Transparent copper foil substrate and its manufacturing method

Abstract

This invention provides a transparent copper foil substrate comprising: a transparent substrate including a first surface and a second surface; a black seed layer formed on the first surface by double chemical plating, the sheet resistance of the black seed layer being less than 10 Ω / sq, and the black seed layer comprising nickel and zinc, wherein the weight ratio of zinc to nickel is 0.018~0.07; and a copper layer formed on the side of the black seed layer away from the transparent substrate, and composited with the black seed layer as a metallic conductive layer; wherein the reflectivity of incident light measured from the second surface of the transparent substrate into the first surface is less than 22% in the range of 400~700 nm. Furthermore, this invention also provides a method for manufacturing the above-mentioned transparent copper foil substrate. By using the aforementioned transparent copper foil substrate and its manufacturing method, it is possible to reduce the sheet resistance of the black seed layer while increasing the plating rate of the black seed layer, and to obtain a transparent copper foil substrate with low reflectivity.

Description

[Technical Field]

[0001] This invention relates to a transparent copper foil substrate and its manufacturing method, and particularly to a transparent copper foil substrate with low reflectivity and its manufacturing method. [Previous Technology]

[0002] In the field of display manufacturing, copper metal wiring is generally formed on a transparent substrate to serve as a transparent copper foil substrate. However, because the wiring has a metallic luster, there is a problem that the visibility of the display is reduced due to light reflection.

[0003] In response to the above problems, some people have proposed to form a black layer between the copper metal wiring and the transparent substrate by a single chemical plating of nickel-zinc alloy, so as to reduce the reflectivity of the transparent conductive substrate. [Summary of the Invention]

[0004] Next, the inventors discovered that the degree of blackening of the black layer is positively correlated with the zinc ion concentration in the plating bath; that is, the higher the zinc ion concentration, the more significant the blackening of the black layer. However, as the zinc ion concentration increases, zinc ions hinder the deposition of the black layer, resulting in a decrease in the plating rate and a loose plating structure, which in turn causes a sharp increase in the sheet resistivity of the plating layer. Furthermore, if the sheet resistivity of the black layer is too high (e.g., greater than 10 Ω / sq), it will adversely affect the production efficiency of roll-to-roll (RTR) continuous electroless plating and subsequent copper electroplating operations.

[0005] Therefore, there is room for further improvement in reducing the sheet resistance of the black layer in the transparent copper foil substrate and increasing the plating rate of the black layer.

[0006] The inventors have discovered that by using a dual chemical plating method and a specific zinc / nickel ratio to form a black seed layer, it is possible to reduce the sheet resistance of the black seed layer, increase the plating rate of the black seed layer, and obtain a transparent copper foil substrate with low reflectivity.

[0007] To solve the above problems, the present invention provides a transparent copper foil substrate comprising: a transparent substrate including a first surface and a second surface; a black seed layer formed on the first surface by double chemical plating, the sheet resistance of the black seed layer being less than 10 Ω / sq, and the black seed layer comprising nickel and zinc, wherein the weight ratio of zinc to nickel is 0.018 to 0.07; a copper layer formed on the side of the black seed layer away from the transparent substrate, and composited with the black seed layer to form a metallic conductive layer; wherein the reflectivity of incident light measured from the second surface of the transparent substrate into the first surface at an incident angle of 5° is less than 22% in the range of 400 to 700 nm.

[0008] To solve the above problems, the present invention provides a method for manufacturing a transparent copper foil substrate, comprising: step (A), providing a transparent substrate including a first surface and a second surface; step (B), forming a black seed layer on the first surface by performing double chemical plating, wherein the sheet resistance of the black seed layer is less than 10 Ω / sq, and the black seed layer includes nickel and zinc, and the weight ratio of zinc to nickel is 0.018 to 0.07; and step (C), forming a copper layer on the side of the black seed layer away from the transparent substrate by electroplating, and the copper layer and the black seed layer are composited into a metallic conductive layer; wherein the reflectivity of incident light measured from the second surface of the transparent substrate into the first surface at an incident angle of 5° is less than 22% in the range of 400 to 700 nm.

[0009] In an embodiment, the transparent substrate has a light transmittance of more than 87% and is selected from the group consisting of: glass, polyimide (PI), polyethylene terephthalate (PET), cyclic olefin polymer (COP), and polycarbonate (PC).

[0010] In the embodiment, the thickness of the copper layer is 0.2~20μm.

