Wiring board and method for manufacturing the same

Abstract

To provide a wiring board that makes it possible to easily match outer shapes of a base film and a solder film in the wiring board that includes the base film and the solder film, and a manufacturing method for the same.SOLUTION: A wiring board 10 includes metal films 12, 13 formed on a substrate 11 and a solder film 14 formed on the metal films 12, 13. The metal films have the first metal film 12 and the second metal film 13 including a metal material different from the first metal film 12. The second metal film 13 is arranged around the first metal film 12 and along the outline of the solder film 14.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a wiring board on which electronic components such as laser elements are mounted. [Background technology]

[0002] When mounting electronic components such as laser elements, a method is employed in which the electronic components are placed at predetermined positions on a wiring board and then a solder film formed on the wiring board is melted and solidified to bond the electronic components to the wiring board. Patent Document 1 discloses a semiconductor laser light source in which a semiconductor laser is mounted on a submount. This semiconductor laser light source includes wiring on the upper side of the submount substrate, the wiring including a solder layer and an underlayer made of, for example, a Ti layer, a Pt layer, an Au layer, and a barrier layer. The solder layer of the submount is bonded to the bonding surface of the semiconductor laser. In this semiconductor laser light source, the solder layer is disposed in an area surrounded by a wall on the barrier layer, the semiconductor laser is spaced a predetermined distance from the inner surface of the wall, and the output end of the semiconductor laser is bonded so as to protrude from the end of the solder layer of the submount. This prevents excessive wetting and spreading of the molten solder layer, thereby improving the output characteristics and reliability of the semiconductor laser light source.

[0003] Furthermore, as disclosed in Patent Document 2, for example, wiring substrates such as submounts are manufactured by patterning wiring on a submount substrate using photolithography technology and then dividing the submount substrate into pieces of predetermined dimensions by dicing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-173218 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-286945 Summary of the Invention [Problem to be solved by the invention]

[0005] When mounting electronic components such as laser devices up to or protruding from the edges of a wiring board, it is necessary to form both the solder film and the base film up to the edges of the wiring board to ensure sufficient bonding strength and heat dissipation for the electronic components. Furthermore, if an Au film, which has higher ductility than the solder film, is used as the top layer of the base film, cutting the base film while the base film is exposed can result in more burrs than cutting the solder film. For these reasons, in areas of the wiring board where it is not necessary to expose the base film for special reasons, it is preferable to keep the base film as close to the solder film as possible and to ensure that the outer shapes of the solder film and the base film are consistent.

[0006] However, when forming wiring using photolithography, it is difficult to form the solder film and the base film so that their outer shapes match. This is due to limitations on the patterning methods for the wiring, such as wet etching, dry etching, and lift-off, depending on the patterning accuracy of the resist film used to form the wiring and the material used for the wiring. In view of this problem, the present invention provides a wiring board including an underlayer and a solder film, and a method for manufacturing the wiring board, which makes it possible to easily match the outer shapes of the underlayer and the solder film. [Means for solving the problem]

[0007] A wiring board having a metal film formed on a substrate and a solder film formed on the metal film, wherein the metal film has a first metal film and a second metal film containing a metal material different from that of the first metal film, and the second metal film is at least a part of the periphery of the first metal film and is arranged along the outer shape of the solder film. Here, the first metal film may contain a noble metal, and the second metal film may not contain a noble metal. Furthermore, the wiring substrate may be such that the first metal film is a laminated film in which a Ti film, a Pt film, and an Au film are laminated from the surface of the substrate, and the second metal film is a TiW film. The method for manufacturing a wiring board includes the steps of forming a first metal film on a substrate, forming a second metal film on the substrate and surrounding at least a portion of the first metal film and containing a metal material different from that of the first metal film, forming a solder film on the entire surface of the first metal film and on the second metal film in an area adjacent to the first metal film, and removing the second metal film exposed from the solder film. Here, the step of removing the second metal film may be a method of manufacturing a wiring board in which the second metal film is wet-etched using the solder film as a mask. [Effects of the Invention]

