PCB Finishes
PCB surface finishes are used to protect the copper traces on the PCB from corrosion and to improve solderability. The most common finishes are HASL, lead-free HASL, immersion silver, and ENIG. The best finish for a particular PCB will depend on the specific requirements of the application, such as cost, solderability, corrosion resistance, and RoHS compliance.
Below lists some of the different surface finishes available and the characteristics they have. We also have a YouTube video explaining each one.
Are you still not sure which finish you require? Contact us so we further discuss all the options available to you.
Standard PCB Finishes
Hot Air Solder Level (HASL)
RoHS Compliant
Lead-free HASL is a ROHS compliant finish – it has been developed as a lead-free alternative to the traditional Leaded HASL finish.
It is applied by solder dipping the PCB followed by removal of excess solder by blowing with air-knives to produce a flat solder finish.
Immersion
Silver
Immersion silver is a RoHS compliant finish.
It is produced by the selective displacement of the copper atoms by silver atoms on the exposed copper surface.
It is compatible with surface mount, BGA and through hole components.
Electroless Nickel Immersion Gold (ENIG)
ENIG is a RoHS compliant finish. It is applied through the deposition of an initial layer of Nickel onto the copper surface, followed by a thin protective layer of gold, Nickel characteristics of hardness, wear resistance, solderability and uniformity of deposition makes this an excellent surface finish.
The thin layer of gold preserves the solderability of the finish by preventing oxidisation of the highly active nickel surface. It is compatible with surface mount, BGA and through hole components.
PCB Surface Finish Characteristics
| Type | Planarity | Solderability | Aluminium Wire Bondable | Gold Wire Bondable | Contact Surface |
|---|---|---|---|---|---|
| HASL | Poor | Good | No | No | No |
| LF-HASL | Fair | Good | No | No | No |
| OSP | Good | Good | No | No | No |
| Immersion Silver | Good | Good | Yes | No | No |
| ENIG | Good | Good | Yes | No | Yes |
| ENEPIG | Good | Good | Yes | Yes | Yes |
| Hard Gold | Good | Good | Yes | No | Yes |
| Soft Gold | Good | Good | Yes | Yes | Yes |
Special Requirement PCB Finishes
Leaded Hot Air Solder Level (HASL)
Not RoHS Compliant
Leaded HASL was the traditional finish prior to RoHS, This finish is still available where RoHS exemption is permitted.
It is applied by solder dipping the pcb followed by removal of excess solder by blowing with air-Knives to produce a flat solder finish.
Electrolytic Nickel Electrolytic Gold
(Hard Gold)
Electrolytic Nickel – Electrolytic Gold is a RoHS compliant finish. Unlike electroless finishes, being an electrolytic process an electric current is required to plate the gold onto the board.
The most common application of hard gold is edge connectors, hard gold may also be plated over the entire pcb.
Electrolytic Nickel Electrolytic Pure Soft Gold
Electrolytic Nickel – Electrolytic Pure Soft Gold is a RoHS compliant finish. Unlike electroless finishes, being an electrolytic process an electric current is required to plate the gold onto the board.
This is 99.99% pure gold. Due to its very high cost, it is typically used only for wirebonding applications.
Organic Solderability Preservatives (OSP)
OSP is a RoHS compliant finish.
It is an anti-oxidant film applied to the exposed copper surface.
It reacts with the copper to form an organo-metallic layer, the coating is virtually invisible.
Advanced PCB Finishes
Immersion Silver / Immersion Gold
(ISIG)
ISIG is a nickel-free surface finish for PCBs that provides excellent performance in high-frequency applications. Unlike ENEPIG, it utilizes a two-step process with a thin layer of silver followed by an even thinner layer of gold.
This combination offers several benefits: outstanding solderability and compatibility with aluminum and gold wire bonding, ideal for fine-line circuitry and flexible PCBs due to its thin profile, and crucially, excellent signal transmission at high frequencies.
However, ISIG comes at a higher cost and has a shorter shelf life compared to other finishes.
Electroless Nickel / Palladium / Gold (ENEPIG)
- Electroless Nickel: Provides a barrier against copper and forms a strong base.
- Electroless Palladium: An extra barrier, unique to ENEPIG, that prevents the nickel from corroding during the next step, avoiding a failure known as “black pad”.
- Immersion Gold: A very thin outer layer that provides an excellent, flat, and corrosion-resistant surface for soldering components.