Method for reducing copper of FPC using acidic etching waste liquid, copper reducing solution and FPC manufacturing system

Abstract

The present application relates to a kind of acidic etching waste liquid for FPC copper reduction method, copper reduction liquor and FPC manufacturing system, the method comprises: obtaining acidic etching overflow waste liquid in circuit etching process, the overflow waste liquid includes copper chloride, hydrochloric acid and chlorate;Citric acid is added to acidic overflow waste liquid, and is dissolved and uniformly formed copper reduction liquor, and the citric acid addition amount is 1-10g / L;The temperature of the copper reduction liquor is adjusted to 15-25 ℃;The flexible copper-clad plate is soaked or sprayed using the copper reduction liquor for a certain time;After the flexible copper-clad plate is rinsed and dried, it is placed for use.The copper reduction liquor is composed of acidic etching overflow waste liquid and citric acid.The FPC manufacturing system includes acidic etching device, copper reduction liquor preparation device, copper reduction device and post-processing device.The copper reduction method has the advantages of moderate rate, good controllability and uniform copper reduction.

Description

Technical Field

[0001] This invention relates to the field of flexible printed circuit boards (FPCs), specifically to a method for using acidic etching waste liquid to reduce copper content in FPCs, a copper reduction solution, and an FPC manufacturing system. Background Technology

[0002] In the manufacturing process of flexible printed circuit boards (Flexible Printed Circuits), when the product involves the fabrication of fine circuits, such as line width and spacing ≤ 50μm, thick copper materials cannot meet the precision requirements, necessitating the use of thin copper materials. Common specifications for the copper thickness of flexible printed circuit board substrates include 18μm and 12μm for thin copper foil. Substrates with copper thicknesses below 12μm are significantly more expensive, typically several times the price of 12μm substrates. Therefore, to save production costs while meeting the processing requirements for fine circuit products, copper reduction processing is frequently used in the flexible printed circuit board manufacturing process. Copper reduction processing involves using chemical etching to reduce the surface copper thickness of 12μm copper raw materials to different thicknesses such as 10μm, 9μm, or 8μm, facilitating subsequent processing of fine circuits.

[0003] Currently, there are two common copper reduction solutions on the market: one is the hydrogen peroxide-sulfuric acid system, which consists of hydrogen peroxide and sulfuric acid with the addition of small amounts of stabilizers such as EDTA-2Na and triethanolamine. The reaction principle is: Cu + H2SO4 + H2O2 = CuSO4 + 2H2O, and the reaction temperature is controlled at 35±5℃. The other is the sodium persulfate system, which includes the addition of small amounts of stabilizers such as amines and chelating agents. The reaction principle is: Cu + Na2S2O8 + H2SO4 = CuSO4 + Na2SO4 + 2H2O, and the temperature is controlled at 45±5℃. Regardless of which system is used, the copper reduction solution needs to be purchased separately, resulting in higher costs. Furthermore, the treatment of the waste liquid after copper reduction also increases labor and economic costs. Summary of the Invention

[0004] To address the above problems, the present invention aims to provide a method, a copper reduction solution, and an FPC manufacturing system for using acidic etching waste liquid for copper reduction. Compared with the prior art, the present invention utilizes acidic copper chloride etching waste liquid with the addition of a small amount of citric acid to achieve uniform copper reduction, eliminating the need to purchase expensive copper reduction solutions and treat copper reduction waste liquid separately, thus significantly reducing production costs.

[0005] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for using acidic etching waste liquid to reduce copper content in FPC, comprising the following steps: s1 Obtain acidic etching overflow waste liquid during the circuit etching process, the overflow waste liquid containing copper chloride, hydrochloric acid and chlorate; s2 Add citric acid to the copper-reducing solution and dissolve and mix it evenly. The amount of citric acid added is 1-10 g / L.

[0006] s3 Adjust the temperature of the copper-reducing solution to 15-25℃; s4. The flexible copper-clad laminate is soaked or sprayed with the copper-reducing solution for a certain period of time to reduce the copper foil thickness; s5 Rinse and dry the flexible copper-clad laminate and set it aside for later use.

