Resist drying apparatus and method of manufacturing ceramic circuit board using the same

Abstract

To provide an etching resist drying device and a ceramic circuit board capable of drying with high quality and excellent cost performance when drying an etching resist printed on a large-sized ceramic metal bonded substrate.SOLUTION: In the preliminary drying, heating is performed at a maximum temperature H1 of 80 °C or more and 150 °C or less and a time T1 of 80 °C or more of 3 minutes or more and 10 minutes or less in a drying part 14 of the preliminary drying oven, and in the main drying, heating is performed at a maximum temperature of 80 °C or more and 150 °C or less and a time of 80 °C or more of 60 minutes or more and 120 minutes or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The embodiments generally relate to a resist drying device and a method for manufacturing a ceramic circuit board using the same. [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 are bonded to each other via a bonding layer using an active metal brazing material or the like, improving bonding strength and heat cycle characteristics. As reliability has improved, ceramic circuit boards are used in automobiles (including electric vehicles), electric railway vehicles, solar power generation facilities, and inverters for industrial machinery, and in semiconductor devices such as power modules, semiconductor elements are mounted on metal circuits. Wire bonding and metal terminals may also be bonded to ensure electrical continuity of the semiconductor elements. In the manufacture of semiconductor devices, semiconductor elements, wire bonding, metal terminals, and the like are bonded to metal circuits.

[0003] In order to reduce the manufacturing cost of ceramic substrates, a method for manufacturing them in larger shapes has been disclosed (Patent Document 1).Patent Document 1 discloses a silicon nitride substrate measuring 220 mm x 220 mm x 0.32 mm, which is a ceramic substrate that has high strength, high toughness, and high heat dissipation properties.

[0004] Also, a method for forming a pattern on a copper plate-bonded ceramic substrate has been disclosed (Patent Document 2). According to Patent Document 2, a pattern circuit can be formed by a process of forming a brazing material by screen printing and a process of forming a pattern on a copper plate using an etching resist and etching it.

[0005] Furthermore, a heat curing method for ceramic circuit board materials has been disclosed in which a post-bake process is carried out after the resist is dried and cured (Patent Document 3). According to Patent Document 3, the resist film can be cured by heating at 200°C to 300°C for 5 to 30 minutes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6399252 [Patent Document 2] Japanese Patent Application Publication No. 4-17088 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-984822 Summary of the Invention [Problem to be solved by the invention]

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

[0008] However, because ceramic substrates are sintered bodies of inorganic materials, they are prone to warping and undulation on the surface when they are made thin and large. Furthermore, when a ceramic substrate is bonded to a metal plate, warping and undulation occur on the surface of the metal plate due to the warping of the ceramic substrate and the difference in thermal expansion between the ceramic and the metal, making it difficult to print the etching resist evenly. The etching resist printed to form metal circuits has high viscosity, making it difficult to print evenly on a warped or undulating surface, resulting in uneven printing. This uneven printing can lead to uneven drying depending on the drying conditions, which in turn causes uneven etching and ultimately leads to poor etching.

[0009] The embodiments are intended to solve such problems, and relate to a resist drying device that enables drying with excellent quality and cost performance when printing and drying an etching resist on a ceramic-metal bonded substrate in which a metal plate is bonded to a large ceramic substrate, and a method for manufacturing a ceramic circuit board using the same. [Means for solving the problem]

[0010] The etching resist drying device for ceramic circuit boards according to the embodiment has a mechanism for performing pre-drying and main drying. In the pre-drying, the maximum temperature is 80°C or higher and 150°C or lower, and the time at or above 80°C is 3 minutes or higher and 10 minutes or lower. In the main drying, the maximum temperature is 80°C or higher and 150°C or lower, and the time at or above 80°C is 60 minutes or higher and 120 minutes or lower. [Brief explanation of the drawings]

