Etching solution for active metal brazing filler metal and method for manufacturing ceramic circuit board using same

Abstract

The present invention relates to an etching solution for an active metal solder, which is used to etch an active metal solder layer containing Ag, Cu, and an active metal, and which contains ammonium fluoride, borohydrofluoride acid, and one or two elements selected from the group consisting of hydrogen peroxide and ammonium peroxydisulfate.

Description

[0001] This application is a divisional application of Chinese National Application No. 201880052773.0, filed on September 7, 2018, entitled "Etching solution for active metal solder and method for manufacturing ceramic circuit board using the same". Technical Field

[0002] The embodiments of the present invention relate to an etching solution for active metal solder and a method for manufacturing a ceramic circuit board using the same. Background Technology

[0003] The trend towards higher output power modules is underway. Along with this, the operating temperature of semiconductor devices is increasing, reaching over 175°C. Therefore, improvements in the TCT (thermal cycling test) characteristics are required for the ceramic circuit boards housing these semiconductor devices.

[0004] For example, International Publication No. 2017 / 056360 (Patent Document 1) describes the optimization of the size of the protrusion of the bonding layer and the inclined structure on the side of the copper plate. Excellent TCT characteristics were obtained in Patent Document 1. In particular, it is considered preferable to optimize the size of the protrusion of the bonding layer.

[0005] To control the protrusion size of the bonding layer, the solder layer is etched. In the bonding of the ceramic substrate and the copper plate, an active metal solder is used. The active metal solder is a solder containing Ag (silver), Cu (copper), and Ti (titanium). Additionally, Sn (tin) and In (indium) may be added as needed. The active metal solder contains components other than Cu. Therefore, after the process of etching the copper plate itself into the specified pattern shape, a solder layer remains. Thus, a solder etching process is required to remove this unwanted solder layer.

[0006] For example, Japanese Patent No. 4811756 (Patent Document 2) uses a solder etching solution composed of a chelating agent, hydrogen peroxide, and a pH adjuster. In Patent Document 2, ethylenediaminetetraacetic acid (EDTA) is used as the chelating agent. Ammonia is used as the pH adjuster. Patent Document 2 uses this solder etching method to control the size of the solder protrusions.

[0007] However, in the method of Patent Document 2, a single solder etching process takes up to 150 minutes. Therefore, it has poor mass production feasibility.

[0008] Existing technical documents Patent documents Patent Document 1: International Publication No. 2017 / 056360 Patent Document 2: Japanese Patent No. 4811756 Summary of the Invention

[0009] The problem that the invention aims to solve One aspect of the present invention addresses the problem of providing an etching solution for active metal solder with excellent mass production properties and a method for manufacturing a ceramic circuit board using the same.

[0010] Methods for solving problems In an etching solution for etching an active metal solder layer containing Ag, Cu and active metal, the etching solution for active metal solder contains ammonium fluoride, borofluoride, and one or two of hydrogen peroxide and ammonium persulfate. Attached Figure Description

[0011] Figure 1 This is a diagram illustrating a method for manufacturing a ceramic circuit board.

[0012] Figure 2 This diagram illustrates other methods for manufacturing ceramic circuit boards. Detailed Implementation

[0013] The active metal solder etching solution of the embodiment is used to etch an active metal solder layer containing Ag, Cu and active metal, wherein the active metal solder etching solution contains ammonium fluoride, borofluoride, and one or two of hydrogen peroxide and ammonium persulfate.

[0014] The etching solution for active metal solder contains ammonium fluoride, borofluoride, and one or two of the following: hydrogen peroxide and ammonium persulfate. The borofluoride is preferably HBF4.

[0015] The ceramic circuit board is described.

[0016] Figure 1 (A) and Figure 1 (B) illustrates a method for manufacturing a ceramic circuit board. Figure 1 (A) and Figure 1 In (B), 1 is the ceramic circuit board, 2 is the ceramic substrate, 3 is the active metal solder layer, 4 is the copper component, and 5 is the solder removal area. Additionally, Figure 1 (A) indicates the ceramic circuit board before the active metal solder layer 3 is etched. Figure 1 (B) indicates the ceramic circuit board after the solder layer has been etched.

[0017] A copper component 4 is bonded to at least one surface of a ceramic circuit board 1 via an active metal solder layer 3. Figure 1The copper components are joined only on one side, but they can also be joined on both sides. Furthermore, the surface-side copper components can be set as circuit patterns. Alternatively, the rear-side copper components can be heat sinks (without patterns) or set as circuit patterns.