[0008] According to the wiring board and the method for manufacturing the wiring board of the present invention, it is possible to easily provide a wiring board in which the outlines of the base film and the solder film match. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of a wiring board according to the present invention; [Figure 2] 1A to 1C are cross-sectional views illustrating an embodiment of a method for manufacturing a wiring board according to the present invention. [Figure 3] 1A to 1C are cross-sectional views illustrating an embodiment of a method for manufacturing a wiring board according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of a wiring board and a method for manufacturing a wiring board according to the present invention will now be described with reference to the accompanying drawings.

[0011] FIG. 1 is a cross-sectional view of an embodiment of a wiring board according to the present invention, in which (a) is a front view of the wiring board and (b) is a cross-sectional view taken along the line AA of (a). The wiring board 10 includes a rectangular substrate 11, a first base film 12 formed on one side of the substrate 11, a second base film 13 made of a different material than the first base film 12, and a solder film 14 formed on the first base film 12 and the second base film 13. The first base film 12 is formed over substantially the entire surface of one side of the substrate 11 at a predetermined distance from the edge of the substrate 11, and includes an extension portion 121 on a portion of the first base film 12. The extension portion 121 of the first base film 12 is formed without a predetermined distance from the edge of the substrate 11, and the first base film 12 extends to the edge of the substrate 11 at the extension portion 121. The second base film 13 is formed around a portion of the periphery of the first base film 12. More specifically, second base film 13 is formed at two locations around the periphery of the side of extension 121 of first base film 12, excluding the side that contacts the edge of substrate 11, and one side of second base film 13 extends to the edge of substrate 11. Solder film 14 is rectangular and is formed on extension 121 of first base film 12, part of the portion connected to extension 121, and on top of second base film 13, and one side of solder film 14 extends to the edge of substrate 11 where extension 121 of first base film 12 is formed. Here, in part of solder film 14, the edge of solder film 14 and the edge of second base film 13 are approximately collinear in a direction perpendicular to one surface of substrate 11, and the outer shape of solder film 14 and the outer shape of second base film 13 are consistent. Therefore, second base film 12 is disposed without being exposed from solder film 14. In addition, the wiring board 10 is configured such that a portion of the first base film 12, excluding the extension portion 121, is exposed to the outside from the solder film 14, and this exposed first base film 12 is used as a connection site for electrical connection means such as wire bonds when electrically connecting the wiring board 10 to external equipment, etc.

[0012] The base film used in wiring board 10 is required to have adhesion to solder film 14 and substrate 11, and diffusion prevention properties to prevent components of the base film and substrate 11 from diffusing into solder film 14. Wiring board 10 of this embodiment is characterized in that first base film 12 is made mainly of a material that has adhesion and diffusion prevention properties, and second base film 13 arranged around first base film 12 is made of a material that has adhesion and can be easily made to match the outer shape of solder film 14 during the manufacturing process described below.

[0013] For example, an AlN sintered body with Y2O3 added as a binder can be used for the substrate 11. When a heating element such as a laser element is mounted on the wiring substrate 10, it is desirable that the wiring substrate 10 have high thermal conductivity, and from that perspective, a SiC substrate or other ceramics can be used for the substrate 11. It is desirable that the surface of the substrate 11 is polished, but a ground surface or the surface as it is after sintering may also be used.

[0014] The first undercoat film 12 is a laminated metal film containing a precious metal, and is composed of a laminated film in which a Ti film, a Pt film, and an Au film are laminated from the side closest to the substrate 11. Here, the Ti film functions as an adhesion layer to ensure adhesion to the substrate 11, the Pt film functions as a diffusion prevention layer to prevent corrosion of the solder into the substrate 11, and the Au film functions as an electrode layer to ensure adhesion and wetting of the solder film 14. In addition to Ti, materials that can be used to form this adhesion layer include Cr, Ni, Ta, compounds of these materials, and alloys containing these materials.

