JP4862196B2 - Method for manufacturing metal ceramic circuit board - Google Patents

Description

  The present invention relates to an excellent metal ceramic circuit board and a manufacturing method thereof, and more particularly to a metal ceramic circuit board excellent in heat cycle resistance suitable for mounting a high power electronic component such as a power module and a manufacturing method thereof.

  In recent years, power modules have been used for large current control of electric vehicles, trains, machine tools, and the like. Since a plurality of semiconductor chips are mainly mounted on the power module and a large current is taken out from the front and back surfaces thereof, the substrate on which the semiconductor chips are fixed is required to have high electrical insulation. Further, in order to control a large current, the temperature of the semiconductor chip during actual operation rises due to heat generation. For this reason, high heat dissipation is requested | required of the whole board | substrate including the base material which fixed this semiconductor chip, and its peripheral material.

  A cross-sectional structure of a conventional power module is shown in FIG. In a conventional power module, a semiconductor chip 1 is fixed to a metal layer 3 on a ceramic substrate 2 as an insulating base material with solder 4, and the ceramic substrate 2 is further bonded to a metal base with solder 6 via the other metal layer 5. It is fixed to the plate 7. Reference numeral 8 denotes a plating layer formed on the metal layers 3 and 5 and the metal base plate 7. In FIG. 5, the display of the wiring between the chips is omitted.

  Prior art techniques for joining aluminum to a ceramic substrate include those disclosed in Japanese Utility Model Publication No. 1-1118588 and Japanese Utility Model Application Publication No.2-68448. Bonding is performed using a -Si or Al-Ge brazing material. This further includes the use of silicon as an aluminum bonding aid in 1976 US Pat. No. 3,994,430.

  However, such a conventional power module has the following problems because the ceramic substrate 2 is fixed to the metal base plate 7 via the metal layer 5 and the solder 6.

  (1) The space between the ceramic substrate 2 and the metal base plate 7 has a complicated structure such as a ceramic substrate 2 -metal layer 5, -plating layer 8 -solder 6 -plating layer 8 -metal base plate 7, and chip When the energization and the energization stop are repeated in FIG. 1, each material is repeatedly cooled, and a problem such as a crack occurring on the joint surface of each material is likely to occur due to the difference in thermal expansion and contraction of each material.

  (2) The presence of the solder 6 between the ceramic substrate 2 and the metal base plate 7 reduces the thermal conductivity and the heat dissipation.

  (3) In recent years, there are many cases where electric manufacturers use lead solder which is trying to reduce the use as much as possible.

  (4) Since the ceramic substrate 2 and the metal base plate 7 are bonded together with the solder 6, many processes such as surface treatment such as plating and soldering for improving the solder wettability are required and the cost is high.

  (5) The copper base plate used as a metal base plate that has been used in the past has a large coefficient of thermal expansion compared to ceramics, and cracks are likely to occur in the ceramic at the joint surface with the copper base plate when it is repeatedly cooled and heated. Chips, base plates such as copper / molybdenum alloys, aluminum / silicon carbide composite materials have problems such as low thermal conductivity and high price.

  Accordingly, an object of the present invention is to solve the above-described problems. Specifically, the present invention is a variety of materials having excellent characteristics in which an aluminum or aluminum base plate is directly bonded to a ceramic substrate. The object is to obtain various shapes of ceramic-metal composite members and a method for mass-producing them at low cost.

  As a result of diligent research, the present inventors have used aluminum or an aluminum alloy as a material for the base plate, and this is brought into contact with the ceramic from the state of the molten metal in the mold and cooled, so that the proof stress is below a predetermined value, It has been found that the above-mentioned problems can be solved if aluminum or an aluminum alloy having a thickness equal to or greater than a predetermined value is bonded to ceramics.

  That is, when ceramics are joined to the base plate, a hard metal is used as the base plate without using a soldering method having a low joining temperature, or when the base plate and the ceramic are joined to each other, brazing of the ceramic may occur. The trouble that a board warps greatly occurs. On the other hand, as a result of intensive studies by the present inventors, it has been found that the above-mentioned problems can be prevented by directly joining aluminum or aluminum alloy having a low yield strength directly to ceramics without using a brazing material. Although the details of this mechanism are unknown, the present inventor believes that aluminum and aluminum alloys with low proof stress relax the residual stress at the time of joining caused by the difference in thermal expansion coefficient with ceramics by their own plastic deformation and the like. Et al.

  The present invention has been made based on such knowledge.

