PCB gold fingers are the plated contact pads along a board edge that slide into a card-edge connector, such as the edge of a PCIe card or a memory module. For boards that will be inserted more than a few times, they should be electroplated hard gold (gold hardened with cobalt or nickel) over a nickel underplate, with the edge beveled and the solder mask and copper kept back from it. Connector makers commonly plate their own contacts with about 30 µin (0.76 µm) of gold for durable applications and 10 µin for many others; match the board’s gold to the connector and its rated mating cycles, and put the thickness, hardness, bevel and keepout on the drawing.
| Item | Typical specification | Why |
|---|---|---|
| Finish | Electroplated hard gold over nickel | Wear resistance for sliding contact |
| Gold hardness | ASTM B488 Type II, Grade C | Recommended by a connector maker for edge-card pads |
| Gold thickness | Match the connector, often 10–30 µin | Sets wear life with the contact force |
| Nickel underplate | Specified minimum, typically a few µm | Barrier and hard base under the gold |
| Bevel | Angle and depth from the connector drawing | Eases insertion, prevents pad lifting |
| Keepout | No mask, legend, vias or plated holes on fingers | Keeps the contact surface clean and flat |
What Are PCB Gold Fingers Used For?
They make a removable connection without a separate connector on the board. Typical examples are PCIe and other expansion cards, memory modules, test and programming fixtures, and plug-in modules in instruments and industrial controllers. The finger pattern and its dimensions come from the mating connector or the interface standard; the board fabricator’s job is to plate, bevel and profile them to that drawing.
Gold is used because it does not oxidize, so contact resistance stays low and stable after storage and many insertions. Bare copper or tin would form oxide films that raise resistance and make the contact unreliable.
Should Gold Fingers Be Hard Gold or ENIG?
Hard gold for anything inserted repeatedly; ENIG only for edges inserted a handful of times. ENIG’s immersion gold is only a few microinches thick (the 2012 edition of IPC-4552 set a 0.05 µm, or about 2 µin, minimum) and soft, so it wears through quickly under sliding contact. Electroplated hard gold is much thicker and alloyed with cobalt or nickel to raise its hardness.
Samtec, a connector maker, recommends cobalt-hardened gold on both edge-card connector contacts and the mating PCB pads, with the pads to ASTM B488 Type 2, Grade C hardness (Samtec connector plating FAQs, 2023). ASTM B488 is the standard for electrodeposited gold for engineering uses (ASTM B488); Grade C covers hardnesses in the 130–200 Knoop range used for wear surfaces.
Do not confuse hard gold with ENEPIG. IPC-4556A covers ENEPIG for soldering, wire bonding and low- or zero-insertion-force contacts, not sliding edge connectors (IPC-4556A contents, 2025). Our comparison of ENIG, hard gold and soft gold covers the three side by side.
How Thick Should the Gold Be?
As thick as the connector and the cycle count need, which the connector maker’s data should tell you. Samtec gives typical contact plating of 30 µin gold for high reliability, 10 µin for many applications and a 3 µin flash for low-cycle use, and notes that its 30 µin connectors are routinely tested to 100 mating cycles; contact force, the base metal, the environment and the whole plating stack also affect durability. A chemical supplier, Technic, gives conventional connector coatings of 1–2 µm nickel under 0.10–0.75 µm hard gold, depending on the application (Technic on electronics coatings).
There is no IPC rule that all gold fingers must carry a fixed thickness or survive a fixed number of insertions. Specify a minimum gold and nickel thickness on the drawing, measured by XRF on the fingers, and set the cycle requirement from the product: a card inserted once at installation, a test fixture plugged in thousands of times, and a field-replaceable module are three different specifications.
How Are Gold Fingers Plated?
By electroplating, with the rest of the board masked. The usual sequence is:
- The board is built and patterned as normal; the finger copper is connected to a plating bar along the edge.
- Everything except the finger area is covered with plating tape or resist.
- Nickel and then hard gold are electroplated onto the exposed fingers.
- The tape is removed, and the rest of the board receives its own finish (often ENIG or HASL) for soldering.
- The plating bar is cut away when the board is profiled and the edge is beveled.