[0011] [Figure 1] Schematic diagram showing an example of a resist-printed substrate according to an embodiment. [Figure 2] FIG. 1 is a top view illustrating an example of a resist drying apparatus according to an embodiment. [Figure 3] 1 is a schematic diagram showing a cross section of an example of a resist drying apparatus according to an embodiment; [Figure 4] 1 is a schematic diagram illustrating an example of a temperature profile for preliminary drying according to an embodiment; [Figure 5] FIG. 1 is a top view illustrating an example of a resist drying apparatus according to an embodiment. [Figure 6] 1 is a schematic diagram showing a cross section of an example of a resist drying apparatus according to an embodiment; [Figure 7] Schematic diagram showing an example of a resist drying setter according to an embodiment. [Figure 8] 1 is a cross-sectional view showing an example of a process flow of a ceramic circuit board according to an embodiment; [Figure 9] 1 is a cross-sectional view showing an example of a semiconductor device using a ceramic circuit substrate according to an embodiment. [Figure 10] Schematic diagrams showing patterns of ceramic circuit substrates of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0012] The etching resist drying device for ceramic circuit boards according to the embodiment has a mechanism for performing pre-drying and main drying. In the pre-drying, the maximum temperature is 80°C or higher and 150°C or lower, and the time at or above 80°C is 3 minutes or higher and 10 minutes or lower. In the main drying, the maximum temperature is 80°C or higher and 150°C or lower, and the time at or above 80°C is 60 minutes or higher and 120 minutes or lower.

[0013] An etching resist drying device for a ceramic circuit board according to an embodiment will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a resist-printed substrate (hereinafter abbreviated as "resist-printed substrate") in which etching resist is printed on a ceramic-metal bonding substrate. Reference numeral 1 denotes the resist-printed substrate, and 2 denotes the ceramic-metal bonding substrate. The ceramic-metal bonding substrate 2 has metal plates 4 bonded to both sides of a ceramic substrate 3. An etching resist 5 is printed on the surface of the ceramic-metal bonding substrate 2.

[0014] FIG. 2 is a top view showing an example of a resist drying apparatus. 6 denotes a preliminary drying oven, 7 denotes a first drying zone, 8 denotes a second drying zone, 9 denotes a main body including a drive unit (hereinafter abbreviated as "drive unit"), 10 denotes a belt unit, and 11 denotes an exhaust port. FIG. 3 is a schematic diagram showing a cross section XX' when a resist-printed substrate 1 is passed through the preliminary drying oven 6 of FIG. 2. 12 denotes a setter containing the resist-printed substrate 1, 13 denotes the oven entrance, 14 denotes the drying unit, and 15 denotes the oven exit. The setter 12 containing the resist-printed substrate 1 is installed on the belt unit 10, and the resist-printed substrate 1 moves from the oven entrance 13 to the oven exit 15. In FIG. 3, the resist-printed substrate 1 is heated in the drying unit 14 and then removed from the oven exit 15 after heating is completed.

[0015] Figure 4 shows a schematic diagram of an example of a temperature profile for pre-drying according to an embodiment. In Figure 4, the horizontal axis represents time, the vertical axis represents temperature, and the solid line represents the temperature over time in the pre-drying oven. The temperature of the resist-printed substrate 1 placed at the oven inlet 13 rises in the drying section 14 until it reaches a maximum temperature H1, at which point cooling begins near the oven outlet 15. If the time above 80°C is T1, then H1 is between 80°C and 150°C, and T1 is between 3 and 10 minutes.

[0016] Pre-drying requires a maximum temperature of 80°C to 150°C and a time above 80°C of 3 to 10 minutes. The purpose of pre-drying is to remove the solvent components contained in the etching resist. As described below, the etching resist hardens during the main drying process following pre-drying. Therefore, if pre-drying is insufficient, pre-drying and main drying may occur simultaneously during main drying, potentially resulting in insufficient hardening of the etching resist. If the maximum temperature for pre-drying is below 80°C, the solvent in the etching resist may not be sufficiently removed, and the remaining solvent may evaporate during main drying, resulting in defects such as pores. Conversely, if the maximum temperature for pre-drying is above 150°C, only the surface portion may harden, forming a two-layer structure with the layer that hardens during main drying, which may lead to delamination between the two hardened layers. Therefore, a more preferable temperature is between 100°C and 130°C. Furthermore, if the time above 80°C is less than 3 minutes, the solvent in the etching resist may not be sufficiently removed, and the remaining solvent may evaporate during main drying, resulting in defects such as pores. Also, if the drying time exceeds 10 minutes, there is no effect even if it is longer, and if the maximum temperature is too high, only the surface part may harden. Therefore, the more preferable time is between 5 and 8 minutes.

