JP7615769B2 - Manufacturing method for insulating circuit board - Google Patents

Description

The present invention relates to a method for manufacturing an insulating circuit board used in power modules that control high currents and high voltages.

For example, a metal-bonded ceramic substrate (insulated circuit substrate) described in Patent Document 1 as an insulating circuit substrate used in conventional power modules and the like, includes a ceramic substrate made of AlN (aluminum nitride), Al ₂ O ₃ (alumina), Si ₃ N ₄ (silicon nitride), or the like, a circuit layer formed by bonding a first metal plate to one surface of the ceramic substrate, and a metal layer formed by bonding a second metal plate to the other surface of the ceramic substrate. The manufacturing process described in Patent Document 1 includes placing a metal plate in contact with a ceramic substrate that can be divided into a plurality of ceramic substrates by forming cutting lines (scribe lines), bonding them together by an active metal method or the like, removing unnecessary portions of the metal plate by etching to form a circuit pattern, and dividing the ceramic substrate along the scribe lines to obtain individual insulating circuit substrates.
When brazing a ceramic plate to a metal plate, if the metal plate is a copper or copper alloy plate, an Ag--Ti or Ag--Cu--Ti brazing material containing an active metal is used.

Patent No. 5642808

However, when manufacturing a bonded body by the etching method, at least two diagonal corners of the ceramic plate must be exposed in order to position the resist printing required for circuit formation, and therefore at least two sides of the continuous metal plate must be located inside the outer periphery of the ceramic substrate after bonding.
Generally, a "dummy part" exists around the outer periphery of a ceramic plate to protect the ceramic plate that will become the product during the manufacturing process. Usually, the two exposed corners of this ceramic plate are used as the reference for the subsequent resist printing.

On the other hand, to ensure bondability, a minimum amount of brazing material must be present in the areas where bonding is required. If the positional relationship between the metal plate and the brazing material is inappropriate while ensuring the required brazing material area, excess brazing material can flow out from between the ceramic plate and the metal plate in the area where the ceramic plate is exposed when bonded (the "dummy area"), and creep up along the sides of the metal plate onto the surface of the metal plate, causing problems such as poor appearance and poor etching when forming circuits.

The present invention was made in consideration of these circumstances, and aims to suppress the impact on the product and prevent poor appearance and etching of the product even if the brazing material flows into the "dummy part" and creeps up onto the metal plate surface.

The method for producing an insulating circuit board of the present invention includes a lamination step of laminating a rectangular ceramic plate and a metal plate, each having a dividing scribe line formed therein, via a brazing material; a joining step of heating the laminate to melt the brazing material and then cooling the laminate to join the ceramic plate and the metal plate; an etching step of etching the metal plate after the joining step to remove unnecessary portions; and a division step of dividing the ceramic plate along the scribe lines after the etching step to form a plurality of insulating circuit boards,
a product portion which will become the insulating circuit board and a dummy portion around the product portion are formed on the ceramic plate by dividing scribe lines, and the dummy portions on two sides constituting one corner are formed to be narrower than the dummy portions on two sides constituting a corner opposite the one corner,
In the stacking process, one corner of the metal plate is aligned with one corner of the ceramic plate, and a portion of the dummy portion of the ceramic plate is positioned so as to extend beyond the metal plate on two sides that form a corner opposite the one corner.

When joining the ceramic plate and the metal plate, two sides are positioned using one corner as a reference, and the two opposing corners of the ceramic plate exposed in the dummy portions of the remaining two sides serve as a reference for resist printing during etching.
In addition, for the dummy portion (other than the product portion) formed on the outer periphery of the ceramic substrate, two sides constituting one corner used for positioning with the metal plate are formed narrower than the other two sides of the dummy portion, which allows the metal plate to overlap more widely in the other wider dummy portion. Therefore, even if the molten brazing material creeps up onto the surface of the metal plate in the wide dummy portion during the joining process, the position is away from the dividing scribe line, and the effect on the product portion can be suppressed.

This manufacturing method includes a metal plate forming process in which the metal plate is cut from a plate material, and in the lamination process, the surface of the cut end of the metal plate on which the burrs are present may be laminated onto the surface of the dummy portion of the ceramic plate.

