Pogo pin

A pogo pin or spring-loaded pin is a type of electrical connector mechanism that is used in many modern electronic applications and in the electronics testing industry.[1] They are used for their improved durability over other electrical contacts, and the resilience of their electrical connection to mechanical shock and vibration.[2]

Sectional drawing of a pogo pin, showing the plunger, barrel, and spring

The name pogo pin comes from the pin's resemblance to a pogo stick – the integrated helical spring in the pin applies a constant normal force against the back of the mating receptacle or contact plate, counteracting any unwanted movement which might otherwise cause an intermittent connection. This helical spring makes pogo pins unique, since most other types of pin mechanisms use a cantilever spring or expansion sleeve.[3]

A complete connection path requires a mating receptacle for the pin to engage, which is termed a target or land. A pogo target consists of a flat or concave metal surface, which unlike the pins, has no moving parts. Targets may be separate components in the complete connector assembly, or in the case of printed circuit boards, simply a plated area of the board.

Spring-loaded pins are precision parts fabricated with a turning and spinning process which does not require a mold, thus allowing the production of smaller quantities at a lower cost.

Structure
Exploded diagram showing components of a standard pogo pin

A basic spring-loaded pin consists of 3 main parts: a plunger, barrel, and spring.[2] When force is applied to the pin, the spring is compressed and the plunger moves inside the barrel. The shape of the barrel retains the plunger, stopping the spring from pushing it out when the pin is not locked in place.

In the design of electrical contacts, a certain amount of friction is required to hold a connector in place and retain the contact finish. However, high friction is undesirable because it increases stress and wear on the contact springs and housings. Thus, a precise normal force, typically around 1 newton, is required to generate this friction.[3] Since a spring-loaded pin needs to have a slight gap between the plunger and barrel so that it can slide easily, momentary disconnections can happen when there is vibration or movement. In order to counter this, the plunger usually has a small tilt to ensure a continuous connection.

Many manufacturers have created their own proprietary variations on this design, most commonly by varying the interface between the plunger and spring. For example, a ball may be added between the two components, or the plunger may have an angled or countersunk tip.[4][5]

Various pogo pin designs

Materials

The plunger and barrel of pogo pins usually use brass or copper as a base material on which a thin layer of nickel is applied. [6]

As common in electrical connectors, manufacturers often apply a gold plating that improves the durability and contact resistance.[7]

The springs are usually made of copper alloys or spring steel.[8][4]

Applications
Some spring-loaded connectors, and the disassembled pogo pins inside them

Spring-loaded connectors are used for a wide variety of applications, in both industrial and consumer electronics:

Connector arrangement
See also: Electrical connector

When pogo pins are used in a connector, they are usually arranged in a dense array, connecting many individual nodes of two electrical circuits. They are commonly found in automatic test equipment in the form of a bed of nails, where they facilitate the rapid, reliable connection of the devices under test (DUTs).[10] In one extremely high-density configuration, the array takes the form of a ring containing hundreds or thousands of individual pogo pins; this device is sometimes referred to as a pogo tower.

They can also be used for more permanent connections, for example, in the Cray-2 supercomputer.[11]

When used in the highest-performance applications, pogo pins must be very carefully designed to allow not only high reliability across many mating/unmating cycles but also high-fidelity transmission of the electrical signals. The pins themselves must be hard, yet plated with a substance (such as gold) that provides for reliable contact. Within the body of the pin, the plunger must make good electrical contact with the body lest the higher-resistance spring carry the signal (along with the undesirable inductance that the spring represents). The design of pogo pins to be used in matched-impedance circuits is especially challenging; to maintain the correct characteristic impedance, the pins are sometimes arranged with one signal-carrying pin surrounded by four, five, or six grounded pins.

Pogo pins connecting logic modules of the Cray-2 supercomputer

Combination with magnets

Spring-loaded connectors may be combined with magnets to form a strong and reliable connection – a technique which has been employed extensively for consumer electronics such as 2-in-1 PCs and high-frequency data transfer.[12] One notable example of this is Apple's MagSafe connector.[13]

Commercial products

Although often used as a generic name, pogo pin is a registered trademark of Everett Charles Technologies (ECT).[14]

See also

References
  1. Hart, Pierre (October 7, 2016). "Using Pogo Pins to Add Electrical Connectivity to Your 3D Printed Fixtures". Javelin. Javelin Tech. Retrieved 22 May 2019.
  2. "Spring-Loaded Contacts & Connectors" (PDF). Cotelec. Retrieved 3 July 2019.
  3. Mroczkowski, Robert S. (1993). "Connector Design/Materials and Connector Reliability". AMP Incorporated. Cite journal requires |journal= (help)
  4. "Basic Pogo Pin Intro". C.C.P. Contact Probes Co. Retrieved 3 July 2019.
  5. US application 20170187137, "Force biased spring probe pin assembly"
  6. "Pogo Pin Catalog" (PDF). pogo-pins.com. Cnomax Technology Co., Limited. Retrieved 3 July 2019.
  7. AMP Incorporated (29 July 1996). "Golden Rules: Guidelines For The Use Of Gold On Connector Contacts" (PDF). Tyco Electronic Corporation. Archived from the original (PDF) on 29 March 2018. Retrieved 1 July 2019. Gold is generally specified as a contact coating for low level signal voltage and current applications, and where high reliability is a major consideration Cite journal requires |journal= (help)
  8. Mroczkowski, Bob (19 August 2009). "Electrical/Electronic Connector Contact Spring Materials". Connector Supplier. Retrieved 3 July 2019.
  9. "Welcome to Qualmax". Qualmax. Retrieved 3 July 2019.
  10. "Preventing Pad Cratering During ICT Using Sherlock" (PDF). DfR Solutions. 21 November 2013. Prior to the ICT, the designer can optimize the process ... change pogo pin pressure
  11. Kilian, Alan. "Cray-2 logic module". bobodyne.com. Retrieved 3 July 2019.
  12. "Magnetic Connectors". C.C.P. Contact Probes Co. Retrieved 3 July 2019.
  13. US patent US7311526B2, "Magnetic connector for electronic device", published 25 December 2007, assigned to Apple Inc. Archived from the original on 15 July 2018.
  14. "Spring Probes for ATE, Connectors, Batteries, Wire Harnesses, Semiconductor Packages and General Purpose Applications" (PDF). L. Bodenmann AG. OSTBY BARTON. 2003. Retrieved 3 July 2019. Pogo is a registered trademark of Everett Charles Technologies
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