Flexible copper clad substrate

Abstract

To provide a flexible copper clad substrate that has electrochemical corrosion resistance and sufficient peel strength.SOLUTION: Provides a flexible copper clad substrate, which includes a polyimide substrate; a nickel-copper alloy layer; and a copper layer. The nickel-copper alloy layer is formed on at least one side of the polyimide substrate by electroless plating and comprises at least nickel, copper and phosphorus. A content of the copper is more than 30 wt.% of the nickel-copper alloy layer, a content of the phosphorus is less than 5 wt.% of the nickel-copper alloy layer, and a corrosion potential of the nickel-copper alloy layer in a 0.02 vol.% sulfuric acid solution is greater than -20 mV. The copper layer is formed on the side of the nickel-copper alloy layer remote from the polyimide substrate and is combined with the nickel-copper alloy layer to form a metal conductive layer. In addition, the flexible copper clad substrate has electrochemical corrosion resistance and sufficient peel strength, facilitating the production of flexible printed circuit boards.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a flexible copper foil substrate, and particularly to a flexible copper foil substrate resistant to electrochemical corrosion.

Background Art

[0002] A flexible copper foil substrate (FCCL, Flexible Cupper Clad Laminate) is generally manufactured by a wet metal method in which a nickel layer is formed on the surface of a polyimide substrate and a copper layer is electroplated on the nickel layer.

[0003] By forming a nickel layer between the copper layer and the polyimide substrate, the peel strength between the metal conductive layer composed of the nickel layer and the copper layer and the polyimide substrate can be improved, so that the structural strength of the flexible copper foil substrate can be improved.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when manufacturing a flexible printed circuit (FPC, Flexible Printed Circuit) with a conventional flexible copper foil substrate and then performing electroless nickel immersion gold (ENIG, Electroless Nickel Immersion Gold), since the reduction potential of metallic nickel (-0.25V) is lower than that of metallic copper (+0.34V), in the process of electroless nickel immersion gold, when gold ions are reduced, metallic nickel is likely to lose electrons, which may cause oxidation corrosion of the nickel layer, also known as electrochemical corrosion.

[0005] In addition, when the nickel layer is oxidized and corroded, the metal circuit on the copper layer may peel off from the polyimide substrate, and the structure of the flexible printed circuit board may be damaged.

[0006] Therefore, the inventors have found that there is still room for improvement in flexible copper foil substrates resistant to electrochemical corrosion.

[0007] The inventors of the present invention have discovered that the nickel - copper alloy layer of the present invention has no corrosion due to electron loss in the acidic gold plating solution and does not affect the etching during circuit production. That is, by using the electroless plating method and the composition of a specific nickel - copper alloy layer, the corrosion potential of the nickel - copper alloy layer in the sulfuric acid solution can be increased, and a flexible copper foil substrate with sufficient peel strength to withstand electrochemical corrosion can be obtained.

Means for Solving the Problem

[0008] In order to solve the above problems, a flexible copper foil substrate according to an embodiment of the present invention has a polyimide substrate, a nickel - copper alloy layer, and a copper layer. The nickel - copper alloy layer contains nickel, copper, and phosphorus, and is formed on at least one side of the polyimide substrate by electroless plating. The content of copper is greater than 30% by weight of the nickel - copper alloy layer, the content of phosphorus is less than 5% by weight of the nickel - copper alloy layer, the corrosion potential of the nickel - copper alloy layer in a 0.02% by volume sulfuric acid solution is greater than - 20 mV. The copper layer is formed on the side of the nickel - copper alloy layer opposite to the polyimide substrate and combines with the nickel - copper alloy layer to form a metal conductive layer.

[0009] In an embodiment of the present invention, the content of copper is less than 80% by weight of the nickel - copper alloy layer.

[0010] In an embodiment of the present invention, the nickel - copper alloy layer is a single plating layer.

[0011] In an embodiment of the present invention, the nickel - copper alloy layer further contains at least one selected from the group consisting of iron, cobalt, molybdenum, tungsten, tin, chromium, and zinc.

