Spring copper plated

Preparation of electroless copper plating bath

(1) Dissolve the required sodium cyanide with cold water.

Add the required cuprous cyanide slowly to the sodium cyanide water to dissolve. This process is an exothermic reaction and cannot be overheated.

(2) Add other additives, stir evenly, take samples for analysis.

(3) According to the analysis results, supplement and correct each component.

(4) Weak electrolysis to remove impurities at low current density for several hours.

4.4.9 Defects of electroless copper plating and their causes

1. The coating is dark red, black, and hydrogen and oxygen are violently precipitated. The reasons are:

Current density is too high bath temperature is too low

Too little copper salt, too much arsenic cyanide

2. The coating is uneven, and some are not plated. The reasons are:

Improper installation, too low current

Too much cyanide

3. The coating blisters, peels, and has poor adhesion due to:

Incomplete surface pretreatment, oil film, oxide film bath temperature is too low

Too much current

4. The plating layer has a white film layer, blue crystals appear, and the plating solution turns blue. The reasons are:

Small anode area, insufficient potassium and sodium tartrate

Insufficient sodium cyanide

4.4.10 Formula for copper plating

(1)  Sodium cyanide NaCN 65~89g/l

Cuprous cyanide CuCN 45~60g/l

Sodium carbonate Na2CO3? 15g/l

Sodium hydroxide NaOH 7.5~22.5g/l

Potassium Sodium Tartrate (rochelle salt) 45g/l

Free sodium cyanide 15~22.5g/l

Bath temperature 60~70℃

(2) Full potassium bath

Potassium cyanide KCN 80~110g/l

Cuprous cyanide CuCN 45~60g/l

Potassium carbonate K2CO3? 15g/l

Potassium hydroxide KOH 7.5~22.5g/l

Rochelle salt 45g/l

Free sodium cyanide 12~22.5g/l

Bath temperature 60~70℃

4.4.11 Gloss cyanide copper plating

1. Add gloss agent:

(1) Lead: use lead carbonate or lead acetate to dissolve in water 0.015~0.03g/l

(2) Sodium thiosulfate: Dissolve in water with Haibo 1.9~2g/l

(3) Sulfur: Use sulfur to dissolve in water 0.1~0.5g/l

(4) Arsenic: Dissolve in NaOH 0.05~0.1g/l with arsenous acid

(5) Selenium: Dissolve in NaOH 1~1.5g/l with selenite

(6) Potassium thiocyanide: Potassium thiocyanide is soluble in water 3~10g/l

2. Use current waveform

(1) PR current:

a. Smoothing: 35 seconds for the cathode and 15 seconds for the anode.

b. Glossing: 15 seconds for cathode and 5 seconds for anode.

(2) AC and DC combined use:

a. Smoothing: DC 25 seconds, AC 10 seconds.

b. Glossing: DC 20 seconds, AC 6 seconds, the cycle of AC is 1.25-10 cycle.

(3) DC interruption: interrupt the current instantly and then resume the current.

4.5 Copper Pyrophosphate Plating Bath

It needs more control and maintenance, but the solution is less toxic than the copper cyanide bath. It is mainly used in printed circuit plastic plating and electroforming. Steel and zinc castings will produce replacement coatings and poor adhesion. You must first strike with a cyanide copper plating bath or a 10:1 P2O7Cu low pyrophosphate copper plating bath.

4.5.1 Copper pyrophosphate base plating bath formula (Strike Bath)

Copper pyrophosphate Cu2P2O7‧3H2O 25~30g/l

Potassium pyrophosphate K2P2O7 95.7~176g/l

Potassium acetate potassium nitrate 1.5~3g/l

Ammonium Hydroxide ?1/2~1ml/l

pH value 8~8.5

Bath temperature 22~30℃

Current density 0.6~1.5A/d㎡

Stirring machine or air

Filter continuous

Copper content 9~10.7g/l

Pyrophosphate 63~107g/l

P2O7/Cu ratio 7~10.1

4.5.2 Maintenance and control of copper pyrophosphate plating bath

1. Ingredients:

(1) Ammonia (ammonia) can help dissolve the anode and make the crystallization fine, and the evaporation loss needs to be supplemented every day.

(2) Acetate (nitrate), increase the current density operating range and remove the cathodic polarization.

(3) The pH value is adjusted and controlled by pyrophosphate or potassium hydroxide.

2. Temperature: Temperature over 60°C will hydrolyze pyrophosphate into ortho phosphate.

3. Stirring: Adequate stirring is required. Air stirring or mechanical stirring is generally used. Ultrasonic wave and solution spraying methods can also be used.

4. Impurities: It is very sensitive to organic impurities such as the decomposition products of oil and organic additives, which will make the coating dark and uneven, and the operating range will be smaller. Cyanide and lead impurities will also make the coating uneven and the operating range smaller. Organic impurities are treated with activated carbon. Add hydrogen peroxide or potassium permanganate before treatment to remove cyanide. Lead can be removed by weak electrolysis.

5. Phosphate: Too high temperature and too low pH will increase phosphate rapidly. Back to list

4.6 Copper Fluoborate Bath

Since the copper borofluoride salt is soluble in water in a large amount and has a large solubility, a higher current density can be used to increase the plating speed. Its disadvantage is corrosiveness, and the use of materials is limited to hard rubber, polypropylene and PVC plastic or carbon.

4.6.1   borofluorate copper plating bath formula

Copper pyrophosphate Cu2P2O7‧3H2O 57.8~73.3g/l

Potassium pyrophosphate K2P2O7? 231~316.5g/l

Potassium acetate 8.2~15.8g/l

Ammonium hydroxide 2.7~7.5m1/1

Additives (improve the ductility and uniformity of the coating) as indicated

pH value 8~8.4

Bath temperature 49~54

Current density 2.5~6A/d㎡

Stirring mechanical or air

Organic impurities will affect the appearance, uniformity and mechanical properties of the coating, especially ductility.

This plating bath requires continuous activated carbon filtration.

Additives usually do not use organics. Molasses will harden the coating and reduce edge effects. Some copper sulfate bath additives can be used.

4.6.2   Advantages of borofluoride copper plating bath

Allows high current density, smooth coating, good appearance

The coating is soft and easy to grind, additives can be used to increase the hardness and strength of the coating

Cathodic current efficiency is nearly 100%, low anodic polarization

No crystallization in the tank, easy to equip with plating bath

Stable plating bath, easy to control, high-speed plating permit

General copper plating process:

Steam degreasing

Inspection before plating (R) Solvent washing (R) Mounting (R) Chemical degreasing (R) Hot water washing (R) Cold water washing (R) Acid leaching (R)

Electrolytic degreasing

Cold water washing (R) Electrolytic degreasing (R) Hot water washing (R) Activation (R) Neutralization (R) Cold water washing (R) Cyanide coating (R) Cold water washing (R) Acid copper plating (R) Cold water washing (R) ) Light emitting (R) Cold water washing (R) Drying (R) Unloading (R) Drying (R) Inspection

4.7 Stainless steel copper plating process

4.8 Stripping of copper plating

(1) Chemical method:

Chromium CrO3? 200~300g/l

Ammonium sulfate (NH4)2SO4? 80~100g/l

Bath temperature room temperature

(2) Electrolysis method:

Sodium nitrate NaNO3? 800~100g/l

Current density 2~4A/d㎡

Bath temperature room temperature