A high-end copper foil surface roughening treatment method for electronic circuits

Abstract

This invention relates to a method for surface roughening of high-end copper foil for electronic circuits, comprising the following steps: sequentially performing acid washing, roughening, blackening, ashing, passivation, and coupling agent coating on raw copper foil, with water washing steps interspersed between these steps, and finally drying and winding. The method is characterized in that the roughening step uses an alkaline plating solution containing copper pyrophosphate. This invention provides an alkaline plating solution for alkaline roughening of raw copper foil, generating grains with lower roughness on the already extremely thin surface of high-end copper foil. The grain size is between 0.02 and 0.1 micrometers. After deposition on the raw foil, the surface roughness of the finished foil increases by approximately 0.2 to 0.3 micrometers, ensuring that the surface roughness of the final product meets the requirements of high-end copper foil while maintaining peel strength.

Description

Technical Field

[0001] This invention belongs to the field of high-end copper foil production technology, and in particular relates to a method for surface roughening treatment of high-end copper foil for electronic circuits. Background Technology

[0002] With the development of communication, cloud computing, cloud storage technologies, and the advancements in Ethernet and cloud servers, PCBs will further evolve towards high-speed / high-frequency directions. However, PCB signal transmission performance will also, to some extent, constrain the development of high-speed transmission technologies. In the 4G era, the single-channel signal transmission rate of PCBs has increased from 10Gbps to 25Gbps, and it is expected to further increase to over 50Gbps in the 5G era. The increasing speed and frequency of signals means that signal transmission is increasingly concentrated on the "surface" of the conductor (known as the skin effect). When the frequency reaches 1GHz, the signal transmission thickness on the conductor surface is only 2.1 micrometers. If the surface roughness of the conductor is 3-5 micrometers, signal transmission only occurs within the roughness range. When the signal transmission frequency increases to 10GHz, the signal transmission thickness on the conductor surface is 0.7 micrometers, and signal transmission occurs even more within the roughness range. Signal transmission within the roughness range leads to increasingly severe standing waves and reflections, resulting in longer signal transmission paths and increased losses.

[0003] Due to the skin effect, if conventional (STD) copper foil continues to be used in high-speed PCBs, the signal distortion caused by the skin effect will become increasingly severe as the signal transmission frequency increases. Therefore, the application of low-roughness copper foil in current high-speed materials is becoming increasingly widespread. For example, Mid-Loss and Low-Loss materials both use Reverse-Flattened Copper Foil (RTF) as standard copper foil; while Very Low-Loss materials also use RTF copper foil as standard, PCB designs now mostly use High-Voltage Low-Profile Copper Foil (HVLP); and for Ultra-Low-Loss materials, HVLP copper foil has become standard. The surface morphology of STD, RTF, and HVLP copper foil can be observed using scanning electron microscopy and metallographic microscopy. The surface roughness (Rz) of STD copper foil is approximately 5 micrometers, and the smooth surface roughness is approximately 3 micrometers; the surface roughness of RTF copper foil is approximately 3 micrometers for both surface roughness and smoothness; and the surface roughness of HVLP copper foil is within 2 micrometers for both smooth and surface roughness. With technological advancements, the surface roughness of copper foil continues to decrease.