[0012] In an embodiment of the present invention, the copper layer is formed on the nickel - copper alloy layer by electroplating and has a thickness of 0.2 - 20 μm.

[0013] In one embodiment of the present invention, the peel strength between the metal conductive layer and the polyimide substrate is 0.7 kgf / cm or more.

Advantages of the Invention

[0014] The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a flexible copper foil substrate having a peel strength sufficient to withstand electrochemical corrosion.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0016] The following describes the implementation mode of the present invention through specific examples, and 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 different examples, and as long as it does not deviate from the spirit of the present invention, the details of this specification can be variously modified and changed based on different viewpoints and applications.

[0017] Unless otherwise specified in this document, the term "A to B" used in the specification and claims includes the meaning of "A or more and B or less". For example, the term "10 to 40% by weight" includes the meaning of "10% by weight or more and 40% by weight or less".

[0018] <Flexible copper foil substrate> First, please refer to FIG. 1. FIG. 1 is a cross-sectional view showing a flexible copper foil substrate 100 according to an embodiment of the present invention. As shown in FIG. 1, the flexible copper foil substrate 100 according to an embodiment of the present invention has a polyimide base material 1, a nickel-copper alloy layer 2, and a copper layer 3. Further, the polyimide base material 1 has a first surface 11 and a second surface 12, and the nickel-copper alloy layer 2 and the copper layer 3 can be bonded to form a metal conductive layer.

[0019] Next, as shown in FIG. 1, a nickel-copper alloy layer 2 is formed on the first surface 11 of the polyimide base material 1, and a copper layer 3 is formed on the side of the nickel-copper alloy layer 2 opposite to the polyimide base material 1. That is, the structure of the flexible copper foil substrate 100 is in the order of the polyimide base material 1, the nickel-copper alloy layer 2, and the copper layer 3. Note that the nickel-copper alloy layer 2 can also be formed on the first surface 11 and the second surface 12 of the polyimide base material 1 at the same time. Furthermore, the flexible copper foil substrate 100 of the present invention will be described in detail.

[0020] <<Polyimide base material>> The polyimide base material is a sheet / film-shaped base material made of polyimide (PI, Polyimide), and its thickness may be about 5 to 150 μm and is not particularly limited. In addition, the polyimide base material can also be made of a transparent polyimide, for example, a polyimide with a light transmittance greater than 87%.

[0021] Note that commercially available products can be used as the polyimide base material. For example, a polyimide film (model number, TX6-025) purchased from TAIMIDE Technology can be used.

[0022] <<Nickel-Copper Alloy Layer>> The nickel-copper alloy layer contains nickel, copper, and phosphorus. Specifically, by including sodium hypophosphite as a reducing agent in the electroless plating solution, phosphorus co-precipitates as one of the alloy components when nickel ions are reductively deposited. In the present invention, the phosphorus content is less than 5 wt% of the nickel-copper alloy layer and can be controlled by the composition of the electroless plating solution and operating conditions. This is because when the phosphorus content is 5 wt% or more of the nickel-copper alloy layer, H 2 O 2 / H 2 SO 4 metal clearly remains in the etching solution, causing a problem that the line width of the circuit increases when subsequent ENIG is performed.

[0023] Also, in the nickel-copper alloy layer of the present invention, the copper content is greater than 30 wt% of the nickel-copper alloy layer. This is because the reduction potential of metallic copper is greater than that of metallic nickel. By including a specific proportion of copper in the nickel-copper alloy layer, it is possible to avoid the situation where metallic nickel is oxidized and corroded by losing electrons when ENIG is performed. Also, when the copper content in the nickel-copper alloy layer is 30 wt% or less, the corrosion potential in a 0.02% by volume sulfuric acid solution of the nickel-copper alloy layer is less than -20 mV, so the effect of preventing electrochemical corrosion may not be achieved.

