Chromium-free environment-friendly passivation solution and electrolytic copper foil preparation method

Abstract

The invention relates to the field of electrolytic copper foil processing and application, and discloses a chromium-free environment-friendly passivation solution and an electrolytic copper foil preparation method, and the passivation solution is composed of 80-120 mg / L of silver phosphate, 5-20 mg / L of o-tert-butylphenol, 60-100 mg / L of potassium pyrophosphate and 10-40 mg / L of sulfuric acid. The o-tert-butylphenol can be adsorbed to the crystal boundary of a silver layer to form antioxidant free radicals, and the antioxidant free radicals are preferentially combined with oxygen molecules to form a stable compound, so that the oxidation resistance is improved; and meanwhile, the o-tert-butylphenol can be combined with a silica group of the silane coupling agent, so that the adhesive force of the silane coupling agent on the metal surface is increased, and the stripping resistance of the copper foil is improved.

Description

Technical Field

[0001] The present invention relates to the field of electrolytic copper foil processing and application, and in particular to a chromium-free, environment-friendly passivation solution and a method for preparing the electrolytic copper foil. Background Art

[0002] Electrolytic copper foil, a fundamental electronic material, is primarily used on printed circuit boards (PCBs). It involves four production processes: copper dissolving, electrolytic foil production, surface treatment, and slitting and packaging. Surface treatment involves pickling, roughening, curing, blackening, ashing, passivation, and silane coating, followed by drying, winding, and slitting. To ensure its oxidation resistance, the copper foil requires passivation. Because chromium metal easily forms a stable oxide layer on its surface, this process currently uses a chromium-containing passivation solution. However, due to the high toxicity of chromium and its significant environmental impact, it is imperative to replace the existing chromate passivation process with a new, environmentally friendly, chromium-free process.

[0003] Existing chromium-free passivation treatment processes are mainly divided into two categories. One is to use other non-chromium metals to form an oxide film on the surface of the copper foil to play a passivation role, and the other is to form an organic layer by coating the surface of an organic substance to protect the copper foil. Chinese patent CN109183018A proposes to use silane coupling agent, vanadium compound, and silica sol to work together to form an inorganic-organic composite film to replace chromate passivation. The metallic activity of vanadium is higher than that of copper, so it is easier to form an oxide film on the surface of copper foil. At room temperature, the resistivity of vanadium is ten times that of copper. When used in printed circuit boards, the electrical signal loss is large. Chinese patent CN101532154B uses a two-stage current deposition of zinc-nickel alloy in the same electrolytic cell, a descending section and an ascending section. In this method, only the zinc-nickel alloy has an antioxidant effect, which is consistent with the blackening and ashing process of electrolytic copper foil, so the antioxidant property is relatively weak. Summary of the Invention

[0004] The present invention aims to solve the technical problems of large electrical signal loss and weak oxidation resistance in the prior art. A chromium-free, environmentally friendly passivation solution is provided, comprising 80-120 mg / L of silver phosphate, 5-20 mg / L of o-tert-butylphenol, 60-100 mg / L of potassium pyrophosphate, and 10-40 mg / L of sulfuric acid.

[0005] In the passivation solution, the mass ratio of o-tert-butylphenol to silver phosphate is 1:5-20.

[0006] In the passivation solution, the mass ratio of o-tert-butylphenol to silver phosphate is 1:10.

[0007] The present invention also relates to a method for preparing electrolytic copper foil, comprising the following steps:

[0008] Step a: prepare a passivation solution, add it to the passivation tank, continue to add pure water to submerge the anode plate, and start mechanical stirring; the passivation solution is composed of 80-120 mg / L silver phosphate, 5-20 mg / L o-tert-butylphenol, 60-100 mg / L potassium pyrophosphate, and 10-40 mg / L sulfuric acid.

[0009] Step b: The copper foil, which has been subjected to electrolytic foiling, pickling, roughening, blackening nickel plating, and ashing zinc plating, is washed with pure water and then pulled into a passivation tank via a roller for passivation treatment;

[0010] Step c: After passivation, the copper foil is washed with water, coated with a silane coupling agent, dried, and then rolled up to obtain a chromium-free passivated electrolytic copper foil.

[0011] The parameters of the electrolytic foil are: copper ion concentration 92±2g / L, sulfuric acid concentration 110±2g / L, chloride ion concentration 18±2mg / L, gelatin concentration 3±1mg / L, temperature 52±1°C, current density 73±2A / dm 2 ;

[0012] The parameters of the pickling are: copper ion concentration of the pickling solution ≤ 5g / L, sulfuric acid: 90±2g / L, temperature maintained at 35±1℃, flow rate 8±2m 3 / h.