[0004] Currently, the industry faces challenges in achieving very fine (copper bud size ≤ 0.5 micrometers) and uniform roughening treatment on the smooth or rough surface of electrolytic raw foil during production of the aforementioned high-end copper foil. In existing technologies, the roughening of traditional standard copper foil (STD) and high-temperature high-elongation copper foil (HTE) consists of two parts: roughening and curing, both of which are acidic systems. Roughening involves low copper and high acid content, with Cu... 2+The concentration is generally 5–15 g / L, the H2SO4 concentration is generally 130–150 g / L, and the temperature is 25–30℃. The purpose is to initially form copper nodules, which are loose and not dense due to the accumulation of grains. Solidification results in a high-copper, low-acid Cu... 2+ The concentration is typically 40–80 g / L, the H₂SO₄ concentration is typically 100–120 g / L, and the temperature is 45–55℃. The purpose is to fill the loose and non-dense copper nodules from the previous step, making them fuller. This method results in very large copper buds in the final product. The copper buds obtained by this surface treatment process are all larger than 0.8 micrometers, with a maximum size of 2 micrometers, which clearly cannot meet the technical requirements of high-end copper foil. Therefore, it is necessary to develop a stable, reliable, high-quality, and high-efficiency surface treatment process to upgrade products and fill market gaps. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for roughening the surface of high-end copper foil for electronic circuits, so that the copper bud size on the surface of the high-end copper foil after surface treatment is less than 0.8 micrometers.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A method for surface roughening of high-end copper foil for electronic circuits is provided, comprising the following steps: sequentially performing acid washing, roughening, blackening, ashing, passivation, and coupling agent coating on raw copper foil, with water washing steps interspersed between each step, and finally drying and winding. The roughening step uses an alkaline plating solution containing copper pyrophosphate, wherein the alkaline plating solution includes Cu₂P₂O₇·4H₂O with a concentration range of 10–30 g / L; K₄P₂O₇ with a concentration range of 150–350 g / L; and additives. The pH range of the alkaline plating solution is 8.5 ± 0.5. The process parameters for the roughening step are controlled as follows: temperature range of 30–50℃; and liquid supply flow rate range of 5–15 m³ / L. 3 / h; current density range is 0.5~1.5A / dm 2 .

[0007] Furthermore, the additives in the alkaline plating solution are ammonia or ammonium salt compounds, and the amount added is 1-3 ml / L, based on ammonia water (25%).

[0008] Furthermore, the blackening step is blackening with nickel plating; the ashing step is ashing with zinc plating; and the passivation step is passivation with chromium plating.

[0009] Furthermore, the pickling, roughening, blackening, ashing, passivation, coupling agent coating, drying, and washing steps are respectively carried out in pickling tank, washing tank one, roughening tank one, roughening tank two, washing tank two, blackening tank, washing tank three, ashing tank, washing tank four, passivation tank, washing tank five, coupling agent coating tank, and drying oven, which are arranged at intervals.

[0010] Furthermore, the raw copper foil is transferred through a winding system and sequentially undergoes pickling, roughening, blackening, ashing, passivation, coupling agent coating, and drying steps. The winding system includes an unwinding roller, a transition roller, a conductive roller, a liquid submersible roller, a tension roller, a squeeze roller, a pressure roller, and a take-up roller. The tension setting range of the tension roller is 10–80 kg, and the tension taper range is 5–15%.

[0011] Beneficial effects

[0012] This invention provides an alkaline plating solution for alkaline roughening treatment of raw copper foil, generating grains with even lower roughness on the already extremely thin surface of high-end copper foil. The grain size is between 0.02 and 0.1 micrometers. After deposition on the raw foil, the surface roughness of the finished foil increases by approximately 0.2 to 0.3 micrometers, ensuring that the surface roughness of the final product meets the requirements of high-end copper foil while maintaining peel strength. In contrast, conventional acid plating solution treatment results in grains with a minimum size of 0.2 micrometers, and a cumulative increase in surface roughness of more than 0.8 micrometers.

[0013] Traditional surface roughening treatment of STD and HTE copper foil typically involves a three-stage roughing and three-stage curing process, requiring six tanks in total, including several water washing tanks. This invention achieves sufficient grain formation with only two roughening tanks. Reducing the number of tanks significantly lowers production costs, including savings on pump power and water treatment costs.

[0014] The alkaline roughening treatment method provided by this invention can simultaneously meet the requirements of smooth surface treatment of RTF, rough surface treatment of HVLP, and electroplating thickening of ultra-thin copper layer of carrier copper foil. It can produce high-end copper foil of different specifications on the same line, ensuring production efficiency and having a wider range of applications. Attached Figure Description

[0015] Figure 1 This is a flowchart of a method for surface roughening of high-end copper foil used in electronic circuits.

[0016] Figure 2 This is an electron microscope image of Example 1.

[0017] Figure 3 This is an electron microscope image of Example 2.

