In the process of PCB manufacturing and Assembly , the surface treatment process directly affects the reliability, durability and electrical performance of the product. How to select the most suitable surface finish?
First. Key Selection Factors
• Cost: OSP < Lead-free HASL < Immersion Ag < Immersion Sn < ENIG < ENEPIG < Hard Gold
• Flatness / Fine pitch: OSP / ENIG / Immersion Ag / Immersion Sn = Excellent; HASL = Poor (not recommended for ≤0.5mm pitch / BGA)
• Reflow cycles: OSP ≤ 2 cycles; ENIG / Immersion Ag / Immersion Sn ≥ 3 cycles; HASL ≥ 5 cycles
• Shelf life: OSP ≤ 6 months; HASL ≤ 1 month; Immersion Ag ≈ 1 year; ENIG ≥ 2 years
• Reliability / Environment: OSP sensitive to moisture; Immersion Ag sensitive to sulfur; ENIG / ENEPIG best for corrosion & high temperature resistance
Second. Brief Introduction of Common Finishes
• OSP (Organic Solderability Preservative)
Lowest cost, flat surface, ideal for fine pitch. Sensitive to moisture, limited reflow, short shelf life. Most common for consumer electronics.
• Lead-free HASL (Hot Air Solder Leveling)
Strong solder strength, good for wave soldering. Rough surface, not suitable for BGA / 0201. Best for power supplies & home appliances.
• Immersion Silver (ImAg)
Good flatness, low RF loss, moderate cost. Sensitive to sulfur. Suitable for high-frequency & fine-pitch circuits.
• ENIG (Electroless Nickel Immersion Gold)
Excellent flatness, oxidation resistance, and reliability. Suitable for BGA, long-term storage, automotive, medical, 5G. Higher cost.
• ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold)
Ultra-high reliability, no black pad, compatible with Au / Al wire bonding. Highest cost, used in high-end packaging, military, medical.
• Hard Gold (Electroplated Gold)
Excellent wear resistance. Used for edge connectors, gold fingers, contact points.
Third. Quick Selection Rules
• Low cost / mass production: OSP
• General circuits / power boards: Lead-free HASL
• Fine pitch / BGA / 0201: Avoid HASL; choose OSP, ENIG, or Immersion Ag
• High frequency / RF: Immersion Ag or ENIG
• Automotive / industrial / medical / high reliability: ENIG or ENEPIG
• Gold fingers / connectors: Hard Gold
• Humid & harsh environment / long lifetime: ENIG / ENEPIG
Forth. Warnings
• OSP: Must be sealed and moisture-proof; assemble soon after opening.
• Immersion Ag: Avoid sulfur environment; use anti-sulfur packaging.
• ENIG: Control Ni thickness ≥ 3 μm to reduce black pad risk.
• HASL: Not recommended for fine pitch or BGA.