[0011] In an embodiment, the black seed layer also contains phosphorus, and the phosphorus content is less than 4 wt% of the black seed layer.

[0012] In the embodiment, there is a polymer coating between the transparent substrate and the black seed layer, and the light transmittance of the polymer coating is greater than 85%.

[0013] In an embodiment, after step (A) and before step (B), a polymer coating is adhered to one side of the transparent substrate and the polymer coating is positioned between the transparent substrate and the black seed layer, and the light transmittance of the polymer coating is greater than 85%.

[0014] In an embodiment, the material of the polymer coating is selected from the group consisting of: polyimide (PI), polyurethane (PU), acrylic resin and epoxy resin.

[0015] This invention is made in view of the aforementioned problems, and its object is to provide a transparent copper foil substrate. The aforementioned transparent copper foil substrate can be formed with high production efficiency while reducing reflectivity.

[0016] Furthermore, this invention is made in view of the aforementioned problems, and its object is to provide a method for manufacturing a transparent copper foil substrate. By the aforementioned manufacturing method, a transparent copper foil substrate with low reflectivity (e.g., less than 22% in the range of 400~700nm) can be obtained.

Implementation Method

[0017] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different embodiments, and various details in this specification can also be modified and changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0018] Unless otherwise stated herein, the term "or" as used in the specification and the appended claims includes the meaning of "and / or".

[0019] Unless otherwise stated herein, the terms "A to B" used in the specification and the appended claims have the meaning of "more than A and less than B". For example, the term "10 to 40 wt%" has the meaning of "more than 10 wt% and less than 40 wt%".

[0020] <Transparent Copper Foil Substrate> First, please refer to Figure 1, which is a cross-sectional schematic diagram of a transparent copper foil substrate according to an embodiment of the present invention. As shown in Figure 1, the transparent copper foil substrate 100 according to an embodiment of the present invention includes: a transparent substrate 1; a black seed layer 2; and a copper layer 3. The transparent substrate 1 includes a first surface 11 and a second surface 12. The black seed layer 2 is formed on the first surface 11 by double chemical plating, and the black seed layer 2 and the copper layer 3 can be composited into a metallic conductive layer. Furthermore, the reflectivity of incident light measured from the second surface 12 of the transparent substrate 1 into the first surface 11 at an incident angle of 5° is less than 22% in the range of 400~700nm (refer to Figure 3 described later).

[0021] Next, as shown in FIG1, the black seed layer 2 is formed on the first surface 11 of the transparent substrate 1, and the copper layer 3 is formed on the side of the black seed layer 2 away from the transparent substrate 1. That is, the structure of the transparent copper foil substrate 100 is, in sequence, the transparent substrate 1, the black seed layer 2 and the copper layer 3. Next, the transparent copper foil substrate 100 of the present invention will be described in detail.

[0022] <<Transparent Substrate>> Any material with a light transmittance greater than 87% can be used as the transparent substrate of this invention. Furthermore, considering factors such as weight reduction, the transparent substrate is preferably made of plastic material. Specifically, the material of the transparent substrate can be selected from the group consisting of: glass, polyimide (PI), polyethylene terephthalate (PET), cyclic olefin polymer (COP), and polycarbonate (PC). In one specific example, the transparent substrate is selected as polyimide (PI). The material of the above-mentioned transparent substrate can be a commercially available product; for example, the transparent substrate can be a transparent polyimide film manufactured by Damai Technology, model OT2-025.

[0023] <<Black Seed Layer>> The sheet resistance of the black seed layer is less than 10 Ω / sq, and it includes nickel and zinc, with a zinc / nickel weight ratio of 0.018 to 0.07. If the zinc / nickel weight ratio is less than 0.018, the obtained transparent copper foil substrate cannot achieve the ideal reflectivity (reflectivity less than 22% in the range of 400 to 700 nm); on the other hand, if the zinc / nickel weight ratio is greater than 0.07, the production conditions of double electroless plating will be limited and will not meet cost requirements. Furthermore, since the electroless plating solution contains sodium hypophosphite as a reducing agent, phosphorus will also precipitate as part of the alloy during the reduction deposition of nickel ions; the phosphorus content is preferably less than 4 wt% of the precipitated alloy, and can be controlled by the composition of the electroless plating solution and the operating conditions. By keeping the phosphorus content to less than 4 wt% of the black seed layer, the black seed layer can be etched cleanly, avoiding its residue on the substrate surface and causing short circuits in the metal wiring.

