Micro-through-hole filled substrate and method for manufacturing the same

Abstract

This invention provides a highly reliable substrate in which fine through-holes are filled with metal, enabling high-density mounting and high reliability, as well as a method for manufacturing the same. [Solution] The above 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, wherein the micro-through holes 2 are filled with a conductive layer (at least 3b) formed on their inner wall surface 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 that 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 fine through-holes are filled with metal, and a fine through-hole filling substrate enabling high-density mounting and high reliability, and a method for manufacturing the same.

Background Art

[0002] With the progress of miniaturization, thinning, and lightening of electronic devices, as well as high-speed, high-function, and multi-function development, substrates for high-density mounting of electronic components such as semiconductor devices are becoming smaller and thinner, and the pitch of external electrode terminals is becoming narrower and the number of pins is increasing. Examples of these substrates include those called BGA (Ball Grid array) and CSP (Chip Size Package), and substrates with various structures have been proposed by semiconductor manufacturers and substrate manufacturers. On the other hand, printed wiring boards for mounting electronic components such as semiconductor devices are required to have finer circuit wiring and multilayered wiring boards in order to accommodate complex circuit wiring and to cope with the narrow pitch and multi-pin of semiconductor devices.

[0003] As multilayer substrates, through-hole multilayer substrates that connect circuits between layers with through-holes, IVH (Interstitial Via Hole) multilayer substrates that connect between layers with IVH, build-up substrates manufactured by a build-up process, etc. are known. Particularly in recent years, glass substrates and quartz substrates are preferably used as substrates. Glass substrates and quartz substrates have high degrees of freedom in thickness and size, are easily available, are relatively inexpensive, are excellent in smoothness and flatness, are advantageous for forming fine wiring with a narrow pitch, have a small linear thermal expansion coefficient, are excellent in mounting stability and dimensional stability, are excellent in chemical stability, and have advantages such as high insulation and excellent transmission characteristics. Also, it is advantageous in that the technology for electrical discharge machining and laser machining of fine through-holes in glass substrates and quartz substrates has also advanced. Therefore, it is required to use a glass substrate or a quartz substrate as a substrate, make the through-holes longer, and reduce the diameter and pitch of the through-holes.

[0004] A technology has also been proposed to fill these through-holes with metal. Generally, this through-hole filling technology involves 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, and then performing a conductive treatment. Next, electroplating is performed by passing an electric current through the entire thin metal layer, thereby filling the through-hole with metal. With this conventional method, for example, to fill the entire inside of a fine through-hole of 50 μm with electroplating, it is necessary to plate the inner wall surface to a thickness of about 25 μm. However, for such fine through-holes, the aspect ratio between the thickness of the substrate (through-hole length) and the hole diameter (through-hole diameter) is large, making it difficult to fill the inner wall surface with an electroplating layer. In addition, there is a possibility that voids or seams may occur in the through-hole conductor.

[0005] Various technologies have been proposed to address these problems. For example, Patent Document 1 proposes a glass circuit board capable of forming fine circuits, although it does not involve filling the entire through-hole with metal. This technology involves laminating a first insulating resin, which has good filling properties into the through-holes, onto both sides of a glass core substrate, which has metal circuits formed on both sides of the glass and through-holes. This effectively suppresses voids generated within the through-holes and achieves long-term connection reliability. Furthermore, the first insulating resin contains a large amount of inorganic filler to suppress the curing shrinkage of the insulating resin filling the through-holes, thereby suppressing depressions caused by curing shrinkage directly above the through-holes and ensuring the flatness of the resin surface.

[0006] Furthermore, Patent Document 2 also proposes a wiring board in which numerous through-holes are formed, although it does not involve filling the entire through-hole with metal. In this board, a copper plating layer is applied to the inner wall surface of the through-holes, and the inside of the through-holes is filled with resin. This technology improves quality by eliminating variations in the thickness of the copper plating layer according to the density of through-holes, and includes a plating film of approximately constant thickness formed along the inner wall surface of the through-holes, with the inside of the through-holes filled 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 [Overview of the project] [Problems that the invention aims to solve]

[0008] As exemplified by the conventional examples above, research is being conducted to achieve highly reliable reduction in diameter and pitch of long through-holes by using glass substrates or quartz substrates with excellent properties as substrates. However, since a conductive layer is formed on the inner wall surface of the through-hole by electroplating, there is a risk that the plating solution or its constituent chemical components may remain inside 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 was made to solve the above-mentioned problems, and its objective is to provide a highly reliable substrate in which fine through-holes are filled with metal, thereby enabling high-density mounting and high reliability, and a method for manufacturing the same. [Means for solving the problem]

[0010] The inventors have proposed a method for manufacturing substrates and electronic components in which copper corrosion, such as that seen in conventional dipping processes, can be significantly suppressed, and which does not cause copper corrosion in subsequent mounting processes. The present invention further applies these technologies to glass substrates and quartz substrates to achieve miniaturization and narrowing of long through-holes with high reliability, thereby solving the above-mentioned problems.

[0011] (1) The micro-through-hole filled substrate according to the present invention is a micro-through-hole filled substrate in which a plurality of micro-through-holes formed in a substrate are filled, wherein the micro-through-holes are filled with a conductive layer formed on their inner wall surface and a metal solder layer formed on the conductive layer, the conductive layer has 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 layer of solidified molten solder is formed on the conductive layer formed on the inner wall surface of a micro-through hole, and the micro-through hole is filled with this metal solder layer. In the micro-through hole filled with this metal solder layer, no plating solution or its constituent chemical components remain, as in conventional methods, and no defects or voids are generated 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 with 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 that no defects or voids are formed in the metal solder layer. In addition, since the molten solder contains nickel, the nickel, along with copper and tin, forms an intermetallic compound that prevents copper corrosion. As a result, copper corrosion of the copper plating layer constituting the conductive layer is suppressed, and the formation of copper-tin alloys with inferior mechanical strength can be suppressed. Furthermore, molten solder treated with an organic fatty acid-containing solution has a lower oxygen content and exhibits a fine-grained crystalline structure compared to untreated molten solder, which can be distinguished by the absence of the columnar structure found in untreated molten solder.

