A method for improving the corrosion resistance of resistive copper foil

Abstract

The present invention discloses a method for improving the corrosion resistance of resistive copper foil, which includes pickling treatment, rough curing treatment and electroplating a resistive layer on the raw foil in sequence; the resistive layer is a nickel-phosphorus resistive layer, and the electroplating solution used includes nickel salt, reducing agent and pH buffer; the reducing agent is selected from sodium hypophosphite and / or phosphorous acid; by adding a pH buffer, the pH value of the electroplating solution is adjusted to 1-3. The present invention can significantly improve the corrosion resistance of resistive copper foil by electroplating a nickel-phosphorus resistive layer and further precisely controlling the phosphorus content in the nickel-phosphorus resistive layer. The sheet resistance of this resistive copper foil is uniform, and the change in sheet resistance can be controlled within 5 Ω / sq, and in the best case, it can be controlled within 2 Ω / sq.

Description

Technical Field

[0001] The present invention belongs to the technical field of printed circuit boards, and particularly relates to a method for improving the corrosion resistance of resistive copper foil. Background Art

[0002] With the rapid development of the electronic information industry and the continuous update of thin, light, short, and high-performance portable electronic products, the printed circuit board (PCB) as the support of electronic components is also developing more and more towards high density, multi-layer, easy encapsulation, and miniaturization. This requires that passive device resistors, which occupy a large surface area of the PCB, be buried inside the PCB. Resistive copper foil can be used to bury resistors into the PCB and can be widely applied in fields such as military, 5G communication, consumer electronics, and automotive electronics.

[0003] The conventional preparation process of resistive copper foil mainly includes: 1. Producing raw foil; 2. Pickling the oxide layer on the surface of the raw foil; 3. Roughening and curing in a copper ion solution to form a copper nodule particle layer on the surface of the raw foil (this layer can increase the peel strength between the resistive copper foil and the resin substrate and ensure the use stability of the circuit board); 4. Electro-depositing a metal material on the surface of the copper nodule layer to form a thin film resistor layer; 5. Electroplating an anti-oxidation metal; 6. Spraying silane (to ensure the peel strength), washing, drying, and inspecting the finished product. This resistive copper foil belongs to electronic components and is used in buried resistor printed boards. End customers are mostly used in mobile phone acoustic components and military radars. The resistive copper foil also needs to go through processes such as acid etching, alkaline etching, and browning during downstream processing. If the corrosion resistance of the resistor layer is poor, it will be etched and dissolved, affecting the resistor accuracy. To ensure the stability of the resistance value, it is very necessary to improve the corrosion resistance of the resistor layer.

[0004] Xu Ruidong et al. (Research on high-phosphorus amorphous nickel-phosphorus alloy coatings, Electroplating & Pollution Control, May 2002) disclosed the preparation of a high-phosphorus amorphous nickel-phosphorus alloy coating using a new type of additive. The composition of the plating solution includes nickel sulfate 25 - 30 g / L, sodium hypophosphite 28 - 35 g / L, and also includes a complexing agent, an additive, and a stabilizer, with a pH value of 4.2 - 4.8. The complexing agent is an organic carboxylic acid, the additive is an inorganic salt, and the stabilizer is a heavy metal salt, but the specific raw material names are not disclosed.

[0005] In this technical solution, a new type of additive is added to obtain a high phosphorus content to achieve the technical effect of improving the corrosion resistance. However, the plating solution formula used in this technical solution contains an organic complexing agent. If this plating solution formula is directly applied to the preparation process of the resistor layer of resistive copper foil, the organic complexing agent will adsorb on the surface of the copper foil, resulting in the inability to normally electroplate the nickel-phosphorus resistor layer; in addition, the heavy metal salt used as a stabilizer will also be reduced to metal by sodium hypophosphite and deposited in the nickel-phosphorus resistor layer, resulting in a decrease in sheet resistance and corrosion resistance. Therefore, the above nickel-phosphorus electroplating solution formula is not suitable for the production of resistive copper foil.

[0006] At present, there is an urgent need to study methods applicable to improving the corrosion resistance of resistive copper foils. Summary of the Invention

[0007] In view of the above problems, the present invention discloses a method for improving the corrosion resistance of resistive copper foils. By electroplating a nickel-phosphorus resistive layer and further precisely controlling the phosphorus content in the nickel-phosphorus resistive layer, the corrosion resistance of the resistive copper foil can be significantly improved. The sheet resistance of this resistive copper foil is uniform, and the change in sheet resistance can be controlled within 5 Ω / sq, and in the best case, it can be controlled within 2 Ω / sq.