[0024] In one embodiment, the black seed layer comprises a ternary alloy of nickel, zinc, and phosphorus. Furthermore, the thickness of the black seed layer is preferably 50-250 nm, more preferably 70-100 nm. If the thickness of the black seed layer is less than 50 nm, the sheet resistance of the black seed layer will be too high (greater than 10 Ω / sq), which is detrimental to subsequent copper plating; if the thickness of the black seed layer is greater than 250 nm, there is a risk of incomplete etching leading to short circuits in the metal wiring.

[0025] In this invention, the black seed layer is formed on one side of a transparent substrate by double electroless plating. Double electroless plating involves performing two electroless plating processes sequentially, with the second plating filling in the deposition defects of the coating formed by the first plating. This improves the problem of excessively high sheet resistance caused by a single electroless plating of the black layer. Without increasing the total coating thickness, the sheet resistance of the black seed layer formed by double electroless plating is significantly reduced, allowing for smooth subsequent RTR copper plating operations. Furthermore, the plating rate during double electroless plating can be maintained at a certain level, ensuring the efficiency of continuous production.

[0026] Furthermore, the reaction conditions for the first and second electroless plating are not particularly limited. The composition of the plating bath and the reaction conditions can be adjusted based on known electroless plating methods to obtain the black seed layer of the present invention. In the present invention, it is preferable to dope zinc ions necessary for the black seed layer in the first plating bath of the first electroless plating, and not to dope zinc ions in the second plating bath of the second electroless plating, in order to fill the deposition defects caused by zinc ions in the coating formed by the first electroless plating.

[0027] <<Copper Layer>> The copper layer of the present invention is not particularly limited, as long as it can form a copper layer for subsequent etching. Furthermore, in one embodiment of the present invention, it is preferred to plate the copper layer onto the black seed layer using electroplating. The electroplating solution used for the copper layer can be a commercially available product, such as copper sulfate electroplating solution (purchased from Jiwei Industrial Co., Ltd.). In addition, the thickness of the copper layer is preferably 0.2~20μm.

[0028] Next, in one embodiment, to increase the adhesion between the transparent substrate and the black seed layer, a polymer coating (not shown) can be placed between the transparent substrate and the black seed layer. Furthermore, to ensure the overall light transmittance of the transparent copper foil substrate, the light transmittance of the polymer coating needs to be greater than 85%. Specifically, the material of the polymer coating can be selected from the group consisting of: polyimide (PI), polyurethane (PU), acrylic resin, and epoxy resin. Similarly, the material of the above-mentioned polymer coating can be a commercially available product.

[0029] <Manufacturing Method of Transparent Copper Foil Substrate> First, please refer to FIG2, which is a flowchart of the manufacturing process of a transparent copper foil substrate according to an embodiment of the present invention. As shown in FIG2, the manufacturing method of a transparent copper foil substrate according to an embodiment of the present invention includes: providing a transparent substrate 1, which includes a first surface 11 and a second surface 12 (step A); forming a black seed layer 2 on the first surface 11 by performing double chemical plating (i.e., performing a first chemical plating and a second chemical plating in sequence) (step B); and forming a copper layer 3 on the side of the black seed layer 2 away from the transparent substrate 1 by electroplating (step C).

[0030] Furthermore, in order to increase the bonding force between the transparent substrate and the black seed layer, in one embodiment, after step A and before step B, a polymer coating (not shown) is applied to the first surface of the transparent substrate, and the polymer coating is positioned between the transparent substrate and the black seed layer.

[0031] Next, regarding electroplating, conventional electroplating methods can be used. For example, the aforementioned transparent substrate with a black seed layer is fixed in a stainless steel frame, first immersed in a 3wt% H2SO4 solution for 1 minute to clean the surface, and then placed in a 20L small copper plating tank (purchased from Hsuan Heng Enterprise Co., Ltd.) for electroplating. The plating area is 15cm*15cm, and the power supply conditions can be 6A current, 3V voltage, and 2 minutes. Furthermore, the electroplating solution can be an electroplating solution containing 150g / L H2SO4, 120g / L CuSO4, and 50ppm chloride ions, and can further contain appropriate amounts of gloss and leveling agents, without particular limitations. After electroplating, the transparent substrate further plated with a copper layer is removed, washed with water, and dried to obtain a single-sided copper foil substrate with a copper thickness of approximately 1µm.