[0018] The ceramic substrate 2 can be a silicon nitride substrate, an aluminum nitride substrate, an alumina substrate, or an Alussir high-silicon heat-resistant aluminum alloy substrate, etc. The thickness of the ceramic substrate is, for example, 0.2 to 0.8 mm. For example, the thermal conductivity of the silicon nitride substrate is 80 W / m·K or higher, and its three-point bending strength is 600 MPa or higher. For example, the thermal conductivity of the aluminum nitride substrate is 150 W / m·K or higher, and its three-point bending strength is 300 to 550 MPa. For example, the thermal conductivity of the alumina substrate is 20 to 40 W / m·K, and its three-point bending strength is 400 to 500 MPa. The Alussir high-silicon heat-resistant aluminum alloy substrate is an alumina substrate containing zirconium oxide. For example, the thermal conductivity of the Alussir high-silicon heat-resistant aluminum alloy substrate is 20 to 40 W / m·K, and its three-point bending strength is 450 to 600 MPa. Because of its high strength, the silicon nitride substrate allows for a substrate thickness of less than 0.33 mm. Aluminum nitride substrates have high thermal conductivity. While alumina substrates and Alusser high-silicon heat-resistant aluminum alloy substrates have lower thermal conductivity, they are inexpensive. The type of ceramic substrate can be appropriately selected according to the purpose. Furthermore, silicon nitride and aluminum nitride substrates are called nitride-based ceramics. Alumina substrates and Alusser high-silicon heat-resistant aluminum alloy substrates are called oxide-based ceramics.

[0019] Copper components are preferably made of oxygen-free copper. If the copper component contains too much oxygen, the bond strength may be reduced during active metal bonding. The copper component can be a copper plate or a copper film formed on the solder layer. The following describes the case where the copper component is a copper plate.

[0020] The thickness of the copper plate is preferably 0.2 mm or more. Furthermore, a thickness of 0.7 mm or more improves the heat dissipation of the copper plate. There is no particular upper limit to the plate thickness, but the thickness of the copper plate is preferably 5 mm or less. If the plate thickness exceeds 5 mm, the warpage of the ceramic circuit board increases when the copper plate is bonded to the ceramic substrate. Additionally, it becomes more difficult to process into patterned shapes by etching.

[0021] The active metal solder contains Ag, Cu, and an active metal as essential components. Ag and Cu form a eutectic combination. By forming an AgCu eutectic, the bonding strength between the ceramic substrate and the copper plate can be improved. Furthermore, the active metal is one or more selected from Ti (titanium), Zr (zirconium), Hf (hafnium), and Nb (niobium). Ti is preferred among the active metals. The active metal can react with the ceramic substrate to form a strong bond. It forms an active metal nitride phase with nitride-based ceramics. For example, when Ti is used as the active metal, a titanium nitride (TiN) phase is formed. It also forms an active metal oxide phase with oxide ceramics. For example, when Ti is used as the active metal, a titanium oxide (TiO2) phase is formed. Additionally, the active metal can be an elemental metal or added in the form of a hydride.

[0022] Additionally, Sn (tin) or In (indium) can be added to the active metal solder as needed. Sn and In can lower the melting point of the active metal solder, thus reducing the bonding temperature. Bonding at lower temperatures reduces residual stress in the joint. This reduction in residual stress effectively improves the thermal cycling reliability of the joint.

[0023] Additionally, carbon (C) can be added to the active metal solder as needed. Adding carbon suppresses the solder's flowability, thus making the solder layer thickness more uniform.

[0024] Furthermore, in the active metal solder, the content of Ag is preferably 40% to 80% by weight, the content of Cu is preferably 15% to 45% by weight, the content of active metal is preferably 1% to 12% by weight, the content of Sn (or In) is preferably 0% to 20% by weight, and the content of C is preferably 0% to 2% by weight. The total content of Ag, Cu, Ti, Sn (or In), and C is set to 100% by weight. Additionally, when Sn or In is added to the active metal solder, the content of Sn or In is preferably 5% by weight or more. When both Sn and In are added, their combined content is preferably in the range of 5% to 20% by weight. Furthermore, when carbon is added to the active metal solder, the carbon content is preferably 0.1% by weight or more.

[0025] The bonding process mainly includes coating and heating processes.

