PCB Blog - Brief Analysis of Copper Electroplating Process of PCB Board

1. Classification of PCB board electroplating process:
Acid Bright Copper Electroplating Nickel Electroplating / Gold Electroplating Tin

2. Process flow:
Pickling → full plate copper plating → pattern transfer → acid degreasing → secondary countercurrent rinsing → micro-etching → secondary → pickling → tin plating → secondary countercurrent rinsing Countercurrent rinsing → pickling → pattern copper plating → secondary countercurrent rinsing → Nickel plating → secondary washing → immersion in citric acid → gold plating → recycling → 2-3 grade pure water washing → drying

3. Process description:
3.1 Pickling
1) Function and purpose: To remove oxides on the board surface and activate the board surface, the general concentration is 5%, and some are kept at about 10%, mainly to prevent the water from being brought into the tank and causing the sulfuric acid content to be unstable;
2) The acid leaching time should not be too long to prevent the surface of the board from oxidizing; after a period of use, the acid solution should be replaced in time when the acid is turbid or the copper content is too high to prevent contamination of the copper electroplating cylinder and the surface of the board;
3) C.P grade sulfuric acid should be used here;

3.2 Full-board copper electroplating: also known as copper, board electricity, Panel-plating
1) Function and purpose: To protect the thin chemical copper just deposited, prevent the chemical copper from being etched by acid after oxidation, and add it to a certain extent by electroplating.
2) Process parameters related to copper electroplating on the whole board: the main components of the bath are copper sulfate and sulfuric acid, and the formula of high acid and low copper is adopted to ensure the uniformity of the thickness distribution of the board surface and the deep plating ability of deep holes and small holes during electroplating; sulfuric acid content Most of them are 180 g/L, and most reach 240 g/L; the content of copper sulfate is generally about 75 g/L, and a trace amount of chloride ions is added to the bath liquid, which acts as an auxiliary gloss agent and copper gloss agent to jointly play a glossy effect; The amount of copper light agent added or the amount of cylinder opening is generally 3-5ml/L, and the addition of copper light agent is generally supplemented according to the method of thousand ampere hours or according to the actual production board effect; the current calculation of full board electroplating is generally 2A / The square decimeter is multiplied by the electroplatable area of the board. For the whole board, it is the board length dm × board width dm × 2 × 2A/DM2; the temperature of the copper cylinder is maintained at room temperature, and the general temperature does not exceed 32 degrees. It is controlled at 22 degrees, so in summer because the temperature is too high, it is recommended to install a cooling temperature control system for the copper cylinder;
3) Process maintenance:
Replenish the copper light agent in time according to the thousand ampere hours every day, and add it according to 100-150ml/KAH; check whether the filter pump is working normally and whether there is air leakage; every 2-3 hours, apply a clean wet cloth to the cathode conductive rod. Scrub clean; regularly analyze the copper jar copper sulfate (1 time/week), sulfuric acid (1 time/week), chloride ion (2 times/week) content, and adjust the light agent content through the Hall cell test, and Relevant raw materials should be replenished in time; the anode conductive rods and the electrical connectors at both ends of the tank should be cleaned every week, the anode copper balls in the titanium basket should be replenished in time, and the electrolysis should be carried out with a low current of 0.2-0.5 ASD for 6-8 hours; it should be checked every month Whether the titanium basket bag of the anode is damaged, the damaged one should be replaced in time; and check whether there is anode sludge accumulated at the bottom of the anode titanium basket, if so, it should be cleaned up in time; and continuously filter with carbon core for 6-8 hours, and at the same time low-current electrolysis to remove impurities ; Every six months or so, it is determined whether large-scale treatment (activated carbon powder) is required according to the pollution of the tank liquid; the filter element of the filter pump should be replaced every two weeks;
4) Major treatment procedure: A. Take out the anode, pour out the anode, clean the anode film on the anode surface, and then put it in the barrel for packaging the copper anode, roughen the surface of the copper corner with a micro-etching agent to a uniform pink color, rinse with water After drying, put it into a titanium basket and put it into an acid tank for use. B. Soak the anode titanium basket and anode bag in 10% alkaline solution for 6-8 hours, rinse with water and dry, then soak in 5% dilute sulfuric acid, rinse with water After drying, it is ready for use; C. Transfer the tank liquid to the standby tank, add 1-3ml/L of 30% hydrogen peroxide, start heating, turn on the air stirring when the temperature is about 65 degrees, and keep the air stirring for 2-4 hours; D. Turn off the air agitation, slowly dissolve the activated carbon powder into the tank liquid at a rate of 3-5 g/L. After the dissolution is complete, turn on the air agitation and keep the temperature for 2-4 hours; E. Turn off the air agitation and heat , let the activated carbon powder slowly settle to the bottom of the tank; F. When the temperature drops to about 40 degrees, use a 10um PP filter element and filter aid powder to filter the tank liquid into a clean working tank, turn on the air stirring, and put in the anode, Hang the electrolytic plate, and electrolyze it at a low current density of 0.2-0.5ASD for 6-8 hours. G. After laboratory analysis, adjust the content of sulfuric acid, copper sulfate and chloride ion in the tank to the normal operating range; according to Hall After the color of the electrolytic plate is uniform, the electrolysis can be stopped, and then the electrolytic film treatment is carried out at the current density of 1-1.5ASD for 1-2 hours, and a uniform layer is formed on the anode. A dense black phosphorous film with good adhesion is enough; I. Trial plating is OK.
5) The anode copper ball contains 0.3-0.6% phosphorus, the main purpose is to reduce the anode dissolution efficiency and reduce the generation of copper powder;
6) When supplementing drugs, such as copper sulfate and sulfuric acid in a large amount; electrolyze with low current after adding; pay attention to safety when supplementing sulfuric acid, and when adding a large amount (above 10 liters), it should be slowly divided into several times. Supplement; otherwise, the temperature of the bath will be too high, the decomposition of the light agent will be accelerated, and the bath will be polluted;
7) Special attention should be paid to the addition of chloride ions, because the chloride ion content is very low (30-90ppm), and it must be accurately weighed with a measuring cylinder or measuring cup before adding; 1ml of hydrochloric acid contains about 385ppm of chloride ions,
8) Calculation formula for drug addition:
Copper sulfate (unit: kg) = (75-X) × tank volume (liter) / 1000
Sulfuric acid (unit: liter) = (10%-X) g/L × tank volume (liter) or (unit: liter) = (180-X) g/L × tank volume (liter)/1840
Hydrochloric acid (unit: ml) = (60-X) ppm × tank volume (liter)/385

