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ENIG stands for Electroless Nickel Immersion Gold. It is a two-layer metal finish on the exposed copper pads of a PCB: a layer of electroless nickel for solderability and as a diffusion barrier, covered by a very thin layer of immersion gold that keeps the nickel from oxidizing. ENIG (also called chemical gold, immersion gold or ENIG PCB finish) gives flat, lead-free pads and a long shelf life. It costs more than HASL or OSP, it needs good process control to avoid "black pad", and it is not meant for contacts that are plugged in repeatedly.
This guide explains how ENIG works, its layer thickness, advantages and disadvantages, black pad, how ENIG compares with other finishes, and how to order it at NextPCB. For a head-to-head with the cheapest alternative, read HASL vs ENIG. For every finish side by side, see the PCB surface finish guide.
ENIG is a chemical (non-electrolytic) surface finish. Both metals are deposited by chemical reaction, with no electric current, so the coating is very uniform across large and small pads alike. The nickel layer is what the solder joint actually forms with. The gold layer only protects the nickel until assembly and dissolves into the solder during reflow.
| Attribute | ENIG |
|---|---|
| Full name | Electroless Nickel Immersion Gold |
| Also called | Chemical gold, immersion gold, electroless nickel/gold |
| Structure | Copper, then electroless nickel, then immersion gold |
| Lead-free / RoHS | Yes |
| Pad flatness | Very flat, which suits fine-pitch SMD and BGA |
| Shelf life | Long; typically about 12 months in sealed packaging |
| Cost | Higher than HASL, lead-free HASL and OSP |
| Main risk | Black pad if the process is not well controlled |
| Not suitable for | Edge connectors and contacts that are mated repeatedly |
| Layer | Typical thickness | Purpose |
|---|---|---|
| Immersion gold (top) | About 0.05–0.1 µm (roughly 2–4 µin) | Protects the nickel from oxidation and keeps the pad solderable until assembly |
| Electroless nickel (middle) | About 3–6 µm (roughly 118–236 µin) | Barrier that stops copper diffusing into the gold; the surface the solder joint forms with |
| Copper (base) | Per your stack-up | The pad itself |
Gold thickness is the part you can usually choose. A thicker gold layer gives more protection for storage and multiple reflow cycles but raises cost. At NextPCB, gold thickness is selectable in the quote form:
| Quote | ENIG gold thickness options | Default |
|---|---|---|
| Standard PCB quote | 1, 2 or 3 µin | 1 µin |
| Advanced PCB quote | 1, 2, 3, 4 or 5 µin, or custom | 1 µin |
One microinch is 0.0254 µm, so 1–5 µin is about 0.025–0.127 µm. The ENIG specification IPC-4552 defines the gold thickness requirements for the finish (a minimum of about 2 µin, or 0.05 µm, is commonly cited). If your design or customer requires IPC-4552 conformance, choose a thickness that meets it and confirm the requirement with your account manager before ordering.
| Step | What happens |
|---|---|
| 1. Cleaning | Oil, oxide and residues are removed from the copper pads. |
| 2. Micro-etching | A very thin layer of copper is etched away to give a clean, active surface. |
| 3. Activation | The copper is seeded, commonly with palladium, so the nickel will deposit on it. |
| 4. Electroless nickel | Nickel (alloyed with phosphorus) is deposited by autocatalytic reaction, with no electric current. |
| 5. Immersion gold | Gold replaces nickel atoms on the surface in a displacement reaction. The reaction stops once the nickel is covered, so the gold stays very thin. |
| 6. Rinse and dry | The board is rinsed, dried and inspected. |
Because the gold forms by displacement, ENIG cannot build the thick gold needed for connectors that are plugged in often. That job belongs to electroplated hard gold, covered in the gold fingers guide.
| Advantages | Disadvantages |
|---|---|
|
|
Black pad is the best-known failure mode of ENIG. During immersion gold deposition, the gold bath can attack the nickel surface unevenly and leave a corroded, phosphorus-rich nickel layer under the gold. The pad can look normal and even solder well at first, but the joint formed on that weakened layer is brittle and can crack under stress. The name comes from the dark, cracked nickel surface seen when a failed joint is pulled apart.
| Aspect | Detail |
|---|---|
| Likely causes | Immersion gold bath that is too aggressive or out of control; nickel layer with too much or too little phosphorus; excess dwell time in the gold bath; contaminated baths |
| Signs | Poor wetting or dewetting on pads; joints that fracture cleanly at the nickel interface; dark, cracked nickel seen under a microscope |
| Prevention | Tight control of nickel and gold bath chemistry, temperature and time; a stable nickel phosphorus content; regular bath analysis; solderability checks |
| Alternative | ENEPIG adds a palladium layer between the nickel and gold, which significantly reduces the risk |
Black pad is a process-control issue, not a defect of every ENIG board. If black pad risk matters for your project, for example a high-reliability or high-pin-count BGA design, discuss inspection and testing requirements with your account manager before ordering.
| Finish | Pad flatness | Shelf life | Cost | Wire bonding | Main difference from ENIG |
|---|---|---|---|---|---|
| ENIG | Very flat | Long | Higher | Not ideal | Reference finish |
| HASL / lead-free HASL | Uneven | Long | Low | No | Cheaper, but uneven pads; see HASL vs ENIG and HASL vs lead-free HASL |
| OSP | Very flat | Short | Lowest | No | Cheaper and flat, but short shelf life and limited reflow; see the OSP guide |
| ENEPIG | Very flat | Long | Highest | Yes (gold and aluminum wire) | Adds a palladium layer; lower black pad risk and suits wire bonding |
| Immersion silver | Flat | Medium | Medium | Aluminum wire | No nickel layer; often preferred for high-frequency RF |
| Hard gold | Flat | Long | High | Yes (gold wire) | Thick, hardened gold for repeated insertion; see the gold fingers guide |
ENIG is an immersion gold finish: the gold is deposited by immersion over an electroless nickel layer. People often say "immersion gold" as shorthand for ENIG. Do not confuse it with electroplated gold, which is thicker and used for contacts. For that comparison, see immersion gold vs gold plating.
