Scraper, screen printing machine using the same, and method for manufacturing ceramic circuit board and semiconductor device using scraper

Abstract

To provide a scraper which is excellent in cost performance and enables uniform printing when paste is printed on a large ceramic substrate, and to provide a screen printing machine using the scraper.SOLUTION: In a scraper for a screen printer that returns paste to the printing start point after printing with a squeegee, both rectangular flat plate portions are bent in the direction of travel at approximately the center of the scraper. The bent angle is 1 to 15°, and by printing active metal paste on a ceramic substrate using a screen printer equipped with the scraper, good bonding with the metal plate is possible. A ceramic circuit board in which a metal plate is bonded to a ceramic substrate, or a semiconductor device using a ceramic circuit board, can be obtained.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments generally relate to a scraper, a screen printing machine using the scraper, and a method for manufacturing a ceramic circuit board and a semiconductor device using the scraper. [Background technology]

[0002] Ceramic circuit boards are used in semiconductor devices equipped with semiconductor elements such as power elements. The ceramic substrate and metal circuit section are bonded to each other via a bonding layer using an active metal brazing material or the like. This improves bonding strength and heat cycle characteristics. As reliability improves, ceramic circuit boards are used in automobiles (including electric vehicles), electric railway vehicles, solar power generation facilities, inverters for industrial machinery, and the like. In semiconductor devices such as power modules, semiconductor elements are mounted on the circuit section. Wire bonding or metal terminals may also be bonded to the semiconductor elements for electrical continuity. In the manufacture of semiconductor devices, semiconductor elements, wire bonding, metal terminals, and the like are bonded to the circuit section.

[0003] As a method for forming a bonding layer for a ceramic circuit board, a method of forming an active metal brazing material into a paste and screen printing it onto a ceramic substrate has been disclosed (Patent Document 1). According to Patent Document 1, an active metal paste is pattern-printed onto a silicon nitride substrate measuring 40 mm × 50 mm × 0.32 mm.

[0004] On the other hand, in order to reduce the manufacturing cost of ceramic substrates, they are being manufactured in larger shapes.Among ceramic substrates, silicon nitride substrates, which have high strength, high toughness, and high heat dissipation properties, have been disclosed in sizes of 220 mm x 220 mm x 0.32 mm (Patent Document 2).

[0005] Furthermore, screen printing is used for pattern printing, and a method has been disclosed for preventing the applied material from spilling out from both ends of a scraper when the scraper is used to smooth out ink placed on the upper surface of a pattern forming member of a screen printing plate (Patent Document 3). According to Patent Document 3, spill-preventing plate-like sections that are inclined inward with respect to the direction of movement are provided on both longitudinal sides of the rectangular flat plate section of the scraper, thereby making effective use of the ink supplied onto the pattern forming member. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2022 / 131273 [Patent Document 2] Patent No. 6399252 [Patent Document 3] Japanese Patent Application Publication No. 6-182967 Summary of the Invention [Problem to be solved by the invention]

[0007] As semiconductor devices become more compact and powerful, ceramic circuit components, which require insulation and heat dissipation properties, are also required to be smaller and have better heat dissipation properties. Among ceramic substrates, silicon nitride substrates combine high strength and high insulation properties, so ceramic circuit substrates are being used to make them thinner. On the other hand, to reduce manufacturing costs, large ceramic substrates are used in manufacturing so that many circuit boards can be produced at once.

[0008] However, because ceramic substrates are sintered bodies of inorganic materials, they are prone to warping and undulations on the surface when they are made thin and large.On the other hand, active metal pastes use large metal particles and require a small amount of organic components to be removed before thermal bonding, making them difficult to print uniformly.

