Electroplating and Gold Plating Process of Multilayer PCB

Electroplating and Gold Plating Process of Multilayer PCB
Electroplating process classification Multilayer PCB: Acid bright copper electroplating nickel/gold plated tin
Multi layer PCB process flow:
Pickling - whole plate copper plating - pattern transfer - acid degreasing - secondary countercurrent flushing - micro etching - secondary pickling - tin plating - secondary countercurrent flushing
Counter current cleaning - acid leaching - pattern copper plating - secondary counter current cleaning - nickel plating - secondary water washing - citric acid leaching - gold plating - recovery - level 2-3 pure water cleaning - drying
printed circuit board

Process description:
1. Pickling
1. Role and purpose:
Remove oxides from the board surface and activate the board surface. In general, the concentration is 5%, and some are kept at about 10%, mainly to prevent water from being brought in, which causes the unstable sulfuric acid content in the tank liquid;
2. The pickling time should not be too long to prevent oxidation of the board surface; After a period of use, if the acid solution is turbid or the copper content is too high, it should be replaced in time to prevent pollution to the surface of the electroplating copper cylinder and plate;
3. C. P grade sulfuric acid is used here;
2. Full plate copper plating: also known as one-time copper plating, plate electroplating, and panel electroplating. Function and purpose:
Protect the thin chemical copper just deposited, prevent the chemical copper from being eroded by acid after oxidation, and add it to a certain extent by electroplating
2. Related process parameters of full plate copper plating: the plating solution is mainly composed of copper sulfate and sulfuric acid. The formula of high acid and low copper is adopted to ensure uniform plate thickness distribution and deep hole deep plating capacity during electroplating; The content of sulfuric acid is mostly 180 g/L, most of which reaches 240 g/L; The content of copper sulfate is generally about 75 g/L. In addition, a small amount of chloride ion is added to the bath solution as an auxiliary luster agent and a copper luster agent to jointly display the luster effect; The addition amount of copper polishing agent or cylinder opening amount is generally 3-5 ml/L. The addition amount of copper polishing agent is generally supplemented by the method of kiloampere hour or according to the actual production effect; The current of the whole plating plate is usually calculated by multiplying 2 A/m2 by the plating area on the plate. For the whole plate, the temperature of the plate length DM * plate width DM * two * 2A/DM2 copper column is kept at room temperature, generally not more than 32 degrees, mainly controlled at 22 degrees. Since the temperature is high in summer, it is recommended to install a cooling temperature control system for the copper cylinder;
3. Process maintenance:
The copper polishing solution shall be replenished in time according to kiloampere hour every day, and the copper polishing solution shall be added according to 100-150ml/kH; Check whether the filter pump works normally and whether there is air leakage; Clean the cathode conductive rod with a clean wet cloth every 2-3 hours; Analyze the content of copper sulfate (once a week), sulfuric acid (once a week) and chloride ion in the copper cylinder regularly (twice a week), adjust the content of brightener through Hall cell test, and timely supplement relevant raw materials; Clean the anode conductive rods and power connectors at both ends of the battery every week, replenish the anode copper balls in the titanium basket in time, and electrolyze for 6-8 hours with a small current of 0.2-0.5 asd; Check whether the anode titanium basket bag is damaged every month, and replace the damaged titanium basket bag in time; Check whether there is anode mud accumulation at the bottom of anode titanium basket, and clean it in time if there is; Filter continuously for 6-8 hours with carbon core, and remove impurities with low current electrolysis; Determine whether to focus on treatment (activated carbon powder) according to the liquid pollution in the tank every half a year or so; Replace filter element of filter pump every two weeks;]
4. Main processing steps: A Take out the anode, pour out the anode, clean the anode film on the anode surface, and then put it into the barrel package of copper anode. Roughen the copper corner surface to uniform pink with micro etchant. After washing and drying, put it into the titanium basket and put it into the acid tank for standby. B. Immerse the anode titanium basket and anode bag in 10% alkaline solution for 6-8 hours, rinse and dry them with water, then soak them in 5% dilute sulfuric acid, rinse and dry them with water for standby; C. Transfer the tank liquid to the standby tank, add 1-3ml/L 30% hydrogen peroxide, start heating, turn on air stirring when the temperature is about 65 ℃, and stir with insulating air for 2-4 hours; D. Turn off the air agitation, slowly dissolve the activated carbon powder in the tank solution at the rate of 3-5 g/L. After dissolution, turn on the air agitation, and keep the temperature for 2-4 hours; E. Turn off the air agitation, heat, 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 bath solution into the cleaned working tank, turn on air agitation, put the anode in it, hang it on the electrolytic plate, and press 0. 2-0 аааај 5asd current density low current electrolysis for 6-8 hours, G After chemical analysis, adjust the content of sulfuric acid, copper sulfate and chloride ion in the tank to the normal operating range; Add whitening agent according to Hall cell test results; H. After the surface color of the electrolytic plate is uniform, stop electrolysis, and then press 1-1. When the current density of 5 asd was treated with electrolytic film for 1-2 hours, a uniform and dense black phosphorus film with good adhesion was formed on the anode; 1. Trial plating is OK;
5. The anode copper ball contains 0. 3-0 аа 6% phosphorus, the main purpose is to reduce the anodic dissolution efficiency and reduce the production of copper powder;
6. When replenishing medicine, if the dosage is large, such as copper sulfate and sulfuric acid; Small current electrolysis shall be carried out after addition; Pay attention to safety when adding sulfuric acid. When the amount of sulfuric acid is large (more than 10 liters), it should be added several times slowly; Otherwise, the temperature of tank liquid is too high, accelerating the decomposition of photocatalyst and polluting the tank liquid;
7. Special attention should be paid to the supplement of chloride ion, 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 hydrochloric acid contains about 385ppm chloride ion,
8. Dosing calculation formula:
Copper sulfate (kg)=(75-x) * tank volume (L)/1000
Sulphuric acid (L)=(10% - x) g/L * tank volume (L)
Or (L)=(180-x) g/L * tank volume (L)/1840
Hydrochloric acid (ML)=(60-x) ppm * tank volume (L)/385
3. Acid degreasing
1. Purpose and function: remove the oxide, ink residue and glue residue on the copper surface of the circuit, and ensure the adhesion between the original copper and the pattern plated copper or nickel
Remember to use acid degreaser here. Why not use alkaline degreaser? The degreasing effect of alkaline degreaser is better than that of acidic degreaser? The main reason is that the graphic ink is not resistant to alkali, which will damage the graphic circuit.