[0032] The details regarding the double chemical plating, transparent substrate, black seed layer, copper layer and polymer coating are as described above and will not be repeated here.

[0033] [Examples] Hereinafter, although the present invention will be specifically described by way of various embodiments and comparative examples, the present invention is not limited to these embodiments and comparative examples.

[0034] [Measurement of Reflectance] The reflectance of the transparent copper foil substrate was measured using a spectrometer main unit (model: JASCO / V-750) and a reflectance measurement kit (model: ISV-922) purchased from Shangwei Co., Ltd. First, a 5cm*5cm sample was fixed at the measurement position on the spectrometer main unit, with the transparent substrate facing the integrating sphere. A calibration whiteboard was placed on the opposite side. The chamber cover was closed, and the analysis software was started. The reflectance at an incident angle of approximately 5° could then be measured. Specifically, please refer to Figure 3, which is a schematic diagram of the reflectance measurement of the transparent copper foil substrate of the present invention. As shown in Figure 3, the incident light was directed from the second surface 12 into the first surface 11. The reflectance of the incident light L with an incident angle of 5° and a wavelength range of 400nm~700nm could then be measured.

[0035] [Determination of Peel Strength] The peel strength between the transparent substrate and the conductive metal layer in a transparent copper foil substrate was determined using a universal tensile testing machine (model: QC-538M1) from Guanglai Instruments. First, the copper layer thickness of the transparent copper foil substrate was adjusted to 18μm, and the circuit was fabricated according to the IPC-TM-650 2.4.9 specification. The peel strength was then tested at a 90° angle on the universal tensile testing machine.

[0036] [Measurement of Sheet Resistance] The sheet resistance of a transparent substrate with a black seed layer was measured using a low impedance analyzer (model: LORESTA / MCP-T370) purchased from Nanbei Trading Co., Ltd., to evaluate whether a copper layer could be further electroplated on the black seed layer. First, a 10cm*10cm sample of the transparent substrate with a black seed layer was placed on the measuring stage. The sheet resistance was measured by uniformly contacting the nickel surface of the black seed layer with four probes. The experimental data is the average value of 5 points.

[0037] [Composition of the black seed layer] Using an ICP optical emission spectrometer (model: PerkinElmer / Avio 200) purchased from Chen Shen Technology Co., Ltd., a 6cm*6cm sample of black seed layer was taken and dissolved in 50ml of nitric acid aqueous solution to form the test solution. Before analysis, a calibration curve was prepared with a standard. Then the test solution was injected into the instrument to obtain the volume concentration of each element, and the composition ratio was calculated accordingly.

[0038] [Etched Circuit Test] Place the transparent flexible circuit board sample on the observation stage of a metallurgical microscope (Nikon LV100 metallurgical microscope, purchased from Guoxiang Trading) with the transparent PI side facing up. Examine the bottom of the circuit with a 20x objective lens to confirm the degree of under-cut of the black plating on the circuit.

[0039] [Overall Evaluation] If at least one of the characteristics in Tables 1 to 2 below does not meet the requirements, the overall evaluation is ×; if at least one barely meets the requirements, the overall evaluation is △; if all characteristics meet the requirements, the overall evaluation is ○.

[0040] <Example 1> (Pretreatment of Transparent Substrate) First, a transparent polyimide film (model OT2-025) manufactured by Damai Technology was used as the transparent substrate. Continuous hydrophilic modification was performed on a corona treatment machine (manufactured by WEDGE, Japan) under the following conditions: power 3kW, speed 3m / min. Next, the transparent substrate was cut to a size of 15cm*15cm and immersed in a 2wt% potassium hydroxide (KOH) solution at 40°C for 150 seconds. Then, following the SLP metallization process of Okuno Pharmaceutical Co., Ltd., Japan, charge conditioning, pre-immersion, catalysis, and acceleration steps were performed using the SLP series of electroless nickel plating reagents (including SLP-200, SLP-300, SLP-400, and SLP-500). The operating conditions are as follows: 1. The transparent substrate was immersed in an SLP-200 solution at 65°C for 75 seconds for charge conditioning, then removed and rinsed with water. 2. Immerse the substrate continuously in SLP-300 solution at 25°C for 25 seconds and SLP-400 solution for 75 seconds to allow the catalyst to adhere to the surface of the transparent substrate. Remove and rinse with water. 3. Then immerse the substrate in SLP-500 solution at 35°C for 75 seconds to activate the catalyst. Remove and rinse with water to form a transparent substrate with palladium catalyst on both sides.