[0009] The embodiments are intended to solve such problems, and relate to a scraper and a screen printer using the same that enable uniform printing with excellent cost performance when printing active metal paste on a large ceramic substrate, as well as a method for manufacturing a ceramic circuit board and a semiconductor device using the scraper. [Means for solving the problem]

[0010] The scraper for a screen printer that returns paste to the printing start point after printing with a squeegee according to an embodiment is a scraper for a screen printer that is characterized in that rectangular flat plate portions on both sides at approximately the center of the scraper are bent in the direction of travel. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is a schematic diagram showing an example of a scraper according to an embodiment. [Figure 2] 5A to 5C are cross-sectional views of a process flow illustrating an example of screen printing by a printing machine according to an embodiment. [Figure 3] FIG. 10 is a schematic diagram illustrating a printing state of the scraper according to the embodiment, as viewed from above. [Figure 4] FIG. 10 is a schematic diagram from above showing the printing state of a scraper of a comparative example. [Figure 5] 1 is a schematic diagram showing an example of a printed ceramic substrate according to an embodiment. [Figure 6] FIG. 1 is a side view showing an example of a ceramic circuit substrate according to an embodiment. [Figure 7] FIG. 1 is a side view showing an example of a semiconductor device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The scraper for a screen printer that returns paste to the printing start point after printing with a squeegee according to an embodiment is a scraper for a screen printer that is characterized in that rectangular flat plate portions on both sides at approximately the center of the scraper are bent in the direction of travel.

[0013] Fig. 1 is a schematic diagram showing an example of a scraper according to an embodiment. In Fig. 1, 1 is a scraper. 2 is a central portion of the scraper. 3 is a rectangular flat plate portion. The rectangular flat plate portion 3 is bent at the central portion 2. The bending angle A here refers to the angle bent from a flat plate perpendicular to the direction of travel of the scraper.

[0014] FIG. 2 is a cross-sectional view showing an example of a printing process using a scraper according to an embodiment. (A) is a cross-sectional view before printing. Paste 5 is placed on a screen 6 with a pattern 7 formed on a frame 8. The paste 5 is positioned in the direction of movement of the squeegee 4. A ceramic substrate 9 is fixed on a printing table 10. The scraper 1 is positioned above and away from the screen stencil. (B) is a cross-sectional view after printing. The pressure on the screen stencil is removed, and the screen returns to the state shown in (A). The paste 5 is printed onto the upper surface of the ceramic substrate 9 by the squeegee 4. The squeegee 4 moves while applying downward pressure, pushing the paste onto the ceramic substrate. The scraper 1 moves in conjunction with the squeegee 4 while remaining in an upward position. (C) shows a state in which the squeegee 4 has moved upward. The scraper 1 moves downward. (D) shows a state in which the scraper has moved in the opposite direction to the printing direction shown in (B), returning the paste on the screen stencil to its position before printing. The squeegee 4 moves while remaining in an upward position. After the state of (D), the scraper 1 moves upward and the squeegee 4 moves downward. The printed ceramic substrate 9 is discharged and a new ceramic substrate 9 is placed on the printing table 10, returning to the state of (A).

[0015] FIG. 3 is a schematic diagram from above showing the printing state of a scraper according to an embodiment. As shown in (a), the scraper moves in the opposite direction of printing to remove paste 5 that did not contribute to printing using the squeegee. At this time, the rectangular flat plate portions 3 on both sides of the scraper are bent in the direction of movement at approximately the center portion 2. This bending allows the paste to be collected at the center portion 2 as the scraper moves. The greater the bending angle A of the rectangular flat plate portions, the easier it is to collect the paste at the center. The angle is 1 to 15°. If the angle is less than 1°, the ability to concentrate at the center is reduced, and the paste may overflow from both ends of the scraper. If the angle is greater than 15°, too much paste may collect at the center portion 2, resulting in uneven printing. Therefore, the angle is preferably 2 to 13°, and more preferably 3 to 11°. Furthermore, as shown in (b), the ends of the rectangular flat plate portions may be bent to form bent portions 11. Since the bent portion 11 prevents the paste from spreading outward, the bent angle A of the central portion 2 can be made smaller for the same amount of paste.

[0016] Figure 4 is a schematic diagram from above showing the printing state of a scraper according to a comparative example. Because the scraper 1 is a flat plate with no bend in the center, the paste 5 moves toward the periphery as it advances, causing the paste to overflow on both sides as printing is repeated. For this reason, compared to Figure 3, if the same amount of paste is used, the paste is more likely to run out in the middle of the print, which can easily cause uneven printing.

