Substrate with micro through holes and method for manufacturing the same

Abstract

A highly reliable substrate in which metal is filled into fine through-holes, enabling high-density mounting and high reliability, and a method for manufacturing the same are provided. [Solution] The above-mentioned problem is solved by a micro-through-hole-filled substrate 10 in which a plurality of micro-through-holes 2 formed in a substrate 1 are filled, the micro-through-holes 2 being filled with a conductive layer (at least 3b) formed on the inner wall surface thereof and a metal solder layer 3c formed on the conductive layer, the conductive layer having a copper plating layer 3b formed on the metal solder layer side, and the metal solder layer 3b being filled with nickel-containing molten solder treated with an organic fatty acid-containing solution. The substrate 1 is preferably a quartz substrate or a glass substrate, and an intermetallic compound layer 4 is formed on the conductive layer 3b side of the metal solder layer 3c, which combines with the copper component constituting the conductive layer 3b to prevent copper corrosion.

Description

[Technical Field]

[0001] The present invention relates to a highly reliable substrate in which metal is filled into fine through holes, enabling high-density mounting and high reliability, and to a method for manufacturing the same. [Background technology]

[0002] As electronic devices become smaller, thinner, and lighter, and faster, more functional, and multifunctional, substrates on which electronic components such as semiconductor devices are densely mounted are becoming smaller and thinner, and their external electrode terminals are becoming narrower in pitch and with more pins. Examples of such substrates include ball grid arrays (BGAs) and chip size packages (CSPs), and semiconductor and substrate manufacturers are proposing substrates with a variety of structures. Meanwhile, printed wiring boards on which electronic components such as semiconductor devices are mounted are being required to have finer circuit wiring and more multilayered wiring boards in order to accommodate complex circuit wiring and accommodate the narrower pitch and higher pin count of semiconductor devices.

[0003] Known examples of multilayer substrates include through-hole multilayer substrates that connect circuits between layers with through-holes, IVH multilayer substrates that connect layers with IVHs (Interstitial Via Holes), and build-up substrates fabricated by a build-up process. In particular, glass substrates and quartz substrates have become popular substrates in recent years. Glass substrates and quartz substrates offer a high degree of freedom in thickness and size, are readily available, are relatively inexpensive, and offer excellent smoothness and flatness, which is advantageous for forming fine wiring with narrow pitches. They also have advantages such as a low coefficient of linear thermal expansion, excellent mounting stability, excellent dimensional stability, excellent chemical stability, high insulation, and excellent transmission characteristics. They are also advantageous in that technologies for drilling fine through-holes in glass substrates and quartz substrates using electrical discharge machining or laser machining have also advanced. Therefore, there is a demand for glass substrates and quartz substrates with longer through-holes, thinner through-holes, and narrower through-hole pitches.

[0004] Technologies for filling such through-holes with metal have also been proposed. These through-hole filling techniques typically involve forming a through-hole using electrical discharge machining or laser processing, first forming a thin metal layer inside the through-hole using known methods such as sputtering, vapor deposition, CVD, or electroless plating, thereby making it conductive. Then, an electric current is passed through the entire thin metal layer to perform electroplating, thereby filling the through-hole with metal. With these conventional methods, filling a minute through-hole, say 50 μm, entirely with electroplating requires plating the inner wall surface to a thickness of approximately 25 μm. However, such minute through-holes have a large aspect ratio between the substrate thickness (through-hole length) and the hole diameter (through-hole diameter), making it difficult to fill the inner wall surface with an electroplated layer. Furthermore, voids and seams may occur in the through-hole conductor.

[0005] Various technologies have been proposed to address these issues. For example, Patent Document 1 proposes a glass circuit board capable of forming fine circuits, although it does not completely fill the through-holes with metal. This technology involves laminating a first insulating resin, which has good filling properties into the through-holes, on both sides of a glass core substrate, in which metal circuits are formed on the through-holes and both sides of the glass. This effectively suppresses voids that occur in the through-holes and ensures long-term connection reliability. Furthermore, the first insulating resin contains a large amount of inorganic filler, which suppresses the amount of shrinkage of the insulating resin filled into the through-holes upon cure, thereby suppressing depressions caused by shrinkage directly above the through-holes and ensuring the flatness of the resin surface.

[0006] Furthermore, Patent Document 2 does not entirely fill the inside of the through-holes with metal, but it proposes a wiring board having numerous through-holes formed thereon, with the inner wall surfaces of the through-holes coated with a copper plating layer and the interiors of the through-holes filled with resin. This technology aims to improve quality by eliminating variations in the thickness of the copper plating layer depending on the density of the through-holes, and includes a plating film of approximately uniform thickness formed along the inner wall surfaces of the through-holes, and fills the insides of the through-holes with a conductive filler. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-182006 [Patent Document 2] Japanese Patent Publication No. 2023-131615 [Patent Document 3] Patent No. 5129898 [Patent Document 4] Patent No. 6150881 Summary of the Invention [Problem to be solved by the invention]

[0008] As exemplified by the above-mentioned conventional examples, research is being conducted to achieve high reliability by using glass or quartz substrates, which have excellent characteristics, to reduce the diameter and pitch of long through-holes. However, because a conductive layer is formed on the inner wall surface of the through-hole using electrolytic plating, there is a risk that the plating solution or its constituent chemical components may remain in the through-hole, or that defects or voids may occur in the through-hole conductor, resulting in a lack of high reliability.

[0009] The present invention has been made to solve the above-mentioned problems, and its object is to provide a highly reliable substrate in which metal is filled into fine through holes, which enables high-density mounting and high reliability, and a method for manufacturing the same. [Means for solving the problem]

[0010] The present inventors have proposed a method for manufacturing substrates and electronic components that can significantly suppress copper corrosion, as seen in conventional dipping processes, and that does not cause copper corrosion in various subsequent mounting processes, in the technology proposed in Patent Documents 3 and 4. The present invention is characterized by further applying the inventors' technology to glass substrates and quartz substrates that enable long through-holes to be made thinner and have narrower pitches with high reliability, thereby solving the above-mentioned problems.

[0011] (1) The micro through-hole filling substrate of the present invention is a micro through-hole filling substrate in which a plurality of micro through-holes formed in a substrate are filled, characterized in that the micro through-holes are filled with a conductive layer formed on the inner wall surface thereof and a metal solder layer formed on the conductive layer, the conductive layer having a copper plating layer formed on the metal solder layer side, and the metal solder layer is filled with nickel-containing molten solder treated with an organic fatty acid-containing solution.

[0012] According to this invention, a metal solder layer formed by solidifying molten solder is formed on the conductive layer formed on the inner wall surface of the micro through-hole, and the micro through-hole is filled with the metal solder layer. Unlike conventional plating solutions and their constituent chemical components, the micro through-hole filled with the metal solder layer does not remain inside the micro through-hole, and defects and voids do not occur in the filled metal layer. As a result, a micro through-hole filled substrate that enables high-density mounting and high reliability can be provided. Furthermore, since the molten solder is purified using an organic fatty acid-containing solution, oxygen components, metal oxides, impurities, etc. present in the molten solder are purified and removed, thereby advantageously preventing defects and voids from forming in the metal solder layer. Furthermore, since the molten solder contains nickel, the nickel, together with copper and tin, forms an intermetallic compound that prevents copper corrosion. As a result, copper corrosion of the copper plating layer that constitutes the conductive layer is suppressed, and the formation of a copper-tin alloy, which has poor mechanical strength, can be suppressed. Furthermore, the molten solder treated with the organic fatty acid-containing solution has a lower oxygen content than the untreated molten solder, and the difference can be seen in that it has a fine granular crystalline structure, but does not have the columnar structure seen in the untreated molten solder.

[0013] Furthermore, when a metal solder layer is formed using molten solder treated with an organic fatty acid-containing solution, the organic fatty acid-containing solution has already penetrated into the fine through-holes, so the molten solder treated with the organic fatty acid-containing solution easily penetrates into the fine through-holes. As a result, a metal solder layer can be easily filled into long through-holes or small-diameter through-holes, and small diameter through-holes and narrow pitches can be achieved with high reliability.

[0014] In the substrate for filling micro through-holes according to the present invention, the substrate is a quartz substrate or a glass substrate.