[0041] (Double Chemical Plating with Black Seed Layer) Two 5-liter cups of SLP-660 chemical nickel plating solution from Okuno Pharmaceutical Co., Ltd., Japan, were prepared. Both solutions contained 17-20 g / L of sodium hypophosphite and 4.6-5.0 g / L of nickel ions. One cup was used as the first plating bath, with 0.004 mole / L of zinc sulfate added and the pH adjusted to 9.0 with ammonia. The other cup was used as the second plating bath, without zinc sulfate added and with the pH adjusted to 8.5 with ammonia. The transparent substrate with palladium catalyst on both sides was immersed in the first plating bath and reacted at 55°C for 80 seconds. After immersion, it was immediately immersed in the second plating bath and reacted at 36°C for 210 seconds. After rinsing and drying, the double chemical plating was completed. Then, one side of the plating layer was removed using a copper chloride etching solution to obtain the PI transparent substrate with a black seed layer on one side as described in Example 1.

[0042] (Electroplated Copper Layer) The aforementioned transparent substrate plated with a black seed layer was fixed with a stainless steel frame and first immersed in a 3wt% H2SO4 solution for 1 minute to clean the surface. Then, it was placed in a 20L small copper plating tank (purchased from Hsuan Heng Enterprise Co., Ltd.) for electroplating. The plating area was 15cm*15cm, and the power supply conditions were 6A current, 3V voltage, and 2 minutes. The electroplating solution contained 150g / L H2SO4, 120g / L CuSO4, and 50ppm chloride ions. After electroplating, the transparent substrate further plated with a copper layer was removed, washed with water, and dried to obtain the single-sided copper foil substrate with a copper thickness of approximately 1µm as described in Example 1.

[0043] (Circuit Etching) The transparent copper foil substrate obtained in Example 1 was subjected to conventional semi-additive circuitry processes, including pretreatment, lamination, exposure, development, copper plating, film removal, and fast etching, to prepare flexible circuit boards with linewidth / spacing of 20 / 100 μm or 30 / 120 μm, respectively. In the fast etching process, the patterned circuit board was fixed in a plastic frame, the dry film photoresist on the copper surface was removed, and then it was placed on the fast etching line for bottom metal etching. Here, the fast etching solution contained 5 wt% sulfuric acid, 10 wt% hydrogen peroxide, copper ions at a concentration of less than 30 g / L, and appropriate additives. The processing speed was 0.9 m / min. The completed product was the flexible circuit board with fine lines as described in Example 1.

[0044] Finally, the dual chemical plating conditions, the composition of the black seed layer, and the characteristics of the black seed layer and the transparent copper foil substrate of Example 1 are summarized in Table 1 below.

[0045] <Examples 2-6> Next, in the same manner as in Example 1, the conditions of the double electroless plating and the composition of the black seed layer were changed based on Table 1 below to form the transparent copper foil substrate and flexible circuit board of Examples 2-6. Furthermore, the double electroless plating conditions, the composition of the black seed layer, and the characteristics of the black seed layer and the transparent copper foil substrate of Examples 2-6 are summarized in Table 1 described below.

[0046] <Comparative Examples 1-3> In the same manner as Example 1, the double electroless plating conditions and the composition of the black seed layer were changed based on Table 1 above to form the transparent copper foil substrate and flexible circuit board of Comparative Examples 1-3. Furthermore, the double electroless plating conditions, the composition of the black seed layer, and the characteristics of the black seed layer and the transparent copper foil substrate of Comparative Examples 1-3 are summarized in Table 1 described below.

[0047] <Comparative Example 4> First, in the same manner as in Example 1, a pretreatment of the transparent substrate was performed to form a transparent substrate with palladium catalyst on both sides. Next, 5 liters of SLP-660 electroless nickel plating solution from Okuno Pharmaceutical Co., Ltd. of Japan was prepared in a beaker, containing 17-20 g / L sodium hypophosphite and 4.6-5.0 g / L nickel ions. The pH was adjusted to 8.5 with ammonia. The aforementioned PI transparent substrate with palladium catalyst on both sides was then immersed in the electroless nickel plating solution and reacted at 36°C for 250 seconds. After removal, it was washed with water and dried, thus completing the electroless plating on both sides of the transparent substrate. Afterward, the plating layer on one side was removed using a copper chloride etching solution to obtain the PI transparent substrate with a nickel layer on one side of Comparative Example 4. Then, circuit etching was performed in the same manner as in Example 1 to obtain a flexible circuit board with fine lines.