[0026] In the coating process, firstly, the aforementioned solder paste is prepared. The solder paste is coated onto a ceramic substrate, and a copper plate is then placed on top of it. The coating thickness of the solder paste is preferably in the range of 10 to 60 μm. If the coating thickness is less than 10 μm, insufficient solder may result in reduced bond strength. Furthermore, if the coating thickness exceeds 60 μm, not only is there no improvement in bond strength, but it also increases costs. When bonding copper plates to both sides, the solder paste is coated on both sides of the ceramic substrate. Preferably, the copper plate is of the same size as the area coated with solder paste. Alternatively, a copper plate pre-patterned may be placed on the ceramic substrate.

[0027] Next, a heating process is performed. The heating temperature is in the range of 700–900°C. Furthermore, it is preferable to perform the heating in a non-oxidizing atmosphere at a temperature of 1×10⁻⁶. -3 The bonding process is carried out in an atmosphere below Pa. By adding Sn or In to the solder, the bonding temperature can be set to below 850°C.

[0028] This process enables the ceramic substrate to be bonded to the copper plate.

[0029] Etching the copper plate 4 is effective in creating exposed areas for the active metal solder layer. A photoresist is applied to the copper plate 4 in a patterned manner. Then, the copper plate is etched using the photoresist as a mask.

[0030] Joining pre-processed copper plates into patterned shapes is also effective. However, if the copper plates are misaligned during the joining process, it can become difficult to handle complex patterns or closely spaced patterns (narrow spacing between adjacent copper plates). Therefore, it is preferable to etch the copper plates into patterned shapes. Closely spaced refers to a spacing of 2 mm or less between adjacent copper plates.

[0031] Ferric chloride is primarily used in copper etching processes. Ferric chloride is effective for etching copper. However, it cannot etch solder layers containing Ag, Cu, or active metals. Therefore, areas where the solder layer becomes exposed may exist. Additionally, a washing process can be performed after the copper etching process if necessary. Copper chloride can also be used instead of ferric chloride in copper etching.

[0032] The exposed active metal solder layer 3 is etched.

[0033] Hydrogen peroxide (H₂O₂) and ammonium peroxydisulfate ((NH₄)₂S₂O₈) are effective at removing Ag and Cu. These etching components can ionize and remove Ag and Cu. In particular, the ionization effect is improved by setting the pH to below 6. In addition, hydrogen peroxide and ammonium peroxydisulfate also have the effect of acting as oxidants that oxidize one or more of the following: active metals, Sn, In, and carbon. For example, when Ti is used in the solder, it becomes TiN (titanium nitride) on the nitride-based ceramic substrate. The above-mentioned etching components have the effect of transforming Ti or TiN into TiO₂. Similarly, they have the effect of transforming Sn in the solder layer 3 into SnO₂. The same applies to In.

[0034] Ammonium fluoride (NH4F) functions as an etchant for oxides. For example, it can remove TiO2 by converting it into TiOF2. Ammonium fluoride also contains ammonium hydrogen fluoride ((NH4)HF2).

[0035] Borofluoride hydrochloric acid can stabilize the pH of the etching solution. Specifically, the pH of the etching solution for active metal solder can be set to 6 or below. Furthermore, as described later, the pH of the etching solution can be set to 4 to 6 by controlling the mixing ratio of hydrogen peroxide or ammonium persulfate with ammonium fluoride and borofluoride hydrochloric acid.

[0036] Furthermore, by using HBF4, the pH of the etching solution can be set to 4.8–5.8. HBF4 also functions as an etchant for the solder layer. Therefore, the etching speed of the active metal solder layer can be accelerated.

[0037] Furthermore, by adding the chelating agent described later, the pH of the etching solution can be lowered to 4.0–4.8. Lowering the pH of the etching solution can accelerate the etching rate.

[0038] The pH of an etching solution containing ammonium fluoride, borofluoride, and one or two of hydrogen peroxide and ammonium persulfate is preferably 4.8 to 5.8. The pH of an etching solution further containing a chelating agent is preferably 4.0 to 4.8.

[0039] Hydrogen peroxide preferably has the qualities shown in JIS-K-1463 (2007). For JIS-K-1463, refer to ISO 6352-2. Additionally, ammonium persulfate preferably has the qualities shown in JIS-K-8252 (2010).