[0007] In the etching process of FPC circuits, acidic copper chloride etching solution is often used. After etching, the overflow waste liquid is often directly recycled for copper extraction. This overflow waste liquid can still etch the copper layer. Therefore, before copper extraction and recycling, using the overflow waste liquid to reduce copper content can, on the one hand, continue to utilize the "etching of the copper layer" effect of the acidic etching solution, and on the other hand, save on the labor, materials, and waste liquid post-treatment costs of adding a separate copper reduction process to the production line. This is beneficial for cost reduction and efficiency improvement in FPC fine circuit products and has good application prospects in FPC manufacturing processes. Currently, no method for copper reduction using acidic etching overflow waste liquid has been found in existing technology.

[0008] The principle of copper reduction using acidic etching solution in this invention is as follows: During the fabrication of FPC circuit boards, acidic etching is generally performed at a reaction temperature of 40-55℃. Through the following chemical reaction: CuCl2 + Cu → 2CuCl, metallic copper is dissolved and removed after forming cuprous chloride. To inhibit the hydrolysis of cuprous chloride, acid (usually hydrochloric acid) is added to the reaction system to maintain a strongly acidic environment. Furthermore, for the recycling of the acidic etching solution, chlorate and hydrochloric acid are added to the etching solution periodically through the following reaction: 6CuCl + ClO3 - +6HCl → 6CuCl2 + 3H2O + Cl - The product cuprous chloride that enters the etching solution is re-oxidized to copper chloride. After being recycled a certain number of times, the acidic etching solution overflows from the reaction system and becomes waste liquid to be treated. Therefore, the acidic etching overflow waste liquid contains components such as copper chloride, hydrochloride, hydrochloric acid and chlorate.

[0009] The purpose of conventional acid etching is to quickly remove copper foil from the corresponding area to create clear lines. This process often has high requirements for etching rate and etching directionality. However, in the process of copper thickness reduction, an excessively fast etching rate is not conducive to copper thickness control and makes it difficult to ensure copper thickness uniformity. Furthermore, the copper thickness reduction process does not require consideration of etching directionality. Therefore, it is necessary to adjust the relevant process parameters to increase the uniformity of copper reduction and reduce the etching rate in order to obtain a good copper reduction effect.

[0010] s2 Add 1-10 g / L citric acid to the overflow waste liquid, mix well, and form a copper-reducing solution; In this approach, adding an appropriate amount of citric acid improves the uniformity of copper reduction and reduces the etching rate. The principle is explained below: Firstly, it can reduce the concentration difference of the etching solution across the copper foil surface: One reason for uneven etching of copper foil caused by conventional acidic etching solutions is that the etching rate of the copper foil depends on the concentration of free etching solution on the surface. Under spraying or immersion conditions, due to the unevenness of the microstructure of the copper surface or the lack of timely replenishment of effective ingredients, the concentration of copper ions (Cu) in the etching solution can be reduced. 2+ Uneven concentration can lead to localized "over-etching" or "under-etching." After adding citric acid, a small amount of dissociated hydrogen citrate ions (HCit2) are released. - It can combine with some copper ions in high-concentration areas to form weakly stable copper complexes. As the drug solution flows, the copper complexes dissolved in the drug solution move to areas with lower copper ion concentrations and then dissociate and release some copper ions. Through the mechanism of "chelation of copper ions in high-concentration areas and dissociation and release in low-concentration areas", the concentration gradient of copper ions in various places is reduced to a certain extent, which alleviates the problem of uneven copper reduction caused by uneven reaction rates due to concentration differences on the copper foil surface.

[0011] Secondly, it can suppress high concentrations of copper ions (Cu) when pH rises. 2+ and cuprous ions Cu + Hydrolysis: Another reason for uneven copper foil etching caused by conventional acidic etching solutions is that as the copper reduction reaction proceeds, cuprous chloride is continuously produced, rapidly consuming chlorate and hydrochloric acid in the solution, leading to drastic changes in the pH of the solution environment. When the local pH increases, copper ions and cuprous ions undergo hydrolysis to produce basic copper chloride precipitate. The change in copper ion concentration causes inconsistent copper reduction rates in different areas. The hydrolytic precipitate can block the contact between the copper foil and the solution, resulting in under-etching. The excellent buffering effect of citric acid can solve this problem: citric acid stabilizes the pH of the solution within a certain range, inhibiting the hydrolysis reaction; in addition, as the pH rises, the chelating ability of citrate ions increases significantly, forming soluble chelates with most of the high-concentration copper ions in the solution, further preventing the generation of copper ion hydrolysis reaction.

[0012] Third, the formation of an adsorption layer reduces the reaction rate: The multiple carboxyl groups of citric acid can be rapidly adsorbed on the copper foil surface through hydrogen bonding and weak electrostatic interaction, forming an adsorption layer. This layer provides a certain barrier to the contact between copper ions and chloride ions in the solution and the copper foil surface, slowing down the etching reaction rate and making the copper reduction process more controllable.

