CN114016098B - A kind of Ni-Co-Ce thin-film electroplating solution and thin-film preparation method for copper-clad board for PCB - Google Patents

Abstract

The present invention provides a plating solution formulation and preparation method for electrodepositing a Ni-Co-Ce alloy film on the copper surface of a printed circuit copper-clad board, and a method for preparing a Ni-Co-Ce alloy film on the surface of a copper-clad board using the plating solution. The plating solution formula includes: nickel chloride 0.03-0.05mol/L, cobalt sulfate 0.03-0.05mol/L, conductive additive 0.1-0.2mol/L, pH buffer 0.1-0.2mol/L, electroplating additive 0.1-0.2mol /L, cerium sulfate 0.005～0.03mol/L, deionized water, etc., the Ni‑Co‑Ce alloy film obtained by electroplating can be used for multilayer printed circuit board electronic circuit protection, interlayer bonding force and high frequency signal integrity Lift etc. At the same time, the formulation of the plating solution is easy to prepare and does not corrode the printed circuit substrate. The electroplating process and equipment are well compatible with the existing conditions in the field of printed circuit manufacturing, which greatly reduces the investment in technological transformation and product manufacturing costs.

Description

A kind of Ni-Co-Ce thin-film electroplating solution and thin-film preparation method for copper-clad board for PCB

technical field

The invention belongs to the technical field of surface modification of printed circuit substrates, and in particular relates to a Ni-Co-Ce thin-film electroplating solution for copper-clad boards for PCBs and a thin-film preparation method.

Background technique

Printed circuit boards are the basic components of electronic equipment manufacturing, and FR-4 copper-clad laminates are currently one of the most used substrate materials. In order to avoid oxidation and pollution of printed circuit boards before packaging components, the printing The surface protection treatment of circuit boards is one of the important processes in the field of printed circuit board manufacturing.

At present, the commonly used surface treatment technologies in the industry include hot air leveling, chemical nickel deposition gold/silver/tin, organic protective film coating, electroplating tin/nickel gold and other processes. For example, Gao Qingyao introduced a tin plating technology for printed circuit boards in the paper "Research and Application of Tin Plating Technology on Copper Surface of Printed Circuit Boards". The tin coating prepared by this technology can improve the etching quality of electronic circuits and components Welding reliability, enhancing the bonding force between layers of multi-layer boards, etc. In the field of printed circuits, the use of electroplating nickel layer to improve the surface performance of the prepared circuit board is based on the good corrosion resistance and high temperature resistance of nickel alone. The nickel coating can be easily passivated in the air and is compatible with common strong alkali, strong acid, The slow action of hydrochloric acid and sulfuric acid can effectively protect copper electronic circuits. The patent "a method for electroplating nickel in printed circuits with ionic liquids" (application publication number CN105018975A) uses ionic liquids as electrolytes to achieve However, the pure nickel coating on the copper surface has disadvantages such as poor stability, easy peeling of the coating, and dull surface. Therefore, the development of alloy coating production technology on the surface of printed circuit boards has become a research hotspot in the industry. The patent "Production Process of Nickel-Cerium Alloy Annealed Copper Wire" (publication number CN101556846A) proposes a production process for annealed copper wire electroplating nickel-cerium alloy on the surface of copper wire, and the obtained nickel-cerium alloy coating has good adhesion on the surface of annealed copper wire , good toughness, excellent ductility and other characteristics, suitable for making aviation wires and cables and special installation conductive cores; the patent "a nickel-gold electroplating process for printed circuit boards" (application publication number CN101835346A) adopts the design of electroplating connections to make printing The brush position on the edge of the board process is connected to the non-edge nickel-gold area to be electroplated, which realizes the electroplating of nickel-gold on the non-edge area of the printed circuit board, ensures the reliability of the electroplated nickel-gold layer of the printed circuit board, and effectively reduces the cost. The waste of metal nickel and gold resources reduces the cost and is more environmentally friendly; the patent "a plating solution for electroplating nickel-cobalt-iron alloy layer on the copper plate of the crystallizer" (application publication number CN105442002A) discloses a method of electroplating on the copper plate of the crystallizer. The plating solution of nickel-cobalt-iron alloy layer, this plating solution consists of: nickel sulfate 220-240g/L, nickel chloride 17-19g/L, cobalt sulfate 4.5-5.5g/L, iron sulfate 7.5-8.5g/L, boric acid 23-27g/L, potassium sulfate 5-7g/L, sodium chloride 30-40g/L, sodium lauryl sulfate 0.2-0.4g/L, additives 20-22m1/L (the additives are sodium gluconate, ascorbic acid, dextrin).

