Copper circuit, printed wiring board and multilayer substrate

Abstract

The present invention relates to a copper circuit in which, in a cross-section orthogonal to the extension direction of the circuit pattern, the recess width defined by the following formula 1 is 1.0 μm or more, [Formula 1] Recess width = (top width - minimum width) / 2.

Description

Technical Field

[0001] This invention relates to copper circuits, printed wiring boards, and multilayer substrates. Background Technology

[0002] The copper circuitry in a printed circuit board containing a multilayer substrate is fabricated by laminating copper foil onto a resin-coated laminate, forming a shielding pattern using photolithography, and then etching using a subtractive etching method. In the case of a multilayer or additive substrate, it is fabricated by stacking multiple printed circuit boards after forming the copper circuit pattern, and then applying heat or pressure to make them tightly bonded.

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

[0004] [Previous Technical Documents] [Patent Literature] [Patent Document 1]: Japanese Patent No. 4955104. Summary of the Invention

[0005] Figure 1 (A) is a cross-sectional photograph of a copper circuit formed using a conventional subtractive method. Figure 1 (B) is a cross-sectional photograph of a copper circuit formed using a conventional additive method. For example... Figure 1 As shown in (A), when formed using a subtractive method, the sides of the copper circuit cross-section become a shape that gently expands from top to bottom; this is common technical knowledge. Furthermore, as... Figure 1 As shown in (B), when formed using the additive method, the cross-section of the copper circuit becomes relatively rectangular, which is common knowledge in the art. However, the inventors have found that if the cross-section of the copper circuit is in such a mountain-shaped or rectangular shape, it is difficult to obtain the anchoring effect when stacking printed circuit boards, resulting in poor adhesion between printed circuit boards.

[0006] The present invention addresses this problem by providing copper circuits, printed wiring boards, and multilayer substrates that achieve good interconnectivity in multilayer printed wiring boards.

[0007] The embodiments of the present invention that solve the above-mentioned problems are described below.

[0008] (1) A copper circuit, wherein in a cross-section orthogonal to the extension direction of the circuit pattern, the recess width defined by Equation 1 below is 1.0 μm or more. [Formula 1] Recess width = (top width - minimum width) / 2.

[0009] (2) A copper circuit, wherein in a cross-section orthogonal to the extension direction of the circuit pattern, the first recess ratio, as defined by Equation 2 below, is 0.05 or higher. [Equation 2] First recess ratio = Recess width / Circuit height (In [Equation 2], the width of the indentation = (top width - minimum width) / 2).

[0010] (3) The copper circuit as described in (1) or (2) above, wherein the angle between the top and the side of the cross section is 50 to 75°.

[0011] (4) The copper circuit described in (3) above, wherein the difference in angle between the top of the cross section and the sides of the cross section does not reach 15°.

[0012] (5) A copper circuit as described in any one of (1) to (4) above, wherein, in this cross-section, the second recess ratio as defined by Equation 3 below is 0.08 or higher. [Equation 3] Second concavity ratio = Concavity width / Top width (In [Equation 3], the width of the indentation = (top width - minimum width) / 2).

[0013] (6) A copper circuit as described in any of (1) to (5) above, wherein the bottom width of the cross section is less than 80 μm.

[0014] (7) A copper circuit as described in any of (1) to (6) above, which is used in a multilayer substrate.

[0015] (8) A printed wiring board having an insulating substrate and a copper circuit described in any one of (1) to (6) above disposed on the insulating substrate.

[0016] (9) A multilayer substrate having the printed wiring board described in (8) above.

[0017] According to embodiments of the present invention, copper circuits, printed wiring boards, and multilayer substrates that can achieve good interconnectivity when multiplying printed wiring boards can be provided. Attached Figure Description

[0018] [ Figure 1 (A) is a cross-sectional photograph of a copper circuit formed using a conventional subtractive method. Figure 1 (B) is a cross-sectional photograph of a copper circuit formed using a conventional additive method.

[0019] [ Figure 2 [This is an example of a cross-sectional photograph of a copper circuit of an embodiment of the present invention, orthogonal to the extension direction of the circuit pattern.]

[0020] [ Figure 3 [A photograph of a cross-section of a copper circuit orthogonal to the direction of extension of the circuit pattern, used to illustrate the "recess angle".]

