Ceramic copper circuit board, semiconductor device, and method for manufacturing ceramic copper circuit board

Abstract

Provided are: a ceramic copper circuit board with which elements can be favorably bonded; a semiconductor device; and a method for manufacturing a ceramic copper circuit board. A ceramic copper circuit board according to an embodiment comprises: a ceramic substrate; a copper member joined to the ceramic substrate; and a solder resist provided on a section of the surface of the copper member. An oxide film is provided to at least a section of a region of the surface of the copper member where the solder resist is not provided. The thickness of the oxide film is 0.2-10 nm.

Description

Ceramic Copper Circuit Board, Semiconductor Device, and Method for Manufacturing Ceramic Copper Circuit Board

[0001] The embodiments described below generally relate to a ceramic copper circuit board, a semiconductor device, and a method for manufacturing a ceramic copper circuit board.

[0002] The ceramic circuit board has excellent heat dissipation and thermal durability. For example, the ceramic circuit board is used in a semiconductor device as a board for mounting semiconductor elements. In particular, it is preferably used for power semiconductor devices that handle large outputs.

[0003] When using a ceramic circuit board as a board for mounting elements, soldering is mainly used as a mounting means. When soldering an element onto a metal circuit board, sufficient bonding strength between the solder and the metal circuit may not be obtained. Also, the molten solder may flow out from the desired position due to excessive wetting spread or the like. In particular, the outflow of the solder causes misalignment of the element and solder bridging.

[0004] Even when using a ceramic copper circuit board as a board for mounting elements, the bonding strength between the solder and the copper circuit may be insufficient. Also, defects such as misalignment of the element and solder bridging may occur due to the outflow of the solder. Since the ceramic copper circuit board is often used in applications of power modules that handle large power, it is particularly required to enhance the reliability of bonding.

[0005] In response to these problems, a ceramic copper circuit board with improved bonding reliability has been proposed. For example, in Japanese Patent Application Laid-Open No. 11-111737 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2006-135347 (Patent Document 2), a ceramic copper circuit board capable of preventing the outflow of solder by providing a solder resist at a position surrounding the application location of the solder has been proposed.

[0006] On the other hand, ensuring the reliability of joints through the formation of solder resist is not always sufficient in conventional copper circuit boards, and further improvements are needed. Furthermore, regarding the formation of solder resist, thermosetting solder resist can be used from the standpoint of heat resistance, etc. In this case, the relationship between the heat treatment conditions for curing and the formation of oxide films on copper components has not been sufficiently clarified. For example, if an excessive oxide film is formed in areas where solder resist is not provided, it adversely affects the wetting and spreading of the solder. Adverse effects on solder wetting and spreading can lead to mounting defects of components.

[0007] Japanese Patent Publication No. 11-111737 Japanese Patent Publication No. 2006-135347

[0008] The problem that this embodiment aims to solve is to provide a ceramic copper circuit board, a semiconductor device, and a method for manufacturing a ceramic copper circuit board that can bond elements well.

[0009] The ceramic copper circuit board of the embodiment comprises a ceramic substrate, a copper member bonded to the ceramic substrate, and a solder resist provided on a part of the surface of the copper member. At least a portion of the area on the surface of the copper member where the solder resist is not provided is provided with an oxide film. The thickness of the oxide film is 0.2 nm or more and 10 nm or less.

[0010] Figure 1 is a schematic cross-sectional view showing an example of a ceramic copper circuit board according to the embodiment. Figures 2(a) and 2(b) are graphs showing an example of an FT-IR spectrum. Figure 3 is a top view showing an example of a ceramic copper circuit board according to the embodiment. Figure 4 is a flowchart showing an example of a method for manufacturing a ceramic copper circuit board according to the embodiment.

[0011] Figure 1 is a schematic cross-sectional view showing an example of a ceramic copper circuit board according to the embodiment. The configuration of the ceramic copper circuit board according to the embodiment will be described with reference to Figure 1. In Figure 1, reference numeral 1 denotes the ceramic copper circuit board, reference numeral 2 denotes the ceramic substrate, reference numeral 3 denotes the copper member, reference numeral 4 denotes the bonding layer, reference numeral 5 denotes the solder resist, and reference numeral 6 denotes the oxide film.

[0012] In the ceramic copper circuit board 1 according to this embodiment, a copper member 3 is provided on a ceramic substrate 2, and a solder resist 5 is provided on a part of the surface of the copper member 3. The copper member 3 includes an oxide film 6 in at least a part of the area on its surface where the solder resist is not provided. The thickness of the oxide film 6 is 0.2 nm or more and 10 nm or less.

[0013] The ceramic copper circuit board 1 according to this embodiment is not limited to the example shown in Figure 1. For example, in the structure illustrated in Figure 1, the copper member 3 is provided on the ceramic substrate 2 via a bonding layer 4, but the method of bonding the ceramic substrate 2 and the copper member 3 is not particularly limited. For example, the bonding layer 4 is an activated metal brazing layer, which will be described later. Alternatively, the copper member 3 may be provided on the ceramic substrate 2 without a bonding layer 4. The copper member 3 may be provided on the ceramic substrate 2 via a thin film layer instead of the bonding layer 4 using an activated metal brazing layer, which will be described later. The thin film layer is formed by depositing a metal material by a method such as sputtering.

[0014] In the structure illustrated in Figure 1, copper members 3 are provided on both sides of the ceramic substrate 2. In this embodiment, copper members 3 may be provided on only one side of the ceramic substrate 2. The number of copper members 3 provided on one side of the ceramic substrate 2 may be one or two or more. When the ceramic copper circuit board 1 includes multiple copper members 3, it is not necessarily required that solder resist 5 be provided on all copper members 3. Also, when the ceramic copper circuit board 1 includes multiple copper members 3, it is not necessarily required that all copper members 3 include an oxide film 6.

[0015] In the structure illustrated in Figure 1, the solder resist 5 is provided only on the copper member 3. In this embodiment, the solder resist 5 may also be provided on other parts of the ceramic copper circuit board 1 (for example, the surface of the bonding layer 4 or the surface of the ceramic substrate 2). The solder resist 5 may be provided continuously on the copper member 3 and on other parts.