[0024] Furthermore, the inventors have found that when the copper content in the nickel-copper alloy layer exceeds 80 wt%, the peel strength between the metal conductive layer and the polyimide substrate significantly decreases, which may reduce the structural strength of the FCCL. Therefore, the copper content is preferably greater than 30 wt% and less than 80 wt% of the nickel-copper alloy layer, and more preferably 40 wt% - 60 wt% of the nickel-copper alloy layer.

[0025] On the one hand, the nickel-copper alloy layer may contain, in addition to nickel, copper, and phosphorus, any metal that can be plated together with nickel, as appropriate according to the required properties, and is not particularly limited. Specifically, the nickel-copper alloy layer of the present invention may further contain at least one selected from the group consisting of iron, cobalt, molybdenum, tungsten, tin, chromium, and zinc. Also, the total thickness of the nickel-copper alloy layer metallized on both sides is 100 to 250 nm, preferably 160 to 200 nm. On the other hand, the thickness of the nickel-copper alloy layer metallized on one side is preferably 80 to 100 nm.

[0026] Here, the thickness of the nickel-copper alloy layer can be measured using an X-ray film thickness measuring device (purchased from General Technology Co., Ltd., model number FISCHERSCOPE® XDL210). Specifically, by placing a 10 cm × 10 cm plating film sample on the measuring table, the total thickness of the nickel-copper alloy layer can be measured.

[0027] Also, the nickel-copper alloy layer of the present invention can be a single plating layer, that is, it can achieve the effect of electrochemical corrosion resistance without bonding to other layers, and the manufacturing cost can be reduced.

[0028] Next, in the present invention, the nickel-copper alloy layer is formed on at least one side of the polyimide substrate by electroless plating. Regarding electroless plating, conventional electroless plating methods (methods based on the principle of oxidation-reduction reaction, using a strong reducing agent in a solution containing metal ions to reduce metal ions to metal and deposit them on the surface of various materials to form a dense plating layer) can be mentioned and are not particularly limited. Also, as a specific example of electroless plating, first, a roll-shaped polyimide substrate (purchased from TAIMIDE Technology Co., Ltd., model number TX6-025) is continuously hydrophilized using a corona treatment machine (Corona treatment machine, purchased from WEDGE Co., Ltd., Japan), and the operating conditions are a power of 3 kw and a speed of 3 m / min.

[0029] Then, the hydrophilized polyimide substrate is cut into a size of 20 cm × 20 cm and immersed in a 2 wt% KOH solution at 40°C for 150 seconds. Then, regarding the application of the catalyst, while referring to the SLP metallization process (SLP process) of Okuno Pharmaceutical Co., Ltd., Japan, electroless nickel plating reagents of the SLP series (including SLP-200, SLP-300, SLP-400, SLP-500) are used, and steps such as charge adjustment, pre-dipping, catalyst activation, and acceleration are carried out in sequence. The operating conditions are as follows.

[0030] 1. After adjusting the charge by immersing the hydrophilized polyimide substrate in an SLP-200 solution at 65°C for 75 seconds, take it out and wash it with water. 2. Continuously immerse it in an SLP-300 solution at 25°C for 25 seconds and an SLP-400 solution at 75 seconds to attach a catalyst to the surface of the polyimide substrate, then take it out and wash it with water. 3. Next, immerse it in an SLP-500 solution at 35°C for 75 seconds to activate the catalyst, and then take it out and wash it with water, whereby a polyimide substrate having a palladium catalyst on one side or both sides can be formed.

[0031] Then, by performing the above electroless plating treatment on the polyimide substrate having a palladium catalyst, a nickel-copper alloy layer can be formed. Here, the palladium catalyst is from the above SLP series of electroless nickel plating reagents.

[0032] <<Copper layer>> The copper layer of the present invention may be any copper layer that can form an etching circuit later and is not particularly limited. In one embodiment of the present invention, the copper layer is preferably formed on the nickel-copper alloy layer by electroplating. As the electroplating solution that can be used for the copper layer, commercially available products can be used. For example, an electroplating solution of copper sulfate (purchased from ALL-IN-LINE-CHEMICALS ENTERPRISE Co., Ltd.) can be used. Also, the thickness of the copper layer is preferably 0.2 to 20 μm.