[0015] According to this invention, a substrate with fine through-holes can be provided which has a high degree of freedom in thickness and size, is easily available, is relatively inexpensive, has excellent smoothness and flatness, is advantageous for forming fine wiring with a narrow pitch, has a small coefficient of linear thermal expansion, has excellent mounting stability, excellent dimensional stability, excellent chemical stability, high insulation and excellent transmission characteristics, and has other advantages.In addition, by applying a quartz substrate or glass substrate in which fine through-holes can be formed by electrical discharge machining or laser machining, a substrate with fine through-holes can be provided which enables high-density mounting and high reliability.

[0016] In the micro through-hole filling substrate according to the present invention, an intermetallic compound layer is formed on the conductive layer side of the metal solder layer, which combines with the copper component constituting the conductive layer to prevent copper corrosion.

[0017] According to this invention, the metal solder layer is filled with nickel-containing molten solder treated with an organic fatty acid-containing solution, and therefore, on the conductive layer side of the metal solder layer, the nickel, together with copper and tin, forms an intermetallic compound that prevents copper corrosion. As a result, the formation of this intermetallic compound layer suppresses copper corrosion of the copper plating layer that constitutes the conductive layer, and suppresses the formation of a copper-tin alloy that has poor mechanical strength.

[0018] In the micro through-hole filling substrate according to the present invention, the metal solder layer contains tin as a main component and at least nickel as a secondary component.

[0019] According to the present invention, a metal solder layer having such a component composition is formed, so that a highly reliable micro through-hole filling substrate can be provided.

[0020] In the micro through-hole filling substrate according to the present invention, the conductive layer comprises a first conductive layer formed on the inner wall surface and a second conductive layer formed on the first conductive layer, and the second conductive layer is a copper plating layer or a copper alloy plating layer.

[0021] According to this invention, the conductive layer can have a two-layer structure consisting of a first conductive layer and a second conductive layer made of a copper plating layer or a copper alloy plating layer. The second conductive layer is preferably an electroless plating layer, which is easy to form with a uniform plating thickness.

[0022] In the micro through-hole filling substrate according to the present invention, the first conductive layer is made of a conductive material selected from the group consisting of ITO, Cr, Ti, Al, Au, Ag, Cu, Ni, and Mo, or a composite material thereof (preferably a PVD film or CD film).

[0023] According to this invention, by using the above material for the first conductive layer, the second conductive layer made of a plating layer can be easily formed. Note that the first conductive layer is preferably a PVD film or a CVD film.

[0024] (2) The method for manufacturing a micro through-hole-filled substrate according to the present invention is a method for manufacturing a micro through-hole-filled substrate in which a plurality of micro through-holes formed in a substrate are filled with a metal solder layer, and is characterized by comprising a conductive layer forming step of forming a conductive layer consisting of a copper plating layer or a copper alloy plating layer on the inner wall surface of the micro through-hole on the side of the metal solder layer, and a metal solder layer forming step of supplying a liquid flow of nickel-containing molten solder treated with an organic fatty acid-containing solution onto the conductive layer on the inner wall surface to fill the micro through-holes with a metal solder layer.

[0025] In the method for manufacturing a substrate for filling a micro through-hole according to the present invention, the metal solder layer forming step includes a molten solder removing step of removing excess molten solder after supplying a liquid flow of the nickel-containing molten solder (molten solder supplying step). According to this invention, the molten solder removing step can remove excess molten solder. Note that the removal of molten solder is preferably carried out by spraying a liquid flow of an organic fatty acid-containing solution.

[0026] In the method for manufacturing a substrate for filling micro through holes according to the present invention, the substrate is a quartz substrate or a glass substrate, which has a small coefficient of linear thermal expansion and excellent dimensional stability and chemical stability, and by using a quartz substrate or a glass substrate, it is possible to manufacture a substrate for filling micro through holes that enables high-density mounting and high reliability.

[0027] In the method for manufacturing a micro through-hole filling substrate according to the present invention, the molten solder preferably contains tin as a main component and at least nickel as a secondary component.

[0028] In the method for producing a substrate filled with fine throughholes according to the present invention, the organic fatty acid-containing solution is a solution containing palmitic acid having 16 carbon atoms.

[0029] The method for manufacturing a substrate for filling micro through-holes according to the present invention includes, after the conductive layer forming step and before the solder layer forming step, an organic fatty acid-containing solution infiltration step of infusing the micro through-holes with an organic fatty acid-containing solution. According to this invention, by infusing the micro through-holes with the organic fatty acid-containing solution before forming the metal solder layer, the molten solder treated with the organic fatty acid-containing solution can be easily infiltrated into the micro through-holes. As a result, the metal solder layer can be easily filled into long through-holes or small-diameter through-holes, and the diameter and pitch of the through-holes can be reduced with high reliability.

[0030] In the method for manufacturing a substrate with micro throughholes according to the present invention, the organic fatty acid-containing solution immersion step includes a liquid immersion step of immersing a cleaning liquid or a surface treatment liquid into the micro throughholes before immersing the organic fatty acid-containing solution into the micro throughholes.

[0031] According to this invention, a liquid (cleaning liquid or surface treatment liquid) is infiltrated into the fine through-holes in advance, facilitating liquid-liquid exchange between the liquid and the organic fatty acid-containing solution. As a result, the organic fatty acid-containing solution can be thoroughly infiltrated into the fine through-holes, and the organic fatty acid-containing solution can selectively capture and remove oxides and impurities (including residual plating solution components) present on the surface of the conductive layer in the fine through-holes, thereby cleaning the surface of the conductive layer. The cleaning liquid may be an aqueous solvent or an organic solvent, and the surface treatment liquid may be an oxide removal solution, etc.

[0032] In the method for manufacturing a substrate for filling micro through holes according to the present invention, the viscosity of the molten solder is in the range of 0.002 Pa·s to 0.004 Pa·s. According to this invention, the viscosity is significantly smaller than the viscosity (approximately 0.005 to 0.007 Pa·s) of molten solder not treated with an organic fatty acid-containing solution, and the molten solder has high fluidity and is easy to fill into micro through holes.

[0033] In the method for manufacturing a micro through-hole filling substrate according to the present invention, the metal solder layer forming step is preferably carried out in a vapor atmosphere of an organic fatty acid-containing solution.

[0034] In the method for manufacturing a substrate with a micro through hole filling according to the present invention, the metal solder layer forming step is performed by spraying the molten solder toward the micro through hole or at a predetermined angle.

[0035] In the method for manufacturing a substrate containing a micro through hole according to the present invention, the molten solder removing step is performed by spraying a liquid flow of an organic fatty acid-containing solution.

[0036] In the manufacturing method of the micro through-hole filling substrate according to the present invention, when the conductive layer is formed on the substrate surface together with the inner wall surface of the micro through-hole, it is preferable to have a conductive layer removal step of removing the conductive layer formed on the substrate surface before the metal solder layer formation step.

[0037] In the method for manufacturing a micro through-hole filling substrate according to the present invention, the conductive layer forming step includes a first conductive layer forming step of forming a first conductive layer on the inner wall surface, and a second conductive layer forming step of forming a second conductive layer made of a copper plating layer or a copper alloy plating layer on the first conductive layer. The copper plating layer or copper alloy plating layer is preferably formed by electroless plating, which is easy to form a plating layer of uniform thickness.

[0038] In the method for manufacturing a substrate for filling fine through holes according to the present invention, the first conductive layer forming step is preferably performed by a PVD method or a CVD method for forming a conductive material selected from ITO, Cr, Ti, Al, Au, Ag, Cu, Ni and Mo, or a composite material thereof.