[0040] If the pH of the solder etchant is greater than 6, the etching rate of the solder layer slows down. Conversely, if the pH is lower than 4, the etching rate of the solder layer may become too fast. To improve the TCT characteristics of the ceramic circuit board, it is necessary to retain the solder protrusions (bonding layer protrusions). If the etching rate of the solder layer is too fast, it becomes difficult to control the size of the solder protrusions. Therefore, the pH of the etchant is preferably 4–6, and more preferably 4.0–5.8.

[0041] When the total weight of hydrogen peroxide, ammonium fluoride, and borofluoride is set to 100% by weight, the hydrogen peroxide content is preferably 30% to 86% by weight. The ammonium fluoride content is preferably 9% to 40% by weight. The borofluoride content is preferably 5% to 50% by weight. Within this range, the effects of each component can be effectively utilized. Furthermore, the redox potential (ORP) during solder etching can be increased. From this perspective, the solder etching speed can also be accelerated.

[0042] Hydrogen peroxide, ammonium fluoride, and borofluoride are preferably prepared separately as aqueous solutions and then mixed. Preferably, an aqueous solution containing 15-70% by weight of hydrogen peroxide is used. Preferably, an aqueous solution containing 15-60% by weight of ammonium fluoride is used. Preferably, an aqueous solution containing 15-60% by weight of borofluoride is used.

[0043] Alternatively, the solder etching solution can be prepared by mixing an aqueous solution containing hydrogen peroxide, an aqueous solution containing ammonium fluoride, and an aqueous solution containing borohydric acid fluoride. The solder etching solution can also be diluted with water. When the total volume of the aqueous solutions containing hydrogen peroxide, ammonium fluoride, and borohydric acid fluoride is set to 1 L, 0.5 to 2 L of water can also be mixed. Furthermore, it is preferable to mix thoroughly and evenly. The water preferably meets the quality standards of JIS-K-0557 (1998). Quality standards A1 to A4 are shown in JIS-K-0557. For JIS-K-0557, refer to ISO 3696.

[0044] Furthermore, when the total weight of ammonium peroxide disulfate, ammonium fluoride, and borofluoride is set to 100% by weight, the content of ammonium peroxide disulfate is preferably 23% to 95% by weight, the content of ammonium fluoride is preferably 3% to 50% by weight, and the content of borofluoride is preferably in the range of 2% to 55% by weight. Within this range, the effects of each component can be effectively utilized. Additionally, the oxidation-reduction potential (ORP) during solder etching can be increased. From this perspective, the solder etching speed can also be accelerated.

[0045] Furthermore, ammonium persulfate, ammonium fluoride, and borofluoride are preferably prepared separately as aqueous solutions and then mixed. Preferably, the ammonium persulfate content is 15-70% by weight in an aqueous solution containing ammonium persulfate. Preferably, the ammonium fluoride content is 15-60% by weight in an aqueous solution containing ammonium fluoride. Preferably, the borofluoride content is 15-60% by weight in an aqueous solution containing borofluoride.

[0046] Alternatively, the solder etching solution can be prepared by mixing an aqueous solution containing ammonium persulfate, an aqueous solution containing ammonium fluoride, and an aqueous solution containing borohydric acid. The solder etching solution can also be diluted with water. When the total volume of the aqueous solutions containing ammonium persulfate, ammonium fluoride, and borohydric acid is set to 1 L, 0.5 to 2 L of water can also be mixed. Furthermore, it is preferable to mix thoroughly and evenly. Additionally, the water preferably meets the quality standards of JIS-K-0557 (1998). Quality standards A1 to A4 are shown in JIS-K-0557.

[0047] Furthermore, when using both hydrogen peroxide and ammonium peroxide disulfate, if the total weight of hydrogen peroxide, ammonium peroxide disulfate, ammonium fluoride, and borofluoride is set to 100% by weight, the total content of hydrogen peroxide and ammonium peroxide disulfate is preferably 35% to 96% by weight, the content of ammonium fluoride is preferably 2% to 50% by weight, and the content of borofluoride is preferably in the range of 2% to 50% by weight. Additionally, it is also preferable to prepare the mixture as an aqueous solution.

[0048] In addition, the solder etching solution may also contain a chelating agent. When the total weight of ammonium fluoride, borofluoride, the chelating agent, and one or two of the ingredients selected from hydrogen peroxide and ammonium persulfate is set to 100% by weight, the content of the chelating agent is preferably in the range of 0.01% to 5% by weight. Furthermore, the chelating agent is preferably one or more of the ingredients selected from glycine, CDTA, dicarboxylic acid, tricarboxylic acid, and hydroxycarboxylic acid.

