PCB Technical - Electroplating and gold plating process of Multilayer PCB board

Classification of electroplating process for Multilayer PCB: Acid bright copper electroplating nickel / gold electroplating tin.

Multilayer PCB process flow:

Pickling - copper plating on the whole board - pattern transfer - acid degreasing - secondary countercurrent rinsing - micro etching - secondary - pickling - tin plating - secondary countercurrent rinsing

Countercurrent rinsing - acid dipping - graphic copper plating - secondary countercurrent rinsing - nickel plating - secondary water washing - citric acid dipping - gold plating - recovery - 2-3-stage pure water washing - drying

Process Description:

1. Pickling

1. Role and purpose:

Remove the oxide on the plate surface and activate the plate surface. Generally, the concentration is 5%, and some are maintained at about 10%, mainly to prevent the water from bringing in and causing the unstable sulfuric acid content in the tank liquid;

2. The acid leaching time should not be too long to prevent oxidation of the plate surface; After use for a period of time, if the acid solution is turbid or the copper content is too high, it shall be replaced in time to prevent contamination of the plated copper cylinder and plate surface;

3. C.P grade sulfuric acid shall be used here;

2. Full plate copper plating: also known as primary copper, plate electricity, panel plating 1. function and purpose:

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 plating on the whole plate: the bath solution is mainly composed of copper sulfate and sulfuric acid. The formula of high acid and low copper is adopted to ensure the uniformity of plate thickness distribution and deep plating ability for deep holes during electroplating; The sulfuric acid content is mostly 180 g / L, and most of them reach 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 tank liquid as an auxiliary gloss agent and copper gloss agent to play the gloss effect together; The addition amount or cylinder opening amount of copper polish is generally 3-5ml / L. the addition of copper polish is generally supplemented according to the method of kiloampere hour or according to the actual production effect; The current of the whole plate electroplating is generally calculated by multiplying 2 A / square decimeter by the electroplating area on the plate. For the whole plate, it is the plate length DM * Plate width DM * two * 2A/ DM2; The temperature of the copper cylinder is maintained at room temperature, generally no more than 32 degrees, mostly controlled at 22 degrees. Therefore, due to the high temperature in summer, it is recommended to install a cooling temperature control system for the copper cylinder;

3. Process maintenance:

Replenish copper polish in time according to kiloampere hours every day, and add it according to 100-150ml / Kah; 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 copper sulfate (once a week), sulfuric acid (once a week) and chloride ion in copper cylinder regularly every week (2 times / week) content, adjust the brightener content through Hall cell test, and supplement relevant raw materials in time; clean the anode conductive rod and the electrical connectors at both ends of the cell every week, supplement the anode copper ball in the titanium basket in time, and electrolyze with low current 0.2-0.5asd for 6-8 hours; check whether the titanium basket bag of the anode is damaged every month, and replace the damaged one in time; and check the bottom of the anode titanium basket Whether anode mud is accumulated, and if so, it shall be cleaned in time; Carbon core was used for continuous filtration for 6-8 hours, and impurities were removed by low current electrolysis at the same time; Every half a year or so, determine whether major treatment (activated carbon powder) is required according to the tank liquid pollution; replace the filter element of the filter pump 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 packaging the 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. soak the anode titanium basket and anode bag in 10% alkaline solution for 6-8 hours, wash and dry with water, and then soak in 5% dilute sulfuric acid, Wash and dry 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 degree Celsius, and stir with insulated air for 2-4 hours; D. Turn off the air stirring, slowly dissolve the activated carbon powder into the tank solution at the rate of 3-5g / L, turn on the air stirring after the dissolution is complete, and keep it warm for 2-4 hours; E. Turn off the air stirring, heat up and let the activated carbon powder settle to the bottom of the tank slowly; F. When the temperature drops to about 40 degree Celsius, use 10um PP filter element and filter aid powder to filter the tank liquid into the cleaned working tank, turn on air stirring, put in the anode, hang it into the electrolytic plate, and press 0. 2-0. 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; Replenish the brightener according to the Hall cell test results; H. After the color of the electrolytic plate surface is uniform, stop electrolysis, and then press 1-1. The current density of 5asd shall be treated with electrolytic film for 1-2 hours, and a uniform and dense black phosphorus film with good adhesion shall be formed on the anode; 1. Trial plating OK OK;