3. In the production process, only the concentration and time of degreaser need to be controlled. The degreaser concentration is about 10%, and the time is guaranteed to be 6 minutes. A little longer time will not have adverse effects; The use and replacement of tank liquid are also based on 15 m2/L working liquid, and the supplement is based on 100 m2. 5-0 аааа 8L а¼›
4. Micro etching:
1. Purpose and function: Clean and rough the copper surface of the circuit to ensure the adhesion between the pattern plated copper and the original copper
2. The micro etchant is mostly sodium persulfate, with stable and uniform roughening rate and good washability. The concentration of sodium persulfate is usually controlled at about 60 g/L and the time is controlled at about 20 seconds. The drug dosage is 3-4 kg per 100 square meters; Copper content shall be controlled below 20g/L; Other maintenance and cylinder replacement are the same as copper precipitation micro corrosion.
5. Pickling
1. Function and application: remove the oxide on the board and activate the board. Generally, the concentration is 5%, and some are kept at about 10%, mainly to prevent water from entering, leading to unstable sulfuric acid content in tank liquid;
2. The pickling time should not be too long to prevent oxidation of the board surface; After a period of use, if the acid solution is turbid or the copper content is too high, it should be replaced in time to prevent pollution to the surface of the electroplating copper cylinder and plate;
3. C. P grade sulfuric acid is used here;
6. Pattern copper plating: also called secondary copper plating and circuit copper plating
1. Purpose and function: In order to meet the rated current load of each line, each line and hole copper needs to reach a certain thickness. In order to facilitate the copper plating of lines, the hole copper and line copper should be thickened to a certain thickness in time;
2. Other items are the same as full plate electroplating
7. Electrotinning
1. Application and function: The use of graphic electroplating pure tin is mainly to protect circuit etching by using pure tin as a metal anti-corrosion layer;
2. The bath is mainly composed of stannous sulfate, sulfuric acid and additives; The stannous sulfate content is controlled at about 35 g/L, and the sulfuric acid content is controlled at about 10%; Tin plating additives are generally added according to the method of kiloampere hours or according to the actual production effect; The current of tin electroplating is usually calculated as 1. 5 amperes per square decimeter multiplied by the plating area on the plate; The temperature of the tin cylinder is kept at room temperature. Generally speaking, the temperature does not exceed 30 degrees, mainly controlled at 22 degrees. Since the temperature is high in summer, it is recommended to install cooling and temperature control systems for tin cans;
3. Process maintenance:
The tin plating additive shall be supplemented timely according to kiloampere hour every day; Check whether the filter pump works normally and whether there is air leakage; Clean the cathode conductive rod with a clean wet cloth every 2-3 hours; Analyze stannous sulfate (once a week) and sulfuric acid in tin cylinder regularly (once a week), adjust the content of tin plating additive through Hall cell test, and timely supplement relevant raw materials; Clean the electric connectors at both ends of the anode conductive rod and battery every week; Electrolysis for 6-8 hours with small current of 0.2-0.5 asd every week; Check whether the anode bag is damaged every month, and replace the damaged anode bag in time; Check whether there is anode mud accumulation at the bottom of the anode bag, if any, replace and clean it in time; Filter continuously for 6-8 hours with carbon core every month, and remove impurities with low current electrolysis; Determine whether to focus on treatment (activated carbon powder) according to tank liquid pollution every half a year; Replace filter element of filter pump every two weeks;
Main processing steps: A Take out the anode, take out the anode bag, clean the anode surface with a copper brush, rinse and dry it with water, put it into the anode bag, and put it into the acid tank for standby. B. Immerse the anode bag in 10% alkaline solution for 6-8 hours, rinse and dry it with water, soak it in 5% dilute sulfuric acid, rinse and dry it with water for standby; C. Transfer the bath solution to the standby tank, slowly dissolve the activated carbon powder in the bath solution at a rate of 3-5 g/L. After complete dissolution, adsorb it for 4-6 hours, filter the bath solution into a clean working tank with 10 um polypropylene filter element and filter aid powder, place it in the anode, hang it on the electrolytic plate, and press 0. 2-0 ааааааа 5asd current density low current electrolysis for 6-8 hours, D After chemical analysis, adjust the content of sulfuric acid and stannous sulfate in the tank to the normal working range; Tin plating additive is added according to Hall cell test results; E. Stop electrolysis after the surface color of the electrolytic plate is uniform; F. Trial plating is OK;