Method for producing a metal-ceramic circuit board of the present invention includes the steps in which to place the aluminum or aluminum alloy in the crucible, placing a ceramic substrate at the bottom of the crucible, within the crucible in a vacuum or inert gas atmosphere A step of melting the aluminum or aluminum alloy to obtain a melt, a step of pouring the melt onto the ceramic substrate via a thin tube and bringing it into contact with one surface of the ceramic substrate, and the melt characterized by having a step of forming a base plate of the direct bonding aluminum or aluminum alloy to said one surface of said ceramic substrate is cooled and the ceramic substrate.

    In addition, the method for manufacturing a metal ceramic circuit board according to the present invention includes a step of joining the metal conductor for electronic circuit to the other surface of the ceramic substrate using a brazing material.

  The metal conductor is selected from at least one of copper, copper alloy, aluminum, and aluminum alloy. Aluminum or an aluminum alloy can be used as the base plate. Aluminum is particularly excellent because it has high thermal conductivity, good heat cycle resistance, a low melting point, and is easy to manufacture.

  The reason for selecting each metal is that copper and a copper alloy are suitable when high conductivity is required or when the heat cycle resistance is 1000 times or less.

  Aluminum and aluminum alloys are suitable when heat cycle resistance of 3000 times or more is required.

  In addition, Au plating, Ni plating, or the like can be performed on these to improve solder wettability and corrosion resistance.

  The ceramic substrate is a kind selected from alumina, aluminum nitride, and silicon nitride.

  Among ceramics, alumina is particularly high in insulation and inexpensive, and is highly versatile, such as being able to manufacture copper circuits by direct bonding. Aluminum nitride has excellent heat dissipation due to its high thermal conductivity, and can be used for large current control. A chip can be mounted, and since silicon nitride has high strength, it has high heat cycle resistance and excellent compatibility in harsh environments such as engine rooms.

  The base plate is intended to reinforce the mechanical strength of the module and to dissipate heat. Further, the direct bonding means that a bonding state having a strength as required is obtained without interposing a bonding aid such as a brazing material.

  According to the present invention, the following advantages can be obtained.

  (1) The ceramic substrate and the base plate have a simple structure between the ceramic substrate and the base plate, and the reliability when repeated cooling is greatly improved. In particular, aluminum or an aluminum alloy was selected as the base plate material, and this was joined directly, so that the softness of the aluminum itself eliminated the irregularity of thermal expansion and contraction with the ceramics during cold, and at the joining interface. This is to prevent the occurrence of cracks.

  (2) Since the ceramic substrate and the base plate have a simple structure between the ceramic substrate and the base plate, and a solder layer having a low thermal conductivity can be eliminated, a high thermal conductivity can be obtained.

  (3) Since the ceramic substrate and the base plate have a simple structure between the ceramic substrate and the base plate, it is no longer necessary to join with solder, so there is no need for surface treatment such as plating or soldering to improve solderability, Cost decreases.

  (4) Although copper conventionally used as a base plate is inexpensive, it has a large thermal expansion coefficient with respect to ceramics, and when it is repeatedly cooled, it tends to crack on the joint surface with ceramics and lacks reliability. Copper / molybdenum alloys and aluminum / silicon carbide composite materials have low thermal conductivity and high prices. On the other hand, aluminum is cheaper and has a higher thermal expansion coefficient than copper, but its proof stress is extremely small. Therefore, it is difficult to cause cracks at the interface with ceramics even when it is repeatedly cooled, and a highly reliable product can be produced.

  (5) As a base plate, a method of manufacturing a circuit board in which aluminum, aluminum alloy, copper, copper / molybdenum alloy, aluminum / silicon carbide composite material or the like is brazed to ceramics using a brazing material can be considered. Due to the difference in thermal shrinkage between the metal and ceramic after bonding, the base plate is very thick relative to the thickness, and a low-flexibility adhesive layer is generated between the base plate and ceramic due to the brazing material. The substrate is greatly warped, and cracks are easily generated in the ceramics. In contrast, in the method of directly joining aluminum or an aluminum alloy as the base plate of the present invention, the joining portion is made of aluminum and very flexible, the proof stress of the base plate is 320 (MPa) or less, and the thickness is Since it is 1 mm or more, conventional defects can be eliminated.

  (6) It is particularly preferable as a high-power power module substrate such as an electric vehicle or a train because it has high reliability, which is difficult to obtain using a conventional substrate, has a high manufacturing yield, and has high cost merit.

