Metallized substrate, semiconductor device using the same, and method for manufacturing metallized substrate

Abstract

To provide a metallized substrate having improved bondability with lead-free solder.SOLUTION: A metallized substrate is provided with a metallized layer on a ceramic substrate and a plating film on the metallized layer, the metallized layer contains one or both of Ag (silver) or Cu (copper), one or both of Sn (tin) or In (indium), and an active metal, and the plating film is obtained by laminating a film mainly composed of Ni (nickel) and a film mainly composed of Sn (tin). The metallized layer preferably contains C (carbon). The thickness of the metallized layer is preferably within a range of 5 μm to 60 μm.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The embodiments described below generally relate to a metallized substrate, a semiconductor device using the same, and a method for manufacturing the metallized substrate.

Background Art

[0002] Ceramic circuit boards are used as circuit boards for mounting semiconductor elements. Some ceramic circuit boards have a metal plate bonded thereto or a metallized layer provided thereon. The metallized layer is formed by applying a metal paste on a ceramic substrate and firing it to form a conductor portion. For those with a bonded metal plate, an etching process is used to impart a circuit shape. The etching process requires management of chemicals and the like. Also, metal plates are expensive. On the other hand, since the metallized layer does not use a metal plate, the cost can be reduced accordingly. Also, by applying the metal paste only to the locations where the conductor portions are desired, it is possible to eliminate the need for etching. Thus, the metallized substrate can reduce costs compared to a ceramic circuit board with a bonded metal plate. For example, Japanese Patent Application Laid-Open No. 6-21261 (Patent Document 1) discloses a metallized layer containing Mo (molybdenum) or W (tungsten) as a main component and adding Ti (titanium). In Patent Document 1, a metallized layer obtained by mixing Mo and TiN (titanium nitride) is used. In Patent Document 1, the adhesion of Ni plating is improved by suppressing the seepage of the grain boundary phase component from the ceramic substrate. Mo is a high melting point metal with a melting point of about 2623°C. In Patent Document 1, the firing process for forming the metallized layer is performed at 1800°C. Since 1800°C is lower than the melting point of Mo powder, Mo powder does not completely melt. It is difficult to completely suppress the seepage of the grain boundary phase component into the gaps between Mo powders. In addition, Japanese Patent Application Laid-Open No. 8-59375 (Patent Document 2) discloses a metallized layer made of an In-Ag-Cu-based metal material containing an active metal. By using an AgCu eutectic as in Patent Document 2, a dense metallized layer can be formed. Thereby, bleeding out of the grain boundary phase component can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, a semiconductor element was mounted on the metallized layer via a solder layer. In recent years, lead-free solder has been used for the solder layer. The bonding strength between the In-Ag-Cu-based metallized layer and the lead-free solder was not always good. Also, as in Patent Document 1, even when a Ni plating film was provided, the improvement in bonding strength was not sufficient. The embodiment is for addressing such problems and for providing a metallized substrate having good bonding strength with lead-free solder.

Means for Solving the Problems

[0005] The metallized substrate according to the embodiment is a metallized substrate having a metallized layer on a ceramic substrate and a plating film on the metallized layer, wherein the metallized layer contains one or two of Ag (silver) or Cu (copper), one or two of Sn (tin) or In (indium), and an active metal, and the plating film is characterized in that a film mainly composed of Ni (nickel) and a film mainly composed of Sn (tin) are laminated.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0007] The metallized substrate according to the embodiment is a metallized substrate provided with a metallized layer on a ceramic substrate and a plating film on the metallized layer. The metallized layer contains one or two of Ag (silver) or Cu (copper), one or two of Sn (tin) or In (indium), and an active metal. The plating film is characterized in that a film mainly composed of Ni (nickel) and a film mainly composed of Sn (tin) are laminated. FIG. 1 shows an example of a metallized substrate according to the embodiment. In the figure, reference numeral 1 is the metallized substrate, reference numeral 2 is the ceramic substrate, reference numeral 3 is the metallized layer, reference numeral 4 is the Ni plating film, and reference numeral 5 is the Sn plating film. The metallized substrate 1 has a laminated structure of a metallized layer 3, a Ni plating film 4, and a Sn plating film 5 on the ceramic substrate 2.