In order to solve the corrosion resistance problem of copper foil, some copper foil manufacturers have developed ternary and quaternary alloy corrosion resistance processes of zinc, nickel, cobalt, tin, iron, arsenic, tungsten and other metals, which greatly improves the corrosion resistance of copper foil. Great improvement, but its process is complicated, the range of process parameters is narrow, there are problems such as unsuitable operation, high cost, difficult recovery of plating solution and wastewater treatment, and environmental protection. Based on the fact that there are unfilled electrons in the 4f layer in the cerium atomic structure and the electronegativity is small, the strong chemical affinity can effectively improve the performance of the traditional electroplating process bath, change the structure of the metal coating, etc., to add cerium salt Copper-based electroplating technology has attracted people's attention. The patent "a surface treatment agent for improving the corrosion resistance of electrolytic copper foil" (application publication number CN 111304709 A) forms a uniform and fine tin-zinc-cerium ternary alloy composite coating on the surface of copper foil to achieve copper foil corrosion resistance. The corrosion resistance is improved, and its hydrochloric acid cracking rate can be achieved below 2%; the patent "a rare earth cerium-copper-zinc alloy electroplating solution and its electroplating method" (application publication number CN105483772A) discloses a rare earth cerium-copper-zinc alloy An electroplating solution and an electroplating method thereof, the electroplating solution comprises 10-80 g/L of copper sulfate, 4-60 g/L of zinc sulfate, 0.1-1 g/L of carbon dioxide, 4-40 g/L of amino acids, and 100-200 g/L of sodium pyrophosphate L. Brightener 3-8g/L, the cerium-copper-zinc alloy coating obtained by electroplating with this plating solution has beautiful color, excellent compactness and corrosion resistance. This literature achievement further improves the stability of electronic circuits in the environment, but it does not involve the core issues of multilayer printed circuit board manufacturing such as interlayer bonding force and electromagnetic compatibility. However, most of the existing interlayer bonding forces need to be treated by browning, which will increase the roughness of the copper surface and increase the insertion loss. With the high-density and multi-layered circuit boards, especially the development of high-frequency signal transmission of electronic products in recent years, the production of metal plating on the copper-based surface of printed circuits not only needs to consider improving the corrosion resistance of copper electronic circuits, At the same time, it is also necessary to consider how to improve the interlayer bonding force of the multilayer board, as well as the signal loss and electromagnetic interference of the protected electronic circuit when transmitting high-frequency signals. In addition, it is found in practice that some alloy layers obtained by electroplating are not fine and uniform in crystallization, and their corrosion resistance cannot achieve the desired effect, which leads to edge corrosion when etching high-precision lines on copper foil circuit boards, which seriously affects manufacturing. The quality of the finished product.

Therefore, it has become a research hotspot to develop a new plating solution formula and achieve good protection of the protective coating of printed circuit copper clad laminates.

