Resistance copper foil with high peel strength and uniform sheet resistance value and preparation method thereof

Abstract

The invention relates to the technical field of electronic copper foils, in particular to a resistance copper foil with high peel strength and uniform sheet resistance and a preparation method thereof. The resistance copper foil with high peel strength has high roughness, and the binding force between the resistance copper foil and a base material can be remarkably enhanced, so that the use stability of a printed circuit board is improved. However, the square resistance value uniformity of the high-roughness resistance copper foil is always a technical difficulty. The sheet resistance uniformity of the resistance copper foil is effectively improved by optimizing the crude foil process, the rough curing process and the nickel-phosphorus layer deposition process, so that the resistance copper foil meets the application standard of the resistance copper foil.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic copper foil, and in particular to a high peel strength and uniform sheet resistance resistance copper foil and a preparation method thereof. BACKGROUND

[0002] With the application of 5G communication technology and the rapid increase of high-speed and high-performance electronic products, the development of printed circuit boards (PCB) tends to be small, easy to package, high frequency and high speed. The mounting of traditional passive devices increases the number of solder pads on the surface of the printed circuit board (PCB), reduces the available surface area of the printed circuit board (PCB), and increases the parasitic effect between the solder pads. This causes unstable high-frequency signal transmission.

[0003] To solve the above problems, on the basis of electronic device miniaturization, ultra-thin type and printed circuit board (PCB) pattern high precision, thin multi-layer, embedded device built-in technology is developed, a large number of passive and active devices are embedded into the printed circuit board (PCB), which can integrate the devices, improve the effective packaging area of the printed circuit board (PCB), shorten the length of the device interconnection line, improve the electrical characteristics, improve the packaging reliability and product integration and reduce the cost. Among them, the resistance is one of the most important passive components. Using resistance copper foil can embed passive components into the printed circuit board, which is an important aspect of the development of printed circuit boards. This type of buried resistance circuit board is mainly used in communication equipment and aerospace equipment, and the peel strength and sheet resistance precision of the resistance copper foil are high. The difference in sheet resistance should be controlled within ±10%, therefore, it is urgent to study a method for improving the peel strength of the resistance copper foil while ensuring the uniformity of the sheet resistance, and further evaluate the performance parameters of the resistance copper foil.

[0004] For example, patent number CN201810001370.5 relates to a manufacturing method for a copper foil and a circuit board assembly for high-frequency signal transmission. The method first forms a green foil layer by electrolysis process, and the green foil layer has a specific surface; then, a roughening treatment layer is formed on the surface, and the layer contains a plurality of copper tumor structures. However, after searching a plurality of related patents, it is found that the existing technology has not yet provided an effective solution to improve the uniformity of the sheet resistance of high-roughness resistance copper foil. SUMMARY

[0005] In view of the deficiencies in the prior art, the present application provides a method for preparing a resistance copper foil with high peel strength and uniform sheet resistance.

[0006] The specific preparation method comprises the following steps: Step 1, green foil process: An additive is added to the green foil electrolyte, and the additive is selected from one or more of cerium sulfate, polyethylene glycol, and disodium salt of dithiobis-1-propane sulfonate; the addition amount of the additive is 6-20 mg / L; The polishing brush is used to polish the cathode roller, the mesh number of the polishing brush is 350-800 meshes, the light surface roughness of the obtained copper foil is controlled in 1.3-1.6 μm, and the rough surface roughness is controlled in 3.6-4.3 μm; The green foil electrolysis is carried out under the process conditions of current 60000-70000 A and linear speed 6.5-7.5 m / min; In the preparation process of the green foil, the additive has a great influence on the quality and performance parameters of the green foil. Because the common additive has many exposure problems, it is difficult to meet the needs of new products. In order to further improve the performance of the product, an additive with superior performance needs to be developed. The additive used in the green foil electrolyte in the present application is cerium sulfate salt or polyethylene glycol or disodium salt of dithiobis-1-propane sulfonate or a composite of the above-mentioned several, which can promote the uniformity and densification of the coating. The amount of additive is controlled in 2-15 mg / L, and the amount of additive is adjusted to obtain green foils with uniform size and regular distribution of mountain shape. Because the light surface of the green foil is in contact with the cathode roller, the uniformity of the light surface roughness directly affects the preferred orientation growth of the green foil crystal, and the light surface roughness is positively correlated with the rough surface roughness. The polishing brush is used to polish the cathode roller before each green foil production, and the light surface roughness, gloss and light surface roughness of the green foil are controlled.

