Understanding PCB Surface Finishing: Types, Pros, and Cons

Sep 25,2017

Printed Circuit Board (PCB) surface finishes are critical in the development of the PCB assembly. Surface finishing in PCB provides a solderable surface between the components and the PCB assembly and prevents the assembly from oxidation. There are different types of surface finishing available in the market. Each of the surface finishing types has its own pros and cons depending upon the application requirement. Therefore, it becomes important to select right surface finishing for the PCB assembly. Are you confused between the different types of surface finishing on the PCB? If, yes then you consider reading this post, which discusses some of the popular surface finishing types, and their impact on the PCB assembly.

What are the Different Surface Finishes Available for a PCB?

Surface finishing in PCBs is decided on the basis of several factors. These factors include price, reliability, assembly processing, performance requirement, and material costs. Below are some of the common surface finishing types available for all printed circuit boards.

HASL

Hot Air Solder Level finishing or HASL is a ROHS-compliant type of surface finishing performed on printed circuit boards. This type of surface finishing is done by dipping HASL circuit boards into molten soldering substrate.

Advantages of HASL

• It is widely available at a low price.
• This surface finishing type offers excellent shelf life owing to its reliable solder joints.

Disadvantage of HASL

• It is not suitable for unevent surfaces.
• The surface finishing is not ideal for fine pitch components due to its coating thickness.

Immersion Silver

Immersion silver is a ROHS directed surface finishing, which has gained immense popularity in the recent years. This type of surface finishing provides a reliable solder joint on various circuit boards. Immersion silver surface finishing is best suited for Surface Mount Technology (SMT) applications.

Advantages of Immersion Silver

• It offers the greatest conductivity among all types of surface finishing.
• This surface finishing offers fine pitch and flat pack coating, which makes it well suited for high-frequency applications.

Disadvantages of Immersion Silver

• It is extremely sensitive to contaminants present in the air or the circuit boards.
• It has a high friction coefficient, which makes it unfit for compliant-pin insertion.

OSP

OSP (Organic Solderability Preservative) is an organic-based surface finishing used in printed circuit boards. It protects the copper surface from oxidation before the soldering process. This type of surface finishing is robust and is specially designed for lead-free assemblies.

Advantages of OSP

• It’s a non-toxic and environmental friendly surface finishing type for circuit boards, as it doesn’t contain lead.
• It’s cost effective in comparison to other surface finishing type.

Disadvantages of OSP

• This surface finishing is not fit for Plated Through Holes (PTH) based circuit boards.
• It offers limited shelf life in most of the circuit boards.

As discussed above, various surface finishing plays a key role in the protection of PCB from environmental elements. Read the next post to understand more some more PCB surface finishing options and their underlying impacts.