[0049] Chelating agents inhibit the precipitation of Cu. The active metal solder layer contains Cu (copper). As etching of the active metal solder layer progresses, the number of Cu ions in the etching solution gradually increases. If the amount of Cu ions exceeds a certain level, saturation occurs, and Cu precipitation reduces the etching rate. By adding a chelating agent, the re-precipitation of Cu ions can be prevented. This prevents a decrease in the etching rate of the active metal solder layer. Furthermore, the presence of a chelating agent can lower the pH of the etching solution.

[0050] The chelating agent is preferably selected from one or more of glycine, CDTA, dicarboxylic acid, tricarboxylic acid, and hydroxycarboxylic acid. These chelating agents readily form complex ions with Cu ions.

[0051] When the total weight of ammonium fluoride, borofluoride, chelating agent, and one or two of the ingredients selected from hydrogen peroxide and ammonium peroxydisulfate is set to 100% by weight, the content of the chelating agent is preferably in the range of 0.01% to 5% by weight. If the content is below 0.01% by weight, the effect of addition is insufficient. Furthermore, if the content exceeds 5% by weight, the addition is excessive and may actually reduce the etching rate. Therefore, the content of the chelating agent is preferably 0.01% to 5% by weight, and more preferably 0.1% to 3% by weight.

[0052] Glycine represents aminoacetic acid or its salt. CDTA is cyclohexanediaminetetraacetic acid ester. CDTA is sometimes also labeled CyDTA. Additionally, dicarboxylic acids represent substances with two carboxyl groups in their molecular formula. Furthermore, hydroxycarboxylic acids represent substances with both hydroxyl and carboxyl groups in their molecular formula. Dicarboxylic acids also include dicarboxylate salts. Additionally, tricarboxylic acids also include tricarboxylate salts. Additionally, hydroxycarboxylic acids also include hydroxycarboxylate salts.

[0053] By using such a solder etchant to etch the solder layer, the etching time can be shortened. If the thickness of the solder layer is less than 60 μm, etching can be performed in less than 30 minutes.

[0054] Etching solutions containing hydrogen peroxide, ammonium persulfate, ammonium fluoride, and borofluoride can etch only the active metal solder layer without etching the copper plate. Therefore, the active metal solder layer can be etched after removing the resist used during the copper plate etching process.

[0055] By etching the solder layer after removing the resist used during copper etching, it is possible to prevent the resist from reacting with the etchant used for active metal soldering. Therefore, the pH of the etchant used for active metal soldering can be maintained at 4–6, and further, 4.0–5.8, for an extended period. Since the pH can be maintained within this range for a longer time, the number of ceramic circuit boards that can be processed can be increased. Even without replenishing the etchant used for active metal soldering, the number of processed boards can be increased. It should be noted that the etching process for the active metal solder layer can also be performed while retaining the resist used during copper etching.

[0056] Heating the solder etching solution is also effective. By heating the solder etching solution to 30–70°C, the etching reaction can be made more active.

[0057] The solder etching process is preferably performed while ultrasonic waves are applied to the ceramic circuit board using a solder etching solution. By performing the solder etching process while applying ultrasonic waves, the solder etching time can be further shortened. Furthermore, the frequency of the ultrasonic waves is preferably between 10 kHz and 100 kHz. The effect of applying ultrasonic waves is minimal when the frequency is below 10 kHz. Moreover, even if the frequency is increased to above 100 kHz, the same effect is not achieved. Additionally, the burden on the device increases. Therefore, the frequency of the ultrasonic waves is preferably between 10 and 100 kHz, and more preferably between 20 and 70 kHz.

[0058] By etching the solder simultaneously with ultrasonic waves, the time for a single solder etching process can be set to less than 20 minutes. It should be noted that there is no specific lower limit to the solder etching process time, but it is preferably more than 1 minute. If the time is less than 1 minute, the removal and oxidation of the solder layer may become insufficient.

[0059] The etching of the active metal solder layer can also be performed in two or more steps. In this case, the composition of the solder etching solution used in the second solder etching step can be different from that used in the first solder etching step. In addition, a washing step with pure water can be performed between each step as needed.

[0060] If the etching process of the active metal solder layer using the solder etchant described in this embodiment is repeated, the etching performance gradually decreases. The main reason for this is the decrease in the concentration of hydrogen peroxide or ammonium persulfate. As mentioned above, these components function as ionizing or oxidizing agents for the active metal solder layer components. Through these functions, etching of the active metal solder layer begins. Therefore, it is gradually consumed by hydrogen peroxide or ammonium persulfate.

