A PCB surface finish is crucial for a printed circuit board as it prevents the copper (exposed traces, pads, holes and ground plains) from oxidation – a critical ingredient to high-level application performance.
A surface finish is essential for making a reliable connection between the PCB and the electronic component. A surface finish has two major functions, to provide a solderable surface for sufficient soldering components to the PCB, and to protect any exposed copper from oxidizing.
When it comes to choosing the right type of final surface finish, it is just as important as selecting the right material for your bare board. Selecting the correct surface finish for your application is critical for performance. For assistance with selecting a surface finish, send our trusted engineers an email or call.
With increasing demands for thin, high-density, fast speeds, and lightweight applications, the solder finish will make all the difference.
Modern surface finishes are lead-free, in accordance with Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE) directives, and include:
- ENIG (Electroless Nickel Immersion Gold)
- ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold)
- Electrolytic Nickel/Gold – Ni/Au (Hard/Soft Gold)
- Immersion Silver
- White Tin or Immersion Tin
- Lead Free HASL (Hot Air Solder Leveling)
- OSP (Organic Solderability Preservatives)
Choosing the correct PCB surface finish for your application requires taking factors into account like cost, the final application environment (e.g. high-heat/thermal, vibration/stability, RF), component density/selection, lead/lead free requirements, shelf life, shock/drop resistance, production volume, and throughput.
Due to the increased demand for improved performance of electronic applications, surface finishes have also been upgrading. Because of tighter PCB topography the HASL surface finish is quickly being replaced by gold-based surface finishes like ENIG, ENEPIG, and soft/hard gold. The gold-based surface finishes have a lot to offer in terms of features and benefits when used in applications.
ENIG (Electroless Nickel Immersion Gold)
ENIG consists of two layers of metallic coating, which are deposited on the copper surface through chemical process, 2-5μ inches of immersion Gold (Au) over 120-240μ inches of electroless Nickel (Ni).
The nickel layer protects the copper from oxidation, and the gold layer protects the nickel layer. This dramatically increases the resistance to corrosion and also maintains a flat surface which is crucial for assembly of leadless components. ENIG usage has become very common now due to the accountability for lead-free regulations.
ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold)
ENEPIG is probably not new to you, but it is a surface finish that has become increasingly popular recently due to the price reductions in palladium. It also has increased in popularity and use because of its many features and benefits. It also has a distinct advantage over the ENIG surface finish, which we’ll get into below.
The ENEPIG surface finish is composed of four metal layers:
The difference between ENEPIG and ENIG is the added layer of palladium. The palladium helps protect the nickel layer from corrosion, which helps prevent “black pad” from occurring. This is one of the distinct advantages of ENEPIG over the ENIG surface finish. The immersion gold layer that sits atop the palladium offers nearly-complete board protection by protecting and preserving the palladium underneath.
When compared to other surface finishes, like hard gold and soft gold plating, ENEPIG has become more affordable in recent years. The cost of the ENEPIG surface finish decreased because the added palladium layer reduces the required thickness of the more expensive gold layer.
ENEPIG is Capable of Your Demanding Requirements
The ENEPIG finish is capable of the majority of the ultra-demanding requirements with multiple package types like, through-holes, SMT, BGA, wire bonding, and even press fit.
The PCB surface finish with ENEPIG is very thin (between 0.05μm and 0.1μm), making the assembly and soldering process very simple and definitely more reliable when compared to ENIG. ENEPIG also has a long shelf life due to its durability and resistance from tarnishing.