[0013] Furthermore, when forming a metal solder layer with molten solder treated with an organic fatty acid-containing solution, the organic fatty acid-containing solution penetrates into the micro-through holes, allowing the molten solder treated with the organic fatty acid-containing solution to easily penetrate these holes. As a result, the metal solder layer can be easily filled into long through-holes and small-diameter through-holes, enabling highly reliable reduction in through-hole diameter and pitch.

[0014] In the micro-through-hole filled substrate 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 that offers a high degree of freedom in thickness and size, is readily available and relatively inexpensive, has excellent smoothness and flatness, is advantageous for forming fine wiring with a narrow pitch, has a low coefficient of linear thermal expansion, has excellent mounting stability and dimensional stability, has excellent chemical stability, and has high insulation and excellent transmission characteristics. Furthermore, by applying a quartz substrate or glass substrate that can be processed with electrical discharge machining or laser machining to create fine through-holes, a substrate with fine through-holes that enables high-density mounting and high reliability can be provided.

[0016] In the micro-through-hole filled 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. As a result, on the conductive layer side of the metal solder layer, an intermetallic compound is formed in which the nickel, along with copper and tin, prevents the corrosion of copper. Consequently, the formation of this intermetallic compound layer suppresses the corrosion of copper in the copper plating layer constituting the conductive layer, thereby suppressing the formation of copper-tin alloys with inferior mechanical strength.

[0018] In the micro-through-hole filled substrate according to the present invention, the metal solder layer mainly consists of tin and contains at least nickel as a minor component.

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

[0020] In the fine through-hole filling substrate according to the present invention, the conductive layer is composed of 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 the present invention, the conductive layer can be formed into a two-layer structure of a first conductive layer and a second conductive layer composed of a copper plating layer or a copper alloy plating layer. The second conductive layer is preferably an electroless plating layer that is easy to form with a uniform plating thickness.

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

[0023] According to the present invention, by using the above materials for the first conductive layer, the second conductive layer composed of a plating layer can be easily formed. The first conductive layer is preferably a PVD film or a CVD film.

[0024] (2) The manufacturing method of the fine through-hole filling substrate according to the present invention is a manufacturing method of a fine through-hole filling substrate in which a plurality of fine through-holes formed in a substrate are filled with a metal solder layer, and a conductive layer composed of a copper plating layer or a copper alloy plating layer is formed on the inner wall surface of the fine 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 fine through-hole with a metal solder layer.

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

[0026] In the method for manufacturing a fine through-hole filling substrate according to the present invention, the substrate is a quartz substrate or a glass substrate. According to this invention, by applying a quartz substrate or a glass substrate having a small linear thermal expansion coefficient and excellent dimensional stability and chemical stability, it is possible to manufacture a fine through-hole filling substrate enabling high-density mounting and high reliability.

[0027] In the method for manufacturing a fine 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 sub-component.

[0028] In the method for manufacturing a fine through-hole filling substrate according to the present invention, the organic fatty acid-containing solution is a solution containing palmitic acid having 16 carbon atoms.

[0029] In the method for manufacturing a fine through-hole filling substrate according to the present invention, before the solder layer forming step and after the conductive layer forming step, an organic fatty acid-containing solution immersion step of immersing an organic fatty acid-containing solution into the fine through-holes is included. According to this invention, by immersing an organic fatty acid-containing solution into the fine through-holes before forming the metal solder layer, the molten solder treated with the organic fatty acid-containing solution can be easily immersed into the fine through-holes. As a result, it is possible to easily fill the metal solder layer in a long through-hole or a through-hole with a small diameter, and to realize a reduction in the diameter and a narrow pitch of the through-hole with high reliability.

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

[0031] According to this invention, since a liquid (cleaning solution or surface treatment solution) is pre-soaked into the micro-through holes, liquid-to-liquid exchange between the liquid and the organic fatty acid-containing solution can be easily performed. As a result, the organic fatty acid-containing solution can thoroughly penetrate the micro-through holes, and the organic fatty acid-containing solution selectively captures and removes oxides and impurities (including plating solution component residues) present on the conductive layer surface within the micro-through holes, thereby cleaning the conductive layer surface. The cleaning solution may be an aqueous solvent or an organic solvent, and the surface treatment solution may be an oxide removal solution, etc.

[0032] In the method for manufacturing a substrate filled with fine 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 lower than that of molten solder not treated with an organic fatty acid-containing solution (approximately 0.005 to 0.007 Pa·s), has high fluidity, and is easy to fill into fine through-holes.

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

[0034] In the method for manufacturing a substrate filled with micro-through holes according to the present invention, the metal solder layer formation step is performed by spraying the molten solder in the direction of the micro-through holes or at a predetermined angle.

[0035] In the method for manufacturing a substrate filled with fine through holes according to the present invention, the molten solder removal step is performed by spraying a liquid stream of an organic fatty acid-containing solution.

[0036] In the method for manufacturing a micro-through-hole filled substrate according to the present invention, if 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 before the metal solder layer formation step to remove the conductive layer formed on the substrate surface.

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

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

[0039] In the method for manufacturing a micro-through-hole filled substrate according to the present invention, the conductive layer formation 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. According to this invention, a conductive layer consisting 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 an underlayer for the copper plating layer or copper alloy plating layer. [Effects of the Invention]

[0040] According to the present invention, unlike conventional electroplating, no plating solution or its constituent chemical components remain in the through-holes, and no defects or voids occur in the through-hole conductors. This makes it possible to achieve a reduction in diameter and pitch of long through-holes with high reliability. The present invention provides a micro-through-hole filled substrate and a method for manufacturing the same that enables 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 can significantly suppress copper corrosion that occurs in conventional dipping processes and prevent copper corrosion in various subsequent mounting processes. [Brief explanation of the drawing]