[0061] In the embodiment of the etching solution for the active metal solder layer, etching performance can be maintained by replenishing the reduced portion when the concentration of hydrogen peroxide decreases. Similarly, etching performance can be maintained by replenishing the reduced portion when the concentration of ammonium persulfate decreases. The standard for concentration reduction is a decrease of 10-20% by weight from the initial concentration. When the concentration reduction is less than 10% by weight, the decrease in etching performance is small. On the other hand, if the concentration reduction exceeds 20% by weight, the decrease in etching performance before replenishment becomes larger. Therefore, it is preferable to replenish hydrogen peroxide when the concentration of hydrogen peroxide in the etching solution for the active metal solder decreases by 10-20% by weight from the initial concentration. Similarly, it is preferable to replenish ammonium persulfate when the concentration of ammonium persulfate in the etching solution for the active metal solder decreases by 10-20% by weight from the initial concentration. In addition, if the concentration of hydrogen peroxide or ammonium persulfate gradually decreases, the change in pH of the etching solution becomes larger.

[0062] Etching solution for active metal solders used in the embodiments, such as Figure 1 (A) and Figure 1 As shown in (B), the solder layer 3 is exposed between the copper plates 4 to form solder removal areas 5. By using the active metal solder etching solution of the embodiment, the solder layer 3 can be etched in a shorter time, and the size of the portion protruding from between the ceramic substrate 2 and the copper plate 4 of the solder layer 3 can be controlled.

[0063] Figure 2 (A) ~ Figure 2 (C) illustrates other methods for manufacturing ceramic circuit boards. Figure 2 (A) ~ Figure 2 (C) shows an example of a process involving multiple etching steps to etch the solder layer 3. First, as... Figure 2 (A) and Figure 2 As shown in (B), the areas where the solder layer 3 is exposed between the copper plates 4 are etched. This reduces the thickness of these areas, forming a solder residue region 6. Subsequently, the solder residue region 6 is further etched away by another etching process, forming a solder removal region 5.

[0064] The composition of the etching solution used in the first etching step can be the same as or different from that used in the second etching step. A washing process can also be performed between the first and second etching steps.

[0065] (Example) (Examples 1-16, Comparative Example 1) As ceramic substrates, the following substrates were prepared: silicon nitride substrate (0.32 mm thickness, thermal conductivity 90 W / m·K, three-point bending strength 650 MPa), aluminum nitride substrate (0.635 mm thickness, thermal conductivity 180 W / m·K, three-point bending strength 350 MPa), alumina substrate (0.635 mm thickness, thermal conductivity 20 W / m·K, three-point bending strength 450 MPa), and Alusier high-silicon heat-resistant aluminum alloy substrate (0.635 mm thickness, thermal conductivity 20 W / m·K, three-point bending strength 500 MPa). All ceramic substrates were uniformly 50 mm long × 40 mm wide.

[0066] Regarding the copper plates, two types were prepared: one with a thickness of 0.5mm and the other with a thickness of 0.8mm. The 0.5mm thick copper plate is designated "Copper Plate 1," and the 0.8mm thick copper plate is designated "Copper Plate 2." Furthermore, the dimensions of the copper plates are uniformly 46mm in length and 36mm in width.

[0067] The solder used for bonding is the solder shown in Table 1.

[0068] An active metal bonding process was performed by combining a ceramic substrate, solder, and copper plate as shown in Table 2. A solder layer corresponding to the size of the copper plate was applied, and the copper plate was then mounted.

[0069] The active metal bonding process is carried out in a non-oxidizing atmosphere at 1×10 -3 The bonding process was carried out at temperatures below Pa. Additionally, samples using solder 1 and solder 2 were bonded at 780–850°C. Samples using solder 3 were bonded at 860–880°C. Furthermore, copper plates were bonded to both sides of the ceramic substrate.

[0070] Through this process, ceramic circuit boards for samples 1 to 6 were prepared.

[0071] Compared to the ceramic circuit boards of samples 1-6, a resist was applied to a copper plate on the surface side, and then etched to form a pattern. The copper plate patterns included areas with a spacing of 1.5 mm and 2.0 mm between patterns. The copper plate etching process exposed the solder layer on the ceramic circuit board.