Contents of the invention

Aiming at problems such as weak bonding between the protective coating prepared by the existing plating solution formula and the printed circuit copper-clad laminate, and the influence of signal transmission, the object of the present invention is to provide a Ni-Co-Ce plated copper-clad laminate for PCB. Thin film plating solution and thin film preparation method. The plating solution formula of the present invention increases the cathodic polarization in the electroplating process of the copper surface of the copper clad laminate by adding cerium ions in the electroplating solution, controls the electrodeposition speed of nickel ions and cobalt ions on the copper surface, and realizes the preparation of Ni-Co-Ce The regulation of alloy composition and surface compactness can effectively improve the peel strength of polymer materials such as epoxy resin on the surface of the prepared alloy layer, which is conducive to the improvement of the interlayer bonding force of multilayer printed circuit boards. In addition, the dense alloy coating is very beneficial to the transmission of high-frequency electronic signals, thereby realizing the balance between the improvement of interlayer bonding force and the reduction of insertion loss of high-frequency transmission signals in the manufacture of multilayer high-frequency printed circuit boards. At the same time, the plating solution formula does not contain precious metals such as gold and highly toxic substances, etc. The plating solution is easy to prepare and does not corrode the organic materials of the printed circuit board. Using this plating solution to make alloy layers on the surface of copper clad laminates and printed circuit manufacturing The existing electroplating equipment in the field has good compatibility, less investment in technological transformation, and low manufacturing costs.

To achieve the above object, the technical scheme of the present invention is as follows:

A Ni-Co-Ce thin-film electroplating solution for copper-clad boards for PCBs, comprising the following components: 0.03-0.05 mol/L of nickel chloride, 0.03-0.05 mol/L of cobalt sulfate, 0.1-0.2 mol/L of conductive additives, pH 0.1-0.2 mol/L buffer, 0.1-0.2 mol/L electroplating additive, 0.005-0.03 mol/L cerium sulfate, deionized water.

Further, the conductive additive may be sodium chloride, sodium sulfate, potassium chloride or potassium sulfate, preferably sodium chloride.

Further, the pH buffering agent can be weak acid, weak salt or ammonium salt, the weak acid is acetic acid, citric acid, boric acid, etc., the weak acid salt is oxalate, tartrate, phosphate, etc., preferably boric acid.

Further, the electroplating additives are sodium lauryl sulfate, thiourea, sodium polydithiodipropanesulfonate (SPS), etc., preferably thiourea and sodium polydithiodipropanesulfonate (SPS).

The method for preparing Ni-Co-Ce ternary alloy film based on above-mentioned plating solution, comprises the following steps:

Step 1. Preparation of plating solution: Take a certain amount of deionized water in a container, add pH buffer, conductive additives, nickel salts, cobalt salts, electroplating additives, rare earth cerium compounds sequentially under continuous stirring, and then use dilute sulfuric acid or Dilute NaOH solution to adjust the pH of the system to a predetermined pH value, and finally use deionized water with a predetermined pH value to constant volume to obtain a plating solution; among them, nickel chloride is 0.03-0.05mol/L, cobalt sulfate is 0.03-0.05mol/L, and sulfuric acid is high Ce 0.005～0.03mol/L, conductive additive 0.1～0.2mol/L, pH buffer 0.1～0.2mol/L, electroplating additive 0.1～0.2mol/L, pH 5～7;

Step 2. Pretreatment of plated parts: Use a brush plate to remove surface stains such as oxide layer and dirt on the printed circuit copper clad laminate to be electroplated, then soak and wash in 5% dilute sulfuric acid for 1 to 10 minutes, take it out and use deionized Wash with water, then use 5% dilute sulfuric acid and 5% sodium persulfate mixed solution for micro-etching treatment, the treatment time is 1-50s, finally clean with deionized water, dry and set aside;

Step 3. Preparation of Ni-Co-Ce alloy thin film: put the pretreated plated parts into the electroplating tank, adopt the constant potential deposition method to prepare the alloy thin film at room temperature, keep the pH value of the solution at 5-7 during the electroplating process, and the electroplating time is 10 ～40min, current density 15～20mA/cm ² , electroplating solution temperature 15～40℃, continuous stirring during the electroplating process to reduce concentration polarization, and the Ni-Co-Ce alloy film covering the copper surface of the copper clad laminate can be prepared .

The invention also provides the Ni-Co-Ce alloy thin film obtained by the above method to be used as a protective layer on the surface of electronic circuits in the manufacture of printed boards, and can be used for the production of anti-corrosion layers and anti-corrosion layers.

