PCB Blog - Introduction to PCB board Electroplating Process

The electroplating process of the PCB board can be roughly classified into acid bright copper electroplating, nickel/gold electroplating, and electroplating.

1. Process flow:

Pickling → full-board copper plating → pattern transfer → acid degreasing → secondary countercurrent rinsing → micro-etching → secondary countercurrent rinsing → pickling → tin plating → secondary countercurrent rinsing → countercurrent rinsing → pickling → pattern copper plating → secondary 1st stage countercurrent rinsing→nickel plating→2nd stage water washing→dipping in citric acid→gold plating→recycling→2-3 stage pure water washing→drying

2. Process description:

2.1 Pickling

Function and purpose: remove the oxide 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;

The acid leaching time should not be too long to prevent oxidation of the board surface; after a period of use, the acid solution should be replaced at a time when the acid is turbid or the copper content is too high to prevent contamination of the electroplating copper cylinder and the surface of the board;

C.P grade sulfuric acid should be used here;

2.2 Full PCB board copper electroplating

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 exert the gloss effect; The amount of copper light agent added or the amount of cylinder opening is generally 3-5ml/L. 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 copper light agent in time according to 1000-150ml/KAH every day; check whether the filter pump is working normally and whether there is air leakage; apply clean wet water every 2-3 hours Wipe the cathode conductive rod with a rag; regularly analyze the copper sulfate (1 time/week), sulfuric acid (1 time/week), and chloride ion (2 times/week) content in the copper cylinder every week, and adjust it through the Hall cell test The content of the light agent and the relevant raw materials should be replenished in time; the anode conductive rod should be cleaned every week, the electrical joints at both ends of the tank body should be cleaned, 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 to 0.5 ASD for 6 to 8 hours. ; Check whether the titanium basket bag of the anode is damaged every month, and 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 in time; Low-current electrolysis removes impurities; every six months or so, it is determined whether large-scale treatment (activated carbon powder) is required according to the pollution status of the tank liquid; the filter element of the filter pump needs to 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 of 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% lye solution for 6 to 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 stirring, and slowly dissolve the activated carbon powder into the tank liquid at 3~5g/L. After the dissolution is complete, turn on the air stirring and keep the temperature for 2~4 hours; E. Turn off the air stirring and heat up, 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, put in the anode, Hang it on the electrolytic plate, and electrolyze it at a low current density of 0.2-0.5ASD for 6 to 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 sufficient; I. Trial plating is OK.

5) The main purpose of the anode copper ball 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; after adding, electrolyze with the low current; 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 content of chloride ions 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,

2.3 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 an acid degreaser is used here, why not use an alkaline degreaser and an alkaline degreaser is better than an 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) It is only necessary 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 will not have adverse effects.

2.4 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.

2.5 Pickling

1) Function and purpose: 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 oxidation of the board surface; after a period of use, the acid solution should be replaced at a time when the acid is turbid or the copper content is too high to prevent contamination of the electroplating copper cylinder and the surface of the board;

3) C.P grade sulfuric acid should be used here;

2.6 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, and 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

2.7 Electroplating tin

1) Purpose and function: The purpose of pattern electroplating pure tin is mainly to use the pure tin as a metal anti-corrosion layer to protect circuit etching;

2) The bath is mainly composed of stannous sulfate, sulfuric acid, and additives; the content of stannous sulfate is controlled at about 35 g/L, and the sulfuric acid is controlled at about 10%; The actual production board effect; the current calculation of electroplating tin is generally calculated by 1.5A/square decimeter multiplied by the electroplatable area on the board; the temperature of the tin cylinder is maintained at room temperature, generally not more than 30 degrees, and more controlled at 22 degrees, so in summer Because the temperature is too high, it is recommended to install a cooling temperature control system in the tin cylinder;

3) Process maintenance: replenish tin-plating additives in time according to the thousand-ampere hours every day; check whether the filter pump is working normally and whether there is air leakage; every 2-3 hours, use a clean wet rag to clean the cathode conductive rod; Every week, the tin cylinder should be regularly analyzed for stannous sulfate (1 time/week) and sulfuric acid (1 time/week), and the content of tin-plating additives should be adjusted through the Hall cell test, and the relevant raw materials should be replenished in time; the anode should be cleaned every week. Rod, electrical connectors at both ends of the tank body; 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 ones in time, and check whether the bottom of the anode bag is piled up If there is anode sludge, it should be cleaned up in time; continuous filtration with carbon core for 6-8 hours every month, and 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 status of the bath liquid; Replace the filter element of the filter pump every two weeks.

4) Large processing procedure: A. Take out the anode, remove the anode bag, clean the surface of the anode with a copper brush, rinse it with water, put it into the anode bag, and put it in the acid tank for standby B. Put the anode bag into 10% alkali Soak in liquid for 6-8 hours, rinse with water and dry, then soak with 5% dilute sulfuric acid, rinse with water and dry for later use; C. Transfer the tank liquid to the standby tank, and slowly dissolve the activated carbon powder at 3-5 g/L. In the tank liquid, after it is completely dissolved, adsorb it for 4-6 hours, filter the tank liquid with a 10um PP filter element and filter aid powder to the cleaned working tank, put it in the anode, hang it on the electrolytic plate, press 0.2-0 .5ASD current density and low current electrolysis for 6-8 hours, D. After laboratory analysis, adjust the sulfuric acid and stannous sulfate content in the tank to the normal operating range; Supplement tin plating additives according to the Hall cell test results; E. The plate to be electrolyzed After the color of the board surface is uniform, stop electrolysis; F. Trial plating is OK.