[0041] [Figure 1] This is a cross-sectional photograph of an example of a micro-through-hole filled substrate according to the present invention (through-hole diameter of 40 μm). [Figure 2] This is a cross-sectional photograph of another example of a micro-through-hole filled substrate according to the present invention (through-hole diameter of 20 μm). [Figure 3] This is a plan view (A) and a magnified view (B) of an example of a micro-through-hole filled substrate according to the present invention. [Figure 4] This is an electron microscope image showing an example of a substrate with micro-through holes prepared for the manufacture of a substrate filled with micro-through holes. [Figure 5] This is an electron microscope image showing the morphology after the first conductive layer has been formed in the through-hole. [Figure 6] This is a microstructure image of a metal solder layer formed with molten solder treated with an organic fatty acid-containing solution. [Figure 7] This is a microstructure image of a metal solder layer formed with molten solder that was not treated with an organic fatty acid-containing solution. [Figure 8] This is an explanatory diagram showing an example of the manufacturing process for a micro-through-hole filled substrate according to the present invention. [Figure 9] This is an explanatory diagram showing another example of the manufacturing process for a micro-through-hole filled substrate according to the present invention. [Figure 10] This is an explanatory diagram showing yet another example of the manufacturing process for a micro-through-hole filled substrate according to the present invention. [Figure 11](A) 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 (B) is a schematic cross-sectional view of an intermetallic compound layer formed by general molten solder. [Figure 12] This graph shows the temperature dependence of viscosity for molten solder treated with an organic fatty acid-containing solution (a) and molten solder not treated with an organic fatty acid-containing solution (b). [Figure 13] This is a schematic diagram illustrating the process of forming a metal solder layer by spraying molten solder. [Figure 14] This is a schematic diagram illustrating the process of removing excess molten solder by spraying an organic fatty acid-containing solution. [Figure 15] This is a schematic diagram illustrating an example of the process of forming a metal solder layer by spraying molten solder, and the process of removing excess molten solder by spraying an organic fatty acid-containing solution. [Figure 16] This is a schematic diagram illustrating another example of the process of forming a metal solder layer by spraying molten solder, and the process of removing excess molten solder by spraying an organic fatty acid-containing solution. [Modes for carrying out the invention]

[0042] The micro-through-hole filled substrate and its manufacturing method according to the present invention will be described with reference to the drawings. The following embodiments show preferred embodiments of the present invention, but are not limited to these embodiments and include various application forms and modifications.

[0043] In this application, "the present invention" may be replaced with "embodiments of this application." "Corrosion prevention layer" refers to a layer that functions to prevent copper or copper alloy from being dissolved by solder (for example, by the diffusion and dissolution of copper atoms). "Inner wall surface" refers to the inner circumferential surface of the micro-through hole 2, and "substrate surface" refers to the upper and / or lower surface of the substrate. "Top," "bottom," "upper," and "downward" refer to the top and bottom when viewing the drawing in plan view.

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

[0045] As shown in Figures 8 to 10, the manufacturing method of the micro-through-hole filled substrate 10 is characterized by having a conductive layer formation step, in which a conductive layer consisting of a copper plating layer or a copper alloy plating layer is formed on the inner wall surface of the micro-through-hole 2 on the metal solder layer side, and a metal solder layer formation step, in which nickel-containing molten solder 5 treated with an organic fatty acid-containing solution is supplied 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 filled substrate 10 and its manufacturing method according to the present invention, a metal solder layer 3c formed from solidified 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 this metal solder layer 3c. In the micro-through-hole filled with this metal solder layer 3c, no plating solution or its constituent chemical components remain, as in the conventional method, and no defects or voids are formed in the filled metal layer 3. As a result, a micro-through-hole filled substrate 10 that enables high-density mounting and high reliability can be provided. Furthermore, since the molten solder 5 is purified with 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 that no defects or voids are formed in the metal solder layer 3c. In addition, since the molten solder 5 contains nickel, the nickel, together with copper and tin, forms an intermetallic compound layer 4 that prevents the corrosion of copper. As a result, the copper corrosion of the copper plating layer constituting the conductive layer can be suppressed, and the formation of a copper-tin alloy (CuSn intermetallic compound layer 7) with inferior mechanical strength can be suppressed. Furthermore, the molten solder 5 treated with the organic fatty acid-containing solution has a lower oxygen content and exhibits a fine-grained crystalline structure compared to untreated molten solder, and the difference can be confirmed in that it does not exhibit the columnar structure seen in untreated molten solder.

[0047] Furthermore, when forming the metal solder layer 3c with molten solder 5 treated with the organic fatty acid-containing solution, the organic fatty acid-containing solution 21 penetrates the micro-through holes 2 (see Figures 8 to 10), allowing the molten solder 5 treated with the organic fatty acid-containing solution 21 to easily penetrate the micro-through holes 2. As a result, the metal solder layer 3c can be easily filled into long through-holes and small-diameter through-holes, enabling the reduction in through-hole diameter and pitch with high reliability.

[0048] The following provides a detailed explanation of each component.

[0049] <Circuit board> Preferably, substrates include quartz substrates and glass substrates. Glass and quartz substrates offer a high degree of flexibility in thickness and size, are readily available and relatively inexpensive, possess excellent smoothness and flatness, are advantageous for forming fine wiring with a narrow pitch, have a low coefficient of linear thermal expansion, excellent mounting stability, dimensional stability, and chemical stability, and have advantages such as high insulation and excellent transmission characteristics. Furthermore, fine through-holes can be machined by electrical discharge machining or laser processing. By applying such quartz or glass substrates, 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 applying a quartz or glass substrate that has a low coefficient of linear thermal expansion even at such temperatures and possesses excellent dimensional and chemical stability, it is possible to manufacture a micro-through-hole filled substrate that enables high-density mounting and high reliability.

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

[0051] The thickness, size, area, and surface shape of substrate 1 are not particularly limited, but for example, the thickness can be about 0.1 mm to 1 mm, and the surface shape can be, for example, a rectangle, a circle, an ellipse, etc.

[0052] <Micro-through holes> As shown in Figure 4, the micro-through-holes 2 are holes provided in the substrate 1, and those with a plated inner wall surface are generally called through-holes. In this invention, all of the through-holes 2 are filled with a conductive layer and metallized. In this application, this may also be referred to as a through-hole for convenience. Such micro-through-holes 2 can be formed by electrical discharge machining, laser processing, etc., as described above.