[0033] Specifically, the electroplated copper layer can be fabricated by the following method. First, a polyimide substrate plated with a nickel-copper alloy layer is fixed with a stainless-steel frame and immersed in a 3 vol% H 2 SO 4 solution for 1 minute to clean the surface.

[0034] Next, the surface-cleaned polyimide substrate is placed in an electroplating tank (for example, a 20-L small electroplated copper tank purchased from SURCHEM Co., Ltd.) to electroplate copper, and the electroplated area is 15 cm × 15 cm. The electroplating solution can contain 150 g / L of H 2 SO 4 , 120 g / L of CuSO 4 , and chloride ions with a concentration of 50 ppm, and can further contain an appropriate amount of brightener and leveling agent as needed.

[0035] Also, the electroplating energization conditions are a current of 6 A, a voltage of 3 V, and a time of 2 minutes. After taking out the copper layer from the electroplating solution, washing it with water and drying it, an electroplated copper layer with a thickness of about 1 μm can be obtained on one or both sides.

[0036] Here, the thickness of the copper layer can be measured using a copper thickness measuring device (purchased from SHIN SHEN Co., Ltd.). Specifically, a 10 cm × 10 cm FCCL sample is placed on the measuring table, and four-probe probes are evenly contacted with the copper surface of the FCCL to measure the thickness of the copper layer.

[0037] <Method for Manufacturing Flexible Copper Foil Substrate> First, refer to FIG. 2. FIG. 2 is a manufacturing flowchart of a flexible copper foil substrate 100 according to an embodiment of the present invention. As shown in FIG. 2, the method for manufacturing a flexible copper foil substrate according to an embodiment of the present invention includes a step of preparing a polyimide substrate 1, a step of forming a nickel-copper alloy layer 2 on a first surface 11 of the polyimide substrate 1 by electroless plating, and a step of forming a copper layer 3 on the side of the nickel-copper alloy layer 2 opposite to the polyimide substrate 1 by electroplating.

[0038] Here, in one embodiment, the nickel - copper alloy layer 2 can also be formed simultaneously on the first surface 11 and the second surface 12. At this time, the copper layer 3 is formed on the opposite side of the polyimide substrate 1 in each of the two nickel - copper alloy layers 2.

[0039] Next, for the electroless plating method and the electroplating method, known electroless plating methods and electroplating methods can be used, and there is no particular limitation. Specifically, the above - mentioned electroless plating method and electroplating method can be used, and detailed descriptions are omitted here.

Example

[0040] The present invention will be further described through the following examples and comparative examples, but the present invention is not limited to these examples and comparative examples.

[0041] (Measurement of corrosion potential of nickel - copper alloy layer) The corrosion potential of the nickel - copper alloy layer can be measured using a potentiostat (model number: BioLogic / SP - 50e) from AUBOTECH and a flat - plate corrosion test cell (model number: ABT - TA - F029).

[0042] First, a sample of the polyimide substrate plated with the nickel - copper alloy layer is immersed in a 3 vol% sulfuric acid solution for 30 seconds, washed with water, and then immediately installed in the flat - plate corrosion test cell as a working electrode to conduct an electrochemistry test. In this test, a platinum electrode is used as the auxiliary electrode, a calomel electrode is used as the reference electrode, and a 0.02 vol% sulfuric acid solution is used as the electrolyte. After connecting the potentiostat and starting the operating software, select the Tafel Plot in the corrosion test mode, set the scan rate to 300 mV / min, and the scan range to - 0.5V to 0.2V, then the corrosion potential of the nickel - copper alloy layer in a 0.02 volume% sulfuric acid solution can be measured.

