Circuit board manufacturing method

Abstract

The present invention provides a method for manufacturing a circuit board that can prevent metallization from occurring within the through-hole when the through-hole is metallized. [Solution] A method for manufacturing a circuit board having metallized through-holes, comprising: a through-hole formation step (process S10) in which a frustoconical through-hole is provided in the circuit board; and a metallization formation step (process S21-S24) in which, when metallizing the through-hole, the circuit board is rotated multiple times with respect to the vertical axis of the surface of the circuit board, which is mounted on a substrate mounting jig, to metallize it. In the through-hole formation step, a frustoconical through-hole is provided in the circuit board by a shot blasting method.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a circuit board having through-holes.

Background Art

[0002] Regarding a method for forming a functional component film inside the through-holes of a substrate having through-holes, attempts have been made to form a uniform film of functional components in the through-holes of the substrate having through-holes.

[0003] In Patent Document 1, "In a film forming method for forming a film made of a predetermined functional component on the inner wall of the through-hole of a substrate having through-holes, a photosensitive resin film is formed on the substrate surface, the film is exposed to a predetermined pattern and developed to remove the film near the through-hole, a predetermined functional component is deposited on the substrate by physical vapor deposition, and then the film is removed from the substrate." is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present inventors have conventionally mass-produced submount products (substrate thickness of about 250 μm) with metallization on through-holes. A submount is an insulating substrate located between a semiconductor laser element and a heat sink (a metal block such as copper), and has the performance of efficiently transmitting heat generated from the semiconductor laser element to the heat sink side.

[0006] In recent years, there has been an extremely strong demand for faster, smaller, lighter (higher density), higher power output, and higher reliability electronic devices. Semiconductor devices are rapidly moving towards higher integration, larger size, multi-chip design, and higher power output. As a result, there has been a high demand for thin submount products with substrate thicknesses of 100-150 μm. However, conventional methods cause disconnections during metallization of through-holes, leading to a strong demand for improved manufacturing methods.

[0007] The present invention was made to solve the aforementioned problems, and aims to provide a method for manufacturing a circuit board that can prevent metallization from occurring within the through-hole when the through-hole is metallized. [Means for solving the problem]

[0008] To solve the aforementioned problems, the present invention provides a method for manufacturing a circuit board having metallized through-holes, comprising: a through-hole forming step of providing frustoconical through-holes in a circuit board; and a metallization forming step of metallizing the through-holes by rotating them in multiple steps with respect to the vertical axis of the surface of the circuit board, which is mounted on a substrate mounting jig. Other aspects of the present invention will be described in the embodiments described below. [Effects of the Invention]

[0009] According to the present invention, when metallization is applied to a through-hole, it is possible to prevent the metallized material from breaking within the through-hole. [Brief explanation of the drawing]

[0010] [Figure 1] This is an explanatory diagram illustrating the schematic manufacturing process of a circuit board according to the embodiment. [Figure 2] This is an explanatory diagram showing the through-hole formation process according to the embodiment. [Figure 3] This is an explanatory diagram showing the metallization formation process according to an embodiment. [Figure 4] This is an explanatory diagram showing metallization formation by vacuum deposition. [Figure 5] This figure shows an example of circuit board placement as viewed from below through a circuit board mounting jig. [Figure 6] This is an explanatory diagram showing the surfaces within a through-hole where vapor deposition is likely to occur and those where it is not. [Figure 7] This is a flowchart showing the manufacturing process of a circuit board according to the embodiment. [Figure 8] This figure shows the metallization status of the through-hole according to the embodiment. [Figure 9] This figure shows the effect of the angle θ between the surface and the wall of the through-hole. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Figure 1 is an explanatory diagram illustrating the schematic of the manufacturing process of a circuit board according to this embodiment. The manufacturing method of a circuit board having metallized through-holes according to this embodiment comprises a through-hole formation step (process S10) in which frustoconical through-holes are formed in the circuit board, and a metallization formation step (process S20) in which the circuit board is metallized in multiple stages at different angles when metallizing the through-holes. Process S10 will be explained with reference to Figure 2, and process S20 will be explained with reference to Figures 3 to 6. Process S20 is specifically implemented by rotating the circuit board, which is mounted on a substrate mounting jig, in multiple stages with respect to the vertical axis of the surface, as will be described later.