ENEPIG (electroless nickel, electroless palladium, immersion gold) adds a thin palladium layer between nickel and gold. That layer protects the nickel during gold deposition, which makes black pad far less likely, and it makes the finish suitable for wire bonding. ENEPIG costs more, so choose it when you need wire bonding or the highest reliability, and ENIG for general fine-pitch SMT.
| If your board... | ENIG fits? |
|---|---|
| Has fine-pitch SMD or BGA parts | Yes; flat pads are the main reason to choose ENIG |
| Will be stored for months before assembly | Yes; long shelf life |
| Needs several reflow passes | Yes |
| Must be RoHS-compliant with flat pads | Yes |
| Is HDI or high-layer-count | Yes; ENIG is a common choice |
| Is cost-driven with large, simple parts | Consider lead-free HASL or OSP |
| Has edge connectors that are plugged in often | No; use hard gold on the fingers |
| Needs wire bonding | No; use ENEPIG |
| Is a very high-frequency RF design | Check; immersion silver is often preferred |
A single board can combine finishes. A common arrangement is ENIG on the soldering pads and hard gold on the edge fingers. The advanced quote also lists an ENIG + OSP option for boards that need both. Compare all options on the PCB surface finish options page.
ENIG is a chemical finish applied to the copper pads, so it is not tied to one laminate. At NextPCB, ENIG is available on every board material offered in the quote forms: FR-4 (including mid-TG, high-TG, halogen-free and high-CTI grades), aluminum, copper-base, ceramic, flexible and rigid-flex boards in the standard quote, plus high-speed, Rogers-type high-frequency and polyimide high-temperature laminates in the advanced quote.
| Board or material | Quote | ENIG |
|---|---|---|
| FR-4 (standard, mid-TG, high-TG, halogen-free, high-CTI) | Standard and advanced | Available |
| Aluminum, copper-base and ceramic boards | Standard | Available |
| Flexible and rigid-flex boards | Standard | Available |
| High-speed laminates | Advanced | Available |
| High-frequency (Rogers-type) laminates | Advanced | Available; for very high-frequency RF, compare with immersion silver |
| High-temperature (polyimide) laminates | Advanced | Available |
ENIG costs more than HASL, lead-free HASL and OSP, because it uses nickel and gold chemistry and needs tighter process control. How much more depends on board area, quantity, layer count and the gold thickness you choose, so there is no fixed percentage. A thicker gold layer costs more. To see the real difference for your board, select ENIG in the quote form and compare it with another finish; the price updates with your selection. For volume orders, high-end boards or special requirements, contact your account manager.
In the standard PCB quote, choose ENIG in the Surface Finish row under PCB Parameters, then pick the ENIG gold thickness (1, 2 or 3 µin). The advanced PCB quote offers 1–5 µin and custom gold thickness, plus hybrid options such as ENIG + OSP.
ENIG stands for Electroless Nickel Immersion Gold. It is a surface finish with a nickel layer deposited by chemical reaction and covered by a thin layer of immersion gold.
ENIG is a two-layer, lead-free finish on exposed copper pads. The nickel provides the solderable surface and a barrier against copper diffusion, and the gold protects the nickel from oxidation until assembly. It gives flat pads and a long shelf life.
Typical ENIG has about 3–6 µm (118–236 µin) of nickel under about 0.05–0.1 µm (2–4 µin) of gold. At NextPCB the ENIG gold thickness is selectable at 1–3 µin in the standard quote and 1–5 µin or custom in the advanced quote.
Yes. ENIG contains no lead, so it meets RoHS requirements.
Black pad is a failure mode in which the gold bath corrodes the nickel layer, leaving a brittle, phosphorus-rich surface that forms weak solder joints. It is a process-control issue, and ENEPIG significantly reduces the risk.
ENIG is an immersion gold finish: immersion gold deposited over electroless nickel. "Immersion gold" is often used as shorthand for ENIG. Electroplated gold is a different, thicker finish used for contacts.
ENEPIG adds a palladium layer between the nickel and gold. This reduces black pad risk and makes the finish suitable for wire bonding. ENEPIG costs more than ENIG.
ENIG gives much flatter pads and a long shelf life, which suits fine-pitch parts and BGA. HASL is cheaper but leaves an uneven surface. See the full comparison in HASL vs ENIG.
ENIG has a long shelf life, typically about 12 months in sealed, moisture-barrier packaging. Actual shelf life depends on storage conditions.
Yes. A common arrangement is ENIG on the soldering pads and electroplated hard gold on the edge fingers, because ENIG is too thin for repeated insertion. See the gold fingers guide.
ENIG is widely used, but at very high RF frequencies the nickel layer can add insertion loss, so immersion silver is often preferred. Confirm the best finish for your stack-up with engineering.
ENIG is not ideal for wire bonding. ENEPIG or soft gold is normally used for gold wire, and ENEPIG or immersion silver for aluminum wire.
ENIG costs more than HASL, lead-free HASL and OSP. The difference depends on board size, quantity and gold thickness. Select ENIG in the NextPCB quote form to compare the price with other finishes for your board.
ENIG is the usual choice for fine-pitch, BGA and long-storage boards. Choose your finish and gold thickness in the quote form, or ask NextPCB engineers to review your design.
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