Copper circuit, printed wiring board and multilayer substrate

Abstract

To provide a copper circuit, a printed wiring board, and a multilayer substrate that achieve excellent adhesion when laminating the printed wiring boards.SOLUTION: A copper circuit has a recess width of 1.0 μm or more in a cross-section perpendicular to the direction of the circuit pattern's extension, as defined by the following Equation 1. [Equation 1] Recess width=((Top width)-(Minimum width)) / 2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to copper circuits, printed wiring boards and multilayer substrates. [Background technology]

[0002] Copper circuits in printed wiring boards, including multilayer boards, are produced by forming a mask pattern using photolithography on a copper-clad laminate, which is made by laminating copper foil to resin, and then etching it using the subtractive method. In the case of multilayer boards and build-up boards, after creating the copper circuit pattern, multiple printed wiring boards are stacked and bonded together by applying heat and pressure.

[0003] For example, Japanese Patent No. 4955104 (Patent Document 1) discloses a copper foil in which a metal layer with an etching rate slower than that of copper is formed on the copper foil on the etching side in order to suppress sagging of the copper circuit during etching. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4955104 Summary of the Invention [Problem to be solved by the invention]

[0005] FIG. 1(A) is a cross-sectional photograph of a copper circuit formed by a typical subtractive method. FIG. 1(B) is a cross-sectional photograph of a copper circuit formed by a typical additive method. As shown in FIG. 1(A), it was common technical knowledge that when formed by a subtractive method, the sides of the cross section of the copper circuit have a shape that gently widens from top to bottom. Furthermore, as shown in FIG. 1(B), it was common technical knowledge that when formed by an additive method, the cross section of the copper circuit is relatively rectangular. However, the present inventors have found that if the cross section of the copper circuit has such a convex or rectangular shape, it is difficult to obtain an anchor effect when stacking printed wiring boards, resulting in poor adhesion between the printed wiring boards.

[0006] In view of the above problems, an object of the embodiments of the present invention is to provide a copper circuit, a printed wiring board, and a multilayer substrate that can provide good adhesion when printed wiring boards are stacked. [Means for solving the problem]

[0007] The embodiments of the present invention that solve the above problems are defined below. (1) A copper circuit having a recess width defined by the following formula 1 in a cross section perpendicular to the extending direction of the circuit pattern of 1.0 μm or more. [Formula 1] Depression width = (top width - minimum width) / 2 (2) A copper circuit having a first depression ratio defined by the following formula 2 in a cross section perpendicular to the extending direction of the circuit pattern of 0.05 or more. [Formula 2] First recess ratio = recess width / circuit height (In [Equation 2], recess width = (top width - minimum width) / 2.) (3) The copper circuit according to (1) or (2), wherein the angle between the top and the side of the cross section is 50 to 75°. (4) The copper circuit according to (3), wherein the difference between the angle formed by the top of the cross section and the sides on both sides is less than 15°. (5) The copper circuit according to any one of (1) to (4), wherein the cross section has a second depression ratio defined by the following formula 3 of 0.08 or more. [Formula 3] Second recess ratio = recess width / top width (In [Equation 3], recess width = (top width - minimum width) / 2.) (6) The copper circuit according to any one of (1) to (5), wherein the bottom width of the cross section is 80 μm or less. (7) The copper circuit according to any one of (1) to (6) above, which is used in a multilayer substrate. (8) A printed wiring board comprising an insulating substrate and the copper circuit according to any one of (1) to (6) above, provided on the insulating substrate. (9) A multilayer substrate comprising the printed wiring board according to (8). [Effects of the Invention]

[0008] According to the embodiments of the present invention, it is possible to provide a copper circuit, a printed wiring board, and a multilayer substrate that can provide good adhesion when printed wiring boards are stacked. [Brief explanation of the drawings]

