plate 150 are close to each other at a distance of several μm to several tens of μm and discharged. Brass (brass) containing about 40% by mass of zinc is often used for the wire 20 as an electrode. When it is made of a material containing zinc such as brass, zinc adheres to the cut end faces S2 of the circuit layer copper plates 151 and 152 cut by electric discharge. If the zinc concentration of the cut end faces S2 of the circuit layer copper plates 151 and 152 is high, it is not possible to prevent the molten brazing material from rising on the cut end faces S2 in the next joining step, and wax stains occur on the circuit layer 12 surface S1. .. The reason why the zinc concentration affects the occurrence of wax stains is not clear, but in order to prevent the occurrence of wax stains, the zinc concentration of the cut end faces S2 of the circuit layer copper plates 151 and 152 should be 1.21 at% or less. There is a need.

Therefore, electric discharge machining is performed under the condition that the zinc concentration of the cut end faces S2 of the circuit layer copper plates 151 and 152 after the cutting process by wire cut electric discharge machining is 1.21 at% or less. As a condition for the zinc concentration to be 1.21 at% or less, it is preferable to use a wire made of oxygen-free copper or tungsten, but when zinc is contained like a Cu-Zn alloy, the zinc concentration should be 20% by mass or less. For example, the cut end face S2 of the processed copper plates 151 and 152 for the circuit layer can be 1.21 at% or less. A wire having a zinc concentration of more than 20% by mass cannot be used because the zinc concentration of the cut end face S2 exceeds 1.21 at% when it is used.

Further, a wire coated with zinc on the surface can be used, but even in that case, it can be used as long as the zinc concentration on the surface is 20% by mass or less.
Further, when the circuit layer copper plate is formed by press working, the circuit layer copper plate is degreased and washed after the processing, and the circuit layer copper plate 151,152 formed by this wire cut electric discharge machining is performed. Is used as it is in the next joining step after processing without being subjected to degreasing / cleaning treatment.

Since the circuit layers 12 are formed in a pattern, the circuit layer copper plates 151 and 152 are formed by wire-cut electric discharge machining, but the heat-dissipating layer copper plate 130 may be formed by wire-cut electric discharge machining. , May be formed by electric discharge machining with a press. In this case, the heat radiating layer 13 has a heat sink or the like bonded to the surface thereof, and unlike the circuit layer 12, wire bonding or the like is not performed. Therefore, even if wax stains occur, the effect on the bonding is small, but the appearance is deteriorated. In the case of wire-cut electric discharge machining, the zinc concentration on the cut end face is 1.21 at% or less using the wire 20 having a surface zinc concentration of 20% by mass or less, as in the case of the circuit layer copper plates 151 and 152. It is good to set it to.

(Joining process)
After forming the circuit layer copper plates 151 and 152 and the heat radiation layer copper plate 130 as described above, the circuit layer copper plates 151 and 152 and the heat radiation layer copper plate 130 are formed on the ceramic substrate 11 as Ag-Ti or Ag-Cu, respectively. -Join using a Ti-based active metal brazing material. Specifically, as shown in FIG. 4, a brazing material foil 30 made of Ag-Cu-Ti or the like is interposed on both sides of the ceramic substrate 11, and the copper plates 151 and 152 for the circuit layer and the copper plates 130 for the heat dissipation layer are respectively interposed. Are laminated. Then, these laminated bodies are sandwiched between carbon plates (not shown) and heated in a vacuum while applying a load in the stacking direction to form the ceramic substrate 11, the copper plates 151 and 152 for the circuit layer, and the copper plate 130 for the heat dissipation layer. Join. As a result, the insulating circuit board 1 in which the circuit layer 12 is bonded to the upper surface of the ceramic substrate 11 via the bonding portion (brazing portion) and the heat radiating layer 13 is bonded to the lower surface via the bonding portion (brazing portion) is formed. It is formed.

