The Surface Finish Guide
Are you doubting which materials to choose for your PCB surface finish?
Choosing the right materials can be a hassle, if you’re not aware of all the standards and requirements for your particular project.
But specifically in regards to mounting the components, can it be a bother.
If your manufacturer cannot easily mount the components, it can be a very costly affair!
Keep reading for an overview of the most common types of surface finish, their advantages and disadvantages.
What’s the deal with surface finish?
Imagine being a scientist on a polar expedition. You’re usually super smart, except for this time, where you equipped yourself with flip flops and an aloha shirt.
It won’t matter much how great of a scientist you are, seeing as you’re exposed to the elements in extreme conditions and thus won’t perform properly.
The same goes for the surface finish of your PCB. If it’s exposed to all sorts of elements and conditions, the components won’t have the ideal conditions to function – and they won’t last long.
Just like a polar scientist wearing flip flops in the snow.
The PCB surface finish, among other things, protects your circuitry, which is why it’s so vital for function. The choice of surface is, therefore, something you have to get right from the very beginning.
Not only that, the choice of materials also affects the high-speed signal trace loss. The table below compares several factors, like high-frequency loss, costs, and more.
Source: Tao, Y; Scharf, F.H. (2012) EM Modeling of Board Surface Finish Effect on
High Speed PCB Performance. DesignCon. 2012, California, USA. UBM Electronics.
Types of surface finish
There are several different surfaces to choose from when making your PCB, including two types of gold, tin, and silver. Like previously mentioned, you’ll have trouble in the long run in terms of reliability, if you make a deplorable decision.
This is why you need to know the pros and cons of your options, before choosing your surface finish. Below you’ll find a quick overview of the most common choices for your surface finish, their advantages and disadvantages.
ENIG gold is one of the types of gold surfaces you can use. Here, nickel and gold is placed on top of some copper. A disadvantage of ENIGgold is that in some cases, the material may crack when you solder.
The advantage, on the other hand, is the very smooth surface, making it very solderable. It is the main reason why it is the most frequently used surface for PCB design.
In continuation of the gold surface mentioned above, there is also ENEPIG gold, where the P stands for palladium. Here there is palladium in the material, so you avoid the cracks that can occur after soldering.
One disadvantage is the cost of palladium. It’s very expensive and the thickness of the palladium layer has to be extremely precise. It will need additional specialists to ensure correct manufacturing.
HASL (Hot Air Solder Level)
When creating a HASL surface, the PCB is immersed in liquid tin, after which high-pressure hot air is blown over the surface. The HASL surface is not as smooth as the gold surface. Consequently, with HASL, you may not be able to solder the smallest components. The advantage, on the other hand, is that it is generally great to solder. It is only for the tiny components that this is not the case. It can be a disadvantage, though, because flecks of tin residue may remain on the PCB.
Keep in mind that tin is both the cheapest but also the worst surface for fine electronics.
You will not see chemical silver in use very often. The downside to it is that the surface can oxidize, making it difficult to solder on.
OSP (Organic Solderability Preservative)
OSP provides a smooth surface that is suitable for small components. However, this surface is not recommended if the PCB is to be stored
for a long time before being fitted with components.
Worried that your copper will oxidise without the correct surface finish?
Book a free PCB consultation below.
In this free consultation, I’ll guide you through your choices and give you the tips you need to safely move on with your electronic project.
I’ve designed more than hundreds of well-functioning PCBs and I have more than 25 years of experience in the field.
Take your tips with you or cooperate with us – the choice is yours.