PCB coating

Advantages

Disadvantages

Organic solderability preservatives (OSP)

Lowest cost lead-free option. Very thin and electrical contact can be made.

Fragile and easily damaged by handling. Protection during storage for shortest of all alternatives, at best 6 months but less if stored in hot humid conditions. Incompatible with some fluxes.

Immersion silver

Thin flat coating with good solder wetting. More robust that OSP and less than half cost of ENIG.

Solder wetting deteriorates if stored in atmosphere with sulphides. Protection during storage for ~ 6 months but can be less.

Immersion tin

Thin flat coating with good solder wetting. More robust that OSP and lower cost than ENIG.

Solder wetting deteriorates during storage, particularly at high humidity. Protection during storage for ~ 6 months but can be less.

Electroless nickel / immersion gold (ENIG)

Best protection of all immersion coatings, up to ~ 1 year in storage. Gold has very good solder wetting.

Most expensive option. Sometimes used to make electrical contacts but these can deteriorate.

Lead-free HASL (SnCu solder)

Good corrosion resistance, flat surface, good solder wetting.

Needs new equipment. High temperature can damage PCB, very good process control needed, boards usually need to be pre-baked.

SnPb HASL (for comparison)

Well understood, good protection, excellent solder wetting and corrosion resistance.

Thermal damage to PCB, surfaces tend to be uneven so not suitable for some large low profile components.