Electroplating Process Learning Materials (1)

1. Classification of Electroplating Processes:

Acid Bright Copper Electroplating Nickel/Gold Electroplating Tin Electroplating

2. Process Flow:

Pickling → copper plating on the whole PCB board → pattern transfer → acid degreasing → secondary countercurrent rinsing → micro-etching → secondary pickling → tin plating → secondary countercurrent rinsing
Countercurrent rinsing→Pickling→Patterned copper plating→Secondary countercurrent rinsing
→ Nickel plating → secondary washing → immersion in citric acid → gold plating → recycling → 2-3 grade pure water washing → drying

3. Flow Description:

(1) Pickling
① 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.
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 in 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) Copper electroplating on the whole board: also known as copper once, board electroplating, panel-plating
① Function and Purpose:
Protect the thin chemical copper just deposited, prevent 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 ability to deep plating deep holes and small holes during electroplating. The sulfuric acid content is high At 180 g/L, most of them reach 240 g/L. The copper sulfate content is generally around 75 g/L, and a trace amount of chloride ions is added to the bath solution, which acts as an auxiliary gloss agent and a 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 2 A/square. The decimeter multiplied by the electroplatable area on the board, for the whole board, 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, and more control 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.Supplement 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 sulfate (1 time/week), sulfuric acid (1 time/week), chloride ion (2 times/week) content of the copper tank every week, and adjust the light agent content through the Hall cell test, and relevant raw materials should be replenished in time. The anode conductive rod should be cleaned every week, the electrical connectors at both ends of the tank body, 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. Check whether the anode titanium basket bag is damaged, 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 any, 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 Large processing 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 and dry. After that, 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 6-8 hours, rinse with water and dry, then soak in 5% dilute sulfuric acid, rinse with water and dry.

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 3-5g/L, after the dissolution is complete, turn on the air agitation, and keep the temperature for 2-4 hours.

E. Turn off the air agitationand 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 the cleaned working tank, turn on the air stirring, put in the anode, hang it up on the electrolytic plate, electrolyze at 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 the Hall cell The test results supplement the light agent.

H. After the color of the surface of the electrolytic plate is uniform, the electrolysis can be stopped, and then proceed at a current density of 1-1.5ASD Electrolysis green film treatment is carried out for 1-2 hours, and a layer of uniform and dense black phosphorus film with good adhesion can be formed on the anode.

I. Trial plating.

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 medicines, 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 the supplementary amount is large (above 10 liters), it should be slowly supplemented several times. 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