[0007] Step two, rough solidification process: The rough solidification process includes roughening treatment, growth of copper crystal nucleus on the green foil mountain, and solidification treatment to make the crystal nucleus grow and not easy to fall off. Improving the morphology, size and uniformity of the rough solidified copper tumor is very helpful to improve the sheet resistance uniformity of high peel-resistant copper foil.

[0008] In order to meet the requirements of high peel-resistant resistance copper foil, rough solidified copper tumors are deposited on green foils with certain roughness. By increasing the number of rough solidified copper tumors and controlling the appropriate size of the copper tumors, the surface area of the resistance copper foil is increased, thereby improving the physical bonding force between the resistance copper foil and the substrate. The uniformity of the number and size of the roughening and solidification copper tumors will directly affect the uniform deposition of the nickel-phosphorus layer. Therefore, the adjustment method of the total current of roughening treatment and the total current of solidification treatment is also a key technology.

[0009] A two-stage or more than two-stage current treatment mode is adopted, wherein the total current of the roughening section is 4500-5500 A, and the total current of the solidification section is 5500-6800 A; Step three, nickel-phosphorus layer deposition process: A nickel-phosphorus alloy layer is deposited on the surface of the copper foil after roughening and solidification by chemical plating; The plating solution composition includes: nickel ions 60-70 g / L, phosphorous acid 15-25 g / L, boric acid 55-65 g / L; The iron sheet is attached to the copper foil, plating is carried out at a temperature of 75-90 ℃, and the plating solution is kept in self-circulating flow, and the nickel-phosphorus layer is plated on the surface of the copper tumor layer formed by rough solidification. The high peel resistance copper foil in this invention has a high roughness. When using the electroplating method for the nickel-phosphorus layer, there is the influence of tip discharge, resulting in more nickel-phosphorus layer deposition at the tips, leading to uneven nickel-phosphorus layer thickness. This affects the uniformity of the sheet resistance value of the high peel resistance copper foil, making it difficult to meet the required sheet resistance accuracy. Therefore, this invention develops a chemical nickel-phosphorus layer production process that avoids the influence of the tip effect during electroplating.

[0010] Step 4, Silane treatment process: A silane coupling agent is used to treat the surface of copper foil after nickel-phosphorus layer treatment. The silane coupling agent is selected from one or more of aminosilane, vinylsilane, and epoxysilane. After hydrolysis of silane, silanol groups are formed and coated on the surface of the resistive copper foil. They can form chemical bonds with both the metal and the substrate at the same time, which can improve the adhesion between the resistive copper foil and the substrate.

[0011] Furthermore, in step one, cerium sulfate is selected as an additive for the raw foil electrolyte, with an additive dosage of 15-20 mg / L, and a polishing brush of 600-800 mesh is used.

[0012] Furthermore, in step two, the mass ratio of copper to acid in the electrolyte is controlled to be 1:9 to 1:10, and the electroplating time is 15 to 25 seconds. This ensures precise control of the polarization and deposition rate of the electroplating solution.

[0013] Furthermore, the electroless plating process in step three takes 50–70 minutes.

[0014] Furthermore, in step four, the coating method is spraying or immersion.

[0015] Furthermore, in step four, the preferred silane coupling agent is a vinylsilane solution with a concentration of 8% to 12%. Optimizing the concentration achieves the best film-forming effect and economic benefits, while avoiding excessive concentration that could lead to multilayer deposition and negatively impact performance.

[0016] This invention discloses a method for improving the uniformity of sheet resistance of high peel resistance copper foil. To obtain high peel resistance copper foil, the raw foil needs to maintain a certain roughness. As a substrate, the surface uniformity of the raw foil directly affects the uniformity of sheet resistance of the resistive layer. The parameters of the raw foil that need to be controlled include smooth surface roughness and gloss, rough surface roughness, morphology of the mountain-shaped area, number of complete mountain-shaped areas, and interface expansion ratio.

[0017] Compared with existing technologies, this invention has the following advantages: the resistive copper foil achieves both high peel strength and uniform sheet resistance. During downstream processing of embedded resistor printed circuit boards, the sheet resistance fluctuation of the nickel-phosphorus resistor layer is small, resulting in high product stability. Attached Figure Description

[0018] Figure 1This is a mountain-shaped morphology diagram after the foil-making process in Embodiment 1 of the present invention; Figure 2 This is a morphological image of the copper nodule after the coarse curing process in Embodiment 1 of the present invention. Detailed Implementation

[0019] The invention can be further understood through the specific embodiments and comparative embodiments given below. However, they are not intended to limit the invention.