[0016] In the structure illustrated in Figure 1, the oxide film 6 is provided not only in the areas of the copper member 3 surface where solder resist is not provided, but also in the areas where solder resist is provided. That is, the solder resist 5 is provided on top of the oxide film 6. In the copper member 3, the oxide film 6 may not be provided in the areas where solder resist is provided, or the oxide film 6 may be provided in part or all of the areas where solder resist is not provided.

[0017] The ceramic copper circuit board 1 according to this embodiment includes a solder resist 5 provided on the copper member 3. The solder resist 5 helps to suppress solder leakage during soldering. Furthermore, by controlling the thickness of the oxide film 6, solder leakage can be suppressed and the bonding strength (bonding properties) between the copper member 3 and the solder can be improved. These effects enable good bonding of semiconductor elements to the copper member 3. If solder leaks, there will be insufficient solder for bonding. Also, it may cause electrical conductivity or insulation failure between adjacent copper members 3. The solder is, for example, lead-free solder.

[0018] Next, the components of the ceramic copper circuit board 1 according to the embodiment will be described. The ceramic substrate 2 is made of a plate-shaped ceramic sintered body. The thickness of the ceramic substrate 2 is, for example, 0.2 to 0.8 mm. The ceramic substrate 2 is, for example, a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, or an argil substrate. An argil substrate refers to an aluminum oxide substrate containing zirconium oxide.

[0019] For example, silicon nitride substrates have a thermal conductivity of 50 W / (m·K) or higher and a three-point bending strength of 600 MPa or higher. Aluminum nitride substrates have a thermal conductivity of 150 W / (m·K) or higher and a three-point bending strength of 300 to 550 MPa. Aluminum oxide substrates have a thermal conductivity of 20 to 40 W / (m·K) and a three-point bending strength of 400 to 500 MPa. Argil substrates have a thermal conductivity of 20 to 40 W / (m·K) and a three-point bending strength of 450 to 600 MPa. Silicon nitride substrates have high strength and can be thinned to, for example, a thickness of 0.33 mm or less. Aluminum nitride substrates have excellent thermal conductivity. Aluminum oxide substrates and Argil substrates have low thermal conductivity, but these substrates are inexpensive. The type of ceramic substrate 2 can be appropriately selected according to the purpose.

[0020] The thermal conductivity of the ceramic substrate 2 is preferably 50 W / (m·K) or higher, and more preferably 80 W / (m·K) or higher. By using a ceramic substrate 2 with excellent thermal conductivity, the heat dissipation of the ceramic copper circuit board 1 can be improved.

[0021] The ceramic substrate 2 is preferably made of a sintered body with a three-point bending strength of 600 MPa or more. A ceramic substrate 2 made of a sintered body with excellent three-point bending strength makes it possible to thin the substrate while maintaining reliability. Thinning the ceramic substrate 2 improves the heat dissipation of the ceramic copper circuit board 1. Furthermore, improved heat dissipation suppresses the occurrence of defects such as cracks due to thermal cycling, thereby improving the reliability of the ceramic copper circuit board 1. If a high-strength ceramic substrate is used, the substrate thickness can be reduced to 0.4 mm or less. Silicon nitride substrates have high strength, making them effective for thinning ceramic substrates. Thinning the substrate leads to improved heat dissipation of the ceramic copper circuit board.

[0022] The copper member 3 is made of, for example, copper, a copper alloy, or a clad material containing copper as a component. In particular, it is preferable to use an oxygen-free copper plate as the copper member 3. The copper member 3 may have a circuit shape depending on the purpose.

[0023] The thickness of the copper member 3 is preferably 0.3 mm or more, and more preferably 0.7 mm or more. By increasing the thickness of the copper member 3, the heat dissipation of the ceramic copper circuit board 1 can be improved. When the copper member 3 is used as a circuit, increasing the thickness of the copper member 3 can increase the current carrying capacity. There is no particular upper limit to the thickness of the copper member 3, but it may be 10 mm or less. If the thickness of the copper member 3 is 10 mm or less, the thermal stress generated at the joint between the ceramic substrate 2 and the copper member 3 or at the joint between the copper member 3 and the element during temperature changes can be reduced, and durability can be improved. For this reason, the thickness of the copper member 3 is preferably in the range of 0.3 mm to 10 mm, and more preferably in the range of 0.7 mm to 5 mm.

[0024] The copper member 3 has a placement area. Here, the "placement area" refers to a continuous portion (flat surface) of the surface of the copper member 3 that is not covered by the solder resist 5. A part or all of an object can be placed in the placement area using at least solder. The object is not particularly limited and may be, for example, a semiconductor element, other electronic components, a heat sink, a lead frame, a metal terminal, or other mounted components. The form of the placement area is not particularly limited. For example, the maximum placement area on the copper member 3 is 0.5 cm. ２ It has the above area. The area of ​​the largest placement area is 1.0 cm². ２ The above is also fine, 2.0 cm ２ The above is also acceptable. There is no particular limit to the area of ​​the placement section, but 200 cm² is recommended. ２ The following is a standard example: 100 cm ２ The following is acceptable: 30 cm ２ The following conditions may apply. If the area of ​​the copper component 3 placement area satisfies the above conditions, the ceramic copper circuit board 1 can be suitably used, for example, for power module applications. As the area increases, the amount of solder applied also increases. Therefore, the impact of solder leakage may become greater. For this reason, it is preferable that the area of ​​the placement area is not excessively large relative to the components mounted.

[0025] At least a portion of the surface of the copper member 3 where the solder resist 5 is not provided is a placement area. The copper member 3 includes an oxide film 6 in a region of its surface that includes at least one of the placement areas. Here, "oxide film 6" refers to Cu ２ This refers to a layer whose main component is at least one selected from the group consisting of O (cuprous oxide) and CuO (copper oxide). In other words, the oxide film 6 is Cu ２ It may contain only oxygen, only CuO, or both. "Main component" refers to a component that is present in an amount of 50% by mass or more.