[0039] In the method for manufacturing a substrate for filling a micro through-hole according to the present invention, the conductive layer forming step is a step of forming an electroless copper-plated layer or an electroless copper alloy-plated layer after providing an electroless plating catalyst on the inner wall surface. According to this invention, the conductive layer made of an electroless copper-plated layer or an electroless copper alloy-plated layer can be formed without providing a first conductive layer that functions as an underlayer for the copper-plated layer or the copper alloy-plated layer. [Effects of the Invention]

[0040] According to the present invention, it is possible to achieve long through-holes with a small diameter and a narrow pitch with high reliability without leaving plating solution or its constituent chemical components in the through-holes or creating defects or voids in the through-hole conductors, as occurs with conventional electroplating. The present invention thus provides a micro-through-hole-filled substrate and a method for manufacturing the same that enable high-density mounting and high reliability. In particular, it is possible to provide a micro-through-hole-filled substrate and a method for manufacturing the same that significantly suppresses copper corrosion that occurs in conventional dipping processes and does not cause copper corrosion in various subsequent mounting processes. [Brief explanation of the drawings]

[0041] [Figure 1] 1 is a cross-sectional photograph of an example of a substrate filled with fine throughholes according to the present invention (throughhole diameter: 40 μm). [Figure 2] 1 is a cross-sectional photograph of another example of a substrate filled with fine throughholes according to the present invention (throughhole diameter: 20 μm). [Figure 3] 1A is a plan view of an example of a substrate filled with fine throughholes according to the present invention, and FIG. 1B is an enlarged view of the same. [Figure 4] 1 is an electron microscope photograph showing an example of a fine throughhole-formed substrate prepared for manufacturing a fine throughhole-filled substrate. [Figure 5] 10 is an electron microscope photograph showing the configuration after a first conductive layer is formed in a through hole. [Figure 6] 1 is a photograph of the structure of a metal solder layer formed with molten solder treated with a solution containing an organic fatty acid. [Figure 7] 1 is a photograph of the structure of a metal solder layer formed with molten solder that has not been treated with a solution containing an organic fatty acid. [Figure 8] 1A to 1C are explanatory views showing an example of a manufacturing process for a micro through-hole filling substrate according to the present invention. [Figure 9] 10A to 10C are explanatory views showing another example of the manufacturing process of the micro through-hole filling substrate according to the present invention. [Figure 10] 10A to 10C are explanatory views showing still another example of the manufacturing process of the micro through-hole filling substrate according to the present invention. [Figure 11]FIG. 1A is a schematic cross-sectional view of an intermetallic compound layer formed between a copper plating layer and a metal solder layer in the present invention, and FIG. 1B is a schematic cross-sectional view of an intermetallic compound layer formed by general molten solder. [Figure 12] 1 is a graph showing the temperature dependence of viscosity for molten solder (a) treated with a solution containing an organic fatty acid and molten solder (b) not treated with a solution containing an organic fatty acid. [Figure 13] 10A and 10B are schematic explanatory views showing a process of forming a metal solder layer by spraying molten solder; [Figure 14] FIG. 10 is a schematic explanatory view showing a step of spraying an organic fatty acid-containing solution to remove excess molten solder. [Figure 15] 1A and 1B are schematic explanatory views showing an example of a step of spraying molten solder to form a metal solder layer, and a step of spraying an organic fatty acid-containing solution to remove excess molten solder. [Figure 16] FIG. 10 is a schematic explanatory diagram showing another example of a step of spraying molten solder to form a metal solder layer, and a step of spraying an organic fatty acid-containing solution to remove excess molten solder. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention will be described with reference to the accompanying drawings, in which: a substrate for filling micro through-holes and a method for manufacturing the same are described; the following embodiments are preferred embodiments of the present invention, but the present invention is not limited to these embodiments and includes various applications and modifications.

[0043] In this application, "the present invention" can be rephrased as "embodiments of the present application." The "corrosion prevention layer" is a layer that functions to prevent copper or a copper alloy from being corroded by solder (for example, when copper atoms diffuse and dissolve). The inner wall surface refers to the inner peripheral surface of the micro through-hole 2, and the substrate surface refers to the upper and / or lower surface of the substrate. "Top," "bottom," "upper," and "lower" refer to the top and bottom when the drawing is viewed from above.

[0044] [Substrate with micro through-holes and method for manufacturing the same] As shown in Figures 1 to 3, the micro through-hole filling substrate 10 of the present invention is a micro through-hole filling substrate 10 in which a plurality of micro through-holes 2 formed in a substrate 1 are filled, and the micro through-holes 2 are filled with a conductive layer (at least 3b) formed on the inner wall surface thereof and a metal solder layer 3c formed on the conductive layer, and the conductive layer is characterized in that a copper plating layer is formed on the metal solder layer side, and the metal solder layer 3c is filled with nickel-containing molten solder that has been treated with an organic fatty acid-containing solution.

[0045] As shown in Figures 8 to 10, the method for manufacturing such a micro through-hole filling substrate 10 is characterized by having a conductive layer forming step of forming a conductive layer consisting of a copper plating layer or a copper alloy plating layer on the metal solder layer side of the inner wall surface of the micro through-hole 2, and a metal solder layer forming step of supplying nickel-containing molten solder 5 treated with an organic fatty acid-containing solution onto the conductive layer on the inner wall surface to fill the micro through-hole 2 with a metal solder layer 3c.

[0046] According to the micro through-hole filling substrate 10 and its manufacturing method of the present invention, a metal solder layer 3c formed by solidifying molten solder is formed on the conductive layer (3a and 3b, or at least 3b) formed on the inner wall surface of the micro through-hole 2, and the micro through-hole 2 is filled with the metal solder layer 3c. Unlike conventional plating solutions or their constituent chemical components, no plating solution or its constituent chemical components remain in the micro through-hole filled with the metal solder layer 3c, and defects or voids do not occur in the filled metal layer 3. As a result, a micro through-hole filling substrate 10 can be provided that enables high-density mounting and high reliability. Furthermore, since the molten solder 5 is purified using an organic fatty acid-containing solution, oxygen components, metal oxides, impurities, etc. present in the molten solder are purified and removed, which has the advantage of preventing defects and voids from forming in the metal solder layer 3c. Furthermore, since the molten solder 5 contains nickel, the nickel, together with copper and tin, forms an intermetallic compound layer 4 that prevents copper corrosion. As a result, copper corrosion of the copper plating layer that constitutes the conductive layer is suppressed, and the formation of a copper-tin alloy (CuSn intermetallic compound layer 7), which has poor mechanical strength, can be suppressed. Note that the molten solder 5 treated with the organic fatty acid-containing solution has a lower oxygen content than the untreated molten solder, and the difference can be confirmed in that a fine granular crystal structure is observed, while the columnar structure seen in the untreated molten solder is not observed.

[0047] Furthermore, when the metal solder layer 3c is formed with the molten solder 5 treated with the organic fatty acid-containing solution, the organic fatty acid-containing solution 21 has already penetrated into the fine through-holes 2 (see FIGS. 8 to 10), so the molten solder 5 treated with the organic fatty acid-containing solution 21 easily penetrates into the fine through-holes 2. As a result, the metal solder layer 3c can be easily filled into long through-holes or small-diameter through-holes, and it is possible to achieve small diameter through-holes and narrow pitches with high reliability.

[0048] Each component will be described in detail below.

[0049] <Substrate> Preferred examples of the substrate include quartz substrates and glass substrates. Glass substrates and quartz substrates have a high degree of freedom in thickness and size, are easily available, are relatively inexpensive, and have excellent smoothness and flatness, which is advantageous for forming fine wiring with narrow pitches. They also have advantages such as a small linear thermal expansion coefficient, excellent mounting stability, excellent dimensional stability, excellent chemical stability, high insulation, and excellent transmission characteristics, and can be machined by electrical discharge machining or laser machining to form fine through holes. By using such a quartz substrate or glass substrate, it is possible to provide a micro-through-hole-filled substrate that enables high-density mounting and high reliability. In particular, when manufacturing a micro-through-hole-filled substrate, the substrate may be sprayed with molten solder heated to around 250°C or exposed to processing temperatures of 150°C to 300°C. However, by using a quartz substrate or glass substrate that has a small linear thermal expansion coefficient and excellent dimensional stability and chemical stability even at such temperatures, it is possible to manufacture a micro-through-hole-filled substrate that enables high-density mounting and high reliability.

[0050] Glass substrates and quartz substrates are advantageous in that they are easy to process by electrical discharge machining or laser machining, and through holes can be made longer and have smaller diameters and narrower pitches. Although electrical discharge machining and laser machining are not described in detail in this application, known methods can be used. Furthermore, through holes of a predetermined diameter and a predetermined pitch can be drilled in glass substrates or quartz substrates of any thickness.

[0051] The thickness, size, area and surface shape of the substrate 1 are not particularly limited, but examples of the thickness include about 0.1 mm to 1 mm, and the surface shape of the substrate can be, for example, rectangular, circular or elliptical.

[0052] <Micro through holes> As shown in Fig. 4, the micro through hole 2 is a hole provided in the substrate 1, and one with a plated inner wall surface is generally called a through hole. In the present invention, the entire through hole 2 of the through hole is filled with a conductive layer and metallized. In this application, this case may also be referred to as a through hole for convenience. Such a micro through hole 2 can be formed by electrical discharge machining, laser machining, or the like, as described above.