[0008] Various ceramic substrates can be applied to the ceramic substrate 2. Examples of the ceramic substrate include a silicon nitride substrate, an aluminum nitride substrate, an alumina substrate, a zirconia substrate, and an aldyl substrate. The aldyl substrate is a ceramic sintered body obtained by mixing alumina and zirconia. The thickness of the ceramic substrate is preferably 0.2 mm or more and 3 mm or less. The silicon nitride substrate preferably has a three-point bending strength of 600 MPa or more. Also, the thermal conductivity is preferably 80 W / m·K or more. By increasing the strength of the silicon nitride substrate, the substrate thickness can be reduced. For this reason, the three-point bending strength of the silicon nitride substrate is preferably 600 MPa or more, and more preferably 700 MPa or more. The silicon nitride substrate can be made thinner to 2 mm or less, and further to 0.40 mm or less in substrate thickness. In addition, the three-point bending strength of the aluminum nitride substrate is about 300 to 450 MPa. On the other hand, the thermal conductivity of the aluminum nitride substrate is 160 W / m·K or more and 250 W / m·K or less. Since the strength of the aluminum nitride substrate is low, the substrate thickness is preferably 0.60 mm or more. In addition, the three-point bending strength of the aluminum oxide substrate is 300 MPa or more and 550 MPa or less, but it is inexpensive. Also, the Aldyl substrate has a high three-point bending strength of about 550 MPa, but its thermal conductivity is about 30 to 50 W / m·K.

[0009] In addition, the silicon nitride substrate or the aluminum nitride substrate is a nitride-based ceramic substrate. Also, the aluminum oxide substrate or the Aldyl substrate is an oxide-based ceramic substrate. When comparing the nitride-based ceramic substrate and the oxide-based ceramic substrate, the nitride-based ceramic substrate is preferred. Many nitride-based ceramic substrates have higher thermal conductivity. Also, as described later, it reacts with the ceramic substrate to form an active metal reaction phase. The active metal reaction phase of the nitride-based ceramic substrate becomes an active metal nitride phase. Also, the active metal reaction phase of the oxide-based ceramics becomes an active metal oxide phase. For example, when Ti (titanium) is used as the active metal, the active metal nitride phase is titanium nitride and the active metal oxide phase is titanium oxide. When comparing titanium nitride and titanium oxide, titanium nitride has higher thermal conductivity. Therefore, the nitride-based ceramic substrate is preferred. In addition, the metallization layer contains one or two of Ag (silver) or Cu (copper), one or two of Sn (tin) or In (indium), and an active metal.

[0010] Ag or Cu is a component that becomes the matrix of the metallization layer. One or two of Ag or Cu may be contained. By using both Ag and Cu, an AgCu eutectic is formed. Thereby, the densification of the metallization layer can be improved. In addition, the metallized layer contains one or both of Sn and In. One or both of Sn and In may be contained. Sn or In can lower the melting point of the metallized paste for forming the metallized layer. The metallized paste added with Sn or In begins to melt at about 400 to 600 °C. Thereby, it forms an alloy with Ag or Cu. Examples of the alloy include one or more of AgSn, CuSn, AgIn, CuIn, AgCuSn, and AgCuIn. Also, the alloy shall include compounds (including intermetallic compounds). The formation of the alloy contributes to the densification of the metallized layer.