[0017] Figure 5 is a top view of an example of a resist drying device. Reference numeral 16 denotes the main drying oven, 17 denotes the main body, and 18 denotes the front door. The door 18 is opened, the resist-printed substrate 1 is placed in the main body 17, and the door 18 is closed to begin drying. Figure 6 is a schematic diagram showing the XX' cross section of the main drying oven 16 shown in Figure 5, with the setter 12 containing the resist-printed substrate 1 installed. Reference numeral 19 denotes a heater, 20 denotes a circulation fan, and 21 denotes an inner tank. Air heated by the heater 19 is sent by the circulation fan 20 into the inner tank 21, as indicated by the arrows, to dry the resist-printed substrate 1. The air used for drying is exhausted from the inner tank 21, heated again by the heater 19, and sent back into the inner tank 20. The solvent components have evaporated in the main drying oven 16, and the main purpose is to harden the etching resist. Therefore, air circulation ensures efficient hardening.

[0018] During the main drying process, the maximum temperature is between 80°C and 150°C, and the time above 80°C is between 60 and 120 minutes. The main drying process following the preliminary drying further dries and hardens the etching resist. Therefore, insufficient main drying may result in insufficient curing of the etching resist. If the maximum temperature for main drying is below 80°C, the etching resist may not be sufficiently cured, resulting in etching failure due to swelling or voids in the resist. Conversely, if the maximum temperature for main drying is higher than 150°C, the resist may be over-cured, reducing the bond strength with the metal plate and causing peeling. Therefore, a more preferable temperature is between 100°C and 130°C. Furthermore, if the time above 80°C is less than 60 minutes, the etching resist may not be sufficiently cured, resulting in etching failure due to insufficient curing. Furthermore, if the drying time exceeds 120 minutes, further drying is ineffective, and if the maximum temperature is too high, the surface may be altered by oxidation, resulting in defects such as peeling or swelling. Therefore, a more preferable time is 80 minutes or more and 100 minutes or less.

[0019] In the etching resist drying apparatus for ceramic-metal bonded substrates, the preliminary drying is performed in a continuous drying oven, and the main drying is performed in a batch drying oven.

[0020] Any furnace capable of setting the temperature and time can be used for pre-drying and main drying. However, considering mass production, a continuous drying furnace is preferred for pre-drying, while a batch drying furnace is preferred for main drying. Specifically, the pre-drying process requires a short period of time (3 to 10 minutes) at or above 80°C, making it suitable for continuous processing of ceramic-metal bonded substrates. Furthermore, because the solvent evaporates during pre-drying, a continuous furnace is preferred, as it allows for the introduction of fresh air and the easy removal of evaporated solvent. In contrast, the main drying process requires a long period of time (60 to 120 minutes) at or above 80°C, making a sealed batch drying furnace more energy efficient. Furthermore, since most of the solvent has evaporated during pre-drying, the introduction of fresh air and the removal of generated gases can be minimized, making a sealed oven more efficient.

[0021] In the etching resist drying apparatus for a ceramic-metal bonding substrate according to the embodiment, the ceramic-metal bonding substrate is dried in a vertical position within a setter.

[0022] Figure 7 is a schematic diagram showing an example of a setter for drying resist. The resist-printed substrate 1 is stored vertically in the setter 12. By placing the resist vertically, the viscosity of the etching resist is adjusted to 50 Pa·S or higher, preferably 100 Pa·S or higher, to prevent the etching resist from flowing downward. This allows drying in a small space, improving productivity. Furthermore, by placing the resist-printed substrate 1 vertically, the difference in drying time between the first side (front side, upper surface) and the second side (back side, lower surface) is reduced. This is because the solvent evaporates upward when heated, so if the substrate is placed horizontally with the first side facing up, the second side will dry more slowly than the first side, which can lead to uneven drying.

[0023] In the etching resist drying apparatus according to the embodiment, the etching resist is a thermosetting type.

[0024] There are two main types of etching resists: heat-curing and UV (ultraviolet)-curing. Heat-curing resists cure at high temperatures because the bonds between molecules are strengthened when heated to a specific temperature. For this reason, they are used in applications that require heat resistance. They are also resistant to many chemicals and are strong and durable. In contrast, UV-curing resists cure by cross-linking the molecules when exposed to ultraviolet light of a specific wavelength. They cure quickly, shortening the process time. They can also be set to have a lower viscosity than heat-curing resists, allowing for the formation of finer patterns. For etching resists used on ceramic-metal bonded substrates, the etching process takes longer as the metal circuit becomes thicker to improve heat dissipation. For this reason, heat-curing resists, which offer strength and durability, are preferable.