[0021] [ Figure 4 [Image 1] is an SEM image of the roughened Ni layer surface of the copper circuit in Example 2.

[0022] [ Figure 5 [Image 1] is a cross-sectional SEM image of the copper circuit of Example 2.

[0023] [ Figure 6 [Image] is a cross-sectional SEM image of the copper circuit of Comparative Example 1.

[0024] [ Figure 7 [Image 1] is a cross-sectional SEM image of the copper circuit of Comparative Example 2. Detailed Implementation

[0025] The following describes specific preferred embodiments of the present invention; however, the invention should not be limited to these embodiments. Various modifications and improvements can be made based on the knowledge of those skilled in the art, provided they do not depart from the spirit of the invention. The various constituent elements disclosed in this embodiment can be appropriately combined to form various inventions. For example, several constituent elements can be deleted from all the constituent elements shown in this embodiment.

[0026] <Copper Circuit> The copper circuit of the embodiments of the present invention is an electronic circuit formed on an insulating substrate. For example, a printed wiring board can also be formed on an insulating substrate. Furthermore, a multilayer substrate can be formed by stacking multiple printed wiring boards on which the copper circuit of the embodiments of the present invention is formed. The insulating substrate can be a resin substrate or a substrate obtained by impregnating a substrate such as paper or glass with resin.

[0027] The raw material for the copper circuit in the embodiment of the present invention is copper or copper alloy, which can be formed from known materials in general copper circuits.

[0028] The thickness of the copper circuit in the embodiments of the present invention is not particularly limited, and can be 9 to 80 μm or 12 to 70 μm.

[0029] Figure 2 An example photograph showing a cross-sectional view of a copper circuit according to an embodiment of the present invention, orthogonal to the extension direction of the circuit pattern. For example... Figure 2As shown, in this invention, the term "top width" refers to the straight-line distance between two points at the top end of the cross-section of the copper circuit. Furthermore, the term "minimum width" refers to the shortest width in the cross-section of the copper circuit, which is the distance of a straight line parallel to the bottom. Furthermore, the term "circuit height" refers to the distance of a straight line (orthogonal to the bottom) from the center of the top end of the cross-section of the copper circuit. Furthermore, the term "bottom width" refers to the straight-line distance between two points at the bottom end of the cross-section of the copper circuit.

[0030] In one example of the copper circuit of the embodiment of the present invention, the recess width defined by Equation 1 below is 1.0 μm or more in a cross-section orthogonal to the extension direction of the circuit pattern.

[0031] [Equation 1] Recess width = (Top width - Minimum width) / 2 In the aforementioned cross-section of the copper circuit, the larger the recess width, the wider the top width of the copper circuit is compared to the minimum width of the copper circuit. This results in a stronger hooking effect and anchoring effect when the copper circuit is laminated onto printed circuit boards, etc. If the recess width is 1.0 μm or more, this anchoring effect becomes more pronounced. 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. While there is no particular upper limit to the recess width, from the viewpoint of suppressing defects at 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.

[0032] The width of the aforementioned indentation can be measured in the following manner.

[0033] That is, firstly, a copper circuit of the object to be measured is prepared and placed on an insulating substrate (in this case, resin). Secondly, the resin and the copper circuit on the resin are cut with scissors so that the plane of the copper circuit of the object to be measured is orthogonal to the extension direction. The resulting cross-section will be referred to as the observation plane below.

[0034] Next, the observation surface is ground using a Grinder (e.g., a Buehler METASERV2000). In cases where the resin is thin and difficult to grind, an adhesive can be used to fix the resin and the copper circuitry on it to an acrylic substrate. Furthermore, when a specific location on the copper circuitry is designated as the observation surface, the position of the observation surface can be adjusted by mounting 80-grit abrasive paper to the grinder and grinding the observation surface at 350 rpm.

[0035] The following describes the grinding sequence. Furthermore, during each step, the surface is observed using an optical microscope. If no major damage is found, the process moves on to the next grinding step.

[0036] (1) Install No. 600 abrasive paper into the grinder and grind at 350 rpm.

[0037] (2) Grind and observe using No. 800 abrasive paper in the same manner.

[0038] (3) Grind and observe using No. 1200 abrasive paper in the same way.