[0011] In addition, the metallized layer contains an active metal. The active metal includes one or more selected from titanium (Ti), niobium (Nb), zirconium (Zr), and hafnium (Hf). The active metal added to the metallized paste reacts with the ceramic substrate to form an active metal reaction phase. The active metal reaction phase of the nitride-based ceramic substrate becomes an active metal nitride phase. Also, the active metal reaction phase of the oxide-based ceramics becomes an active metal oxide phase. For example, when Ti (titanium) is used as the active metal, the active metal nitride phase is titanium nitride and the active metal oxide phase is titanium oxide. The active metal reaction phase is formed at the interface between the metallized layer and the ceramic substrate. By forming the active metal reaction phase, the bonding strength between the metallized layer and the ceramic substrate can be improved. Note that the active metal reaction phase shall be included as part of the metallized layer. Also, titanium is preferred among the active metals. Titanium easily forms an active metal reaction phase with the ceramic substrate. Also, Ti is the least expensive among Ti, Nb, Zr, and Hf.

[0012] Also, it is assumed that the active metal that has not become the active metal reaction phase may be distributed in the metallized layer. Also, in the metallized layer 2, it is preferable to contain one or both of Ag and Cu in a total of 40% by mass or more and 90% by mass or less, one or both of Sn and In in a total of 1% by mass or more and 50% by mass or less, and an active metal or an active metal compound in a total of 1% by mass or more and 15% by mass or less. In addition, the metallized layer may contain 0.1 mass% or more and 2 wt% or less of C (carbon). By containing C (carbon) in the metallized layer, the fluidity of the metallized paste can be controlled. Also, when both Ag and Cu are used, it is preferable that the metallized layer satisfies 20 mass% or more and 70 mass% or less of Ag, 20 mass% or more and 70 mass% or less of Cu, 5 mass% or more and 40 mass% or less of Sn, 1 mass% or more and 15 mass% or less of active metal (active metal compound), and 0.1 mass% or more and 1 mass% or less of C.

[0013] In addition, the thickness of the metallized layer is preferably in the range of 5 μm or more and 60 μm or less. The thickness of the metallized layer is the distance from the interface between the ceramic substrate and the active metal reaction phase to the surface of the metallized layer. It can be measured by cross-sectional SEM. If the thickness of the metallized layer is less than 5 μm, the grain boundary phase of the ceramic substrate may ooze out to the surface of the metallized layer. Also, if it is thicker than 60 μm, not only is there no further effect, but it also becomes a factor in cost increase. For this reason, the thickness of the metallized layer is preferably in the range of 5 μm or more and 60 μm or less, and more preferably in the range of 10 μm or more and 40 μm or less.

[0014] In addition, a plating film is provided on the metallized layer. The plating film is a laminate of a film mainly composed of Ni (nickel) and a film mainly composed of Sn (tin). The film mainly composed of Ni may be called a Ni plating film, and the film mainly composed of Sn may be called a Sn plating film. A Ni plating film 4 is provided on the metallized layer 3, and a Sn plating film 5 is provided on the Ni plating film 4. The Ni plating film has good adhesion to the metallized layer. The Ni plating film does not react with Ag, Cu, Sn, and In, which are the main components of the metallized layer. Therefore, it is possible to suppress the oozing out of Ag, Cu, Sn, and In to the surface of the Ni plating film. Also, the Ni plating film shall include a Ni alloy plating film. Examples of the Ni alloy plating film include Ni-P. Also, the Sn plating film does not react with the Ni plating film. On the other hand, the Sn plating film reacts with the components of the metallization layer. The Ni plating film serves as a barrier layer to prevent the Sn plating film from reacting with the metallization layer. Also, the Sn plating film has good joinability with lead-free solder. Also, the Sn plating film shall include an Sn alloy plating film.

[0015] Since the metallization layer, Ni plating film, and Sn plating film each suppress the reaction, their respective boundaries can be observed by cross-sectional SEM. The thickness of the plating film is preferably in the range of 0.5 μm or more and 20 μm or less. The thickness of the plating film is the total thickness of the Ni plating film and the Sn plating film. If the thickness of the plating film is less than 0.5 μm, the effect of providing the plating film may be insufficient. Also, if it is thicker than 20 μm, not only will no further effect be obtained, but it will also be a factor in increasing costs. For this reason, the thickness of the plating film is preferably in the range of 0.5 μm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less. Also, the thickness of the Ni plating film is preferably in the range of 0.2 μm or more and 10 μm or less. Also, the thickness of the Sn plating film is preferably in the range of 0.2 μm or more and 10 μm or less.