  (7) Since the heat treatment is performed in vacuum or in an inert gas, the material is prevented from being oxidized and the bonding is improved. The furnace temperature may be 550 ° C to 850 ° C.

  Embodiments of a metal ceramic substrate and a manufacturing method thereof according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a principle diagram of equipment for manufacturing a metal ceramic circuit board of the present invention. In the present invention, aluminum having a purity of 99.9% is set on the upper part of the crucible 9, and the ceramic substrate 2 of aluminum nitride to be joined is set on the lower part of the crucible 9. The crucible 9 is covered with the piston 10 and the crucible 9 is filled with nitrogen gas. Next, the crucible 9 is heated to 750 ° C. by the heater 11 to melt aluminum, and then the aluminum melt 13 is extruded by the piston 10 through the thin tube 12 at the center of the crucible 9, and the extruded aluminum melt 13 is the ceramic substrate. The aluminum melt 13 is bonded and solidified to the ceramic substrate 2 and the plurality of aluminum nitride ceramic substrates 2 are directly applied to one surface of the aluminum base plate 7. What was joined was obtained. Here, the thickness of the obtained aluminum base plate was 5 mm, and the proof stress of aluminum was 40 MPa. This proof stress was measured in accordance with JIS Z2241 after preparing a test piece with JIS Z2201.

  Next, in order to form a circuit part on the ceramic substrate 2 made of aluminum nitride, a brazing material having a composition of Al 87.5 wt% / Si 12.5% is printed in a desired pattern shape using a screen printing machine, and the temperature is 80 ° C. After drying, the aluminum layered plate having a desired pattern shape is placed thereon as the metal layer 3 and heated at 575 ° C. in a vacuum furnace, followed by electroless nickel plating, and a brazing material on the metal layer 3. The semiconductor chip 1 was fixed via the solder 4, and the module shown in FIG. 2 was comprised.

  When the heat cycle resistance of this module was examined, no change was observed at the ceramic-base plate interface even after 4000 heat cycles.

  A power module having a metal ceramic circuit board having the shape shown in FIG. 2 was formed by the same means as in Example 1 except that the thickness of the aluminum base plate 7 was changed from 5 mm to 1 mm. Further, when the heat cycle tolerance was examined, no change was observed at the ceramic-base plate interface even after 4000 heat cycles as in Example 1.

  A power module having a metal ceramic circuit board having the shape shown in FIG. 2 was formed by the same means as in Example 1 except that the thickness of the aluminum base plate 7 was changed from 5 mm to 10 mm. Further, when the heat cycle resistance was examined, no change was observed at the ceramic-base plate interface even after 3000 heat cycles as in Example 1.

  A power module having a metal ceramic circuit board having the shape shown in FIG. 2 was formed by the same means as in Example 1 except that the thickness of the aluminum base plate 7 was changed from 5 mm to 30 mm. Further, when the heat cycle resistance was examined, no change was observed at the ceramic-base plate interface even after 3000 heat cycles as in Example 1.

  The base plate 7 has a metal ceramic circuit board of the form shown in FIG. 2 in the same manner as in Example 1 except that the material of the base plate 7 is changed from aluminum of purity 99.99% to aluminum alloy of Al 95.5% and Cu 4.5%. A power module was formed. Here, the thickness of the base plate 7 was 5 mm, and the proof stress was 95 MPa. Further, when the heat cycle resistance was examined, no change was observed at the ceramic-base plate interface even after 3000 heat cycles as in Example 1.

  The base plate 7 has a metal ceramic circuit board of the form shown in FIG. 2 in the same manner as in Example 1 except that the material of the base plate 7 is changed from aluminum of purity 99.99% to aluminum alloy of Al 87.5% and Si 12.5%. A power module was formed. Here, the thickness of the base plate 7 was 5 mm, and the proof stress was 320 MPa. Further, when the heat cycle resistance was examined, no change was observed at the ceramic-base plate interface even after 3000 heat cycles as in Example 1.

  A power module having a base-integrated ceramic substrate as shown in FIG. 2 was formed by the same means as in Example 1 except that silicon nitride was used as the ceramic substrate 2 instead of aluminum nitride. Further, when the heat cycle tolerance was examined, no change was observed at the ceramic-base plate interface even after 4000 heat cycles as in Example 1.