[0013] In use, citric acid is added to the overflow waste liquid and stirred to dissolve it. The citric acid then dissociates into a small amount of citrate dihydrogen ions (H₂Cit). - HCl (Hydrogen citrate ion) 2- and citrate ions Cit3- As the concentration decreases, all three types of ions can combine with copper ions to form complexes. These complexes exhibit weak stability in acidic environments, showing a dynamic change of dissociation and recombination. Therefore, copper-reducing solutions contain both high concentrations of copper ions and low concentrations of copper ion complexes.

[0014] During copper reduction, the copper foil comes into contact with the copper reduction solution, and the following reaction occurs: High concentrations of copper ions diffuse rapidly, first adsorbing and reacting with metallic copper: Cu 2+ +Cu → 2Cu + (Reaction 1) At this point, copper ions begin to be consumed. Due to the different activities and reaction rates at different points on the copper foil surface, the concentration of copper ions varies. The equilibrium between the dissociation and bonding of the copper ion complex begins to change. Taking the copper-citrate hydrogen ion complex as an example, the following reaction 2 continues to occur: Cu(HCit)⇌Cu 2+ +HCit - (Reaction 2) After a certain period of time, in areas with a smooth microstructure on the copper foil surface, the specific surface area is relatively small, the reaction consumes fewer copper ions, and the concentration of free copper ions in this area remains high. At this time, the copper complex dissociates less copper ions. In areas with an uneven microstructure on the copper foil surface, the specific surface area is larger, the reaction consumes more copper ions, and the concentration of free copper ions in this area decreases faster. Before the copper ions outside the area can diffuse to replenish the area, the copper complex dissociates more copper ions, which can replenish the copper ion concentration difference in this local area and improve the uniformity of all areas. After the etching reaction occurs, the consumed copper ions and copper are converted into cuprous ions, which then react with hydrogen ions and chlorate ions in the solution. 6Cu + +ClO 3- +6H + → 6Cu 2+ +3H₂O+Cl - (Reaction 3) The regeneration of copper ions back into the solution consumes H+ from the reagent. + This causes a rapid increase in the local pH value of the reaction zone, and a rapid increase in the local concentration of copper ions. A large amount of chloride ions are also present in the solution, and the H+ concentration outside the reaction zone... + If diffusion is insufficient, a trace amount of hydrolysis may occur in the reaction area, producing basic copper chloride precipitate that adheres to the copper foil, hindering the continued etching reaction and resulting in localized under-etching. 2Cu 2+ +2Cl -+2H₂O→Cu₂(OH)₂Cl₂↓ (Reaction 4) Citric acid exists in solution in the following chemical equilibrium reaction 5, and can dissociate stepwise to release H+ according to changes in pH value. +， It stabilizes the pH value of the drug solution microenvironment, inhibits hydrolysis, and dissolves trace precipitates. H₃Cit ⇌ H⁺ + H₂Cit⁻ ⇌ H⁺ + HCit²⁻ ⇌ H⁺ + Cit³⁻ (Reaction 5) The dissociated H2Cit⁻, HCit²⁻ and Cit³⁻ can form soluble complexes with high concentrations of copper ions, reducing the copper ion concentration and further inhibiting hydrolysis, while also effectively regulating the copper ion concentration.

[0015] In addition, when copper foil comes into contact with copper-reducing chemicals, due to hydrogen bonding, coordination bond energy, and electrostatic interactions, the dihydrogen citrate ions (H₂Cit) in the chemicals... - HCl (Hydrogen citrate ion) 2- and citrate ions Cit 3- An adsorption layer will form on the surface of the copper foil. Copper ions need to diffuse through the adsorption layer before they come into contact with the copper foil and react. This allows copper ions outside the reaction area more time to diffuse to the vicinity of the copper foil, thus avoiding concentration differences caused by an excessively fast reaction rate to some extent.

[0016] Therefore, the complexing and buffering effects of citric acid can optimize the uniformity of copper layer thinning to a certain extent; its adsorption on the copper foil surface can slow down the reaction rate, making the copper reduction process more controllable.

[0017] In the copper reduction process, in order to better control the uniformity of copper thickness, it is necessary to reduce the etching rate of the copper layer. This invention sets the reaction temperature at 15-25℃ to reduce the diffusion coefficient of copper ions in the reaction system and reduce the problem of insufficient uniformity caused by local concentration fluctuations.