[0016] Also, since thin Ni plating and Sn plating are applied on the metallization layer, the generation of voids can be suppressed. For this reason, the tensile strength of the metallization layer (the metallization layer provided with the Ni plating film and the Sn plating film) can be made 180 N or more. Also, as will be described later, the tensile strength can be improved without subjecting the plating film to sintering treatment.

[0017] Also, the appearance of the Sn plating film shows white or light gray. The appearance of the Ni plating film shows silver or dark gray. The color tones of the Sn plating film and the Ni plating film are different. Since the thin-colored Sn plating film is provided on the dark-colored Ni plating film, poor formation of the Sn plating film is easily observable. For this reason, inspection by an image inspection device or visual inspection can be easily performed.

[0018] When the Sn plating film has a degree of becoming white, the bondability with lead-free solder is good. Also, if it is white, even if the grain boundary phase component oozes out on the plating surface by any chance, it can be identified. It is easy to perform a good product inspection.

[0019] The metallized substrate as described above can be used for a semiconductor device on which a semiconductor element is mounted. An example of a semiconductor device according to an embodiment is shown in FIG. 2. In the figure, reference numeral 1 is a metallized substrate, reference numeral 6 is a semiconductor element, reference numeral 7 is a solder layer, and reference numeral 10 is a semiconductor device. The semiconductor device 10 is obtained by mounting a semiconductor element 6 via a solder layer 7 on the Sn plating film 5 of the metallized substrate 1. In FIG. 2, an example in which the metallized layer 3 is made into one is illustrated, but a plurality of them may exist. Also, an example in which one semiconductor element 6 is mounted is shown, but a plurality of them may be mounted. Also, if necessary, wire bonding, a lead frame, terminals, etc. may be provided. Also, if necessary, resin molding may be performed. Also, the solder layer 7 is preferably lead-free solder. Lead-free solder is a general term for solder that contains almost no lead. Lead-free solder is sometimes called lead-free solder. Lead-free solder is defined in JIS-Z-3282 (2017) and has a lead content of 0.10 mass% or less. In Table 2 of JIS-Z-3282, "Types and Chemical Compositions of Lead-Free Solder", the components of lead-free solder are shown. As can be seen from these, lead-free solder contains Sn. The metallized substrate 1 according to the embodiment has an Sn plating film 5 on its outermost surface. The Sn plating film 5 and the lead-free solder containing Sn have good bondability. In other words, it is suitable for a semiconductor device that mounts a semiconductor element using lead-free solder.

[0020] Next, a method for manufacturing the metallized substrate according to the embodiment will be described. If the metallized substrate according to the embodiment has the above configuration, its manufacturing method is not particularly limited, but a method for obtaining it with good yield is as follows. First, prepare a ceramic substrate 2. Examples of the ceramic substrate include a silicon nitride substrate, an aluminum nitride substrate, an aluminum oxide substrate, and an aldyl substrate. Next, perform a step of preparing a metallizing paste for forming the metallizing layer 3. The step of preparing the metallizing paste involves a step of mixing the components constituting the metallizing layer. The components constituting the metallizing layer are the metal components (including metal compounds) remaining in the metallizing layer after the firing step. Also, each component is mixed as a powder.

[0021] The components constituting the metallizing layer are preferably mixed such that one or two of Ag or Cu total 40% by mass or more and 90% by mass or less, one or two of Sn or In total 1% by mass or more and 50% by mass or less, and the active metal or active metal compound totals 1% by mass or more and 15% by mass or less. Also, the active metal is one or more selected from Ti, Nb, Zr, and Hf. Further, examples of the active metal compound include hydrides, oxides, and nitrides. For example, when using Ti, one or more selected from titanium hydride (TiH2), titanium oxide (TiO2), and titanium nitride (TiN) can be mentioned. The active metal is preferably added as a hydride. As a hydride, the metallizing layer can be formed while suppressing oxidation. Also, the metallizing layer may be added with C (carbon) at 0.1% by mass or more and 2 wt% or less. Note that the mass ratio of the components constituting the metallizing layer is such that the total of the mixed metal components (including metal compounds) is 100% by mass. For example, when mixing Ag, Cu, Sn, TiH2, and C, Ag + Cu + Sn + TiH2 + C = 100% by mass.