[0053] As shown in Figures 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 using a manufacturing method that leaves no plating solution or components behind. The metal layer 3 can be composed of 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 copper alloy plating layer provided on the first conductive layer 3a, and a metal solder layer 3c provided on the second conductive layer 3b to fill the micro-through-hole 2. Alternatively, as shown in Figure 10, the metal layer 3 can be composed of a conductive layer 3b made of a copper plating layer or 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 to fill the micro-through-hole 2.

[0054] The through-hole length of the micro-through-hole 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. Similarly, the diameter of the micro-through-hole 2 is not particularly limited, but can be in the range of 5 μm to 500 μm. In particular, by setting the length of the micro-through-hole 2 to 0.1 mm to 0.5 mm and the diameter to 10 μm to 50 μm, it is possible to provide a micro-through-hole filled substrate that achieves smaller diameter and narrower pitch for long through-holes.

[0055] The micro-through hole 2 can also be expressed as the ratio of the depth (L) of the micro-through hole 2 to its diameter (D) (aspect ratio: L / D). For example, L / D may be 4 or greater, or 10 or greater, or 20 or greater.

[0056] The pitch of the micro-through holes 2 is not particularly limited, but is designed considering its relationship with the hole diameter. The present invention makes it possible to use a narrow pitch, for example, 50 μm to 200 μm.

[0057] <Metal layer> As shown in Figures 1 to 3, a metal layer 3 is filled into the micro-through hole 2. The metal layer 3 can be formed by a process as illustrated in Figures 8 to 10. A feature of the present invention is that the final filling metal layer is a metal solder layer 3c, and this metal solder layer 3c is filled with nickel-containing molten solder 5 treated with an organic fatty acid-containing solution 21.

[0058] (Metal solder layer 3c) First, the metal solder layer 3c will be explained. The metal solder layer 3c is provided on the conductive layer 3b (Figures 8 to 10), which is already formed and consists of a copper plating layer or a copper alloy plating layer, to fill the micro-through holes 2. In Figures 8 and 9, the conductive layer 3b is provided on the first conductive layer 3a, forming a two-layer structure together with the first conductive layer 3a. In Figure 10, it consists of a copper plating layer or a copper alloy plating layer.

[0059] As shown in Figure 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, which combines with the copper component constituting the conductive layer 3b or the second conductive layer 3b to prevent copper corrosion. Since this metal solder layer 3c is filled with nickel-containing molten solder 5 treated with an organic fatty acid-containing solution 21, the nickel, together with copper and tin, forms an intermetallic compound layer 4 that prevents copper corrosion. As a result, the formation of this intermetallic compound layer 4 suppresses copper corrosion of the copper plating layer constituting the conductive layer 3b or the second conductive layer 3b, and suppresses the formation of a copper-tin alloy (CuSn intermetallic compound layer 7) which has inferior mechanical strength.

[0060] The metal solder layer 3c mainly consists of tin and contains at least nickel as a minor component. More preferably, it contains one or more elements selected from silver, copper, zinc, bismuth, antimony, and germanium as optional minor components. Because a metal solder layer 3c with this composition is formed, a highly reliable fine through-hole filled substrate 10 can be provided.

[0061] (molten solder) As the specific molten solder 5 used to form the metal solder layer 3c, a lead-free molten solder mainly composed of tin and containing at least nickel as a minor component is preferably used. A low-melting-point molten solder containing at least nickel as a minor component in a tin-bismuth-based solder is also preferably used. Such lead-free molten solder may further optionally contain one or more components selected from copper, germanium, and phosphorus as minor components. Furthermore, silver may be included to further improve wettability. For example, 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, SnSbNi-based solder, etc. can be used. Examples of low-melting-point solders include SnBiNi-based solder, SnBiZnNi-based solder, and SnBiAgInNi-based solder. This molten solder 5 is heated and melted, and then sprayed as a liquid flow 5a from the spray nozzle 31 (filling means) towards the fine through-hole 2, as shown in Figure 13. The heating temperature is arbitrarily selected depending on the solder composition, but usually a suitable temperature is set within the range of 150°C to 300°C.

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

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

[0064] In addition, other elements such as zinc, copper, germanium, and antimony may be added as needed. 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, which has already been cleaned with the organic fatty acid-containing solution. The organic fatty acid-containing solution 21 is preferably a solution containing organic fatty acids with 12 to 20 carbon atoms. Organic fatty acids with 11 or fewer carbon atoms can also be used, but such organic fatty acids are hygroscopic and therefore not very desirable. Furthermore, organic fatty acids with 21 or more carbon atoms have drawbacks such as a high melting point, poor permeability, and difficulty in handling. A typical example is palmitic acid with 16 carbon atoms. As the organic fatty acid, it is particularly preferable to use only palmitic acid with 16 carbon atoms, but if necessary, organic fatty acids with 12 to 20 carbon atoms, such as stearic acid with 18 carbon atoms, can also be included.

[0066] The organic fatty acid-containing solution 21 preferably contains 5% to 25% by mass of organic fatty acids, with the remainder being ester synthetic oil. By using such an organic fatty acid-containing solution 21, oxides and impurities (including plating solution component residues; the same applies hereinafter) present on the surface of the conductive layer 3b formed on the inner wall surface of the micro-through holes 2 can be selectively taken up, and the surface of the conductive layer 3b can be cleaned. In particular, an organic fatty acid-containing solution 21 containing approximately 10% by mass (for example, 5% to 15% by mass) of palmitic acid with 16 carbon atoms is preferred. Note that the organic fatty acid-containing solution 21 does not contain metal salts such as nickel salts or cobalt salts, or additives such as antioxidants. If the concentration of organic fatty acids is less than 5% by mass, the effect of selectively taking up and purifying oxides and impurities present on the surface of the conductive layer 3b is somewhat low, and management at low concentrations may become complicated. On the other hand, if the concentration of organic fatty acids exceeds 25% by mass, problems arise such as increased viscosity of the organic fatty acid-containing solution 21, and smoke and foul odors in high-temperature regions exceeding 280°C. Therefore, the content of organic fatty acids is preferably 5% to 20% by mass, and in particular, when using only palmitic acid with 16 carbon atoms, the content is preferably around 10% by mass (for example, 5% to 15% by mass).