Because the fingers are plated through a connection to the edge, traces to the plating bar are needed during fabrication; leave room for them in the layout. Selective plating also means the finger finish and the solder-pad finish can differ, and the drawing should name both.
What Design Rules Apply to Gold Fingers?
Follow the connector’s card drawing first; it defines finger pitch, width, length, card thickness and the chamfer. On top of that, the common layout rules are:
- Keep solder mask, legend and silkscreen off the finger area.
- Keep vias and plated holes away from the fingers; a hole on the contact path breaks the wiping surface.
- Pull inner-layer and outer copper planes back from the beveled edge so the bevel does not expose copper.
- Orient all fingers to the same edge so the plating bar and bevel can run in one pass.
- Keep finger widths and pitch consistent; staggered fingers of different lengths are possible but set the mating sequence, so take them from the connector drawing.
Bevel angles of 20°, 30° and 45° are common, but the right angle and remaining land length come from the connector. Our DFM guide for PCB design covers the wider layout checks.
Which Defects Cause Gold Finger Failures?
| Defect | Effect | Prevention |
|---|---|---|
| Gold worn through | Nickel or copper exposed, rising resistance | Thicker hard gold matched to cycles |
| Thin or missing nickel | Gold diffusion, poor wear base | Specified nickel minimum, XRF check |
| Lifted or peeled fingers | Open contact | Proper bevel, copper pullback, adhesion test |
| Mask or legend on fingers | Poor contact, debris | Clear keepout on the drawing |
| Burrs on the bevel | Connector damage | Bevel finish inspection |
| Contamination | Intermittent contact | Clean handling and packaging |
Adhesion is checked with a tape test on the plated fingers, and thickness with XRF. Visual inspection under magnification catches scratches, pits, nodules and mask encroachment.
How Should Gold Fingers Be Specified and Inspected?
| Drawing note | Example |
|---|---|
| Finish | “Edge fingers: electroplated hard gold over nickel” |
| Thickness | “Au ≥ 30 µin, Ni ≥ 100 µin, measured by XRF on fingers” (example values) |
| Hardness | “ASTM B488 Type II, Grade C” |
| Bevel | “30° × depth per connector drawing, both sides” |
| Keepout | “No mask, legend or vias within finger area” |
| Other pads | “ENIG on remaining solder pads” |
| Evidence | “XRF readings and tape-test result per lot” |
Ask for the XRF readings from the fingers themselves, not from a coupon elsewhere on the panel; plating thickness varies across a panel.
How Can We Help?
QueenEMS makes gold fingers with electroplated hard gold over nickel, bevels the edge to your connector drawing, and checks finger layout and keepout in the DFM review; plating thickness is measured by XRF so the readings can travel with each lot. Send the Gerber files with the connector’s card drawing, the gold and nickel thickness you need and the expected insertion cycles; our free DFM check flags mask, vias or copper too close to the edge, with bare-board pricing to follow inside 2 hours.
Conclusion
| Use | Finger finish |
|---|---|
| Inserted once at installation | ENIG or thin hard gold |
| Field-replaceable module | Hard gold, about 10–30 µin per connector data |
| Test fixture or frequent insertion | Hard gold at the connector’s high-durability thickness |
| Wire bonding or low-insertion contacts | ENEPIG or soft gold, not hard gold |
Take the geometry from the connector, choose hard gold for sliding contacts, and put thickness, hardness, bevel and keepout in the fabrication notes. Contact us with your Gerber files, connector part number, plating requirement and quantities.
FAQ
Are gold-plated connectors better? For contacts that are mated repeatedly or must stay reliable after storage, yes; gold does not oxidize, so contact resistance stays stable.
What kind of circuit boards have gold fingers? Expansion cards, memory modules, plug-in modules and test boards that connect through a card-edge connector.
What are PCIe gold fingers? The edge contacts on a PCIe card; their layout and dimensions follow the PCIe card specification and the slot connector.
Can ENIG be used for gold fingers? Yes, for edges inserted only a few times. For repeated insertion, ENIG wears through and hard gold is needed.
How is gold finger thickness measured? By X-ray fluorescence (XRF) on the fingers, reported for gold and nickel separately.
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