[0022] Also, after mixing the components constituting the metallizing layer, perform a step of preparing a metallizing paste by adding an organic binder, an organic solvent, etc. Next, perform a step of applying the metallizing paste onto the ceramic substrate. It is preferable to apply the metallizing paste to the location where the metallizing layer is to be formed. After forming the metallizing paste layer, a drying step may be performed as necessary. Next, a step of heating to form a metallized layer is performed. The step of heating to form a metallized layer is sometimes referred to as a firing step. The firing step preferably has a heating temperature in the range of 1200°C or higher and 1950°C or lower. By performing the firing step, a metallized layer is formed.

[0023] Next, a step of forming a Ni plating film is performed. The step of forming a Ni plating film is sometimes referred to as a Ni plating step. The Ni plating step may be either electroless plating or electroplating. Also, a mask member shall be provided at locations where Ni plating is not desired to be formed. Further, the thickness of the Ni plating film is preferably in the range of 0.2 μm or more and 10 μm or less. Next, a step of forming a Sn plating film is performed. The step of forming a Sn plating film is sometimes referred to as a Sn plating step. The Sn plating step may be either electroless plating or electroplating. Also, a mask member shall be provided at locations where Sn plating is not desired to be formed. Further, the thickness of the Sn plating film is preferably in the range of 0.2 μm or more and 10 μm or less.

[0024] Also, it is assumed that a heating step at 500°C or higher may not be performed after either or both of the step of forming a Ni plating film and the step of forming a Sn plating film. In order to improve the adhesion between the plating film and the metallized layer, heat treatment at 500°C or higher may be performed. The heat treatment on the plating film is sometimes referred to as sintering treatment. With the above plating film, excellent tensile strength can be obtained without performing sintering treatment. Through the above steps, a metallized substrate can be fabricated. Also, a semiconductor device can be fabricated by mounting a semiconductor element on the Sn plating film via a solder layer.

[0025] (Example) (Examples 1 to 4, Comparative Examples 1 to 2) Ceramic substrates shown in Table 1 were prepared.

[0026]

Table 1

[0027] Next, a metallizing paste was prepared. Components shown in Table 2 were prepared as components constituting the metallizing layer. After mixing the components constituting the metallizing layer, an organic binder and the like were added to obtain a metallizing paste.

[0028]

Table 2

[0029] The metallizing paste was applied onto the ceramic substrate, and a firing process was performed within a range of a heating temperature of 1200°C or higher and 1950°C or lower. By this process, a metallizing layer was formed. Next, a Ni plating film and a Sn plating film were formed to fabricate a metallized substrate according to the example. Also, Comparative Example 1 had only a Ni plating film, Comparative Example 2 had only a Sn plating film, and Comparative Example 3 had no plating film. The metallizing layer, Ni plating film, and Sn plating film were as shown in Table 3.

[0030]

Table 3

[0031] As described above, metallized substrates according to the example and comparative examples were fabricated. Also, no sintering treatment was performed on any of the metallized substrates after the plating treatment. For each metallized substrate, the presence or absence of voids between the Sn plating film and the Ni plating film and between the Ni plating film and the metallizing layer was examined. The presence or absence of voids was observed on an arbitrary cross-section, and the total area ratio (%) of the voids was determined. When the total area ratio of the voids was 0% or more and 1% or less, it was defined as "the best product"; when it exceeded 1% and was 5% or less, it was defined as "good product"; and when it exceeded 5%, it was defined as "defective product". Also, the appearance color of the Sn plating film was examined. The appearance color was observed visually. Also, the tensile strength of the metallizing layer was measured. The tensile strength was measured by joining a metal terminal using lead-free solder. When the tensile strength was 200 N or more, it was defined as "the best product"; when it was 180 N or more and less than 200 N, it was defined as "good product"; and when it was less than 180 N, it was defined as "defective product". The results are shown in Table 4.

