PCB surface finish is a coating between a component and a bare board PCB. It is applied for two basic reasons: to ensure solderability, and to protect exposed copper circuitry. As there are many types of surface finishes,selecting the right one is no easy task, especially as surface mounts have become more complex and regulations such as RoHS and WEEE have changed industry standards.
HASL(Hot Air Solder Leveling) / Lead Free HASL
HASL is the predominant surface finish used in the industry. The process consists of immersing circuit boards in a molten pot of a tin/lead alloy and then removing the excess solder by using 'air knives', which blow hot air across the surface of the board.
Pros: Low-cost, Available, Repairable
Cons: Uneven Surfaces, Not good for fine pitch components, Thermal Shock, Not good for plated through-hole (PTH), Poor wetting
OSP (Organic Solderability Preservative)
OSP is a water-based, organic surface finish that is typically used for copper pads. It selectively bonds to copper and protects the copper pad before soldering. OSP is environmentally friendly, provides a coplanar surface, is lead-free, and requires low equipment maintenance. However, it’s not as robust as HASL and can be sensitive while handling.
Pros:Lead-free, Flat surface, Simple process, Repairable
Cons:Not good for PTH, Sensitive, Short Shelf life
ENIG(Electroless Nickel Immersion Gold )
ENIG is quickly becoming the most popular surface finish in the industry. It’s a double layer metallic coating, with nickel acting as both a barrier to the copper and a surface to which components are soldered. A layer of gold protects the nickel during storage. ENIG is an answer to major industry trends such as lead-free requirements and rise of complex surface components (especially BGAs and flip chips), which require flat surfaces. But ENIG can be expensive, and at times can result in what is commonly known as “black pad syndrome,” a buildup of phosphorous between the gold and nickel layers that can result in fractured surfaces and faulty connections.
Pros: Flat surfaces, Strong, Lead-free, Good for PTH
Cons: Black pad syndrome, Expensive, Not good for rework
Above types of PCB surface finish are commonly used in PCBWay. Besides, there are Immersion silver,Immersion Tin,Hard Gold,Nickel palladium (ENEPIG) and so on. Now, according to your own requirements, you can choose a suitable surface finish type.