[0018] Immersion and spraying are common etching processes in FPC production. The immersion process involves introducing copper reduction solution into a constant temperature immersion tank and immersing the FPC to be treated into the copper reduction solution to ensure that the FPC is completely submerged. During the immersion process, the FPC can be gently shaken every 1-10 seconds or ultrasonic technology can be used to assist ion diffusion to avoid uneven local concentration of copper reduction solution.

[0019] The spraying process refers to fixing the FPC to be treated in the spraying equipment, adjusting the nozzle pressure, nozzle spacing, spraying angle and spraying flow rate to ensure the uniformity of mass transfer of the copper reduction solution and full coverage of the surface of the copper foil to be treated. During the spraying process, the copper reduction solution is kept circulating and stirred to ensure uniform concentration and temperature.

[0020] Immediately after copper reduction, remove the FPC and rinse it to remove any residual etching solution and prevent further etching by the residual solution. After rinsing, dry it for later use to prevent residual moisture from causing copper foil oxidation.

[0021] The waste liquid generated after the copper reduction process of this invention can still be recycled using the copper extraction process of acid etching waste liquid. The newly introduced citrate ions can be treated together with the original stabilizers and other organic matter in the waste liquid without adding a new waste liquid recycling process.

[0022] Furthermore, the amount of citric acid added is 4-6 g / L, particularly preferably 5 g / L.

[0023] If too little citric acid is added, it will not provide sufficient complexation and buffering effects; if too much is added, it will easily increase the viscosity of the reaction system, which is not conducive to the diffusion of copper ions.

[0024] Furthermore, prior to step S4, the flexible copper-clad laminate is soaked or sprayed with a citric acid-sodium citrate compound solution to achieve pre-complexation of the copper foil surface.

[0025] Because the copper reduction process of this invention is carried out at a relatively low reaction temperature, the diffusion rate of citric acid is relatively slow. This may result in insufficient time for the formation of a surface adsorption layer or a thin adsorption layer due to the microscopic depressions on the copper foil surface during the etching reaction, leading to a more intense initial stage of the reaction and uneven etching. To address this issue, this invention further proposes a pretreatment method involving immersion or spraying the flexible copper-clad laminate with a citric acid-citrate compound solution to form a uniform copper-citric acid complex layer on the copper foil surface beforehand. The reaction principle is as follows: The treated copper foil surface has a trace amount of natural oxide layer (CuO) and free copper ions. When the copper foil comes into contact with a citric acid-sodium citrate compound solution, the hydrogen citrate ions HCit²⁻ in the citric acid-sodium citrate compound solution can form a stable copper complex [CuCit]⁻ with these trace amounts of copper oxide and free copper ions on the copper foil surface. The reaction principle is: Cu²⁺ + HCit²⁻ → [CuCit]⁻ + H⁺.

[0026] The adsorption layer has a certain blocking effect on copper ions, which can regulate the reaction rate. In addition, when the pre-complexed copper foil comes into contact with the copper reduction solution, the copper complex adsorbed on the surface will slowly dissociate in a strong acid environment, releasing copper ions and citrate hydrogen ions. Among them, copper ions participate in the etching reaction, and citric acid continues to participate in complexation, improving the uniformity of the copper reduction process.

[0027] The pH value of the compound solution of citric acid and sodium citrate should not be less than 4.0 to ensure that the dissociation degree of hydrogen citrate ions HCit²⁻ is within the optimal pH range.

[0028] Furthermore, the pre-complexation time is 2-5 minutes.

[0029] The time required for citrate hydrogen ions to reach adsorption equilibrium with the copper foil surface varies depending on the process selection and parameter changes. Immersion process requires a slightly longer time due to the slower ion diffusion rate, and ultrasonic assistance can be used. The cavitation effect of ultrasound can promote the thinning of the liquid boundary layer to facilitate adsorption. Spraying process promotes ion diffusion through the flow of the solution, and the adsorption equilibrium time is relatively shorter than that of immersion process. The specific time varies depending on the spraying pressure, flow rate and other parameters.

[0030] The present invention sets the pre-complexation time to 2-5 minutes to achieve the formation of an adsorption layer by micro-depressions on the copper foil surface, thereby improving the uniformity of copper reduction.

