Surface Finishes for PCBs

VAC Consulting | Published September 28, 2022

Different types of surface finishes for your PCBs

PCB Surface Finishes Introduction and Comparison

The electric connection on a PCB depends solely on the conductivity of the copper – and therefore it must be well protected, to be able to function to its full potential, for as long as possible.

That is why the choice of surface finishes for your PCBs are such an important one, that can affect the end product in many ways.

The surface finish is responsible for two key areas when it comes to the performance of your PCBs; to protect the copper from oxidation and to provide a surface for high solderability for when components are to be assembled on your PCBs, to provide a reliable and long lasting end product.

There are a few surface finishes to choose from, and we want to make it as easy for you as possible. Down below we have listed the different types, along with a pros and cons list for each of them. And to create the ultimate overview – a table near the end.

HASL (Hot Air Solder Leveling)

When dealing with this specific surface finish, the PCB is lowered into a bath of molten solder to cover all the exposed copper surfaces by said solder. The extra solder is then removed by passing the PCB between hot air knives.


Pros of HASL Surface Finish:

  • Excellent wetting during component soldering
  • Copper corrosion avoided


Cons of HASL Surface Finish:

  • Low planarity on vertical levelers leads HASL unacceptable for fine pitch components
  • High thermal stress during process causes defects into circuit board


It’s also important to note that in order to be in line with regulations concerning environment protection, HASL has developed into two subcategories: Lead HASL and Lead-free HASL. The Lead-free variety follows the law and regulations of RoHS (restrictions of hazardous substances) which are guidelines, first adopted by the EU.

ENIG (Electroless Nickel Immersion Gold)

ENIG (Electroless Nickel Immersion Gold) is made of electroless nickel plating covered with a thin layer of immersion gold that protects the nickel from oxidation.



  • Flat surface
  • Simple process mechanism
  • High temperature resistance
  • Suitable for lead-free soldering
  • Suitable for SMT
  • BGA (ball grid array) etc.

ENIPIG (Electroless Nickel Electroless Palladium Immersion Gold)

ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold), is a bit different to the ENIG because of the fact that a layer of palladium is applied as a resistance layer to stop nickel from oxidation and diffusion to the copper layer.



  • Capable of withstanding excellent multiple reflow cycles
  • Very reliable wire bonding capability
  • Capable of meeting strict requirements of multiple types of packages including;
    • THT
    • SMT
    • BGA (ball grid array)
    • Wire bonding
    • Press fit etc.

ENIG & ENEPIG advantages

Provide the highest solderability for PCBs but the cost is much higher. To read more about how to cost optimize your PCBs, click here.

ImSn (Immersion Tin)

ImSn shares a lot of similarities with the ImAg surface finish. The main difference being that the ImSn surface finish is Tin, whereas ImAg is with silver.


The advantages when dealing with ImSn consists of an extremely planar finish on the copper pads, and therefore makes it a suitable choice for SMT application. And due to its surface, it is also easily detectable by Automated Optical Inspection techniques.

OSP (Organic Solderability Preservatives)

OSP is a surface finish with transparent organic materials. It uses a water-based organic compound that bonds to copper and protects it until the soldering process.


Pros of OSP Surface Finish:

  • Flat/planar
  • Short, easy process cycle
  • Inexpensive
  • Reworkable
  • Not affect finished hole size
  • Copper/tin solder joint


Cons of OSP Surface Finish:

  • Multiple reflows
  • Short shelf life
  • Not conductive
  • Difficult to inspect
  • Limited thermal cycles

However, due to the short shelf life (depending on the environment, temperature and humidity of where it’s stored) it requires thorough planning! As soon as the OSP layer breaks, there will be direct contact to the copper in the pads which will then start corroding.

Meaning that this is not a surface finish we recommend – unless you have all of your components on stock and are ready to assemble as soon as the PCBs have been produced.

Another thing to consider is reflow soldering. This surface finish can become problematic if the board needs to go through reflow several times. Which is often the case with PCBs that have components on the top and as well as the bottom.

What to keep in mind when deciding on a specific surface finish

To sum it all up, each type of surface finish has its own set of strengths and weaknesses, all things you want to consider before making your choice. It’s important to find the surface finish, best suited to your electronic product in all areas. Such as utilisation purposes, corrosion resistance, in-circuit test, cost, performance requirements, etc. The more aware you are of the requirements during the selection process, the more equipped you are to make the best possible choice for your specific project.


As mentioned above, cost is also a major factor to be mindful of. Generally when speaking of cost, the HASL and OSP are the cheapest options. You can read more in depth about cost optimization of your PCBs here.

Corrosion resistance

Another thing mentioned is the corrosion resistance. Here HASL and ImSn present themselves as the best choice regarding their corrosion resistance capabilities. While ImAg has the worst capabilities in terms of corrosion resistance.

In-circuit testing (ICT)

The only bad one in terms of ICT is the OSP surface finish. The others are the same level of good.

Hole fill

When it comes to hole fill, the HASL surface finish and the ENIG surface finish are the best, compared to the others.

How to choose a surface finish

Within your team there might be a difference of opinion regarding the standards. The sustaining engineer might want to go for the cheapest surface finish, but it must still be reliable! The PCB Engineer might be inclined to make a decision based on the supplier’s convenience as long as it is a quick and easy turn-around etc.


To help your team make a decision regarding surface finish, have a look at the table below. The table factors in the attributes each type of surface finish has and does not have.

Making the right choice

Making a choice regarding a surface finish, is just one of the many decisions you need to make prior to ordering your PCBs. Decisions regarding solder mask, silkscreen, size and thickness of the board, blind and buried vias, SMT, panels, tolerances etc.


We can help you with the production and advice regarding your PCBs. You can read more about our PCB solutions here, we also provide components procurement and assembly.


Or you can get in touch with us directly, by clicking below.