[0017] FIG. 5 is a schematic diagram showing an example of a printed ceramic substrate according to an embodiment. An active metal paste 5 is printed on the upper surface of a ceramic substrate 9 using the manufacturing method shown in FIG. 2. The printed active metal paste 5 is dried to remove solvent components. A metal plate is placed in contact with the surface of the dried active metal paste and heated to bond the ceramic substrate and metal plate, thereby obtaining a ceramic circuit substrate. In other words, the metal plate is bonded to the ceramic substrate 9 via a bonding layer 13 made of the active metal paste. In the example shown in FIG. 6, multiple upper metal plates 14 are bonded to the upper surface of the ceramic substrate via multiple bonding layers 13, respectively, to form metal circuits. The embodiment is not limited to the illustrated form; one, two, or four or more metal circuits may be bonded to the ceramic substrate. Also, in the example shown in FIG. 6, a lower metal plate 14 is bonded to the lower surface of the ceramic substrate. The lower metal plate 14 functions as a heat sink rather than a circuit.

[0018] Active metal pastes are more prone to print unevenness than pastes used for ceramic joining. Molybdenum (Mo) pastes used for high-melting-point metal metallization are typically made by adding manganese (Mn) powder to Mo powder and crushing it to reduce particle size and make it uniform. This is to promote reaction with the glass component of the ceramic. Furthermore, because joining is performed at high temperatures of 1400°C or higher, it is possible to increase the organic component content in the paste, which improves printability. The organic component is removed during the high-temperature heating process. In contrast, active metal pastes are typically made by mixing metal components including active metals. This is because active metal joining reacts with ceramics at low temperatures of 900°C or lower, allowing the active metal powder's properties to be fully utilized. Furthermore, because active metal pastes are heated at low temperatures, organic components are difficult to remove, so it is desirable to keep the amount of organic component low. Thus, compared to high-melting-point metal pastes, active metal pastes are more prone to print unevenness due to their large particle size metal components and low organic component content.

[0019] Ceramic circuit boards bond a ceramic substrate and a metal plate with a bonding layer made of paste. The metal plate to be bonded is flat compared to the ceramic substrate, with little surface irregularity. In contrast, the ceramic substrate is a sintered body, so warping and unevenness remain unless polishing or other processes are performed. In addition, differences in warping and unevenness are likely to occur between the ceramic substrates. As a result, the printed surface is not nearly flat, and printing unevenness is likely to occur. Furthermore, the active metal paste used to form the bonding layer must be thick enough to not only bond the ceramic substrate and metal plate, but also to mitigate differences in thermal expansion. For this reason, it is necessary to apply the active metal paste evenly to the ceramic substrate without causing printing unevenness.

[0020] The ceramic substrate 9 is preferably one of a silicon nitride substrate, an aluminum nitride substrate, and an aluminum oxide substrate. An aridil substrate is also a type of aluminum oxide substrate. Aridil is a sintered body composed of 20 to 80% by mass of aluminum oxide and the remainder being zirconium oxide. The three-point bending strength of aluminum nitride substrates and aluminum oxide substrates is approximately 300 to 450 MPa. The strength of an aridil substrate is also approximately 550 MPa. The three-point bending strength of a silicon nitride substrate can be increased to 600 MPa or more, even 700 MPa or more. The thermal conductivity of a silicon nitride substrate can be increased to 50 W / (m·K) or more, even 80 W / (m·K) or more. In particular, in recent years, silicon nitride substrates have been developed that combine both high strength and high thermal conductivity. Because of their high strength, silicon nitride substrates can be made thin, enabling improved heat dissipation. Therefore, the thickness of a silicon nitride substrate is preferably 0.635 mm or less, more preferably 0.3 mm or less. Although there is no particular lower limit for the thickness, it is preferably 0.1 mm or more. This is to ensure the electrical insulation of the silicon nitride substrate. The thickness here refers to the dimension in the direction connecting the upper and lower surfaces of the ceramic substrate. These ceramic substrates may be single-layered or may have a three-dimensional structure such as a multilayer structure. The thickness of the ceramic substrate is not particularly limited. By making the ceramic circuit substrate thinner and the metal circuit thicker, heat dissipation performance is improved.

[0021] The metal plate 14 used for the metal circuit may be copper, copper alloy, aluminum, aluminum alloy, etc. Copper and copper alloy have high electrical conductivity and are excellent for electrical circuits, and also have high thermal conductivity and are excellent for heat dissipation of the mounted semiconductor element.