By overlapping the burrs on the metal plate with the surface of the dummy part, the burrs can block the molten solder during the joining process, preventing it from flowing out of the metal plate.

In this manufacturing method, the plate material is a long material set to the width of the metal plate, and in the metal plate forming process, the plate material is cut to the length of the metal plate by a shear while being intermittently conveyed in the length direction to form the metal plate, and in the lamination process, the cut end of the metal plate on the rear side in the conveying direction in the metal plate forming process is placed on the dummy part, and the surface of the cut end with a burr is overlapped on the surface of the dummy part.

When a plate material is cut by a shear while being conveyed intermittently, the metal plate is cut off on the forward side of the cutting blade in the conveying direction. At this time, the cut end surface of the cut-off metal plate on the rear side in the conveying direction has a rough surface due to a fracture surface caused by the cutting. Furthermore, a burr protruding from the front side of the metal plate is generated by the cutting, and the back side has a droopy surface. Meanwhile, the cut end surface of the plate material after the metal plate is cut off is rubbed by the surface of the cutting blade that is pulled up after cutting the metal plate, resulting in a relatively smooth cut end surface. Furthermore, the front side of the plate material has a droopy surface due to the cutting, and a burr protruding from the back side. However, since it is scraped up by the cutting blade after cutting, the height of the burr is smaller than that of the metal plate.
Therefore, by placing the cut end of the cut-off metal plate on the rear side in the transport direction on a dummy part of the ceramic plate and overlapping the burr on the surface of the dummy part, the burr has a great effect of blocking the molten brazing material during the joining process, effectively preventing it from flowing out of the metal plate.

According to the present invention, even if the brazing material flows into the "dummy portion" and creeps up onto the metal plate surface, the effect on the product can be suppressed, and defects in the product's appearance and etching can be prevented.

1 is a flowchart showing a method for manufacturing an insulating circuit board according to an embodiment of the present invention. 1 is a vertical cross-sectional view showing an example of an insulating circuit board manufactured by a manufacturing method according to an embodiment. 3 is a plan view showing a ceramic plate in the middle of manufacturing the insulating circuit board of FIG. 2. 4 is a plan view showing a state in which a brazing material is formed on the ceramic plate shown in FIG. 3. FIG. FIG. 5 is a perspective view showing a state before a metal plate is laminated on the state shown in FIG. 4 . 6 is a plan view showing a state in which a metal plate is laminated from the state shown in FIG. 5 . FIG. FIG. 7 is a plan view similar to FIG. 6 in which all the dummy portions are set to the same width. FIG. 2 is a schematic diagram showing a state in which a plate material is being cut by a shear. 4 is a cross-sectional view showing both cut ends of a metal plate cut by a shear. FIG. FIG. 4 is a cross-sectional view showing the vicinity of a cut end portion of the metal plates after joining.

Hereinafter, an embodiment of the method for producing an insulating circuit board of the present invention will be described.
The insulating circuit board 1 manufactured by the manufacturing method of this embodiment is, for example, a power module board used in a power supply circuit. As shown in Fig. 2, this insulating circuit board 1 has a rectangular ceramic substrate 2, a circuit layer 3 formed on one surface of the ceramic substrate 2, and a heat dissipation layer 4 formed on the other surface of the ceramic substrate 2. The circuit layer 3 and the heat dissipation layer 4 are smaller in planar shape than the ceramic substrate 2, and the ceramic substrate 2 is exposed to the periphery. For convenience, both the circuit layer 3 and the heat dissipation layer 4 are shown as rectangular in Fig. 2 and other figures, but the planar shapes are not particularly limited.

The ceramic substrate 2 prevents electrical connection between the circuit layer 3 and the heat dissipation layer _{4 ,} and may be made of aluminum nitride (AlN), silicon nitride ( _Si3N4 ), aluminum oxide ( _Al2O3 ), etc., of which silicon nitride is preferred due to its high strength. The thickness of the ceramic substrate 2 is set within the range of 0.2 mm to 1.5 mm.

