Surface Finish Options
ENIG, ENEPIG, immersion tin/silver, OSP and hard gold to match assembly and reliability needs.
PCB Technology & Capabilities
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Surface Finish — Process Capabilities & DFM Guide
The right finish stabilizes solderability, protects copper, and supports special needs like RF loss control, edge connectors, and Au/Al wire bonding—directly impacting yield and field reliability.
Process Capability Matrix（Thickness & Use Cases）
|
Finish |
Thickness (typ.) |
Shelf Life (sealed) |
Best For |
Notes |
|
OSP |
0.20–0.60 µm |
6–12 months |
Cost-effective SMT, fine pitch |
Copper-organic film; limited reflow cycles; clean handling needed |
|
ENIG (Ni/Au) |
Ni 2.5–5.0 µm; Au 0.03–0.12 µm |
12 months |
General SMT, BGA, RF |
Flat pads; manage black-pad risk via Ni-P control |
|
Selective ENIG |
Ni 2.5–5.0 µm; Au 0.03–0.12 µm |
12 months |
Localized gold needs |
Masked areas remain bare/other finish |
|
ENEPIG (Ni/Pd/Au) |
Ni 5–10 µm; Au 0.05–0.125 µm (Pd barrier internal) |
12 months |
Wire bonding (Au/Al), mixed assembly |
Excellent solder & bond compatibility; avoids black-pad |
|
Hard Gold (edge) |
Au 0.2–1.5 µm; Ni ≥2.5 µm |
12 months |
Edge connectors, wear |
Electrolytic; abrasion-resistant; not for solder joints |
|
Soft Gold |
Au 0.15–0.5 µm; Ni ≥2.5 µm |
12 months |
Au wire bonding, ENEPIG alt. |
Excellent bondability; manage solder embrittlement if used for joints |
|
Immersion Silver (ImmAg) |
0.15–0.45 µm |
6–12 months |
RF/High-speed, flat pads |
Low loss; protect from sulfur/handling; packaging critical |
|
Immersion Tin (ImmSn) |
≥1.0 µm |
6–12 months |
Fine-pitch SMT |
Tin-on-copper intermetallic; control whisker/handling |
|
LF-HASL |
1–25 µm (solder height) |
12 months |
Robust, thru-hole, power |
Not as flat; check coplanarity for fine BGA/QFN |
DFM & Pad Rules
- BGA/QFN: Prefer ENIG/ENEPIG/ImmAg/ImmSn for flatness; HASL is not recommended for 0.5 mm pitch or below.
- Wire bonding: Use ENEPIG or Soft Gold; define Au thickness per bond spec (e.g., 0.3–0.5 µm).
- Edge connectors: Hard Gold with Ni underplate ≥2.5–5 µm; Au per mating cycles (0.5–1.0 µm typical).
- Selective finishes: Keep ≥0.25–0.30 mm mask keep-out between finishes to avoid bleed.
- Thermal pads: With ENIG/ENEPIG use windowed mask patterns for paste release; verify void targets.
- VIP/VIPPO: Prefer ENIG/ENEPIG/ImmAg to maintain planarity; define Cu-cap before finish.
Finish Selection Cheatsheet
- Fine-pitch & RF → ENIG / ImmAg
- Wire bonding → ENEPIG / Soft Gold
- Edge connectors / Wear → Hard Gold
- Cost-sensitive SMT → OSP / ImmSn
- Mixed assembly (bond + solder) → ENEPIG
Manufacturing Flow & Controls
Clean → Micro-etch → Finish process (per type) → Rinse/dry → Thickness test (XRF) → Solderability test (J-STD-003) → Packaging.
Controls: Ni-P % for ENIG to prevent black-pad; Pd continuity for ENEPIG; sulfur exposure control for ImmAg; tin whisker mitigation for ImmSn; coplanarity for LF-HASL.
Quality & Standards
- Thickness specs: XRF per sampling plan.
- Solderability: IPC J-STD-003.
- Finish specs: IPC-4552 (ENIG), IPC-4556 (ENEPIG), IPC-4553 (ImmAg), IPC-4554 (ImmSn), IPC-4555 (OSP).
- Acceptance: IPC-A-600 / IPC-6012 per class.
Common Issues → Countermeasures
- Black-pad (ENIG) → Control Ni-P, fresh baths, Pd barrier (ENEPIG).
- ImmAg tarnish/creep corrosion → Sulfur-free packaging, gloves, humidity control.
- ImmSn whiskers → Post-plate aging/bake per spec; layout stress relief.
- LF-HASL coplanarity → Tight height SPC; switch to ENIG for fine BGA.
- Wire bond lift → Increase Au thickness or move to ENEPIG; verify bond pull.
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