[0009] [Figure 1] (A) is a cross-sectional photograph of a copper circuit formed by a typical subtractive method. (B) is a cross-sectional photograph of a copper circuit formed by a typical additive method. [Figure 2] 1 is an example of an observation photograph of a cross section perpendicular to the extending direction of a circuit pattern of a copper circuit according to an embodiment of the present invention. [Figure 3] 1 is a photograph showing a cross section of a copper circuit perpendicular to the extending direction of the circuit pattern, for explaining the "depression angle." [Figure 4] 1 is an SEM image of the surface of a roughened Ni layer of a copper circuit in Example 2. [Figure 5] 1 is an SEM image of a cross section of a copper circuit in Example 2. [Figure 6] 1 is an SEM image of a cross section of a copper circuit in Comparative Example 1. [Figure 7] 1 is an SEM image of a cross section of a copper circuit in Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be described in detail below, but the present invention should not be construed as being limited thereto. Various modifications and improvements can be made based on the knowledge of those skilled in the art without departing from the gist of the present invention. The multiple components disclosed in this embodiment can be appropriately combined to form various inventions. For example, some components may be omitted from all the components shown in this embodiment.

[0011] <Copper circuit> The copper circuit according to the embodiment of the present invention is an electronic circuit formed on an insulating substrate, and may be formed on an insulating substrate to form a printed wiring board, for example. Furthermore, a multilayer substrate may be formed by stacking a plurality of printed wiring boards on which the copper circuit according to the embodiment of the present invention is formed. The insulating substrate may be a resin substrate, or a substrate obtained by impregnating a base material such as paper or glass with a resin.

[0012] The material of the copper circuit according to the embodiment of the present invention is copper or a copper alloy, and can be formed from a known material for a general copper circuit.

[0013] The thickness of the copper circuit according to the embodiment of the present invention is not particularly limited, but may be 9 to 80 μm or 12 to 70 μm.

[0014] FIG. 2 shows an example of an observation photograph of a cross section perpendicular to the extension direction of the circuit pattern of a copper circuit according to an embodiment of the present invention. As shown in FIG. 2, in the present invention, "top width" refers to the linear distance between two ends of the top in the cross section of the copper circuit. Furthermore, "minimum width" refers to the shortest width in the cross section of the copper circuit, and is the distance of a straight line parallel to the bottom. Furthermore, "circuit height" refers to the distance of a straight line (a straight line perpendicular to the bottom) from the top at the center of the top in the cross section of the copper circuit. Furthermore, "bottom width" refers to the linear distance between two ends of the bottom in the cross section of the copper circuit.

[0015] In one aspect, the copper circuit according to the embodiment of the present invention has a recess width defined by the following formula 1 of 1.0 μm or more in a cross section perpendicular to the extending direction of the circuit pattern. [Formula 1] Depression width = (top width - minimum width) / 2

[0016] In the cross section of the copper circuit, the larger the recess width, the wider the top width of the copper circuit becomes compared to the minimum width of the copper circuit, and the stronger the copper circuit is caught when a printed wiring board or the like is laminated to the copper circuit, resulting in a stronger anchoring effect. When the recess width is 1.0 μm or more, this anchoring effect is improved. The recess width is preferably 1.0 μm or more, more preferably 2.0 μm or more, even more preferably 2.5 μm or more, even more preferably 3.0 μm or more, and even more preferably 3.5 μm or more. There is no particular upper limit to the recess width, but from the viewpoint of suppressing chipping of the top end, it is preferably 15.0 μm or less, more preferably 10.0 μm or less, and even more preferably 7.0 μm or less.

[0017] The recess width can be measured as follows. First, prepare a copper circuit to be measured on an insulating substrate (resin in this example). Next, cut the resin and the copper circuit on the resin with scissors so that the cross section is perpendicular to the direction of extension of the copper circuit to be measured. Hereafter, the resulting cross section will be referred to as the observation surface. Next, the observation surface is polished using a grinder (e.g., Buehler METASERV 2000, etc.). If the resin is thin and polishing is difficult, the resin and the copper circuit on the resin can be fixed to a substrate such as acrylic with adhesive. Furthermore, if a specific position on the copper circuit is to be the observation surface, the position of the observation surface can be adjusted by attaching 80 grit abrasive paper to the polisher and grinding the observation surface at a rotation speed of 350 rpm.

