Pcbwave can provide four surface finish options: HASL, Lead-free HASL, ENIG, OSP. PCB surface finish is applied to the exposed copper pads to protect from oxidation, which would strongly inhibit the contact pad's ability to bond with molten solder.
HASL - Hot Air Solder Leveling
HASL is a type of finish used on printed circuit boards (PCBs). For hot air solder leveling finish, the board will be dipped in a bath of molten solder and then passed through a conveyor of hot air knives that brush the excess solder off. Basically, the copper pads are pre-tinned with the thinnest layer of solder, and the tinning protects the bare copper underneath. which can provide the board with a good shelf-life, and the existing layer of solder makes the molten joints much easier to join. It is a commonly used and cheap finish for most DIY projects. However, it is not suitable for fine pitch components since HASL leaves uneven surfaces.
Pros:
Cheap
Avoids copper corrosion
Cons:
Uneven Surfaces
Not good for fine pitch components
Thermal Shock
Poor wetting
High thermal stress during process may introduce defects into PCB
Lead-free HASL
Lead-free HASL is variant from HASL, which is lead-free and qualified for ROHS compliance products. Please note that higher soldering temperatures are required for lead-free solder.
ENIG -Electro-less Nickel / Immersion Gold
ENIG is quickly becoming the most popular surface finish for industry use. In the ENIG plating process, the copper pads are protected by a coating of nickel, and a layer of gold protects the nickel during storage. This offers superior corrosion resistance compared to HASL due to the high corrosion resistance of gold. In addition, the excellent surface planarity of the nickel/gold finish allows components to besoldered flat onto the pad, making it an ideal 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.
Pros:
Flat surfaces
Strong Lead-free
Good for PTH
Cons:
Black pad syndrome
Expensive
Not good for rework
OSP-Organic Solderability Preservatives
OSP is to grow an organic film on the clean bare copper surface by chemical method. This film has oxidation resistance, heat shock resistance, and moisture resistance to protect the copper surface from further rusting (oxidation or vulcanization, etc.) in the normal environment; However, in the subsequent high welding temperature, this protective film must be easily removed by the flux, so that the exposed clean copper surface can be immediately combined with the molten solder to form a solid welding spot in a very short time.
Pros:
Flat surfaces
High welding strength
Good weldability
Good for to rework
Cons:
High contact resistance affects electrical measurement
The process time is short, and the subsequent welding must be completed within 24 hours after the first welding
Non corrosion resistance
The printing requirements are high and wrong printing is not allowed, because cleaning will damage the OSP film
The thermal stability is poor
