Maintenance and Control of Acid Copper Plating Bath (Maintenance and Control)
Composition: Copper sulfate is the source of copper ions in the solution. Since the current efficiency of the cathode and anode is normally close to 100%, the copper ions supplemented by the anode copper is quite stable. Sulfuric acid improves the conductivity of the solution and reduces the polarization of the anode and cathode, prevents salt precipitation and improves throwing power. The ratio of copper to sulfuric acid in the high uniformity plating bath should be maintained at 1:10. When the sulfuric acid content exceeds 11 vol%, the current efficiency decreases. Chloride ions can reduce polarization and eliminate striated deposits with high current density in the high uniformity and gloss plating bath. Phosphor bronze spring
# Temperature: Too part of the plating bath is operated at room temperature. If the temperature is too low, the current efficiency and plating range will be reduced. If gloss is not required, the bath temperature can be increased to 50°C to increase the electroplating range, which can be used in electroforming, printed circuits or printed boards.
# Stirring: It can be stirred by air, mechanical, solution jet or moving plating. The better the stirring, the greater the allowable current density.
# Impurities: Organic impurities are the most common in acid plating baths, and their sources are the decomposition products of brighteners. The tank lining and anode bag are not filtered to the substances, electroplating stopoffs, rust prevention substances and Impurities of acid and salt. The green of the plating bath indicates a considerable amount of organic pollution. Activated carbon must be used to remove organic impurities. Sometimes hydrogen peroxide and potassium permanganate can help activated carbon to remove organic impurities, but cellulose filters cannot used.
Metal impurities and their effects are as follows:
Antimony (antimony): 10-80 g/l, rough and embrittled coating, adding glue (gelatin) or monocitrate (tannin) can inhibit antimony co-precipitation (codeposition).
Arsenic 20-100 ppm: same as antimony.
Bismuth: Same as antimony.
Cadmium>500ppm: It will cause immersion deposit and anodic polarization, which can be controlled by chlorine.
Nickel>1000 ppm: same as iron.
Iron>1000 ppm: reduce uniformity and conductivity.
Tin 500-1500ppm: same as cadmium.
Zinc>500ppm: same as cadmium.
4.3.4 Failures and causes of acid copper plating bath
1. Burn in high current density area:
Too little copper, organic pollution
The temperature is too low and there are too few chloride ions
Not enough stirring
2. Loss of luster:
Too little gloss agent, too high temperature
Organic pollution, too little copper
Low chloride ion concentration
3. Rough coating:
Solid particle pollution Poor quality of anode copper
Broken anode bag, insufficient chloride ion content
Organic matter pollution Too little chloride ion
Anode bag rot
5. The current is too low:
Organic pollution too much chlorine
The sulfuric acid content is not enough, the current density is too small
Insufficient additive temperature too high
6. Anode polarization:
Tin and gold pollution, too much chlorine
Temperature is too low too much sulfuric acid
Anode copper quality is not good enough copper sulfate content is insufficient
4.3.5 Additives for acid copper plating bath
There are many additives such as glue, dextrin, sulfur, interface active agent, dye, urea, etc. The main purposes are:
Smooth coating, reduce dendrites
Increase current density and gloss
Hardness change prevents pinholes
4.4 Copper Cyanide Baths
Cyanide copper plating brings human health hazards and waste disposal problems. The use of thick plating has been reduced, but it is still widely used in primer plating. Cyanide copper plating The most important chemical composition of the plating bath is the free cyanide and total cyanide content. The calculation equation is as follows:
K2Cu(CN)3 total potassium cyanide amount = cuprous cyanide required amount × 1.45 + free potassium cyanide required amount
K2Cu(CN)3 Total sodium cyanide amount = cuprous cyanide required amount × 1.1 + free sodium cyanide required amount
Example: The plating bath requires 2.0g/l copper cyanide and 0.5g/l free potassium cyanide. How much potassium cyanide is required?
The amount of potassium cyanide needed for solution=2.0×1.45+0.5=3.4g/l
The anode copper whisker is pure copper without oxides. It can be packed in a steel basket with copper plates or copper blocks and wrapped in anode bags. The steel anode plate is used to adjust the copper content. The area ratio of cathode to anode should be 1:1 and 1:2.