[0018] The polishing procedure is as follows: At each step, the surface is observed with an optical microscope, and if no major scratches are found, the next polishing step is carried out. (1) Attach 600 grit sandpaper to the sander and sand at a rotation speed of 350 rpm. (2) Polish and observe in the same way with 800 grit sandpaper. (3) Polish and observe in the same way with 1200 grit sandpaper. (4) Polish and observe in the same way with 2000 grit sandpaper. (5) Using an alumina abrasive with a grain size of 0.3 μm (for example, alumina liquid manufactured by Refine Tech Co., Ltd.), polishing is performed at a rotation speed of 100 rpm. If no major scratches are found when observing the observation surface with an optical microscope, polishing is considered complete.

[0019] After the above-mentioned polishing is completed, an image of the observation surface is taken using an SEM (for example, SEM S3400N manufactured by Hitachi High-Tech Corporation). The accelerating voltage during photography is 15.0 kV. The magnification during photography is selected so that the entire observation surface fits in the image, but the observation surface is not too small. Based on the SEM image of the observation surface of the copper circuit obtained in this way, the above-mentioned depression width can be measured.

[0020] In another aspect, the copper circuit according to the embodiment of the present invention has a first depression ratio defined by the following formula 2 in a cross section perpendicular to the extending direction of the circuit pattern of 0.05 or more. [Formula 2] First recess ratio = recess width / circuit height (In [Equation 2], recess width = (top width - minimum width) / 2.)

[0021] In the cross section of the copper circuit, the larger the first recess ratio, the wider the top width of the copper circuit becomes compared to the minimum width of the copper circuit. This increases the adhesion of the copper circuit when a printed wiring board or the like is laminated to the copper circuit, resulting in a stronger anchoring effect. Furthermore, since the first recess ratio is calculated by dividing the recess width by the circuit height, controlling the first recess ratio can improve the adhesion between printed wiring boards, even for circuits with low circuit heights. When the first recess ratio is 0.05 or greater, the anchoring effect is improved. The first recess ratio is preferably 0.07 or greater, more preferably 0.08 or greater, and even more preferably 0.10 or greater. While there are no particular limitations on the upper limit of the first recess ratio, from the viewpoint of preventing chipping at the top edge, it is preferably 0.30 or less, more preferably 0.20 or less, and even more preferably 0.15 μm or less. The first dent ratio can be obtained by obtaining an SEM image in the same manner as the above-mentioned method for measuring the dent width, and then measuring the SEM image.

[0022] In the copper circuit according to the embodiment of the present invention, the angle between the top and the side of a cross section perpendicular to the extension direction of the circuit pattern (recess angle) is preferably 50 to 75°. FIG. 3 shows an observation photograph of a cross section of a copper circuit perpendicular to the extension direction of the circuit pattern to illustrate the "recess angle." As shown in FIG. 3, the recess angle is the angle between a line drawn on the top and a line drawn from the end of the top so as to touch the side within the cross section. When the recess angle is 75° or less, the recess on the side of the cross section of the copper circuit becomes steep, which strengthens the adhesion of the copper circuit when a printed wiring board or the like is laminated to the copper circuit, thereby enhancing the anchor effect. When the recess angle is 50° or more, the thickness of the protruding portion is large, making it less likely to break when an external force is applied, and maintaining good adhesion between printed wiring boards. The recess angle is more preferably 50 to 70°, and even more preferably 50 to 65°. The recess angle can be obtained by obtaining an SEM image in the same manner as the recess width measurement method described above, and then measuring the SEM image. Specifically, for example, the SEM image is displayed in PowerPoint (registered trademark) manufactured by Microsoft Corp., and the ruler function of PowerPoint is used to measure the angle between a straight line drawn on the top and a line drawn from the end of the top so as to be tangent to the side in the cross section, and this angle can be evaluated as the recess angle.

[0023] In the copper circuit according to the embodiment of the present invention, the difference in the angle between the top and both sides of a cross section perpendicular to the extension direction of the circuit pattern is preferably less than 15°. If the recess angles on both sides of the cross section of the copper circuit are significantly different, when an external force is applied, the external force tends to concentrate on the protruding portion on the side with the smaller recess angle, making that portion more susceptible to damage, and there is a possibility that the adhesion between printed wiring boards will not be sufficiently improved. In contrast, if the difference in the angle between the top and both sides of the cross section of the copper circuit is less than 15°, the external force is prevented from concentrating on one portion, thereby preventing damage to the copper circuit. This difference is more preferably less than 10°, and even more preferably less than 7°. The difference in angle can be obtained by obtaining an SEM image in the same manner as in the above-mentioned method for measuring the recess width, and then measuring the SEM image.