[0015] The second underlayer film 13 is a single-layer metal film containing no precious metals and is composed of a TiW alloy. The wiring substrate 10 is manufactured using, for example, photolithography. However, if the metal film to be patterned contains a precious metal, the chemical stability of the precious metal means that there is no practical method for processing the metal film without damaging the substrate 11 or the photoresist film used during the manufacturing process, making wet etching virtually unusable. Here, the absence of a precious metal in the second underlayer film 13 allows for wet etching to be employed as a patterning method for the second underlayer film 13, which is effective for matching the contours of the solder film 14 and the second underlayer film 13. The second underlayer film 13 is preferably made of a material that adheres to the substrate 11 and has good wettability with the solder film 14. Examples of suitable materials include TiW, Cr, Ni, Ti, TiN, TaN, compounds of these materials, and alloys containing these materials.

[0016] The solder film 14 is made of AuSn solder. In addition to AuSn solder, other materials that can be used for the solder film 14 include AuGe-based solder, SnAg-based solder, SnCu-based solder, SnBi-based solder, SnSb-based solder, SnAgCu-based solder, and SnIn-based solder.

[0017] Next, a method for manufacturing wiring board 10 will be described. Figures 2 and 3 are cross-sectional views showing one embodiment of a method for manufacturing wiring board 10 according to the present invention, showing the AA cross section of wiring board 10 in Figure 1. Wiring board 10 is manufactured by the following steps.

[0018] [First metal film formation process: Figure 2(a)] First, a base material 111 that will become the substrate 11 is prepared, and a first metal film 112 made of a material that will form the first base film 12 is formed on the entire surface of one surface of the base material 111. The first metal film 112 is formed by sequentially forming the materials that make up the Ti film, Pt film, and Au film that make up the first base film 12 using a vapor deposition method, a sputtering method, or the like.

[0019] [First resist pattern formation process: Figure 2(b)] Next, a first resist film 115 is formed on the first metal film 112 formed on the base material 111 in an area corresponding to the first base film 12 of the wiring board 10. The first resist film 115 is formed by first forming a resist film all over the first metal film 112 and then patterning it by photolithography so as to leave an area corresponding to the first base film 12. A liquid resist or a dry film resist can be used as the first resist film 115.

[0020] [First metal film etching process: Figure 2(c)] Next, the first resist film 115 is used as a mask to etch the first metal film 112 that is not covered by the first resist film 115. Since the first metal film 112 contains a Pt film that constitutes the first base film 12 and is therefore difficult to remove by wet etching, the first metal film 112 is instead etched by dry etching, specifically milling with Ar ions. The first metal film 112 from which unnecessary portions have been removed by etching becomes the first base film 12 of the wiring substrate 10. Steps (a) to (c) are an example of a formation method using etching, but lift-off may also be used for formation.

[0021] [Second metal film formation process: Figure 2(d)] Next, using the first resist film 115 as a mask, a second metal film 113 made of TiW, which is the material that constitutes the second base film 13, is formed on the substrate 111. The second metal film 113 has the same thickness as the first metal film 112, and can be formed by a vapor deposition method, a sputtering method, or the like.

[0022] [Second resist pattern formation process: Figure 3(e)] Next, first resist film 115 is removed, and second resist film 116 is formed on second metal film 113 formed on base material 111, excluding the area corresponding to solder film 14 of wiring board 10. Second resist film 116 is formed by first forming a resist film on the entire surfaces of first metal film 112 and second metal film 113, and then patterning by photolithography. Photoresist liquid or dry film resist can be used as second resist film 116.

[0023] [Solder film formation process: Figure 3(f)] Next, a solder film 14 is formed on the surfaces of the first metal film 112 and the second metal film 113 exposed from the openings in the second resist film 116. The solder film 14 can be formed by a vapor deposition method, a sputtering method, or the like.