[0043] (Measurement of peel strength) In a flexible copper foil substrate, the peel strength between the polyimide base material and the metal conductive layer can be measured using a universal tensile testing machine (model number: QC-538M1) from COMETECH Testing Machine. First, adjust the copper layer thickness of the flexible copper foil substrate to 18 μm, fabricate circuits according to the standards of IPC-TM-650 2.4.9, and measure the peel strength at a 90° angle with a universal tensile testing machine.

[0044] Also, in the present invention, when the peel strength is 0.9 kgf / cm or more, it is marked as ○; when it is 0.7 kgf / cm or more and less than 0.9 kgf / cm, it is marked as △; when it is less than 0.7 kgf / cm, it is marked as ×.

[0045] (Measurement of the elemental composition of the nickel-copper alloy layer) Using a scanning electron microscope (SEM / EDS) from JIE DONG Co., Ltd., place the sample of the polyimide base material with the nickel-copper alloy layer directly on the SEM without gold plating on the sample surface, set it to a vacuum state, and then analyze the elemental composition of the nickel-copper alloy layer within a range of 200 μm × 150 μm by EDS.

[0046] (Remaining of the plating layer (etchability)) Using a microscope (VK-X3000) from Keyence, Taiwan, place the sample of the etched flexible circuit board directly on the analysis table, and observe the area of the thinnest circuit (line width / line spacing = 25 / 25 μm) using a 50x optical lens to confirm whether there is any remaining metal on its shape and outer periphery.

[0047] Also, in the present invention, when there is no remaining metal, it is marked as ○; when there is a trace amount of remaining metal, it is marked as △; when there is clearly remaining metal (not completely etched), it is marked as ×. Here, no remaining metal means that there is no trace at the edge of the circuit; a trace amount of remaining metal means that the width of the trace at the edge of the circuit is less than 2 μm; clearly remaining metal means that the width of the trace at the edge of the circuit is greater than 2 μm.

[0048] (Adhesion of circuit lines after ENIG) In the present invention, the adhesion of circuit lines after ENIG is visually determined, and the observation range is the area of fine circuit lines with a line width / line pitch of 25 / 25 μm. If there is peeling or lifting visible to the naked eye in the area of fine circuit lines on the entire flexible circuit board, the adhesion of the circuit lines is defined as defective and marked with an "×". Conversely, if the circuit lines are perfect and well-bonded to the polyimide substrate in the area of the entire fine circuit lines, the adhesion of the circuit lines is defined as good and marked with an "○".

[0049] (Absorbance value) First, a polyimide (PI) substrate with a nickel-copper alloy layer of about 200 nm in total thickness plated on both sides is prepared as a sample, and this is immersed in a rapid etching solution of H 2 O 2 / H 2 SO 4 at room temperature for 20 seconds, then taken out, washed with water, and dried. Next, using the unplated PI substrate as a reference, a UV-Vis spectrometer is used to analyze the degree to which the plated layer remains on the PI substrate, and the absorbance value of the etched sample at a wavelength of 500 nm is measured. Also, the larger the absorbance value, the larger the remaining amount of the plated layer, which means that the nickel-copper alloy layer is difficult to etch.

[0050] (Comprehensive evaluation) Among the characteristics in Table 1 below, if at least one is "×", the comprehensive evaluation is "×"; if at least one is "△", the comprehensive evaluation is "△"; if all characteristics are "○" or meet the requirements, the comprehensive evaluation is "○".

[0051] <Example 1> (Pretreatment of polyimide substrate) A roll-shaped polyimide substrate (purchased from TAIMIDE Technology Co., Ltd., model number TX6-025) was continuously hydrophilized using a corona treatment machine (Corona treatment machine, purchased from WEDGE Co., Ltd., Japan). The operating conditions were a power of 3 kw and a speed of 3 m / min. Next, the hydrophilized polyimide substrate was cut into a size of 20 cm × 20 cm and immersed in a 2 wt% KOH solution at 40°C for 150 seconds.