5. The anode copper ball contains 0. 3-0. 6% phosphorus, the main purpose is to reduce the anodic dissolution efficiency and reduce the production of copper powder;

6. When replenishing drugs, if the amount is large, such as copper sulfate and sulfuric acid; Low current electrolysis shall be conducted after addition; Pay attention to safety when adding sulfuric acid. When the amount of sulfuric acid is large (more than 10 liters), it shall be added slowly several times; otherwise, the tank liquid temperature will be too high, the photocatalyst decomposition will be accelerated, and the tank liquid will be polluted;

7. Special attention shall be paid to the supplement of chloride ions, because the content of chloride ions is particularly low (30-90ppm), it must be weighed accurately with a measuring cylinder or cup before adding; 1ml hydrochloric acid contains about 385ppm of chloride ions,

8. Drug addition calculation formula:

Copper sulfate (kg) = (75-x) * Tank volume (L) / 1000

Sulfuric acid (in liters) = (10% - x) g / L * Tank volume (L)

Or (in liters) = (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 on the copper surface of the line, residual film of ink and residual glue, and ensure the adhesion between primary copper and pattern electroplating copper or nickel

2. Remember to use acid degreaser here. Why not use alkaline degreaser, and the degreasing effect of alkaline degreaser is better than that of acid degreaser? The main reason is that the graphic ink is not alkali resistant and will damage the graphic circuit, so only acid degreaser can be used before graphic electroplating.

3. During production, it is only necessary to control the concentration and time of degreaser. The concentration of degreaser 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 is also based on 15 m2 / L working liquid, and the supplementary addition is based on 100 m2 0. 5-0. 8L;

4. Micro etching:

1. Purpose and function: clean and roughen the copper surface of the circuit to ensure the bonding force between pattern electroplating copper and primary copper

2. Sodium persulfate is mostly used as the micro etchant, with stable and uniform coarsening rate and good water washability. The concentration of sodium persulfate is generally controlled at about 60 g / L and the time is controlled at about 20 seconds. The addition of drugs is 3-4 kg per 100 square meters; Copper content shall be controlled below 20 g / L; Other maintenance and cylinder replacement are the same as copper precipitation micro corrosion.

5. Pickling

1. Function and purpose: remove the oxide on the plate surface and activate the plate surface. The general concentration is 5%, and some are maintained at about 10%, mainly to prevent the water from bringing in and causing the unstable sulfuric acid content in the tank liquid;

2. The acid leaching time should not be too long to prevent oxidation of the plate surface; After use for a period of time, if the acid solution is turbid or the copper content is too high, it shall be replaced in time to prevent contamination of the plated copper cylinder and plate surface;

3. C.P grade sulfuric acid shall be used here;

6. Graphic copper plating: also known as secondary copper, circuit copper plating

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. For the purpose of line copper plating, the hole copper and line copper shall be thickened to a certain thickness in time;

2. Other items are the same as full plate electroplating

7. Electroplated tin

1. purpose and function: the purpose of graphic electroplated pure tin mainly uses pure tin as a metal resist layer to protect circuit etching;

2. The bath liquid is mainly composed of stannous sulfate, sulfuric acid and additives; Stannous sulfate content is controlled at about 35 g / L and sulfuric acid is controlled at about 10%; The addition of tin plating additives is generally supplemented according to the method of kiloampere hour or according to the actual production effect; The current of electroplated tin is generally calculated as 1. 5 A / square decimeter multiplied by the electroplating area on the plate; The temperature of the tin cylinder is maintained at room temperature. Generally, the temperature does not exceed 30 degrees and is mostly controlled at 22 degrees. Therefore, due to the high temperature in summer, it is recommended to install a cooling and temperature control system for the tin cylinder;