[0053] As shown in FIGS. 1 to 3, the interior of the micro through hole 2 is filled with a conductive material. Specifically, a metal layer 3 is formed on the inner wall surface of the micro through hole 2 by a manufacturing method that leaves no plating solution or plating solution components behind. As will be described later in the description sections for FIGS. 8 and 9, the metal layer 3 may be configured as follows: a first conductive layer 3a provided on the inner wall surface of the micro through hole 2; a second conductive layer 3b made of a copper plating layer or a copper alloy plating layer provided on the first conductive layer 3a; and a metal solder layer 3c provided on the second conductive layer 3b and filling the micro through hole 2. Alternatively, as shown in FIG. 10, the metal layer 3 may be configured as follows: a conductive layer 3b made of a copper plating layer or a copper alloy plating layer provided on the inner wall surface of the micro through hole 2; and a metal solder layer 3c provided on the conductive layer 3b and filling the micro through hole 2.

[0054] The penetration length of the fine through holes 2 is not particularly limited, but can be in the range of 0.1 mm to 1 mm, which is the thickness of the substrate. The diameter of the fine through holes 2 is also not particularly limited, but can be in the range of 5 μm to 500 μm. In particular, by making the length of the fine through holes 2 in the range of 0.1 mm to 0.5 mm and the diameter in the range of 10 μm to 50 μm, it is possible to provide a fine through hole-filled substrate in which the diameter of long through holes is reduced and the pitch is narrowed.

[0055] The micro through holes 2 can also be expressed by the depth ratio (aspect ratio: L / D) when the depth (L) of the micro through holes 2 is divided by the diameter (D) of the micro through holes 2. For example, L / D may be 4 or more, 10 or more, or 20 or more.

[0056] The pitch of the fine through holes 2 is not particularly limited either, but is designed in consideration of the relationship with the hole diameter. The present invention makes it possible to achieve a narrow pitch, for example, 50 μm to 200 μm.

[0057] <Metal layer> As shown in Figures 1 to 3, the micro through-holes 2 are filled with a metal layer 3. The metal layer 3 can be formed by the steps illustrated in Figures 8 to 10. The present invention is characterized in that the metal layer that is finally filled is a metal solder layer 3c, and the metal solder layer 3c is filled with a nickel-containing molten solder 5 that has been treated with an organic fatty acid-containing solution 21.

[0058] (Metal solder layer 3c) First, the metal solder layer 3c will be described. The metal solder layer 3c is provided on the conductive layer 3b (FIGS. 8 to 10) made of an already formed copper plating layer or copper alloy plating layer, and fills the micro through-holes 2. In FIGS. 8 and 9, the conductive layer 3b is provided on the first conductive layer 3a, and forms a two-layer structure together with the first conductive layer 3a. In FIG. 10, the conductive layer 3b is made of a copper plating layer or copper alloy plating layer.

[0059] 11, an intermetallic compound layer 4 is formed on the conductive layer 3b side or the second conductive layer 3b side of the metal solder layer 3c. The intermetallic compound layer 4 prevents copper corrosion by combining with the copper component constituting the conductive layer 3b or the second conductive layer 3b. This metal solder layer 3c is filled with nickel-containing molten solder 5 treated with an organic fatty acid-containing solution 21, and the nickel, together with the copper and tin, forms the intermetallic compound layer 4 that prevents copper corrosion. As a result, the formation of the intermetallic compound layer 4 inhibits copper corrosion of the copper plating layer constituting the conductive layer 3b or the second conductive layer 3b, and can suppress the formation of a copper-tin alloy (CuSn intermetallic compound layer 7) that has poor mechanical strength.

[0060] The metal solder layer 3c contains tin as a main component and at least nickel as a secondary component. More preferably, it contains one or more optional secondary components selected from silver, copper, zinc, bismuth, antimony, and germanium. The metal solder layer 3c having this component composition can provide a highly reliable micro through-hole filling substrate 10.

[0061] (molten solder) The specific molten solder 5 used to form the metal solder layer 3c is preferably a molten lead-free solder containing tin as the main component and at least nickel as a secondary component. Also, a low-melting-point molten solder containing tin-bismuth solder and at least nickel as a secondary component is also preferably used. Such molten lead-free solder may optionally further contain one or more secondary components selected from copper, germanium, and phosphorus. It may also contain silver to further improve wettability. Examples of solders that can be used include SnNi-based solder, SnCuNi-based solder, SnGeNi-based solder, SnPNi-based solder, SnCuGeNi-based solder, SnCuGePNi-based solder, SnAgCuNi-based solder, SnZnAlNi-based solder, SnAgCuGeNi-based solder, and SnSbNi-based solder. Examples of low-melting-point solder include SnBiNi solder, SnBiZnNi solder, SnBiAgInNi solder, etc. Such molten solder 5 is heated and melted to form a liquid flow 5a of molten solder 5, which is then sprayed from a spray nozzle 31 (filling means) toward the fine through-hole 2, as shown in Fig. 13. The heating temperature is selected arbitrarily depending on the solder composition, but a suitable temperature is usually set within the range of 150°C to 300°C.

[0062] Particularly preferred molten solders 5 include Sn-Ni-Ag-Cu-Ge quinary solder alloys, Sn-Ni-Cu-Ge quaternary solder alloys, Sn-Ni-Cu ternary solder alloys, and Sn-Ni-Ge ternary solder alloys. The Sn-Ni-Ag-Cu-Ge quinary solder is preferably a solder alloy containing, for example, 0.01% to 0.5% by mass of nickel, 2% to 4% by mass of silver, 0.1% to 1% by mass of copper, 0.001% to 0.02% by mass of germanium, and the remainder being tin. The Sn-Ni-Cu-Ge quaternary solder is preferably a solder alloy containing, for example, 0.01% to 0.5% by mass of nickel, 0.1% to 1% by mass of copper, 0.001% to 0.02% by mass of germanium, and the remainder being tin. The Sn-Ni-Cu ternary solder is preferably a solder alloy containing, for example, 0.01% to 0.5% by mass of nickel, 0.1% to 1% by mass of copper, and the remainder being tin. Molten solder 5 made of such a solder alloy is preferred for forming a CuNiSn intermetallic compound layer 4 as the copper corrosion prevention layer 4, which can stably suppress corrosion of copper in the copper plating layer or copper alloy plating layer that constitutes the conductive layer 3b. A particularly preferred composition for forming such a CuNiSn intermetallic compound layer 4 is a solder alloy containing 0.01% to 0.1% by mass of nickel. When soldering with such a solder alloy, it is preferable to use molten solder 5 at a temperature of 240°C to 260°C.

[0063] Furthermore, low-melting-point solder containing bismuth can further lower the heating temperature of molten solder 5, and by adjusting its component composition, the soldering temperature can be lowered, for example, to nearly 150°C. As with the above, the bismuth-containing solder composition also preferably contains 0.01% to 0.5% by mass of nickel, more preferably 0.01% to 0.1% by mass. This allows for a low-temperature molten solder 5 in which a CuNiSn intermetallic compound layer 4 can be easily formed as a copper corrosion prevention layer.

[0064] Other elements such as zinc, copper, germanium, and antimony may also be added as needed, but in any case, the solder composition preferably contains at least 0.01% to 0.5% by mass of nickel, and more preferably 0.01% to 0.1% by mass.

[0065] (Organic fatty acid containing solution) The molten solder 5 is treated with an organic fatty acid-containing solution. The molten solder 5 treated with the organic fatty acid-containing solution is effective in easily forming a copper corrosion prevention layer 4 on the surface of the conductive layer 3b that has already been cleaned with the organic fatty acid-containing solution. The organic fatty acid-containing solution 21 is preferably a solution containing an organic fatty acid having 12 to 20 carbon atoms. Although organic fatty acids having 11 or fewer carbon atoms can also be used, such organic fatty acids are less preferred due to their water absorption. Furthermore, organic fatty acids having 21 or more carbon atoms have drawbacks such as a high melting point, poor permeability, and difficulty in handling. A representative example is palmitic acid having 16 carbon atoms. It is particularly preferable to use palmitic acid having 16 carbon atoms alone as the organic fatty acid. However, if necessary, an organic fatty acid having 12 to 20 carbon atoms, such as stearic acid having 18 carbon atoms, can also be added.

