Copper circuits, printed wiring boards and multi-layer boards

Abstract

Provided are a copper circuit, a printed wiring board, and a multilayer board that provide good adhesion when laminated with printed wiring boards. The present invention relates to a copper circuit having a recess width, as 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

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 technology on a copper-clad laminate made by laminating copper foil to resin, and then etching using the subtractive method. In the case of multilayer boards and build-up boards, after the copper circuit pattern is created, multiple printed wiring boards are laminated and bonded by applying heat and pressure.

[0003] For example, Japanese Patent No. 4955104 (Patent Document 1) discloses a copper foil in which a metal layer having 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 observation photograph of a copper circuit formed by a general subtractive method. FIG. 1(B) is a cross-sectional observation photograph of a copper circuit formed by a general additive method. As shown in FIG. 1(A), it was technically common knowledge that when formed by a subtractive method, the sides of the cross section of the copper circuit have a shape that gently expands from the top to the bottom. Also, as shown in FIG. 1(B), it was technically common 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 mountain-like or rectangular shape, it is difficult to obtain an anchor effect when stacking printed wiring boards, and the adhesion between the printed wiring boards is poor.

[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 board that provide good adhesion when printed wiring boards are laminated. [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, as 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) The copper circuit according to (1) or (2) above, 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 between the top of the cross section and 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 board. (8) A printed wiring board comprising an insulating substrate and the copper circuit according to any one of (1) to (6) provided on the insulating substrate. (9) A multilayer substrate comprising the printed wiring board according to (8). Effect 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 board that provide good adhesion when laminated with printed wiring boards. [Brief description of the drawings]

[0009] [Figure 1] (A) is a cross-sectional photograph of a copper circuit formed by a typical subtractive method, and (B) is a cross-sectional photograph of a copper circuit formed by a typical additive method. [Diagram 2] 4 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. [Diagram 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 "dent angle." [Figure 4] 1 is an SEM image of the roughened Ni layer surface of the copper circuit in Example 2. [Diagram 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 PREFERRED EMBODIMENTS

[0010] The following describes in detail preferred embodiments of the present invention, but the present invention should not be interpreted as being limited to these, and 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 combined appropriately to form various inventions. For example, some components may be deleted 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. A multi-layer substrate may be formed by stacking a plurality of printed wiring substrates 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 it 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. Also, "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. Also, "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. Also, "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 is than 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 anchor effect. When the recess width is 1.0 μm or more, such an anchor effect is good. 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. The upper limit of the recess width is not particularly limited, 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. That is, first, prepare the 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 plane perpendicular to the extension direction of the copper circuit to be measured becomes the cross section. Hereafter, the cross section resulting from the cut is called the observation surface. Next, the observation surface is polished with a grinder polisher (e.g., METASERV 2000 manufactured by Buehler, etc.). If the resin is thin and polishing is difficult, the resin and the copper circuit on the resin may be fixed to a substrate such as acrylic with an adhesive. In addition, if a specific position on the copper circuit is to be the observation surface, the position of the observation surface may 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 shown below. At each step, the surface is observed with an optical microscope, and if no major scratches are found, the next polishing step is performed. (1) Attach 600 grit sandpaper to the sander and sand at 350 rpm. (2) Polish and observe in the same manner with 800 grit abrasive paper. (3) Polish and observe in the same manner using 1200 grit abrasive paper. (4) Polish and observe in the same manner using 2000 grit abrasive paper. (5) Using an alumina abrasive with a grain size of 0.3 μm (for example, Alumina Liquid manufactured by Refine Tech Co., Ltd.), polish at a rotation speed of 100 rpm. If no significant scratches are found when observing the observation surface with an optical microscope, polishing is complete.

