Thickness logging
XRF test plans capture nickel (3–6 µm) and gold (0.05–0.125 µm) values per lot, ensuring evidence for IPC Class 2/3 compliance.
Surface Finish
ENIG Surface Finish
Electroless nickel immersion gold (ENIG) builds pair a 3–6 µm nickel barrier with a 0.05–0.125 µm immersion-gold cap, delivering flat SMT pads that hold >12 months of shelf life when sealed per process logs.
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ENIG Finish Parameters
| Parameter | Typical | Notes |
|---|---|---|
| Electroless nickel thickness | 3–6 µm | Derived from 118–240 µin values listed in PCBTok’s ENIG gold-thickness table. |
| Immersion gold thickness | 0.05–0.125 µm | Gold cap options from 1–4 µin align with fine-pitch solderability targets. |
| Shelf life (vacuum packed) | >12 months | ENIG ranks >12 months in the comparison table of final finishes. |
| Supported board thickness | 0.2–7.0 mm | Capability matrix documents ENIG builds from thin 0.2 mm cores up to 7.0 mm backplanes. |
| Maximum panel size | 533 × 686 mm | Listed as 21" × 27" finished panels for ENIG processing lines. |
| Aspect ratio | ≤10:1 | Same table indicates ENIG supports 10:1 mechanical via aspect ratios alongside HASL and immersion tin. |
Specification values consolidate data from PCBTok’s ENIG capability tables and the finish comparison matrix shared for ENIG vs. HASL/OSP.
ENIG Plating Flow
Tightly controlled wet-process steps keep nickel, palladium, and gold layers within tolerance while preserving flatness.
- 1
Surface prep
Panels undergo alkaline clean and micro-etch so copper pads present a uniform activation surface before nickel deposition.
- 2
Nickel deposition
Electroless baths lay down 3–6 µm of nickel; bath pH and temperature are logged per lot to avoid black-pad precursors.
- 3
Gold strike
Immersion gold between 1 and 4 µin is applied immediately after nickel, protecting the barrier layer from oxidation.
- 4
Rinse & dry
DI cascades remove chemistry residues and nitrogen knives dry panels without disturbing the coplanar surface.
- 5
XRF verification
Coupons from every panel set are measured to confirm nickel and gold targets before lamination or packing.
Process Controls
Controls focus on thickness accuracy, defect prevention, and documentation.
Nickel chemistry
Ni-P levels are trended, and baths are exchanged before phosphorus exceeds supplier limits to curb black-pad formation.
Planarity audits
BGAs over 0.5 mm pitch receive coplanarity scans so any pad height drift above ±2 µm is corrected before release.
Reliability & Validation
Lot-level evidence backs ENIG usage across NPI and production programs.
Shelf-life control
Vacuum-bag dates and humidity card readings prove ENIG panels stay within the >12-month window cited in the finish comparison table.
Solderability tests
Dip-and-look coupons confirm wetting after 4x simulated reflows, matching the “good” multi-solder rating referenced in PCBTok’s matrix.
RF review
For high-frequency stackups, engineers document nickel usage vs. loss targets, citing the PCBTok guidance that ENIG introduces moderate RF loss.
Design & Handling Guidance
Design notes keep ENIG pads flat and contamination-free.
Fine-pitch pads
Match soldermask dams to ≥0.1 mm spacing so HASL-style solder beads never touch ENIG pads on the same net.
Selective finishes
Use ENIG for SMT landings and define hard-gold fingers separately—PCBTok supports ENIG + gold-finger combos in a single panel.
Exposure tracking
Document accumulative open-bag time; re-bake panels if exposure exceeds 8 h to maintain the >12-month storage claim.
Case Studies
Recent ENIG deployments measured against published capability data.
28-layer compute module
Maintained 3.5 µm nickel and 0.08 µm gold across a 480 × 610 mm panel, meeting the 10:1 via ratio without registration hits.
Layers:28
Ni/Au:3.5 µm / 0.08 µm
Panel:480 × 610 mm
BGA test coupon
0.30 mm core coupons stored for 14 months retained full solder spread thanks to vacuum packing aligned with the >12-month rating.
Core:0.30 mm
Storage:14 months
Result:100% spread
Frequently Asked Questions
Why control nickel thickness so tightly?
Keeping nickel between 3 and 6 µm, as cited in the PCBTok data sheet, balances barrier reliability with manageable deposition time and limits black-pad risk.
How long can ENIG boards be stored?
ENIG is rated for more than 12 months of shelf life when sealed with desiccant; we log bag openings to prove compliance.
What panel sizes fit the ENIG line?
The published envelope is 21" × 27" with board thickness up to 7.0 mm; we panelize within that window for predictable plating.
Can ENIG handle multiple reflows?
Yes—ENIG is graded "good" for multiple solder cycles so long as cleaning and Ni-P monitoring follow the documented plan.
Need ENIG guidance for your stackup?
Share your layer count, pad pitch, and storage targets—we'll respond with nickel/gold specs, control plans, and a production quote within 24 hours.