[0066] The organic fatty acid-containing solution 21 preferably contains 5% to 25% by mass of organic fatty acid, with the remainder being an ester synthetic oil. The use of such an organic fatty acid-containing solution 21 selectively captures oxides and impurities (including residual plating solution components; the same applies below) present on the surface of the conductive layer 3b formed on the inner wall surface of the fine through-hole 2, thereby cleaning the surface of the conductive layer 3b. The organic fatty acid-containing solution 21 preferably contains palmitic acid, which has 16 carbon atoms, at a concentration of approximately 10% by mass (e.g., 5% to 15% by mass). The organic fatty acid-containing solution 21 does not contain additives such as metal salts, such as nickel salts or cobalt salts, or antioxidants. If the concentration of the organic fatty acid is less than 5% by mass, the effect of selectively capturing and purifying oxides and impurities present on the surface of the conductive layer 3b is somewhat reduced, and management at low concentrations can be complicated. On the other hand, if the concentration of the organic fatty acid exceeds 25% by mass, problems arise such as an increase in the viscosity of the organic fatty acid-containing solution 21, and problems such as smoke and foul odors at high temperatures exceeding 280° C. Therefore, the content of the organic fatty acid is preferably 5% to 20% by mass, and particularly when palmitic acid having 16 carbon atoms is used alone, the content is preferably around 10% by mass (for example, 5% to 15% by mass).

[0067] By contacting the conductive layer 3b with the organic fatty acid-containing solution 21, oxides and impurities present on the surface of the conductive layer 3b can be removed and cleaned. Furthermore, a coating film (not shown) of the organic fatty acid constituting the organic fatty acid-containing solution 21 is formed on the surface of the conductive layer 3b that has come into contact with the organic fatty acid-containing solution 21. This coating film has the advantage of cleaning the surface of the conductive layer 3b and further suppressing oxidation of the surface of the conductive layer 3b, thereby minimizing the formation of a copper oxide film and the adhesion of impurities. As a result, the molten solder 5 can be brought into contact with the surface of the conductive layer 3b while minimizing the presence of such oxides and impurities on the electrode surface. This allows the copper corrosion prevention layer 4 to be formed on the cleaned surface of the conductive layer 3b with a uniform thickness and no defects.

[0068] Although there are no particular limitations on the liquid temperature of the organic fatty acid-containing solution 21, it is preferable to set it at a relatively high temperature. For example, a range of 50° C. to 280° C. is preferable. If the temperature exceeds 280° C., smoke or a foul odor may be generated.

[0069] (Copper corrosion prevention layer 4) As shown in FIG. 11(A), the copper corrosion prevention layer 4 is formed between the conductive layer 3b and the metal solder layer 3c when molten solder 5 is supplied onto the conductive layer 3b to fill the micro through-hole 2 with the metal solder layer 3c. This copper corrosion prevention layer 4 is a compound layer formed when the nickel and tin components contained in the molten solder 5 combine with the copper component constituting the conductive layer 3b. The copper corrosion prevention layer 4 is formed with a uniform thickness and minimizes defects. The formation of this intermetallic compound layer 4 can suppress or stop the corrosion of copper in the conductive layer 3b constituting the copper plating layer or copper alloy plating layer. As a result, the formation of a copper-tin alloy (CuSn intermetallic compound layer 7), which has poor mechanical strength, can be suppressed. On the other hand, when a ternary lead-free solder consisting of, for example, 3 mass % Ag, 0.5 mass % Cu, and the remainder Sn is used as a nickel-free molten solder material, as shown in FIG. 11(B), the CuNiSn intermetallic compound layer acting as copper corrosion prevention layer 4 is not present, and a thick CuSn intermetallic compound layer 7 with poor mechanical strength is formed.

[0070] The thickness of the copper corrosion prevention layer 4 is not particularly limited, but is likely to be in the range of approximately 0.5 μm to 3 μm. If the copper corrosion prevention layer 4 is too thick, there is a risk of cracks or fractures occurring in the copper corrosion prevention layer itself, so it is preferable that the thickness of the thickest part be 3 μm or less. It is particularly preferable that the thinnest part of the copper corrosion prevention layer 4 be 0.5 μm or more and the thickest part be 3 μm or less, and that the average thickness of the entire copper corrosion prevention layer 4 be 1 μm to 2 μm. The thickness can be calculated from the results of observing the cross section with a scanning electron microscope or a transmission electron microscope, and from the results of measuring 100 points.

[0071] The copper corrosion prevention layer 4 has a composition primarily composed of tin and at least nickel as a secondary component. If the molten solder 5 contains one or more elements selected from silver, copper, zinc, bismuth, antimony, and germanium, the copper corrosion prevention layer 4 also contains these elements as optional secondary components. The CuNiSn intermetallic compound layer, which serves as the copper corrosion prevention layer 4, is formed by cooling the molten solder 5 to a temperature below the melting point of approximately 217°C. The minimum thickness of the formed CuNiSn intermetallic compound layer can be set to 0.5 μm or more, and the average thickness can be set to a range of 1 μm to 2 μm. This allows a crack-free, non-brittle CuNiSn intermetallic compound layer to be uniformly formed between the conductive layer 3b and the metal solder layer 3c, preventing damage or loss of the conductive layer 3b due to corrosion of the copper contained in the conductive layer 3b.

[0072] (molten solder treated with organic fatty acid-containing solution) The molten solder 5 used is treated with an organic fatty acid-containing solution 21. Specifically, a solution containing 5% to 25% by mass of an organic fatty acid having 12 to 20 carbon atoms is heated to 180°C to 280°C, and the heated solution is brought into contact with the molten solder 5, followed by stirring and mixing. This process purifies the molten solder 5 that is contaminated with oxides and impurities (including flux components, etc.; the same applies below) before the refining process, thereby obtaining molten solder 5 from which the oxides and impurities have been removed. Thereafter, for example, the mixture containing the molten solder 5 from which the oxides and impurities have been removed is introduced into a storage tank for the organic fatty acid-containing solution, and the purified molten solder 5, which separates due to the difference in specific gravity in the storage tank for the organic fatty acid-containing solution, is returned to the storage tank for the lead-free solder liquid by a pump from the bottom of the storage tank for the organic fatty acid-containing solution. By carrying out such a refining process, it is possible to suppress increases over time in the copper concentration and impurity concentration in the molten solder 5 used as the liquid flow, and to prevent oxides and impurities from being carried into the lead-free solder liquid storage tank. As a result, it is possible to suppress changes over time in the composition of the molten solder 5 in the lead-free solder liquid storage tank, allowing the use of molten solder 5 with stable joint reliability.

[0073] The treated molten solder 5 contains as few oxides and impurities as possible, which minimizes the variation in the characteristic quality of the metal solder layer 3c formed with the molten solder 5, contributing to quality stability over time. The treated molten solder 5 has the desirable result of having superior solder wettability compared to molten solder not refined with an organic fatty acid-containing solution. Furthermore, the molten solder 5 treated with an organic fatty acid-containing solution has a lower oxygen content than untreated molten solder, and the difference can be confirmed in that it exhibits a fine granular crystalline structure as shown in Figures 6(A) and (B), but does not exhibit the columnar structure seen in untreated molten solder (Figures 7(A) and (B)).

[0074] Furthermore, the results show that the viscosity of molten solder 5 treated with the organic fatty acid-containing solution is significantly lower than that of molten solder not purified with the organic fatty acid-containing solution. The viscosity of molten solder 5 treated with the organic fatty acid-containing solution is in the range of 0.002 Pa·s to 0.004 Pa·s in the molten state. Specifically, in the example of FIG. 12, a quinary lead-free solder consisting of 0.05% by mass of Ni, 0.005% by mass of Ge, 3% by mass of Ag, 0.5% by mass of Cu, and the remainder being Sn is used. The viscosity of molten solder 5 treated with the organic fatty acid-containing solution is 0.003 Pa·s to 0.004 Pa·s, as shown by symbol a in FIG. 12. In contrast, the viscosity of unpurified molten solder, even though it is the same quinary lead-free solder, is in the range of 0.005 Pa·s to 0.008 Pa·s in the molten state. Specifically, the viscosity of unrefined molten solder, even for the same 5-element lead-free solder, was 0.005 Pa·s to 0.006 Pa·s, as shown by symbol b in Figure 12, a difference of about 1.5 times between the two. Note that the molten solders used in the examples and comparative examples described below all had melting points of about 217°C, and the viscosity ranges mentioned above were obtained over a temperature range of at least 240°C to 260°C. The viscosity was measured using a vibrating reed viscometer.

