Analysis of PCB Copper Plating Process

Analysis of PCB Copper Plating Process
1 Classification PCB board electing 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
PCB board

3. Process description:
3.1 Pickling
1) Function and purpose: To remove oxides on the board surface and activate the board surface, the total concentration is 5%, and some remain at about 10%, mainly to prevent the water from being broken into the tank and causing the sulfur 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 plate copper plating: also known as copper, panel plating
1) Function and purpose: To protect the thin chemical copper just deposited, to prevent chemical copper from being corroded by acid after oxidation, and to a certain extent by electroplating
2) Process parameters related to copper electroplating on the whole board:; The content of sulfuric acid is mostly 180 g/L, and the content of copper sulfate reaches 240 g/L, which is generally about 75 g/L. Add a small amount of chloride ions to the bath solution as an auxiliary luster agent and a copper luster agent to jointly play a luster effect; The amount of copper light agent added or bottle opened is generally 3-5 ml/L, while the amount of copper light agent added is generally supplemented according to the method of kiloampere hours or according to the actual production effect; The electroplating current of the whole board is generally calculated as 2A/square decimeter times the electroplating area of the circuit board For the entire board of directors, it is the board chairman dm à — Board width dm à — 2à — 2A/DM2；  The temperature of the copper column shall be kept at room temperature, which generally does not exceed 32 ℃ It is recommended to install a cooling temperature control system for the copper cylinder in summer because the temperature is too high;
3) Process maintenance:
Replenish the copper light agent in time according to the same sample hours every day, press 100-150ml to join/KAH; Check whether the filter pump works normally and whether there is air leakage; Every 2-3 hours, apply a clean wet cloth on the cathode conductive rod Scrub clean;  Regularly analyze the copper jar copper sulfate (1 time/week), sulfur acid (1 time/week), chlorine ion (2 times/week) content, and adjust the content of the photocatalyst through the Hall cell test to timely supplement relevant raw materials; The anode conductive rod and the electric connector at both ends of the oil tank shall be cleaned every week. The anode copper ball in the titanium basket shall be replenished in time. The electrolysis shall be conducted at a low current of 0. 2 - 0.5 ASD, lasting for 6-8 hours; Check whether the anode titanium basket bag is damaged every month, and replace the damaged one in time; Check whether there is anode sludge accumulation at the bottom of anode titanium basket, and if so, clean it in time; Filter continuously for 6-8 hours with carbon core, and remove impurities with low current electrolysis; About every six months, it is determined which large scale treatment (activated carbon powder) is required according to the polling 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 the copper anode into a barrel to package it. Roughen the copper corner surface to uniform pink with micro etchant. After drying, rinse it with water, put it into a titanium basket, and put it into an acid bath for use B. Immerse the anode titanium basket and anode bag in 10% alkaline solution for 6-8 hours, rinse and dry them with water, and then soak them in 5% dilute sulfuric acid. After drying, rinse them with water and they can be used at any time; C. Transfer the liquid in the storage tank to the standby storage tank, add 1-3ml/L 30% hydrogen peroxide, and start heating. When the temperature is about 65 ℃, turn on air stirring, and keep air stirring for 2-4 hours; D. Turn off the air agitation, and slowly dissolve the activated carbon powder into the tank solution at the rate of 3-5 g After dissolution, turn on air agitation and keep the temperature for 2-4 hours; E. Turn off air agitation and heating, and let the activated carbon powder slowly settle to the tank bottom; F. When the temperature drops to about 40 ℃, use 10um polypropylene filter element and filter aid powder to filter the tank liquid into a clean working tank, turn on air agitation, put the anode in, hang the electrolytic plate, and electrolyze for 2-0.5ASD 6-8 hours at a low current density of 0 G. After laboratory analysis, adjust the sulfuric acid content, and the copper sulfate and chloride ions in the tank reach the normal working range; According to the uniform color of Hall rear electrolysis plate, electrolysis can be stopped, and then electrolytic membrane treatment is carried out under the current density of 1-1 5ASD for 1-2 hours, and form a uniform layer on the anode The dense black phosphorus film with good adhesion is sufficient; I. Trial plating is OK
5) The anode copper ball contains 0.3-0.6% phosphorus, the main purpose is to reduce the anode dispersion efficiency and reduce the generation of copper powder;
6) When supplying drugs, such as a large amount of copper sulfate and sulfuric acid; Electrolysis with low current after adding; Pay attention to safety when adding a large amount (above 10 liters) Otherwise, if the bath temperature is too high, the decomposition of light reagent will be accelerated;
7) Special attention should be paid to the addition of chloride ions, because the chloride ion content is very low (30-90ppm); 1ml hydrochloric acid contains about 385ppm chloride ion,
8) Calculation formula for drug addition:
Copper sulfate (unit: kg) = (75-X) à —  tank volume (liter) / 1000
Sulfuric acid (unit: liter) = (10%-X) g/L à —  tank volume (liter) or (unit: liter) = (180-X) g/L à —  tank volume (liter)/1840
Hydrochloric acid (unit: ml) = (60-X) ppm à —  tank volume (liter)/385
3.3 Acid degreasing
1) Purpose and function: remove the oxides on the copper surface of the circuit
2) Remember that acid degreaser is used here, why not use alkaline degreaser? Is alkaline degreaser better than acidic degreaser? This is mainly because the graphic ink is not alkali resistant and will damage the graphic circuit. Only acid degreaser can be used before electroplating
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; For working fluid, add 0.5-0.8L per 100m2;
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 most used for micro cutting agents, with stable and uniform coarsening rate and good water washability The concentration of sodium persulfate is usually controlled at about 60 g/L and the time is controlled at about 20 seconds The copper content per kilogram shall be controlled below 20g/L Other maintenance and replacement cylinders are slightly corroded due to copper sinking

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