Owing to adopted above-mentioned technical scheme, the beneficial effect of the present invention is:

1. By adding cerium salt to the plating solution, not only the Ni-Co-Ce alloy coating can be obtained, but also the electrodeposition rate of nickel and cobalt on the surface of the copper clad laminate and the microstructure of the coating can be changed through the characteristic adsorption of cerium ions on the copper surface, which is beneficial to Form a coating with a dense surface and good bonding force with the substrate copper, breaking through the technical problem of poor bonding force of the coating in the prior art. The existence of elemental cerium in the coating can not only improve the bonding force between the alloy coating and the copper surface of the substrate, but also improve the corrosion resistance of the prepared alloy coating due to the passivation of the active metal cerium in air. In addition, the ultra-thin layer of high-oxidation state substances produced by the passivation of elemental cerium increases the wettability of the alloy layer to organic materials for printed circuit board manufacturing such as epoxy resin (or Affinity), effectively improve the peel strength of the organic resin material used in the manufacture of printed circuits on the surface of the coating, thereby realizing the protection of electronic circuits, the improvement of the interlayer bonding force of multilayer boards, and the reduction of insertion loss of high-frequency signal transmission (improve signal integrity ) take into account the three objectives.

2. The plating solution provided by the present invention does not contain precious metals such as Au, and cyanide, etc., and the raw materials of the plating solution are easy to obtain and have good stability, easy maintenance, cost saving and environmental friendliness. At the same time, the plating solution proposed by the present invention is a weakly acidic system, which will not cause corrosion with the organic material of the substrate of the copper clad laminate, simplifies the preparation operation of the alloy film, reduces the process controllability and process complexity, and simplifies the requirements for equipment and processes , which can better realize large-scale application.

3. The Ni-Co-Ce ternary alloy film prepared based on the plating solution formula of the present invention has excellent electromagnetic properties and special chemical properties of cerium, and can realize interlayer bonding force and signal integrity in the manufacture of multilayer high-frequency printed circuit boards Improved compatibility. The binding force between the coating and the copper-clad laminate substrate is as high as 57.47N/cm ² , which is far higher than the technical standard of the industry.

Description of drawings

Fig. 1 is the SEM image of the copper substrate before alloy plating after pretreatment in the present invention.

Fig. 2 is an SEM image of the copper-based Ni-Co-Ce alloy thin film prepared in the present invention.

Fig. 3 is an EDS diagram of the copper-based Ni-Co-Ce alloy thin film prepared in the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the implementation methods and accompanying drawings.

Based on the fact that nickel-cobalt alloy is a typical magnetic metal alloy and has synergistic properties, combined with the characteristics of cerium ion adsorption on copper surface, which contributes to the negative shift of nickel and cobalt cathode deposition potential, a printed circuit coating is proposed. An electroplating solution produced by Ni-Co-Ce ternary alloy electrodeposition on the copper surface of a copper plate, and a method for producing the alloy layer using the electroplating solution. Nickel chloride is selected as the nickel source of the electroplating solution of the present invention, cobalt sulfate is selected as the cobalt source, and +4 cerium sulfate is selected as the cerium source, and then chloride ions in the solution are controlled by adding conductive substances containing chloride ions and sulfate ions The ratio of the concentration to the concentration of sulfate ions achieves the purpose of controlling the conductivity of the plating solution system, so that the invented Ni-Co-Ce sulfate-chloride plating solution system on the copper surface of the copper clad laminate exhibits fast deposition speed and low coating stress. And other advantages, which can not only improve the quality of the coating, but also improve the efficiency of electroplating.

The substrate for selective electrodeposition of Ni-Co-Ce alloy thin film is copper clad laminate for printed circuit board manufacture. First of all, it is necessary to pre-clean the printed circuit copper clad laminate to ensure that the copper surface of the plated part is clean. In the electroplating process, the pretreated printed circuit copper-clad laminate is placed in the plating solution as the negative electrode, and the metal ions in the plating solution are deposited on the surface of the substrate through electroplating, and an alloy coating is formed on the copper surface of the copper-clad laminate, which is confirmed by EDS This alloy becomes a Ni-Co-Ce alloy thin film.