[0031] Furthermore, before step S4, the flexible copper-clad laminate is pretreated by low-pressure spraying with copper-reducing solution so that the temperature difference between the flexible copper-clad laminate and the copper-reducing solution is no more than 2°C.

[0032] Temperature has a significant impact on the etching rate of the copper foil in the flexible copper-clad laminate (CCL) by the copper-reducing solution. If the temperature of the flexible CCL is high when it comes into contact with the copper-reducing solution, and the temperature difference between the flexible CCL and the solution is large, it may cause an excessively high initial etching rate, resulting in uneven etching. Therefore, before etching, this invention employs a low-pressure spray pretreatment on the flexible CCL to reduce the temperature difference between the flexible CCL and the copper-reducing solution, ensuring that the copper-reducing reaction proceeds gently from the beginning of etching.

[0033] Furthermore, in step s3, the temperature of the copper-reducing solution is adjusted to 18-22℃.

[0034] Furthermore, the Cu in the overflow waste liquid 2+ The concentration is 100-150 g / L, and the hydrochloric acid equivalent concentration is 1.5-3 mol / L.

[0035] Furthermore, the copper foil thickness of the flexible copper-clad laminate is no greater than 18 μm.

[0036] Secondly, the present invention provides an FPC copper reduction solution, which is composed of acidic etching overflow waste liquid and citric acid. The acidic etching overflow waste liquid contains copper chloride, hydrochloric acid and chlorate. The Cu²⁺ concentration in the overflow waste liquid is 100-150 g / L, the equivalent concentration of the hydrochloric acid is 1.5-3 mol / L, and the concentration of the citric acid is 1-10 g / L.

[0037] Thirdly, the present invention provides an FPC manufacturing system, comprising: An acid etching apparatus is used to perform acid etching on FPCs and generate overflow waste liquid; A copper reduction solution preparation device includes a pipeline and a citric acid adding device. The pipeline is connected to the acid etching device and is used to receive the overflow waste liquid. The citric acid adding device is used to add citric acid to the overflow waste liquid. Copper reduction device, used to reduce the copper content of flexible copper-clad laminates; The post-processing unit is used to rinse and dry the copper-clad laminate after copper reduction.

[0038] By adopting the above solution, the beneficial effects of the present invention are as follows: 1. The copper reduction method of the present invention has the advantages of moderate rate, good controllability, and uniform copper reduction; 2. This invention effectively solves the problem of uniformity in copper reduction of waste liquid by adding citric acid to provide chelation and buffering effects and controlling low-temperature reaction conditions, thus meeting the process requirements of fine circuit fabrication.

[0039] 3. This invention provides a new copper reduction solution that directly utilizes the overflow waste liquid from acid etching for copper reduction in FPC, replacing expensive hydrogen peroxide or sodium persulfate system solutions, significantly reducing raw material costs and improving production efficiency; 4. It enables the reuse of waste liquid without generating new production waste liquid, thus reducing environmental pressure. 5. A new copper reduction production process route is provided, which is easy to integrate into existing FPC production lines without major equipment modifications.

[0040] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, these descriptions and drawings are only for illustrating the invention and are not intended to limit the scope of protection of the invention in any way. Attached Figure Description

[0041] Figure 1 This is a process flow diagram of an FPC copper reduction method using acidic etching waste liquid according to the present invention. Figure 2 This is a schematic diagram of the five-point sampling positions in the copper reduction uniformity test; Figure 3 This is a schematic diagram of the FPC manufacturing system of the present invention. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] Example 1

[0044] like Figure 1 As shown, this embodiment provides a method for using acidic etching waste liquid to reduce copper content in FPCs, including the following steps: s1 Obtain the acidic etching overflow waste liquid during the circuit etching process. During the acquisition process, the overflow waste liquid is initially filtered to remove suspended solid impurities such as substrate or insoluble metal fragments to avoid scratching the copper foil. The filtered overflow waste liquid is introduced into the soaking tank, and the total amount of waste liquid is enough to completely submerge the flexible copper-clad laminate to be copper-reduced. The concentration of copper ions and hydrochloric acid equivalent in the waste liquid were tested. The results showed that Cu... 2+ The content is 116 g / L, and the hydrochloric acid equivalent is 2.1 mol / L; s2 Add 5g / L citric acid to the overflow waste liquid in the soaking tank, stir until completely dissolved and mixed evenly to form a copper-reducing solution; s3 Adjust the temperature of the copper-reducing solution to 20°C; s4 Prepare a flexible copper-clad laminate to be copper-reduced, the copper foil thickness of the flexible copper-clad laminate is 12μm; the flexible copper-clad laminate has been surface cleaned and dried, and the copper-reducing solution is used to immerse the flexible copper-clad laminate for 30s; After rinsing and drying with S5, a flexible copper-clad laminate with reduced copper content is obtained.