[0048] <Comparative Example 5> First, in the same manner as in Example 1, a pretreatment of the transparent substrate was performed to form a transparent substrate with palladium catalyst on both sides. Next, 5 liters of SLP-660 electroless nickel plating solution from Okuno Pharmaceutical Co., Ltd. of Japan were prepared in a beaker, containing 17-20 g / L sodium hypophosphite, 4.6-5.0 g / L nickel ions, and 0.004 mole / L zinc sulfate. The pH was adjusted to 9.0 with ammonia water. The aforementioned PI film with palladium catalyst was then immersed in the plating bath and reacted at 55°C for 400 seconds. After removal, it was washed with water and dried, thus completing the electroless plating on both sides of the transparent substrate. Afterward, the plating layer on one side was removed using a copper chloride etching solution to obtain the PI transparent substrate with a nickel-zinc alloy layer on one side of Comparative Example 5. Then, the circuit etching was performed in the same manner as in Example 1, but it was found that with a line width of 20 µm, a flexible circuit board with fine lines could not be obtained due to line stripping.

[0049] <Comparative Examples 6-7> Except for changing the electroless plating conditions as shown in Table 2, PI transparent substrates with a nickel-zinc alloy layer on one side were obtained in Comparative Examples 6-7, similar to Comparative Example 5. Then, circuit etching was performed in the same manner as in Example 1, but it was found that with line widths of 20µm and 30µm, the etching was impossible due to line peeling or excessively high resistance, thus failing to obtain the flexible circuit boards with fine lines of Comparative Examples 6-7. Furthermore, the electroless plating conditions, plating composition, and characteristics of the plating and transparent copper foil substrate of Comparative Examples 4-7 are summarized in Table 2 described later.

[0050] [Table 1] experiment serial number First plating bath conditions Second plating bath conditions Characteristics of black seed layer Characteristics of transparent copper foil substrate Overall evaluation First plating solution Zn 2+ concentration (mmole / L) pH Temperature (°C) time (sec) second plating solution Zn 2+ concentration (mmole / L) pH temperature (°C) time (sec) Elemental composition (wt%) Single-sided thickness (nm) Plating rate (nm / sec) sheet resistor (Ω / sq) 400~700nm Reflectance (%) Peel strength (kgf / cm) Line etching nickel Zinc phosphorus Zinc / Nickel 20µm line width 30µm line width Example 1 SLP-660 4.0 9.0 55 80 SLP-660 0 8.5 36 210 94.1 2.5 3.4 0.027 85 0.293 6.3 20.2 0.54 20 30 ○ Example 2 5.5 90 93.8 2.7 3.5 0.029 86 0.286 6.2 18.7 0.63 20 30 ○ Example 3 7.0 110 94.4 1.8 3.8 0.019 87 0.272 5.9 20.5 0.53 19 29 ○ Example 4 7.0 140 93.9 2.6 3.5 0.028 92 0.263 5.8 18.3 0.52 20 30 ○ Example 5 7.0 170 92.5 3.9 3.6 0.042 97 0.255 5.1 17.6 0.52 twenty two 31 ○ Actual example 6 8.5 170 93.7 2.8 3.5 0.030 91 0.239 5.3 18.0 0.54 twenty one 31 △ Comparative Example 1 7.0 50 97.0 0.6 2.4 0.006 77 0.296 7.7 29.8 0.61 16 20 × Comparative Example 2 7.0 80 95.4 1.5 3.1 0.016 82 0.283 7.0 24.0 0.55 18 28 × Comparative Example 3 10.0 170 95.8 1.3 2.9 0.014 86 0.226 6.5 29.1 0.56 17 26 ×