[0072] Next, the solder etching solution shown in Table 3 was prepared. The solder etching solution represents the mass ratio when hydrogen peroxide (H2O2), ammonium fluoride (NH4F), and borofluoride (HBF4) are combined to 100% by weight. The solutions were mixed in aqueous solutions according to the mass ratios shown in Table 3. The volume (L: liter) of pure water mixed relative to 1 L of the total aqueous solutions containing hydrogen peroxide (H2O2), ammonium fluoride (NH4F), and borofluoride (HBF4) is also shown. The pH of the solder etching solution is also shown.

[0073] In addition, as a comparative example, the etchant using EDTA instead of HBF4 is set as solder etchant 5.

[0074] Table 4 shows the etching solution using ammonium persulfate. The mass ratios of ammonium persulfate ((NH4)2S2O8), ammonium fluoride (NH4F), and borofluoride hydrofluoric acid (HBF4) are shown, totaling 100% by weight. The solutions were mixed in aqueous solution according to the mass ratios shown in Table 4. The volume of pure water (L: liter) mixed with a total of 1 L of the aqueous solution containing ammonium persulfate ((NH4)2S2O8), ammonium fluoride (NH4F), and borofluoride hydrofluoric acid (HBF4) is also shown. The pH of the solder etching solution is also shown.

[0075] Next, the etchants with added chelating agents compared to solder etchants 1-4 and 6-8 were designated as solder etchants 9-15. The pH was measured similarly. Furthermore, the amount of chelating agent added was expressed as the ratio of the total weight of either hydrogen peroxide or ammonium persulfate to ammonium fluoride, borofluoride, and the chelating agent, set at 100%. The results are shown in Table 5.

[0076] Solder etching solutions 8-13 are solder etching solutions with added chelating agents. By adding chelating agents, the pH of the etching solution can be lowered.

[0077] The ceramic circuit boards of samples 1 to 6 were manufactured using solder etchant solutions 1 to 15 according to the ceramic circuit board manufacturing methods of Examples 1 to 18. Additionally, the sample using solder etchant solution 5 was designated as Comparative Example 1.

[0078] 14L of solder etching solution was prepared. Forty ceramic circuit boards with etched copper plates were etched in batches for solder etching. Examples 1-9 and Comparative Example 1 were performed after removing the resist used during copper plate etching. Examples 10-18 were performed with the resist used during copper plate etching retained. The dimensions of the ceramic circuit boards were set to 180mm x 140mm. The etching area of ​​each ceramic circuit board was set to 200mm². 2 .

[0079] Furthermore, examples in which the solder etching process is performed while "ultrasonic waves" are applied are referred to as "ultrasonic waves". Regarding the frequency of the ultrasonic waves, Examples 1-12 and Comparative Example 1 are set to 50 kHz, while Examples 13-21 are set to 70 kHz.

[0080] The pH change of the solder etching solution was measured after four batches (40 pieces × 4 batches = 160 pieces). Etching solutions with a pH change within ±0.3 were designated as "◎", those within ±0.8 as "○", and those with a change exceeding 1.0 as "×". The results are shown in Tables 6 and 7.

[0081] As can be seen from the table, the pH variation of the solder etchant in the embodiment is small. A longer solder etchant lifespan allows for a later replenishment of the etchant. Therefore, a solder etching process with good mass production performance and reduced costs can be achieved. Furthermore, in the example where the etching process is performed while applying ultrasound, the active metal solder layer is removed earlier.

[0082] Furthermore, the pH changes were small for solder etchants 9-15 (Examples 13-21) with added chelating agents. Conversely, the pH changes were slightly larger for etchants without added chelating agents, as in Examples 15 and 16. The results show that the pH changes are small even when solder etching is performed on a copper plate with resist present. In other words, the solder etchants with added chelating agents can suppress pH changes regardless of the presence or absence of resist, thus proving their effectiveness.

[0083] In contrast, the pH of the etching solution in the comparative example varied significantly. Therefore, it is necessary to increase the frequency of replenishing the solder etching solution.

[0084] Next, the solder etching process of the embodiment was repeated. It was confirmed that the concentration of hydrogen peroxide or ammonium persulfate in the solder etching solution decreased by 10-20% by weight from the initial concentration. Afterwards, the reduced portion was replenished to make it the same as the initial concentration, and the same solder etching process was performed. The pH change of the replenished solder etching solution was measured. The results are shown in Table 8.