The circuit layer 3 can be made of aluminum or an aluminum alloy, or copper or a copper alloy, but copper or a copper alloy, which have excellent electrical properties, is preferred. The heat dissipation layer 4 is also made of the same metal material as the circuit layer 3, for example, copper or a copper alloy. The circuit layer 3 and heat dissipation layer 4 are formed, for example, by brazing a copper plate made of oxygen-free copper with a purity of 99.96% by mass or more to the ceramic substrate 2 with an active metal brazing material (for example, a brazing material made of Ag-Ti or Ag-Cu-Ti). The thickness of the circuit layer 3 and heat dissipation layer 4 is set within the range of 0.1 mm to 5 mm.

A method for manufacturing the insulating circuit board 1 thus configured will be described.
1, the insulating circuit board 1 is manufactured through a ceramic plate forming step S1, a metal plate forming step S2, a lamination step S3, a joining step S4, an etching step S5, and a division step S6. The order of the ceramic plate forming step S1 and the metal plate forming step S2 does not matter, and either may be performed first, or they may be performed simultaneously.
The steps will be described below in order of the steps. The circuit layer 3 and the heat dissipation layer 4 are formed through a metal plate forming step S2, a lamination step S3, a bonding step S4, and an etching step S5, except that the etching shapes in the etching step are different, and the insulating circuit board 1 having the circuit layer 3 and the heat dissipation layer 4 is formed through a final dividing step S6. In the following, when the same processing content is applied to the circuit layer 3 and the heat dissipation layer 4, the circuit layer 3 and the heat dissipation layer 4 will be described without any particular distinction between them.

(Ceramic plate forming process: S1)
As shown in FIG. 3 and other figures, a single ceramic plate 11 large enough to form a plurality of ceramic substrates 2 is prepared, and groove-shaped dividing scribe lines (hereinafter simply referred to as scribe lines) 12 are formed on one or both sides of the ceramic plate 11 by laser processing (FIG. 5 and other figures show an example in which the scribe lines 12 are formed on one side). By dividing the ceramic plate 11 along the scribe lines 12, a plurality of ceramic substrates 2 (3×4=12 in the illustrated example) are divided, and dummy portions 13A and 13B having a width of 3 mm to 20 mm are formed on the periphery of the ceramic plate 11, which are not used as products. If the width is less than 3 mm, it becomes difficult to divide the ceramic plate 11 in the subsequent dividing process. If the width exceeds 20 mm, material is wasted, leading to high costs. The inner portion excluding the dummy portions 13A and 13B is the product portion 17 that becomes the product.
In this case, the width of the dummy portion 13A on two sides constituting one corner of the ceramic plate 11 is made different from that of the dummy portion 13B on the other two sides. In the illustrated example, the dummy portion 13A is formed to be narrower than the dummy portion 13B.
In FIG. 3 etc., a notch 16 at the upper right corner of the ceramic plate 11 is provided for identifying the orientation of the ceramic plate 11.

(Metal plate forming process S1)
The metal plate 21 for forming the circuit layer 3 and the heat dissipation layer 4 is large enough to integrally cover the product portion 17 (the portion that will become the ceramic substrate 2) of the ceramic plate 11 defined by the scribe lines 12. 6, the ceramic plate 11 is formed with two sides 22a, 22b aligned with two sides 15a, 15b constituting one corner 14 of the ceramic plate 11. In this state, the other two sides 22a and 22b are formed to a size that protrudes onto the dummy portion 13B.
The metal plate 21 is formed by cutting a long plate material (long material) 31 by a shear 32 while intermittently conveying the plate material 31 in the length direction. 21, and can be used as the metal plate 21 by cutting it to the length of the metal plate 21.

As shown in Fig. 8 , the shear 32 for cutting the plate material 31 has a conveying table 33 for conveying the plate material 31 in the length direction indicated by the arrow M, a plate presser 34 for pressing the plate material 31 on the conveying table 33, an upper blade 35, and a lower blade 36. The lower blade 36 is fixedly provided at the tip of the conveying table 33, and the upper blade 35 moves up and down. In general, the upper blade 35 is formed at a slight inclination angle (shar angle) with respect to the horizontal direction (the direction perpendicular to the paper surface of Fig. 8 ).

Then, the plate material 31 is protruded forward from the cutting position between the upper blade 35 and the lower blade 36 by the length of the metal plate 21, and the upper blade 35 is lowered while the plate material 31 is held down by the plate holder 34, thereby cutting the plate material 31 between the upper blade 35 and the lower blade 36 to form the metal plate 21. After one metal plate 21 has been cut, the plate material 31 is transported a length equivalent to the length of the metal plate 21, and the next metal plate 21 is cut. Thereafter, the metal plates 21 are cut one by one while being transported intermittently in sequence.