[0052] (Electroless Nickel-Copper Alloy Layer) First, as described above, according to the SLP metallization process (SLP process) of Okuno Pharmaceutical Co., Ltd. in Japan, for the hydrophilized polyimide substrate, steps such as charge adjustment, pre-dipping, catalyst activation, and acceleration are sequentially performed to obtain a polyimide substrate with a palladium catalyst on both sides.

[0053] Next, the electroless plating solution was placed in a 5-liter beaker (the bath volume is 5L). The electroless plating solution contains 98.5 g of nickel sulfate, 7.9 g of copper sulfate, 106 g of sodium hypophosphite, 205 g of sodium citrate, and 124 g of boric acid, and was adjusted to pH = 8.5 with 50 wt% NaOH solution.

[0054] Then, the above polyimide substrate with a palladium catalyst was immersed in the electroless plating solution and reacted at a temperature of 40°C for 2 - 3 minutes so that the total thickness of the plating layer was 200 ± 20 μm. Subsequently, it was taken out, washed with water and dried to form a polyimide substrate with a nickel-copper alloy layer (a ternary alloy containing nickel / copper / phosphorus) plated on both sides.

[0055] (Electroplated Copper Layer) By the above method, a flexible copper foil substrate can be obtained in which a copper layer with a copper thickness of about 1 μm is electroplated on both sides on the nickel-copper alloy layer of the polyimide substrate with a nickel-copper alloy layer.

[0056] (Fabrication of Circuit) Next, please refer to FIG. 3. FIG. 3 is a manufacturing flowchart of the flexible circuit board 900 of the present invention. As shown in FIG. 3, for the flexible copper foil substrate 100 obtained in Example 1, by sequentially performing conventional semi-additive processes such as pretreatment, lamination, exposure, development, copper plating, film removal, and rapid etching, a flexible circuit board 900 with a line width / line spacing = 25 / 25 μm can be fabricated.

[0057] (Electroless Nickel Immersion Gold) Then, as shown in FIG. 3, after performing the semi-additive process, the copper circuit pattern of the flexible printed circuit board is subjected to a surface treatment by conventional electroless nickel immersion gold. Specifically, with Atotech's ENIG reagents (including ProSelect UC K, MicroEtch C, Aurotech Activator conc., Aurotech FL Plus Post Dip K, Aurotech SIT Plus, and Aurotech SF Plus), steps such as cleaning, micro-etching, pre-dipping, activation, post-dipping, nickel plating, and gold plating are performed in sequence.

[0058] The specific procedure is as follows. 1. Immerse the FPC in a solution of ProSelect UC K at 40°C for 5 minutes to clean the surface, then take it out and wash it with water. 2. Then, immerse it in a solution of MicroEtch C at 30°C for 60 seconds to remove the oxide layer on the copper circuit pattern surface by micro-etching, then take it out and wash it with water. 3. Immerse it in a 25 vol% sulfuric acid solution at 25°C for 3 minutes, then take it out and wash it with water. 4. Immerse it in a solution of Aurotech Activator conc. at 25°C for 1 minute to activate the catalyst, then take it out and wash it with water. 5. Immerse it in a solution of Aurotech FL Plus Post Dip K at 25°C for 3 minutes to remove the catalyst on the polyimide substrate, then take it out and wash it with water. 6. Next, immerse it in a solution of Aurotech SIT Plus at pH = 4.8 and 78°C for 6 minutes to deposit a nickel-phosphorus alloy layer with a thickness of 2 to 4 μm, then take it out and wash it with water. Finally, immerse the solution of Aurotech SF Plus containing potassium cyanide gold salt (purchased from Jialong Technology Co., Ltd.) in a solution at pH = 5.5 and 82 °C for 4 minutes, deposit a gold layer with a thickness of 0.04 μm to 0.06 μm (for example, reference numeral 4 in FIG. 3) on the nickel-phosphorus alloy layer, and then take it out and wash it with water to complete the surface treatment of the copper circuit of the flexible circuit board.