[0026] The thickness of the oxide film 6 is preferably 0.2 nm or more and 10 nm or less. When the thickness of the oxide film 6 is 0.2 nm or more, when the element is joined to the copper member 3 using solder, excessive wetting and spreading of the solder is suppressed, which helps to prevent solder leakage. If the thickness of the oxide film 6 is less than 0.2 nm, the effect of providing the oxide film may not be sufficiently obtained. The thickness of the oxide film 6 may be 1.0 nm or more, 1.8 nm or more, or 3.0 nm or more. In the area of ​​the placement portion where solder is applied, it is preferable that the thickness of the oxide film 6 is within the range of 0.2 nm or more and 10 nm or less, regardless of where it is measured.

[0027] On the other hand, if the thickness of the oxide film 6 exceeds 10 nm, the wettability of the solder decreases, and proper wetting and spreading of the solder during joining is inhibited. As a result, it can cause non-wetting and void formation at the joining interface, potentially reducing the heat dissipation and joining reliability of the ceramic copper circuit board 1. When the thickness of the oxide film 6 is 10 nm or less, proper wetting and spreading of the solder is not inhibited when joining an element to the copper member 3 using solder, and problems such as non-wetting and void formation are suppressed. As a result, the element can be joined to the copper member 3 well. In addition, the formation of an alloy layer at the interface between the copper member 3 and the solder is further promoted, improving the bonding properties and allowing the element to be joined to the copper member 3 well. The thickness of the oxide film 6 is preferably 7.0 nm or less, more preferably 5.0 nm or less, and most preferably 4.0 nm or less.

[0028] For example, the thickness of the oxide film 6 can be increased by performing an oxidation treatment during the manufacturing process. The thickness of the oxide film 6 can be decreased by performing a cleaning or reduction treatment with a chemical solution. It is preferable to perform treatments such as oxidation, reduction, and cleaning before applying the solder resist 5, as described later. Furthermore, the increase in the thickness of the oxide film 6 can be suppressed by curing the solder resist 5 under the conditions described later.

[0029] The copper component 3 does not necessarily need to be coated with a rust inhibitor. A rust inhibitor refers to a chemical solution that has a rust-preventive effect. By applying a rust inhibitor to the copper component 3, a rust inhibitor film can be formed. Rust inhibitor films include oxide film type, precipitate film type, and adsorption film type. For example, oxide film type rust inhibitors include chromates, molybdates, tungstates, and nitrites. These rust inhibitors do not contain copper oxide. Therefore, the oxide film 6 on the surface of the copper component and the rust inhibitor can be distinguished. Furthermore, the film containing the rust inhibitor is formed by applying the rust inhibitor. For this reason, it is difficult to control the thickness of the film containing the rust inhibitor within the range of 0.2 nm to 10 nm.

[0030] In this embodiment, since no rust inhibitor is applied to the copper member 3, the inhibition of solder wetting by the rust inhibitor can be avoided. Furthermore, the deterioration of the electrical, mechanical, or chemical properties of the ceramic copper circuit board 1 and the semiconductor device equipped therewith by the rust inhibitor can be avoided. The cost incurred by applying the rust inhibitor can be reduced, and the yield can be improved by eliminating a process step. For example, by curing the solder resist 5 using the conditions described in the manufacturing method described later, the thickness of the oxide film 6 can be reduced without using a rust inhibitor.

[0031] Here, the "thickness of the oxide film 6" refers to the value measured under the following conditions by the sequential electrochemical reduction method (SERA). For the measurement, a QC-100 manufactured by ECI TECHNOLOGY or a measurement device equivalent thereto is used. When a rust preventive coating is formed on the copper member 3, the coating is removed using means such as ultrasonic cleaning prior to the measurement. The ultrasonic cleaning is performed, for example, in a 2-butoxyethanol solution or a 2-propanol solution. The time for ultrasonic cleaning is, for example, 3 minutes or more and 30 minutes or less. If necessary, ultrasonic cleaning may be performed in a 2-butoxyethanol solution and then in a 2-propanol solution.

[0032] As the buffer solution, a boric acid buffer solution is used. The boric acid buffer solution consists of 6.18 g / L of H ３ BO ３ (boric acid), 9.55 g / L of Na ２ B ４ O ７ ・10H ２ O (sodium tetraborate decahydrate), and pure water, and its pH is 8.4. A constant current of 30 μA / cm ２ is passed through the ceramic copper circuit board 1 in the buffer solution, and the reduction reaction time is measured. The measured reduction time is applied to the following formulas (1) and (2) to calculate the thicknesses of Cu ２ O (copper(I) oxide) and CuO (copper(II) oxide). The sum of the calculated thicknesses of Cu ２ O (copper(I) oxide) and CuO (copper(II) oxide) is used as the thickness of the oxide film 6. (Formula 1) Cu ２ O [nm] = 0.0012 [(nm·cm ２ ) / (s·μA)] × current density [μA / cm ２ ] × reduction time [s] (Formula 2) CuO [nm] = 0.0006 [(nm·cm ２ ) / (s·μA)] × current density [μA / cm ２ ] × reduction time [s]

[0033] Equations 1 and 2 are based on the SERA method. The coefficients 0.0012 and 0.0006 are conversion factors applied in the SERA method. The conversion factor is a value used to convert the amount of electricity required for reduction into the thickness of the oxide film. This conversion factor is derived based on Faraday's law, taking into account the molecular weight, density, and number of electrons required for reduction for each oxide. The reduction reaction time is given for copper oxide (Cu ２ This indicates the duration of the reduction reaction in the potential range where the reduction of O (CuO) is dominant. Specifically, it indicates the time during which the potential remained around -0.35 to -0.65 V. ２ The reduction time for O is defined as the time during which the potential is maintained at approximately -0.65 to -0.85 V. In other words, the thickness can be determined by the amount of electricity expended in the reduction of each oxide, based on the reduction reaction time.

[0034] The bonding layer 4 is formed by joining the ceramic substrate 2 and the copper member 3 using a bonding material such as brazing material. The bonding layer 4 is formed, for example, by bonding using brazing material. In particular, the brazing material is preferably an active metal brazing material.