[0018] Figure 4 This is an electron microscope image of Example 3. Detailed Implementation

[0019] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0020] This invention provides a method for surface roughening of high-end copper foil for electronic circuits, specifically including the following steps:

[0021] Step 1: Unwind the roll

[0022] A roll of raw electrolytic copper foil is placed at the unwinding end of the surface treatment machine's winding system. The foil is then smoothly wound onto the various rollers of the equipment via a guide belt, with the surface to be treated facing downwards. A tension roller is located after the unwinding roller; the tension taper can be adjusted to ensure constant and adjustable tension throughout the winding process. The raw copper foil is then transferred through the winding system and sequentially undergoes pickling, roughening, blackening, ashing, passivation, coupling agent coating, and drying steps.

[0023] Step 2: Surface Treatment

[0024] The raw foil is continuously transferred between the unwinding and rewinding rollers. The first wave of transfer involves acid pickling pretreatment to remove the oxide layer and dirt from the surface of the electrolytic raw foil to be treated. This is followed by roughening treatment, which crystallizes and grows copper buds on the surface of the electrolytic raw foil to improve its peel resistance. Next, a blackening nickel plating-ashing zinc plating-passivation chromium plating treatment is performed to enhance the chemical resistance of the copper foil. Finally, after coupling agent coating and oven drying, it is wound onto the rewinding roller. Water washing is interspersed between the acid pickling, roughening, blackening, ashing, passivation, and silane coating processes to remove residual solution and dirt from the previous treatment stages. The coupling agent coating uses silane coating.

[0025] Step 3: Roll up

[0026] The finished copper foil is automatically wound onto a take-up roller located at the end of the drying oven, and is wound up according to the production situation.

[0027] The pickling, washing, blackening, ashing, passivation, silane coating, and oven drying processes in step two are identical to the commonly used preparation methods for standard copper foil (STD) and high-temperature high-elongation copper foil (HTE) in the industry. However, the roughening treatment method in step two differs from the commonly used methods for standard copper foil (STD) and high-temperature high-elongation copper foil (HTE). The roughening treatment in step two employs an alkaline plating solution system of copper pyrophosphate. This alkaline plating solution includes Cu₂P₂O₇·4H₂O at a concentration range of 10–30 g / L; K₄P₂O₇ at a concentration range of 150–350 g / L; and additives. The pH of the alkaline plating solution is adjusted to 8.5 ± 0.5 using H₄P₂O₇ and KOH. The process parameters for the roughening step are controlled as follows: temperature range of 30–50℃; and supply flow rate range of 5–15 m³ / L. 3 / h; current density range is 0.5~1.5A / dm 2 .

[0028] Furthermore, the winding system described in step one includes a series of rollers such as unwinding rollers, transition rollers, conductive rollers, submersible rollers, tension rollers, extrusion rollers, pressure rollers, and take-up rollers. The arrangement and number of each roller can vary depending on the arrangement of the trough and the actual situation.

[0029] Furthermore, the winding system described in step one also includes a tension control system. By setting the tension value and tension taper on the control panel, the speed of the intermediate servo motor is adjusted to achieve constant, stable, and uniform tension among the rollers in the winding system. The tension setting range is 10–80 kg, and the tension taper range is 5–15%.

[0030] Furthermore, the additive is an ammonia or ammonium salt compound, and the amount added is 1 to 3 mL / L, calculated as ammonia water (25%).

[0031] Example 1

[0032] A roll of RTF electrolytic green foil (smooth surface roughness ≤ 1.2 micrometers) is placed at the unwinding end and wound onto the various roller systems of the surface treatment equipment by a guide belt. It sequentially passes through an acid pickling tank, a water washing tank (1), a roughening tank (1), a roughening tank (2), a water washing tank (2), a blackening tank, a water washing tank (3), an ashing tank, a water washing tank (4), a passivation tank, a water washing tank (5), a coupling agent coating tank, and an oven to treat the smooth surface of the green foil. Except for roughening, the process parameters for the steps are as follows: Acid pickling: pure aqueous solution of H2SO4 with a concentration of 140 g / L; Blackening: Co... 2+ The concentration is 1 g / L, Ni 2+ The concentration was 0.5 g / L, the K4P2O7 concentration was 50 g / L, the pH was 10, and the temperature was 40℃; ashing: Zn 2+ The concentration is 2 g / L, Ni 2+The concentration was 1 g / L, the K4P2O7 concentration was 110 g / L, the pH was 10.2, and the temperature was 40℃; passivation: Cr 6+ The concentration was 1 g / L, pH was 12, and the temperature was 30℃; the coupling agent was silicon with a concentration of 2500 ppm; the oven temperature was 180℃. The intermediate tension was set at 50 kg, and the tension taper was 10%.