3.3 Acid degreasing
1) Purpose and function: remove the oxides on the copper surface of the circuit, the residual glue of the ink film, and ensure the bonding force between copper and pattern electroplating copper or nickel.
2) Remember that acid degreaser is used here, why not use alkaline degreaser and alkaline degreaser is better than acidic degreaser? Mainly because the graphic ink is not resistant to alkali and will damage the graphic circuit, only acid degreaser can be used before graphic plating.
3) Only need to control the concentration and time of the degreaser during production. The degreaser concentration is about 10%, and the time is guaranteed to be 6 minutes. A little longer time will not have adverse effects; Working fluid, supplemented according to 100 square meters 0.5-0.8L;

3.4 Micro-etching:
1) Purpose and function: Clean and roughen the copper surface of the circuit to ensure the bonding force between the patterned copper and copper.
2) Sodium persulfate is mostly used for micro-etching agents, the roughening rate is stable and uniform, and the water washability is good. The concentration of sodium persulfate is generally controlled at about 60 g/L, and the time is controlled at about 20 seconds. kg; copper content is controlled below 20 g/L; other maintenance and replacement cylinders are micro-corroded with copper sinking.

3.5 Pickling
1) Function and purpose: To remove oxides on the board surface and activate the board surface, the general concentration is 5%, and some are kept at about 10%, mainly to prevent the water from being brought into the tank and causing the sulfuric acid content to be unstable;
2) The acid leaching time should not be too long to prevent the surface of the board from oxidizing; after a period of use, the acid solution should be replaced in time when the acid is turbid or the copper content is too high to prevent contamination of the copper electroplating cylinder and the surface of the board;
3) C.P grade sulfuric acid should be used here;

3.6 Pattern copper plating: also known as secondary copper, copper plating on the circuit
1) Purpose and function: In order to meet the rated current load of each line, each line and hole copper need to reach a certain thickness. The purpose of copper plating the line is to thicken the hole copper and line copper to a certain thickness in time;
2) Other items are the same as the whole plate electroplating on PCB board.