[0039] (4) Grind and observe using No. 2000 abrasive paper in the same manner.

[0040] (5) Use an alumina abrasive with a particle size of 0.3 μm (e.g., alumina liquid manufactured by Refine Tec Co., Ltd.) to grind at a speed of 100 rpm. Observe the surface under an optical microscope. If there are no large scratches, the grinding is complete.

[0041] After the above polishing is completed, an image of the observation surface is captured using a SEM (e.g., a SEMS3400N manufactured by Hitachi High-Tech Co., Ltd.). The accelerating voltage during imaging is set to 15.0 kV. The magnification during imaging is selected such that the entire observation surface falls within the image without appearing too small. Based on the SEM image of the observation surface of the copper circuit obtained in this manner, the width of the aforementioned indentation can be determined.

[0042] In another example of the copper circuit of the embodiment of the present invention, the first recess ratio defined by the following formula 2 is 0.05 or higher in a cross-section orthogonal to the extension direction of the circuit pattern.

[0043] [Equation 2] First recess ratio = Recess width / Circuit height (In [Equation 2], the width of the indentation = (top width - minimum width) / 2.) In the aforementioned cross-section of the copper circuit, a larger first recess ratio results in a wider top width of the copper circuit compared to its minimum width. This leads to stronger hooking and anchoring of the copper circuit when stacking it onto printed circuit boards. Furthermore, since the first recess ratio is the value obtained by dividing the recess width by the circuit height, controlling the first recess ratio can improve the tightness of the printed circuit boards, even for circuits with low circuit heights. If the first recess ratio is 0.05 or higher, this anchoring effect is optimal. The first recess ratio is preferably 0.07 or higher, more preferably 0.08 or higher, and even more preferably 0.10 or higher. While there is no particular upper limit to the first recess ratio, from the viewpoint of suppressing defects at the top edge, it is preferably 0.30 or lower, more preferably 0.20 or lower, and even more preferably 0.15 or lower.

[0044] The first depression ratio can be obtained by measuring the SEM image after obtaining it, in the same way as the method for measuring the depression width.

[0045] In the embodiments of the present invention, the copper circuit preferably has an angle (recess angle) of 50 to 75° between the top and side of the cross-section orthogonal to the extension direction of the circuit pattern. Figure 3 A photograph showing a cross-section of a copper circuit, orthogonal to the direction of extension of the circuit pattern, used to illustrate the "recess angle." For example... Figure 3 As shown, the concavity angle is the angle between the straight line drawn on the top and the line drawn from the top end to the side of the cross-section. If the concavity angle is 75° or less, the concavity on the side of the cross-section of the copper circuit becomes steeper, resulting in stronger hooking of the copper circuit and a stronger anchoring effect when stacking copper circuits in printed circuit boards. If the concavity angle is 50° or more, the thickness of the protruding portion is large, making it less susceptible to damage when external force is applied, thus maintaining good adhesion between printed circuit boards. The concavity angle is more preferably 50 to 70°, and even more preferably 50 to 65°.

[0046] The aforementioned indentation angle can be obtained by measuring the SEM image after acquisition, in the same way as the aforementioned indentation width measurement method. Specifically, for example, the SEM image can be displayed using PowerPoint (registered trademark) manufactured by Microsoft Corporation, and then the ruler function of PowerPoint can be used to measure the angle between the straight line drawn on the top and the line drawn from the top end in the aforementioned cross-section to the side, and this angle can be evaluated as the indentation angle.

[0047] In the embodiments of the present invention, the copper circuit preferably has an angle difference of less than 15° between the top of the cross-section orthogonal to the extension direction of the circuit pattern and the two side surfaces. In the aforementioned cross-section of the copper circuit, if the difference in the concavity angles on both sides is large, when an external force is applied, the force tends to concentrate on the protruding portion on the side with the smaller concavity angle, making that portion susceptible to damage, and potentially hindering the adequate sealing of the printed circuit boards. Conversely, if the angle difference between the top of the cross-section of the copper circuit and the two side surfaces is less than 15°, the concentration of external force on a single area can be suppressed, thus preventing damage to the copper circuit. More preferably, this difference is less than 10°, and even more preferably less than 7°.