[0067] By bringing the conductive layer 3b into contact with the liquid 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 acids 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 suppressing oxidation of the surface of the conductive layer 3b, thereby minimizing the formation of copper oxide films 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 with minimal presence of oxides and impurities on the electrode surface. In this way, a copper corrosion prevention layer 4 can be formed on the cleaned surface of the conductive layer 3b with a uniform thickness and no defects.

[0068] The temperature of the organic fatty acid-containing solution 21 is not particularly limited, but it is preferable to have a relatively high temperature. For example, a temperature range of 50°C to 280°C is preferred. If the temperature exceeds 280°C, smoke or unpleasant odors may be generated.

[0069] (Copper corrosion prevention layer 4) As shown in Figure 11(A), the copper corrosion prevention layer 4 is a layer that forms between the conductive layer 3b and the metal solder layer 3c when molten solder 5 is supplied onto the conductive layer 3b and the fine through-holes 2 are filled 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, and defects are minimized, resulting in a uniform thickness. The formation of this intermetallic compound layer 4 suppresses or stops the corrosion of copper in the conductive layer 3b that constitutes 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 inferior mechanical strength, can be suppressed. On the other hand, when using a nickel-free molten solder material, such as a ternary lead-free solder consisting of Ag: 3% by mass, Cu: 0.5% by mass, and the remainder: Sn, as shown in Figure 11(B), there is no CuNiSn intermetallic compound layer that acts as a copper corrosion prevention layer 4, and a thick CuSn intermetallic compound layer 7 with inferior mechanical strength is formed.

[0070] The thickness of the copper corrosion prevention layer 4 is not particularly limited, but it tends to be in the range of approximately 0.5 μm to 3 μm. If the thickness of the copper corrosion prevention layer 4 is too thick, cracks or fissures may occur 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 is 0.5 μm or more, the thickest part is 3 μm or less, and the overall average thickness of the copper corrosion prevention layer 4 is 1 μm to 2 μm. The thickness can be calculated from the results of 100 measurement points obtained by observing the cross-section with a scanning electron microscope or a transmission electron microscope.

[0071] The composition of the copper corrosion prevention layer 4 is primarily tin with at least nickel as a minor component, and if the molten solder 5 contains one or more elements selected from silver, copper, zinc, bismuth, antimony, and germanium, these elements are also included as optional minor components. In this case, the CuNiSn intermetallic compound layer, which is 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 0.5 μm or more, and the average thickness can be in the range of 1 μm to 2 μm. In this way, a crack-free and non-brittle CuNiSn intermetallic compound layer can be uniformly formed between the conductive layer 3b and the metal solder layer 3c, preventing the defect or disappearance of the conductive layer 3b due to the corrosion of copper contained in the conductive layer 3b.

[0072] (Molten solder treated with an organic fatty acid-containing solution) The molten solder 5 used is one that has been treated with an organic fatty acid-containing solution 21. Specifically, a solution containing 5% to 25% by mass of organic fatty acids 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 and stirred and mixed. In this way, the molten solder 5 before purification treatment, which is contaminated with oxides and impurities (including flux components, etc.; the same applies hereinafter), can be purified, and molten solder 5 from which oxides and impurities have been removed can be obtained. After that, for example, the mixture containing the molten solder 5 from which oxides and impurities have been removed is introduced into a storage tank of the organic fatty acid-containing solution, and the purified molten solder 5 separated by the difference in specific gravity in the storage tank of the organic fatty acid-containing solution is returned to the storage tank of lead-free solder liquid by pump from the bottom of the storage tank of the organic fatty acid-containing solution. By performing this purification process, it is possible to suppress the time-dependent increase in copper and impurity concentrations in the molten solder 5 used as liquid flow, and to prevent oxides and impurities from being introduced into the lead-free solder solution reservoir. As a result, it is possible to suppress time-dependent changes in the composition of the molten solder 5 in the lead-free solder solution reservoir, thereby enabling the use of a stable and reliable molten solder 5 for reliable bonding.

[0073] Since the treated molten solder 5 contains as few oxides and impurities as possible, the variation in the characteristic quality of the metal solder layer 3c formed with the molten solder 5 can be made extremely small, contributing to quality stability over time. The treated molten solder 5 shows the desirable result of having superior solder wettability compared to molten solder that has not been purified with the organic fatty acid-containing solution. Furthermore, 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 it exhibits a fine granular crystalline structure as shown in Figures 6(A) and 6(B), while it does not exhibit the columnar structure (Figures 7(A) and 7(B)) seen in the untreated molten solder.

[0074] Furthermore, the molten solder 5 treated with the organic fatty acid-containing solution showed significantly lower viscosity compared to molten solder that had not been purified with the organic fatty acid-containing solution. The viscosity of molten solder 5 treated with the organic fatty acid-containing solution was in the range of 0.002 Pa·s to 0.004 Pa·s in the molten state. Specifically, in the example in Figure 12, a pentagonal lead-free solder consisting of Ni: 0.05 mass%, Ge: 0.005 mass%, Ag: 3 mass%, Cu: 0.5 mass%, and the remainder being Sn was used. The viscosity of molten solder 5 treated with the organic fatty acid-containing solution was 0.003 Pa·s to 0.004 Pa·s, as indicated by symbol a in Figure 12, whereas the viscosity of unpurified molten solder, even with the same pentagonal lead-free solder, was in the range of 0.005 Pa·s to 0.008 Pa·s in the molten state. Specifically, the viscosity of unrefined molten solder ranged from 0.005 Pa·s to 0.006 Pa·s, even for the same pentameric lead-free solder, as indicated by symbol b in Figure 12, showing a difference of approximately 1.5 times between the two. The molten solders used in the examples and comparative examples described later all had melting points of approximately 217°C, and the viscosity ranges mentioned above were obtained at a temperature range of at least 240°C to 260°C. Viscosity was measured using a vibrating viscometer.