[0013] The parameters of the roughening treatment are: copper ion concentration 11±0.5g / L, sulfuric acid concentration 110±2g / L, electrolyte parameters in the curing tank: copper ion concentration 58±2g / L, sulfuric acid concentration 110±2.5g / L, temperature 50±1°C, flow rate 10±2m 3 / h, and perform three roughening and curing treatments.

[0014] The blackening treatment conditions are as follows: nickel ion concentration: 20±1 g / L, boric acid concentration: 20±2 g / L, and the ashing treatment conditions are: zinc ion concentration: 5±0.5 g / L, boric acid concentration: 20±2 g / L.

[0015] The parameters of the passivation process are:

[0016] Current density: 10±1A / dm 2 , the current density of the non-roughened surface is 13±1A / dm 2 , copper foil linear speed: 15±2m / min, temperature: 35±1℃, pH: 4.0±0.2.

[0017] The present invention has the following beneficial effects:

[0018] In the solution of the present invention, since the metallic activity of silver is weaker than that of copper, when an ultra-thin silver layer is plated on the surface of the copper foil, it can prevent the copper foil from being oxidized by water vapor and oxygen in the air during storage, transportation and application. At the same time, the conductivity of the surface silver layer is better than that of copper. When used in electronic circuit foil, it can have better electrical signal transmission performance.

[0019] The o-tert-butylphenol of the present invention can be adsorbed at the grain boundaries of the silver layer to form antioxidant free radicals, which preferentially combine with oxygen molecules to form stable compounds, thereby improving antioxidant properties. At the same time, the o-tert-butylphenol can also combine with the siloxy groups of the silane coupling agent to increase the adhesion of the silane coupling agent to the metal surface, which is beneficial to improving the anti-peeling performance of the copper foil. DETAILED DESCRIPTION

[0020] The terms "first," "second," "third," "fourth," and so on (if any) in the description and claims of the present invention are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. In addition, the terms "comprises," "comprising," "having," and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements explicitly listed, but may include other steps or elements not explicitly listed or inherent to the process, method, product, or apparatus.

[0021] The present invention introduces silver ions into the passivation solution, replacing traditional hexavalent chromium ions, and then utilizes adapted process parameters to plate an ultrathin silver layer on the copper foil surface. Co-deposition of o-tert-butylphenol and silver ions further enhances the passivation ability of the copper foil surface. Experiments conducted by the present invention have shown that when the silver phosphate content remains constant, the oxidation resistance of the copper foil first increases and then decreases as the o-tert-butylphenol content increases. The optimal oxidation resistance of the copper foil is achieved when the silver phosphate to o-tert-butylphenol content ratio is 10:1.

[0022] Example 1

[0023] Step a: Electrolytic foil. Prepare 18 μm HTE foil using the following parameters: copper ion concentration 92 ± 2 g / L, sulfuric acid concentration 110 ± 2 g / L, chloride ion concentration 18 ± 2 mg / L, gelatin concentration 3 ± 1 mg / L, temperature 52 ± 1°C, and current density 73 A / dm².

[0024] Step b: Pickling. The pickling solution has a copper ion concentration of ≤5 g / L, sulfuric acid: 90 ± 2 g / L, the temperature is maintained at 35 ± 1°C, and the flow rate is 8 m³ / h. The oxide layer on the surface of the raw foil is removed by pickling.

[0025] Step c: Roughening treatment. The electrolyte parameters in the roughening tank are: copper ion concentration 11±0.5 g / L, sulfuric acid concentration 110±2 g / L. The electrolyte parameters in the curing tank are: copper ion concentration 58±2 g / L, sulfuric acid concentration 110±2.5 g / L. The temperature is 50±1°C, and the flow rate is 10 m³ / h. Three roughening and curing treatments are performed to increase the density of surface copper nodules.

[0026] Step d: Blackening nickel plating and ashing zinc plating. After washing, blackening and ashing treatments were performed. The blackening electroplating conditions were as follows: nickel ion concentration: 20 ± 1 g / L, boric acid concentration: 20 ± 2 g / L. The ashing zinc plating conditions were: zinc ion concentration: 5 ± 0.5 g / L, boric acid concentration: 20 ± 2 g / L.

[0027] Step e: prepare a passivation solution, weigh 100 mg / L of silver phosphate, 10 mg / L of o-tert-butylphenol, 80 mg / L of potassium pyrophosphate, and 20 mg / L of 98% sulfuric acid, and add them into the passivation tank, continue to add pure water to submerge the anode plate, and start mechanical stirring.

[0028] Step f: The copper foil that has been subjected to electrolytic foiling, surface roughening, blackening nickel plating, and ashing zinc plating is washed with pure water and then pulled into a passivation tank via rollers for passivation. The passivation current density of the roughened surface is: 10±1A / dm 2 , the current density of the non-roughened surface is 13±1A / dm 2 , copper foil linear speed: 15m / min, temperature: 35±1℃, pH: 4.0±0.2.