[0020] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention can be purchased commercially.

[0021] Example 1 (1) Foil production process The electrolyte for the raw foil used a copper ion concentration of 80 g / L and a sulfuric acid concentration of 100 g / L. Cerium sulfate was selected as the additive for the raw foil electrolyte, with an additive dosage of 6 mg / L. A 400-mesh polishing brush was used, with a smooth surface roughness of 1.5 μm and a rough surface roughness of 4.0 μm. The current was 65000 A, and the line speed was 7.0 m / min. A total of 161 complete mountain shapes were formed, with an interface expansion ratio of 14%. The mountain shape morphology is as follows... Figure 1 .

[0022] (2) Coarse curing process To ensure a sufficient number and uniform distribution of copper nodules, the total roughening current was 4500A; the total curing current was controlled at 5500A, the copper-acid ratio at 1:10, and the electroplating time at 20s, allowing the copper crystal nuclei to grow and preventing them from easily detaching. The roughness after rough curing was 5.8μm. The morphology, size, and uniformity of the rough-cured copper nodules were as follows: the average size of the nodules was 1.68μm, the nodules were densely packed, and the morphology of the nodules was as follows... Figure 2 As shown.

[0023] (3) Nickel-phosphorus layer deposition process The electroless plating method was selected, with a nickel ion concentration of 65 g / L, phosphorous acid concentration of 20 g / L, and boric acid concentration of 60 g / L. A thin iron sheet was attached to a copper foil, and the solution was allowed to circulate at 75°C to deposit the nickel-phosphorus layer onto the surface of the coarsely cured copper nodule layer. The electroless plating process lasted for 50 minutes.

[0024] (4) Silane process 8% vinyl silane is applied evenly to the surface of the resistive copper foil using a spraying method, and then the product is finally rolled up.

[0025] Example 2 (1) Foil production process The electrolyte for the raw foil was a solution with a copper ion concentration of 80 g / L and a sulfuric acid concentration of 100 g / L. A mixture of cerium sulfate and disodium dithiobis-1-propanesulfonate was selected as the electrolyte additive, with a cerium sulfate concentration of 6 mg / L and a disodium dithiobis-1-propanesulfonate concentration of 10 mg / L. A 300-mesh polishing brush was used, achieving a smooth surface roughness of 1.6 μm and a rough surface roughness of 4.3 μm. The current was 65000 A, and the linear speed was 7.0 m / min. A total of 180 complete mountain-shaped patterns were formed, with an interface expansion ratio of 16%.

[0026] (2) Coarse curing process To ensure a sufficient number of copper nodules with uniform distribution, the total roughening current was 5500A; the total curing current was controlled at 6500A, the copper-acid ratio was 1:9, and the electroplating time was 20s. This allowed the copper crystal nuclei to grow and prevented them from easily detaching. The roughness after rough curing was 6.1μm. The average size of the copper nodules was 2.30μm.

[0027] (3) Nickel-phosphorus layer deposition process The electroless plating method was selected, with a nickel ion concentration of 65 g / L, phosphorous acid concentration of 20 g / L, and boric acid concentration of 60 g / L. A thin iron sheet was attached to a copper foil, and the solution was allowed to circulate at 80°C to deposit the nickel-phosphorus layer onto the surface of the coarsely cured copper nodule layer. The electroless plating process lasted for 55 minutes.

[0028] (4) Silane process 10% vinyl silane is applied evenly to the surface of the resistive copper foil using a spraying method, and then the product is finally rolled up.

[0029] Example 3 (1) Foil production process The electrolyte for the raw foil used a copper ion concentration of 80 g / L and a sulfuric acid concentration of 100 g / L. Cerium sulfate was selected as the additive for the raw foil electrolyte, with an additive dosage of 15 mg / L. A 600-mesh polishing brush was used, with a smooth surface roughness of 1.3 μm and a rough surface roughness of 3.8 μm. The current was 65000 A, and the line speed was 7.0 m / min. A total of 145 complete mountain shapes were formed, with an interface expansion ratio of 13%.

[0030] (2) Coarse curing process To ensure a sufficient number of copper nodules with uniform distribution, the total roughening current was 4800A; the total curing current was controlled at 6000A, the copper-acid ratio was 1:10, and the electroplating time was 20s. This allowed the copper crystal nuclei to grow and prevented them from easily detaching. The roughness after rough curing was 5.6μm. The average size of the copper nodules was 1.86μm.

