Pogo pin

Spring pins (short spring contacts or spring pins ) are contacting, are used for the testing of circuit boards, electronic components, components such as connectors and other components in the electronics industry.

Other applications include permanent connections in battery - charging stations, battery compartments of mobile electronic devices and similar applications. As the name suggests, the contact, ie the closing of an electrical circuit, not like the connectors is generated by the insertion of a pin into a socket, but by touching with a spring-loaded pin. Other names from the jargon of testing are test pin, probe, spring-loaded contact Prüfpin or pogo pin, but the latter is the registered trademark of a U.S. manufacturer. English names are Spring Contact Probe, test sample or sample Spring, also the terms Spring Loaded Contact and Spring Loaded Connector can be used, for which the abbreviation SLC has prevailed.

Design and functional principle

Except for some special designs, which will be discussed later, the spring contact of three components of: a guide tube (also called pen sleeve or housing ), a spring and a piston. The three components are installed by special Crimptechniken each other in such a way that they can not fall apart, but the piston can perform a certain travel dates still in the longitudinal direction. When obstruct the items the compression spring is biased so that the spring contact pin in its zero position has a certain initial force - normally referred to as a bias - has. The nominal value as the product associated spring force reaches the contact after the so-called nominal spring deflection, which is usually at 2/3 of the maximum possible suspension travel. Usually this nominal travel is matched to the design of the test adapter, in which the spring pin is mounted.

The shape and size of the actual probe forwards at the top of the spring contact pin may vary in some great variety. So often, the user has his own preferences and desires that he would like to see implemented, and the various types of connector contacts, solder pads, etc. are correspondingly many different variants advance.

Market standards

Market are usual maximum spring travel of about 2 mm to 12 mm, depending on the type and structure of the test adapter, in which the spring contacts are usually installed. In diameter, spring contact pins are dependent on the distance between the test points on the circuit board with each other. This distance is called the grid spacing or pitch. Usual Pitch sizes are 2.54 mm, 1.91 mm and 1.27 mm - each inspired by the imperial units. For example, many connectors have a spacing of 1/10 inch ( or 2.54 mm) between the plug pins. On the circuit board the solder pads or vias are then consequently created in this grid spacing, and to this the electrical test to be able to contact you will need, the spring contact pins fit into the 2.54 mm. More common today standard grid in electronics are 1.91 mm ( corresponding to 75 MIL or 0.075 inches) and 1.27 mm (50 MIL or 0.050 inch).

The corresponding spring contact probes are designed on the diameter forth on these distance measures through. So has a standard spring contact for 2.54mm (ie 1/10-Zoll-Raster ) a housing diameter of about 1.37 mm to max. 1.66 mm, and thus has sufficient distance to the next contact to prevent short circuiting.

Receptacles

Another special feature are the receptacles commonly used (English Receptacles ). Because of the spring contact pin very frequently used and is worn after a certain time of use, it is inserted in a socket for easy interchangeability. The replacement may be a new carried out by simply pulling the worn contact and insertion. The electrical connection cable ( soldered or wrapped in wire-wrap technique ) remains unchanged and unaffected in the socket. In the calculation of the minimum distance in the respective mounting grid (pitch) of course is the outside diameter of the socket decisive.

Spring force

The spring force of each spring contact pin is an additional variable size. Most are several different spring options to choose from within a series. Here the tradeoff between reliable contact force on the one hand, and the total force of all spring contacts must be made in a test adapter on the other. As a rule, achieved a reliable contact of test points soldered on a printed circuit board having a spring force of 1.5 N (about 150 grams) or more. But has now a test adapter, a total of 1,000 accepted piece of spring contacts, this leads to a total force of 1,500 Newtons ( or about 150 kg), the need to overcome the mechanical test adapter. In other words, the assembled module must be pressed with force of at least 150 kg on the needle bed of spring contacts, to produce the desired Prüfkontaktierung.

