Detailed Explanation of Practical Electroplating Technology Training
I. Electrolytic passivation process
Process parameters
The electrolytic passivation process in this electroplating practical technology has clear parameter requirements. The temperature is set at room temperature. This condition is quite convenient as it doesn't require additional heating or cooling equipment, thus reducing energy consumption and costs. The anode is made of stainless steel, which has good corrosion resistance and stability and can maintain its own performance during the electrolysis process. The time is controlled within 1 - 1.5 minutes. This time period is the optimal range obtained through multiple tests, which can ensure the passivation effect and improve production efficiency at the same time.
Key points of operation
During electrolytic passivation, the plated part serves as the cathode. In this process, the cleaning of the anode surface is of crucial importance. Once a black film forms on the anode surface, it should be immediately taken out of the plating bath, and then subjected to water washing, pickling, and water washing in sequence. After thoroughly removing impurities and contaminants, it can be put back into the plating bath. This is done to ensure the activity of the anode and the normal progress of the electrolytic reaction.
To ensure the passivation quality, the pH value of the bath solution should not be lower than 12.5. A higher pH value helps to form a stable passivation film. The current needs to be maintained above 1A/dm². If the constant voltage mode is adopted, it should be controlled at 5 - 6V. These two parameters cooperate with each other and jointly affect the quality and performance of the passivation film.
Subsequent processing procedures
The passivated workpieces must be thoroughly washed with water to remove the residual bath solution and impurities on the surface. Then, water and oil removal treatments are carried out. Water removal is to use a water-removing agent to remove the water on the surface of the workpieces, making the surface non-hydrophilic and preparing for the subsequent oil removal treatment. Oil removal is to remove the non-hydrophilic water-removing agent on the surface of the workpieces. Finally, the workpieces are dried and painted to complete the entire surface treatment process. The complete process flow is as follows: imitation gold → water washing → water washing → electrolytic passivation → ultrasonic water cleaning → one-time water washing → water removal → oil removal.
II. 24K Imitation Gold Electroplating
The 24K imitation gold electroplating in Wenzhou's technological innovation deserves special attention. It is not only the optimization of the complex in the formula, the ternary content of copper, zinc and tin, and the temperature, but more importantly, the selection of current and time. The current is divided into three levels with different amperages, and these three levels of current are controlled by time. By setting high, medium and low cathode currents, starting with high current and then reducing it, and making the hanger gently shake continuously, under the action of the current, the color of the coating will gradually change from pale white to slightly yellow, and finally approach the color of 24K gold.
The golden tone of the plating is closely related to the drying temperature of the varnish. When the color is close to 24K gold, the drying temperature of the varnish should be relatively low, and it is best if the surface color of the plating has a slight pink tint. After the varnish is sprayed, dried and cooled, the plating will turn into a pure 24K gold color, presenting an excellent visual effect.
III. Electroplating process for black coatings
The electroplating process for black coatings is a popular decorative electroplating process, second only to the imitation gold electroplating process. Common black coatings include black nickel (nickel-zinc alloy coating) and nickel-tin alloy coating (gunmetal coating or pearl black).
Nickel-zinc alloy (black nickel)
In black nickel mainly composed of nickel-zinc alloy, it contains about 40% - 60% nickel, 20% - 30% zinc, 0% - 15% sulfur, and about 10% organic matter. Its typical process formula is shown in the following table:
Composition (g/L) and process conditions12
NiSO₄·7H₂O90 - 12076 - 100
ZnSO₄·7H₂O40 - 6040 - 50
(NH₄)₂SO₄20 - 30 -
NiSO₄·(NH₄)₂SO₄·6H₂O40 - 60 -
NH₄CNS25 - 3525 - 35
H₃BO₃25 - 3525 - 35
PH5 - 64.5 - 5.5
Temperature °C30 - 3530 - 35
DK (A/dm²)0.1 - 0.30.1 - 0.4
During the electroplating process, the sulfur in the thiocyanate ion reacts with nickel to form black NiS. Since the current density is very low, the obtained coating is relatively brittle, so it is impossible to plate it too thick. The brightness of the coating mainly depends on the brightening effect of the underlying coating. The brighter the underlying coating is, the blacker the black nickel layer appears. Otherwise, the blackness will decrease.