  The shape of the base plate 7 is a plate having a thickness of 5 mm. In addition to this plate, a metal ceramic circuit board having the shape shown in FIG. A power module was formed. Further, when the heat cycle tolerance was examined, no change was observed at the ceramic-base plate interface even after 4000 heat cycles as in Example 1.

  In order to form a circuit part on the ceramic substrate 2 made of aluminum nitride, an active metal brazing material having a composition of Ag 90 wt% / Ti 5% / Cu 5% is printed using a screen printer, dried at 80 ° C., and then a metal layer thereon. A copper rolled plate was placed as No. 3, heated at 800 ° C. in a vacuum furnace, and bonded to the ceramic substrate 2. Next, an etching resist is printed on the copper portion with a screen printer, and after UV drying, etching is performed with a ferric chloride solution to form a desired pattern 14, which is then crucible as shown in FIG. Set the lower surface of the ceramic substrate 2 so that the lower surface of the ceramic substrate 2 is on the top, set 99.9% pure aluminum on the top of the crucible 9, cover the crucible 9 with the piston 10, and put nitrogen gas inside the crucible 9. Fill. Next, the crucible 9 is heated to 750 ° C. by the heater 11 to melt aluminum, and then the aluminum melt 13 is extruded by the piston 10 through the thin tube 12 at the center of the crucible 9, and the extruded aluminum melt 13 is the ceramic substrate. The aluminum melt 13 is bonded and solidified to the ceramic substrate 2 to form a base plate 7, and a semiconductor is formed on the metal layer 3 via the solder 4. The chip 1 was fixed and the module shown in FIG. 2 was configured. Here, the thickness of the obtained aluminum base plate was 5 mm, and the proof stress of aluminum was 40 MPa.

  When the heat cycle resistance of this base-integrated ceramic substrate was examined, no change was observed at the ceramic-base plate interface even after 4000 heat cycles as in Example 1.

  After directly joining a plurality of aluminum nitride ceramic substrates 2 to the aluminum base plate 7 by the same means as in Example 1, using a crucible 15 as shown in FIG. The aluminum nitride ceramic substrate 2 directly bonded to the base plate 7 is set on the upper side, and the aluminum base plate 7 is set on the lower side. Further, a mold 18 in which a desired circuit pattern shape is cut out is placed on the aluminum nitride ceramic substrate 2. The crucible 15 is covered with the piston 10 and the crucible 15 is filled with nitrogen gas. Next, the crucible 15 is heated to 750 ° C. by the heater 11 to melt aluminum, and then the aluminum melt is formed on the mold 18 of each pattern from the thin tube 16 at the center of the crucible 15 by the piston 10 through the thin tubes 17a to 17c. Extrude 13 At this time, in order to protect the base plate 7 from heat, a heat sink 19 is disposed below the base plate 7 to cool it. The extruded aluminum melt 13 flows into a mold 18 on an aluminum nitride ceramic substrate 2 and is filled to a predetermined height, and is gradually cooled to solidify the aluminum melt 13 while adhering to the ceramic substrate 2. The metal layer 3 was formed on the ceramic substrate 2 by the above method, and the semiconductor chip 1 was fixed on the metal layer 3 via the solder 4 to constitute the power module shown in FIG. Here, the thickness of the obtained aluminum base plate was 5 mm, and the proof stress of aluminum was 40 MPa.

  When the heat cycle resistance of this power module was examined, no change was observed at the ceramic-base plate interface even after 4000 heat cycles as in Example 1.

  (Comparative Example 1)

  The following samples were made for comparison purposes. First, in order to form a circuit part on one side of an aluminum nitride ceramic substrate, a brazing material with a composition of Al 87.5 wt% and Si 12.5% is printed in a desired pattern shape using a screen printer and dried at 80 ° C. After that, a rolled aluminum plate having a desired pattern shape was placed thereon, the same brazing material was printed on the other side on the other side, the same aluminum rolling plate was placed on the other side, and heated at 575 ° C. in a vacuum furnace. . Next, this substrate was subjected to electroless nickel plating, and the three substrates obtained here were soldered and fixed onto an aluminum base plate subjected to electroless nickel plating. Further, a semiconductor chip was provided thereon to constitute a module having the shape shown in FIG. When the heat cycle resistance was examined as in the example, cracks were found in the solder layer at the ceramic-base plate interface after 1000 heat cycles.

  (Comparative Example 2)

  The following samples were made for comparison purposes. A copper / molybdenum alloy having a thickness of 5 mm was used for the base plate instead of the aluminum base plate, and a module having the shape shown in FIG. When heat cycle resistance was examined as in the example, cracks were found in the solder layer at the ceramic-base plate interface after 3000 heat cycles.