5) When supplementing medicines, such as stannous sulfate and sulfuric acid in a large amount; after adding, it should be electrolyzed at a low current; when supplementing sulfuric acid, pay attention to safety. Add slowly; otherwise, the temperature of the bath will be too high, the stannous will be oxidized, and the aging of the bath will be accelerated.

2.8 Nickel Plating

1) Purpose and function: The nickel-plated layer is mainly used as a barrier layer between the copper layer and the gold layer to prevent the mutual diffusion of gold and copper, which affects the solderability and service life of the board; at the same time, the nickel layer also greatly increases the gold layer. mechanical strength;

2) Process parameters related to copper electroplating on the whole board: the addition of nickel plating additives is generally supplemented by the method of thousand-ampere hours or according to the actual production board effect, the addition amount is about 200ml/KAH; the current calculation of pattern nickel electroplating is generally 2 ampere/square The decimeter is multiplied by the electroplatable area on the board; the temperature of the nickel cylinder is maintained at 40-55 degrees, and the general temperature is about 50 degrees, so the nickel cylinder should be equipped with a heating and temperature control system;

3) Process maintenance: replenish nickel plating additives in time according to the thousand ampere hours every day; check whether the filter pump is working properly and whether there is air leakage; every 2-3 hours, use a clean wet rag to clean the cathode conductive rod; every 2-3 hours Weekly, the copper cylinder should be regularly analyzed for nickel sulfate (nickel sulfamate) (1 time/week), nickel chloride (1 time/week), boric acid (1 time/week) content, and the Hall cell test to adjust the nickel plating Additive content, and replenish relevant raw materials in time; clean the anode conductive rods and the electrical connectors at both ends of the tank body every week, replenish the anode nickel corners in the titanium basket in time, and use low current 0.2 to 0.5 ASD for 6 to 8 hours of electrolysis; Check whether the anode titanium basket bag is damaged every month, and replace the damaged one in time; and check whether there is anode sludge accumulated at the bottom of the anode titanium basket, if so, it should be cleaned in time; 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 status of the tank liquid; the filter element of the filter pump is replaced 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 for packing the nickel corner, and roughen the surface of the nickel corner with a micro-etchant to a uniform pink color. After washing and drying, Put it into a titanium basket, and put into an acid tank for use. B. Soak the anode titanium basket and anode bag in 10% lye solution for 6 to 8 hours, rinse with water, and then soak with 5% dilute sulfuric acid. ;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. Close Turn off the air agitation, slowly dissolve the activated carbon powder into the tank liquid at 3~5g/L. After the dissolution is complete, turn on the air agitation and keep the temperature for 24 hours; E. Turn off the air agitation, heat it, and 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 powder to filter the tank liquid into a clean working tank, turn on the air stirring, put in the anode, and hang it on the electrolytic plate, According to 0. 2-0. 5ASD current density low current electrolysis for 6 to 8 hours, G. After laboratory analysis, adjust the nickel sulfate or nickel sulfamate, nickel chloride, and boric acid content in the tank to the normal operating range; according to Huo The results of the cell test are supplemented with nickel plating additives; H. After the color of the electrolytic plate is uniform, the electrolysis can be stopped, and then the anode is activated by electrolytic treatment at a current density of 1-1.5ASD for 10-20 minutes; I. Trial plating is OK. You can;

5) When supplementing drugs, such as nickel sulfate or nickel sulfamate, nickel chloride, should be electrolyzed at a low current after adding; when adding boric acid, the supplementary amount of boric acid should be put into a clean anode bag to hang. It can be put into the nickel cylinder, not directly into the tank;

6) After nickel plating, it is recommended to add a recycled water wash, open the cylinder with pure water, which can be used to supplement the liquid level volatilized by the nickel cylinder due to heating, and then follow the secondary countercurrent rinsing after recycling water washing;

2.9 Gold plating:

Divided into electroplating hard gold (gold alloy) and water gold (pure gold) process, the composition of hard gold plating and soft gold bath is basically the same, but there are some trace metals such as nickel or 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 alloy wear resistance, and other excellent characteristics;

2) At present, the gold electroplating of circuit boards is mainly citric acid gold bath, which is widely used because of its simple maintenance and simple and convenient operation;

3) The gold content of water is controlled at about 1 g/L, the pH value is about 4.5, the temperature is 35 degrees, the specific gravity is about 14 Baume degrees, and the current density is about 1ASD;

4) Mainly added medicines include acid adjusting salt and basic adjusting salt for adjusting PH value, conductive salt for adjusting specific gravity, supplementary additives for gold plating and gold salt, etc.;

5) In order to protect the gold jar, a citric acid dip tank should be added in front of the gold jar, which can effectively reduce the pollution to the gold jar and maintain its stability of the gold jar;

6) After the gold plate is electroplated, a pure water wash is used as the recovery water wash, and it can also be used to supplement the liquid level of the gold vat evaporation change. Liquid to prevent oxidation of gold plate;

7) The gold cylinder should be made of platinum-plated titanium mesh as the anode. Generally, stainless steel 316 is easy to dissolve, causing nickel-iron-chromium and other metals to contaminate the gold cylinder, resulting in white gold plating, exposed plating, blackening, and other defects;

8) The organic pollution of the gold cylinder should be continuously filtered by carbon core, and an appropriate amount of gold plating additives should be supplemented on PCB board.