In the departments for quality check of the electronics manufacturer is therefore very often find vacuum adapter in use. The vacuum adapter uses a simple physical principle: it evacuates the air from a sealed chamber pushes the atmospheric air of the environment with uniform distribution on the walls of this chamber. The vacuum fixture, the test assembly is in a way the lid of a rectangular parallelepiped -shaped chamber, and is thus pressed with a force of about 10 N / cm ² (theoretical value for 100% vacuum ) downwards. In practice, a vacuum of 70 % is achieved to 80%, consequently would be the 7 to 8 N / cm ². The problem with vacuum adapter, however, is that these values ​​are only achieved when the vacuum chamber is sufficiently tight. Any small leakage reduces the efficiency climbed dramatically. Just as the test assembly is the "cover" of the vacuum chamber, the needle support plate forms with the installed spring contact pins its bottom. Consequently, all sockets and spring contacts installed therein shall be made ​​air-tight, so as not to destroy as the sum of many tiny leaks the vacuum.

Product Features

Since the spring contact pin is an essential element in the quality control of quality electronic components, the qualitative requirements for this component are very high. The most important are:

  • Possible low ohmic resistance
  • This constant as possible resistance value over a longer period of use of time
  • Durable possible spring constant spring force
  • Possible dirt-repellent surface to avoid contact reducing buildup of contamination ( flux residues, tin oxides, other substances from the surrounding space )

Special designs for special applications allow the transmission of very high currents ( 20-400 A) have a built-in switching function or for the transmission of high frequency signals suitable ( coaxial spring contacts with shielding ).

For varied applications in electronics over the past 20 to 30 years a lot of different Tastkopfformen have developed, always in an effort to create one on the contacting toward optimally adapted counter surface. There are new developments in the field of printed circuit boards and assembly technology again and again, the spring contact pins is no end in sight and in creating new shapes and sizes.

In the global market, certain standards have been established, however, were not yet set in concrete standards or similar standards. So have almost all major manufacturers for a certain type of selection that are compatible with designs of other manufacturers. By this is meant that the spring contact pins are interchangeable with respect to their geometrical size and the spring travel and forces and fit into the receptacles of the other manufacturers. In its interior, in the surface coatings and base materials used but requires each manufacturer has his own principle, and here are also qualitative differences. Major manufacturers for these niche products can be found in Germany, Japan and the United States.

Materials / Materials

Since it is a contact element when spring contact pin, only good electrical conductors are to be used as materials in the normal case. Usual and commonly used materials are:

  • Beryllium Copper BeCu for the piston / probes
  • Brass or nickel silver for the housing
  • Spring steel wire, stainless steel or beryllium copper, for the compression spring

Surfaces

As with other contact elements - for example in connectors - also get the items of spring contact probes a high quality surface coating. Firstly, this is necessary to improve the electrical conductivity, on the other hand, the base materials made ​​of Cu - alloy or steel must be protected against corrosion and oxidation. Typical surface finishes are:

  • Hard gold, nickel, or rhodium for the pistons
  • Hard gold for the housing and sockets
  • Silver or gold, for the pressure springs

To avoid buildup on the contacts that led to massive problems mainly due to the introduction of lead- free pewter in the electronics industry, there are, for example, a new development in the nanotechnology sector. These designated as XXLonglife surface nano-coating prevents accumulation of dirt and ensures extremely long life compared to conventional gold-plated contacts.

Technologies

For the manufacture of the components of the spring contact pins, the following basic technologies are necessary:

  • Turned parts manufacturing ( CNC technology and conventional), comparable to the watch industry
  • Deep drawing of sleeves
  • Tube processing
  • Spring coiling technique
  • Galvanic processing
  • Handling and assembly of precision parts

A few manufacturers have their own expertise and vertical integration in all these areas, while others let the components of suitable suppliers manufacture and are limited to the installation of the finished product. In principle, this does not say much about the quality of the final product, in terms of flexibility for special types of new designs or customer specific requirements are of course the manufacturer with great production depth advantage.

Use in rigid needle adapter

When rigid needle adapter, the spring contact pins are arranged in a fine grid ( > 0.6 mm) to achieve a high test point density. Of these grid points from then the bonding force of the spring contact pins is deflected by a rigid needle to the desired test point. This adapter design has the advantage that up to 280 test points / cm ² dissolved and Kontaktierabstände > 150 microns can be achieved.

  • Construction and connection technology of the electronics
  • Electrical Measurement
Crimp (joining) Horology
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