If it is a flexible copper clad laminate, it needs to be strengthened in advance.

Example 1

A method for electroplating a Ni-Co-Ce film on a copper-clad board for PCB, comprising the following steps:

Step 1: Preparation of plating solution: Take a certain amount of deionized water in a container, and add boric acid, sodium chloride, nickel chloride, cobalt sulfate, thiourea, sodium polydithiodipropanesulfonate, sulfuric acid in sequence under constant stirring For high cerium, fully stir to dissolve the components, then adjust the pH of the system to pH = 6 with dilute sulfuric acid or dilute NaOH solution, and finally use deionized water with pH = 6 to obtain the plating solution; among them, nickel chloride 0.04mol/L, 0.035mol/L cobalt sulfate, 0.1mol/L sodium chloride, 0.2mol/L boric acid, 0.1mol/L thiourea, 0.1mol/L sodium polydithiodipropane sulfonate, 0.005 ceric sulfate mol/L;

Step 2: Pretreatment of plated parts: Cut the FR-4 copper-clad laminate into a size of 1cm×1cm, use a brush to remove surface stains such as oxide layer and dirt on the surface, then rinse with tap water, dry and immerse in 5% dilute sulfuric acid After 5 minutes, take it out, rinse it and dry it, then micro-etch it with 5% dilute sulfuric acid and 5% sodium persulfate mixed solution for 5 seconds, finally clean it with deionized water, and dry it for later use;

Step 3: Prepare Ni-Co-Ce ternary alloy film: use AUT85266 electrochemical workstation to prepare alloy film by constant potential deposition method, use the copper clad laminate cleaned in step 2 as the working electrode, and the pure platinum electrode as the counter electrode, and saturate Potassium sulfate electrode is used as reference electrode, carries out electroplating in the plating solution prepared in step 1, keeps temperature during electroplating process and is 25 ℃, solution pH value is 6, electroplating time constant is 5min, and current density is 20mA/cm ; Electroplating ^process In order to reduce the concentration polarization, the desired Ni-Co-Ce ternary alloy thin film can be prepared.

The peel strength of the resin layer on the surface of the copper clad laminate prepared in this example was 47.02 N/cm ² .

Example 2

Prepare Ni-Co-Ce ternary alloy thin film according to the steps of Example 1, only adjust the plating solution preparation of step 1 to: nickel chloride 0.04mol/L, cobalt sulfate 0.035mol/L, sodium chloride 0.1mol/L , boric acid 0.2 mol/L, thiourea 0.1 mol/L, sodium polydithiodipropane sulfonate 0.1 mol/L, ceric sulfate 0.01 mol/L, pH=6, other steps remain unchanged.

The peel strength of the resin layer on the surface of the copper clad laminate prepared in this embodiment was 49.21N/cm ² .

Example 3

Prepare Ni-Co-Ce ternary alloy thin film according to the steps of Example 1, only adjust the plating solution preparation of step 1 to: nickel chloride 0.04mol/L, cobalt sulfate 0.035mol/L, sodium chloride 0.1mol/L , boric acid 0.2 mol/L, thiourea 0.1 mol/L, sodium polydithiodipropane sulfonate 0.1 mol/L, ceric sulfate 0.02 mol/L, pH=6, other steps remain unchanged.

The peel strength of the resin layer on the surface of the copper clad laminate prepared in this embodiment was 57.47 N/cm ² .

Fig. 1 is the SEM image of the copper substrate before alloy plating after pretreatment in the present invention. It can be seen from the figure that the surface of the substrate is very rough with many faults and gaps.

Fig. 2 is an SEM image of the copper-based Ni-Co-Ce alloy thin film prepared in the present invention. As can be seen from the figure, the surface of the alloy film prepared by the method of the present invention is smooth and dense, the crystal grains are refined, the graininess is reduced, the brightness of the coating is improved, and the surface pH and chemical properties are easy to change. Such surface modification is conducive to Improve the corrosion resistance of the alloy layer while reducing surface roughness.