[0019] After the above-mentioned polishing is completed, an image of the observation surface is taken with an SEM (e.g., 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 and the observation surface does not become too small. Based on the SEM image of the observation surface of the copper circuit thus obtained, the above-mentioned dent 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, of 0.05 or more in a cross section perpendicular to the extending direction of the circuit pattern. [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 is than 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 anchor effect. In addition, since the first recess ratio is a value obtained by dividing the recess width by the circuit height, by controlling the first recess ratio, the adhesion between printed wiring boards can be improved even in a circuit with a low circuit height. When the first recess ratio is 0.05 or more, such an anchor effect is good. The first recess ratio is preferably 0.07 or more, more preferably 0.08 or more, and even more preferably 0.10 or more. The upper limit of the first recess ratio is not particularly limited, but from the viewpoint of suppressing chipping of the top end, 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 in 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 the cross section perpendicular to the extending direction of the circuit pattern (recess angle) is preferably 50 to 75°. FIG. 3 shows an observation photograph of a cross section perpendicular to the extending direction of the circuit pattern of the copper circuit to explain the "recess angle". As shown in FIG. 3, the recess angle is 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. If the recess angle is 75° or less, the recess on the side of the cross section of the copper circuit becomes steep, and when a printed wiring board or the like is laminated on the copper circuit, the copper circuit is more strongly caught, and the anchor effect is stronger. If the recess angle is 50° or more, the thickness of the protruding part is large, making it difficult to break when an external force is applied, and good adhesion between the printed wiring boards is maintained. 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 between the angle between the top of the cross section perpendicular to the extending direction of the circuit pattern and both sides 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 is likely to concentrate on the protruding part on the side with the smaller recess angle, and this part is likely to be destroyed, and the adhesion between the printed wiring boards may not be sufficiently improved. In contrast, if the difference between the angle between the top of the cross section of the copper circuit and both sides is less than 15°, the concentration of the external force on one part is suppressed, and the destruction of the copper circuit is suppressed. The difference is more preferably less than 10°, and even more preferably less than 7°. The difference in the angles 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 becomes relative to the recessed portion of the side, so that the anchor effect with the insulating substrate such as a resin substrate becomes stronger, and the adhesion between the printed wiring boards is improved. The second recess ratio is more preferably 0.10 or more, even more preferably 0.12 or more, and even more preferably 0.14 or more. The upper limit of the second recess ratio is not particularly limited, but from the viewpoint of suppressing chipping of the end 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. A circuit with a fine L (line) / S (space) is prone to contact (short circuit) between adjacent circuits. Even in a fine circuit with 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 expands from the top to the bottom of the circuit as shown in FIG. 1(A), and can satisfactorily suppress 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 of copper circuit> Next, a method for manufacturing a copper circuit according to an embodiment of the present invention will be described in detail. First, a copper foil having a specified thickness is hot pressed with an insulating substrate such as a resin substrate to produce a copper clad laminate (CCL). Next, this CCL is degreased and pickled, and then the copper foil is roughened with Ni plating. The conditions for roughening Ni plating are shown below. During plating, the plating solution is agitated using a stirrer, bubbling, etc. 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 manner, 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%. The thickness of the nickel layer can be evaluated by photographing the cross section of the copper circuit by SEM and measuring the thickness of the nickel layer from the obtained SEM image. In this way, by providing a nickel layer with a roughened surface on the top surface of the copper circuit, a depression having a width smaller than the width of the bottom and top can be created in the cross section of the copper circuit, and the adhesion between the printed wiring boards is improved by the anchor effect.

[0029] The nickel deposition weight can be measured by the following procedure. A sample of 0.5 dm x 0.5 dm is cut out from the copper foil with a nickel plating layer or from the CCL containing the copper foil, and the metal layer is dissolved in a nitric acid solution. The nickel concentration in the sample solution is quantified using an ICP emission spectrometer, and the amount of nickel attached per unit area (μg / dm 2 Specifically, the ICP emission spectrometer is 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 a solution containing nitric acid and copper with the Ni concentration adjusted to 2 ppm by adding Kanto Chemical's JCSS standard solution for chemical analysis (nickel standard solution (Ni 1000), specifications: for atomic absorption spectrometry and ICP analysis), and a solution with a Ni concentration of 0 ppm to which Kanto Chemical's JCSS standard solution for chemical analysis has not been added. A calibration curve is then created using these as standard solutions, 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 addition of Kanto Chemical's JCSS standard solution for chemical analysis is prepared using the following procedure. (1) Cut out copper foil without a nickel-plated layer to weigh 15.68 g. (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 the copper foil. (4) After cooling, add pure water to make the final volume 500 mL. In addition, the surface to be measured (the surface with the nickel plating layer) is masked to prevent metal from the opposite surface from being mixed in before the analysis is performed.

[0030] After that, a resist pattern with a specified L / S is formed on the surface of the roughened Ni plating layer of the copper foil by laminating a dry film resist (e.g., RY-5115 manufactured by Resonac Co., Ltd.) and performing an exposure and development process, and unnecessary parts of the copper foil are removed by an etching process to produce a copper circuit with the specified L / S. The etching conditions are shown below. Etching solution composition: Cupric chloride or ferric chloride ·Copric chloride system: CuCl 2 232-254g / L, HCl 117-121g / L Ferric chloride: FeCl 2 37wt% Transport speed: 0.4 to 1.0 m / min (etching tank length 770 mm)

[0031] In the method for producing a copper circuit according to an embodiment of the present invention, as described above, when forming a copper circuit from the copper foil of CCL using a subtractive method, a roughened Ni layer is provided on the surface (S surface) opposite to the surface laminated with an insulating substrate such as a resin substrate. Here, Ni has a slower etching rate than copper in a cupric chloride or ferric chloride etching solution, so the top of the copper circuit is protected. At this time, the surface of the roughened Ni layer has irregularities, which improves adhesion to the dry film (DF) and prevents the top of the copper circuit from being dissolved by the etching solution that has soaked in from the end of the DF, causing the peripheral portion of the top to be scraped off. This creates a depression with a width smaller than the width between the bottom and top of the copper circuit, which makes the copper circuit more likely to catch when a printed wiring board or the like is laminated on the copper circuit, and the anchor effect is strengthened. As a result, good adhesion to the printed wiring board is obtained.