3. Process maintenance:

Timely supplement tin 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 rag every 2-3 hours; Analyze stannous sulfate (once a week) and sulfuric acid in tin cylinder regularly every week (once a week), adjust the content of tin plating additives through Hall cell test, and timely supplement relevant raw materials; clean the anode conductive rod and the electrical connectors at both ends of the cell every week; electrolyze with low current 0.2-0.5asd for 6-8 hours every week; check whether the anode bag is damaged every month, and replace the damaged one in time; check whether there is anode mud accumulated at the bottom of the anode bag, and if so, timely replace it Clean up; Filter continuously with carbon core for 6-8 hours every month, and remove impurities by low current electrolysis; Determine whether major treatment (activated carbon powder) is required according to the tank liquid pollution every half a year; replace the filter element of the filter pump every two weeks;

Major treatment procedure: A. take out the anode, remove the anode bag, clean the anode surface with a copper brush, wash and dry it with water, put it into the anode bag and put it into the acid tank for standby. B. soak the anode bag in 10% alkaline solution for 6-8 hours, wash and dry it with water, soak it in 5% dilute sulfuric acid, and wash and dry it with water for standby; C. Transfer the tank liquid to the standby tank, slowly dissolve the activated carbon powder into the tank liquid at the rate of 3-5g / L. after it is completely dissolved, adsorb it for 4-6 hours, filter the tank liquid with 10um PP filter element and filter aid powder into the cleaned working tank, put it into the anode, hang it into the electrolytic plate, and press 0. 2-0. 5asd current density low current electrolysis for 6-8 hours, D. after chemical analysis, adjust the sulfuric acid and stannous sulfate content in the tank to the normal operating range; Add tin plating additives according to the Hall cell test results; E. Stop electrolysis after the color of the electrolytic plate surface is uniform; F. Trial plating OK OK;

4. When replenishing drugs, if the addition amount is large, such as stannous sulfate and sulfuric acid; Low current electrolysis shall be conducted after addition; Pay attention to safety when adding sulfuric acid. When the amount of sulfuric acid is large (more than 10 liters), it shall be added slowly several times; otherwise, the tank liquid temperature will be too high, stannous oxide will be oxidized, and the tank liquid aging will be accelerated;

5. Drug addition calculation formula:

Stannous sulfate (unit: kg) = (40-x) * Tank volume (L) / 1000

Sulfuric acid (in liters) = (10% - x) g / L * Tank volume (L)

Or (in liters) = (180-x) g / L * Tank volume (L) / 1840

9. Nickel plating

1. Purpose 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 board; At the same time, the backing of nickel layer also greatly increases the mechanical strength of gold layer;

2. Process parameters related to copper plating on the whole plate: the addition of nickel plating additives is generally supplemented according to the method of kiloampere hour, or the addition amount is about 200ml / Kah according to the actual production effect of the plate; The current of pattern electroless nickel plating is generally calculated by multiplying 2 A / square decimeter by the electroplating area on the plate; The temperature of the nickel cylinder is maintained at 40-55 degrees, and the general temperature is about 50 degrees. Therefore, the nickel cylinder should be equipped with heating and temperature control system;

3. Process maintenance:

Timely 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 rag every 2-3 hours; The copper cylinder nickel sulfate (nickel sulfamate) (once a week), nickel chloride (once a week) and boric acid shall be analyzed regularly every week (once a week), adjust the content of nickel plating additives through Hall cell test, and supplement relevant raw materials in time; clean the anode conductive rod and the electrical connectors at both ends of the cell every week, supplement the anode nickel angle in the titanium basket in time, and electrolyze with low current 0.2-0.5asd for 6-8 hours; check whether the titanium basket bag of the anode is damaged every month, and replace the damaged one in time; and check the anode titanium Whether anode mud is accumulated at the bottom of the basket, and if so, it shall be cleaned in time; Carbon core was used for continuous filtration for 6-8 hours, and impurities were removed by low current electrolysis at the same time; Determine whether major treatment (activated carbon powder) is required according to the tank liquid pollution every half a year; replace the filter element of the filter pump every two weeks;]

