PROPERTIES OF ELECTROLESS NICKEL
• Properties of electroless nickel coating changes according to below conditions.
- % the phosphorus content in the layer,
- Thickness of coating,
- Pretreatment conditions,
- The contaminations in the electrolytes
• Electroless nickel is plated over a large number of metallic and nonmetallic substrates, such as ferrous, steel, stainless steel, bronze, aluminium, magnesium.
• Coating thickness is homogeneous.
• The coating structure varies from microcrystalline for low phosphorous versions to amorphous for the highest phosphorous variety (giving best corrosion properties), and a mixture of microcrystalline and amorphous for the the medium phosphorous type, the most common
• Electroless nickel coating thickness can be reached up to 250 microns.
• There is three different applications.
- Low phos electroless nickel,
- Mid phos electroless nickel,
- High phos electroless nickel,
• Ni-P-layers with < 10 % P are increasingly ferrousmagnetic with removing P content.
• Ni-P-layers with > 10 % P are completely non-magnetic, which for coated surfaces in the range of the electronics industry of special value is.
• Density pure nickel = 8,9 g/cmᶾ.
| phosphorus content in % ||density|
|4||8,5 +/- 0,2|
|6||8,3 +/- 0,2|
|7||8,1 +/- 0,2|
|10||7,9 +/- 0,2|
|12||7,8 +/- 0,2|
Photo1: Microscobic structure of electroless nickel…
• P-rich layers are chemically more resistant than P-poorer layers. A cause for this is the phosphorus content and the different structure of the deposited layers.
• Particularly to the determination of the hardness of Ni-P-layers the Vickers hardness is very common and most extensive in application. For avoidance of wrong measurements the minimum layer thickness must amount to approx. 20 µm since the penetration depth of the pyramid needs up to 15µms.
- Hardness is 450 HV to 600 HV as coated,
- Hardness increases up to 1200 HV after treatment
• EN layers are Ni-P-alloys. They have smaller elongation values than galvanic Ni layers.
- Fast deposited, bright coatings up to 0,5 % with phosphorus content of 5 to 8 %.
- Slowly deposited coatings up to 2 % with phosphorus content of 10 to 13 %
• Ni-P-layers with < 10 % P are increasingly ferrousmagnetic with removing P content. Ni-P-layers with > 10 % P are completely non-magnetic, which for coated surfaces in the range of the electronics industry of special value is. If HP layers are heated, result from the Nickelphosphide relocating ferrousmagnetic properties.
- The soft soldering plays the layer thickness an important role. Good results are obtained between 2 and 5 µm.
- The hard soldering is it recommendable to work under inert gas and considering the melting point.
- The solderability of aluminum materials can be made possible only with an en coat - approx. 5 µm.
- P-poorer layers are better to solder than P-rich
- also thinner layers are better to solder than thicker
- Dull layers are rather suitable than shining
- For good soldering; if the Ni-P-layer not to long stored temporarily and on longer stored surfaces to remove the oxide film.
• Abrasion test as criterion for the wear protection. Abrasion in mg per 1000 turns with a load of 10 N and CS 10 role;
- For ductile high phos layers without heat treatment approx. 22 mg +/- 4.
- For high phos layers with heat treatment depending upon time and temperature approx.16 mg +/- 4.
- P-poorer layers without heat treatment approx. 15 mg +/- 3.
- The same layers with heat treatment depending upon time and temperature approx. 10 mg +/- 4.
• Thermal expansion coefficient (µm/(mK)) : 13