[0048] The difference in the aforementioned angles can be obtained by measuring the SEM image after obtaining it, in the same way as the method for measuring the width of the depression.

[0049] In the embodiments of the present invention, the copper circuit preferably has a second recess ratio of 0.08 or more in a cross-section orthogonal to the extension direction of the circuit pattern, as defined by the following formula 3.

[0050] [Equation 3] Second concavity ratio = Concavity width / Top width (In [Equation 3], the width of the recess = (top width - minimum width) / 2.) In the aforementioned cross-section of the copper circuit, the larger the second recess ratio, the larger the protruding portion at the top is relative to the recessed portion on the side, thus strengthening the anchoring effect with the insulating substrate such as the resin substrate and improving the tightness of the printed circuit boards. The aforementioned second recess ratio is more preferably 0.10 or higher, more preferably 0.12 or higher, and even more preferably 0.14 or higher. While there is no particular upper limit to the aforementioned second recess ratio, from the viewpoint of suppressing defects at the top end, it is preferably 0.30 or lower, more preferably 0.25 or lower, and even more preferably 0.20 or lower.

[0051] The second depression ratio can be obtained by measuring the SEM image after obtaining it, in the same way as the method for measuring the depression width.

[0052] In the copper circuit embodiments of the present invention, the bottom width of the cross-section orthogonal to the extension direction of the circuit pattern is preferably 80 μm or less. Circuits with very fine L (line) / S (gap) ratios are prone to contact (short circuits) between adjacent circuits. Even in very fine circuits with a bottom width of 80 μm or less as described above, the copper circuits of the present invention will not become like... Figure 1 The shape shown in (A), which gently expands from the top to the bottom of the circuit, effectively suppresses contact between adjacent circuits. The bottom width is more preferably 70 μm or less, 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; it may be 9 μm or more, 12 μm or more, or 18 μm or more.

[0053] The bottom width of the above-mentioned cross-section can be obtained by measuring the SEM image after obtaining the SEM image, in the same way as the method for measuring the width of the above-mentioned depression.

[0054] <Methods for Manufacturing Copper Circuits> Next, the manufacturing method of the copper circuit according to the embodiment of the present invention will be described in detail.

[0055] First, a copper-clad laminate (CCL) is fabricated by hot-pressing a copper foil of a specified thickness with an insulating substrate such as a resin substrate. Next, after degreasing and pickling the CCL, a roughened Ni plating is performed on the copper foil. The conditions for roughened Ni plating are described below. Furthermore, the plating solution is stirred using a stirrer and a bubbler during the plating process.

[0056] Plating solution: Roughening nickel plating solution (product name "Roughening nickel plating solution", manufactured by JX Metal Trading Co., Ltd.) Bath temperature: 57~63℃ Current density: 9–11 A / dm 2 Plating time: 0.5–20 seconds In this way, CCLs with roughened Ni plating are prepared.

[0057] The preferred nickel adhesion amount of the roughened Ni plating layer is 400–15000 μg / dm². 2 More preferably, it is 600–9000 μg / dm³. 2 The thickness of the nickel layer can be evaluated by taking a cross-section of the copper circuit using SEM and measuring the thickness of the nickel layer from the obtained SEM image. In this way, by applying a roughened nickel layer to the top surface of the copper circuit, a recess with a width smaller than that at the bottom and top can be formed in the cross-section of the copper circuit, thereby improving the tightness between printed circuit boards due to the anchoring effect.

[0058] The amount of nickel deposited can be determined in the following order.

[0059] A 0.5 dm × 0.5 dm sample was cut from a copper foil with a nickel plating layer or a CCL containing such a copper foil. The metal layer was dissolved in a nitric acid solution, and the nickel concentration in the sample solution was quantified using an ICP emission spectrometer to calculate the amount of nickel adhered per unit area (μg / dm²). 2 Specifically, the PS3520UVDD2 (AN-063 ICP3520UV-DD2) manufactured by Hitachi High-Tech Co., Ltd. was used as the ICP emission spectrometer, and measurements were performed under the following conditions.