  (Comparative Example 3)

  The following samples were made for comparison purposes. A solid aluminum layer was formed in such a manner that a molten aluminum as shown in Example 1 was brought into direct contact with both surfaces of an aluminum nitride ceramic substrate and cooled and solidified. Next, in order to form a circuit part on one side, an etching resist was printed by a screen printer, UV-dried, and then etched with a ferric chloride solution to form a circuit with a desired pattern. Next, electroless nickel plating was applied to the substrate, and the three substrates obtained here were soldered and fixed onto an aluminum base plate having a thickness of 5 mm and a purity of 99.99%, which had been subjected to electroless nickel plating. Further, a semiconductor chip was provided thereon to constitute a module having the shape shown in FIG. When heat cycle resistance was examined as in the example, cracks were found in the solder layer at the ceramic-base plate interface after 3000 heat cycles.

  (Comparative Example 4)

  The following samples were made for comparison purposes. In order to join three aluminum nitride ceramics substrates on an aluminum base plate with a thickness of 5mm and a purity of 99.99%, using a screen printer on the base plate, the composition of Al87.5wt% / Si12.5% The brazing material was printed and dried at 80 ° C., and then a ceramic substrate made of aluminum nitride was placed thereon and heated at 575 ° C. in a vacuum furnace. Further, after this, an attempt was made to form a circuit on the opposite side of the base plate by the same brazing method, but when the base plate was joined, the ceramic substrates were all broken together.

  (Comparative Example 5)

  The following samples were made for comparison purposes. An attempt was made to form a power module having a metal ceramic circuit board of the form shown in FIG. 2 by the same means as in Example 1 except that the thickness of the aluminum base plate 7 in Example 1 was changed from 5 mm to 0.5 mm. It was. However, the strength of the base plate was insufficient, and the base plate was easily deformed.

  (Comparative Example 6)

  The following samples were made for comparison purposes. The material of the base plate 7 in Example 1 is changed from aluminum of purity 99.99% to aluminum alloy of Al88%, Cu2%, Mg3%, Zn7%, in the form shown in FIG. An attempt was made to form a module having a metal ceramic circuit board. Here, the thickness of the base plate 7 was 5 mm, and the proof stress was 540 MPa. However, at the time of joining with the base plate, the ceramic substrate all broke along.

  The results are shown in Table 1.

It is a principle figure of the joining apparatus of the base board used for implementing this invention method, and a ceramic board. It is a longitudinal cross-sectional view of the power module obtained by the method of this invention. It is another Example explanatory drawing of the apparatus for forming a circuit part with what joined the ceramic board to the base board by the method of this invention. It is further another Example explanatory drawing of the joining apparatus of the base board used for implementing this invention method, and a ceramic board. It is a longitudinal cross-sectional view of the conventional power module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor chip 2 Ceramic substrate 3 Metal layer 4 Solder 5 Metal layer 6 Solder 7 Base plate 8 Plating layer 9 Crucible 10 Piston 11 Heater 12 Narrow tube 13 Aluminum melt 14 Pattern 15 Crucible 16 Narrow tube 17a Narrow tube 17b Narrow tube 17c Narrow tube 18 Type 19 Heat sink

Claims (4)

A step in which to place the aluminum or aluminum alloy in the crucible,
Placing a ceramic substrate below the crucible;
Making the inside of the crucible a vacuum or an inert gas atmosphere;
Dissolving the aluminum or aluminum alloy to obtain a melt;
A step of pouring the melt onto the ceramic substrate through a narrow tube and bringing it into contact with one surface of the ceramic substrate; and cooling the melt and the ceramic substrate and directly bonding the aluminum to the one surface of the ceramic substrate Alternatively, a method of manufacturing a metal ceramic circuit board comprising a step of forming a base plate of an aluminum alloy. 2. The method of manufacturing a metal ceramic circuit board according to claim 1, further comprising the step of joining the metal conductor for electronic circuit to the other surface of the ceramic board using a brazing material. The ceramic substrate is alumina, aluminum nitride, claim 1 or 2 metal-ceramic circuit substrate manufacturing method according to said kind der Rukoto selected from silicon nitride. Claim 2 or 3 metal-ceramic circuit substrate manufacturing method according to said Rukoto selected from at least one or more of the above metal conductor of copper, copper alloy, aluminum, an aluminum alloy.

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