[0022] Furthermore, the ceramic substrate 9 and the metal plate 14 are preferably bonded via a bonding layer 13. The bonding layer 13 preferably contains at least two selected from the group consisting of silver, copper, titanium, zirconium, hafnium, niobium, tin, indium, zinc, aluminum, silicon, carbon, and magnesium. When the metal circuit is made of copper or a copper alloy, a bonding layer containing Cu (copper) and Ti (titanium) is preferably provided between the ceramic substrate and the circuit. The bonding layer containing Cu and Ti is formed using an active metal brazing material. Ti is an active metal. Examples of active metals other than Ti include Zr (zirconium), Hf (hafnium), and Nb (niobium). Examples of active metal brazing materials include mixtures of Ti, Cu, and Ag (silver). For example, the metal components contain 0.1 to 10% by mass of Ti, 10 to 60% by mass of Cu, and the remainder is Ag. If necessary, 1 to 15 mass % of one or more elements selected from the group consisting of In (indium), Sn (tin), Al (aluminum), Si (silicon), C (carbon), and Mg (magnesium) may be added. In the active metal bonding method using an active metal brazing material, an active metal brazing material paste is printed on the surface of a ceramic substrate, and a metal plate is placed on top of it. This is then heated to 600 to 900°C for bonding. The active metal bonding method can achieve a bonding strength of 50 MPa or more between the ceramic substrate and the metal circuit.

[0023] Furthermore, a metal thin film containing one selected from the group consisting of Ni (nickel), Ag (silver), and Au (gold) as a main component may be provided on the surface of the metal circuit. Examples of such a metal thin film include a plated film and a sputtered film. By providing a metal thin film, corrosion resistance, solder wettability, and the like can be improved.

[0024] Such a ceramic circuit board is suitable for a semiconductor device in which a semiconductor element is mounted on a metal circuit portion via a bonding layer. FIG. 7 shows an example of a semiconductor device. In FIG. 7, 15 denotes a semiconductor device, 12 denotes a ceramic circuit board, 16 denotes a semiconductor element, 17 denotes wire bonding, 18 denotes a lead frame, and 19 denotes a resin mold. In FIG. 7, a semiconductor element 16 is bonded to the circuit portion of the ceramic circuit board 12 via a bonding layer (not shown). Adjacent circuit portions are electrically connected by wire bonding 17. The semiconductor device according to the embodiment is not limited to this structure. For example, multiple semiconductor elements 16 and multiple wire bonding 17 may be provided on the upper metal plate 14. Furthermore, semiconductor elements and wire bonding may be bonded to the lower metal plate 14 as needed. Metal terminals such as lead frames may also be bonded to these circuit boards. Furthermore, solder, brazing filler metal, etc. are used for the bonding layer that bonds the semiconductor element 16. Lead-free solder is preferred. Solder refers to a material with a melting point of 450°C or less. Brazing filler metal refers to a material with a melting point above 450°C. Materials with a melting point above 500°C are called high-temperature brazing filler metals. Examples of high-temperature brazing filler metals include those with Ag as the main component.

[0025] Furthermore, while semiconductor elements are becoming smaller, the amount of heat generated from the chips is increasing. Therefore, improving heat dissipation is becoming increasingly important for ceramic circuit substrates that mount semiconductor elements. Furthermore, to improve the performance of semiconductor devices (semiconductor modules), multiple semiconductor elements can be mounted on ceramic circuit substrates. If even one semiconductor element exceeds its intrinsic temperature, its resistance changes to a negative temperature coefficient. This can lead to thermal runaway, where power flows intensively, instantly destroying the semiconductor device. Therefore, improving the reliability of the connection between the semiconductor element and the circuit is highly effective. Furthermore, semiconductor devices according to the embodiments can be used in PCUs, IGBTs, and IPM modules used in inverters for automobiles (including electric vehicles), electric railcars, industrial machinery, and air conditioners. Regarding automobiles, electric vehicles are becoming increasingly popular. The more reliable the semiconductor device, the greater the safety of the automobile. The same is true for electric railcars, industrial equipment, and other applications.

