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Surface Finishes on Printed Circuit Boards: Types and Selection Tips Offered

 Sep 23, 2022

Printed Circuit Boards

Printed circuit boards are quite like the core or backbone of electronic or electromechanical devices. Hence, they need to be accurate in terms of structure, function, and surface finish. Surface finishes on printed circuit boards are a crucial aspect of the overall PCB manufacturing and assembly. This is because surface coating or layering protects the board from contamination, damage, exposure to air, moisture, and more. There are various types of surface finishes on printed circuit boards, and one needs to select an appropriate type based on application requirements, operating environments, and so on. This post discusses the types of surface finishes for PCBs and some pointers to choose the correct one.

Types of Circuit Finishes on Printed Circuit Boards 

There are various types of surface finishes on printed boards. Here are some of them.

  • Hot Air Solder Level (HASL): This is a commonly used surface finish especially for basic PCBs or the ones with relatively simpler components. This type has two versions- tin-lead solder finish and lead free or RoHS compliant. Both these versions offer good solderability and a large processing window.
  • Chemical or metal immersion surface finishes: These surface finishes feature various metals such as tin, silver, and gold. All of these offer a flat finish, good solderability, and heat dissipation. However, tin and silver are sensitive when handling. Electroless nickel immersion gold surface finish comprises a finish of electrolytic nickel or gold. The gold plating is either hard or wire bondable, and offers durability. This type increases the operating life of the boards. However, they have a short operating window.
  • Carbon surface finishes: This type also strengthens the board making it durable. It offers excellent mechanical strength and conductivity. It remains unaffected during the soldering process.

How to Choose the Right Surface Finish?

Based on the types of surface finishes and their features one needs to weigh them against the application requirements. Here are some pointers that may help you select the correct surface finishes on printed circuit boards.

  • If your board design is simple with minimal components, you can opt for HASL or hot air solder level surface finishing. This is economical and has a long shelf life. This may not be suitable for complex PCBs or HDI PCBs as the finishing in terms of thickness between large and small pads as well as bridging is not very fine.
  • Alternatively, you can opt for lead-free HASL, especially for RoHS compliant boards. Here, instead of tin-lead, a formulation of tin and copper, nickel, or germanium is used. This finishing is also suitable for relatively less complex boards and not the ones with miniature components. It facilitates heat dissipation and prevents overheating. You can opt for this if the SMDs and BGA pitches on the boards are less than 20mil.
  • Immersion tin and immersion silver finishing types may be used for boards with complex and miniature components with small BGAs. They offer an almost flat finish regardless of the variation in pad thickness. If the boards need to be upgraded or fixed, one can rework comfortably with this type of surface finish.
  • If you require a long operating window, immersion finishes are not suitable, instead HASL may be better. However, if your application has any restrictions regarding lead related hazards and related compliance, you can opt for the lead free or RoHS compliant HASL surface finishes.
  • For structural stability and excellent mechanical strength, gold or carbon finishing may be suitable.
  • All in all, one should check factors such as tight pitch components, wire bonding, sensitivity while handling, lead related compliance, shelf life and so on to be able to choose the right type of surface finish.

If you are an OEM manufacturing mechanical, electromechanical, or electrical devices, parts or products, you may want to partner with a reliable PCB manufacturer and assembly services provider. Ensure they offer end-to-end services and understand your requirements at length before offering a solution. Ensure they offer a variety of surface finishes on printed circuit boards and assist you in the selection process. Accelerated Assemblies offers end-to-end PCB manufacturing and assembling solutions and various surface finishes. The company has many years of market presence and hence the privilege of working with clients from diverse industries. The team at Accelerated Assemblies has developed expertise in customization, regardless of the complexity of the requirement.

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