Fig. 3 is an EDS diagram of the copper-based Ni-Co-Ce alloy thin film prepared in the present invention. It can be seen from the figure that the effective components of the alloy film prepared by the method of the present invention include Co, Ni, and Ce, wherein Co accounts for 41.45%, Ni accounts for 50.13%, and Ce accounts for 8.42%.

The above is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All method or process steps may be combined in any way, except for mutually exclusive features and/or steps.

Claims (3)

1. The plating solution for electroplating the Ni-Co-Ce film on the copper-clad plate for the PCB is characterized by comprising the following components: 0.03 to 0.05mol/L of nickel chloride, 0.03 to 0.05mol/L of cobalt sulfate, 0.1 to 0.2mol/L of conductive additive, 0.1 to 0.2mol/L of pH buffer, 0.1 to 0.2mol/L of electroplating additive, 0.005 to 0.03mol/L of cerous sulfate and deionized water;

the plating solution is prepared according to the following preparation process: taking a certain amount of deionized water in a container, sequentially adding a pH buffer, a conductive additive, nickel chloride, cobalt sulfate, an electroplating additive and a ceric sulfate compound under continuous stirring, then adding an acid solution or an alkali solution to adjust the pH value of the system to pH value=5-7, and finally, using deionized water with the same pH value as the system to fix the volume to obtain the required plating solution;

the conductive additive is sodium chloride, sodium sulfate, potassium chloride or potassium sulfate; the pH buffering agent is weak acid, weak acid salt or ammonium salt; the electroplating additive is thiourea and sodium polydithio-dipropyl sulfonate or sodium dodecyl sulfate;

the Ni-Co-Ce alloy film obtained based on the plating solution is used as a protective layer for the surface of an electronic circuit in the manufacturing of a printed board.

2. The plating solution of claim 1, wherein the weak acid is acetic acid, citric acid, or boric acid, and the weak acid salt is an oxalate or a tartrate.

3. The preparation method of the electroplated Ni-Co-Ce alloy film of the copper-clad plate for the PCB is characterized by comprising the following steps of:

step 1: pretreatment of a copper matrix: removing surface stains on the printed circuit copper-clad plate to be electroplated, immersing the printed circuit copper-clad plate in 5% dilute sulfuric acid for 1-10 min, taking out the printed circuit copper-clad plate, cleaning the printed circuit copper-clad plate by using deionized water, carrying out microetching treatment by using a mixed solution of 5% dilute sulfuric acid and 5% sodium persulfate for 1-50 s, cleaning the printed circuit copper-clad plate by using deionized water, and drying the printed circuit copper-clad plate for later use;

step 2: preparing a Ni-Co-Ce ternary alloy film: taking the printed circuit copper-clad plate to be electroplated after the cleaning in the step 1 as a cathode, taking a platinum or titanium net as an anode, adopting a constant potential deposition method to prepare an alloy film by electroplating on the copper surface of the copper-clad plate, wherein the electroplating time is 10-40 min, and the current density is 15-20 mA/cm ² The temperature of the electroplating solution is 15-40 ℃, and stirring is continuously carried out in the electroplating process; wherein, the electroplating solution comprises the following components: 0.03 to 0.05mol/L of nickel chloride, 0.03 to 0.05mol/L of cobalt sulfate, 0.1 to 0.2mol/L of conductive additive, 0.1 to 0.2mol/L of pH buffer, 0.1 to 0.2mol/L of electroplating additive, 0.005 to 0.03mol/L of ceric sulfate and deionized water; wherein the conductive additive is sodium chloride, sodium sulfate, potassium chloride or potassium sulfate; the pH buffering agent is weak acid, weak acid salt or ammonium salt; the electroplating additive is thiourea and sodium polydithio-dipropyl sulfonate or sodium dodecyl sulfate.

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