[0008] To achieve the above object, the specific technical solution of the present invention is as follows:

[0009] A method for improving the corrosion resistance of resistive copper foils includes successively pickling, rough curing, and electroplating a resistive layer on the raw foil. The resistive layer is a nickel-phosphorus resistive layer, and the electroplating solution used includes a nickel salt, a reducing agent, and a pH buffer.

[0010] The reducing agent is selected from sodium hypophosphite and / or phosphorous acid.

[0011] In the electroplating solution, the concentration of the nickel salt is (19 - 26) g / L, and the concentration of the reducing agent is (2 - 5) g / L.

[0012] By adding the pH buffer and adjusting the pH value of the electroplating solution to 1 - 3.

[0013] The method disclosed in the present invention can control the phosphorus content in the prepared nickel-phosphorus resistive layer within a suitable range (12 - 16 wt%) by regulating the concentrations of the nickel salt and the reducing agent, and by regulating the dosage of the pH buffer to adjust the pH value of the electroplating solution within a suitable range, thereby obtaining a highly corrosion-resistant amorphous nickel-phosphorus resistive layer. Through further corrosion resistance tests, it is found that the sheet resistance of the finally prepared resistive copper foil is uniform, and the change in sheet resistance can be controlled within 5 Ω / sq.

[0014] Through comparative tests, it is found that if the pH value of the electroplating solution is too high, such as pH reaching 4, the electroplating solution is unstable and continuous electroplating cannot be carried out. For the resistive copper foil prepared in a short time, the uniformity of the surface resistance value is poor, and the change in sheet resistance is extremely large.

[0015] Through further comparative tests, if the concentration of the reducing agent in the electroplating solution is too high, such as adding the nickel salt and the reducing agent in equal mass concentrations, the amount of nickel precipitation increases, and the amount of phosphorus precipitation no longer increases after increasing to a certain value, but instead leads to a decrease in the phosphorus content in the prepared nickel-phosphorus resistive layer, resulting in poor uniformity of the surface resistance value and extremely large change in sheet resistance of the finally prepared resistive copper foil.

[0016] Preferably:

[0017] In the electroplating solution, the concentration of nickel salt is (19 - 25) g / L, and the concentration of reducing agent is (3 - 4.5) g / L;

[0018] After adding the pH buffer, the pH value of the electroplating solution is adjusted to 1 - 2.

[0019] It is found through experiments that when the parameters are optimized within the above ranges, the phosphorus content in the prepared nickel - phosphorus resistance layer can be controlled within the range of 13 - 16 wt%; through further corrosion resistance tests, it is found that the sheet resistance values of the finally prepared resistive copper foil are more uniform, and the change in sheet resistance value can be controlled within 2.5 Ω / sq, and it has more excellent corrosion resistance.

[0020] Further optimization:

[0021] In the electroplating solution, the concentration of nickel salt is (19 - 25) g / L, and the concentration of reducing agent is 3 g / L;

[0022] It is found through experiments that when the parameters are optimized within the above ranges, the phosphorus content in the prepared nickel - phosphorus resistance layer can be controlled within the range of 15 - 16 wt%; through further corrosion resistance tests, it is found that the sheet resistance values of the finally prepared resistive copper foil are more uniform, and the change in sheet resistance value can be controlled within 2 Ω / sq, and it has the most excellent corrosion resistance.

[0023] In this method:

[0024] The pH buffer is selected from conventional types in the art, such as one or more of boric acid, sodium bicarbonate, and sodium citrate.

[0025] There are no special requirements for the nickel salt, and it is selected from conventional types in the art, such as one or more of nickel sulfate, nickel sulfate hydrate, nickel chloride, and nickel chloride hydrate.

[0026] Preferably, a conductive agent is also added to the electroplating solution; the content of the conductive agent in the electroplating solution is (10 - 20) g / L.

[0027] When electroplating the resistance layer, the current density is (5 - 15) A / dm 2 , and the temperature of the electroplating solution is 50 - 65 °C.

[0028] Preferably, the current density is (8 - 10) A / dm 2 .

[0029] Before preparing the electroplated resistance layer, pickling treatment and rough curing treatment are also included for the raw foil in sequence, but the above processes are all conventional processes in the art.

[0030] For the pickling treatment, it can be carried out in an aqueous solution of copper sulfate.