[0035] When the bonding layer 4 is formed by bonding using an activated metal brazing material, the bonding layer 4 contains at least one activated metal selected from Ti (titanium), Zr (zirconium), Hf (hafnium), and Nb (niobium). In particular, it is preferable that the bonding layer 4 contains Ti. The activated metal can react with the ceramic substrate during brazing to form a strong bonding state. The activated metal forms an activated metal nitride phase with the nitride-based ceramics. When Ti is used as the activated metal, a titanium nitride (TiN) phase may be formed. The activated metal forms an activated metal oxide phase with the oxide ceramics. When Ti is used as the activated metal, titanium oxide (TiO) may be formed. ２ A phase may be formed.

[0036] The activated metal brazing material may contain one or two selected from Ag (silver) and Cu (copper). When the bonding layer 4 is formed by bonding using the activated metal brazing material, the bonding layer 4 may contain one or two selected from Sn (tin) and In (indium). The bonding layer 4 may also contain C (carbon). Sn or In added to the brazing material can lower the melting point of the brazing material and reduce the bonding temperature during brazing. Bonding at low temperatures can reduce residual stress in the bonded body and improve the thermal cycle reliability of the ceramic copper circuit board 1. Carbon added to the brazing material can suppress the fluidity of the brazing material during brazing and contribute to the uniformity of the thickness of the bonding layer 4.

[0037] Solder resist 5 is made of, for example, a resin. Solder resist 5 has a role in preventing short circuits caused by solder bridges. The type of resin is not particularly limited. For example, the resin may be photocurable or thermosetting. The resin may be selected according to the purpose. Thermosetting resins include phenolic resins and epoxy resins. Photocurable resins include bismaleimide resins and cyanate resins. Photocurable resins and thermosetting resins may be used in mixture form. Solder resist 5 may be made of a single resin, a mixture of multiple resins, or a resin mixed with additives. Additives include, for example, pigments. Solder resist 5 may be colored green, black, white, blue, or red depending on the purpose. For example, general solder resist 5 is colored green.

[0038] For example, solder resist 5 made of a thermosetting resin generally has excellent heat resistance. When heat resistance is important, it is preferable to use a thermosetting resin. On the other hand, when a thermosetting resin is used, heat treatment is required for curing. As a result, the thickness of the oxide film 6 may become excessively large. However, even when using a thermosetting resin, the excessive increase in the thickness of the oxide film 6 can be suppressed by using curing conditions, for example, as described later.

[0039] When a thermosetting resin is used for the solder resist 5, it is preferable that the solder resist 5 contains epoxy resin. Preferably, the solder resist 5 contains 10% by mass or more of epoxy resin. The solder resist 5 may contain 20% by mass or more of epoxy resin, or 30% by mass or more and 100% by mass or less. When the solder resist 5 contains epoxy resin, the heat resistance and corrosion resistance of the solder resist 5 can be improved. In addition, the epoxy resin can adhere well to the copper member 3 and is easy to handle during manufacturing.

[0040] The solder resist 5 may be a resin obtained by mixing a thermosetting resin and a UV-curing resin. When mixing a thermosetting resin and a UV-curing resin, the proportion of epoxy resin is preferably 30% by mass or more.

[0041] Epoxy resins generally contain epoxy rings and aromatic rings. During the curing reaction, the structure of the aromatic rings remains unchanged, but the epoxy rings open. Therefore, the peak intensity I in the FT-IR spectrum originates from the aromatic rings. ２ and peak intensity I derived from the epoxy ring １ The intensity ratio I ２ / I １ This can be used as an indicator of the progress of the hardening reaction.

[0042] "Peak intensity" is expressed as the difference between the absorbance at the peak of the peak and the absorbance at the baseline corresponding to that peak. If there are no flat, linear portions on either side of the peak in question, the baseline can be obtained by identifying the valleys (local minimums) located on either side of the peak and connecting the absorbances at these two valleys. If the FT-IR spectrum measuring instrument is equipped with analysis software capable of calculating peak intensity, the peak intensity may be obtained using that software.

[0043] When using a resin containing epoxy resin, the peak intensity ratio I of the cured resin ２ / I １ It is preferably 0.6 or higher, and more preferably 0.8 or higher. Peak intensity I derived from aromatic ring ２and peak intensity I derived from the epoxy ring １ The selection shall conform to JIS-K-7148-2. JIS-K-7148-2 corresponds to ISO 20368.

[0044] Figures 2(a) and 2(b) are graphs showing examples of FT-IR spectra. In Figures 2(a) and 2(b), the horizontal axis represents wavenumber, and the vertical axis represents absorbance. Figure 2(a) shows a value of 915 cm⁻¹. －１ The spectrum of the vicinity is shown. Figure 2(b) is 1505 cm⁻¹. －１ The spectrum of the vicinity is shown. The peak originating from the epoxy ring is at 915 cm⁻¹. －１ It appears at 1505 cm. The peak derived from the aromatic ring is at 1505 cm. －１ It appears at 915 cm. －１ The intensity of the peak that appears is I １ Let's assume it's 1505cm. －１ The intensity of the peak that appears is I ２ Figures 2(a) and 2(b) are I ２ / I １ This shows the measurement result for epoxy resin with a value of 0.8.

[0045] Peak intensity ratio I ２ / I １ It is preferably 0.6 or higher, and more preferably 0.8 or higher. Peak intensity ratio I ２ / I １ The upper limit is not particularly limited, but it is preferably 5 or less.

[0046] Peak intensity ratio I ２ / I １ This is an index indicating the proportion of epoxy groups consumed in the curing reaction. Peak intensity ratio I ２ / I １ A value of 0.6 or higher indicates that the curing reaction is progressing and the number of epoxy groups is decreasing. This is because the aromatic rings of epoxy resin remain unchanged during the curing reaction, while the epoxy rings are consumed by the reaction.