[0075] The above-mentioned difference in properties (viscosity and solder wettability) between the processed molten solder 5 and the unrefined molten solder means that, as shown in Figure 13, when the liquid flow 5a of the molten solder 5 is sprayed onto the substrate 1, the organic fatty acid-containing solution 21 easily penetrates into every corner of the fine through-holes 2 into which the organic fatty acid-containing solution enters, replacing the original solution, and spreads evenly with good solder wettability. In particular, by allowing the organic fatty acid-containing solution 21 to penetrate into the fine through-holes 2 before spraying the liquid flow 5a of the molten solder 5 onto the substrate 1 (Figure 13), the organic fatty acid-containing solution 21 cleans the surface of the conductive layer 3b inside the fine through-holes 2 by removing copper oxides and impurities. By spraying a liquid stream 5a of molten solder 5, which has been purified 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 the spray nozzle 31, the molten solder 5 can be spread evenly and uniformly 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 components that make up the conductive layer 3b to form a CuNiSn intermetallic compound layer, which is a copper corrosion prevention layer 4, to every corner of the surface of the conductive layer 3b, and the fine through holes 2 can be filled without any gaps.

[0076] On the other hand, when a liquid stream of unrefined molten solder is sprayed onto the surface of the conductive layer 3b inside the micro-through hole 2, the viscosity in the molten state is high, between 0.005 Pa·s and 0.008 Pa·s, and it does not spread evenly with good wettability as described above, making it impossible to evenly wet the surface of the conductive layer 3b with the molten solder.

[0077] The temperature of the organic fatty acid-containing solution used for purification is determined by the melting point of the molten solder 5 to be purified. The organic fatty acid-containing solution and the molten solder 5 are stirred and brought into contact at a high temperature range at least above 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). Furthermore, the upper limit temperature of the organic fatty acid-containing solution is around 280°C from the viewpoint of smoke generation and energy saving, and preferably in the range of above the melting point of the molten solder 5 to be purified to 260°C. For example, a solder alloy consisting of nickel: 0.01% to 0.1% by mass, silver: 0.1% to 4% by mass, copper: 0.1% to 1% by mass, germanium: 0.001% to 0.01% by mass, and the remainder: tin has a melting point of around 217°C and is used as molten solder 5 at a temperature of 240°C to 260°C, so it is preferable that the temperature of the organic fatty acid-containing solution is also around the same 240°C to 260°C.

[0078] <Conductive layers other than the metal solder layer> Aside from the metal solder layer 3c that constitutes the metal layer 3, any conductive layer formed on the inner wall surface of the micro-through hole 2 is acceptable. Examples of conductive layers include, for example, a first conductive layer 3a provided on the inner wall surface of the micro-through hole 2 and a second conductive layer 3b consisting of a copper plating layer or copper alloy plating layer provided on the first conductive layer 3a, as shown in Figures 8 and 9. The metal solder layer 3c can be provided on such a two-layer conductive layer structure to fill the micro-through hole 2. Alternatively, as shown in Figure 10, for example, a conductive layer 3b consisting of a copper plating layer or copper alloy plating layer directly provided on the inner wall surface of the micro-through hole 2 without providing the first conductive layer 3a may be used. The metal solder layer 3c can be provided on such a conductive layer 3b to fill the micro-through hole 2.

[0079] (Conductive layer 3b, second conductive layer 3b) The layer represented by reference numeral 3b is a copper plating layer or copper alloy plating layer provided as a lower layer to the metal solder layer 3c described above. In Figures 8 and 9, it is labeled "second conductive layer 3b," and in Figure 10, it is labeled "conductive layer 3b." Such a copper plating layer or copper alloy plating layer is preferably an electroless plating layer that is easy to form with a uniform plating thickness.

[0080] The plating solution used to form the electroless copper plating layer is not particularly limited, but one example is an electroless copper plating solution using sodium hypophosphite as a reducing agent. Similarly, the plating solution used to form the electroless copper alloy plating layer is not particularly limited, but one example 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 it can 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] Furthermore, the electroless copper plating method can be the general reducing type of electroless copper plating commonly used in industry. The reducing type of electroless plating may be non-catalytic or autocatalytic, and is not particularly limited. Examples of electroless plating solutions include those containing copper salts (e.g., copper sulfate or copper chloride), reducing agents (e.g., formaldehyde, glyoxylic acid, hypophosphate, DMAB, etc.), complexing agents (e.g., Rochelle salt or EDTA, etc.), pH adjusters, stabilizers, etc.

[0082] (first conductive layer 3a) As illustrated in Figure 5, the first conductive layer 3a is provided on the inner wall surface of the micro-through hole 2 and is provided as a lower layer when forming the second conductive layer 3b. This first conductive layer 3a is a conductive material or composite material selected from ITO, Cr, Ti, Al, Au, Ag, Cu, Ni, and Mo, and is preferably a PVD film or CVD film formed by the PVD method or CVD method. By using the above material for the first conductive layer 3a, the second conductive layer 3b, which consists of 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 about 0.1 μm to 1.5 μm, or it may be about 0.2 μm to 1 μm.

[0083] (others) In this configuration, the micro-through-hole filled substrate 10, in which the micro-through-holes 2 are filled, may have wiring patterns formed on one or both of its substrate surfaces 1a and 1b. Furthermore, although the metal solder layer 3c is flush with the substrate surface by removing the molten solder 5 that protrudes from the substrate surface in the molten solder removal process, the metal solder layer 3c may protrude from the substrate surfaces 1a and 1b by not removing the molten solder 5 or removing only a small amount. By making the metal solder layer 3c protrude from the substrate surfaces 1a and 1b, the protruding portion can be utilized as wiring or lands.