[0026] Next, a method for manufacturing a ceramic copper circuit board according to an embodiment of the present invention will be described. The manufacturing method of a ceramic circuit board is not particularly limited as long as it has the above-described configuration. Here, an example of a method for obtaining a ceramic circuit board with a high yield will be described. First, a ceramic substrate and a metal plate are prepared. The ceramic substrate is preferably one selected from a silicon nitride substrate, an aluminum nitride substrate, and an aluminum oxide substrate. In particular, considering the heat dissipation properties of the entire circuit board, the ceramic substrate is preferably a silicon nitride substrate with a thermal conductivity of 50 W / (m·K) or more and a three-point bending strength of 600 MPa or more. Furthermore, the metal plate is preferably one selected from copper or a copper alloy. Furthermore, when the circuits on the upper and lower surfaces of the ceramic substrate are electrically connected via through holes, a ceramic substrate with through holes is prepared. When through holes are provided in the ceramic substrate, the through holes may be provided in advance at the molded body stage. Alternatively, the through holes may be provided in the ceramic substrate (ceramic sintered body). The through holes may be provided by laser processing, cutting, or the like. An example of cutting processing is drilling using a drill or the like.

[0027] The ceramic substrate and the copper or copper alloy plate are preferably joined by an active metal joining method. This method uses an active metal brazing material, which is a mixture of an active metal such as Ti and a brazing material metal such as Cu. Examples of active metal brazing materials include a mixture of Ti and Cu, and a mixture of Ti, Ag, and Cu. For example, in the case of a mixture of Ti and Cu, the metal components contain 50% or more by mass of Cu, 4% to 30% by mass of Ti, 5% to 45% by mass of one or two elements selected from Sn and In, and 0% to 2% by mass of C. In the case of a mixture of Ti, Ag, and Cu, the metal components contain 20% to 60% by mass of Ag, 15% to 40% by mass of Cu, 1% to 15% by mass of Ti, and 5% to 25% by mass of one or two elements selected from Sn and In. If necessary, one or more elements selected from the group consisting of Al, Si, and Mg may be added in an amount within the range of 1 to 15 mass %.

[0028] Next, the active metal brazing material is made into a paste. A metal powder with the metal mass ratio to be used in the active metal brazing material paste is prepared. If the metal powder is too fine, it tends to clump and is difficult to disperse uniformly. Furthermore, if it is too coarse, the metal components do not mix well when melted during joining. For this reason, a metal powder with an average particle size of 1 to 5 μm is preferred for the aforementioned composition. If the proportion of metal powder in the paste is too small, the brazing material metal components required for joining will not be obtained when the organic components evaporate due to heating during drying and joining. Furthermore, if the proportion is too large, the paste will not have the viscosity required for printing. For this reason, although the overall specific gravity will vary depending on the active metal brazing material composition, it is preferable for the metal powder to comprise 60 to 95 mass% of the paste.

[0029] The active metal paste is printed onto the ceramic substrate. Printing is performed using a method such as screen printing to ensure uniform thickness. As described above, the ceramic substrate is fixed to the printing table by suction or other means, the active metal paste is placed on the screen, and the active metal paste is printed onto the surface of the ceramic substrate by moving the squeegee. The printing thickness of the active metal paste is preferably 15 to 40 μm. The paste moved by the squeegee is then moved to the printing start position by a scraper. After printing, the ceramic substrate is heated in the air to dry the active metal paste. For ceramic circuit boards with metal circuits on both sides, one side is printed and the paste is dried, and then the other side is printed and the active metal paste is dried in the same way.

[0030] Next, a metal plate is placed on the ceramic substrate on which the active metal paste has been printed and dried. The ceramic substrate on which the metal plate has been placed is heated to 700 to 900°C for copper and copper alloy plates, and 500 to 700°C for aluminum and aluminum alloy plates, to bond them. The heating step is carried out in a vacuum or a non-oxidizing atmosphere as required. When carried out in a vacuum, the temperature is 1×10 -2 The pressure is preferably not more than Pa. Examples of the non-oxidizing atmosphere include a nitrogen atmosphere and an argon atmosphere. By performing heat bonding, the paste functions as a bonding layer.

[0031] If a circuit is already formed on the metal plate, it becomes a ceramic circuit board by bonding. If a metal plate without a circuit is bonded, the circuit is formed by etching or other processes. It is also possible to form a circuit not only on the metal plate but also on the bonding layer by etching.