[0045] This embodiment also provides a copper reduction solution, which is composed of acidic etching overflow waste liquid and citric acid. The acidic etching overflow waste liquid contains copper chloride, hydrochloric acid and chlorate. The Cu²⁺ concentration in the overflow waste liquid is 116 g / L, the equivalent concentration of the hydrochloric acid is 2.1 mol / L, and the concentration of the citric acid is 5 g / L.

[0046] This embodiment also provides an FPC manufacturing system, including: The acid etching apparatus is used to perform acid etching on FPC and generate overflow waste liquid. Acid etching usually requires a fast etching rate, and the etching reaction temperature is usually 40-55℃. Therefore, the temperature of the overflow waste liquid generated is also between 40-55℃. A copper reduction solution preparation device includes pipelines, a preparation tank, and a citric acid adding device. The pipelines are connected to the acid etching device and are used to receive the overflow waste liquid and transfer it to the preparation tank. The pipelines include a filtration device to filter suspended solid impurities in the overflow waste liquid, such as substrate debris or insoluble metals, to prevent scratching the copper foil surface. The citric acid adding device is used to add citric acid to the overflow waste liquid. The copper reduction solution preparation device also includes a temperature control device to adjust and control the temperature of the copper reduction solution to 15-25°C. A copper reduction device is used to reduce the copper content of flexible copper-clad laminates. The copper reduction device is an immersion tank in which the flexible copper-clad laminate is immersed in a copper reduction solution. The copper reduction device includes a temperature control device to maintain the temperature of the solution within the required temperature range during the immersion process.

[0047] The post-processing unit is used to rinse and dry the copper-clad laminate after copper reduction.

[0048] Example 2

[0049] The difference from Example 1 is that the flexible copper-clad laminate has a thickness of 18 μm; Example 3

[0050] The difference from Example 1 is that the temperature of the copper-reducing solution was adjusted to 15°C, and the amount of citric acid added was 1 g / L; This embodiment also provides a copper-reducing solution, which differs from Embodiment 1 in that the concentration of citric acid is 1 g / L.

[0051] Example 4

[0052] The difference from Example 1 is that the temperature of the copper-reducing solution was adjusted to 25°C, and the amount of citric acid added was 10 g / L; This embodiment also provides a copper-reducing solution, which differs from Embodiment 1 in that the concentration of citric acid is 10 g / L.

[0053] Example 5

[0054] The difference from Example 1 is that the Cu 2+ The concentration is 100 g / L, the hydrochloric acid equivalent is 1.5 mol / L, and the citric acid addition is 4 g / L; This embodiment also provides a copper-reducing solution, which differs from Embodiment 1 in that the Cu... 2+ The content is 100 g / L, the hydrochloric acid equivalent is 1.5 mol / L, and the concentration of citric acid is 4 g / L.

[0055] Example 6

[0056] The difference from Example 1 is that the Cu 2+ The content is 150 g / L, the hydrochloric acid equivalent is 3.0 mol / L, and the citric acid addition is 6 g / L; This embodiment also provides a copper-reducing solution, which differs from Embodiment 1 in that the Cu... 2+ The content is 150 g / L, the hydrochloric acid equivalent is 3.0 mol / L, and the concentration of citric acid is 6 g / L.

[0057] Example 7

[0058] The difference from Example 1 is that the temperature of the copper-reducing solution is adjusted to 18°C ​​and the soaking time is 60 seconds. Example 8

[0059] The difference from Example 1 is that the temperature of the copper-reducing solution is adjusted to 22°C and the soaking time is 20 seconds. Example 9

[0060] The difference from Example 1 is that, in step S4, the flexible copper-clad laminate is sprayed with the copper-reducing solution for 30 seconds; wherein the spraying pressure is 2.0 kg / cm². 2 ; This embodiment also provides an FPC manufacturing system, which differs from Embodiment 1 in that... The copper reduction device is a spraying device, which includes a liquid storage and delivery module. The liquid storage module has a stirring function to continuously stir the stored liquid to ensure the uniformity of the reaction system. The spraying device also includes a temperature control device to maintain the liquid temperature within the required temperature range during the spraying process.