[0084] (Substrate filled with fine through-holes) In the fine through-hole filled substrate 10 constructed in this way, no plating solution or its constituent chemical components remain in the fine through-holes 2 filled with the metal solder layer 3c, and no defects or voids are formed in the filled metal layer 3. As a result, a fine through-hole filled substrate is obtained that enables high-density mounting and high reliability. Furthermore, since the molten solder 5 is purified with an organic fatty acid-containing solution 21, oxygen components, metal oxides, impurities, etc. present in the molten solder 5 are purified and removed, so no defects or voids are formed in the metal solder layer 3c. In addition, since the molten solder 5 contains nickel, the nickel, along with copper and tin, forms an intermetallic compound layer 4 that prevents the corrosion of copper. As a result, the corrosion of copper constituting the conductive layer 3b is suppressed, and the formation of copper-tin alloys with inferior mechanical strength can be suppressed.

[0085] <Manufacturing method> The present invention relates to a method for manufacturing a micro-through-hole filled substrate 10, as illustrated in Figures 8 to 10, wherein a plurality of micro-through-holes 2 formed in a substrate 1 are filled with a metal solder layer 3c, 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, wherein a copper plating layer is formed on the metal solder layer 3c side; and a metal solder layer formation step of supplying a liquid stream 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 the metal solder layer.

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

[0087] This conductive layer formation process may include a first conductive layer formation step of forming a first conductive layer 3a on the inner wall surface of the micro-through hole 2, as shown in the examples of Figures 8(A) to 9(C) and 9(A) to 9(D) in <Process Example 1>, and a second conductive layer formation step of forming a second conductive layer 3b consisting of a copper plating layer or a copper alloy plating layer on the first conductive layer 3a. Alternatively, as shown in Figure 10 in <Process Example 2>, it may be a process of forming a conductive layer 3b consisting 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 micro-through hole 2. In the conductive layer formation step of Process Example 2, the conductive layer 3b consisting 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 consisting of a copper plating layer or a copper alloy plating layer.

[0088] Furthermore, as shown in Figure 8(B), if the conductive layers (3a, 3b) are formed on the substrate surfaces 1a, 1b together with the inner wall surface of the micro-through hole 2, it is preferable to have a conductive layer removal step before the metal solder layer formation step shown in Figure 8(E) to remove the conductive layers (3a, 3b) formed on the substrate surfaces 1a, 1b. The means for removal 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 Figure 9(A), a resist film 22 can be provided only on the substrate surfaces 1a and 1b, and then, as shown in Figure 9(B), a first conductive layer 3a can be formed on the substrate surfaces 1a and 1b and in the micro-through holes 2 using the method described above. After that, as shown in Figure 9(C), the resist film can be peeled off to remove the first conductive layer 3a provided on the substrate surfaces 1a and 1b. Subsequently, as shown in Figure 9(D), electroless plating can be formed 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. After that, a micro-through hole filled substrate 10 can be manufactured using the same procedure as in Figures 8 and 10.

[0090] (Organic fatty acid-containing solution immersion process) After the conductive layer formation process and before the metal solder layer formation process, as shown in Figures 8(D), 9(E), and 10(D), the process includes an organic fatty acid-containing solution infiltration step in which an organic fatty acid-containing solution 21 is infiltrated into the micro-through holes 2. 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, and 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, the metal solder layer can be easily filled into long through holes and small-diameter through holes, and the miniaturization and narrowing of the pitch of through holes can be achieved with high reliability. To facilitate the infiltration of the organic fatty acid-containing solution 21, for example, means of reducing the pressure in the space 42 inside the container as shown in Figures 15 and 16 may be applied. By creating a reduced pressure state, air and air bubbles that have entered the micro-through holes 2 can be removed by the 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 immersion step described above preferably includes a liquid immersion step in which a cleaning solution or surface treatment solution is immersed in the micro-through holes 2 before the organic fatty acid-containing solution 21 is immersed in the micro-through holes 2. By immersing the liquid (cleaning solution or surface treatment solution) in the micro-through holes 2 in advance in this way, liquid-to-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 immersed in the micro-through holes 2, and oxides and impurities (including plating solution component residues) present on the surface of the conductive layer 3b in the micro-through holes 2 can be selectively taken up and removed by the organic fatty acid-containing solution 21, thereby cleaning the surface of the conductive layer 3b. The cleaning solution may be an aqueous solvent or an organic solvent, and the surface treatment solution may be an oxide removal solution, etc. In this case as well, a means of reducing the pressure may be applied to facilitate the immersion of the cleaning solution or surface treatment solution. By reducing the pressure, air and air bubbles that have entered the micro-through holes 2 can be removed by the so-called degassing phenomenon, and the cleaning solution or surface treatment solution can be easily immersed in the micro-through holes 2.

[0092] (Metal solder layer formation process) The metal solder layer formation process involves 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 micro-through hole 2, thereby filling the micro-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 that explanation will be omitted here.

[0093] This metal solder layer formation process may include a molten solder removal process to remove excess molten solder 5b after supplying a liquid flow 5a of nickel-containing molten solder 5 (molten solder supply process), as shown in Figure 13, as shown in Figure 14. The excess molten solder 5b can be removed by the molten solder removal process shown in Figure 14. It is preferable to remove the excess molten solder 5b by injecting a liquid flow 32a of an organic fatty acid-containing solution or a gaseous flow of air or an inert gas, as shown in Figures 14 to 16. The injection is preferably performed from an injection nozzle 32, and it is preferable to arbitrarily adjust the injection angle θ of the liquid flow 32a or gaseous flow.

[0094] In this metal solder layer formation process, it is preferable to create an atmosphere of vapor from the organic fatty acid-containing solution 41 in the space 42, as shown in Figures 15 and 16, and to form the metal solder layer 3c in that vapor atmosphere. Furthermore, it is preferable to perform the metal solder layer formation process by spraying molten solder 5 in the direction of the micro-through holes 2 or at a predetermined angle. The examples in Figures 13, 15, and 16 show examples in which the liquid flow of molten solder is sprayed from the spray nozzle 31 in the direction of the micro-through holes 2 (so as to hit the substrate surface perpendicularly).

