Nickel based finishing coating
The application of chemical nickel (Electroless Ni) as a finishing coating for printed circuit boards is one of the alternatives to HASL. But this method itself is rarely used in the production, due to the essence of Electroless Ni - the formation of an intermediate (barrier) precipitating layer between the dielectric and the metal (immersion silver, palladium, immersion gold, etc.).
Application
Copper plating is used as an effective protection against cementation of printed circuit boards. Also nickel proved itself to be good in galvanoplasty, when making copies from metals.
Features of applying a protective coating
Dissolving in a metallized bath, any metal has a certain electrical potential (often positive). Then in the process of long metallization — the flow of special chemicals into the electrons — the potential of the chemical alloy/substance is neutralized.
When applying Electroless Ni, dimethylamine borane or hypophosphate act as neutralizing chemicals. The resulting nickel coating is etched in alkaline copper chloride solutions and further activated. The thickness of the protective layer of precipitation varies from 2.5 to 5 μm.
The advantages of chemical nickel application
- High resistance to alkaline conditions, the effects of sudden temperature fluctuations or moisture.
- Special appearance: making a shiny surface.
- It increases hardness, general index of mechanical wear.
- Safe for living organisms, non-toxic.
- Durable appearance.
Characteristics of finishing coating
|
Technology opportunities |
Index |
|
Period of storage, months |
6 |
|
Solderability quality |
Good |
|
Multiple solderability |
Available |
|
Thermal profile state when melting with soldering |
Not critical, but it requires the use of methods that ensure the preservation of gold thickness within the range of 0.3 mm |
|
Availability of gold unwelding process compatibility |
It is available, but if necessary, soldering with melting below 240˚ - the board requires pre-drying. This process removes moisture delamination of fiberglass. |
|
Availability of aluminum unwelding process compatibility |
Available |
|
Finishing coating thickness, μm |
2,5-5 |
|
Optimum pitch of landing areas, mm |
<0,5 |
|
Process temperature characteristics, ˚С |
90-95 |
|
Torsion, bending and dimensional stability problems |
Absent |
|
Complanarity state of landing areas |
Excellent |
|
Surface cleanness state |
Good |
|
Corrosion resistance index |
Good |
|
Visual defects |
No |
|
Qualitative risks |
The possibility of the emergence of black areas |
|
Solder reliability index |
Medium |
|
Compatibility with lead free methods |
Yes |
|
Index of the environmental damage, safety for the human body |
Medium |
|
Cost characteristics |
Medium |
Copyright: Sai Fon LLC