[0029] Step g: After passivation, the copper foil is washed with water, coated with a silane coupling agent, dried, and then rolled up to obtain a chromium-free passivated electrolytic copper foil.

[0030] Step h: The finished copper foil is subjected to a double 85 oxidation resistance test and a high-temperature oxidation resistance test. The double 85 oxidation resistance test involves placing the copper foil in a constant temperature and humidity chamber at 85°C and 85% humidity for 48, 72, and 120 hours, and observing whether the foil exhibits any oxidative discoloration. The high-temperature oxidation resistance test involves placing the copper foil in an oven at 230°C for 30 and 60 minutes, and observing whether the foil exhibits any oxidative discoloration.

[0031] Example 2

[0032] The only difference from Example 1 is that the content of o-tert-butylphenol in step e is 5 mg / L, the contents of other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0033] Example 3

[0034] The only difference from Example 1 is that the content of o-tert-butylphenol in step e is 15 mg / L, the contents of other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0035] Example 4

[0036] The only difference from Example 1 is that the content of o-tert-butylphenol in step e is 20 mg / L, the contents of other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0037] Example 5

[0038] The only difference from Example 1 is that the silver phosphate content in step e is 80 mg / L, the o-tert-butylphenol content is 8 mg / L, the contents of the other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0039] Example 6

[0040] The only difference from Example 1 is that the silver phosphate content in step e is 120 mg / L, the o-tert-butylphenol content is 12 mg / L, the contents of the other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0041] Example 7

[0042] The only difference from Example 1 is that the silver phosphate content in step e is 70 mg / L and the o-tert-butylphenol content is 7 mg / L, the contents of the other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0043] Comparative Example 1

[0044] The only difference from Example 1 is that the silver phosphate content in step e is 100 mg / L, the o-tert-butylphenol content is 0 mg / L, the contents of the other components remain unchanged, and the experiment is carried out according to the same process as Experimental Example 1.

[0045] Comparative Example 2

[0046] The only difference from Example 1 is that the silver phosphate content in step e is 0 mg / L, the o-tert-butylphenol content is 10 mg / L, and the contents of the other components remain unchanged. The experiment is carried out according to the same process as in Experimental Example 1.

[0047] Comparative Example 3

[0048] During the passivation treatment, the existing hexavalent chromium ion passivation technology was used. The electrolysis conditions were as follows: hexavalent chromium concentration: 1.1±0.05g / L, phosphate concentration: 120±2g / L, and the roughened surface passivation current density: 10±1A / dm 2 , the current density of the non-roughened surface is 13±1A / dm 2, copper foil linear speed: 15m / min, temperature: 35±1℃, pH: 4.0±0.2.

[0049] In order to understand this experiment more intuitively, the concentrations of each component in the experimental examples and comparative examples are given in table form, as shown in Table 1.

[0050] Table 1 Concentration of each component in experimental examples and comparative examples

[0051]

[0052] The test results of the experimental examples and comparative examples are shown in Table 2. When copper foil is oxidized, the surface color changes with the degree of oxidation. In this experiment, 18μm HTE copper foil was used. When unoxidized, it appears red, when slightly oxidized, it appears light orange, when moderately oxidized, it appears purple-red, and when heavily oxidized, it appears multicolored or black.

[0053] Table 2 Test results of experimental examples and comparative examples

[0054]

[0055]

[0056] As shown in Table 2, the silver phosphate to o-tert-butylphenol ratio of 10:1 in Examples 1, 5, and 6 all showed no oxidative discoloration after 120 hours at 85°C and 85% relative humidity, and no oxidative discoloration after 60 minutes of baking at 230°C, demonstrating optimal antioxidant properties. Combining Examples 1-4, it can be seen that when the silver phosphate content remains constant, the antioxidant properties first increase and then decrease with increasing o-tert-butylphenol content. Due to the low silver phosphate content, the silver layer formed by electrodeposition in Example 7 is not continuous, resulting in oxidation to a purple-red color after 120 hours at 85°C and 85% relative humidity.

[0057] Comparative Examples 1 and 2, which contained only one of the two components, silver phosphate or o-tert-butylphenol, oxidized to light purple after 72 hours at 85°C and 85% relative humidity, and to purple-red after 120 hours. Similarly, baking at 230°C also showed significant inferiority to Example 1. Comparative Example 3, which employed existing hexavalent chromium ion passivation technology, oxidized to light orange after 72 hours at 85°C and 85% relative humidity, and to light orange after baking at 230°C for 30 minutes.

[0058] In summary, silver phosphate and o-tert-butylphenol can replace existing chromium-based passivation technologies in the electrolytic copper foil passivation process. In particular, when the ratio of silver phosphate to o-tert-butylphenol was 10:1 in a passivation solution containing 80-120 mg / L of silver phosphate, the product exhibited optimal oxidation resistance, exhibiting no oxidative discoloration after 120 hours at 85°C and 85% relative humidity, and no oxidative discoloration after baking at 230°C for 60 minutes.