[0095] (Draining the liquid from the organic fatty acid-containing solution) After removing excess molten solder 5b by spraying a stream of organic fatty acid-containing solution, an air knife (not shown) may be provided as needed to remove excess organic fatty acid-containing solution. As shown in Figure 16, the air knife is preferably used to remove excess organic fatty acid-containing solution 41 adhering to the surface of the substrate 53 from which the excess molten solder has been removed, by being pulled out of the organic fatty acid-containing solution 41. The gas sprayed from the air knife may be clean air or an inert gas such as nitrogen gas or argon gas. This removal process can remove any excess organic fatty acid-containing solution 41. It is preferable to use an air nozzle or the like for this removal. The spray pressure of the air nozzle or the like at this time is not particularly limited and can be set arbitrarily.

[0096] (Other components) Note that the details explained in the section on "Configuration of the micro-through-hole filled substrate 10" have been omitted in this section on the manufacturing method to avoid duplication. [Examples]

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

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

[0099] The molten solder 5 used was a pentagonal lead-free solder consisting of Ni: 0.05 mass%, Ge: 0.005 mass%, Ag: 3 mass%, Cu: 0.5 mass%, with the remainder being Sn, and was prepared as molten solder 5 by heating to 250°C. The solder structure of the filled metal solder layer 3c was a fine granular crystalline structure similar to the microstructure shown in Figure 6. In addition, a copper corrosion prevention layer 4 as shown in Figure 11(A) was formed, suppressing the formation of the CuSn intermetallic compound layer 7. The obtained micro-through-hole filled substrate 10 did not have any residual plating solution or its constituent chemical components in the through-holes, nor did it have defects or voids in the through-hole conductors.

[0100] [Example 2] As another example, a micro-through-hole formation substrate was prepared by forming micro-through-holes 2 with a diameter of 20 μm at a pitch of 150 μm on a quartz substrate 1 with a diameter of 4 inches and a thickness of 0.26 mm. Otherwise, the procedure was the same as in Example 1, and the micro-through-hole filled substrate 10 of Example 2 shown in Figure 2 was fabricated. In this micro-through-hole filled substrate 10 as well, the solder structure of the filled metal solder layer 3c was a fine granular crystalline structure similar to the microstructure shown in Figure 6. Similarly in Example 2, a copper corrosion prevention layer 4 as shown in Figure 11(A) was formed, suppressing the formation of the CuSn intermetallic compound layer 7. Furthermore, the obtained micro-through-hole filled substrate 10 did not have any residual plating solution or its constituent chemical components in the through-holes, nor did it have any defects or voids in the through-hole conductors.

[0101] [Example 3] As another example, a micro-through-hole formed substrate with 700,000 holes, as shown in Figure 4, was prepared by forming 150 μm diameter micro-through-holes 2 at a 300 μm pitch on an alkali-free glass substrate 1 with a diameter of 12 inches and a thickness of 0.30 mm. The first conductive layer 3a was made 0.8 μm (8000 angstroms) thick, as shown in Figure 5. Otherwise, the same procedure as in Example 1 was followed to fabricate the micro-through-hole filled substrate 10 of Example 3. In this micro-through-hole filled substrate 10 as well, the solder structure of the filled metal solder layer 3c was a fine granular crystalline structure similar to the microstructure shown in Figure 6. Similarly in Example 3, a copper corrosion prevention layer 4 was formed as shown in Figure 11(A), suppressing the formation of the CuSn intermetallic compound layer 7. Furthermore, the obtained micro-through-hole filled substrate 10 did not have any residual plating solution or its constituent chemical components in the through-holes, nor did it have defects or voids in the through-hole conductors. [Explanation of Symbols]

[0102] 1 circuit board 1a Top surface of the substrate 1b Bottom surface of the substrate 2 Through-holes in the circuit board 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-hole filled substrate 21 Organic fatty acid containing solution 22 Resist film 23 Electroless Plating Catalyst 31. Filling means (molten solder spray 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 Substrate treated with organic fatty acid-containing solution 52. Substrate filled with molten solder. 53. Circuit board with excess molten solder removed.

Claims

1. A micro-through-hole filled substrate, wherein a plurality of micro-through holes formed in the substrate are filled, the micro-through holes are filled with a conductive layer formed on their inner wall surface and a metal solder layer formed on the conductive layer, the conductive layer has 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.

2. The micro-through-hole filling substrate according to claim 1, wherein the substrate is a quartz substrate or a glass substrate.

3. The micro-through-hole filling substrate according to claim 1 or 2, wherein 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.

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

5. The fine through-hole filling substrate according to claim 1 or 2, 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. The fine through-hole filling substrate according to claim 1 or 2, wherein the first conductive layer is a conductive material selected from 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, wherein a plurality of micro-through holes formed in a substrate are filled with a metal solder layer, comprising: a conductive layer formation 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 holes on the metal solder layer side; and a metal solder layer formation step of supplying a liquid stream 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. The method for manufacturing a micro-through-hole filled substrate according to claim 7, wherein the metal solder layer formation step includes a molten solder removal step in which excess molten solder is removed after supplying a liquid flow of nickel-containing molten solder (molten solder supply step).

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

10. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the molten solder mainly comprises tin and contains at least nickel as a minor component.

11. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the organic fatty acid-containing solution is a solution containing palmitic acid having 16 carbon atoms.

12. A method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, further comprising an organic fatty acid-containing solution immersion step, in which an organic fatty acid-containing solution is immersed in the micro-through-holes after the conductive layer formation step and before the solder layer formation step.

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

14. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the viscosity of the molten solder is 0.002 Pa·s or more and 0.004 Pa·s or less.

15. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the metal solder layer formation step is carried out in a vapor atmosphere of an organic fatty acid-containing solution.

16. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the metal solder layer formation step is performed by spraying the molten solder in the direction of the micro-through-hole or at a predetermined angle.

17. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the molten solder removal step is performed by spraying a liquid stream of an organic fatty acid-containing solution.

18. If the conductive layer is formed on the substrate surface together with the inner wall surface of the micro-through hole, the method for manufacturing a micro-through hole filled substrate 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.

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

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

21. The method for manufacturing a micro-through-hole filled substrate according to claim 7 or 8, wherein the conductive layer formation 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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