[0060] Wavelength: 231.675 nm Integrating time: 1.0 second Points awarded: 3 times Quantitative method: Calibration curve method Blank deduction: None Output: 1.2 kW Pre-spraying time: 30 seconds Cleaning time: 30 seconds Furthermore, the standard solutions used in the determination were prepared by adding JCSS chemical analysis standard solution (Ni 1000, manufactured by Kanto Chemical Co., Ltd., for atomic absorption spectrometry and ICP analysis) to a solution containing nitric acid and copper, adjusting the Ni concentration to 2 ppm, and using a solution with a Ni concentration of 0 ppm without adding JCSS chemical analysis standard solution manufactured by Kanto Chemical Co., Ltd. as standard solutions to create a calibration curve. The Ni concentration in the sample solution was adjusted to be within the range of the calibration curve. In addition, the solution containing nitric acid and copper before adding the JCSS chemical analysis standard solution manufactured by Kanto Chemical Co., Ltd. was prepared in the following order.

[0061] (1) Cut out copper foil without nickel plating to a weight of 15.68 g.

[0062] (2) Add the cut copper foil to 100 mL of pure water and 60 mL of 65 wt% nitric acid.

[0063] (3) Heat the solution to dissolve all the copper foil.

[0064] (4) After cooling, add pure water and measure it in 500 mL.

[0065] Furthermore, the opposite side is shielded to prevent metal from mixing into the side to be measured (the side with the nickel plating), and then the analysis is performed.

[0066] Then, through the lamination, exposure, and development steps of dry film photoresist (e.g., manufactured by Risennoco Co., Ltd., RY-5115), a resist pattern with a specified L / S is formed on the surface of the roughened Ni plating layer of the copper foil. Subsequently, the unwanted portions of the copper foil are removed by etching, thus fabricating a copper circuit with the specified L / S. The etching conditions are described below.

[0067] Etching solution composition: copper chloride-based or ferric chloride-based • Copper chloride system: CuCl2 232~254 g / L, HCl 117~121 g / L Ferric chloride system: FeCl2 37 wt% Handling speed: 0.4~1.0 m / min (etching tank length 770 mm) In the copper circuit manufacturing method according to an embodiment of the present invention, as described above, when forming a copper circuit from copper foil using a subtractive process from CCL, a roughened Ni layer is provided on the side opposite to the side where the insulating substrate such as a resin substrate is laminated (S-side). Here, Ni etches more slowly than copper in a copper chloride-based or ferric chloride-based etching solution, thus protecting the top of the copper circuit. The roughened Ni layer has an uneven surface, improving adhesion to the dry film (DF), preventing the top of the copper circuit from being dissolved by the etching solution penetrating from the DF end, thus preventing the peripheral portion of the top from being scraped off. This creates a recess with a width smaller than the bottom and top widths of the copper circuit, resulting in stronger adhesion and anchoring effect when the copper circuit is laminated to a printed circuit board. Therefore, good adhesion to the printed circuit board is obtained.

[0068] In the embodiments of the present invention, the copper circuit is disposed 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 substrate can be fabricated by stacking printed wiring boards on the printed wiring board having the copper circuit of the embodiments of the present invention. In this case, due to the anchoring effect of the copper circuit of the embodiments of the present invention, the adhesion between the stacked printed wiring board and the insulating substrate such as the resin substrate becomes excellent.

[0069] [Example] The present invention will be described in more detail below through embodiments, but the present invention is not limited to these embodiments in any way.

[0070] (Example 1) A copper-clad laminate (CCL) is fabricated by hot-pressing a 35 μm thick copper foil with an insulating resin (manufactured by Mitsubishi Gas Chemical Co., Ltd., GHPL-830NX). After degreasing and pickling the CCL, a roughened Ni plating is applied to the copper foil. The plating conditions are described below. Furthermore, the plating solution is stirred using a stirrer and a bubbler during the plating process.

[0071] Plating solution: Roughening nickel plating solution (product name "Roughening nickel plating solution", manufactured by JX Metal Trading Co., Ltd.) Bath temperature: 60℃ Current density: 10 A / dm 2 Plating time: 2 seconds Therefore, a CCL with a roughened Ni plating layer is prepared.

[0072] Next, through the lamination and exposure and development steps of dry film photoresist (manufactured by Lisennoco Co., Ltd., RY-5115), an etching pattern of L / S = 46 μm / 34 μm is formed on the surface of the roughened Ni plating layer of the copper foil. Then, the useless parts of the copper foil are removed by etching to produce a copper circuit of L / S = 40 μm / 40 μm.