[0051] [Table 2] experiment serial number Plating bath conditions Coating characteristics FCCL characteristics overall evaluate Chemical plating solution Zn 2+ concentration (mmole / L) pH temperature (°C) time (sec) Elemental composition (wt%) Single-sided thickness (nm) Plating rate (nm / sec) sheet resistor (Ω / sq) 400~700nm Reflectance (%) Peel strength (kgf / cm) Line etching nickel Zinc phosphorus Zinc / Nickel 20µm line width 30µm line width Comparative Example 4 SLP-660 0 8.5 36 250 96.8 0.0 3.2 0.000 82 0.328 5.2 39.7 0.62 twenty one 30 × Comparative Example 5 4.0 9.0 55 400 88.0 3.9 8.1 0.044 84 0.210 64 20.4 0.59 Line stripping 28 × Comparative Example 6 7.0 500 84.3 6.8 8.9 0.081 83 0.166 141 16.7 0.52 Line stripping Line stripping × Comparative Example 7 10.0 800 82.5 7.9 9.6 0.096 81 0.101 215 14.0 0.50 Unable to work Unable to work ×

[0052] First, as can be seen from Table 2, Comparative Example 4 does not contain zinc (zinc content is too low), and does not meet the condition that the zinc / nickel weight ratio is 0.018~0.07. As a result, the reflectivity of the transparent copper foil substrate of Comparative Example 4 in the 400~700nm range is 39.7%, which does not meet the standard. Therefore, the overall evaluation is X. In addition, as for Comparative Example 5, although it meets the condition that the zinc / nickel weight ratio is 0.018~0.07, the plating rate of Comparative Example 5 is reduced (less than 0.24nm / sec) because it is a single chemical plating process. This results in a loose plating structure and excessively high sheet resistance (greater than 30Ω / sq). With a line width of 20µm, it is impossible to obtain a flexible circuit board with fine lines due to line stripping.

[0053] Then, it can be seen from Table 2 that because the zinc content of Comparative Examples 6 to 7 is too high, it does not meet the condition that the weight ratio of zinc to nickel is 0.018 to 0.07. Furthermore, Comparative Examples 6 to 7 are single-pass electroless plating, which reduces the plating rate (less than 0.24 nm / sec), resulting in a loose plating structure and excessively high sheet resistance (greater than 30 Ω / sq). In cases with line widths of 20 µm and 30 µm, the circuit cannot be processed due to line peeling or excessively high sheet resistance, and thus a flexible circuit board with fine lines cannot be obtained.

[0054] Next, as can be seen from Table 1, although Comparative Examples 1-3 used double chemical plating, the zinc content of Comparative Examples 1-3 was too low, failing to meet the condition that the zinc / nickel weight ratio was 0.018-0.07. As a result, the reflectivity of the transparent copper foil substrates of Comparative Examples 1-3 at 400-700 nm was 29.8%, 24.0%, and 29.1%, respectively, which did not meet the standard. Therefore, the overall evaluation was X. In addition, the linewidth of Comparative Examples 1 and 3 was too thin and not resistant to etching.

[0055] Furthermore, as can be seen from Table 1, because Examples 1-6 all used double chemical plating to form a black seed layer with a sheet resistance of less than 10 Ω / sq, and the weight ratio of zinc to nickel in the black seed layer was between 0.018 and 0.07, Examples 1-6 were able to obtain transparent copper foil substrates with a reflectivity of less than 22% at 400-700 nm. In addition, Examples 1-6 were also able to subsequently produce flexible circuit boards with excellent line etching. Furthermore, because the plating rate of Example 6 was 0.239 nm / sec, which barely met the requirement of a plating rate of 0.24 nm / sec or higher, the overall evaluation was △; the overall evaluation of the other examples (Examples 1-5) was ○.

[0056] Next, please refer to Figure 4, which is a comparison chart of reflectance between Example 5 and Comparative Examples 4-5 of the present invention. As shown in Figure 4, since Comparative Example 4 does not contain zinc, its average reflectance in the 400-700 nm range is 39.7%, which does not meet the requirements. In addition, although the zinc content in the black seed layer of Comparative Example 5 and Example 5 is 3.9 wt%, and the weight ratio of zinc to nickel in the black seed layer is also similar (both are about 0.043), Example 5, through double electroless plating, can further reduce the reflectance of the transparent copper foil substrate, reduce the sheet resistance of the black seed layer, and increase the plating rate of the black seed layer compared to Comparative Example 5, which is subjected to single electroless plating. It can be seen that, under the same zinc content, the coating obtained by double electroless plating can achieve a better effect in reducing reflectance.

[0057] Finally, please refer to Figure 5. Figure 5(a) is a photograph of the appearance of the etched circuit of Example 5; Figure 5(b) is a photograph of the appearance of the etched circuit of Comparative Example 1. As shown in Figure 5(a), when the line width / spacing of the etched circuit is 30 / 120 μm, the line width / spacing of Example 1 is normal and meets the standard. On the other hand, as shown in Figure 5(b), when the line width / spacing of the etched circuit is 30 / 120 μm, the circuit of Comparative Example 1 is over-etched, resulting in a thinner line width and a larger line spacing, which does not meet the standard.