When joining the ceramic substrate 11, the circuit layer copper plates 151 and 152, and the heat dissipation layer copper plate 130, the pressing force in the stacking direction is preferably 0.1 MPa to 1.0 MPa, and the heating temperature is preferably 800 ° C. to 930 ° C. The brazing material foil 30 such as Ag-Cu-Ti has a thickness of 5 μm to 15 μm. Instead of the foil, a paste may be used. For example, the paste may be applied to both surfaces of the ceramic substrate 11, and the circuit layer copper plates 151 and 152 and the heat radiation layer copper plate 130 may be laminated and joined.

In this joining step, the brazing foil 30 interposed between the ceramic substrate 11 and the copper plates 151 and 152 for the circuit layer melts, and the surplus leaks from between the ceramic substrate 11 and the copper plates 151 and 152 for the circuit layer. Even so, since the concentration of zinc on the side surfaces (cut end faces during wire-cut electric discharge machining) S2 of the copper plates 151 and 152 for the circuit layer is low, the phenomenon that the molten brazing material rises along the side surfaces S2 is suppressed, and the phenomenon is suppressed. As a result, the occurrence of wax stains on the surface S1 of the circuit layer 12 is prevented.

In addition, the detailed configuration is not limited to that of the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above embodiment, the heat radiating layer is formed on the surface of the ceramic substrate opposite to the circuit layer, but the present invention can be applied to an insulated circuit board having no heat radiating layer.

A copper plate having a thickness of 0.8 mm made of oxygen-free copper was cut into a circuit pattern by wire-cut electric discharge machining to prepare a copper plate for a circuit layer.
At this time, the surface of the wire used for the wire cut discharge processing and the cut end face of the copper plate for the circuit layer were respectively component-analyzed by energy dispersive X-ray spectroscopy (SEM-EDX) using a scanning electron microscope, and the zinc concentration thereof. Was measured.
Next, the wire-cut copper plate is laminated on the surface of a ceramic substrate made of silicon nitride via an active metal brazing paste of Ag-Cu-Ti coated so as to have a thickness of 10 μm, and this is pressurized and heated. Joined by. The joining conditions at this time were a vacuum atmosphere, a pressing force of 0.2 MPa, and a temperature of 815 ° C.

With respect to the obtained bonded body, the presence or absence of wax stains on the surface of the circuit layer was confirmed. When wax stains occur, they are formed by wetting and spreading from the peripheral edge of the circuit layer to the surface in the surface direction, and the wax stains appear to be rough with respect to the copper surface. The presence or absence of wax stains was judged based on the presence or absence of visible parts.
The results are shown in Table 1.

As is clear from the results shown in Table 1, when the zinc concentration on the cut end face of the copper plate before joining is 1.21 at% or less, the occurrence of wax stains can be suppressed. Further, it was found that when the zinc concentration on the wire surface used in wire cut electric discharge machining is 20% by mass or less, the zinc concentration on the cut end surface of the copper plate is 1.21 at% or less, and the occurrence of wax stains can be suppressed. It was.

10 Insulated circuit board 11 Ceramic board 12 Circuit layer 121,122 Small circuit layer 150 Copper plate 151,152 Copper plate for circuit layer S1 Surface S2 Cut end face (side surface)
13 Heat dissipation layer 131 Heat dissipation layer metal plate 20 Wire 30 Active metal brazing material foil

Claims (2)

A method for manufacturing a circuit board having a circuit layer formed in a circuit pattern on the surface of a ceramics substrate. A copper plate made of copper or a copper alloy is cut into the circuit pattern by wire-cut discharge processing, and zinc on the cut end face is formed. A circuit layer copper plate forming step of forming a circuit layer copper plate having a concentration of 1.21 at% or less, and a joining step of joining the circuit layer copper plate to the ceramic substrate with an active metal brazing material to form the circuit layer. A method for manufacturing an insulated circuit board. The method for manufacturing an insulated circuit board according to claim 1, wherein the zinc concentration on the surface of the wire used for wire cut electric discharge machining is 20% by mass or less.

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