[0075] The difference in properties (viscosity and solder wettability) between the processed molten solder 5 and unrefined molten solder means that when a liquid flow 5a of the molten solder 5 is sprayed onto the substrate 1, the liquid flow 5a easily penetrates into every corner of the micro through-hole 2 into which the organic fatty acid-containing solution has penetrated, replacing the organic fatty acid-containing solution 21, and spreads evenly with good solder wettability, as shown in Fig. 13. In particular, by allowing the organic fatty acid-containing solution 21 to penetrate into the micro through-hole 2 before the liquid flow 5a of the molten solder 5 is sprayed onto the substrate 1 (Fig. 13), the organic fatty acid-containing solution 21 is purified to remove copper oxides, impurities, etc. present on the surface of the conductive layer 3b in the micro through-hole 2. By spraying a liquid flow 5a of molten solder 5, which has also been refined with an organic fatty acid-containing solution and has a viscosity within the above range (0.002 Pa·s to 0.004 Pa·s) onto the surface of the thus-cleaned conductive layer 3b from a spray nozzle 31, the molten solder 5 can be spread evenly and thoroughly over the conductive layer 3b with good solder wettability. As a result, the nickel and tin components contained in the molten solder 5 combine with the copper component that makes up the conductive layer 3b to form a CuNiSn intermetallic compound layer, which serves as the copper corrosion prevention layer 4, all over the surface of the conductive layer 3b, and the micro through-holes 2 can be filled without gaps.

[0076] On the other hand, when a liquid flow of unrefined molten solder is sprayed onto the surface of the conductive layer 3b inside the fine through-hole 2, the viscosity in the molten state is high, at 0.005 Pa·s or more and 0.008 Pa·s or less, and the molten solder does not wet and spread well as described above, and it may not be possible to wet and spread the molten solder evenly over the surface of the conductive layer 3b.

[0077] The temperature of the organic fatty acid-containing solution used for refining is determined by the melting point of the molten solder 5 to be refined. The organic fatty acid-containing solution and the molten solder 5 are stirred and brought into contact with each other at a high temperature range at least equal to or higher than the melting point of the molten solder 5 (for example, 240°C to 260°C for solder with a melting point of around 217°C). The upper limit temperature of the organic fatty acid-containing solution is approximately 280°C from the viewpoint of smoke generation and energy conservation, and is preferably in the range of a temperature equal to or higher than the melting point of the molten solder 5 to be refined to 260°C. For example, a solder alloy containing 0.01% to 0.1% by mass of nickel, 0.1% to 4% by mass of silver, 0.1% to 1% by mass of copper, 0.001% to 0.01% by mass of germanium, and the remainder tin has a melting point of around 217°C and is used as the molten solder 5 at a temperature of 240°C to 260°C. Therefore, the temperature of the organic fatty acid-containing solution is preferably the same, approximately 240°C to 260°C.

[0078] <Conductive layers other than metal solder layers> Other than the metal solder layer 3c constituting the metal layer 3, any conductive layer other than the metal solder layer 3c may be formed on the inner wall surface of the micro through hole 2. As shown in FIGS. 8 and 9, an example of the conductive layer is a first conductive layer 3a formed on the inner wall surface of the micro through hole 2 and a second conductive layer 3b consisting of a copper plating layer or a copper alloy plating layer formed on the first conductive layer 3a. The micro through hole 2 can be filled with a metal solder layer 3c formed on the conductive layer of this two-layer structure. Another example of a conductive layer is a conductive layer 3b consisting of a copper plating layer or a copper alloy plating layer formed directly on the inner wall surface of the micro through hole 2 without forming the first conductive layer 3a, as shown in FIG. 10. The micro through hole 2 can be filled with a metal solder layer 3c formed on the conductive layer 3b.

[0079] (Conductive layer 3b, second conductive layer 3b) The layer denoted by the reference symbol 3b is a copper plating layer or copper alloy plating layer provided as an underlying layer of the metal solder layer 3c. It is designated as the "second conductive layer 3b" in Figures 8 and 9, and as the "conductive layer 3b" in Figure 10. Such a copper plating layer or copper alloy plating layer is preferably an electroless plating layer, which is easy to form with a uniform plating thickness.

[0080] The plating solution for forming the electroless copper plating layer is not particularly limited, but an example thereof is an electroless copper plating solution using sodium hypophosphite as a reducing agent. The plating solution for forming the electroless copper alloy plating layer is also not particularly limited, but an example thereof is an electroless copper-nickel plating solution using sodium hypophosphite as a reducing agent. The thickness of the formed electroless plating layer is not particularly limited, but may be, for example, about 1 μm to 10 μm, and preferably 2 μm to 6 μm. This thickness can be measured with a thickness gauge or by measuring the cross section with a microscope.

[0081] The electroless copper plating method can be a general reduction-type electroless copper plating method that is used industrially. The reduction-type electroless plating method can be either non-catalytic or autocatalytic, and is not particularly limited. The electroless plating solution can include, for example, a copper salt (e.g., copper sulfate, copper chloride, etc.), a reducing agent (e.g., formaldehyde, glyoxylic acid, hypophosphite, DMAB, etc.), a complexing agent (e.g., Rochelle salt, EDTA, etc.), a pH adjuster, a stabilizer, etc.

[0082] (first conductive layer 3a) As shown in FIG. 5, the first conductive layer 3a is provided on the inner wall surface of the fine through-hole 2 and serves as an underlying layer when the second conductive layer 3b is formed. The first conductive layer 3a is made of a conductive material selected from ITO, Cr, Ti, Al, Au, Ag, Cu, Ni, and Mo, or a composite material thereof, and is preferably a PVD film or CVD film formed by a PVD method or a CVD method. By using the above material for the first conductive layer 3a, the second conductive layer 3b, which is an electroless plating layer, can be easily formed on the first conductive layer 3a. The thickness of the first conductive layer 3a is not particularly limited, but can be in the range of approximately 0.1 μm to 1.5 μm, and may be approximately 0.2 μm to 1 μm.

[0083] (others) The micro through-hole filled substrate 10 having the micro through-holes 2 filled in this manner may have a wiring pattern formed on one or both of its substrate surfaces 1a, 1b. Furthermore, the metal solder layer 3c is flush with the substrate surface by removing the molten solder 5 protruding from the substrate surface in the molten solder removal step, but the metal solder layer 3c may be made to protrude from the substrate surfaces 1a, 1b by not removing the molten solder 5 or by removing only a small amount of it. By making the metal solder layer 3c protrude from the substrate surfaces 1a, 1b, the protruding portions can also be used as wiring or lands.

[0084] (Micro through-hole filling substrate) In the micro through-hole filling substrate 10 constructed in this manner, the micro through-holes 2 filled with the metal solder layer 3c are free of the conventional plating solution and its constituent chemical components, and defects and voids are not formed in the filled metal layer 3. As a result, a micro through-hole filling substrate is obtained that enables high-density mounting and high reliability. Furthermore, since the molten solder 5 is purified using the organic fatty acid-containing solution 21, oxygen components, metal oxides, impurities, and the like present in the molten solder 5 are purified and removed, preventing defects and voids from forming in the metal solder layer 3c. Furthermore, since the molten solder 5 contains nickel, the nickel, together with the copper and tin, forms an intermetallic compound layer 4 that prevents copper corrosion. As a result, corrosion of the copper that constitutes the conductive layer 3b is suppressed, and the formation of a copper-tin alloy, which has poor mechanical strength, is suppressed.

[0085] <Manufacturing method> The method for manufacturing a micro through-hole-filled substrate 10 according to the present invention is a method for manufacturing a micro through-hole-filled substrate 10 in which a plurality of micro through-holes 2 formed in a substrate 1 are filled with a metal solder layer 3c, as illustrated in Figures 8 to 10, and is characterized by comprising a conductive layer formation step of forming a conductive layer 3b on the inner wall surface of the micro through-holes 2, with a copper plating layer formed on the metal solder layer 3c side, and a metal solder layer formation step of supplying a liquid flow 5a of nickel-containing molten solder 5 treated with an organic fatty acid-containing solution 21 onto the conductive layer 3b on the inner wall surface to fill the micro through-holes with a metal solder layer.

[0086] (Conductive layer formation process) The conductive layer forming step is a step of forming a conductive layer 3b made of a copper plating layer or a copper alloy plating layer on the inner wall surface of the fine through-hole 2 on the side of the metal solder layer 3c.