Nickel - tin alloy (pearl black coating)
The Ni - Sn coating is often referred to as a gun - colored coating or pearl - black coating due to its black appearance. Generally, the coating contains 35% Ni and 65% Sn. Sometimes, Cu is appropriately added to increase the coating's hardness and improve its appearance. The black Ni - Sn coating is made by adding a blackening agent, such as S - and N - containing compounds (sulfur - containing amino acids, etc.), on the basis of a mixture of Ni and Sn in a certain proportion.
Like the black Ni - Zn coating, the blackness of the Ni - Sn coating often also depends on the brightening effect of the underlying coating. Generally speaking, the blackness of the Ni - Sn coating is slightly inferior to that of the Ni - Zn coating. However, this color tone is very solemn and elegant, which is deeply loved by people and has been widely used in industries such as daily hardware, bicycles, lamps, and jewelry.
Composition (g/L) and process conditions12
SnCL₂·2H₂O5010
NiCL₂·6H₂O25075
NiSO₄·7H₂O20 -
K₄P₂O₇250 -
Methionine5 -
Startup agent200 ml/L -
Blackening agent10 - 15ml/L -
PH4.5 - 5.58.5
Temperature °C50 - 6550
DK A/dm²0.5 - 12
Coating protection
Both the Ni - Zn and Ni - Sn black coatings are prone to discoloration, especially the Ni - Zn coating. This situation is more likely to occur in the Ni - Zn coating. The electroplated surface will lose its luster and the blackness will be uneven, which seriously affects the appearance. Since such coatings are extremely prone to discoloration when exposed to harmful gases in the electroplating workshop before dehydration after plating, passivation treatment must be carried out after plating. The following passivation solution has a good effect on preventing discoloration of the Ni - Zn and Ni - Sn black coatings: CrO₃ 3 - 5g/L, pH 2 - 4, and treat for 10 - 20 seconds at room temperature.
Passivation treatment can only prevent discoloration for a short time or between processes. Since this type of coating is thin and brittle, not wear-resistant and not durable, in order to improve its practical effect and service life, the passivated black coating generally needs to be coated with a protective paint. The black Sn - Ni alloy, black Sn - Co alloy, and white chromium - substitute Sn - Cr alloy launched by OMI Company and Taizhou Ensen Company, a wholly - owned Singaporean enterprise, all have good effects and are favored by users. The typical process flow is as follows:
1. Nickel-free process: Pretreatment → Running water rinsing × 3 → Acidic bright copper plating → Running water rinsing × 3 → White copper-tin alloy as nickel substitute → Running water rinsing × 3 → → Running water rinsing × 3 → → Running water rinsing × 3 → Drying → Packaging
2. Electroplating of nickel-containing alloys: Pretreatment → Running water cleaning × 3 → Acidic bright copper plating → Running water cleaning × 3 → Fully bright nickel plating → Running water cleaning × 3 → → Running water cleaning × 3 → → Running water cleaning × 3 → Drying → Packaging
3. Two-color alloy electroplating: Pretreatment → Running water cleaning × 3 → Acidic bright copper plating → Running water cleaning × 3 → Fully bright nickel plating → Running water cleaning × 3 → Imitation gold electroplating → Running water cleaning × 3 → Paint protection → Acid activation → Running water cleaning × 3 → → Running water cleaning × 3 → Treatment for removing protective paint → Running water cleaning × 3 → Electrophoretic painting or dip painting → Drying → Packaging
IV. Electronic Electroplating - PCB Electroplating
Overview of the PCB electroplating industry
In 2000, the output value of PCB in China was 3.635 billion US dollars, accounting for 8.7% of the global PCB output value and ranking the 4th in the world. Among them, the output value of PCB in Guangdong region accounted for as high as 83.5% of that in China. It can be seen that PCB electroplating in Guangdong region is an industry of considerable scale.
According to incomplete statistics, the annual consumption of only one raw material, phosphor copper, by PCB manufacturers in Guangdong reaches about 10,000 tons. Large PCB enterprises consume 400 - 600 tons of phosphor copper annually, while medium-sized enterprises consume 200 - 300 tons. The annual demand for PCB acid copper brightener in the Guangdong region exceeds 1,000 tons. The annual sales output value of only phosphor copper and acid copper brightener reaches 400 - 500 million yuan.
Multiple surface treatment processes are involved in PCB production, such as degreasing, removing contamination on the inner wall of holes, activation treatment, electroless copper plating, direct electroplating process, electroplating lead-tin alloy, copper foil etching, electroless nickel plating, gold process, etc. Therefore, a large amount of special electroplating chemicals and common chemical raw materials are required, and the total value amounts to several billion RMB.