[0059] In the present invention, when the ratio of o-tert-butylphenol to silver phosphate in a passivation solution containing a fixed amount of silver phosphate is 10:1, the oxidation resistance is optimal, and the product can be placed at 85°C and 85% relative humidity for 120 hours without oxidative discoloration, and after baking at 230°C for 60 minutes without oxidative discoloration. This may be because during the silver electroplating deposition process, o-tert-butylphenol and silver co-deposit. When the o-tert-butylphenol content is low, the silver ion concentration is too high, which preferentially deposits the silver ion, thereby inhibiting the deposition of o-tert-butylphenol. This results in a low o-tert-butylphenol content on the copper foil surface, resulting in a small number of antioxidant free radicals and weak oxidation resistance. As the o-tert-butylphenol content gradually increases, the inhibitory effect of silver gradually weakens, the number of antioxidant free radicals formed gradually increases, and the oxidation resistance increases. Furthermore, as the o-tert-butylphenol content gradually increases, the deposition of silver ions is inhibited, and the resulting ultra-thin silver layer gradually becomes less dense, reducing the oxidation resistance. Therefore, there is a balance point between the two, and when the content ratio of silver phosphate and o-tert-butylphenol is 10:1, it is the balance point explored in this experiment. At this content ratio, the ultra-thin silver layer formed is a dense and continuous film, and the number of antioxidant free radicals formed by o-tert-butylphenol is also sufficient, so the oxidation resistance of the copper foil is the best at this time.

[0060] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chromium-free environmentally friendly passivation solution, characterized in that: The passivation solution consists of 80-120 mg / L of silver phosphate, 5-20 mg / L of o-tert-butylphenol, 60-100 mg / L of potassium pyrophosphate, and 10-40 mg / L of sulfuric acid.

2. A chromium-free, environmentally friendly passivation solution according to claim 1, characterized in that: In the passivation solution, the mass ratio of o-tert-butylphenol to silver phosphate is 1:5-20.

3. A chromium-free environmentally friendly passivation solution according to claim 1, characterized in that: In the passivation solution, the mass ratio of o-tert-butylphenol to silver phosphate is 1:

10.

4. A method for preparing electrolytic copper foil, characterized in that: The following steps are involved: Step a: prepare a passivation solution, add it to the passivation tank, continue to add pure water to submerge the anode plate, and start mechanical stirring; the passivation solution is composed of 80-120 mg / L silver phosphate, 5-20 mg / L o-tert-butylphenol, 60-100 mg / L potassium pyrophosphate, and 10-40 mg / L sulfuric acid. Step b: The copper foil, which has been subjected to electrolytic foiling, pickling, roughening, blackening nickel plating, and ashing zinc plating, is washed with pure water and then pulled into a passivation tank via a roller for passivation treatment; Step c: After passivation, the copper foil is washed with water, coated with a silane coupling agent, dried, and then rolled up to obtain a chromium-free passivated electrolytic copper foil.

5. The method for preparing an electrolytic copper foil according to claim 4, wherein: The parameters of the electrolytic foil are: Copper ion concentration 92±2 g / L, sulfuric acid concentration 110±2 g / L, chloride ion concentration 18±2 mg / L, gelatin concentration 3±1 mg / L, temperature 52±1°C, current density 73±2 A / dm 2 .

6. The method for preparing an electrolytic copper foil according to claim 4, wherein: The parameters of the pickling are: The copper ion concentration of the pickling solution is ≤5g / L, sulfuric acid: 90±2g / L, the temperature is maintained at 35±1℃, and the flow rate is 8±2m 3 / h.

7. The method for preparing an electrolytic copper foil according to claim 4, wherein: The parameters of the roughening process are: Copper ion concentration 11±0.5 g / L, sulfuric acid concentration 110±2 g / L, electrolyte parameters in the solidification tank: copper ion concentration 58±2 g / L, sulfuric acid concentration 110±2.5 g / L, temperature 50±1℃, flow rate 10±2m 3 / h, and perform three roughening and curing treatments.

8. The method for preparing an electrolytic copper foil according to claim 4, wherein: The blackening treatment conditions are as follows: nickel ion concentration: 20±1 g / L, boric acid concentration: 20±2 g / L, and the ashing treatment conditions are: zinc ion concentration: 5±0.5 g / L, boric acid concentration: 20±2 g / L.

9. The method for preparing an electrolytic copper foil according to claim 4, wherein: The parameters of the passivation process are: Current density: 10±1A / dm 2 , the current density on the non-roughened surface is 13±1 A / dm 2 , copper foil linear speed: 15±2m / min, temperature: 35±1℃, pH: 4.0±0.2.

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