[0061] Example 10

[0062] The difference from Example 1 is that, before step S4, the flexible copper-clad laminate is pre-complexed using a citric acid-sodium citrate compound solution.

[0063] The citric acid-sodium citrate compound solution has a pH of not less than 4.0 to ensure the degree of dissociation of citrate ions, and is prepared using the following method: Taking a target pH of 4.5 as an example, prepare 0.1 mol / L citric acid solution and 0.1 mol / L sodium citrate solution respectively. Mix the citric acid solution and sodium citrate solution evenly at a volume ratio of 10.3:9.7 and then test the pH value. If the pH is too high, add citric acid solution in small amounts multiple times; if the pH is too low, add sodium citrate solution in small amounts multiple times until the solution reaches the target pH value.

[0064] The flexible copper-clad laminate is immersed in the citric acid-sodium citrate compound solution for 5 minutes for pre-complexation, and then transferred to a copper-reducing solution for further treatment.

[0065] Example 11

[0066] The difference from Example 10 is that, before step S4, the flexible copper-clad laminate is subjected to a pre-complexation treatment by spraying with a citric acid-sodium citrate compound solution at a spraying pressure of 2.0 kg / cm². 2 The pre-complexation time is 2 minutes.

[0067] Example 12

[0068] The difference from Example 9 is that, before step S4, the flexible copper-clad laminate is pretreated with low-pressure spray for 5 seconds to reduce its temperature to within 2°C of the copper-reducing solution temperature. The spray pressure of the low-pressure spray is 0.5 kg / cm². 2 .

[0069] Comparative Example 1 The difference from Example 1 is that citric acid is not added to the overflow waste liquid.

[0070] Comparative Example 2 The difference from Example 1 is that citric acid is not added to the overflow waste liquid, and the temperature of the copper reduction solution is maintained at the conventional etching temperature of 45°C.

[0071] This invention uses a weight reduction method to determine the micro-etching amount H of flexible copper-clad laminates: H = (M1 - M2) / (S * ρ), where: M1: Copper material quality before copper reduction; M2: The quality of the copper material after copper reduction; S: Surface area of ​​copper material; ρ: Density of copper, ρ = 8.96 g / cm³ 3 .

[0072] This invention uses a micro-thickness measuring instrument to detect the copper thickness of flexible copper-clad laminates after the copper reduction step. The detection method is a five-point method: such as... Figure 3 As shown, on a 300mm×300mm substrate, the thickness values ​​are measured at the center point P1 and the four corner points P2, P3, P4, and P5, which are 15mm away from the four edges. The difference between the maximum and minimum thickness values ​​is calculated, which is the copper thickness range.

[0073] The uniformity standard for FPC in this invention is: thickness range ≤ 10% × average thickness.

[0074] Table 1 Micro-etching amount (μm) Average copper thickness (μm) Copper thickness range (μm) Uniformity Example 1 0.86 11.2 0.4 qualified Example 2 0.87 17.1 0.4 qualified Example 3 0.62 11.4 0.4 qualified Example 4 0.89 11.1 0.4 qualified Example 5 0.82 11.2 0.3 qualified Example 6 0.92 11.1 0.4 qualified Example 7 1.68 10.3 0.5 qualified Example 8 0.57 11.4 0.2 qualified Example 9 0.87 11.2 0.3 qualified Example 10 0.85 11.1 0.2 qualified Example 11 0.87 11.1 0.2 qualified Example 12 0.82 11.2 0.2 qualified Comparative Example 1 1.1 10.9 0.8 qualified Comparative Example 2 2.96 9.0 1.5 Unqualified The data in the table shows that: 1. Based on the data analysis of Examples 1 and 2, under the preferred conditions of the present invention, a good copper reduction effect can be achieved for both 18μm and 12μm copper foils, and the copper reduction uniformity is good; 2. According to the data analysis of Examples 3 and 4, the present invention significantly reduces the amount of micro-etching and slightly increases the copper thickness range when the temperature is low and the amount of citric acid added is small, and the copper reduction uniformity is better; when the temperature is high and the amount of citric acid added is large, the amount of micro-etching increases slightly and the copper thickness range increases slightly, and the copper reduction uniformity is better. 3. Based on the data analysis of Examples 5 and 6, the amount of micro-etching increased significantly with the increase of Cu2+ concentration and hydrochloric acid equivalent, but the copper thickness variation did not change much, and the copper reduction uniformity was good. The solution of the present invention has good adaptability to the range of Cu2+ concentration and hydrochloric acid equivalent concentration of acid etching overflow waste liquid; 4. According to the data analysis of Examples 7 and 8, the amount of micro-etching increases with the increase of reaction time, the micro-etching rate does not change significantly, the copper thickness difference increases slightly with the increase of micro-etching amount, and the copper reduction uniformity is qualified. 5. Based on the data analysis of Examples 1 and 9, both the immersion process and the spraying process can achieve good copper reduction uniformity. The spraying process, due to its excellent mass transfer uniformity, achieves even better copper reduction uniformity.