4. When replenishing medicine, such as stannous sulfate and sulfuric acid, the dosage is large; Small current electrolysis shall be carried out after addition; Pay attention to safety when adding sulfuric acid. When the amount of sulfuric acid is large (more than 10 liters), it should be added several times slowly; Otherwise, the tank liquid temperature is too high, stannous oxide is oxidized, and tank liquid aging is accelerated;
5. Dosing calculation formula:
Stannous sulfate (tissue: kg)=(40-x) * tank volume (L)/1000
Sulphuric acid (L)=(10% - x) g/L * tank volume (L)
Or (L)=(180-x) g/L * tank volume (L)/1840
9. Nickel plating
1. Application and function: nickel plating layer is mainly used as the barrier layer between copper layer and gold layer to prevent the mutual diffusion of gold and copper and affect the weldability and service life of the plate; At the same time, the backing of the nickel layer also greatly improves the mechanical strength of the gold layer;
2. Process parameters related to full plate copper plating: nickel plating additives are generally added by the method of kiloampere hours, or according to the actual production effect of the plate, the added amount is about 200ml/Kah; The current of pattern electroless nickel plating is usually calculated by multiplying the decimeter of 2 A/m2 by the electroplating area on the plate; The temperature of nickel cylinder is kept at 40-55 ℃, and the general temperature is about 50 ℃. This nickel cylinder shall be equipped with heating and temperature control system;
3. Process maintenance:
Supplement nickel plating additives according to kiloampere hours every day; Check whether the filter pump works normally and whether there is air leakage; Clean the cathode conductive rod with a clean wet cloth every 2-3 hours; Regularly analyze nickel sulfate (nickel sulfamate), nickel chloride (once a week) and boric acid of copper column every week (once a week), adjust the content of nickel plating additive through Hall cell test, and timely supplement relevant raw materials; Clean the anode conductive rods and electrical connectors at both ends of the battery every week, supplement the anode nickel angle in the titanium basket in time, and electrolyze for 6-8 hours with low current of 0.2-0.5 asd; Check whether the anode titanium basket bag is damaged every month, and replace the damaged titanium basket bag in time; Check whether anode mud accumulates at the bottom of the basket for anode titanium, and clean it in time if any; Filter continuously for 6-8 hours with carbon core, and remove impurities with low current electrolysis; Determine whether to focus on treatment (activated carbon powder) according to tank liquid pollution every half a year; Replace filter element of filter pump every two weeks;]
4. Main processing steps: A Take out the anode, pour out the anode, clean the anode, and then put it into the barrel with nickel corner. Roughen the nickel corner surface to uniform pink with micro etchant. After washing and drying, put it into the titanium basket and put it into the acid tank for standby. B. Immerse the anode titanium basket and anode bag in 10% alkaline solution for 6-8 hours, rinse and dry them with water, then soak them in 5% dilute sulfuric acid, rinse and dry them with water for standby; C. Transfer the tank liquid to the standby tank, add 1-3ml/L 30% hydrogen peroxide, start heating, turn on air stirring when the temperature is about 65 ℃, and stir with insulating air for 2-4 hours; D. Turn off the air agitation, slowly dissolve the activated carbon powder in the tank solution at the rate of 3-5 g/L. After dissolution, turn on the air agitation, and keep the temperature for 2-4 hours; E. Turn off the air agitation, heat, 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 bath solution into the cleaned working tank, turn on air agitation, put in the anode, hang it on the electrolytic plate, and press 0. 2-0 аааај 5asd current density low current electrolysis for 6-8 hours, G After chemical analysis, adjust the content of nickel sulfate or nickel sulfamate, nickel chloride and boric acid in the tank to the normal operating range; Add nickel plating additive according to Hall cell test results; H. After the surface color of the electrolytic plate is uniform, stop electrolysis, and then press 1-1. 5asd current density electrolysis for 10-20 minutes to start the anode; 1. Trial plating is OK;
5. When replenishing medicine, if the dosage is large, such as nickel sulfate or nickel sulfamate, nickel chloride, etc., small current electrolysis should be used after the dosage is added; When adding boric acid, put the added boric acid into a clean anode bag and hang it in the nickel cylinder. Can not be directly added into the tank;
6. After nickel plating, it is recommended to add recycled water for cleaning, and open the cylinder with pure water to supplement the liquid level in the nickel cylinder that is heated and volatilized. After washing with recycled water, connect for secondary countercurrent washing;

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