When the shear 32 cuts the metal plate 21, burrs 25 are generated on the cut ends 23, 24 on both ends in the conveying direction. In this case, as shown in FIG. 8, at the cut end 23 on the rear side in the conveying direction of the plate material 31 (metal plate 21), a burr 25 protrudes toward the front surface 21a of the metal plate 21 (the direction in which the upper blade 35 is disposed) when it is cut off by the upper blade 35. In addition, the cut end surface has a sag surface 26 on the back surface 21b side, a fracture surface 27 on the side where the burr 25 is protruding (the front surface 21a side), and a relatively smooth shear surface 28 is formed between the sag surface 26 and the fracture surface 27.

After cutting off the metal plate 21, the cut end 24 of the plate material 31 (the cut end 24 on the front side of the conveying direction of the plate material 31 (metal plate 21)) also has a burr 25, a sagging surface 26, a shear surface 28, and a fracture surface 27. However, since the cut is made between the cut end 23 on the rear side of the conveying direction of the metal plate 21, the burr 25 is formed on the back surface 21b of the metal plate 21 opposite the cut end 23, and the sagging surface 26 is formed on the front surface 21a. In addition, when the upper blade 35 of the shear 32 returns to the initial position after cutting the metal plate 21, it comes into contact with the cut end surface of the plate material 31 and moves while scraping it up, so the burr 25 and the fracture surface 27 are smaller than those of the cut end 23 on the rear side of the conveying direction of the metal plate 21. In other words, the burr 25 and the fracture surface 27 are formed larger on the cut end 23 on the rear side of the conveying direction of the metal plate 21, and the burr 25 and the fracture surface 27 are formed smaller on the cut end 24 on the front side of the conveying direction than on the cut end 23 on the rear side.

(Lamination process)
First, as shown in Fig. 4 and Fig. 5, the brazing material 41 is placed on the ceramic plate 11. The brazing material 41 may be either a paste-like material or a foil-like material formed into a rectangular shape. In either case, the brazing material 41 is provided so as to cover the entire area of the product portion 17 defined by the scribe lines 12, except for the dummy portions 13A and 13B of the ceramic plate 11.

5 and 6, the metal plate 21 is placed on the brazing material 41. The metal plate 21 is placed in a state where two sides 22a, 22b of the metal plate 21 are positioned and aligned with two sides 15a, 15b that form one corner 14 of the ceramic plate 11. In this state, the other two sides 22c, 22d of the metal plate 21 are placed on the dummy portion 13B of the ceramic plate 11.
This metal plate 21 is formed with a larger planar area than the product portion 17 of the ceramic plate 11, while the width of the dummy portion 13B of the ceramic plate 11 is formed to be larger than that of the dummy portion 13A. Therefore, when the two sides 22a, 22b are positioned on the two sides 15a, 15b that constitute one corner portion 14 of the ceramic plate 11, the metal plate 21 is positioned in a state in which it protrudes significantly over the dummy portion 13B of the ceramic plate 11 with a protrusion width L1.
In the laminated state shown in FIG. 6, the notch 16 formed in the ceramic plate 11 is exposed.

Also, as explained above, in the metal plate forming process, burrs 25 are generated on the metal plate 21, but in this lamination process, the cut end 24 that was located on the front side in the conveying direction in the metal plate forming process is located on one of the two sides 22a, 22b that are positioned on the two sides 15a, 15b of the ceramic plate 11, and the cut end 23 that was located on the rear side in the conveying direction is arranged so that its burr 25 overlaps the surface of the dummy portion 13B. As a result, the burr 25 on this cut end 23 is arranged facing the surface of the ceramic plate 11 (see FIG. 10 ).
On the other hand, the cut end 24 that was positioned on the front side in the conveying direction in the metal plate forming process has a burr 25 formed in the opposite direction to the protruding direction of the burr 25 of the cut end 23 that is on the rear side in the conveying direction, and the opposite side is formed into a drooping surface 26, so that the drooping surface 26 side is superimposed on the ceramic plate 11 (see Figure 10 ).

