Surface Finishing - The Advantages & Disadvantages

Surface finish is necessary for 2 key reasons:

To prevent oxidation of exposed copper surfaces which would lead to poor solderability/reliability.
To provide a reliable, solderable surface which acts as the connection between the PCB and the components.

	HASL	OSP	ENIG
Advantages	Excellent Solderability Low Cost Long Shelf Life Long industry experience / well-known finish	Good planarity for surface mount and HDI Simple Process Low Cost Environmentally Friendly	Flat Surface Long shelf life Excellent oxidation resistance and wetting properties Robust for multiple thermal cycles Ideal for fine pitch surface mount, BGA ETC...
Disadvantages	Poor surface planarity and variation Extremely aggresive thermal shock and stresses on PCB Not Recommended for HDI products (no BGA, SMD)	6 Months or less shelf life Very sensitive to handling poor Solderability Usually requires aggresive flux / cleaning Issues with multiple assembly process step	Expensive finish nickel corrosion / black pad complicated process Possible damage from electrical test and routing

	Immersion Silver	Immersion Tin	Electrolytic Nickel Gold (Hard or Soft Bondable)
Advantages	Metallic Finish Very flat and planar surface Ideal for surface mount, BGA ETC...	Flat surface fine grain and non-porous	Can be applied in varying thicknesses Gold can be deposited in varying degrees of hardness depending on application 12 month shelf life good planarity
Disadvantages	Sensitive to handling and packaging Possible damage from electrical test Limited shelf life (up to 12 months) Creep-corrosion	6 month shelf life upleasant chemistry with carcinogenic substance – Thiourea Handling issues Potential for tin whisker growth over time – short circuits	Undercut of copper under nickel creates overhang and potential for flaking/shorts Expensive