[0033] In the roughening step, the concentration of Cu₂P₂O₇·4H₂O in the alkaline plating solution is 19 g / L, the concentration of K₄P₂O₇ is 250 g / L, and the content of the additive NH₃·H₂O is within the range of 2 ml / L. After process adjustment, the pH is 8.7, the temperature is 40℃, and the solution flow rate is 10 m³ / L. 3 / h, current density range is 0.5A / dm 2 .

[0034] Example 2

[0035] A roll of HVLP electrolytic green foil (surface roughness ≤ 1.0 micrometers) is placed at the unwinding end and wound onto the various roller systems of the surface treatment equipment by a guide belt to treat the rough surface of the green foil. It sequentially passes through an pickling tank, a water washing tank 1, a roughening tank 1, a roughening tank 2, a water washing tank 2, a blackening tank, a water washing tank 3, an ashing tank, a water washing tank 4, a passivation tank, a water washing tank 5, a coupling agent coating tank, and an oven to treat the smooth surface of the green foil. Except for roughening, the process parameters for the steps are as follows: Pickling: pure aqueous solution of H2SO4 with a concentration of 140 g / L; Blackening: Co... 2+ The concentration is 1 g / L, Ni 2+ The concentration was 0.5 g / L, the K4P2O7 concentration was 50 g / L, the pH was 10, and the temperature was 40℃; ashing: Zn 2+ The concentration is 2 g / L, Ni 2+ The concentration was 1 g / L, the K4P2O7 concentration was 110 g / L, the pH was 10.2, and the temperature was 40℃; passivation: Cr 6+ The concentration was 1 g / L, pH was 12, and the temperature was 30℃; the coupling agent was silicon with a concentration of 2500 ppm; the oven temperature was 180℃. The intermediate tension was set at 50 kg, and the tension taper was 10%.

[0036] In the roughening step, the concentration of Cu₂P₂O₇·4H₂O in the alkaline plating solution is 19 g / L, the concentration of K₄P₂O₇ is 250 g / L, and the content of the additive NH₃·H₂O is within the range of 2 ml / L. After process adjustment, the pH is 8.7, the temperature is 40℃, and the solution flow rate is 10 m³ / L. 3 / h, current density range is 1A / dm 2 .

[0037] Example 3

[0038] A roll of RTF electrolytic green foil (surface roughness ≤ 1.2 micrometers) is placed at the unwinding end and wound onto the various roller systems of the surface treatment equipment by a guide belt to treat the smooth surface of the green foil. It sequentially passes through an acid pickling tank, a water washing tank (1), a roughening tank (1), a roughening tank (2), a water washing tank (2), a blackening tank, a water washing tank (3), an ashing tank, a water washing tank (4), a passivation tank, a water washing tank (5), a coupling agent coating tank, and an oven to treat the smooth surface of the green foil. Except for roughening, the process parameters for the steps are as follows: Acid pickling: pure aqueous solution of H2SO4 with a concentration of 140 g / L; Blackening: Co... 2+ The concentration is 1 g / L, Ni 2+ The concentration was 0.5 g / L, the K4P2O7 concentration was 50 g / L, the pH was 10, and the temperature was 40℃; ashing: Zn 2+ The concentration is 2 g / L, Ni 2+ The concentration was 1 g / L, the K4P2O7 concentration was 110 g / L, the pH was 10.2, and the temperature was 40℃; passivation: Cr 6+ The concentration was 1 g / L, pH was 12, and the temperature was 30℃; the coupling agent was silicon with a concentration of 2500 ppm; the oven temperature was 180℃. The intermediate tension was set at 50 kg, and the tension taper was 10%.