[0047] Also, the peak intensity ratio I ２ / I １This also serves as an indicator of the proportion of aromatic rings in the resin that makes up the solder resist 5. In epoxy resin, an increase in aromatic rings improves heat resistance. Improved heat resistance makes the solder resist 5 less susceptible to damage from the heat of soldering. On the other hand, if the number of aromatic rings increases too much, the flexibility of the solder resist 5 after curing decreases. Reduced flexibility can make the solder resist 5 more prone to cracking under environmental conditions such as thermal cycling. Therefore, the peak intensity ratio I ２ / I １ It is preferably in the range of 0.6 to 5, and more preferably in the range of 0.8 to 4.

[0048] The FT-IR spectrum is measured using the Attenuated Total Reflection (ATR) method. Solder resist 5 that satisfies the above characteristics identified from the FT-IR spectrum indicates that the contained resin has been well cured. Solder resist 5 that satisfies the above characteristics can be obtained using the heat treatment conditions described later. In addition, the number of integration cycles in the ATR method is set to 64 or more.

[0049] The thickness of the solder resist 5 is preferably between 2 μm and 100 μm. When the thickness of the solder resist 5 is within this range, the solder resist 5 acts as a barrier to suppress solder leakage when joining elements to the copper member 3 using solder, contributing to the prevention of solder leakage. If the thickness of the solder resist 5 exceeds 100 μm, it may become a factor in increasing costs. Also, if the solder resist 5 is too thick, the solder resist 5 will act as a thermal resistor, which may reduce the heat dissipation performance of the ceramic copper circuit board 1. For this reason, the thickness of the solder resist 5 is preferably within the range of 2 μm to 100 μm, and more preferably within the range of 5 μm to 30 μm.

[0050] If the thickness of the solder resist 5 varies across different sections, the maximum thickness should be used as the "thickness of the solder resist 5". A dial gauge can be used to measure the thickness of the solder resist 5. Alternatively, the thickness of the solder resist 5 may be measured by cross-sectional observation.

[0051] The width of the solder resist 5 may be 0.1 mm or more (100 μm or more). When the width of the solder resist 5 is 0.1 mm or more, when molten solder rides onto the solder resist 5 during soldering, the solder can be kept on the solder resist 5. As a result, the formation of solder bridges can be suppressed. There is no particular upper limit to the width of the solder resist 5, but it may be 10 mm or less, or 2 mm or less. Here, the "width" of the solder resist 5 refers to the shortest distance between the outer wall and the inner wall of the solder resist 5. For example, when the solder resist 5 is provided in a ring shape, the width of the solder resist 5 is the value obtained by subtracting the radius to the inner wall (inner radius) from the radius to the outer wall (outer radius).

[0052] The pencil hardness of the solder resist 5 is preferably 4H or higher, more preferably 5H or higher, and most preferably 6H or higher. The pencil hardness is measured in accordance with JIS-K-5600-5-4. JIS-K-5600-5-4 corresponds to ISO 15184 (2020). When the pencil hardness of the solder resist 5 is 4H or higher, sufficient hardness for holding the solder resist 5 can be ensured. This increases the durability of the solder resist 5 and allows for good bonding of the components.

[0053] For the solder resist 5, the classification of the cross-cut test result is preferably "0" or "1" out of 6 levels, and more preferably "0". The cross-cut test is measured in accordance with JIS-K-5600-5-6. JIS-K-5600-5-6 corresponds to ISO 2409 (2020). If the result of the cross-cut test is "0" or "1", it indicates that sufficient adhesion for holding the solder resist 5 has been ensured. High adhesion can suppress damage or misalignment of the solder resist 5 during solder application. As a result, the durability of the solder resist 5 is increased and the elements can be joined well.

[0054] The area where the solder resist 5 is provided may be determined according to the purpose. For example, the solder resist 5 may be provided so as to surround the area where solder is expected to be placed. Alternatively, the solder resist 5 may be provided so as to partially surround the area where solder is expected to be placed. The solder resist 5 may also be provided only in areas where solder leakage may be a problem.

[0055] The area of ​​the region where the solder resist 5 is provided is not particularly limited, for example, 30 mm². ２ The above is sufficient; 50 mm ２ The above is sufficient, and 100 mm ２ The above is sufficient, and 200 mm ２ The above is sufficient, and 1000 mm ２ The above is sufficient. The area of ​​the region where the solder resist 5 is provided is 200 cm². ２ The following is a standard example: 100 cm ２ The following is acceptable: 30 cm ２ The following may be used: 20 cm ２ The following is acceptable. Note that 1000 mm ２ It is 10 cm ２ The area of ​​the region provided with solder resist 5 is the total area of ​​one or more solder resists 5 provided on the surface of a single copper member 3.

[0056] Figure 3 is a top view showing an example of a ceramic copper circuit board according to the embodiment. The reference numerals in Figure 3 are the same as those in Figure 1. Note that the oxide film 6 is omitted in Figure 3.

[0057] In the example shown in Figure 3, the upper copper member 3 is provided with solder resist 5 surrounding the edge (edge) of its upper surface. The lower copper member 3 is also provided with solder resist 5 surrounding the central part of its upper surface. The area enclosed by the solder resist 5 is the area where solder joining will be performed on the surface of the copper member 3. The area enclosed by the solder resist 5 becomes the solder application area.

[0058] Next, a method for manufacturing the ceramic copper circuit board according to the embodiment will be described. The manufacturing method of the ceramic copper circuit board 1 according to the embodiment is not particularly limited as long as it has the above configuration. Here, an example of a method for manufacturing with good yield will be described.

[0059] As an example, the manufacturing method according to the embodiment comprises a lamination step, a bonding step, a coating step, and a curing step. In the lamination step, a ceramic substrate and a copper member are laminated via a brazing material. In the bonding step, the laminate is heat-bonded. In the coating step, solder resist ink is applied to the copper member of the bonded body. In the curing step, the solder resist ink is cured by a curing treatment such as exposure treatment or heat treatment.

[0060] Figure 4 is a flow chart showing an example of the manufacturing process for a ceramic copper circuit board according to the embodiment. In Figure 4, reference numeral S11 denotes the lamination process. Reference numeral S12 denotes the heat bonding process. Reference numeral S21 denotes the solder resist ink application process. Reference numeral S22 denotes the solder resist ink curing process. Reference numeral S31 denotes the oxide film formation process. Note that the manufacturing process according to the embodiment is not limited to this method, and other processes may be performed in between. The solder resist ink may be transparent or colored.

