Every gold surface finish decoded — structure, RF loss, solderability and bondability — so you never pick the wrong finish for a high-frequency board.
Gold surface finishes can be extremely confusing: ENIG, plating gold, nickel-gold, immersion gold, thick gold, thin gold, palladium-gold, DIG… One tiny difference in name leads to huge gaps in cost, reliability, high-frequency performance, solderability, and bondability.
This guide breaks down every finish clearly: name → structure → process → pros and cons → applications → restrictions → cost. After reading, you will never choose wrong again.
All gold processes fall into just two types:
Nickel-gold, palladium-gold, thick gold, and thin gold are all sub-types.
Common names: Immersion Gold, ENIG, Chemical Gold, Nickel-Gold. Structure: Cu → Electroless Ni (3–5 μm) → Au (0.05–0.1 μm).
Key features:
Critical disadvantage (for RF and high frequency): ENIG contains nickel. Nickel is ferromagnetic (μr ≈ 100–600) with conductivity only 1/4 of copper. At high frequency, skin effect causes signals to penetrate the thin gold into the nickel layer, causing hysteresis loss and eddy current loss — loss explodes at higher frequencies. RF and mmWave boards must avoid ENIG.
Performance data (microstrip):
Applications and restrictions: Use for consumer electronics, BGA, high-volume production. Avoid for RF, high-frequency, mmWave, connectors, and gold fingers. For a wider comparison see our ENIG vs immersion silver vs immersion tin guide.
Common names: Palladium Gold, ENEPIG, Black-Pad-Free ENIG. Structure: Cu → Ni → Pd (0.05–0.1 μm) → Au.
Key features: Eliminates black pad issues; extremely high reliability; cost 30–50% higher than ENIG.
RF performance: Still contains nickel → still very high RF loss. Only reliability improves; RF performance does not.
Applications and restrictions: Use for automotive, medical, military, and other high-reliability products. Avoid for RF and high-frequency boards.
Common names: Gold Plating, Electroplated Gold. Standard structure: Cu → Electroplated Ni (5–8 μm) → Electroplated Au (0.1–3 μm).
Important fact: All standard PCB electroplated gold contains nickel. Nickel is required for adhesion and as a barrier layer. Gold without nickel is DIG, not plated gold.
Thick gold vs thin gold: Thin gold (0.1–0.3 μm) is low cost and used for test points and simple gold fingers; thick gold (0.5–3 μm) is used for wire bonding.
Hard gold vs soft gold: Hard gold (cobalt-doped) is wear-resistant → connectors and contacts; soft gold (pure) is for wire bonding → die bonding.
Why plated gold is bad for RF? Not the gold — the nickel. Even thin gold still has a nickel layer, causing massive RF loss.
Why thick gold is bad for SMT? Poor wettability; forms brittle Au-Sn intermetallics; poor flatness → BGA head-in-pillow issues. Thick gold is for bonding only, not soldering.
Recommendations for RF and microassembly:
Common names: DIG, Nickel-Free Gold, Pure Immersion Gold. Structure: Cu → Au — no nickel, no palladium.
Features:
Applications and restrictions: Use for RF, microwave, mmWave, and high-speed transmission lines. Avoid for wire bonding, connectors, and high-reliability harsh environments.
| Surface Finish | Common Name | Structure | Nickel? | Solderability | Bondability | RF/HF Performance | Typical Applications | Restrictions |
|---|---|---|---|---|---|---|---|---|
| ENIG | Immersion Gold | Cu→Ni→Au | Yes | Excellent | No | Poor (3–5x loss) | BGA, consumer electronics | RF, mmWave |
| ENEPIG | Palladium Gold | Cu→Ni→Pd→Au | Yes | Excellent | No | Poor (same as ENIG) | Auto, medical, military | RF, high frequency |
| Electroplated Gold | Plated Gold | Cu→Ni→Au | Yes | Poor | Fair | Poor | Bonding, gold fingers | Full-board, BGA |
| Thick Plated Gold | Thick Gold | Cu→Ni→Thick Au | Yes | Very Poor | Excellent | Poor | Wire bonding | RF traces, solder |
| Thin Plated Gold | Thin Gold | Cu→Ni→Thin Au | Yes | Poor | Fair | Poor | Test points, fingers | RF traces |
| DIG | Direct Immersion Gold | Cu→Au | No | Good | No | Best (near Cu) | RF, mmWave | Bonding, mating |
| OSP | Anti-Oxidation | Cu→Organic | No | Good | No | Best | RF, low cost | Contact, mating |
| Immersion Ag | Immersion Silver | Cu→Ag | No | Good | No | Best | RF, high frequency | Harsh environment |
| HASL | Spray Tin | Cu→Sn | No | Good | No | Poor | Power, through-hole | BGA, high frequency |
| Immersion Sn | Immersion Tin | Cu→Sn | No | Good | No | Excellent | Low-cost HF | High-reliability |
Common questions about gold surface finishes.
ENIG's nickel layer is ferromagnetic with only 1/4 of copper's conductivity. At high frequency, skin effect pushes current into the nickel, causing hysteresis and eddy current losses — measured 100–200% higher than copper at 10 GHz and 3–5x higher at mmWave bands.
Plated gold always includes a nickel layer (for adhesion and barrier), is thicker and bondable. DIG is direct immersion gold with no nickel or palladium — thinner, not bondable, but the best RF performance of any gold finish.
Thick gold (0.5–3 μm) is for wire bonding only — it solders poorly and forms brittle Au-Sn intermetallics. Thin gold (0.1–0.3 μm) suits test points and simple gold fingers. Neither belongs on RF traces.
Nickel-free finishes: DIG, immersion silver, or OSP. If bonding pads are also needed, combine nickel-free finishes on RF traces with local thick gold plating on the pads.
Send us your application — RF, bonding, connectors or BGA — and our engineers will recommend the right surface finish with a confirmed quote.
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