Currently, more than 90% of the special chemicals used in the PCB industry are monopolized by large international companies, such as the well - known American companies MacDermind and Shipley, and the former German companies Schering and Schlotter, etc. (Now LeaRona has been merged by Shipley, Schering has merged into Atotech, and MacDermind has merged the British company Canning). Only the products of a few domestic research institutes and electroplating additive manufacturers have entered a small number of small - scale PCB enterprises. On the one hand, this is because PCB production has very strict requirements for all raw materials. On the other hand, it is because PCB production involves many processes and is of high value, and the economic responsibility is significant in case of quality problems. Therefore, only when domestic research institutes engaged in surface treatment and electroplating additive production enterprises increase investment, introduce professional high - tech talents, and purchase special instruments and equipment for research and development, is it possible for them to enter this industry with huge market potential.
Traditional PCB electroplating process
The industrial - scale production of printed circuit boards (double - sided and multi - layer) became possible thanks to the electroless copper plating formula patented by PCK Company in 1963 and the colloidal palladium formula patented by Shipley Company in 1961. They are the foundation for the through - hole plating to be run on an automatic production line and also the basic processes for PCB manufacturing that were widely accepted later.
Since entering the 1990s, the traditional PTH (Plated Through Hole) process mainly based on electroless copper plating has faced various pressures and challenges. In the traditional PCB manufacturing process, electroless copper plating solutions have the following common characteristics: i. They all contain complexing agents or chelating agents, such as potassium sodium tartrate, EDTA, and EDTP; ii. Formaldehyde is used as the reducing agent for electroless copper plating, and most stabilizers are cyanides. The presence of complexing agents EDTA or EDTP has brought great difficulties to wastewater treatment. Formaldehyde is a well - known carcinogen, and there are also side reactions in traditional electroless copper plating, which makes the maintenance and management of the electroless copper plating bath difficult and then causes quality problems in electroless copper plating. The cost of electroless copper plating also varies greatly depending on the utilization efficiency. The cost of a non - continuously operating bath is several times higher than that of a continuously operating one. Therefore, the electroless copper plating process has always been a difficult problem for PCB manufacturers.
Direct electroplating technology
After entering the 1980s, European and American countries put forward stricter requirements for environmental protection, especially regarding the emission restrictions on toxic formaldehyde and difficult-to-treat chelating agents. This forced most solution suppliers to search for new methods to achieve hole metallization as an alternative to traditional electroless copper plating. After a relatively long period of trial use, direct electroplating technology and its products were recognized by PCB manufacturers in the mid-1990s.
The direct electroplating technology as a substitute for electroless copper plating must meet the following conditions:
1. On non-conductors (including hole wall substrates such as epoxy glass cloth, polyimide, and polytetrafluoroethylene), a conductive layer is formed through special treatment to enable metal electroplating. At the same time, good adhesion between the plating layer and the substrate should be ensured.
2. The chemical solutions used to form the conductive layer cause little environmental pollution, are easy to handle in terms of "three wastes" treatment, and will not cause serious pollution.
3. The shorter the process flow for forming the conductive layer, the better, and the operating range should be relatively wide to facilitate operation and maintenance.
4. It can adapt to the production of various printed circuit boards, such as printed circuit boards with a high board thickness/aperture ratio, blind via printed circuit boards, printed circuit boards with special substrates, etc.
At present, the direct electroplating technologies in the world can be classified into three major types according to materials: Type I is the technology that uses the colloidal palladium process to produce a thin conductive metal layer of Pd on the surface of non - conductors; Type II is the so - called MnO₂ grafting technology that uses conductive polymer materials as the conductive layer; Type III is the direct electroplating technology based on the coating film of carbon or graphite suspension.
Printed circuit board electroplating and surface coating process
During the manufacturing process of printed circuit boards, in order to meet the requirements of the board surface, various surface coating processes need to be selected, such as hole metallization, copper plating, nickel plating, gold plating, electroless nickel plating, electroless gold plating, organic solderability preservative, and electroplating of tin-based alloys. The quality of these surface coating layers directly affects the appearance, solderability, corrosion resistance, wear resistance and other properties of printed circuit boards.
The summary of the surface coating process for printed circuit boards is as follows:
1. Hole metallization: Either the chemical copper deposition process or the direct copper plating process can be selected. After hole metallization, the printed circuit board has a surface coated with 5 - 8μm of metallic copper.
2. Hot air leveling or hot melting process: The process flow is as follows: [The details are not provided in the original text and relevant content needs to be further supplemented.]