Among the various plating methods (electroplating, electroless plating, hot-dip plating, dry plating, etc.), this is an overview of typical electroplating and electroless plating.
[Basic knowledge] Electroplating VS electroless plating
Electroplating and electroless plating
Wet plating includes electroplating, which uses an external power source for cathodic reduction, and electroless nickel, which uses an external power source for oxidation and reduction reactions.
In electroplating, as shown in Fig. 1, DC is applied to the product (cathode: cathode) that is plated with the anode in the plating solution using an external DC power supply.
In the plating solution, metal ions dissolved in the solution are carried to the vicinity of the product by an electric current, and the metal ions at the electrolytic interface are reduced to form a plating film on the surface of the product.
At the electrolytic interface on the anode side, the anode (anode) emits electrons and dissolves into the plating solution as metal ions.
The emitted electrons enter the DC power supply via the anode and conductor and are supplied to the cathode.
Electroplating requires an external power source in this way, and the products that you want to plate are limited to conductors.
Since the current flows perpendicular to the equipotential surface of the electrode surface, the current distribution on the electrode surface is uneven except in limited cases, and when the plate-shaped product is electroplated, a film is formed on the corners and sides. It will be thicker.
For products with complex shapes with irregularities, the current distribution becomes more uneven, the plating film becomes thicker at the convex parts where the current density is high, and the plating film becomes thinner at the concave parts where the current density is low.
For these reasons, in order to form a film with a more uniform plating thickness by electroplating, it is necessary to devise ways to equalize the current density, and it is difficult to apply a uniform plating film to plated products with complicated shapes. , It will be a showcase for the skills of each plating company.
Electroless nickel plating principle
In electroplating, the metal ions at the electrode interface are reduced by the electrons supplied from the external DC power supply, and the plating film is deposited as metal.
In electroless nickel plating, metal ions are reduced and precipitated by the electrons emitted when the reducing agent oxidizes on the surface of the plated product, forming a metal film.
In electroless plating, a partial anode reaction and a partial cathode reaction occur on the surface of the plated product, and electroless plating proceeds. Since the magnitudes of the cathode reaction and the anode reaction are equal and the plating rate depends on the cathode reaction rate at the mixed potential, it is necessary to know in advance how these reactions change depending on the plating bath composition and bath conditions. It is important in speed management.
Unlike electroplating, electroless plating does not allow electricity to flow through the plating solution, so not only conductors such as metals but also non-conductors such as resins and ceramics can be plated by the oxidation reaction of the reducing agent. Become.
In addition, it is possible to form a uniform plating film because it is not easily affected by the plating film thickness distribution due to the product shape of the plating process.
Electroplating requires replenishment of metal from the anode, so it is not necessary to replenish metal at all times, but electroless plating consumes components such as metal and reducing agents by processing, so it is always replenished. need to do it.
I explained general electroless plating, but there are also electroless plating that uses substitution reaction and disproportionation reaction.
Comparison of film characteristics between electro-nickel plating and electroless nickel plating
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