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#144 Electroless Plating, Electroless Nickel Plating - 1

Category : Electroless Plating
December28, 2012

Electroless Plating

Electroless plating is also called chemical plating. Unlike the electroplating where metal is deposited on objects by reduction precipitation using a DC current, this method uses chemical reduction agents to plate, and therefore does not require DC power sources, cathodes, or anodes.

One of such platings is Displacement Plating. It is also called Immersion Plating, and the plating layer is obtained by displacement reaction caused by differential in ionization tendency by simply immersing in the plating solution. Zincate treatment used as a pre-process for aluminum plating belongs to this category.

In a case of electroless plating using hypophosphite as the reduction agent, Nickel-Phosphorus (Ni-P) alloy plating is obtained, and Nickel-Boron (Ni-B) alloy plating if boron compounds are used.

There are Nickel, Cobalt, Palladium, Copper, Silver, and Gold for electroless platings, though the ones that are put to practical industrial uses are Nickel, Copper, and Gold platings.
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Electroless nickel plating -1

Nickel-Phosphorus (2~15%) alloy plating which is a representative of the electroless platings is valued high and utilized in a various application fields due to its excellent mechanical, electrical, and physical properties with its ability to uniformly coat complex shaped components. The properties are shown in [Table] below.

[Table] Physical properties of Nickel-Phosphorus Alloy Plating
Chemical compositionNi:83〜98%, P:2〜15%, Others: 0〜2%
Organization of the coatingAmorphous in precipitation state, crystallized when heat treated, and precipitation hardened.
Specific gravityPrecipitation state: 7.9, Heat treated at 400℃ or more: 7.8
Melting temperature890℃
Electrical resistance60μΩ/cm/cm2,Lowers to 1/3 or less if heat treated.
Coefficient of thermal expansion13×10-6cm/cm・℃
Thermal conductivity0.0105〜0.0135cal/cm・sec・℃
Wear resistanceSuperior to electroplating. Superior to industrial plating when heat treated at 650℃. (Usage dependent)
MagnetismNon-magnetic in precipitation state, magnetic when heat treated depending on P content. Low P content will be magnetic, high P content will be non-magnetic.
UniformityExcellent. Accuracy of ±10% or better.
AdhesionExcellent
Heat resistanceWithstands high temperature oxidation.
Corrosion resistanceEquivalent to pure nickel.
HardnessPrecipitation state: 500~550Hv, Heat treated at 400℃: 800~1000Hv

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