[0012] The target circuit board is a ceramic substrate. Common ceramic substrate materials include polycrystalline alumina (thermal conductivity: approximately 23 W / m·K), polycrystalline aluminum nitride (thermal conductivity: approximately 170 W / m·K), and polycrystalline silicon carbide (thermal conductivity: approximately 300 W / m·K). In addition, polycrystalline silicon carbide with a thermal conductivity of 300 W / m·K is sometimes used as a substrate material. Furthermore, single-crystal silicon carbide (single-crystal SiC) with a thermal conductivity of approximately 490 W / m·K is also a target substrate material.

[0013] Figure 2 is an explanatory diagram showing the through-hole formation process (process S10) according to the embodiment. As described above, the submount circuit board 1 is an insulating substrate located between the semiconductor laser element and the heat sink (metal block such as copper), with the semiconductor laser element side being the front surface 1a (front side) and the heat sink side being the back surface 1b (back side).

[0014] The through-hole formation process involves shot blasting SiC (silicon carbide) powder from the back surface 1b to form the through-hole 5. While the usual pressure is 0.35 MPa, in this embodiment, a frustoconical through-hole was achieved by reducing the pressure to 0.15 MPa. This is because the straight-line propagation of the SiC powder is weakened. Conversely, if the pressure is high and the straight-line propagation is high, the through-hole will be closer to a cylindrical shape.

[0015] Figure 9 shows the effect of the angle θ between surface 1a and the wall surface of through-hole 5. If θ is the angle between surface 1a and the wall surface of through-hole 5, then by reducing θ, unintended resist adhering to the wall surface of through-hole 5 can be removed during the photolithography process.

[0016] In the case of the right side of FIG. 9 (when θ is small), before the metallization forming process, light (ultraviolet light) is irradiated onto the back surface 1b side. The unintentional resist attached to the wall surface of the through hole 5 can be sufficiently irradiated with light. Then, when the exposed circuit board is immersed in a developer and developed, the photoresist attached to the wall surface of the through hole 5 can be removed. That is, the unintentional resist is easily irradiated with ultraviolet light. Therefore, since the ultraviolet light completely hits the inclined surface, the resist can be completely dissolved by development. As a result, the subsequent metallization forming process using vapor deposition can be appropriately performed.

[0017] On the other hand, in the case of the left side of FIG. 9 (when θ is large), the unintentional resist attached to the wall surface of the through hole 5 cannot be sufficiently irradiated with light. That is, the unintentional resist is difficult to be irradiated with ultraviolet light. Therefore, since the ultraviolet light hitting the inclined surface is insufficient, some of the resist may not be dissolved during development.

[0018] FIG. 3 is an explanatory diagram showing a metallization forming process (process S20) according to an embodiment. FIG. 3 is a cross-sectional view showing a metallization forming process of a circuit board 1 having through holes 5. Here, the surface 1a and the back surface 1b of the ceramic circuit board 1 are metallized. Metallization means metallizing the surface of a non-metal (it is a process of forming a metal film on the surface of a non-metal). Specifically, a metal film is formed on the surface of the ceramic circuit board 1. First, the circuit board 1 to be used is prepared. Through holes 5 exist in the flat plate-shaped ceramic circuit board 1 to be used. Here, metal is metallized by an electron beam evaporation film forming method or a resistance heating evaporation film forming method. As the metal, at least one of copper, silver, gold, nickel, and palladium is preferably used because of its high electrical conductivity. In addition, it may be formed by a multilayer film (Ti / Pt / Au multilayer film) in which a platinum (Pt) layer is formed on a titanium (Ti) layer and a gold (Au) layer is formed on the platinum layer.

[0019] In electron beam deposition, an evaporation material is placed in a crucible in a high vacuum atmosphere, and an electron beam is irradiated onto the evaporation material in the crucible, heating and evaporating the material. The evaporated material then deposits onto a substrate placed above the evaporation source, forming a thin film. In resistance heating deposition, an evaporation material is placed in a resistor in a high vacuum atmosphere and heated by applying an electric current to evaporate it. The evaporated material then deposits onto a substrate placed above the evaporation source, forming a thin film.

[0020] (Processing S21) The surface 1a of the circuit board 1 is metallized (first metallization from the front side). The first metallized film 2a metallizes not only the surface 1a but also up to about the middle of the substrate on the wall of the through-hole 5. In the figure, the left side of the through-hole 5 is called the first side portion 1c and the right side is called the second side portion 1d.