[0025] There are also types of thermosetting etching resists, such as those in which the etching resist paste (ink) is removed with an alkaline solvent and those in which it is removed with an organic solvent. The resist is removed after the etching process is complete, so the metal where the resist is printed does not dissolve. Resists that are removed with alkaline include cresol novolata (an alkali-soluble resin made by condensing cresol and formaldehyde), which is removed with an alkaline solvent after etching. Etching resists that are removed with organic solvents are used when metals are corroded by alkaline solvents. Furthermore, organic solvents are more environmentally friendly and safer than alkaline solvents, making them easier to handle when removing.

[0026] The etching resist drying apparatus according to the embodiment has mechanisms for pre-drying and main drying, allowing for efficient drying and thermal curing. When pre-drying and main drying are performed in the aforementioned continuous furnace, the furnace structure becomes complex in order to simultaneously provide a mechanism for discharging evaporated solvent and a mechanism for maintaining a constant temperature for a long period of time. Furthermore, when pre-drying and main drying are performed in the aforementioned batch furnace, an additional structure is required to simultaneously provide a mechanism for discharging evaporated solvent and a mechanism for maintaining a constant temperature for a long period of time, as with the continuous furnace. Furthermore, the temperature profile becomes complex. For this reason, the etching resist drying apparatus according to the embodiment is suitable for thermosetting etching resists.

[0027] The ceramic circuit board according to the embodiment is etched by etching a ceramic-metal bonding substrate in which the etching resist has been dried by the etching resist drying device described above.

[0028] A ceramic-metal bonded substrate is formed by bonding a ceramic substrate and a metal plate with a bonding layer made of paste. The metal plate to be bonded is flat relative to the ceramic substrate, with minimal surface irregularities. In contrast, the ceramic substrate is a sintered body, and therefore warping and unevenness remain unless polishing or other processing is performed. Furthermore, differences in warping and unevenness are likely to occur between the ceramic substrates. Therefore, the metal plate on which the etching resist is printed is not flat, which can easily lead to differences in printing thickness. Differences in printing thickness can easily lead to differences in drying and hardening. However, as described above, the etching resist drying device according to the embodiment reduces differences in drying and hardening between the pre-drying and main drying processes, making it possible to form a robust resist pattern that can withstand subsequent etching processes.

[0029] The aforementioned FIG. 1 is a schematic diagram showing an example of a state in which an etching resist is printed on a ceramic-metal bonded substrate in which a metal plate is bonded to a ceramic substrate according to an embodiment. A ceramic-metal bonded substrate 2 has a ceramic substrate 3 and a metal plate 4 bonded to each other, and an etching resist 5 is printed on the surface of the metal plate 4. In FIG. 1, the etching resist 5 is printed in nine locations in a 3 x 3 pattern, but in the embodiment, the shape is not limited to that shown, and other shapes and numbers may be printed. After printing the etching resist 5, the resist-printed substrate 1 is etched to form a ceramic circuit substrate.

[0030] In the ceramic circuit board according to the embodiment, the ceramic substrate and the metal plate of the ceramic-metal bonding substrate are bonded together by a bonding layer containing 0.1 mass % to 15 mass % of an active metal element.

[0031] The bonding layer bonding the ceramic substrate and the metal plate contains 0.1% by mass or more and 15% by mass or less of an active metal element. Examples of the active metal element include titanium (Ti), zirconium (Zr), hafnium (Hf), and niobium (Nb). The bonding layer is formed by printing and heating an active metal brazing paste. The active metal brazing paste preferably contains at least two selected from the group consisting of silver (Ag), copper (Cu), tin (Sn), indium (In), zinc (Zn), aluminum (Al), silicon (Si), carbon (C), and magnesium (Mg). When the metal circuit is made of copper or a copper alloy, a bonding layer containing Cu and Ti is preferably provided between the ceramic substrate and the circuit. The active metal brazing paste may, for example, have a metal component with a Ti content of 1 to 10% by mass, a Cu content of 10 to 60% by mass, and the remainder being Ag. If necessary, 1 to 15 mass % of one or more elements selected from the group consisting of In, Sn, Al, Si, C, and Mg may be added.

[0032] In the method for manufacturing a ceramic circuit board according to the embodiment, the ceramic substrate is any one of a silicon nitride substrate, an aluminum nitride substrate, and an aluminum oxide substrate.

