Which Materials Are Used in Each Part of a Pogo Pin?
The published drawing for CPG-16-SMT-B, revision 1.0, gives a concrete example. It specifies different gold thicknesses for two parts of the same pin.
| Component | Material and finish in this model | What matters in use |
|---|---|---|
| Plunger | Brass with at least 0.25 µm of gold over at least 1.25 µm of nickel | The tip must retain its profile, and the guide surface must move freely inside the finished barrel. |
| Barrel | Brass with at least 0.10 µm of gold over at least 1.25 µm of nickel | The bore guides the plunger. Its finished diameter affects both sliding clearance and internal electrical contact. |
| Spring | Stainless steel wire | The assembled pin must supply the specified force at working height and return freely when released. |
| Mating pad | Specified on the device or dock drawing | Pad finish, usable area, and the path swept by the tip determine where wear occurs. |
Other designs use beryllium copper for a plunger or spring. When comparing candidates, request the alloy grade and temper. For example, C17200 copper beryllium is available in several conditions, including TH04, a hard, precipitation-treated temper. The grade identifies the alloy. The temper identifies a material condition relevant to hardness and strength. Neither establishes how much resistance or wear the assembled pin will exhibit.
How Do Plunger and Barrel Alloys Affect Resistance and Heating?
Trace the current from the mating pad to the solder termination. In a design that presses the plunger against the barrel wall, current crosses the pad-to-tip interface, travels through the plunger, crosses the sliding interface, and continues through the barrel to the termination. The metal sections contribute resistance according to their resistivity, length, and cross-sectional area. At the interfaces, current passes through small areas of actual contact, which change with force, surface films, and wear.
This distinction matters when a charging pin runs hot. A more conductive barrel can reduce resistance in the barrel itself. If most of the voltage drop occurs where the plunger meets the bore, the more productive checks are finished clearance, surface condition, and contact force. A four-wire measurement from the mating pad to the solder tail gives the resistance of that complete path. Locating the loss more precisely requires additional sensing points or a fixture that isolates the interface of interest.
To compare two alloys, hold the pin dimensions, plating, working height, mating pad, current, and sensing points constant. Measure loaded voltage drop and temperature rise after the assembly stabilizes. For scale, an extra 10 mΩ at 2 A adds 20 mV of drop and 40 mW of local heat. The resulting temperature depends on how heat leaves the pin through the board, cable, and surrounding structure.
How Does Spring Material Affect Contact Force Over Time?
Spring force depends on wire material, wire diameter, mean coil diameter, active coil count, and preload. Preload is the compression already present when the spring is installed inside the barrel. Two springs with the same free length can therefore give different forces at the same pin height. Measure the assembled pin along its axis so that the result includes friction between the plunger and barrel.
A handheld scanner returned to its dock many times a day needs a cycling test. Record the force at working height before and after the specified cycles, then check that the plunger returns promptly. A device left in a warm dock for weeks needs a compression-hold test. Hold the pin at its installed height and specified temperature, then remeasure force at the same height under a defined temperature and recovery procedure. A spring can lose force under sustained compression even when it still returns visibly after release.
Before selecting a spring for its conductivity, check the internal current path. Where the plunger bears directly against the barrel, that interface provides a route around the spring. If the design relies on the spring to carry a significant share of the current, its electrical resistance and heating also need to be evaluated under load.
How Do Gold Plating and the Mating Pad Affect Wear?
On a production drawing, identify the finish separately at the tip, the internal sliding surface, and the solder termination. Specify the base material, underplate, topcoat, minimum thickness, and inspection location for each critical region. An exterior thickness reading documents that location. The bore may need a different inspection method. Keep the mating pad finish on the companion drawing so both sides of the contact are controlled.
How the device closes can change the wear pattern. A rounded tip that presses straight onto a pad may leave a compact mark. If the user tilts the device as it leaves the dock, the same tip can slide across the pad under spring load and leave a longer track. Tip radius, pad finish, force, and sliding distance all influence how quickly that track develops.
Photograph the tip and pad at the same magnification before and after cycling. At each inspection interval, measure contact resistance at the same working height. Pairing the images with the readings helps distinguish an acceptable witness mark from wear that causes intermittent contact or an excessive voltage drop.
How Should Engineers Select and Verify Materials for an Application?
| Application | Material behavior to verify | Evidence for approval |
|---|---|---|
| High-current charging contact | Electrical loss through the pin and its internal interfaces | Loaded voltage drop and terminal temperature rise at the intended current, with the actual mating pad and adjacent contacts energized as in service |
| Dock that stays mated | Spring force retained during prolonged compression | Force at the same working height before and after a hold at the specified temperature and duration |
| Frequently used test fixture | Tip wear, material pickup, and damage to the test point | Tip and pad images, contact-resistance history, first-pass results, and cleaning intervals |
| Device exposed to sweat or humidity | Corrosion and stability of the exposed contact pair | Surface condition and resistance before and after a defined exposure representative of use |
A published semiconductor-probe study illustrates why the first resistance reading can favor a different finish from the one that performs better after cycling. Tseng and colleagues compared a conventional gold-plated pogo pin with a gold-plated pin carrying titanium and onion-like carbon layers. Kim and colleagues report the following contact-resistance results from that comparison.
| Probe finish | Initial contact resistance | After 200,000 touchdowns |
|---|---|---|
| Conventional gold-plated probe | 49.1 mΩ | 43.0 mΩ |
| Gold-plated probe with titanium and onion-like carbon layers | 50.6 mΩ | 38.6 mΩ |
The conventional probe began 1.5 mΩ lower. After cycling, the coated probe measured 4.4 mΩ lower. The study also found less surface wear with a 70 nm titanium adhesion layer. These are semiconductor test-probe results. The published summary does not identify a catalog part number, substrate temper, sample count, or production acceptance limit for those resistance values.
For a custom pogo pin, Dongguan Xinteng Electronics Co., Ltd. can review the mating-pad drawing, installed height, load, temperature, and cycle target together. Once sample testing establishes a suitable combination, the production drawing should identify the alloy and temper, plating thickness at the specified locations, and force and resistance limits under the same conditions used to approve the samples.
Technical References
Tseng, S. C., Lee, C.-T., Chen, W.-C., and Tsai, H.-Y. "Effect of onion-like carbon on the resistance and adhesion of pogo pins with titanium adhesive layer of varying thicknesses." Surface and Coatings Technology, vol. 479, 2024, article 130585. DOI 10.1016/j.surfcoat.2024.130585.
Kim, M.-S., Hong, W. S., Kim, Y.-J., In, C.-H., and Moon, J. T. "Materials and Evaluation Methodology of Pogo Pin for Semiconductor Package Testing." Journal of Welding and Joining, vol. 43, no. 2, 2025, pp. 134–144. DOI 10.5781/JWJ.2025.43.2.3.