[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. A multi-layer board can be produced by stacking a printed wiring board on the printed wiring board having the copper circuit according to the embodiment of the present invention. At this time, the anchor effect of the copper circuit according to the embodiment of the present invention improves the adhesion between the laminated printed wiring board and the insulating substrate such as a resin substrate. EXAMPLES

[0033] The present invention will be described 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 a 35 μm thick copper foil and an insulating resin (GHPL-830NX, manufactured by Mitsubishi Gas Chemical Co., Inc.). After degreasing and pickling the CCL, the copper foil was roughened with Ni plating. The plating conditions are shown below. During plating, the plating solution was stirred 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 L / S=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 L / S=40 μm / 40 μm. The etching solution used was an aqueous solution of copper (II) chloride. The etching conditions are as follows: Etching solution composition: CuCl 2 243g / L, HCl 120g / L Liquid temperature: 50℃ Transport 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 operation 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 with an SEM (Hitachi High-Tech Corporation, SEM S3400N). The accelerating voltage during photographing was 15.0 kV. The SEM image is shown in Figure 4. It can be seen from Figure 4 that the surface of the copper foil is roughened by the roughened Ni layer.

[0036] Example 3 A copper circuit with L / S=40 μm / 40 μm was produced by the same operation 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 operation as in Example 1, except that a roughened Ni layer was not formed, the transport speed during etching was 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 Co., Inc.). After degreasing and pickling this CCL, the copper foil was subjected to smooth Ni plating instead of roughening Ni plating. The plating conditions are shown below. During plating, the plating solution was agitated using a stirrer and bubbling. Plating solution composition: NiSO 4 6H 2 O 60g / L, Na 2 (C 3 H 5 O(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 L / S=40μm / 20μm 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 L / S=30 / 30μm. The etching solution used was an aqueous solution of copper (II) chloride. The etching conditions are as follows: Etching solution composition: CuCl 2 243g / L, HCl 120g / L Liquid temperature: 50℃ Transport 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 extension 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 Buehler 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 abrasive paper was attached to the polishing machine and polished at 350 rpm. (2) The specimen was similarly polished with 800 grit abrasive paper and observed. (3) The specimen was similarly polished with 1200 grit abrasive paper and observed. (4) The specimen was similarly polished with 2000 grit abrasive paper and observed. (5) The sample was polished at 100 rpm using an alumina abrasive having a grain size of 0.3 μm (alumina liquid, manufactured by Refine Tech Co., Ltd.). The observation surface was examined using an optical microscope and no major scratches were found, so polishing was deemed complete. After polishing was completed, images of the observation surface were taken with 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 included in the image and the observation surface was not too small. Specifically, the copper circuits of Examples 1 to 3 and Comparative Example 1 were observed at 2000x, and the copper circuit of Comparative Example 2 was observed at 4000x. SEM images of the cross sections of the copper circuits 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. It should be noted that 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 according to Examples 1 to 3 had a depression width 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 above cross section of the copper circuit of Example 2, the bottom (side surface) was clearly depressed from the top to the bottom. Similarly, depressions were formed in the copper circuits according to Examples 1 and 3 in the above cross section. Therefore, when a printed wiring board is further laminated on the printed wiring board having the copper circuits according to Examples 1 to 3, the copper circuits according to Examples 1 to 3 are strongly caught and the anchor effect is improved, so that it is considered that good adhesion can be obtained between the copper circuits according to 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 according to Comparative Examples 1 and 2. For this reason, the copper circuits according to Comparative Examples 1 and 2 have weak adhesion and a strong anchor effect cannot be expected, and it is considered that the adhesion between the copper circuits according to Comparative Examples 1 and 2 and the resin substrate of the printed wiring board to be laminated thereon is inferior to that of Examples 1 to 3. 7, in Comparative Example 2, no depressions were formed in the above cross section of the copper circuit, even though a Ni layer was formed on the etched side of the copper foil. This is thought to be because the surface of the Ni layer was smooth, which resulted in insufficient adhesion to the dry film, and the etching solution seeped 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 boards that provide good adhesion when laminated with printed wiring boards, which may contribute to improving the reliability of electronic devices. In order to realize an Al·loT 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), "Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation."

Claims

1. In a cross section perpendicular to the extending direction of the circuit pattern, the recess width defined by the following formula 1 is 2.5 μm or more, [Formula 1] Depression width = (top width - minimum width) / 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.)

2. In a cross section perpendicular to the extension direction of the circuit pattern, the recess width defined by the following formula 1 is 2.5 μm or more, [Formula 1] Depression width = (top width - minimum width) / 2 A copper circuit in which the angle between the top and side of the cross section is 50 to 75 degrees.

3. 3. The copper circuit of claim 2, wherein the difference between the angle between the top and both sides of the cross section is less than 15 degrees.

4. 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. [Formula 3] Second recess ratio = recess width / top width (In [Equation 3], recess width = (top width - minimum width) / 2.)

5. The copper circuit according to claim 1 or 2, wherein the bottom width of the cross section is 80 μm or less.

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

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

8. A multilayer substrate comprising the printed wiring board according to claim 7.

Images