[0033] The ceramic substrate is preferably one of silicon nitride substrates, aluminum nitride substrates, and aluminum oxide substrates. Arsil substrates are also a type of aluminum oxide substrate. Arsil 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 Arsil substrates is also around 550 MPa. The three-point bending strength of silicon nitride substrates can be increased to 600 MPa or more, even 700 MPa or more. These ceramic substrates are suitable for ceramic circuit substrates due to their aforementioned properties. Furthermore, the thermal conductivity of silicon nitride substrates can be increased to 50 W / (m·K) or more, even 80 W / (m·K) or more. In particular, silicon nitride substrates that combine both high strength and high thermal conductivity have recently become available. Because of their high strength, silicon nitride substrates can be made thin, thereby improving heat dissipation. For this reason, the thickness of the silicon nitride substrate is preferably 0.635 mm or less, and more preferably 0.3 mm or less. There is no particular lower limit for the thickness, but 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 board thinner and the metal circuit thicker, heat dissipation performance is improved.

[0034] In the method for manufacturing a ceramic circuit board according to the embodiment, the metal circuit is made of copper or a copper alloy.

[0035] Metal plates used in metal circuits include copper, copper alloys, aluminum, and aluminum alloys. Copper and copper alloys have high electrical conductivity, making them excellent for electrical circuits, and also have high thermal conductivity, making them excellent for heat dissipation from the semiconductor elements they are mounted on. Copper (pure copper) includes oxygen-free copper, tough pitch copper, and deoxidized copper, while copper alloys include beryllium copper, chromium copper, titanium copper, and copper tungsten.

[0036] Next, a method for manufacturing a ceramic circuit board according to an embodiment will be described. The method for manufacturing a ceramic circuit board is not particularly limited as long as the ceramic circuit board has the above-described configuration. Here, an example of a method for obtaining a ceramic circuit board with a high yield will be described.

[0037] FIG. 8 is a cross-sectional view of a process flow illustrating an example of a ceramic circuit substrate according to an embodiment. In FIG. 8(a), a ceramic substrate 3 is prepared. The ceramic substrate 3 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 ceramic circuit substrate, the ceramic substrate 3 is preferably a silicon nitride substrate having a thermal conductivity of 50 W / (m·K) or more and a three-point bending strength of 600 MPa or more. Furthermore, when the circuits on the upper surface and the lower surface of the ceramic substrate 3 are electrically connected via through holes, a ceramic substrate 3 having through holes is prepared. The through holes may be formed in advance in the molded body. Alternatively, the through holes may be formed in the ceramic substrate (ceramic sintered body). The through holes are formed by laser processing, cutting, or the like. Examples of cutting include drilling using a drill or the like.

[0038] FIG. 8(b) shows a state in which an active metal brazing paste 22 has been printed on both surfaces (top and bottom) of the ceramic substrate 3. The printed active metal brazing paste 22 is dried to remove the solvent components. The active metal brazing paste 22 is mixed with metal components containing an active metal with large particle size. This is because bonding with an active metal reacts with ceramics at low temperatures of 900°C or less, allowing the properties of the active metal powder to be fully utilized. Furthermore, since bonding with an active metal brazing paste is heated at low temperatures, it is difficult to remove organic components, so it is desirable to set the amount of organic components to a small amount.

[0039] In Figure 8(c), a metal plate 4 is placed on the surface of the active metal brazing paste 22 printed on both sides of the ceramic substrate 3 and bonded to it. By heating in this state, a bonding layer is formed between the ceramic substrate 3 and the metal plate 4. Examples of metal plates 4 used for the metal circuit include copper, copper alloys, aluminum, and aluminum alloys. Copper and copper alloys have high electrical conductivity and are excellent for use in electrical circuits, and also have high thermal conductivity and are excellent for dissipating heat from the semiconductor elements mounted on them.

[0040] In the active metal bonding method using an active metal brazing paste, an active metal brazing paste 22 is printed and dried on the surface of a ceramic substrate 3, and a metal plate 4 is placed on the surface. This is heated at 600 to 900°C to form a bonding layer 23. According to the active metal bonding method, the bonding strength between the ceramic substrate and the metal circuit can be 50 MPa or more.

[0041] FIG. 8(d) shows the state in which etching resist 5 has been printed on the surface of metal plate 4. Printing is performed using a method such as screen printing to ensure uniform thickness. The printing thickness of etching resist 5 is preferably 15 to 40 μm. After printing, the etching resist 5 on the ceramic-metal bonding substrate 2 is pre-dried as described above. In the case of a ceramic-metal bonding substrate 2 in which metal plates 4 are bonded on both sides, etching resist 5 is printed and pre-dried on one side, and then printed on the other side, and etching resist 5 is pre-dried in the same manner. The pre-dried etching resist hardens during main drying as described above.