[0073] The etching solution used is an aqueous solution of copper chloride. The etching conditions are as follows.

[0074] Etching solution composition: CuCl2 243 g / L, HCl 120 g / L Liquid temperature: 50℃ Handling speed: 0.58 m / min (etching tank length 770 mm) (Example 2) The plating time for forming the roughened Ni layer was set to 5 seconds and the transport speed during etching was set to 0.61 m / min. Otherwise, the same operation as in Example 1 was performed to fabricate a copper circuit with L / S = 40 μm / 40 μm.

[0075] Regarding the copper circuit with a roughened Ni layer on its surface in Example 2, the surface of the roughened Ni layer was photographed using a SEM (SEM S3400N manufactured by Hitachi High-Tech Co., Ltd.). The accelerating voltage during imaging was set to 15.0 kV. The SEM image is shown below. Figure 4 .from Figure 4 It can be seen that the surface of the copper foil is roughened due to the roughening of the Ni layer.

[0076] (Example 3) The plating time for forming the roughened Ni layer was set to 10 seconds and the transport speed during etching was set to 0.60 m / min. Otherwise, the same operation as in Example 1 was performed to fabricate a copper circuit with L / S = 40 μm / 40 μm.

[0077] (Comparative Example 1) Without forming a roughened Ni layer, the etching speed was set to 0.46 m / min, and a resist pattern with L / S = 52 μm / 28 μm was formed. Otherwise, the same operation as in Example 1 was performed to fabricate a copper circuit with L / S = 40 μm / 40 μm.

[0078] (Comparative Example 2) A copper-clad laminate (CCL) is fabricated by hot-pressing an 18 μm thick copper foil with an insulating resin (manufactured by Mitsubishi Gas Chemical Co., Ltd., GHPL-830NX). After degreasing and pickling the CCL, a smooth Ni plating is applied to the copper foil, rather than a roughened Ni plating. The plating conditions are described below. Furthermore, the plating solution is stirred using a stirrer and a bubbler during the plating process.

[0079] Plating solution composition: NiSO4·6H2O 60 g / L, Na2(C3H5O(COO)3) 8 g / L Bath temperature: 50℃ Current density: 4 A / dm 2 Plating time: 3 seconds Therefore, a CCL with a smooth Ni plating layer is prepared.

[0080] Next, through the lamination, exposure, and development steps of dry film photoresist (manufactured by Lisennoco Co., Ltd., RY-5115), an etching pattern of L / S = 40 μm / 20 μm is formed on the surface of the smooth Ni plating layer of the copper foil. Then, the useless parts of the copper foil are removed by etching to create a copper circuit of L / S = 30 / 30 μm.

[0081] The etching solution used is an aqueous solution of copper chloride. The etching conditions are as follows.

[0082] Etching solution composition: CuCl2 243 g / L, HCl 120 g / L Liquid temperature: 50℃ Handling speed: 0.75 m / min (etching tank length 770 mm) <Measurement> The resin and the copper circuitry on it are cut with scissors, using a plane orthogonal to the direction of the circuit pattern's extension as a cross-section. The resulting cross-section will be referred to as the observation plane.

[0083] The observation surface was then ground using a Grinder grinder (manufactured by Buehler GmbH, METASERV 2000).

[0084] The following describes the grinding sequence. Furthermore, during each step, the surface is observed using an optical microscope. If no major damage is found, the process moves on to the next grinding step.

[0085] (1) Install No. 600 abrasive paper into the grinder and grind at 350 rpm.

[0086] (2) Grind and observe using No. 800 abrasive paper in the same way.

[0087] (3) Grind and observe using 1200 grit abrasive paper in the same way.

[0088] (4) Grind and observe using No. 2000 abrasive paper in the same way.

[0089] (5) Use alumina abrasive with a particle size of 0.3 μm (manufactured by Refine Tec Inc., liquid alumina) to grind at a speed of 100 rpm.

[0090] The surface was examined using an optical microscope. Since there were no major scratches, the grinding process was completed.