[0021] (Process S22) Then, the circuit board 1 is rotated 180 degrees with respect to the vertical axis 1g of the surface of the circuit board 1 which is mounted on the board mounting jig 7 (see Figure 6). Details will be described later with reference to Figure 6. As a result, in the figure, the second side portion 1d is positioned on the left side of the through-hole 5 and the first side portion 1c is positioned on the right side.

[0022] (Processing S23) Then, the surface 1a of the circuit board 1 is metallized (second time from the front side of the metallization). The second metallized film 3a metallizes not only the first metallized film 2a, but also up to about the middle of the substrate on the wall surface of the through-hole 5.

[0023] (Processing S24) Finally, the back surface 1b of the circuit board 1 is metallized (first metallization from the back side). The third metallized film 4b is metallized not only on the back surface 1b but also to about the middle of the substrate on the wall surface of the through-hole 5. This makes it possible to achieve electrical conductivity between the first metallized film 2a and the second metallized film 3a and the third metallized film 4b within the through-hole 5.

[0024] Figure 4 is an explanatory diagram showing metallization formation by vacuum deposition. Figure 5 is a diagram showing an example of circuit board arrangement viewed from below with the substrate mounting jig 7. The vacuum deposition apparatus has a deposition material heating section 6 in a high vacuum atmosphere, and the substrate mounting jig 7 is positioned on the opposite side of it. The substrate mounting jig 7 is attached to a rotating shaft 7b via a flange 7a. The substrate mounting jig 7 is rotated during film formation to eliminate uneven deposition within the plane. As shown in Figure 5, the substrate mounting jig 7 has a circular shape and can mount a large number of circuit boards 1. The challenge when metallizing with this vacuum deposition apparatus was whether uneven deposition could be eliminated within the through-holes 5.

[0025] Figure 6 is an explanatory diagram showing the surfaces within a through-hole where vapor deposition is likely to adhere and where it is not. If the direction in which the vapor deposition material flies (arrow) and the vertical axis 1g of the surface of the circuit board 1 (= axis of the through-hole) are misaligned, uneven vapor deposition may occur within the through-hole 5. In Figure 6, the wall surface portion 5a where vapor deposition is likely to adhere in the first vapor deposition on the front side and the wall surface portion 5b where vapor deposition is not likely to adhere in the first vapor deposition on the front side are shown. In this embodiment, in order to reduce uneven vapor deposition, after the first vapor deposition, the circuit board 1 is rotated 180 degrees around its axis (reversed left and right in the drawing), fixed again to the board mounting jig 7, and a second vapor deposition is performed. This eliminates uneven vapor deposition on the wall surface inside the through-hole 5. In this embodiment, the substrate is fixed to the same position when re-securing it to the substrate mounting jig 7, but the fixing position may be changed between the first and second deposition processes.

[0026] In this embodiment, the circuit board 1 is rotated 180 degrees around its axis and the coating is deposited in two separate steps, but this is not the only option. It could also be done in three steps, rotating every 120 degrees, or in four steps, rotating every 90 degrees.

[0027] Figure 7 is a flowchart showing the manufacturing process of a circuit board according to the embodiment. (Processing S10) Through-holes 5 are made on the circuit board by shot blasting. In this embodiment, after creating the through-hole 5, the following metallization process is performed using lift-off. Lift-off is a technique in which metal is deposited onto a pattern made of resist, and then the resist is removed, leaving a metal pattern only in the areas where the resist was absent. For this reason, photoresist is formed around the through-hole 5. Then,

[0028] (Processing S21) Perform metallization (first time from the front side) (Process S22) The circuit board 1 is rotated 180 degrees around its axis and then fixed again to the board mounting jig 7. (Process S23) Metallization (second time from the front side) is performed, and then the resist is removed. (Processing S24) Metallization (first time from the back side) is performed. The back side of circuit board 1 is the surface that contacts the heat sink, so the entire surface of the back side 1b is subjected to metallization.

[0029] Figure 8 shows an example of the metallization status of a through-hole 5 according to the embodiment. The figure is a cross-sectional view of the through-hole 5 portion of the circuit board 1. The wall surface inside the through-hole 5 is metallized without any breaks in the wire.

[0030] In this embodiment, deposition has been described using electron beam deposition or resistance heating deposition, but it is not limited to these methods. The first metallized film 2a, the second metallized film 3a, and the third metallized film 4b may be formed by sputtering deposition or ion plating deposition.