[0024] [Second metal film etching process: Figure 3(g)] Next, the second resist film 116 is removed, and the second metal film 113 not covered by the solder film 14 is etched using the solder film 14 as a mask. The second metal film 113 is etched by wet etching. An etching solution that can be used is, for example, an etching solution in which a chelating agent is added to hydrogen peroxide. The second metal film 113 from which unnecessary portions have been removed by etching becomes the second base film 13 of the wiring substrate 10.

[0025] In this embodiment, the second metal film 113 (second base film 13) is made of a material that does not contain precious metals, and can be etched by wet etching. For example, dry etching can be considered as an alternative to wet etching, but in this case, a masking material such as a resist film must be placed on the solder film 14. However, it is very difficult to precisely position the masking material to be placed on the solder film 14 so that it matches the outer shape of the solder film 14, and dry etching can result in the film underlying the solder film 14 being exposed from the solder film 14. However, in the wiring board 10 of this embodiment, wet etching can be applied to the etching of the second metal layer 113 using the solder film 14 as a mask, making it possible to precisely match the outer shapes of the solder film 14 and the film underlying it.

[0026] [Substrate cutting process: Figure 3(h)] Finally, the substrate 111 is cut to desired dimensions. Cutting of the substrate 111 can be performed by a dicing method using a blade electrodeposited with diamonds, for example, by cutting the substrate 111 from above the portion where the solder film 14 is formed. At this time, the outlines of the solder film 14 and its base film, specifically the second metal film 113, are consistent, and no portion of the second metal film 113 is exposed from the solder film 14, so the generation of burrs due to cutting can be suppressed. By cutting the substrate 111 having the first metal film 112 (first base film 12), the second metal film 113 (second base film 13), and the solder film 14 on its surface to desired dimensions, the wiring substrate 10 can be obtained.

[0027] The wiring board and the method for manufacturing the wiring board of the present invention have been described above based on the examples. However, the present invention is not limited to these examples. The present invention allows for the selection of an etching method for the base film by configuring the base film for the solder film 14 with a first base film 12 and a second base film 13, each containing a different metal material, and as a result, allows for accurate matching of the contours of the solder film 14 and the base film. The materials, shapes, and locations illustrated in the above examples can be modified as appropriate without departing from the spirit of the present invention. For example, in the above example, the second base film 13 is formed only around the periphery of the extension 121 of the first base film 12, which is the portion that will be cut into the substrate 111. However, the second base film 13 may be formed around the entire periphery of the first base film 12 in the portion corresponding to the contour of the solder film 14. [Explanation of symbols]

[0028] 10. Wiring board 11 Circuit Board 12 First base coat 13 Second base film 14 Solder film 111 Base material 112 First metal film 113 Second metal film 115 First resist film 116 Second resist film 121 Extension

Claims

1. A wiring board comprising a metal film formed on a substrate and a solder film formed on the metal film, wherein the metal film has a first metal film and a second metal film containing a metal material different from that of the first metal film, the second metal film being at least a part of the periphery of the first metal film and being arranged along the outer shape of the solder film, and the first metal film and the second metal film being formed on the same plane of the substrate.

2. 2. The wiring substrate according to claim 1, wherein the first metal film contains a noble metal, and the second metal film does not contain a noble metal.

3. 3. The wiring board according to claim 2, wherein the first metal film is a laminated film in which a Ti film, a Pt film, and an Au film are laminated from the surface of the substrate, and the second metal film is a TiW film.

4. forming a first metal film on a substrate; forming a second metal film on the substrate, the second metal film including a metal material different from that of the first metal film, at least partially surrounding the first metal film; forming a solder film on the entire surface of the first metal film and on the second metal film in a region adjacent to the first metal film; removing the second metal film exposed from the solder film; A method for manufacturing a wiring board, comprising:

5. 5. The method for manufacturing a wiring board according to claim 4, wherein the step of removing the second metal film comprises wet etching the second metal film using the solder film as a mask.

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