[0042] In Figure 8(e), the metal plate 4 and bonding layer 23 are in an etched state. The ceramic-metal bonding substrate on which the etching resist 5 has been printed and dried is immersed in a solution that dissolves (corrodes) the metal plate, thereby carrying out etching. Similarly, the bonding layer 23 is immersed in a solution that dissolves the metal plate, and is then etched in the same manner. At this time, the area where the etching resist is printed is protected and does not dissolve, forming a circuit.

[0043] 8(f) shows the state after the etching resist has been removed. For example, the etching resist is removed by immersing it in an alkaline solvent in the case of an alkaline solvent-based etching resist, or in an organic solvent in the case of an organic solvent-based etching resist. This leaves the ceramic circuit board 24.

[0044] Furthermore, a metal thin film containing a metal selected from the group consisting of nickel (Ni), silver, and 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.

[0045] A ceramic circuit board 24 can be manufactured using the above-described process. Such a ceramic circuit board is suitable for a semiconductor device (semiconductor module) in which a semiconductor element is mounted on a metal circuit portion via a bonding layer. FIG. 9 shows an example of a semiconductor device. In FIG. 9, 25 denotes a semiconductor device, 24 denotes a ceramic circuit board, 26 denotes a semiconductor element, 27 denotes a wire bond, 28 denotes a lead frame, and 29 denotes a resin mold. In FIG. 9, a semiconductor element 26 is bonded to the circuit portion of the ceramic circuit board 24 via a bonding layer (not shown). Adjacent circuit portions are electrically connected by wire bonds 27. The semiconductor device is not limited to this structure. For example, multiple semiconductor elements 26 and multiple wire bonds 27 may be provided on the upper metal plate. Furthermore, semiconductor elements and wire bonds may be bonded to the lower metal plate as needed. Metal terminals such as lead frames may also be bonded to these circuit boards. Furthermore, solder, brazing material, etc., are used for the bonding layer that bonds the semiconductor element 26. Lead-free solder is preferable. Solder refers to solder with a melting point of 450°C or less. Brazing filler metal refers to solder with a melting point above 450°C. Brazing filler metals with a melting point of 500°C or higher are called high-temperature brazing filler metals. Examples of high-temperature brazing filler metals include those containing Ag as the main component.

[0046] Furthermore, while semiconductor elements continue to become 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, 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 bond between the semiconductor element and the circuit is highly effective. Furthermore, semiconductor devices according to 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.

[0047] (Examples 1 to 9, Comparative Examples 1 to 8) The ceramic substrates 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 70 mm long and 90 mm wide. The silicon nitride substrate was 0.32 mm thick, and the aluminum nitride substrate was 0.635 mm thick. The metal plates shown in Table 1 were also prepared. The metal plates measured 70 mm long, 90 mm wide, and 0.5 mm thick, and were bonded to both sides. In Table 1, the silicon nitride substrate is abbreviated as Si3N4, and the aluminum nitride substrate is abbreviated as AlN.

[0048] 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-TiH). 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 TiH. The ratios of the copper-based powder in the metal components were 68% by mass of Cu, 20% by mass of Sn, and 12% by mass of TiH. 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 6 μm for TiH. Next, 20% by mass of a binder prepared by dissolving an organic component in a solvent was added to 100% by mass of the metal powder and kneaded to prepare an active metal brazing paste.

[0049] The active metal brazing paste was printed on both sides of the ceramic substrate, leaving a pullback (non-printed area) of 1 mm from the periphery of the substrate, and then dried. Next, metal plates 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 silver-based paste (Ag-Cu-Sn-Ti) and 650°C for copper-based paste (Cu-Sn-TiH). 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.

[0050] Next, a thermosetting etching resist was prepared as shown in Table 1. The etching resists used were an organic solvent-removable etching resist (main components: copolymer resin, phenolic resin, oxide powder, butyl ether, etc.) and an alkaline solvent-removable etching resist (main components: resin, barium sulfate, talc, naphtha, etc.). The etching resist was printed using a screen printer to form the top surface (front surface, circuit side) pattern shown in Figure 10(a) and the bottom surface (back surface, heat dissipation side) pattern shown in Figure 10(b). The printed pattern in Figure 10(a) had a 2 mm pullback on the periphery, and two 0.5 mm-wide rectangular non-printed areas were provided 10 mm from the periphery of the ceramic substrate. The printed pattern in Figure 10(b) had a 2 mm pullback on the periphery.

