Discussion on Electroless Nickel Gold Technology (2)

2. Management of Electroless Nickel Tank

Composition and Control: The formula of the bath solution is generally the secret of the supplier. The main components are nickel salt, reducing agent, and various organic additives.

PH: (4.6-5.2) can be adjusted with lemon or ammonium water when adjusting. Note: when adjusting with ammonium water, it must be added slowly and carried out in small amounts and several times.

Temperature: Above 80℃ to ensure the smooth progress of the nickel bath reaction.

Phosphorus Content: (6-8%) low content, its corrosion resistance and solderability will become poor, and the surface of the nickel layer is easy to passivate, high content will affect the quality of the nickel layer, increase the internal stress of the nickel layer, make the bonding force between gold and nickel deteriorates.

Ni2+: (4.6-5.2g) low content, affecting the deposition rate, high content, poor stability of the bath, too strong activity and easy to plate out.

Surface Additives: The additives mainly include complexing agents (to make Ni2+ form complexes to avoid the formation of hydroxide or phosphite precipitation); accelerators, stabilizers. Due to the addition of accelerators (mostly lactic acid) in the bath, it is easy to mold after the bath is turned off. Therefore, when the output is not large or it is not used for a long time, the temperature should be heated up for false plating every 3-4 days (especially important in summer) to maintain its quality and activity.

The precipitation of the bath liquid: it must be soaked in 50% nitric acid for 8 hours before the bath is prepared, so that a passivation film is formed on the wall of the bath to prevent nickel from adhering. Inhibit nickel plating on the tank wall, and the auxiliary equipment (filters, pipelines) should also be nitrified clean when the nitrification tank is used. It is possible to prevent the precipitation of the bath liquid. The activity of the bath liquid needs to be very stable, and it is best to use an automatic addition system to stabilize the components of the bath liquid. This will slow down the precipitation of the bath liquid. The service life will be extended, but in order to ensure the reliability of solderability, the service life of the bath liquid can only be changed with 4-5MTO.

3. Management of Chemical Gold Tank

Ingredient: The gold salt is potassium aurous cyanide. The gold content is 63.8%.PH:5.1-6.1

The chemical gold is carried out by the principle of potential displacement reaction. A gold layer of 1-3µm can be plated on the nickel surface, and the deposition rate is very fast within one or two minutes of the beginning of the reaction, and then only through the sparse pores of the gold layer Nickel dissolves out, and continues to promote the deposition of the gold layer. Due to the continuous dissolution of nickel, the nickel content in the gold tank continues to increase. Once it exceeds 0.5y/L, not only the appearance is not good, but also the adhesion is not good. Therefore, the life of the gold tank Only 3-4MTO can be maintained.

According to the long-term work experience, the following dry rules are made for reference by peers.
Change the nickel tank twice and replace the activation tank once.

Change the nickel tank twice and change the activation tank once.

Change the activation slot twice and change the gold slot once.

Change the gold tank twice and change the degreasing tank once.