[0058] The present invention is not limited to the above-described embodiments. Various changes can be made within the scope shown in the claims. Furthermore, embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included within the technical scope of the present invention. [Simplified Explanation of the Diagram]

[0059] Figure 1 is a cross-sectional schematic diagram of a transparent copper foil substrate according to an embodiment of the present invention. Figure 2 is a manufacturing process flowchart of a transparent copper foil substrate according to an embodiment of the present invention. Figure 3 is a schematic diagram of the measurement of reflectivity of the transparent copper foil substrate according to the present invention. Figure 4 is a reflectivity comparison chart between Embodiment 5 and Comparative Examples 4-5 of the present invention. Figure 5(a) is a photograph of the appearance of the etched lines of Embodiment 5; Figure 5(b) is a photograph of the appearance of the etched lines of Comparative Example 1.

Claims

1. A transparent copper foil substrate, comprising: a transparent substrate including a first surface and a second surface; a black seed layer formed on the first surface by double chemical plating, the sheet resistance of the black seed layer being less than 10 Ω / sq, and the black seed layer comprising nickel and zinc, wherein the weight ratio of zinc to nickel is 0.018~0.07; and a copper layer formed on the side of the black seed layer away from the transparent substrate, and composited with the black seed layer as a metallic conductive layer; wherein... The reflectivity of incident light at an incident angle of 5°, measured from the direction through the second surface of the transparent substrate to the first surface, is less than 22% in the range of 400~700nm.

2. The transparent copper foil substrate as described in claim 1, wherein, The transparent substrate has a light transmittance of more than 87% and is selected from the group consisting of: glass, polyimide (PI), polyethylene terephthalate (PET), cyclic olefin polymer (COP), and polycarbonate (PC).

3. The transparent copper foil substrate as described in claim 1, wherein, A polymer coating exists between the transparent substrate and the black seed layer, and the light transmittance of the polymer coating is greater than 85%.

4. The transparent copper foil substrate as described in claim 3, wherein, The materials for the polymer coating are selected from the group consisting of: polyimide (PI), polyurethane (PU), acrylic resin and epoxy resin.

5. The transparent copper foil substrate as described in any one of claims 1 to 4, wherein, The black seed layer further includes phosphorus, and the phosphorus content is less than 4 wt% of the black seed layer.

6. A method for manufacturing a transparent copper foil substrate, comprising: step (A), providing a transparent substrate including a first surface and a second surface; step (B), forming a black seed layer on the first surface by performing double chemical plating, the sheet resistance of the black seed layer being less than 10 Ω / sq, and the black seed layer comprising nickel and zinc, wherein the weight ratio of zinc to nickel is 0.018~0.07; and step (C), forming a copper layer on the side of the black seed layer away from the transparent substrate by electroplating, wherein the copper layer and the black seed layer are composited into a metallic conductive layer; wherein... The reflectivity of incident light at an incident angle of 5°, measured from the direction through the second surface of the transparent substrate to the first surface, is less than 22% in the range of 400~700nm.

7. A method for manufacturing a transparent copper foil substrate as described in claim 6, wherein, The transparent substrate has a light transmittance of more than 87% and is selected from the group consisting of: glass, polyimide (PI), polyethylene terephthalate (PET), cyclic olefin polymer (COP), and polycarbonate (PC).

8. A method for manufacturing a transparent copper foil substrate as described in claim 6, wherein, The thickness of the copper layer is 0.2~20μm.

9. A method for manufacturing a transparent copper foil substrate as described in claim 6, wherein, After step (A) and before step (B), a polymer coating is applied to the first surface of the transparent substrate, and the polymer coating is positioned between the transparent substrate and the black seed layer.

10. A method for manufacturing a transparent copper foil substrate as described in claim 9, wherein, The polymer coating has a light transmittance of more than 85%, and the material of the polymer coating is selected from the group consisting of: polyimide (PI), polyurethane (PU), acrylic resin and epoxy resin.

11. A method for manufacturing a transparent copper foil substrate as described in any one of claims 6 to 10, wherein, The black seed layer further includes phosphorus, and the phosphorus content is less than 4 wt% of the black seed layer.

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