[0051] [Table 1]

[0052] Ceramic-metal bonded substrates printed with etching resist were pre-dried and dried under the conditions listed in Table 2. The resist removal rate was tested by attaching adhesive tape (Nichiban cellophane tape) to the dried etching resist and lifting it 90 degrees upward. The area removed by the adhesive tape was image-processed using image analysis software (Image-J), and the percentage (%) of the measured area was calculated as the resist removal rate. Next, the ceramic-metal bonded substrates printed with etching resist were etched by spraying a metal plate etching solution from above and below. Then, the substrates were immersed in a brazing filler metal solvent for brazing filler metal etching. The resist was then removed by spraying a resist remover from above and below, yielding a ceramic-copper circuit substrate with the pattern shown in Figure 10. The dimensions of eight opposing non-circuit areas (0.5 mm rectangular frame shapes) of the resulting ceramic circuit substrate were measured, and the process capability (Cpk) for the pattern dimension design value (0.50 mm) was calculated and used as the pattern process capability. The resist removal rate and pattern process capability are shown in Table 2.

[0053] [Table 2]

[0054] The resist stripping rate was low in the Examples. This was because the etching resist was strongly cured during pre-drying and main drying. In contrast, the resist stripping rate was high in the Comparative Examples. This was because the pre-drying temperature, pre-drying time, main drying temperature, and main drying time were outside of the preferred ranges, causing uneven curing of the etching resist. Furthermore, the Examples showed high process capability in terms of pattern process capability, but the Comparative Examples showed low process capability. This was because there were areas where the etching resist was not sufficiently cured or where it had hardened excessively, causing peeling, resulting in pattern defects and overflow, which reduced process capability.

[0055] As described above, the etching resist drying apparatus according to the present embodiment has a low resist stripping rate and a high patterning process capability, making it ideal for ceramic circuit boards.

[0056] 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]

[0057] 1...Resist printed board 2...Ceramics-metal bonded substrate 3...Ceramic substrate 4...Metal plate 5...Etching resist 6...Pre-drying oven 7...First drying zone 8...Second drying zone 9...Drive unit 10...Belt section 11...Exhaust port 12...Setter 13...Furnace entrance 14...Drying section 15…Furnace outlet part 16…Main drying oven 17...Main body 18...Opening and closing door 19...Heater 20...Circulation fan 21…Inner tank 22...Active metal brazing paste 23...Joining layer 24...Ceramic circuit board 25...Semiconductor equipment 26...Semiconductor element 27...Wire bonding 28...Lead frame 29...Resin mold

Claims

1. In the etching resist drying device for ceramic metal bonded substrates, It has a mechanism for pre-drying and main drying. In the preliminary drying, the maximum temperature is 80°C or more and 150°C or less, and the time above 80°C is 3 minutes or more and 10 minutes or less. In this drying, the maximum temperature is between 80°C and 150°C, and the time at or above 80°C is between 60 and 120 minutes. An etching resist drying apparatus characterized by heating the resist by a

2. 2. The etching resist drying apparatus according to claim 1, wherein the preliminary drying is performed in a continuous drying oven, and the main drying is performed in a batch drying oven.

3. 3. The etching resist drying apparatus according to claim 1, wherein the ceramic-metal bonded substrate is dried in a vertical position.

4. 3. The etching resist drying apparatus according to claim 1, wherein the etching resist used in said etching resist drying apparatus is a thermosetting type.

5. 3. A ceramic circuit board obtained by etching a ceramic-metal bonded substrate in which an etching resist has been dried by the etching resist drying apparatus according to claim 1 or 2.

6. 6. The ceramic circuit board according to claim 5, wherein the ceramic substrate and the metal plate of the ceramic-metal bonded substrate are bonded together by a bonding layer containing 1% by mass or more and 15% by mass or less of an active metal element.

7. 7. The ceramic circuit board according to claim 6, wherein the ceramic substrate is one of an aluminum oxide substrate, an aluminum nitride substrate, and a silicon nitride substrate.

8. 7. The ceramic circuit board according to claim 6, wherein the metal plate is made of copper or a copper alloy.

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