[0091] After grinding, an image of the observation surface was captured using a SEM (SEM S3400N manufactured by Hitachi High-Tech Co., Ltd.). The accelerating voltage during imaging was set to 15.0 kV. The magnification during imaging was selected such that the entire observation surface fell within the image without the observation surface being too small. Specifically, the copper circuits of Examples 1-3 and Comparative Example 1 were observed at 2000x magnification, and the copper circuit of Comparative Example 2 was observed at 4000x magnification.

[0092] The SEM image of the aforementioned cross-section of the copper circuit obtained at this time is shown below. Figure 5 (Example 2) Figure 6 (Comparative Example 1) Figure 7 (Comparative Example 2).

[0093] For the SEM images of the above cross-section of the copper circuit obtained in this manner, the following values ​​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 the left side]", "recess angle (right side) [= angle between the top and the right side]", "angle difference [= difference between the angles between the top and the two sides]", "recess angle (average of right and left sides)", and "etching factor (EF) [= circuit height / (bottom width - top width)]".

[0094] The evaluation results are shown in Table 1.

[0095] Furthermore, the nickel adhesion amount shown in Table 1 is not a value measured using the above method, but an estimated value calculated based on the plating conditions.

[0096] [Table 1] <Inspection> In the copper circuits of Examples 1-3, the recess width is 1.0 μm or more in a cross-section orthogonal to the extension direction of the circuit pattern. Therefore, the SEM image of the aforementioned cross-section of the copper circuit of Example 2 (…) Figure 5 As shown, the folded edge (side) is clearly concave from the top to the bottom. Similarly, the copper circuits of Examples 1 and 3 also have concavities in the above cross-section. Therefore, when a printed circuit board having the copper circuits of Examples 1 to 3 is further laminated, the copper circuits of Examples 1 to 3 have stronger hooks and improved anchoring effect. Thus, it is believed that good adhesion is obtained between the copper circuits of Examples 1 to 3 and the resin substrate of the laminated printed circuit board.

[0097] On the other hand, no recess was formed in the copper circuits of Comparative Examples 1 and 2. Therefore, the copper circuit hooking of Comparative Examples 1 and 2 was weak, and a strong anchoring effect could not be expected. It was believed that the adhesion between the copper circuits of Comparative Examples 1 and 2 and the resin substrate of the multilayer printed wiring board was worse than that of Examples 1 to 3.

[0098] Furthermore, such as Figure 7 As shown, in Comparative Example 2, although a Ni layer was formed on the etched side of the copper foil, no depression was formed in the aforementioned cross-section of the copper circuit. This is believed to be because the surface of the Ni layer is smooth, resulting in insufficient adhesion to the dry film. The etching solution seeps in from the periphery of the interface between the Ni layer and the dry film, causing etching to occur at the top periphery.

[0099] According to one embodiment of the present invention, copper circuitry and multilayer substrates that provide good interconnectivity during multilayer printed circuit board manufacturing can be provided, potentially contributing to improved reliability of electronic devices. Improving the reliability of electronic devices is required to realize an AI·IoT society. Therefore, one embodiment of the present invention has the potential to contribute to Goal 9 of the UN-led Sustainable Development Goals (SDGs): “Building resilient infrastructure, promoting inclusive and sustainable industrialization and fostering innovation.”

Claims

1. A copper circuit, in a cross section orthogonal to an extending direction of a circuit pattern, having a recess width defined by the following Formula 1 of 1.0 μm or more, [Formula 1] Recess width = (Top width - Minimum width) / 2.

2. A copper circuit, in a cross section orthogonal to an extending direction of a circuit pattern, having a first recess ratio defined by the following Formula 2 of 0.05 or more, [Formula 2] First recess ratio = Recess width / Circuit height (In [Formula 2], recess width = (Top width - Minimum width) / 2).

3. The copper circuit of claim 1 or 2, wherein, The angle of the top of the cross section with the side surface is 50 to 75°.

4. The copper circuit of claim 3 wherein, The difference in the angle of the top of the cross section with the side surface on both sides is not more than 15°.

5. The copper circuit of claim 1 or 2, wherein, In the cross section, a second recess ratio defined by the following Formula 3 is 0.08 or more, [Formula 3] Second recess ratio = Recess width / Top width (In [Formula 3], recess width = (Top width - Minimum width) / 2).

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

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

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

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

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