[0031] (3) Nickel-phosphorus layer deposition process The electroless plating method was selected, with a nickel ion concentration of 65 g / L, phosphorous acid concentration of 20 g / L, and boric acid concentration of 60 g / L. A thin iron sheet was attached to a copper foil, and the solution was allowed to circulate at 85°C to deposit a nickel-phosphorus layer onto the surface of the coarsely cured copper nodule layer. Electroless plating was performed for 60 minutes.

[0032] (4) Silane process 10% vinyl silane is applied evenly to the surface of the resistive copper foil using a spraying method, and then the product is finally rolled up.

[0033] Example 4 (1) Foil production process The electrolyte for the raw foil used a copper ion concentration of 80 g / L and a sulfuric acid concentration of 100 g / L. Cerium sulfate was selected as the additive for the raw foil electrolyte, with an additive dosage of 20 mg / L. An 800-mesh polishing brush was used, with a smooth surface roughness of 1.3 μm and a rough surface roughness of 3.6 μm. The current was 65000 A, and the linear speed was 7.0 m / min. A total of 150 complete mountain shapes were formed, with an interface expansion ratio of 12%.

[0034] (2) Coarse curing process To ensure a sufficient number of copper nodules with uniform distribution, the total roughening current was 5500A; the total curing current was controlled at 6800A, the copper-acid ratio was 1:9, and the electroplating time was 20s. This allowed the copper crystal nuclei to grow and prevented them from easily detaching. The roughness after rough curing was 5.7μm. The average size of the copper nodules was 2.35μm.

[0035] (3) Nickel-phosphorus layer deposition process The electroless plating method was selected, with nickel ion concentration of 65 g / L, phosphorous acid concentration of 20 g / L, and boric acid concentration of 60 g / L. A thin iron sheet was attached to a copper foil, and the solution was allowed to circulate at 90°C to deposit the nickel-phosphorus layer onto the surface of the coarsely cured copper nodule layer. The electroless plating process lasted for 70 minutes.

[0036] (4) Silane process 12% vinyl silane is applied evenly to the surface of the resistive copper foil using a spraying method, and then the product is finally rolled up.

[0037] Example 5 (1) Foil production process The electrolyte for the raw foil used a copper ion concentration of 80 g / L and a sulfuric acid concentration of 100 g / L. Polyethylene glycol was selected as the additive for the raw foil electrolyte, with an additive dosage of 15 mg / L. A 600-mesh polishing brush was used, with a smooth surface roughness of 1.3 μm and a rough surface roughness of 3.8 μm. The current was 60,000 A, and the line speed was 6.5 m / min. A total of 145 complete mountain shapes were formed, with an interface expansion ratio of 13%.

[0038] (2) Coarse curing process To ensure a sufficient number of copper nodules with uniform distribution, the total roughening current was 4800A; the total curing current was controlled at 6000A, the copper-acid ratio was 1:10, and the electroplating time was 15s. This allowed the copper crystal nuclei to grow and prevented them from easily detaching. The roughness after rough curing was 5.5μm. The average size of the copper nodules was 1.84μm.

[0039] (3) Nickel-phosphorus layer deposition process The electroless plating method was selected, with a nickel ion concentration of 60 g / L, phosphorous acid concentration of 15 g / L, and boric acid concentration of 55 g / L. A thin iron sheet was attached to a copper foil, and the solution was allowed to circulate at 85°C to deposit a nickel-phosphorus layer onto the surface of the coarsely cured copper nodule layer. Electroless plating was performed for 60 minutes.

[0040] (4) Silane process 10% vinyl silane is applied evenly to the surface of the resistive copper foil using a spraying method, and then the product is finally rolled up.

[0041] Example 6 (1) Foil production process The electrolyte for the raw foil used a copper ion concentration of 80 g / L and a sulfuric acid concentration of 100 g / L. Polyethylene glycol was selected as the additive for the raw foil electrolyte, with an additive dosage of 20 mg / L. A 600-mesh polishing brush was used, with a smooth surface roughness of 1.3 μm and a rough surface roughness of 3.8 μm. The current was 70,000 A, and the line speed was 7.5 m / min. A total of 140 complete mountain shapes were formed, with an interface expansion ratio of 13%.

[0042] (2) Coarse curing process To ensure a sufficient number of copper nodules with uniform distribution, the total roughening current was 4800A; the total curing current was controlled at 6000A, the copper-acid ratio was 1:10, and the electroplating time was 25s. This allowed the copper crystal nuclei to grow and prevented them from easily detaching. The roughness after rough curing was 5.5μm. The average size of the copper nodules was 1.84μm.