[0031] The rough curing treatment includes roughening treatment and curing treatment, and the specific process parameters can be selected from the conventional parameters in the art.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention discloses a method for improving the corrosion resistance of resistive copper foil. After pickling and rough curing treatment of the raw foil, a nickel-phosphorus resistive layer is further electroplated, and the phosphorus content in the nickel-phosphorus resistive layer is precisely controlled (controlled between (12-16) wt%) by controlling the nickel salt, reducing agent and pH value of the electroplating solution in the electroplating solution, which can significantly improve the corrosion resistance of the resistive copper foil. The sheet resistance of the resistive copper foil is uniform, and the change in sheet resistance can be controlled within 5 Ω / sq, and in the best case, it can be controlled within 2 Ω / sq. When applied to the harsh processing environment of the downstream PCB, the resistive copper foil will have better stability. Specific Embodiments

[0034] The present invention will be further described in detail below with reference to examples and comparative examples, but the embodiments of the present invention are not limited thereto.

[0035] Unless otherwise specified, the raw materials in the examples of this application are all purchased through commercial channels.

[0036] Example 1

[0037] (1) Pickling treatment

[0038] The raw foil is pickled, and the pickling conditions are carried out in an aqueous copper sulfate solution of 11 g / L at a temperature of 25°C.

[0039] (2) Rough curing treatment

[0040] The raw foil after pickling treatment is subjected to rough curing treatment, and the treatment process is roughening → curing;

[0041] The copper ion concentration in the plating solution used for roughening treatment is 18 ± 2 g / L, the sulfuric acid concentration is 100 ± 10 g / L, the plating solution temperature is 25°C, and the current density of roughening treatment is 50 ± 2 A / dm 2 , and the electroplating time is 4.5 ± 1 s.

[0042] The copper ion concentration in the plating solution used for curing treatment is 40 g / L, the sulfuric acid concentration is 100 g / L, the plating solution temperature is 25°C, and the current density of curing treatment is 55 ± 2 A / dm 2 , and the electroplating time is 4.5 ± 1 s.

[0043] (3) Electroplating nickel-phosphorus resistive layer

[0044] In the electroplating solution used, nickel sulfate hexahydrate is used as the main salt, sodium hypophosphite is used as the reducing agent, boric acid is used as the pH buffer, and phosphoric acid is used as the conductive agent; the nickel ion concentration in the electroplating solution is 25 g / L, the sodium hypophosphite concentration is 3 g / L, the boric acid concentration is 19 g / L, and the phosphoric acid concentration is 15 g / L; at this concentration, the pH value of the electroplating solution is 1, the solution temperature is 55 °C, and the current density is 8.4 A / dm 2 , the electroplating time is 4.5 s, and a corrosion-resistant resistive copper foil is prepared.

[0045] Example 2

[0046] The preparation process is basically the same as that in Example 1, except that in step (3):

[0047] Sodium citrate is added as the pH buffer, and the concentration of sodium citrate in the electroplating solution is 14 g / L. At this time, the pH value of the electroplating solution is 2.

[0048] Example 3

[0049] The preparation process is basically the same as that in Example 1, except that in step (3):

[0050] The concentration of boric acid in the electroplating solution is 13 g / L. At this time, the pH value of the electroplating solution is 3.

[0051] Comparative Example 1

[0052] The preparation process is basically the same as that in Example 1, except that in step (3):

[0053] The concentration of boric acid in the electroplating solution is 12 g / L. At this time, the pH value of the electroplating solution is 4.

[0054] During the test, it was found that the electroplating solution decomposed and continuous electroplating could not be carried out. The reason may be that: when using the copper foil as the cathode, there is a hydrogen evolution reaction, producing hydroxide ions, with a pH value of 4. Some of the hydroxide ions are not neutralized and react with the main salt nickel ions to form a precipitate, resulting in the deterioration of the solution.

[0055] Example 4

[0056] The preparation process is basically the same as that in Example 1, except that in step (3):

[0057] The nickel ion concentration in the electroplating solution is replaced with 26 g / L, and the reducing agent in the electroplating solution is replaced with phosphorous acid, with a concentration of phosphorous acid of 4.5 g / L. At this time, the pH value of the electroplating solution is 1.3.

[0058] Example 5

[0059] The preparation process is basically the same as that in Example 1, except that in step (3):

[0060] Replace the nickel ion concentration in the electroplating solution with 24 g / L, and the concentration of sodium hypophosphite is 2.3 g / L. At this time, the pH value of the electroplating solution is 1.5.

[0061] Example 6

[0062] The preparation process is basically the same as that in Example 1, except that in step (3):

[0063] Replace the nickel ion concentration in the electroplating solution with 19 g / L. At this time, the pH value of the electroplating solution is 1.6.

[0064] Comparative Example 2

[0065] The preparation process is basically the same as that in Example 1, except that in step (3):

[0066] Replace the nickel ion concentration in the electroplating solution with 28 g / L.