[0061] (Lamination Process) First, a ceramic substrate 2 is prepared. As mentioned above, the ceramic substrate 2 is preferably one of a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, or an argil substrate. More preferably, the ceramic substrate 2 is a silicon nitride substrate with a thermal conductivity of 80 W / (m·K) or more and a three-point bending strength of 600 MPa or more.

[0062] Next, prepare the copper member 3. As mentioned above, the copper member 3 is made of copper, a copper alloy, or a clad material containing copper as a component. In particular, the copper member 3 is preferably an oxygen-free copper plate. The thickness of the copper member 3 is preferably 0.3 mm or more and 10 mm or less. The copper member 3 may have a circuit shape pre-formed on it by processing such as pressing or wire cutting.

[0063] Next, a brazing material to form the bonding layer 4 is prepared. As mentioned above, the brazing material preferably contains an active metal, and is particularly preferably Ti. The brazing material may also contain Ag (silver), Cu (copper), Sn (tin), or In (indium), and may also contain C (carbon). After mixing the brazing material components, a solvent or binder is added as needed to prepare a paste. The brazing paste is applied to at least one of the ceramic substrate 2 and the copper member 3. Then, the copper member 3 is placed on the ceramic substrate 2 to obtain a laminate. In this method, a bonding material such as brazing foil may be used instead of brazing paste.

[0064] (Drying process) If necessary, a drying process for the laminate may be performed prior to the subsequent joining process. The drying process involves heat treatment of the laminate at a temperature of 40°C to 80°C. By performing the drying process, some of the solvent in the brazing paste can be removed, and the contact between the brazing paste and the copper member 3 can be improved.

[0065] (Heat Bonding Process) The laminate is heat-bonded. In heat bonding, the bonding temperature is preferably 600°C or higher and 960°C or lower. The bonding atmosphere is preferably a vacuum or an inert gas. Using these atmospheric conditions can also suppress excessive oxidation of the copper member 3. Heat bonding may be performed while applying a load to the laminate.

[0066] (Etching process) If necessary, the copper member 3 may be etched to impart a desired shape, such as a circuit shape. If the circuit shape is already imparted to the copper member 3, or if there is no need to use the etching process, this process may be omitted.

[0067] (Rust Inhibitor Application Process) A rust inhibitor may be applied to the copper member 3 as needed. By applying a rust inhibitor, for example, when heat treatment is performed in the solder resist ink curing process described later, the increase in the thickness of the oxide film 6 due to heat treatment can be suppressed. Specifically, even if the treatment temperature is 140°C or higher, a significant increase in the thickness of the oxide film 6 can be suppressed.

[0068] The rust inhibitor application step may be omitted. As mentioned above, if this step is not performed, the rust inhibitor will not be applied to the copper member 3. By not applying the rust inhibitor to the copper member 3, improvements in properties or yield can be obtained.

[0069] (Solder Resist Ink Coating Process) Next, uncured solder resist ink is applied to the copper member 3. The solder resist ink is, for example, a resin. As mentioned above, the type of resin may be selected according to the purpose. As mentioned above, the resin may include epoxy resin, and after heat curing treatment, the FT-IR spectrum may satisfy the conditions described above.

[0070] Note that the peak intensity ratio after curing is I ２ / I １ If the above range is met, the peak intensity ratio of the solder resist ink before curing is not particularly limited. Preferably, the peak intensity ratio of the solder resist ink before curing is ２ / I １ The peak intensity ratio of the solder resist after curing is I ２ / I １ It is smaller than that. As mentioned above, the epoxy groups decrease due to the curing reaction. A ratio of peak intensity after curing that is larger than the ratio of peak intensity before curing indicates that the epoxy groups have decreased due to the curing reaction. For example, the peak intensity before curing is １ and peak intensity I after curing １ Comparing the two, the peak intensity after curing I １ Peak intensity I before curing １ Ratio (before hardening I １ / After curing I １ ) is preferably 1.5 or higher, and more preferably 2.0 or higher.

[0071] When heat treatment is performed under the conditions described later, the target peak intensity I after curing １ In contrast, peak intensity I １By using a solder resist ink with a ratio of 1.5 or higher, a solder resist with good properties after curing can be obtained. The upper limit of the ratio is not particularly limited, but it is preferably 20 or less, and more preferably 12 or less. If the ratio is too high, that is, if the amount of epoxy groups in the solder resist ink before curing is too high compared to the amount of epoxy groups in the solder resist after curing, the amount of epoxy groups will not be sufficiently reduced even if heat treatment is performed under the conditions described later. As a result, the proportion of aromatic rings in the solder resist after curing decreases, and the heat resistance of the solder resist may decrease.

[0072] The uncured solder resist ink may be applied not only to the copper member 3 but also to areas other than the copper member 3. In the final ceramic copper circuit board 1, the solder resist 5 is provided on a portion of the surface of the copper member 3. In this step, the uncured solder resist ink may be applied only to the ultimately desired locations, or it may be applied to areas other than the ultimately desired locations. If the uncured solder resist ink is applied to areas other than the ultimately desired locations, the uncured or cured solder resist applied to the unnecessary areas is removed in a subsequent step.

[0073] The method of applying the solder resist ink is not particularly limited, and methods such as screen printing, spray coating, and curtain coating can be used. During application, a mask or other component may be placed to apply the solder resist ink only to the desired location. Here, only the method of applying the solder resist ink has been described, but other methods such as placing a dry film resist may also be used.

[0074] (Solder Resist Ink Curing Process) Next, the uncured solder resist ink is cured. If the uncured solder resist ink is photocurable, it can be cured by exposure treatment using an exposure device or the like. If the solder resist 5 in the following process is to be removed from unnecessary areas, the solder resist ink in the desired areas may be cured by exposure treatment through a negative film or the like.

