Where Is Plating Used on a Spring-Loaded Pogo Pin?
At the tip and mating pad. A rounded tip pressed straight onto a flat pad tends to leave a compact contact mark. If the device pivots as it docks or lifts out, the loaded tip sweeps across the pad and leaves a longer track. Inspect both sides of that track. A pin can retain much of its finish while repeatedly wearing the same narrow area on the mating pad.
Inside the barrel. In a design that brings the plunger against the barrel wall, current travels from the mating pad through the tip, across the internal sliding contact, and into the barrel and termination. Both the plunger's guide surface and the contacting region of the bore experience repeated motion. Their finished dimensions matter because plating adds material to the plunger and reduces the bore diameter wherever it deposits.
The spring has its own material specification. One published low-profile contact design uses machined brass for the plunger and sleeve, each plated with 20 µin of gold over 100 µin of nickel. Its alloy 172 beryllium-copper spring carries 10 µin of gold over 50 µin of nickel. The spring provides restoring force; the share of current it carries depends on the internal contact design.
At the solder tail or surface-mount base. A solder termination needs a finish that wets under the specified assembly process. Selective plating allows a manufacturer to apply gold to the mating region and tin to the soldering region. On the drawing, dimension the transition from a fixed reference so that manufacturing tolerances keep the finish boundary clear of the contact's wear track.
Gold, Nickel, Tin, and Specialty Finishes Compared
| Plating material | Typical use | What to verify |
|---|---|---|
| Gold | Outer finish on a plunger tip or designated contact band | Gold deposit type, hardness, minimum thickness, and finish on the mating pad. Check wear at the actual contact force and sliding distance. |
| Nickel | Underplate between a copper alloy and gold | Thickness and coverage beneath the working surface. Nickel limits diffusion of base-metal constituents into the gold and provides a harder supporting layer. |
| Tin | Solder tails and other solderable terminations | Extent of the tinned area, storage conditions, and solderability with the intended flux, alloy, and process. |
| Rhodium | Hard contact finish on selected test-probe tips | Probe model, tip geometry, target material, permitted witness mark, and cleaning method. For example, probe GKS-502-0039 specifies a rhodium finish on a 2.5 mm steel three-point crown. |
How Do You Read "Gold Over Nickel" on a Drawing?
Read the layers from the substrate outward. The CPG-16-SMT-B drawing, revision 1.0, specifies a brass plunger with at least 1.25 µm of nickel beneath at least 0.25 µm of gold. The brass barrel has the same nickel minimum but a lower gold minimum of 0.10 µm. A quotation that says only "gold over nickel" leaves open which of those two thicknesses the supplier has priced.
Check the units and the qualifier beside each value. 10 µin equals 0.254 µm. A 10 µin minimum sets a lower acceptance limit at the specified measurement location. A 10 µin nominal value needs a tolerance or other acceptance rule before an inspector can judge an individual reading.
"Gold flash" describes a thin deposit. "Hard gold" describes a deposit with specified hardness characteristics. A hard gold layer can also be thin. For a frequently mated contact, specify both the gold thickness and hardness requirement, then identify where they apply: the tip, a dimensioned contact band, or the entire plunger.
Which Finish Fits a Charging Contact or a Test Probe?
For a charging dock, evaluate the pin and pad as a pair. Cycle samples through the actual insertion and removal path, including any tilt allowed by the housing. At the same working height, compare contact resistance, voltage drop under charging load, and wear on both surfaces. For a wearable, include the expected exposure to sweat residue and the intended cleaning procedure.
For a PCB test fixture, keep tip shape, force, stroke, and test-point finish constant while comparing coatings. Record how often the first touchdown gives a valid reading, how many touchdowns occur before cleaning, and whether solder or flux residue accumulates on the tip. A coating that preserves a sharp crown may still leave a deeper mark than the board specification allows.
For a custom connector, Dongguan Xinteng Electronics Co., Ltd. can review the pin and mating-pad drawings together. Marking the wear track, soldering region, and inspection points before sampling gives the plating supplier and the buyer the same boundaries to work from.
How Can Buyers Verify Plating Quality?
A thickness report should identify the part number, drawing revision, production lot, sample count, and measurement locations. For X-ray fluorescence (XRF) measurements on a small rounded tip, check that the measurement spot fits inside the specified area and that the setup accounts for curvature. A reading taken on the flat barrel exterior establishes thickness there. If the drawing controls the bore or the tip apex, agree on a measurement method that can resolve that location. ISO 3497 describes X-ray spectrometric methods for metallic coating thickness.
For functional verification, repeat electrical measurements with the same mating finish, working stroke, and sensing points before and after cycling. If salt spray or another environmental exposure forms part of acceptance, record the exposure conditions, the mated or unmated state, and the electrical limit applied afterward.
The following published sample record shows the difference between evidence of coating thickness and evidence of mating performance.
| Specified finish | Local thickness measurement | Performance after mating cycles |
|---|---|---|
| Low-profile contact family: brass plunger and sleeve, each specified at 20 µin gold over 100 µin nickel | The public report gives the coating specification but does not publish individual tip or bore thickness readings. A lot-specific inspection report would supply those values. | Against gold-plated copper pads at 0.0275 in compression, average resistance was 7.2 mΩ initially and 6.4 mΩ after 1,000,000 cycles. The four-wire test used 0.5 A, two samples, and three readings per sample. The acceptance limit was below 20 mΩ. |
The tested pair met the reported resistance limit under those conditions. For a shipment decision, the buyer still needs the local thickness readings from the delivered lot. For a design decision, the buyer needs cycling results with the pad finish and mating motion used in the actual device.
Technical References
ISO 3497:2000. Metallic Coatings - Measurement of Coating Thickness - X-ray Spectrometric Methods.
Spring Loaded Contact: Specifications, Mechanical & Climatic Tests. Version 2.0, October 2005. Material specifications, Test T2, and Group I mechanical test results.