[0032] A ceramic circuit board can be manufactured by the above-described steps. Next, a step of bonding a semiconductor element or the like to the ceramic circuit board is performed. A bonding layer is provided at the location where the semiconductor element is to be bonded. The bonding layer preferably contains solder or brazing material. The semiconductor element is provided on the bonding layer. Wire bonding is also provided as necessary. The required number of semiconductor elements and wire bonding are provided.

[0033] (Examples 1 to 6, Comparative Examples 1 to 6) Twenty-five of each ceramic substrate shown in Table 1 were prepared. The ceramic substrates were silicon nitride substrates and aluminum nitride substrates. The thermal conductivity of the silicon nitride substrate was 90 W / (m·K) and the three-point bending strength was 650 MPa. The thermal conductivity of the aluminum nitride substrate was 170 W / (m·K) and the three-point bending strength was 300 MPa. The ceramic substrates measured 100 mm long and 100 mm wide. The silicon nitride substrates were 0.32 mm thick, and the aluminum nitride substrates were 0.635 mm thick. In Table 1, silicon nitride substrates are abbreviated as Si3N4 and aluminum nitride substrates as AlN.

[0034] Next, metal powders were prepared, which are the metal components of the paste shown in Table 1. The metal powders were silver-based powder (Ag-Cu-Sn-Ti) and copper-based powder (Cu-Sn-TiH2). The ratios of the silver-based powder in the metal components were 58% by mass of Ag, 30% by mass of Cu, 10% by mass of Sn, and 2% by mass of Ti. The ratios of the copper-based powder were 68% by mass of Cu, 20% by mass of Sn, and 12% by mass of TiH2. The average particle sizes of the respective metal powders were 2 μm for Ag, 1 μm for Cu, 5 μm for Sn, 5 μm for Ti, and 26 μm for TiH. Next, 20% by mass of a binder prepared by dissolving organic components in a solvent was added to 100% by mass of the metal powder and kneaded to prepare an active metal paste.

[0035] Active metal paste was printed onto ceramic substrates. A 320mm x 320mm screen with a 200μm mesh size and 10 vertical and 10 horizontal rows of square circuits (100 total) was used. 25g of each active metal paste was weighed out and placed on the screen at two locations on the screen: the center of the squeegee and the center of both ends, i.e., approximately one-quarter of the distance from the edge of the squeegee. The squeegee was then moved to print the active metal paste onto one side of the ceramic substrate, and the scraper was moved to return the paste to its original position. After 25 prints, the surfaces of the active metal paste were visually inspected for unevenness. A complete print pattern was marked with a 'Good' in Table 1, indicating no unevenness. Missing areas were marked with an 'X' in Table 1, indicating unevenness. After printing, the ceramic substrates were washed in an organic solvent to remove the active metal paste, then dried and used under different printing conditions.

[0036] [Table 1]

[0037] In Examples 1 to 6, no printing unevenness occurred. This was because the bent portion formed on the scraper allowed the active metal paste to be properly returned to the specified position without spreading to the surrounding area. In contrast, in Comparative Examples 1, 3, and 5, which used a scraper with a 0-degree angle and no bent portion, there were unprinted areas, mainly on the far side of the center row in the direction of travel, resulting in printing unevenness. This was because the active metal paste overflowed from both ends of the scraper, preventing the active metal paste required for printing the center row from being obtained. In addition, in Comparative Examples 2, 4, and 6, which used a scraper with a 21-degree scraper angle, there were unprinted areas, mainly on the far side of both end rows in the direction of travel, resulting in printing unevenness. This was because the bent angle of the scraper was too large, causing a large amount of active metal paste to gather in the center, preventing the active metal paste required for printing the end rows from being obtained.

[0038] Following the test for evaluating the print unevenness described above, one ceramic substrate of the same type was printed on each of Examples 1, 3, and 5 and Comparative Examples 1, 3, 5 to 6. After printing on one side, the paste was dried by heating at 120°C in air for 1 minute, and then the other side was printed and dried in the same manner. For these ceramic substrates, which had been printed and dried on both sides, as in the print unevenness test described above, no print unevenness occurred on both sides in the Examples, but print unevenness occurred on both sides in the Comparative Examples.