[0087] 8(A) to 8(C) and 9(A) to 9(D), the conductive layer forming step may include a first conductive layer forming step of forming a first conductive layer 3a on the inner wall surface of the fine through hole 2 and a second conductive layer forming step of forming a second conductive layer 3b made of a copper plating layer or a copper alloy plating layer on the first conductive layer 3a, or may be a step of forming a conductive layer 3b made of an electroless copper plating layer or an electroless copper alloy plating layer after providing an electroless plating catalyst 23 on the inner wall surface of the fine through hole 2 as shown in <Process Example 2> Fig. 10. In the conductive layer forming step of Process Example 2, the conductive layer 3b made of an electroless copper plating layer or an electroless copper alloy plating layer can be formed without providing a first conductive layer that functions as a base layer for the conductive layer 3b made of a copper plating layer or a copper alloy plating layer.

[0088] As shown in Fig. 8(B), when the conductive layers (3a, 3b) are formed on the substrate surfaces 1a, 1b together with the inner wall surfaces of the micro through-holes 2, it is preferable to have a conductive layer removal step of removing the conductive layers (3a, 3b) formed on the substrate surfaces 1a, 1b before the metal solder layer formation step of Fig. 8(E). The removal means at this time is not particularly limited, but the conductive layers (3a, 3b) on the substrate surfaces 1a, 1b can be removed by mechanical polishing.

[0089] Alternatively, as shown in FIG. 9(A), a resist film 22 may be formed only on the substrate surfaces 1a and 1b. Then, as shown in FIG. 9(B), a first conductive layer 3a may be formed on the substrate surfaces 1a and 1b and in the micro through-holes 2 by the above-described method. Then, as shown in FIG. 9(C), the resist film may be peeled off to remove the first conductive layer 3a formed on the substrate surfaces 1a and 1b. Then, as shown in FIG. 9(D), electroless plating may be performed on the first conductive layer 3a to form the first conductive layer 3a and the second conductive layer 3b in the micro through-holes 2. Then, a micro through-hole-filled substrate 10 may be fabricated using the same procedures as those shown in FIGS. 8 and 10.

[0090] (Organic fatty acid-containing solution immersion process) As shown in FIGS. 8(D), 9(E), and 10(D), an organic fatty acid-containing solution infiltration step is performed after the conductive layer formation step and before the metal solder layer formation step. This organic fatty acid-containing solution infiltration step allows the organic fatty acid-containing solution 21 to infiltrate the micro through-holes 2 before the formation of the metal solder layer 3c. This allows the molten solder 5 treated with the organic fatty acid-containing solution 21 to easily infiltrate the micro through-holes 2. As a result, a metal solder layer can be easily filled into long or narrow through-holes, thereby achieving narrower diameters and narrower pitches of the through-holes with high reliability. To facilitate the infiltration of the organic fatty acid-containing solution 21, a means for reducing the pressure in the space 42 within the container shown in FIGS. 15 and 16 may be used. By creating a reduced pressure, air or air bubbles trapped in the micro through-holes 2 are removed by a so-called degassing phenomenon, allowing the organic fatty acid-containing solution to easily infiltrate the micro through-holes 2.

[0091] In particular, the organic fatty acid-containing solution infiltration step preferably includes a liquid infiltration step of infiltrating a cleaning liquid or a surface treatment liquid into the micro through-holes 2 before infiltrating the organic fatty acid-containing solution 21 into the micro through-holes 2. In this manner, by infiltrating the liquid (cleaning liquid or surface treatment liquid) into the micro through-holes 2 in advance, liquid-liquid exchange between the liquid and the organic fatty acid-containing solution 21 can be easily performed. As a result, the organic fatty acid-containing solution 21 can be thoroughly infiltrated into the micro through-holes 2, and the organic fatty acid-containing solution 21 can selectively capture and remove oxides and impurities (including plating solution component residues) present on the surface of the conductive layer 3b in the micro through-holes 2, thereby cleaning the surface of the conductive layer 3b. The cleaning liquid may be an aqueous solvent or an organic solvent, and the surface treatment liquid may be an oxide removal solution, etc. Even in this case, a means for reducing pressure may be applied to facilitate the infiltration of the cleaning liquid or surface treatment liquid. By creating a reduced pressure state, air and air bubbles trapped in the micro through-holes 2 are removed by a so-called defoaming phenomenon, allowing the cleaning liquid or surface treatment liquid to easily infiltrate into the micro through-holes 2.

[0092] (Metal solder layer formation process) The metal solder layer forming step is a step of supplying a liquid flow 5a of nickel-containing molten solder 5 treated with an organic fatty acid-containing solution 21 onto the conductive layer 3b on the inner wall surface of the fine through-hole 2, thereby filling the fine through-hole 2 with a metal solder layer 3c. The formation of the metal solder layer 3c with the molten solder 5 has already been explained in detail, so a detailed explanation will be omitted here.

[0093] This metal solder layer forming process may include a molten solder removal process in which, after supplying a liquid flow 5a of nickel-containing molten solder 5 (molten solder supply process) as shown in Fig. 13, excess molten solder 5b is removed as shown in Fig. 14. The molten solder removal process shown in Fig. 14 allows excess molten solder 5b to be removed. The excess molten solder 5b is preferably removed by spraying a liquid flow 32a of an organic fatty acid-containing solution or a gas flow of air or an inert gas, as shown in Figs. 14 to 16. Spraying is preferably performed from a spray nozzle 32, and the spray angle θ of the liquid flow 32a or gas flow is preferably adjusted as desired.

[0094] In this metal solder layer forming step, it is preferable to fill space 42 with an atmosphere of vapor from organic fatty acid-containing solution 41, and form metal solder layer 3c in that vapor atmosphere, as shown in Figures 15 and 16. It is also preferable to perform the metal solder layer forming step by spraying molten solder 5 toward micro through-hole 2 or at a predetermined angle. The examples in Figures 13, 15, and 16 are examples in which a liquid flow of molten solder is sprayed from spray nozzle 31 toward micro through-hole 2 (so as to hit the substrate surface at a right angle).

[0095] (Draining of organic fatty acid-containing solution) After spraying the liquid flow of the organic fatty acid-containing solution to remove the excess molten solder 5b, an air knife (not shown) may be provided as needed to drain the organic fatty acid-containing solution. As shown in FIG. 16, the air knife is preferably used to drain the organic fatty acid-containing solution 41 adhering to the surface of the substrate 53, which has been pulled out of the organic fatty acid-containing solution 41 and from which the excess molten solder has been removed. The gas sprayed from the air knife may be clean air or an inert gas such as nitrogen gas or argon gas. This draining process allows the excess organic fatty acid-containing solution 41 to be removed. An air nozzle or the like is preferably used for this draining. The spray pressure of the air nozzle or the like is not particularly limited and can be set as desired.

[0096] (Other components) The details explained in the section explaining "Configuration of the micro through-hole filling substrate 10" have been omitted in the section explaining this manufacturing method to avoid duplication. [Example]

[0097] The present invention will be explained in more detail with reference to examples.

[0098] [Example 1] As an example, a substrate with micro through-holes was prepared by forming micro through-holes 2 with a diameter of 40 μm at a pitch of 150 μm in a quartz substrate 1 with a diameter of 4 inches and a thickness of 0.22 mm. A first conductive layer 3a with a thickness of 0.25 nm was formed on both surfaces (1a, 1b) of the substrate and on the inner wall surfaces of the micro through-holes 2 by sputtering, as shown in FIG. 8(A). Then, as shown in FIG. 8(B), a second conductive layer 3b with a thickness of 5 μm, consisting of a copper plating layer, was formed on the first conductive layer 3a by electroless plating using an electroless copper plating solution. Then, as shown in FIG. 8(C), the first conductive layer 3a and the second conductive layer 3b formed on the substrate surfaces 1a, 1b were removed by mechanical polishing. Then, as shown in FIG. 8(D), an organic fatty acid-containing solution 21 was introduced into the micro through-holes. Thereafter, as shown in Fig. 8(E) and Fig. 13, molten solder 5 treated with organic fatty acid-containing solution 21 was sprayed to fill metal solder layer 3c into micro through-hole 2. After that, excess molten solder 5b was removed by the means shown in Fig. 14. In this way, micro through-hole-filled substrate 10 shown in Fig. 1 and Fig. 3 was produced.