[0059] Finally, the metal concentrations in the electroless plating solution, the composition of the nickel-copper alloy layer, and the characteristics of the nickel-copper alloy layer in Example 1 are summarized in Tables 1 to 2. For the measurement methods of each characteristic, please refer to the above content and will not be repeated here.

[0060] <Comparative Example 1> Immerse the polyimide substrate with palladium catalyst on both sides in the SLP-660 plating solution (purchased from Okuno Pharmaceutical Co., Ltd.), react it under the conditions of a temperature of 36 °C and 2 minutes and 30 seconds, and then wash it with water and dry it to form a polyimide substrate plated with a nickel-phosphorus alloy with a total thickness of 200 μm on both sides.

[0061] After that, in the same manner as in Example 1, perform electroplating of the copper layer, production of the circuit, electroless nickel immersion gold, etc. to obtain the flexible copper foil substrate and the flexible circuit board of Comparative Example 1.

[0062] <Comparative Examples 2 to 6 and Examples 2 to 6> Next, in the same manner as in Example 1, based on Table 1 below, by changing the metal concentrations of Ni and Cu in the electroless plating solution (that is, changing the amounts of nickel sulfate and copper sulfate) and the composition of the nickel-copper alloy layer, flexible copper foil substrates and flexible circuit boards of Comparative Examples 2 to 6 and Examples 2 to 6 can be obtained. Also, the metal concentrations in the electroless plating solution, the composition of the nickel-copper alloy layer, and the characteristics of the nickel-copper alloy layer in Comparative Examples 2 to 6 and Examples 2 to 6 are summarized in Tables 1 to 2.

[0063]

Table 1

[0064]

Table 2

[0065] First, as can be seen from Table 1, in Examples 1 to 7, a nickel - copper alloy layer was formed using electroless plating. In the nickel - copper alloy layer, since the copper content is greater than 30% by weight and the phosphorus content is less than 5 wt%, the corrosion potential of the nickel - copper alloy layer in a 0.02% by volume sulfuric acid solution can be greater than - 20 mV, and it has the effect of withstanding electrochemical corrosion.

[0066] Next, in Comparative Examples 1 to 5, since the copper content in the nickel - copper alloy layer is less than 30% by weight, the corrosion potential of the nickel - copper alloy layer produced by these comparative examples is less than - 20 mV, and it is considered that the needs are not met. In addition, in Comparative Examples 2 to 5, since the phosphorus content in the nickel - copper alloy layer is greater than 5 wt%, when etching, there is remaining metal, resulting in a situation where it is not completely etched.

[0067] Specifically, please refer to FIG. 4. (a) of FIG. 4 is a photograph of the etching circuit of Comparative Example 5 of the present invention, and (b) of FIG. 4 is a photograph of the etching circuit of Example 1 of the present invention. Also, as shown in FIG. 4(a), in Comparative Example 5, after etching, there is remaining metal, resulting in a situation where it is not completely etched, so it is considered that the needs are not met. In contrast, as shown in FIG. 4(b), in Example 1, only a trace amount of metal remains after etching, so it is considered that the needs are met.

[0068] Furthermore, in Comparative Examples 1 to 3, the copper content in the nickel-copper alloy layer is very low in all cases. Since the nickel-copper alloy layers in Comparative Examples 1 and 2 do not even contain copper, the corrosion potential is very low (lower than -70 mV) in these comparative examples. Therefore, after ENIG, the situation of line peeling occurs, and the line adhesion is poor, so it is considered that the needs are not met.

[0069] Specifically, please refer to FIG. 5. FIG. 5(a) is a photograph after ENIG of Comparative Example 1 of the present invention, and FIG. 5(b) is a photograph after ENIG of Example 1 of the present invention. Also, as shown by the circled part in FIG. 5(a), in Comparative Example 1, after ENIG, the situation of line peeling occurs, and the line adhesion is poor, so it is considered that the needs are not met. On the contrary, as shown by the circled part in FIG. 5(b), in Example 1, after ENIG, the line adhesion is still good, so it is considered that the needs are met.