[0039] Next, oxygen-free copper plates measuring 100 mm long x 100 mm wide x 0.8 mm thick were placed on both sides of the ceramic substrate on which the paste had been printed and dried, and thermal bonding was performed. The bonding temperature was 820°C for the silver-based paste (Ag-Cu-Sn-Ti) and 600°C for the copper-based paste (Cu-Sn-TiH2). The bonding time for each was set to 10 minutes, and the bonding was performed in a vacuum (1 x 10 -2 The bonding was performed at a temperature of 100 Pa or less.

[0040] Next, the ceramic substrate bonded with the oxygen-free copper plate was etched to form metal circuits in 100 locations on each side of the ceramic substrate. Visual inspection of the bonded state of the metal circuits revealed a good bond in the Examples. This was because a good bonding layer was formed without uneven printing of the active metal paste. In contrast, in the Comparative Examples, unbonded areas were observed where printing unevenness occurred. This was because the active metal paste required to form the bonding layer could not be obtained due to the uneven printing.

[0041] Next, to confirm the bonding strength between the metal circuit and the ceramic substrate using the paste according to the examples, the peel strength was measured as the bonding strength between the metal circuit and the ceramic substrate. The peel strength was measured by fixing the ceramic circuit substrate to a jig and peeling off a portion of the upper surface metal circuit in the vertical direction at 50 mm / min. The peel strengths were 31 KN / m for Example 1, 29 KN / m for Example 3, 19 KN / m for Example 5, and 18 KN / m for Example 6, which were good strengths. This is because a strong bonding layer was formed between the metal plate and the ceramic due to the absence of unevenness in the printing of the active metal paste.

[0042] As described above, the ceramic circuit board according to the embodiment has few bonding defects and high bonding strength, and is therefore ideal for semiconductor devices equipped with semiconductor elements.

[0043] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other. [Explanation of symbols]

[0044] 1. Scraper 2...Central part 3…Rectangular flat plate part 4...Squeegee 5... Active metal paste 6...Screen version 7...Printing pattern 8...Frame 9...Ceramic substrate 10…Print stand 11...Bend 12...Ceramic circuit board 13...Joining layer 14...Metal circuit 15...Semiconductor device 16...Semiconductor element 17...Wire bonding 18...Lead frame 19...Resin mold

Claims

1. A method for manufacturing a ceramic circuit board in which a ceramic substrate and a metal circuit are bonded together using a paste printed by a screen printing machine in which the paste is returned to the printing start point by a scraper, The rectangular flat plate portions on both sides are bent in the direction of travel of the scraper at approximately the center of the scraper, The bending angle of the rectangular flat plate portions on both sides is 1° or more and 6° or less, A method for manufacturing a ceramic circuit board, wherein both ends of the rectangular flat plate portion are bent so as to be approximately parallel to the direction of travel of the scraper.

2. 2. The method for manufacturing a ceramic circuit board according to claim 1, wherein the size of the ceramic substrate on which the paste is printed is 100 mm x 100 mm or more.

3. 3. The method for manufacturing a ceramic circuit substrate according to claim 1, wherein the metal components of the paste contain 50% by mass or more of copper, 4% by mass or more and 30% by mass or less of an active metal element, 5% by mass or more and 45% by mass or less of one or two elements selected from tin and indium, and 0% by mass or more and 2% by mass or less of carbon.

4. 3. The method for manufacturing a ceramic circuit substrate according to claim 1 or 2, characterized in that the metal components of the paste contain 20% by mass or more and 60% by mass or less of silver, 15% by mass or more and 40% by mass or less of copper, 1% by mass or more and 15% by mass or less of an active metal element, and 5% by mass or more and 25% by mass or less of one or two types selected from tin and indium.

5. 3. The method for manufacturing a ceramic circuit board according to claim 1, wherein the ceramic substrate is one of an aluminum oxide substrate, an aluminum nitride substrate, and a silicon nitride substrate.

6. 3. The method for manufacturing a ceramic circuit board according to claim 1, wherein the metal circuit is made of one of copper, a copper alloy, aluminum, and an aluminum alloy.

7. 3. A method for manufacturing a semiconductor device, comprising: a step of manufacturing the ceramic circuit board according to claim 1; and a step of mounting a semiconductor element on the metal circuit via a bonding layer.

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