[0075] If the uncured solder resist ink is thermosetting, it can be cured by heat treatment using a drying oven or a constant temperature oven. In the manufactured ceramic copper circuit board 1, it may be necessary to reduce the thickness of the oxide film 6 within the range of 0.2 nm to 10 nm. For example, a reduction in the thickness of the oxide film 6 may be required for reasons such as the need to further improve the bonding properties of the elements. In that case, it is preferable to perform heat treatment at a processing temperature of 110°C to 160°C and a processing time of 15 minutes to 60 minutes. By performing heat treatment under these conditions, a significant increase in the thickness of the oxide film 6 can be suppressed. According to experimental results described later, when heat treatment is performed under the above conditions in air, even if no rust inhibitor is applied to the copper member 3, the increase in the oxide film thickness is at most about 0.2 nm.

[0076] The copper component 3 used in the fabrication of the ceramic copper circuit board 1 is preferably stored in a non-oxidizing atmosphere to prevent oxidation. A non-oxidizing atmosphere is such as a vacuum or a nitrogen atmosphere. If the copper component 3 is not stored under appropriate conditions, the thickness of the oxide film on the copper component 3 may reach at least 50 nm before the solder resist ink coating step. If the oxide film is thick, it is necessary to perform an oxide film thickness control step to thin the oxide film.

[0077] In the manufacturing method, if the desired oxide film thickness for the ceramic copper circuit board 1 is 4.0 nm or less, it is preferable to heat-treat the copper component stored in a non-oxidizing atmosphere under the above conditions. As a result, the oxide film thickness can be within the desired range without the need for an oxide film thickness control step. The "oxide film thickness control step" includes one or more steps selected from an oxide film formation step, an oxide film thickening step, and an oxide film thinning step. The steps to be performed can be selected depending on the situation.

[0078] Instead of performing heat treatment under the above conditions, heat treatment may be carried out in an inert atmosphere using an apparatus capable of controlling the atmosphere. On the other hand, heat treatment in air is preferred from the viewpoint of yield or environmental impact. Even when performing heat treatment in air, a significant increase in the thickness of the oxide film 6 can be suppressed by performing the heat treatment under the above conditions. As a result, the thickness of the oxide film 6 can be controlled within the range of 0.2 nm to 10 nm.

[0079] (Oxide film formation process) An oxide film 6 is formed on at least a portion of the area on the surface of the copper member 3 where the solder resist 5 is not provided. If the desired oxide film is obtained at the time of the heat treatment to cure the solder resist ink described above, that oxide film may be used as the oxide film 6. In the process of forming the oxide film 6, for example, the ceramic copper circuit board 1 is held or heat-treated in an oxidizing atmosphere. An oxidizing atmosphere is an atmosphere containing oxygen, such as air. For the heat treatment performed in the oxide film formation process, the heat treatment temperature is preferably 80°C to 160°C and the time is preferably 20 minutes to 90 minutes. If the solder resist ink has been cured, there will be no adverse effect on the solder resist 5 even if heat treatment is performed again.

[0080] The oxide film formation process may be performed before applying the solder resist ink. If the oxide film is thick, the thickness of the oxide film 6 may be controlled by cleaning or reducing the copper member 3 with a chemical solution. The chemical solution may be, for example, flux.

[0081] (Solder Resist Ink Removal Process) If necessary, the solder resist 5 may be removed from unnecessary areas. For example, chemical treatment such as etching may be used to remove the solder resist 5.

[0082] By the above manufacturing method, a ceramic copper circuit board according to the embodiment can be manufactured.

[0083] (Examples 1-7, Comparative Examples 1-3) Ceramic copper circuit boards were fabricated by joining a silicon nitride substrate and an oxygen-free copper plate with an activated metal brazing material. In each of the examples and comparative examples, the following tests were performed on the ceramic copper circuit boards. The method for preparing the samples is as follows.

[0084] The silicon nitride substrate has a thickness of 0.32 mm, a three-point bending strength of 650 MPa, and a thermal conductivity of 90 W / (m·K). The copper plate has a thickness of 0.8 mm. The activated metal brazing material is a Cu-Sn-Ti type brazing material that does not contain Ag. First, activated metal brazing paste is applied to both sides of the silicon nitride substrate. The copper plate is placed on top of the activated metal brazing paste. The resulting laminate is heat-bonded at a bonding temperature of 800-900°C, a bonding time of 20-50 min, and in a nitrogen atmosphere to obtain a bonded body. After bonding, the copper plate is etched to fabricate a ceramic copper circuit board. The surface area of ​​the copper plate is 800 mm². ２ This is the extent of the problem. Furthermore, the oxide film on the copper plate surface of the ceramic copper circuit board was within the range of 0.1 nm or less.

[0085] Next, in Examples 1-7 and Comparative Examples 2-3, solder resist ink was applied to the copper plate surface. A thermosetting resin containing epoxy resin was used as the solder resist ink. Using a screen printing machine, the solder resist ink was applied to a thickness of 10-20 μm and 130 mm. ２ The design was printed over an area of ​​a certain size. Afterward, a heat treatment was performed to form a solder resist. The heat treatment was carried out in air. The heat treatment conditions are shown in Table 1.

[0086] The solder resist was formed to surround the solder application area on the upper surface of the copper plate. After the formation of the solder resist, an oxide film was formed in the solder application area. In Comparative Example 3, the oxide film in the solder application area was removed. The thickness of the oxide film is as shown in Table 1. No rust inhibitors were used in either the examples or the comparative examples.

[0087] The ceramic copper circuit boards according to the examples and comparative examples were subjected to a pencil hardness test and a cross-cut test of the solder resist.

[0088] The pencil hardness test was conducted in accordance with JIS-K-5600-5-4. The cross-cut test was conducted in accordance with JIS-K-5600-5-6. Regarding the results of the cross-cut test, the samples classified as "0" according to the criteria of JIS-K-5600-5-6 were evaluated as "◎ (best)". The samples classified as "1" were evaluated as "〇 (good)". The samples classified as "2" or higher were regarded as not having achieved a desirable curing state and were evaluated as "× (poor)".