(Joining process)
The laminate of the ceramic plate 11 and the metal plate 21 thus laminated via the brazing material 41 is placed in a heating furnace under pressure, heated to a bonding temperature in a vacuum atmosphere, and then cooled to bond the metal plate 21 to the ceramic plate 11. The bonding conditions in this case are, for example, pressing the laminate with a load of 0.03 MPa to 0.25 MPa, heating in a vacuum atmosphere of 10 ⁻⁶ Pa to 10 ⁻³ Pa at a bonding temperature of, for example, 790° C. to 850° C. for 1 minute to 60 minutes.

In this joining process, the brazing material 41 between the ceramic plate 11 and the metal plate 21 melts. Also, because pressure is applied in the stacking direction, the ceramic plate 11 and the metal plate 21 are pushed apart, but at the cut end 23 of the metal plate 21, which is arranged with the burr 25 facing the surface of the dummy portion 13B, the burr 25 can block the outflow of the molten brazing material 41, preventing the brazing material 41 from adhering to the exposed portion of the dummy portion 13B. If the outflow of the brazing material 41 to the exposed portion of the dummy portion 13B can be prevented, the brazing material 41 can also be prevented from creeping up onto the surface of the metal plate 21, preventing the occurrence of brazing stains, etc.

In the unlikely event that the molten brazing material 41 flows over the cut end 23 of the metal plate 21 and onto the exposed portion of the dummy portion 13B, there is a risk that it will creep up along the end face of the metal plate 21 to the surface of the metal plate 21. However, since the dummy portion 13B of the ceramic plate 11 is formed with a sufficiently wide width and the overlap width L1 of the metal plate 21 is also large, even if the brazing material creeps up onto the surface of the metal plate 21, it is prevented from spreading beyond the position of the scribe line 12 on the surface of the metal plate 21 to the product portion 17.

7 shows a case where the dummy portions 13 on all four sides of the ceramic plate 11 have the same width. In this Fig. 7, the same reference numerals are used for the same parts as in Fig. 6. The overall size of the ceramic plate 11 and the metal plate 21 is the same as that shown in Fig. 6.
As shown in Fig. 7, if the dummy portions 13 on all four sides are the same width, when a metal plate 21 of the same size as the metal plate 21 used in Fig. 6 is stacked, the protruding width L2 of the metal plate 21 in the dummy portion 13 becomes smaller than that in the case shown in Fig. 7. When the molten brazing material 41 protrudes into the dummy portion 13 and creeps up onto the surface of the metal plate 21, the brazing material may spread to the product portion, making it impossible to prevent the occurrence of brazing stains.

In the embodiment of FIG. 6, the ceramic plate 11 and metal plate 21 are the same size as in the example of FIG. 7, but the widths of the dummy portions 13A and 13B are different, so that the overlap width L2 of the metal plate 21 in the dummy portion 13B is larger, preventing the effect of solder stains on the product portion 17.

On the other hand, at the other cut end 24 of the metal plate 21, the sides 15a, 15b, 22a, and 22b of the ceramic plate 11 and the metal plate 21 were aligned in the lamination process, but at the time of bonding , the metal plate 21 protrudes slightly from the ceramic plate 11 due to the difference in thermal expansion between the ceramic plate 11 and the metal plate 21, as shown in Fig. 10. Also, at the cut end 24, a sagging surface 26 of the metal plate 21 faces the surface of the ceramic plate 11.
Therefore, excess molten brazing material 41 is stored between the metal plate 21 and the ceramic plate 11, and between the metal plates 21 protruding from the ceramic plate 11. In the portion where the ceramic plate 11 and the metal plate 21 are aligned, even if the molten brazing material 41 flows out onto the side surfaces, it solidifies in a lump shape, and therefore, creeping up onto the surface of the metal plate 21 is prevented.

(Etching step S4)
A resist film is printed on the metal plate 21 using two opposing corners P and Q (see FIG. 6) exposed on the ceramic plate 11 as references, and unnecessary portions of the metal plate 21 are removed by etching. Specifically, the portions of the ceramic plate 11 above the scribe lines 12 are removed along the scribe lines 12 by a predetermined width, and the metal plate 21 that will become the circuit layer 3 is formed into a pattern shape required for the circuit layer 3.
As mentioned above, even if the brazing material 14 creeps up onto the surface of the metal plate 21 in the dummy portion 13B, the metal plate 21 protrudes significantly beyond the scribe line 12, preventing the brazing material 14 from crossing the scribe line 12 and penetrating into the product portion 17. Therefore, a resist film can be reliably formed even near the cut end portion 23 of the metal plate 21, and etching defects are prevented.