[0070] Also, in Example 1, since a trace amount of metal remained, the etching property and the overall evaluation were Δ. In Example 6, although the corrosion potential reached -11.6 mV, the peel strength was 0.868 kgf / cm, which was slightly smaller than the reference value of 0.9 kgf / cm, so the peel strength and the overall evaluation were Δ.

[0071] On the other hand, in Comparative Example 6, the etching property, the corrosion potential, and the line adhesion are all ○, or the needs are met, but since the copper content in the nickel-copper alloy layer is greater than 80 wt%, the peel strength is significantly reduced, only 0.654 kgf. Therefore, the peel strength and the overall evaluation were ×.

[0072] And from Table 2 and FIG. 6, the relationship between the absorbance value and the appearance of the etched sample can be known. Here, FIG. 6(a) is a photograph of the sample after etching of Example 4 of the present invention, FIG. 6(b) is a photograph of the sample after etching of Example 1 of the present invention, and FIG. 6(c) is a photograph of the sample after etching of Comparative Example 5 of the present invention.

[0073] First, as shown in Table 2 and FIG. 6(a), the absorbance value of Example 4 is 0.273. The nickel-copper alloy layer is completely etched, the color of the sample is lighter, and it has an appearance close to that of the PI substrate, so it is considered to meet the needs. Further, as shown in Table 2 and FIG. 6(b), the absorbance value of Example 1 is 0.463. There are trace residues in the nickel-copper alloy layer, and the sample has a darker color appearance than Example 4, but it is still considered to meet the needs. On the other hand, as shown in Table 2 and FIG. 6(c), the absorbance value of Comparative Example 5 is 0.730. There are more residues in the nickel-copper alloy layer, and it is not completely etched. The sample has a darker color appearance than Example 1, so it is considered not to meet the needs.

[0074] By using the electroless plating method and the composition of a specific nickel-copper alloy layer, the present invention can increase the corrosion potential of the nickel-copper alloy layer in a sulfuric acid solution and obtain a flexible copper foil substrate with sufficient peel strength to withstand electrochemical corrosion.

[0075] The present invention is not limited to the above-described embodiments, and various changes can be made within the scope of the claims. Embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Explanation of Signs

[0076] 1 Polyimide substrate 11 First surface 12 Second surface 2 Nickel-copper alloy layer 3 Copper layer 4 Gold layer 100 Flexible copper foil substrate 900 Flexible circuit board

Claims

1. A flexible copper foil substrate having a polyimide substrate, a nickel-copper alloy layer, and a copper layer, the nickel-copper alloy layer contains nickel, copper and phosphorus, and is formed on at least one surface of the polyimide substrate by electroless plating, the copper content is greater than 30% by weight and less than 80% by weight of the nickel-copper alloy layer, the phosphorus content is less than 5% by weight of the nickel-copper alloy layer, and the corrosion potential of the nickel-copper alloy layer in a 0.02 vol. % sulfuric acid solution is greater than -20 mV; The copper layer is formed on the nickel-copper alloy layer on the opposite side to the polyimide substrate and is bonded to the nickel-copper alloy layer to form a metal conductive layer. Flexible copper foil board.

2. The nickel-copper alloy layer is a single plating layer; The flexible copper foil substrate according to claim 1 .

3. The nickel-copper alloy layer further contains at least one selected from the group consisting of iron, cobalt, molybdenum, tungsten, tin, chromium and zinc. The flexible copper foil substrate according to claim 1 .

4. The copper layer is formed on the nickel-copper alloy layer by electroplating and has a thickness of 0.2 to 20 μm. The flexible copper foil substrate according to any one of claims 1 to 3.

5. The peel strength between the metal conductive layer and the polyimide substrate is 0.7 kgf / cm or more. The flexible copper foil substrate according to any one of claims 1 to 3.

6. The peel strength between the metal conductive layer and the polyimide substrate is 0.7 kgf / cm or more. The flexible copper foil substrate according to claim 4.

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