[0099] The molten solder 5 used was a quinary lead-free solder consisting of 0.05% by mass of Ni, 0.005% by mass of Ge, 3% by mass of Ag, 0.5% by mass of Cu, and the remainder being Sn. It was heated to 250°C to prepare the molten solder 5. The solder structure of the filled metal solder layer 3c was a fine granular crystalline structure similar to the structure shown in Figure 6. Furthermore, a copper corrosion prevention layer 4 was formed as shown in Figure 11(A), suppressing the formation of a CuSn intermetallic compound layer 7. The resulting micro-through-hole-filled substrate 10 did not contain any residual plating solution or its constituent chemical components in the through-holes, and no defects or voids were formed in the through-hole conductors.

[0100] [Example 2] As another example, a micro-through-hole-filled substrate was prepared by forming micro-through-holes 2 with a diameter of 20 μm at a pitch of 150 μm in a quartz substrate 1 having a diameter of 4 inches and a thickness of 0.26 mm. The remaining steps were the same as in Example 1, and a micro-through-hole-filled substrate 10 of Example 2 shown in FIG. 2 was fabricated. In this micro-through-hole-filled substrate 10, the solder structure of the filled metal solder layer 3c also had a fine granular crystal structure similar to the structure shown in FIG. 6. Similarly in Example 2, a copper corrosion prevention layer 4 was formed as shown in FIG. 11(A), suppressing the formation of a CuSn intermetallic compound layer 7. Furthermore, the resulting micro-through-hole-filled substrate 10 did not have any plating solution or its constituent chemical components remaining in the through-holes, and no defects or voids were formed in the through-hole conductors.

[0101] [Example 3] As another example, a micro-through-hole-filled substrate (10) was prepared as shown in FIG. 4 by forming 150 μm diameter micro-through-holes (2) at a 300 μm pitch in a 12-inch diameter, 0.30 mm thick, non-alkali glass substrate (1). The first conductive layer (3a) had a thickness of 0.8 μm (8,000 angstroms), as shown in FIG. 5. The remaining conditions were the same as in Example 1, resulting in a micro-through-hole-filled substrate (10) of Example 3. In this micro-through-hole-filled substrate (10), the solder structure of the filled metal solder layer (3c) was a fine granular crystal structure similar to the structure shown in FIG. 6. Similarly in Example 3, a copper corrosion prevention layer (4) was formed, as shown in FIG. 11(A), to suppress the formation of a CuSn intermetallic compound layer (7). Furthermore, the resulting micro-through-hole-filled substrate (10) did not contain any residual plating solution or its constituent chemical components in the through-holes, and no defects or voids were formed in the through-hole conductors. [Explanation of symbols]

[0102] 1 board 1a Top surface of the board 1b Bottom surface of the board 2 PCB through holes 3 metal layer 3a First conductive layer 3b Conductive layer (second conductive layer) 3c Metal solder layer 4 Copper corrosion prevention layer (intermetallic compound layer) 5 Molten solder 5a Molten solder flow 5b Excess molten solder 7 CuSn compound layer 10. Micro-through-hole filling substrate 21 Organic fatty acid containing solution 22 Resist film 23 Electroless plating catalyst 31 Filling means (molten solder injection nozzle) 32 Injection means (injection nozzle for organic fatty acid-containing solution) 32a Injection liquid (solution containing organic fatty acids) 41 Organic fatty acid containing solution 42 Space section 51 Substrates treated with organic fatty acid-containing solutions 52 Board filled with molten solder 53 Board with excess molten solder removed

Claims

1. A micro-through-hole-filled substrate in which a plurality of micro-through-holes formed in a substrate are filled, characterized in that the micro-through-holes are filled with a conductive layer formed on the inner wall surface thereof and a metal solder layer formed on the conductive layer, the conductive layer having a copper plating layer formed on the metal solder layer side, and the metal solder layer being filled with nickel-containing molten solder that has been treated with an organic fatty acid-containing solution.

2. The substrate according to claim 1 , wherein the substrate is a quartz substrate or a glass substrate.

3. 3. The micro through-hole filling substrate according to claim 1, wherein an intermetallic compound layer is formed on the conductive layer side of the metal solder layer, the intermetallic compound layer combining with the copper component constituting the conductive layer to prevent copper corrosion.

4. The micro through-hole filling substrate according to claim 1 or 2, wherein the metal solder layer contains tin as a main component and at least nickel as a secondary component.

5. 3. The micro through-hole filling substrate according to claim 1, wherein the conductive layer comprises a first conductive layer formed on the inner wall surface and a second conductive layer formed on the first conductive layer, and the second conductive layer is a copper plating layer or a copper alloy plating layer.

6. 3. The substrate according to claim 1, wherein the first conductive layer is made of a conductive material selected from the group consisting of ITO, Cr, Ti, Al, Au, Ag, Cu, Ni and Mo, or a composite material thereof.

7. A method for manufacturing a micro through-hole-filled substrate in which a plurality of micro through-holes formed in a substrate are filled with a metal solder layer, the method comprising: a conductive layer forming step of forming a conductive layer consisting of a copper plating layer or a copper alloy plating layer on the metal solder layer side of the inner wall surface of the micro through-hole; and a metal solder layer forming step of supplying a liquid flow of nickel-containing molten solder treated with an organic fatty acid-containing solution onto the conductive layer on the inner wall surface to fill the micro through-holes with a metal solder layer.

8. 8. The method for manufacturing a micro through-hole filling substrate according to claim 7, wherein the metal solder layer forming process includes a molten solder removal process for removing excess molten solder after supplying a liquid flow of the nickel-containing molten solder (molten solder supply process).

9. The method for manufacturing a substrate with a micro through-hole filling according to claim 7 or 8, wherein the substrate is a quartz substrate or a glass substrate.

10. 9. The method for manufacturing a micro through-hole filling substrate according to claim 7, wherein the molten solder contains tin as a main component and at least nickel as a secondary component.

11. 9. The method for producing a substrate for filling fine throughholes according to claim 7, wherein the organic fatty acid-containing solution is a solution containing palmitic acid having 16 carbon atoms.

12. 9. The method for manufacturing a substrate for filling fine through holes according to claim 7, further comprising, after the conductive layer forming step and before the solder layer forming step, an organic fatty acid-containing solution immersion step of immersing an organic fatty acid-containing solution into the fine through holes.

13. 13. The method for manufacturing a substrate with a micro through-hole filling method according to claim 12, wherein the organic fatty acid-containing solution infiltration step includes a liquid infiltration step of infiltrating a cleaning liquid or a surface treatment liquid into the micro through-hole before infiltrating the organic fatty acid-containing solution into the micro through-hole.

14. 9. The method for manufacturing a fine through-hole filling substrate according to claim 7, wherein the viscosity of the molten solder is 0.002 Pa·s or more and 0.004 Pa·s or less.

15. 9. The method for manufacturing a fine through-hole filling substrate according to claim 7, wherein the metal solder layer forming step is carried out in a vapor atmosphere of an organic fatty acid-containing solution.

16. 9. The method for manufacturing a fine through-hole filling substrate according to claim 7, wherein the metal solder layer forming step is performed by spraying the molten solder toward the fine through-hole or at a predetermined angle.

17. 9. The method for manufacturing a fine through-hole filled substrate according to claim 7, wherein the molten solder removing step is performed by spraying a liquid flow of an organic fatty acid-containing solution.

18. 9. The method for manufacturing a substrate for filling a fine through hole according to claim 7 or 8, further comprising a conductive layer removal step of removing the conductive layer formed on the substrate surface before the metal solder layer formation step, when the conductive layer is formed on the substrate surface together with the inner wall surface of the fine through hole.

19. 9. The method for manufacturing a micro through-hole filling substrate according to claim 7 or 8, wherein the conductive layer forming step includes a first conductive layer forming step of forming a first conductive layer on the inner wall surface, and a second conductive layer forming step of forming a second conductive layer made of a copper plating layer or a copper alloy plating layer on the first conductive layer.

20. 20. The method for manufacturing a substrate with a micro through hole filling according to claim 19, wherein the first conductive layer forming step is performed by a PVD method or a CVD method for forming a conductive material selected from ITO, Cr, Ti, Al, Au, Ag, Cu, Ni, and Mo, or a composite material thereof.

21. 9. The method for manufacturing a micro through-hole filling substrate according to claim 7, wherein the conductive layer forming step is a step of forming an electroless copper plating layer or an electroless copper alloy plating layer after providing an electroless plating catalyst on the inner wall surface.

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