4. Major treatment procedure: A. take out the anode, pour out the anode, clean the anode, and then put it in the barrel packed with nickel corner, roughen the surface of nickel corner with micro etchant to uniform pink. After washing and drying, put it into the titanium basket and put it into the acid tank for standby. B. soak the anode titanium basket and anode bag in 10% alkaline solution for 6-8 hours, wash and dry with water, and then soak in 5% dilute sulfuric acid, Wash and dry 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 degree Celsius, and stir with insulated air for 2-4 hours; D. Turn off the air stirring, slowly dissolve the activated carbon powder into the tank solution at the rate of 3-5g / L, turn on the air stirring after the dissolution is complete, and keep it warm for 2-4 hours; E. Turn off the air stirring, heat up and let the activated carbon powder settle to the bottom of the tank slowly; F. When the temperature drops to about 40 degree Celsius, use 10um PP filter element and filter aid powder to filter the tank liquid into the cleaned working tank, turn on air stirring, put in the anode, hang it into the electrolytic plate, and press 0. 2-0. 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 additives according to the Hall cell test results; H. After the color of the electrolytic plate surface is uniform, stop electrolysis, and then press 1-1. The current density of 5asd is electrolyzed for 10-20 minutes to activate the anode; 1. Trial plating OK OK;

5. When supplementing drugs, if the addition amount is large, such as nickel sulfate or nickel sulfamate and nickel chloride, it shall be electrolyzed with low current after addition; When adding boric acid, put the added boric acid into a clean anode bag and hang it in the nickel cylinder. It cannot be directly added into the tank;

6. After nickel plating, it is recommended to add a recovery water wash and open the cylinder with pure water, which can be used to supplement the liquid level volatilized by heating in the nickel cylinder. After recovery water wash, it is connected with secondary countercurrent rinsing;

7. Drug addition calculation formula:

Nickel sulfate (kg) = (280-x) * Tank volume (L) / 1000

Nickel chloride (kg) = (45-x) * Tank volume (L) / 1000

Boric acid (kg) = (45-x) * Tank volume (L) / 1000

10. Electroplating gold: it is divided into electroplating hard gold (gold alloy) and water gold (pure gold) processes. The composition of hard gold plating is basically the same as that of soft gold bath, but there are some trace metals such as nickel, cobalt or iron in the hard gold bath;

1. Purpose and function: as a precious metal, gold has good weldability, oxidation resistance, corrosion resistance, low contact resistance, good wear resistance and so on;

2. At present, gold plating on circuit board is mainly citric acid gold bath, which is widely used because of its simple maintenance, simple and convenient operation;

3. The gold content of water is controlled at about 1g / L, and the pH value is 4. About 5, the temperature is 35 degree Celsius, the specific gravity is about 14 Baume degrees, and the current density is about 1asd;

4. The main added drugs include acid adjusting salt and basic adjusting salt for adjusting pH value, conductive salt for adjusting specific gravity, gold plating supplementary additives and gold salt, etc;

5. In order to protect the gold cylinder, a citric acid leaching tank should be added in front of the gold cylinder, which can effectively reduce the pollution to the gold cylinder and maintain the stability of the gold cylinder;

6. After plating, the gold plate shall be washed with primary pure water as recovery water. At the same time, it can also be used to supplement the evaporation level of the gold cylinder. After recovery water washing, it shall be followed by secondary countercurrent pure water washing. After gold plate washing, 10 g / L alkaline solution shall be added to prevent gold plate oxidation;

7. Platinum plated titanium mesh shall be used as the anode of the gold cylinder. Generally, stainless steel 316 is easy to dissolve, resulting in nickel iron chromium and other metals polluting the gold cylinder, resulting in defects such as gold plating whitening, exposed plating and blackening;

8. The organic pollution of gold cylinder shall be continuously filtered with carbon core, and an appropriate amount of gold plating additives shall be added.