[0024] In the copper circuit according to the embodiment of the present invention, it is preferable that the second depression ratio defined by the following formula 3 in a cross section perpendicular to the extending direction of the circuit pattern is 0.08 or more. [Formula 3] Second recess ratio = recess width / top width (In [Equation 3], recess width = (top width - minimum width) / 2.)

[0025] In the cross section of the copper circuit, the larger the second recess ratio, the larger the protruding portion of the top relative to the recessed portion of the side, thereby strengthening the anchor effect with an insulating substrate such as a resin substrate and improving the adhesion between printed wiring boards. The second recess ratio is preferably 0.10 or more, even more preferably 0.12 or more, and even more preferably 0.14 or more. There is no particular upper limit to the second recess ratio, but from the viewpoint of suppressing chipping of the edge of the top, it is preferably 0.30 or less, more preferably 0.25 or less, and even more preferably 0.20 or less. The second dent ratio can be obtained by obtaining an SEM image in the same manner as in the above-mentioned method for measuring the dent width, and then measuring the SEM image.

[0026] The copper circuit according to the embodiment of the present invention preferably has a bottom width of 80 μm or less in a cross section perpendicular to the extending direction of the circuit pattern. Circuits with a fine L (line) / S (space) ratio are prone to contact (short circuit) between adjacent circuits. Even in a fine circuit having a bottom width of 80 μm or less in the cross section, the copper circuit according to the embodiment of the present invention does not have a shape that gradually widens from the top to the bottom of the circuit as shown in FIG. 1(A), and can effectively prevent contact between adjacent circuits. The bottom width is more preferably 70 μm or less, even more preferably 50 μm or less, and even more preferably 45 μm or less. The lower limit of the bottom width is not particularly limited, but may be 9 μm or more, 12 μm or more, or 18 μm or more. The bottom width of the cross section can be obtained by obtaining an SEM image in the same manner as in the above-mentioned method for measuring the recess width, and then measuring the SEM image.

[0027] <Manufacturing method for copper circuits> Next, a method for manufacturing a copper circuit according to an embodiment of the present invention will be described in detail. First, a copper clad laminate (CCL) is produced by hot pressing copper foil of a specified thickness onto an insulating substrate such as a resin substrate. Next, the CCL is degreased and pickled, and then the copper foil is subjected to roughening Ni plating. The conditions for roughening Ni plating are shown below. During plating, the plating solution is agitated using a stirrer or bubbling device. Plating solution: Roughened nickel plating solution (product name: "Roughened Nickel Plating Solution", manufactured by JX Metals Trading Co., Ltd.) Bath temperature: 57~63℃ Current density: 9~11A / dm 2 Plating time: 0.5 to 20 seconds In this way, a CCL having a roughened Ni plating layer is prepared.

[0028] The nickel coating weight of the roughened Ni plating layer is 400 to 15,000 μg / dm 2 It is preferable that the concentration is 600 to 9000 μg / dm 2 It is more preferable that the thickness of the nickel layer is 100% or more. The thickness of the nickel layer can be evaluated by photographing the cross section of the copper circuit with an SEM and measuring the thickness of the nickel layer from the obtained SEM image. In this way, by providing a surface-roughened nickel layer on the top surface of the copper circuit, it is possible to create a depression in the cross section of the copper circuit that has a width smaller than the width of the bottom and top, and the adhesion between printed wiring boards is improved by the anchor effect.