[0043] (3) Nickel-phosphorus layer deposition process The electroless plating method was selected, with a nickel ion concentration of 70 g / L, phosphorous acid concentration of 25 g / L, and boric acid concentration of 65 g / L. A thin iron sheet was attached to a copper foil, and the solution was allowed to circulate at 85°C to deposit a nickel-phosphorus layer onto the surface of the coarsely cured copper nodule layer. Electroless plating was performed for 60 minutes.

[0044] (4) Silane process 10% vinyl silane is applied evenly to the surface of the resistive copper foil using a spraying method, and then the product is finally rolled up.

[0045] Performance testing: The resistance copper foil product is cut into 12.5mm peel strips, pressed onto an epoxy substrate, and then the peel strength is tested using a universal peeling machine. The resistance copper foil is cut into 10*10cm squares, pressed onto an epoxy substrate, and then the copper layer is etched away using an alkaline etching solution. The sheet resistance value is then tested using a sheet resistance meter.

[0046] Table 1

[0047] Table 2

[0048] As shown in Table 1, the peel strength of the resistive copper foils prepared in Examples 1-6 is ≥1.10 N / mm, which meets the product requirements. Higher peel strength is better; the current maximum peel strength is 1.28 N / mm.

[0049] As shown in Table 2, the sheet resistance accuracy of the resistive copper foils prepared in Examples 1-6 is within ±10%, which meets the product's requirements for the uniformity of the resistive layer. The sheet resistance accuracy of the resistive layer is related to the "maximum value minus the minimum value"; the smaller the value, the more uniform the resistance.

[0050] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A method for preparing resistive copper foil with high peel strength and uniform sheet resistance, characterized in that, Includes the following steps: Step-by-step foil process: Additives are added to the raw foil electrolyte. The additives are one or more of cerium sulfate, polyethylene glycol, and disodium dithiobis-1-propanesulfonate. The amount of additives added is 6 to 20 mg / L. The cathode roller is polished using a polishing brush with a mesh size of 350–800 to control the surface roughness of the resulting copper foil to be 1.3–1.6 μm and the surface roughness to be 3.6–4.3 μm. Electrolysis of green foil is carried out under process conditions of current 60,000–70,000 A and linear velocity 6.5–7.5 m / min; Step 2: Coarse curing process A two-stage or higher current treatment mode is adopted, in which the total current of the roughening stage is 4500-5500A and the total current of the curing stage is 5500-6800A. Step 3: Nickel-phosphorus layer deposition process: A nickel-phosphorus alloy layer was deposited on the surface of the roughened and cured copper foil using a chemical plating method. The plating solution composition includes: nickel ions 60-70 g / L, phosphorous acid 15-25 g / L, and boric acid 55-65 g / L; The iron sheet and copper foil are bonded together and plated at a temperature of 75-90°C. The plating solution is kept in a self-circulating flow to deposit the nickel-phosphorus layer onto the surface of the copper nodule layer formed by coarse curing. Step 4: Silane treatment process The copper foil after nickel-phosphorus layer treatment is surface treated with a silane coupling agent, which is selected from one or more of aminosilane, vinylsilane, and epoxysilane.

2. The method for preparing resistive copper foil with high peel strength and uniform sheet resistance according to claim 1, characterized in that, In the aforementioned step of the foil production process, cerium sulfate is selected as an additive for the foil electrolyte, with an additive dosage of 15-20 mg / L, and a polishing brush of 600-800 mesh is used.

3. The method for preparing resistive copper foil with high peel strength and uniform sheet resistance according to claim 1, characterized in that, In the second step of the coarse curing process, the mass ratio of copper to acid in the electrolyte is controlled to be 1:9 to 1:10, and the electroplating time is 15 to 25 seconds.

4. The method for preparing resistive copper foil with high peel strength and uniform sheet resistance according to claim 1, characterized in that, In the nickel-phosphorus layer deposition process described in step three, the electroless plating time is 50–70 minutes.

5. The method for preparing resistive copper foil with high peel strength and uniform sheet resistance according to claim 1, characterized in that, In step four of the silane treatment process, the coating method is spraying or immersion.

6. The method for preparing resistive copper foil with high peel strength and uniform sheet resistance according to claim 1, characterized in that, In step four, the silane coupling agent is a vinylsilane solution with a concentration of 8% to 12%.

7. A resistive copper foil with high peel strength and uniform sheet resistance, characterized in that, According to any one of claims 1 to 6, the method for preparing a resistive copper foil with high peel strength and uniform sheet resistance has a peel strength ≥ 1.10 N / mm and a sheet resistance accuracy deviation within ±10% of the nominal value.

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