[0032]

Table 4

[0033] As can be seen from the table, the porosity of the examples was small. The Sn plating film, Ni plating film, and metallization layer had good adhesion. Also, the tensile strength of the examples was good. On the other hand, in the case where the Sn plating film was not used as in Comparative Example 1, the tensile strength decreased. It was found that using lead-free solder had an impact on the tensile strength. Also, in the case where the Ni plating film was not provided as in Comparative Example 2, a reaction occurred between the metallization layer and the Sn plating film. For this reason, voids were generated and the tensile strength decreased. Also, since neither Sn plating nor Ni plating film was used as in Comparative Example 3, the tensile strength decreased. Thus, the examples were able to improve the tensile strength without performing a sintering process after the plating process. Also, it was possible to improve the bonding strength with lead-free solder.

[0034] As described above, some embodiments of the present invention have been illustrated. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalent scope. Also, the above-described embodiments can be implemented in combination with each other.

Explanation of Reference Numerals

[0035] 1... Metallized substrate 2... Ceramic substrate 3... Metallization layer 4... Ni plating film 5... Sn plating film 6... Semiconductor element 7... Solder layer 10…Semiconductor device

Claims

1. A metallized substrate having a metallized layer on a ceramic substrate and a plating film on the metallized layer, wherein the metallized layer contains one or two of Ag (silver) or Cu (copper), one or two of Sn (tin) or In (indium), and an active metal; the plating film is characterized in that a film mainly composed of Ni (nickel) and a film mainly composed of Sn (tin) are laminated, the metallized substrate.

2. The metallized substrate according to claim 1, wherein the metallized layer contains C (carbon).

3. The metallized substrate according to claim 1 or claim 2, wherein the thickness of the metallized layer is in the range of 5 μm or more and 60 μm or less.

4. The metallized substrate according to claim 1 or claim 2, wherein the thickness of the plating film is in the range of 0.5 μm or more and 20 μm or less.

5. The metallized substrate according to claim 1 or claim 2, wherein the metallized layer satisfies 20% by mass or more and 70% by mass or less of Ag, 20% by mass or more and 70% by mass or less of Cu, 5% by mass or more and 40% by mass or less of Sn, 1% by mass or more and 15% by mass or less of an active metal (including an active metal compound), and 0.1% by mass or more and 1% by mass or less of C.

6. The metallized substrate according to claim 4, wherein the metallized layer satisfies 20% by mass or more and 70% by mass or less of Ag, 20% by mass or more and 70% by mass or less of Cu, 5% by mass or more and 40% by mass or less of Sn, 1% by mass or more and 15% by mass or less of an active metal (including an active metal compound), and 0.1% by mass or more and 1% by mass or less of C.

7. The metallized substrate according to claim 1 or claim 2, wherein the surface of the Sn plating film shows white or light gray.

8. The metallized substrate according to claim 1 or claim 2, wherein the ceramic substrate is one of an aluminum nitride substrate and a silicon nitride substrate.

9. The metallized substrate according to claim 6, wherein the ceramic substrate is one of an aluminum nitride substrate and a silicon nitride substrate.

10. A semiconductor device, characterized in that a semiconductor element is mounted on the metallized substrate according to claim 1.

11. A step of applying an active metal paste containing one or two of Ag (silver) or Cu (copper), Sn (tin), and an active metal on a ceramic substrate; A step of heating to form a metallized layer A step of forming a Ni plating film on a metallized layer and a step of forming a Sn plating film A method for manufacturing a metallized substrate, characterized by comprising the above steps. ​ ​ ​ ​

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