[0039] In the roughening step, the concentration of Cu₂P₂O₇·4H₂O in the alkaline plating solution is 19 g / L, the concentration of K₄P₂O₇ is 250 g / L, and the content of the additive NH₃·H₂O is within the range of 2 ml / L. After process adjustment, the pH is 8.7, the temperature is 40℃, and the solution flow rate is 10 m³ / L. 3 / h, current density range is 1.5A / dm 2 .

[0040] The finished foils of the above embodiments were subjected to conventional surface roughness, tensile strength, elongation and peel strength tests, and the results are shown in the table below.

[0041]

[0042] Note: The basic parameter requirements for various high-end copper foils are as follows:

[0043] RTF: Roughness ≤ 2.5 micrometers, tensile strength at room temperature ≥ 29 kg / mm² 2 Elongation at room temperature ≥15%, tensile strength at high temperature ≥17kg / mm 2 High temperature elongation ≥8%, peel strength ≥0.71kg / cm.

[0044] HVLP: Roughness ≤ 2.5 micrometers, tensile strength at room temperature ≥ 29.4 kg / mm² 2Elongation at room temperature: 7–25%; Tensile strength at high temperature: ≥16.7 kg / mm² 2 High temperature elongation 5-20%, peel strength ≥0.4kg / cm.

[0045] Conclusion: Based on experimental data and scanning electron microscopy morphology, the current density ranges from 0.5 to 1.5 A / dm² in the basic roughening system. 2 At the same time, all physical property data can meet the requirements of RTF or HVLP. Comparing the roughness Rz of the green foil and the finished foil, it can be found that, compared with the traditional surface treatment method, this method successfully miniaturizes, homogenizes and densifies the grown grains. The Rz of the embodiment is between 0.2 and 0.3, which is effectively controlled within a reasonable range.

Claims

1. A method for surface roughening of high-end copper foil for electronic circuits, comprising the following steps: sequentially performing acid pickling, roughening, blackening, ashing, passivation, and coupling agent coating on raw copper foil, with water washing steps interspersed between the steps, and finally drying and winding, characterized in that, The roughening step employs an alkaline plating solution containing copper pyrophosphate. The alkaline plating solution comprises Cu₂P₂O₇·4H₂O at a concentration ranging from 10 to 30 g / L; K₄P₂O₇ at a concentration ranging from 150 to 350 g / L; and additives. The pH range of the alkaline plating solution is 8.5 ± 0.

5. The process parameters for the roughening step are controlled as follows: temperature range of 30–50 °C; and solution flow rate range of 5–15 m³ / L. 3 / h; current density range is 0.5~1.5A / dm 2 , The additive in the alkaline plating solution is ammonia water, and the amount added is 1-3 ml / L based on ammonia water.

2. The method for surface roughening of high-end copper foil for electronic circuits according to claim 1, characterized in that, The blackening step is blackening and nickel plating; the ashing step is ashing and zinc plating; the passivation step is passivation and chromium plating.

3. The method for surface roughening of high-end copper foil for electronic circuits according to claim 1, characterized in that, The pickling, roughening, blackening, ashing, passivation, coupling agent coating, drying, and washing steps are respectively carried out in the pickling tank, washing tank 1, roughening tank 1, roughening tank 2, washing tank 2, blackening tank, washing tank 3, ashing tank, washing tank 4, passivation tank, washing tank 5, coupling agent coating tank, and drying oven, which are set at intervals.

4. The method for surface roughening of high-end copper foil for electronic circuits according to claim 3, characterized in that, The raw copper foil is transferred through a winding system and sequentially undergoes pickling, roughening, blackening, ashing, passivation, coupling agent coating, and drying steps. The winding system includes an unwinding roller, a transition roller, a conductive roller, a liquid submersible roller, a tension roller, a squeeze roller, a pressure roller, and a take-up roller. The tension setting range of the tension roller is 10–80 kg, and the tension taper range is 5–15%.

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