[0029] The nickel deposition weight can be measured by the following procedure. A 0.5 dm x 0.5 dm sample was cut out from copper foil with a nickel plating layer or CCL containing the copper foil, and the metal layer was dissolved in a nitric acid solution. The nickel concentration in the sample solution was quantified using an ICP emission spectrometer, and the amount of nickel attached per unit area (μg / dm 2 Specifically, the ICP optical emission spectrometer is a PS3520UVDD2 (AN-063 ICP3520UV-DD2) manufactured by Hitachi High-Tech Corporation, and measurements are performed under the following conditions. Wavelength: 231.675nm Integration time: 1.0 seconds Number of integrations: 3 Quantitative method: calibration curve method Blank Subtraction: None Output: 1.2kW Pre-spray time: 30 seconds Cleaning time: 30 seconds The standard solutions used during measurement are prepared by adding Kanto Chemical Co., Inc.'s JCSS Standard Solution for Chemical Analysis (Nickel Standard Solution (Ni 1000), specifications: for atomic absorption spectrometry, for ICP analysis) to a solution containing nitric acid and copper to adjust the Ni concentration to 2 ppm, and by creating a calibration curve using a solution with an Ni concentration of 0 ppm to which Kanto Chemical Co., Inc.'s JCSS Standard Solution for Chemical Analysis has not been added, and the Ni concentration in the sample solution is adjusted to be within the range of the calibration curve. The solution containing nitric acid and copper before the Kanto Chemical Co., Inc.'s JCSS Standard Solution for Chemical Analysis is added is prepared using the following procedure. (1) Cut out copper foil without a nickel plating layer to weigh 15.68g. (2) Add the cut copper foil to 100 mL of pure water and 60 mL of 65 wt% nitric acid. (3) Heat the solution to dissolve all of the copper foil. (4) After cooling, add pure water to make a final volume of 500 mL. The analysis is performed after masking the opposite surface to the surface to be measured (the surface with the nickel plating layer) to prevent contamination with metal from the opposite surface.

[0030] Then, a dry film resist (e.g., RY-5115 manufactured by Resonac Corporation) is laminated and exposed / developed to form a resist pattern with the desired L / S on the surface of the roughened Ni plating layer of the copper foil. The unnecessary portions of the copper foil are then removed by etching to produce a copper circuit with the desired L / S. The etching conditions are as follows: Etching solution composition: Cupric chloride or ferric chloride ·Copric chloride system: CuCl2232~254g / L, HCl 117~121g / L Ferric chloride: FeCl2 37wt% Conveying speed: 0.4-1.0 m / min (etching tank length 770 mm)

[0031] In the copper circuit manufacturing method according to an embodiment of the present invention, as described above, when forming a copper circuit from a CCL copper foil using a subtractive process, a roughened Ni layer is formed on the surface (S-side) opposite to the surface laminated with an insulating substrate such as a resin substrate. Here, Ni etches at a slower rate than copper in cupric chloride or ferric chloride-based etching solutions, thereby protecting the top of the copper circuit. The unevenness of the roughened Ni layer surface improves adhesion to the dry film (DF), preventing the top of the copper circuit from being dissolved by the etching solution seeping in from the DF edge, resulting in the peripheral edge being scraped off. This creates a depression with a width smaller than the width between the bottom and top of the copper circuit, which provides a stronger grip for the copper circuit when laminating a printed wiring board or the like onto the copper circuit, enhancing the anchoring effect. This results in good adhesion to the printed wiring board.

[0032] The copper circuit according to the embodiment of the present invention is provided on an insulating substrate such as a resin substrate, and the insulating substrate and the copper circuit constitute a printed wiring board. Furthermore, a multilayer board can be produced by stacking another printed wiring board on the printed wiring board having the copper circuit according to the embodiment of the present invention. In this case, the anchoring effect of the copper circuit according to the embodiment of the present invention improves the adhesion of the laminated printed wiring board to the insulating substrate such as a resin substrate. [Example]

[0033] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0034] Example 1 A copper-clad laminate (CCL) was produced by hot pressing 35 μm thick copper foil and insulating resin (GHPL-830NX, manufactured by Mitsubishi Gas Chemical Company, Inc.). After degreasing and pickling the CCL, the copper foil was plated with roughened Ni. The plating conditions are shown below. During plating, the plating solution was agitated using a stirrer and bubbling. Plating solution: Roughened nickel plating solution (product name: "Roughened Nickel Plating Solution", manufactured by JX Metals Trading Co., Ltd.) Bath temperature: 60℃ Current density: 10A / dm 2 Plating time: 2 seconds In this way, a CCL having a roughened Ni plating layer was prepared. Next, a dry film resist (RY-5115, manufactured by Resonac Corporation) was laminated and exposed / developed to form a resist pattern with an L / S of 46 μm / 34 μm on the surface of the roughened Ni plating layer of the copper foil. Unnecessary portions of the copper foil were then removed by etching to produce a copper circuit with an L / S of 40 μm / 40 μm. The etching solution used was an aqueous solution of cupric chloride. The etching conditions are as follows: Etching solution composition: CuCl2 243g / L, HCl 120g / L Liquid temperature: 50℃ Conveying speed: 0.58 m / min (etching tank length: 770 mm)

