PCB SURFACE FINISHES: the main options!

In terms of surface finishes, the customer has a wide range of different types depending on needs, budget and applications. We will review the mains types of finishes available on the market from the cheapest to the most advanced.

WHAT IS A PCB SURFACE FINISH?

Surface finishes are an important part of the manufacturing PCB process, which occurs after applying the solder mask to the panel. The purpose of the surface finish is to protect the copper from oxidation, which can make the PCB unusable. The finish protects the pattern from oxidation, but also from deterioration. Indeed, the surface finishes must provide perfect solderability when the assembly components are placed and welded on the board.


The different options available at ICAPE Group

With more than 20 years in the PCB industry, ICAPE Group has developed a solid knowledge in the different types of surface finishes. With our 25 partner factories in Asia, ICAPE Group can fully manage and control all the stages of the PCB manufacturing process, which guarantees complete satisfaction to our 1,700 customers worldwide.


Lead Free Hot Air Solder Leveling - LF HASL

The panels are immersed in a bath of molten tin, for a few seconds at 265°C, and the excess is removed with high pressurized hot air (air knives) through the panels. Immersing the board in such a hot bath will help identify defects or damage before assembling the components. This process was one of the most used surface finishes but has reached its limits. Due to high density boards, this process leaves uneven surfaces, can create electrical short circuits and is not suitable for fine pitch components.


- Excellent solderability
- CCost-efficient
- Widely available technology


- Possible thickness difference on the surface
- Not suitable for fine pitch components
- Abrasive with copper, depending on the alloy
- Thermal stress on the board


Immersion Tin

Immersion Tin or ISn, is a chemically deposited metallic finish, applied to the metal base of the PCB. The typical thickness of less than 1µm gives this finish a perfect flatness but also makes it very sensitive and the PCB must be handled with gloves carefully. Copper and Tin can create an intermetallic layer which reduces the shelf life to 6 months. Tin whiskers can also be a problem, generally this finish ensures high reliability and is suitable for fine pitch and small components.


- Perfect flatness
- No Lead used
- Possible rework
- Top choice for press fit


- Sensitive, possible damage during handling
- Environmental problems with Thiourea used in the process


Immersion Silver Ag

Immersion Silver is a chemical process which ensures excellent surface flatness. The thickness of the finish varies from 0.12 to 0.40 µm and the shelf life is 6 months. Mostly used in US, it can be reworked and is a competitive solution for a lead-free finish. In addition, this technology is weldable with aluminum wire, but it also brings constrains such as sensitive to handling, the requirement for special packaging and the reduced supply chain options to support this finish.


- Excellent Flatness
- Perfect for fine pitch and small components
- Competitive price
- No lead
- Rework possible
- Aluminium wire bondable


- Sensitive to handling
- Reduced supply chain options
- Short window between operations


ENIG – Electroless Nickel Immersion Gold

This process quickly became the most used surface finish. It is a double layer metallic coating with nickel and gold. A 3-5 micron layer of nickel is chemically deposited in a bath. It is a barrier for copper and a surface where the components are soldered. Then, 0.05 micron of pure gold is applied to the boards to protect the nickel during storage time. It is a lead-free process that offers a very flat surface and excellent solderability as well as reliability. But all advanced technologies come at a cost and the cost of ENIG finishing is one of the highest on the market.


- Flat surfaces
- Strong solderability
- Bonding friendly


- Not cost effective
- Electroless nickel/phosphorous can have undesirable magnetic properties
- Aluminum wire bondable, but not gold wire
- Oxidation of Nickel can cause a solder failure


ENEPIG – Electroless Nickel Electroless Palladium Immersion Gold

The process is the same as for the ENIG finish. But despite being a high quality finish, ENIG, due to nickel oxidation, can cause failure when it comes to soldering the components to the board. To eliminate this risk, it is possible to apply a layer of palladium between nickel and gold, which resists corrosion. However, the solderability could be affected if the palladium layer is too thick.


- Flat surfaces
- Strong solderability
- Bonding friendly
- Palladium layer eliminates potential corrosion from immersion reaction


- Expensive technology
- Electroless nickel/phosphorous can have undesirable magnetic properties
- Solderability performance is reduced due to too thick palladium layer
- Slower to be wet


OSP - Organic Solderability Preservative

OSP is a water-based finish, applied in a bath and generally used for copper pads. This organic solder mask bonds to copper and protects it from corrosion. However, this is not the most robust finish, and the shelf life is short. This process is environmentally friendly.


- Flatness
- Rework possible
- Clean and environmentally friendly
- Low cost


- Limited Shelf life
- Limited thermal cycles
- Difficult to inspect
- Request relatively aggressive flux at assembly