[0075] 6. According to the data analysis of Examples 10-11, pre-complexing the flexible copper-clad laminate by immersion or spraying helps to improve the uniformity of copper reduction. 7. According to the data analysis of Example 12, the pre-spraying method before copper reduction treatment to reduce the temperature of the flexible copper-clad laminate to a temperature difference of no more than 2°C with the copper reduction solution helps to improve the uniformity of copper reduction. 8. According to the data analysis of Comparative Example 1, without adding citric acid, only reducing the temperature of the reaction system significantly increased the copper reduction rate and significantly worsened the copper reduction uniformity. Although the uniformity index was still within the acceptable range, it was close to the critical value. With changes in other factors of the reaction system, the uniformity may become unacceptable. 9. According to the data analysis of Comparative Example 2, without adjusting the temperature, directly using the overflow waste liquid of acid etching for copper reduction significantly increases the copper reduction rate, but also significantly reduces the uniformity of copper reduction and results in poor controllability.

[0076] In summary, the method for using acidic copper chloride etching waste liquid for copper reduction in FPC provided by the present invention can reuse the acidic etching waste liquid discharged from the production line, with a moderate and controllable copper reduction rate and good copper reduction uniformity.

Claims

1. A method for using acidic etching waste liquid to reduce copper content in FPC, characterized in that... Includes the following steps: s1 Obtain acidic etching overflow waste liquid during the circuit etching process, the overflow waste liquid containing copper chloride, hydrochloric acid and chlorate; s2 Add citric acid to the overflow waste liquid and dissolve and mix evenly to form a copper reduction solution, wherein the amount of citric acid added is 1-10 g / L; s3 Adjust the temperature of the copper-reducing solution to 15-25℃; s4. The flexible copper-clad laminate is soaked or sprayed with the copper-reducing solution for a certain period of time; S5 After rinsing and drying the flexible copper-clad laminate, set it aside for later use.

2. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 1, characterized in that, The amount of citric acid added is 4-6 g / L.

3. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 1, characterized in that, Before step S4, the flexible copper-clad laminate is soaked or sprayed with a citric acid-sodium citrate compound solution to achieve pre-complexation of the copper foil surface.

4. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 3, characterized in that, The pre-complexation time is 2-5 minutes.

5. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 1, characterized in that, Before step S4, the flexible copper-clad laminate is subjected to low-pressure pre-spraying treatment with copper-reducing solution so that the temperature difference between the flexible copper-clad laminate and the copper-reducing solution is no more than 2°C.

6. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 1, characterized in that, In step s3, the temperature of the copper-reducing solution is adjusted to 18-22℃.

7. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 1, characterized in that, The copper ion concentration in the overflow waste liquid is 100-150 g / L, and the hydrochloric acid equivalent is 1.5-3.0 mol / L.

8. The method for using acidic etching waste liquid for copper reduction in FPC as described in claim 1, characterized in that, The copper foil thickness of the flexible copper-clad laminate is no greater than 18 μm.

9. A copper-reducing solution, characterized in that, It is composed of acidic etching overflow waste liquid and citric acid. The acidic etching overflow waste liquid contains copper chloride, hydrochloric acid and chlorate. The copper ion concentration in the overflow waste liquid is 100-150 g / L, the equivalent concentration of hydrochloric acid is 1.5-3 mol / L, and the concentration of citric acid is 1-10 g / L.

10. An FPC manufacturing system, characterized in that, include: An acid etching apparatus is used to perform acid etching on FPCs and generate overflow waste liquid; A copper reduction solution preparation device includes a pipeline and a citric acid adding device. The pipeline is connected to the acid etching device and is used to receive the overflow waste liquid. The citric acid adding device is used to add citric acid to the overflow waste liquid. Copper reduction device, used to reduce the copper content of flexible copper-clad laminates; The post-processing unit is used to rinse and dry the copper-clad laminate after copper reduction.

Images