[0089] In addition, the degree of progress of the curing reaction was evaluated. The degree of progress of the curing reaction was evaluated based on the IR spectrum of the solder resist using an FT-IR evaluation apparatus. For the measuring apparatus for evaluating the degree of progress of the curing reaction, NICOLET iN10 (manufactured by Thermo Fisher Scientific) was used. For the measurement of the FT-IR spectrum, the ATR method was used. In the ATR method, a crystal made of Ge, having a cone shape and a tip diameter of 350 μm was used. The number of integrations was 64 or more. In the evaluation, the peak intensity ratio (I －１ / I －１ ) of the peak derived from the aromatic ring (1505 cm （１５０５ｃｍ－１） ) and the peak derived from the epoxy ring (915 cm （９１５ｃｍ－１） ) was used as the degree of progress of the curing reaction. The peak derived from the aromatic ring (1505 cm －１ ) and the peak derived from the epoxy ring (915 cm －１ ) were selected in accordance with JIS-K-7148-2. The measurement results are shown in Table 1.

[0090]

[0091] In each of the examples, the pencil hardness of the solder resist was 4H or higher, and the cross-cut test was ◎ or 〇, and good results were obtained. The pencil hardness is an index indicating the strength of the solder resist. The cross-cut test is an index indicating the adhesion of the solder resist. Also, in the evaluation of the degree of progress of the curing reaction in each example, the strength ratio (I （１５０５ｃｍ－１ ) / I （９１５ｃｍ－１） ) was 0.6 or higher. Hereinafter, the strength ratio (I （１５０５ｃｍ－１） / I （９１５ｃｍ－１） [[ID=2*]] （９１５ｃｍ－１） ) may also be simply referred to as the evaluation of the degree of progress of the curing reaction.

[0092] In Comparative Example 2, the heat treatment conditions were similar to those of the example, so the curing reaction progress evaluation was 0.6 or higher. In Comparative Example 3, the heat treatment conditions were outside the preferred conditions, so the curing reaction progress evaluation was less than 0.6. This indicates that the curing reaction was insufficient in Comparative Example 3.

[0093] Next, a test was conducted on the wetting spread of the solder using the following method. Specifically, a 20 μm thick layer of solder paste (Sn-Cu type) was applied to the entire solder application area of ​​the sample. The solder paste was melted at a temperature above its melting point for 30 seconds and then cooled. This process was performed on four samples for each example and comparative example, and the presence or absence of solder bridges and non-wetting was examined. The wettability of the solder was also evaluated. The results are shown in Table 2.

[0094] In Table 2, "solder bridge" indicates that solder has flowed over the solder resist. In Comparative Example 1, where no solder resist is provided, it indicates that the solder flowed outside the applied area. "Unwetting" indicates that in the sample after the above treatment, areas not covered by solder are observed within the solder applied area. In the results for unwetting in Table 2, samples in which no unwetting was observed are listed as "None".

[0095] In evaluating wettability, the area over which solder spread within the solder application region was measured. For each example and comparative example, the area over which solder spread was averaged across four samples. In Table 2, "100% wettability" indicates that the solder spread over the entire solder application region. The presence or absence of solder bridges and non-wetting was evaluated as "present" if observed in at least one of the four samples, and as "absent" if not observed in any of the four samples.

[0096]

[0097] No solder bridges occurred in any of the examples. However, solder bridges occurred in Comparative Example 1, where no solder resist was provided. In Comparative Example 1, because no solder resist was provided, areas were observed where the solder had flowed and spilled over to the edges of the copper plate surface. Solder bridges also occurred in Comparative Example 3. This is thought to be due to insufficient adhesion of the solder resist itself. Due to the low adhesion of the solder resist, displacement of the solder resist itself occurred. In Comparative Example 2, areas that were not wetted were observed because the oxide film was thick.

[0098] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, 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, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

[0099] 1...Ceramic copper circuit board 2...Ceramic substrate 3...Copper component 4...Bonding layer 5...Solder resist 6...Oxide film

Claims

1. A ceramic copper circuit board comprising: a ceramic substrate; a copper member provided on the ceramic substrate; and a solder resist provided on a part of the surface of the copper member, wherein the copper member includes an oxide film in at least a part of the area on its surface where the solder resist is not provided, and the thickness of the oxide film is 0.2 nm or more and 10 nm or less.

2. The ceramic copper circuit substrate according to claim 1, wherein the thickness of the oxide film is 1.8 nm or more and 4.0 nm or less.

3. The ceramic copper circuit board according to claim 1 or claim 2, wherein the pencil hardness of the solder resist is 4H or higher, and the thickness of the solder resist is 2 μm or more and 100 μm or less.

4. The ceramic copper circuit board according to any one of claims 1 to 3, wherein the solder resist comprises an epoxy resin.

5. The solder resist has a peak intensity derived from the epoxy ring in the FT-IR spectrum. １ , the peak intensity derived from the aromatic ring is I ２ In that case, I ２ / I １ The ceramic copper circuit board according to claim 4, wherein the ratio is 0.6 or greater.

6. A ceramic copper circuit board according to any one of claims 1 to 5, wherein no rust inhibitor is applied.

7. A semiconductor device comprising a ceramic copper circuit board according to any one of claims 1 to 6, and a semiconductor element mounted on the copper member.

8. A method for manufacturing a ceramic copper circuit board, comprising: a coating step of applying a solder resist ink containing resin to the surface of a copper member bonded to a ceramic substrate; a curing step of forming a solder resist by curing the applied solder resist ink by heat treatment at 110°C to 160°C for 15 minutes to 60 minutes; and a forming step of forming an oxide film with a thickness of 0.2 nm to 10 nm on at least a portion of the area on the surface of the copper member where no solder resist is provided.

9. The solder resist ink contains an epoxy resin, and the peak intensity originating from the epoxy ring in the FT-IR spectrum of the cured solder resist is 1 １ , the peak intensity derived from the aromatic ring is I ２ In that case, I ２ / I １ A method for manufacturing a ceramic copper circuit board according to claim 8, wherein the ratio is 0.6 or greater.

10. In the coating step, the coating area of the solder resist ink is 100 mm ２ or more, and the method for manufacturing a ceramic copper circuit board according to claim 8 or 9.

11. The method for manufacturing a ceramic copper circuit board according to any one of claims 8 to 10, wherein no rust inhibitor is applied to the copper member before the hardening step.

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