[0035] Example 2 A copper circuit with L / S = 40 μm / 40 μm was produced by the same procedure as in Example 1, except that the plating time for forming the roughened Ni layer was 5 seconds and the conveying speed during etching was 0.61 m / min. For the copper circuit having the roughened Ni layer on its surface in Example 2, the surface of the roughened Ni layer was photographed using an SEM (Hitachi High-Tech Corporation, SEM S3400N). The accelerating voltage during photography was 15.0 kV. The SEM image is shown in Figure 4. From Figure 4, it can be seen that the surface of the copper foil was roughened by the roughened Ni layer.

[0036] Example 3 A copper circuit with L / S = 40 μm / 40 μm was produced by the same procedure as in Example 1, except that the plating time for forming the roughened Ni layer was 10 seconds and the conveying speed during etching was 0.60 m / min.

[0037] (Comparative Example 1) A copper circuit with L / S = 40 μm / 40 μm was produced by the same procedure as in Example 1, except that a roughened Ni layer was not formed, the transport speed during etching was set to 0.46 m / min, and a resist pattern with L / S = 52 μm / 28 μm was formed.

[0038] (Comparative Example 2) A copper-clad laminate (CCL) was produced by hot pressing 18 μm thick copper foil and insulating resin (GHPL-830NX, manufactured by Mitsubishi Gas Chemical Company, Inc.). After degreasing and pickling this CCL, the copper foil was plated with smooth Ni instead of roughened Ni. The plating conditions are shown below. During plating, the plating solution was agitated using a stirrer and bubbling. Plating solution composition: NiSO4·6H2O 60g / L, Na2(C3H5O(COO)3) 8g / L Bath temperature: 50℃ Current density: 4A / dm 2 Plating time: 3 seconds In this way, a CCL having a smooth Ni plating layer was prepared. Next, a dry film resist (RY-5115, manufactured by Resonac Corporation) was laminated and exposed / developed to form a resist pattern with an L / S of 40 μm / 20 μm on the surface of the smooth Ni plating layer of the copper foil. Unnecessary portions of the copper foil were then removed by etching to produce a copper circuit with an L / S of 30 / 30 μm. The etching solution used was an aqueous solution of cupric chloride. The etching conditions are as follows: Etching solution composition: CuCl2 243g / L, HCl 120g / L Liquid temperature: 50℃ Conveying speed: 0.75 m / min (etching tank length: 770 mm)

[0039] <Measurement> The resin and the copper circuit on the resin were cut with scissors so that the plane perpendicular to the extending direction of the circuit pattern was the cross section. The cross section resulting from the cutting is hereafter referred to as the observation surface. Subsequently, the observation surface was polished with a grinder polisher (METASERV 2000, manufactured by Buhler Co., Ltd.). The polishing procedure is shown below. At each step, the surface was observed with an optical microscope, and if no major scratches were found, the next polishing was performed. (1) 600 grit sandpaper was attached to the sander and sanded at a rotation speed of 350 rpm. (2) The specimen was similarly polished with 800 grit sandpaper and observed. (3) The specimen was similarly polished with 1200 grit sandpaper and observed. (4) The specimen was similarly polished with 2000 grit sandpaper and observed. (5) Polishing was carried out at a rotation speed of 100 rpm using an alumina abrasive with a grain size of 0.3 μm (alumina liquid, manufactured by Refine Tech Co., Ltd.). The surface was examined with an optical microscope and no major scratches were found, so polishing was completed. After polishing was completed, images of the observation surface were taken using an SEM (Hitachi High-Tech Corporation, SEM S3400N). The accelerating voltage during photography was 15.0 kV. The magnification during photography was selected so that the entire observation surface could be captured in the image, but the observation surface was not too small. Specifically, the copper circuits of Examples 1 to 3 and Comparative Example 1 were observed at 2000x magnification, and the copper circuit of Comparative Example 2 at 4000x magnification. SEM images of the cross section of the copper circuit obtained at this time are shown in FIG. 5 (Example 2), FIG. 6 (Comparative Example 1), and FIG. 7 (Comparative Example 2).

