(9) 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 performance of the gold layer’s mechanical strength.
② Relevant process parameters of 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 minutes multiply the plated area of the board by the meter. 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.
Supplement nickel 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. Wipe the cathode conductive rod with a clean wet rag every 2-3 hours. Analyze cylinder nickel sulfate (nickel sulfamate) (1 time/week), nickel chloride (1 time/week), boric acid (1 time/week) content, and adjust the content of nickel plating additives through Hall cell test, and timely supplement related raw materials. 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 0.2-0.5 ASD for 6-8 hours of electrolysis. Check the anode every month Check whether the 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 status of the tank liquid. The filter element of the filter pump is replaced every two weeks.
④Large 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. Put it into the titanium basket, and put it into the 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 with 5% dilute sulfuric acid, rinse with water and dry 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 reaches about 65 degrees, and keep the air stirring for 2-4 hours.
D. Turn off Air stirring, slowly dissolve the activated carbon powder into the tank liquid at 3-5 g/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, heat, and let the activated carbon The powder slowly settles 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 to stir, put in the anode, and hang it on the electrolytic plate, according to 0. 2-0. 5ASD current density low current electrolysis 6-8 hours.
G. After laboratory analysis, adjust the nickel sulfate or nickel sulfamate, nickel chloride, boric acid content in the tank to the normal operating range. According to The Hall cell test results 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. Test Plating.
⑤ When supplementing medicines, if the amount of addition is large, such as nickel sulfate or nickel sulfamate, and nickel chloride, it 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 It can be placed in the nickel cylinder, and cannot be directly added to the tank.
⑥After 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 of the nickel cylinder volatilized due to heating, and then follow the secondary countercurrent rinsing after recycling water washing.
⑦Calculation formula of drug addition:
Nickel sulfate (unit: kg) = (280-X) × tank volume (liter)/1000
Nickel chloride (unit: kg) = (45-X) × tank volume (liter) / 1000
Boric acid (unit: kg) = (45-X) × tank volume (liter)/1000
(10) Gold electroplating: It is divided into electroplating hard gold (gold alloy) and water gold (pure gold) processes. The composition of hard gold plating and soft gold bath is basically the same, but there is some trace metal nickel or cobalt in the hard gold bath or elements such as iron.
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 printed 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 The main medicines added are acid-type adjustment salt and basic-type adjustment 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 should be used as the recovery water wash, and it can also be used to supplement the liquid level of the gold vat evaporating change. To prevent oxidation of the 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, which leads to the contamination of the gold cylinder by metals such as nickel, iron and chromium, resulting in defects such as white gold plating, exposed plating, and blackening.
⑧ The organic pollution of the gold tank should be continuously filtered by carbon core, and an appropriate amount of gold plating additives should be supplemented.
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