[0031] Sputtering is a method of film deposition that uses plasma or other high-energy particles to collide with a material (target), knocking out material components with the impact and depositing these particles onto a substrate. In other words, in sputtering, particles (such as Ar ions) are directed at the target material, and the particles of the target material are ejected to form a film on the substrate. Rotating the device around a vertical axis of 1g allows for film deposition in areas where film adhesion is poor, such as on the sides of sloped surfaces, making it an effective method.

[0032] Ion plating is based on almost the same principle as electron beam evaporation, but the difference is that ion plating involves passing evaporated particles through a plasma to impart a positive charge, and then applying a negative charge to the substrate to attract and deposit the evaporated particles, thereby forming a film. In other words, since both ion plating methods involve heating the deposition material and ejecting the material particles to deposit a film on the substrate, rotating around a vertical axis of 1g is effective.

[0033] The manufacturing method of the circuit board according to this embodiment has the following features. (1) A method for manufacturing a circuit board 1 having metallized through-holes 5, comprising a through-hole formation step (process S10) in which frustoconical through-holes 5 are provided in the circuit board 1, and a metallization formation step (process S20) in which, when metallizing the through-holes 5, the circuit board 1 is rotated in multiple stages with respect to the vertical axis 1g of the surface 1a of the circuit board 1, which is mounted on a substrate mounting jig 7, and metallized. By making the through-holes frustoconical, metallization can be efficiently performed, for example, by vapor deposition. Furthermore, by performing metallization in multiple stages and changing the angle of the circuit board each time, it is possible to prevent metallization from leaking during the process.

[0034] (2) In the through-hole formation step (processing S10) of (1) above, a frustoconical through-hole 5 is formed in the circuit board 1 by the shot blasting method. A frustoconical through-hole can be easily formed by shot blasting.

[0035] (3) In the metallization process (process S20) described above, when metallizing the frustoconical through-hole 5 using the electron beam deposition method, the deposition is carried out in two stages, rotating 180 degrees with respect to the vertical axis. By depositing the film in two stages, changing the angle by 180 degrees, it becomes possible to form a leak-free metallized layer in fewer steps.

[0036] (4) In the metallization formation step (process S20) of (1) above, metallization is performed in multiple steps from the narrow side (front side) of the opening of the frustoconical through-hole. Since metallization tends to be unsuccessful when deposited from the narrow side, performing multiple deposits from the narrow side (surface 1a side) of the opening of the through-hole 5 makes it possible to form a complete metallization even in areas where metallization deposition is difficult.

[0037] (5) The circuit board referred to in (1) above is a ceramic substrate or a resin substrate. In this embodiment, a circuit board made of a ceramic substrate has been described, but it is not limited to this. The manufacturing method of the circuit board of this embodiment can also be applied to a resin substrate. Examples of resins include phenolic resin, epoxy resin, and polyimide resin.

[0038] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. It is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of Symbols]

[0039] 1 Circuit board 1a surface 1b back side 1c First side 1d Second side 1g vertical axis 2a First metallized film 3a Second metallized film 4b Third metallized film 5 through holes 6. Heating section for vapor-deposited material 7. Circuit board mounting jig 7a Flange 7b Rotation axis

Claims

1. A method for manufacturing a circuit board having metallized through-holes, A through-hole formation process in which a frustoconical through-hole is provided in a circuit board, A metallizing formation step is performed in which, when metallizing the through-hole, the circuit board is rotated in multiple steps relative to the vertical axis of the surface of the circuit board, which is mounted on a substrate mounting jig, to metallize the through-hole. A method for manufacturing a circuit board having the following characteristics.

2. In the through-hole formation process, The frustoconical through-holes are formed on the circuit board by shot blasting. A method for manufacturing a circuit board according to claim 1.

3. In the metallization formation step, When metallizing the aforementioned frustoconical through-hole using electron beam deposition, the deposition is carried out in two stages, rotating 180 degrees with respect to the vertical axis. A method for manufacturing a circuit board according to claim 1.

4. In the metallization formation step, When metallizing the aforementioned frustoconical through-hole using electron beam deposition, the deposition is carried out in two stages, rotating 180 degrees with respect to the vertical axis. The method for manufacturing a circuit board according to claim 2.

5. In the metallization formation step, The metallization process is performed in multiple steps, starting from the narrow side of the opening of the aforementioned frustoconical through-hole. A method for manufacturing a circuit board according to any one of claims 1 to 4.

6. The circuit board is a ceramic substrate or a resin substrate. A method for manufacturing a circuit board according to claim 1.

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