Nickel Plating for PCBs
Nickel plating for printed circuit boards comes in two categories: semi-bright nickel and bright nickel. It acts as a base layer for gold-plated boards and must have a thickness of at least 2 to 2.5 μm. The plating should be uniform, smooth, low in porosity, and ductile, suitable for brazing or pressure welding.
Gold Plating in PCB Production
Gold plating in PCB production includes board surface gold plating and plug gold plating.
Board Surface Gold Plating
- The gold plating on the board surface consists of 24K pure gold with excellent conductivity and solderability, ranging from 0.01 to 0.05 μm in thickness.
- The gold-plated layer is deposited on a nickel base layer, acting as a barrier between gold and copper to prevent diffusion and increase hardness.
- It serves as a protective layer against alkaline etching and as the final surface plating for IC aluminum wire bonding and button-type PCBs.
Plug Gold Plating
- Gold-plated plugs, known as hard gold or “golden fingers,” have higher hardness and wear resistance due to alloy elements like Co, Ni, Fe, and Sb.
- The hard gold plating layer thickness ranges from 0.5 to 1.5 μm, offering stability and reliability for electrical connections.
- To enhance bonding strength, reduce porosity, and protect against contamination, a thin layer of pure gold is deposited between the nickel and hard gold layers.
Other Plating Options
- Tin: Electroless tinning provides a solderable coating on bare copper PCBs through a chemical immersion method.
- Silver: Electroless silver plating is used for soldering and bonding applications, where copper displaces silver ions to form a silver layer.
- Palladium: Electroless palladium serves as a protective layer for PCBs, offering high heat resistance and stability, especially in Ni/Au plating.
Advantages of Palladium
- Palladium can be soldered and bonded directly on copper, with a relatively thick plating layer ranging from 0.08 to 0.2 μm.
- Unlike gold, palladium remains stable on the solder’s surface during assembly and soldering, enhancing reliability.
- Although more expensive than gold, palladium’s role in chip-scale package assembly is expected to grow with advancements in IC integration and assembly technology.