[0067] Comparative Example 3

[0068] The preparation process is basically the same as that in Example 1, except that in step (3):

[0069] Replace the concentration of sodium hypophosphite in the electroplating solution with 25 g / L.

[0070] Example 7

[0071] The preparation process is basically the same as that in Example 1, except that in step (3):

[0072] Replace the liquid temperature of the electroplating solution with 60 °C, and replace the current density with 9 A / dm 2 。

[0073] Performance test:

[0074] 1. Nickel and phosphorus content test

[0075] Heat the resistance copper foil samples prepared in each example and comparative example and dissolve them in 30 wt% nitric acid aqueous solution. After filtration, washing, and dilution by 10 times, use an inductively coupled plasma spectrometer to test the nickel content and phosphorus content. The specific values are listed in Table 1 below. The table also records the mass percentage of phosphorus content in the nickel-phosphorus resistance layer.

[0076] Table 1

[0077]

[0078]

[0079] 2. Corrosion resistance test

[0080] 2.1 Acid corrosion resistance

[0081] The resistive copper foil prepared in Example 1 (cut into 10×10 cm square pieces) was laminated with an epoxy resin substrate (at 200 °C, 17.7 MPa, for 90 min), and then placed in an alkaline etching solution to etch the copper layer, leaving the nickel-phosphorus resistive layer. It was soaked in a 5 wt% sulfuric acid aqueous solution at 75 °C for 30 s. After taking it out, a surface resistance meter was used to measure the surface resistance values at the four corners and the middle position of the 10×10 cm square. The surface resistance values before and after soaking are listed in Table 2 below.

[0082] 2.2, Alkali corrosion resistance

[0083] The resistive copper foil prepared in Example 1 (cut into 10×10 cm square pieces) was laminated with an epoxy resin substrate (at 200 °C, 17.7 MPa, for 90 min), and then placed in an alkaline etching solution to etch the copper layer, leaving the nickel-phosphorus resistive layer. It was soaked in an 8 wt% ammonia aqueous solution at 75 °C for 30 s. After taking it out, a surface resistance meter was used to measure the surface resistance values at the four corners and the middle position of the 10×10 cm square. The surface resistance values before and after soaking are listed in Table 2 below.

[0084] The corrosion resistance tests of other examples and comparative examples were carried out using the same method as in Example 1, and the specific surface resistance values are also listed in Table 2 below.

[0085] Table 2

[0086]

[0087]

[0088]

[0089] The above-disclosed are preferred embodiments, but the protection scope of the present invention is not limited thereto. Those of ordinary skill in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not depart from the spirit of the present invention, they are within the protection scope of the present invention.

Claims

1. A method for improving the corrosion resistance of a resistor copper foil, comprising sequentially performing pickling treatment, rough curing treatment, and electroplating a resistor layer on the raw foil; characterized in that: The resistance layer is a nickel-phosphorus resistance layer, and the electroplating solution used includes a nickel salt, a reducing agent and a pH buffer; The nickel salt is selected from one or more of nickel sulfate, nickel sulfate hydrate, nickel chloride, and nickel chloride hydrate; The reducing agent is selected from sodium hypophosphite and / or phosphorous acid; In the electroplating solution, the nickel salt concentration is (19-25) g / L, and the reducing agent concentration is 3 g / L; A conductive agent is also added to the electroplating solution, wherein the conductive agent is selected from phosphoric acid, and the content of the conductive agent in the electroplating solution is (10-20) g / L; Adjusting the pH value of the electroplating solution to 1-3 by adding the pH buffer; The phosphorus content in the nickel-phosphorus resistor layer is controlled to be 15-16 wt %.

2. The method for improving the corrosion resistance of resistor copper foil according to claim 1, characterized in that: The pH buffer is selected from one or more of boric acid, sodium dihydrogen carbonate, and sodium citrate.

3. The method for improving the corrosion resistance of resistor copper foil according to claim 1, characterized in that: The pH value of the electroplating solution is adjusted to 1-2 by adding the pH buffer.

4. The method for improving the corrosion resistance of resistor copper foil according to claim 1, characterized in that: When electroplating the resistor layer, the current density is (5~15) A / dm 2 , the plating solution temperature is 50~65℃.

5. The method for improving the corrosion resistance of resistor copper foil according to claim 1, characterized in that: The pickling treatment uses a copper sulfate aqueous solution.

6. The method for improving the corrosion resistance of resistor copper foil according to claim 1, characterized in that: The rough curing process includes a roughening process and a curing process.

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