[0040] For the SEM image of the cross section of the copper circuit thus obtained, the following were measured or calculated: "top width," "minimum width," "bottom width," "recess width [= (top width - minimum width) / 2]," "first recess ratio [= recess width / circuit height]," "second recess ratio [= recess width / top width]," "recess angle (left side) [= angle between the top and left side]," "recess angle (right side) [= angle between the top and right side]," "angle difference [= difference between the angles between the top and both sides]," "recess angle (average value of right and left sides)," and "etch factor (EF) [= circuit height / (bottom width - top width)]." The results of the above evaluations are shown in Table 1. The nickel deposition weights shown in Table 1 are not values ​​measured by the above-mentioned method, but are estimated values ​​calculated from the plating conditions.

[0041] [Table 1]

[0042] <Consideration> The copper circuits of Examples 1 to 3 had depression widths of 1.0 μm or more in a cross section perpendicular to the extending direction of the circuit pattern. Therefore, as shown in the SEM image ( FIG. 5 ) of the cross section of the copper circuit of Example 2, the skirt (side surface) was clearly depressed from the top to the bottom. Similarly, depressions were formed in the cross section of the copper circuits of Examples 1 and 3. Therefore, when a printed wiring board is laminated on a printed wiring board having the copper circuits of Examples 1 to 3, the copper circuits of Examples 1 to 3 have a strong grip and an improved anchor effect, which is thought to result in good adhesion between the copper circuits of Examples 1 to 3 and the resin substrate of the printed wiring board to be laminated. On the other hand, no depressions were formed in the copper circuits of Comparative Examples 1 and 2. For this reason, the copper circuits of Comparative Examples 1 and 2 had weak grip and could not be expected to have a strong anchor effect, and it is thought that the adhesion between the copper circuits of Comparative Examples 1 and 2 and the resin substrate of the printed wiring board to be laminated thereon was inferior to that of Examples 1 to 3. 7, in Comparative Example 2, no depressions were formed in the cross section of the copper circuit, even though a Ni layer was formed on the side of the copper foil to be etched. This is thought to be because the smooth surface of the Ni layer resulted in insufficient adhesion to the dry film, allowing the etching solution to seep in from the periphery of the interface between the Ni layer and the dry film, causing etching of the periphery of the top to proceed.

[0043] According to one embodiment of the present invention, it is possible to provide copper circuits and multilayer substrates that exhibit good adhesion when laminated with printed wiring boards, which may contribute to improving the reliability of electronic devices. To realize an AI-IoT society, improving the reliability of electronic devices is required. For this reason, one embodiment of the present invention may contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

Claims

1. A copper circuit having a recess width defined by the following formula 1 of 1.0 μm or more in a cross section perpendicular to the extending direction of the circuit pattern. [Formula 1] Depression width = (top width - minimum width) / 2

2. A copper circuit having a first depression ratio defined by the following formula 2 in a cross section perpendicular to the extending direction of the circuit pattern of 0.05 or more. [Formula 2] First recess ratio = recess width / circuit height (In [Equation 2], recess width = (top width - minimum width) / 2.)

3. 3. The copper circuit according to claim 1, wherein the angle between the top and the side of the cross section is 50 to 75 degrees.

4. The copper circuit of claim 3 , wherein the difference between the angle formed by the top of the cross section and the angle formed by the sides on both sides is less than 15°.

5. The copper circuit according to claim 1 or 2, wherein a second depression ratio defined by the following formula 3 in the cross section is 0.08 or more. [Equation 3] Second recess ratio = recess width / top width (In [Equation 3], recess width = (top width - minimum width) / 2.)

6. 3. The copper circuit according to claim 1, wherein the bottom width of the cross section is 80 μm or less.

7. The copper circuit according to claim 1 or 2, which is used in a multilayer substrate.

8. A printed wiring board comprising an insulating substrate and the copper circuit according to claim 1 or 2 provided on the insulating substrate.

9. A multilayer substrate comprising the printed wiring board according to claim 8.

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