(Dividing step)
Ceramic plate 11 is divided along scribe lines 12 exposed in the etching process to form a plurality of insulating circuit boards 1, each having a circuit layer 3 on one surface of ceramic substrate 2 and a heat dissipation layer 4 on the opposite surface. Dummy portions 13A and 13B are discarded.

Insulated circuit board 1 manufactured by this manufacturing method, even if brazing material 41 creeps up onto the surface of metal plate 21 during the joining process, the area is away from dividing scribe line 12, and therefore adhesion of brazing material to metal plate 21 on scribe line 12 is suppressed, and the portion of metal plate 21 to be removed can be accurately etched in the subsequent etching process, preventing etching defects. In addition, because adhesion of brazing material 41 to the surface of product portion 17 of metal plate 21 is suppressed, so-called brazing stains are prevented as a product, and an insulated circuit board 1 with a good appearance can be obtained.

The present invention is not limited to the configuration of the above embodiment, and various changes can be made to the details of the configuration without departing from the spirit of the present invention.
Although the ceramic plate has a size capable of forming a plurality of ceramic substrates, the number of ceramic substrates is not limited. The present invention can be applied to a ceramic plate capable of forming a single ceramic substrate.
Moreover, the metal plate is formed by cutting a plate material of a predetermined width with a shear, but it may be formed by punching with a press.
Furthermore, although the embodiment has been described as a power module substrate, the present invention is applicable to insulating circuit substrates other than power module substrates.

REFERENCE SIGNS LIST 1: Insulated circuit board 2: Ceramic board 3: Circuit layer 4: Heat dissipation layer 11: Ceramic plate 12: Scribe line 13: Dummy portion 14: Corner portion 15a, 15b: Side 16: Notch 17: Product portion 21: Metal plate 21a: Surface 21b: Back surface 22a to 22d: Side 23, 24: Cut end portion 25: Burr 26: Droop surface 27: Fracture surface 28: Shear surface 31: Plate material 32: Shear 33: Transport table 35: Upper blade 36: Lower blade

Claims (3)

A method for manufacturing an insulating circuit board, comprising: a lamination step of laminating a rectangular ceramic plate, on which a dividing scribe line is formed, and a metal plate via a brazing material; a joining step of heating the laminate to melt the brazing material and then cooling to join the ceramic plate and the metal plate; an etching step of etching the metal plate after the joining step to remove unnecessary portions; and a division step of dividing the ceramic plate along the dividing scribe lines after the etching step to form a plurality of insulating circuit boards,
a product portion which will become the insulating circuit board and a dummy portion around the product portion are formed on the ceramic plate by dividing scribe lines, and the dummy portions on two sides constituting one corner are formed to be narrower than the dummy portions on two sides constituting a corner diagonally disposed to the one corner,
a lamination step of laminating a ceramic plate on a substrate by laminating the ceramic plate on a substrate in a state in which the ceramic plate is laminated on a substrate, the lamination step being performed by laminating the ceramic plate on a substrate in a state in which the ceramic plate is laminated ... The method for manufacturing an insulating circuit board according to claim 1, characterized in that it includes a metal plate forming process in which the metal plate is formed by cutting it from a plate material, and in the lamination process, the surface of the cut end of the metal plate on which the burrs are present is laminated onto the surface of the dummy portion of the ceramic plate. 3. The method for manufacturing an insulating circuit board according to claim 2, wherein the plate material is a long material set to a width of the metal plate, and in the metal plate forming process, the plate material is cut to the length of the metal plate by a shear while being intermittently transported in the longitudinal direction to form the metal plate, and in the lamination process, a cut end portion of the metal plate on a rear side in the transport direction in the metal plate forming process is arranged on the dummy portions on two sides that constitute a corner diagonally arranged to one corner, and a surface of the cut end portion having a burr is overlapped on a surface of the dummy portion on two sides that constitute a corner diagonally arranged to one corner.

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