[0085] As can be seen from the table, the solder etching solution of the embodiments achieves equivalent solder etching performance when supplemented with hydrogen peroxide or ammonium persulfate. Therefore, it is understood that the etching performance of the active metal solder etching solution of the embodiments can be maintained by supplementation when the concentration of hydrogen peroxide or ammonium persulfate decreases by 10-20% by weight from the initial concentration.

[0086] The above embodiments of the present invention have been illustrated, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents. Furthermore, the above-described embodiments can be combined with each other for implementation.

Claims

1. A method for manufacturing a ceramic circuit board, comprising bonding a ceramic substrate to a copper plate via an active metal solder layer containing Ag, Cu, and an active metal, wherein... The active metal solder layer with a thickness of less than 60 μm is etched using an etching solution containing one or two of hydrogen peroxide and ammonium persulfate, ammonium fluoride and borofluoride, with a pH of 4-6. In the etching of the active metal solder layer, the temperature of the etching solution for the active metal solder is set to 30~70℃, ultrasonic waves above 10kHz are applied, and the etching time for one pass is set to less than 30 minutes.

2. The method for manufacturing a ceramic circuit board according to claim 1, wherein, During the etching of the active metal solder, when the concentration of hydrogen peroxide or ammonium peroxide disulfate in the etching solution for the active metal solder decreases by 10-20% by weight from the initial concentration, the etching solution for the active metal solder is replenished.

3. The method for manufacturing a ceramic circuit board according to claim 1 or 2, wherein, The borofluorinated hydrochloric acid is HBF4.

4. The method for manufacturing a ceramic circuit board according to claim 1 or 2, wherein, The etching solution for the active metal solder contains one or more chelating agents selected from glycine, CDTA, dicarboxylic acid, tricarboxylic acid, and hydroxycarboxylic acid.

5. The method for manufacturing a ceramic circuit board according to claim 3, wherein, The etching solution for the active metal solder contains one or more chelating agents selected from glycine, CDTA, dicarboxylic acid, tricarboxylic acid, and hydroxycarboxylic acid.

6. The method for manufacturing a ceramic circuit board according to claim 1 or 2, wherein, When the etching solution for the active metal solder contains hydrogen peroxide but not ammonium persulfate, and the total weight of hydrogen peroxide, ammonium fluoride, and borofluoride is set to 100% by weight, the content of hydrogen peroxide is 30% by weight or more and 86% by weight or less, the content of ammonium fluoride is 9% by weight or more and 40% by weight or less, and the content of borofluoride is 5% by weight or more and 50% by weight or less.

7. The method for manufacturing a ceramic circuit board according to claim 5, wherein, When the etching solution for the active metal solder contains hydrogen peroxide but not ammonium persulfate, and the total weight of hydrogen peroxide, ammonium fluoride, and borofluoride is set to 100% by weight, the content of hydrogen peroxide is 30% by weight or more and 86% by weight or less, the content of ammonium fluoride is 9% by weight or more and 40% by weight or less, and the content of borofluoride is 5% by weight or more and 50% by weight or less.

8. The method for manufacturing a ceramic circuit board according to claim 1 or 2, wherein, When the etching solution for the active metal solder contains ammonium persulfate but not hydrogen peroxide, and the total weight of ammonium persulfate, ammonium fluoride and borofluoride is set to 100% by weight, the content of ammonium persulfate is 23% by weight or more and 95% by weight or less, the content of ammonium fluoride is 3% by weight or more and 50% by weight or less, and the content of borofluoride is 2% by weight or more and 55% by weight or less.

9. The method for manufacturing a ceramic circuit board according to claim 5, wherein, When the etching solution for the active metal solder contains ammonium persulfate but not hydrogen peroxide, and the total weight of ammonium persulfate, ammonium fluoride and borofluoride is set to 100% by weight, the content of ammonium persulfate is 23% by weight or more and 95% by weight or less, the content of ammonium fluoride is 3% by weight or more and 50% by weight or less, and the content of borofluoride is 2% by weight or more and 55% by weight or less.

10. The method for manufacturing a ceramic circuit board according to claim 1 or 2, wherein, The active metal solder layer contains at least one of Sn or In.

11. The method for manufacturing a ceramic circuit board according to claim 5, wherein, The active metal solder layer contains at least one of Sn or In.

12. The method for manufacturing a ceramic circuit board according to claim 1 or 2, further comprising a step of etching the copper plate, wherein, The active metal solder layer, which has become exposed due to the etching of the copper plate, is etched using the active metal solder etching solution.

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