Comprehensive Introduction to PCB Surface Finish Types

 The PCB is the cornerstone of the electronics sector. In many electronic gadgets, it is a necessary component. When making a PCB, the smoothness of its surface is a crucial consideration. The performance, longevity, and regulatory compliance of a board can all be greatly improved by choosing the appropriate coating.

The various types of PCB surface finish will be covered in great detail in this blog. Additionally, you will learn how to choose the best finish for your particular PCB requirements.

1.The Definition of Surface Finishing on PCBs
Learn a bit about the surface finishes of PCBs.

In essence, a PCB surface finish is a protective layer applied to the copper trace of PCBs. It can increase PCB reliability and longevity. Surface finish promotes solder joints that are strong, which allows for reliable soldering.

Each type of finish is unique. This makes PCBs more suitable for specific applications. Most surface finishes work well with fine-pitch parts. These finishes can also prevent problems like solder mask shifting or tombstoning.

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different pcb surface finish

2.There are different types of PCB surface finishes.
Understanding the importance of surface finish on your PCB. The best option for your project can then be selected. Each has unique benefits and drawbacks.

The various surface finish types will now be covered in detail.

 

2.1 Hot Air Solder Level (HASL)
The most widely used and reasonably priced surface finish is HASL. The procedure is fairly easy. Dip the PCB into the metal that has melted. The copper is then soldered to be removed from the tank. The PCB surface is leveled using hot-air knives. The surface is now solderable.

HASL can be used with both large components and SMTs. SMTs that are too small will not perform as they should. Fine Pitch Technology and Fine Pitch Technology are not compatible. Process temperatures can range between 260 and 270 degrees. High temperatures can damage circuit boards. This alloy contains a high amount of lead. Lead in the alloy is carcinogenic. It’s usually dipped into tin-lead. This means it’s not RoHS compliant.

 

2 .2 Lead-Free HASL
Lead-free HASL has the same properties as conventional HASL, but does not contain any lead. There are numerous applications for it. It is RoHS-compliant. It has all the advantages of traditional HASL.

 

2.3 Organic Soderability Preservatives(OSP)
OSP is the process used to finish printed boards with copper foil. It meets the RoHS directive. OSP stands for organic solvents preservatives.

OSP is resistant to heat shock, moisture, and oxidation. Under normal conditions, it can only protect copper surfaces from further corrosion. In the high-temperature weld process, it is necessary to remove the protective film quickly and easily by using flux. It is an easy way to quickly and efficiently form a solid connection by combining the clean copper surface with the molten metal.

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hasl vs lead-free hasl vs osp

This surface finish is a water-based finish that protects the copper until soldering. This coating prolongs the life span of copper by preventing oxidation. This coating is less durable on organic surfaces and more sensitive. This product has a very short lifespan.

 

OSP is a cost-effective surface finish. It is an easy operation that takes very little time. The coating does not affect the size of holes on the PCB. It has a flat surface and a good finish. It is perfect for areas where PCBs are handled with caution. It is durable.

 

2.4 Immersion Tin
Immersion Tin is a surface finish that does not contain any lead. This surface finish can be used for small parts. This surface finish is ideal for Fine Pitch Technology due to its flat and thin finish.

PCBs with a surface finish are not only affordable, but they also have their disadvantages. Tin can react and shorten the shelf life of PCBs by reacting with their copper layers. It is also important to use it as soon as possible because it is easily tarnished. It is very sensitive. You will see tin whiskers after a few weeks. All current solders are tin-based, so the tin can be used with any solder.

 

2.5 Immersion Silver
The price of immersion silver surface finish is reasonable. The finish is flat. Silver plating protects the copper from oxidation. The silver layer, although thin, is very conductive. The silver layer does not affect the size of the hole, which is perfect for Fine Pitch Technology.

 

This type of finish can tarnish easily. The silver layer tarnishes when exposed to air. Anti-tarnish packaging is used to prevent this. After removing it from the package, silver is extremely sensitive and must be soldered. Immersion silver has a moderate durability. It is also affordable and compliant with RoHS standards.

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immersion tin vs immersion silver

 

Immersion silver is a process that falls between electroless Nickel and Immersion Gold and OSP. This is an easy and quick process. Even if the PCB is exposed to humidity or heat, it can still be soldered well. However, the PCB’s luster will fade. Immersion silver does not have the same physical strength as electroless Nickel/immersion Gold because it doesn’t contain nickel.

 

2.6 Plated old
Hard Gold is another name for Plated Gold. Surface finish is expensive because it adds a layer of gold to the PCB. The PCB is coated with a gold layer by electroplating. The circuit board is strengthened by the gold layer, which is tightly bonded. Gold is a superior conductor and offers a high-quality electrical performance. The gold finish also has a commendable resistance to oxidation. PCBs are ideal for this finish, since they can withstand high wear. The gold surface finish can last a long while.

 

This type of finish is expensive due to the extra processing needed. The thickness of the gold affects the price. As the thickness of the gold immersion rises, so does the cost. Processing surface finish is challenging. It is a rare material because of its high cost, but it has a great surface finish. Hard gold is not solderable.

 

2.7Electroless nickel immersion gold (ENIG)
ENIG is the most common ENIG due to its RoHS compliance and properties. The copper is coated with nickel and then a thin gold layer is placed on top. The nickel layer is soldered to the components and the thin layer of gold protects them until soldering has been completed. ENIG produces a PCB with a pure top gold layer. It is softer than gold electroplated. It is commonly known as “soft plating”.

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plated gold vs enig

ENIG is durable and has a long shelf life. Due to the two layers, it is expensive. It’s thin, flat and has a smooth finish. This allows it to be used on smaller components. The black pad syndrome is ENIG’s sole problem. This is caused by the accumulation of phosphorus between the gold and the nickel layers.

 

2.8 Electroless nickel palladium immersion gold (ENEPIG)
ENEPIG’s surface finish prevents air reactions and corrosion. Its best feature is its long shelf life. This type of surface finish is made up of three layers of gold, palladium and nickel. They provide long-lasting performance when combined.

Unlike ENIG, there is no “black-pad” syndrome. RoHS compliant and lead-free. Its high price and complicated processing are the main concerns when using this product.

You can utilize more mixed processes in addition to the ones mentioned above. For optimal results, it is advised to combine two or three surface finishes. PCBs can have multiple finishes. ENIG+ OSP or ENIG+HASL is the most common surface finish.