6. Physical Constraints for the Use of Spring Contact Probes

6.1 Temperature Range

Testing tasks in automotive industry or scientific research and similar applications sometimes require high and/or low temperatures throughout the run of the electrical test. Similar requirements apply for the burn-in test of semiconductor devices where these devices are exposed to cycling temperatures of a climate cabinet for several days to obtain accelerated ageing. The user must answer the question whether the designated spring contact probes will maintain their functional capability under these extreme conditions.

In chapter 4.3 the topic has been briefly discussed: it’s the pressure spring which has the greatest influence on the available temperature range.

But it’s not only the absolute height of temperature, but also the time of exposure. Typically a test contact probe is exposed to cyclic loads. A cycle could, for example, sweep between room temperature and a raised temperature of 120 °C with a cycle time of five minutes. In another application the contacts are continuously exposed to 155 °C for 120 hours, followed by a four hour cooling phase at room temperature and finally re-exposed to high temperature for 120 hours in the climate chamber. The continuous exposure to high temperatures means particularly high stress for the contacting elements as diffusion processes in plated surfaces are enhanced.

The following tables show typical standard ranges, depending on spring material. If you are looking for spring contact probes for special high-temperature applications, you should call us – we will be happy to advise you. Together we will find the optimum solution.

Temperature 
short-term
Music WireStainless SteelCuBe
Min. -55°C -55°C -55°C
Max. +120°C +250°C +205°C
Temperature
Constant
Music WireStainless SteelCuBe
Min. -55°C -55°C -55°C
Max. +85°C +180°C +120°C

But our spring contact probes are fulfilling their duties far outside the nominal temperature limits of the tables. Let the case studies tell their stories:

Case study for low temperature application:  

Non-magnetic spring contacts in a hall-effect measuring head for measurements according to “Van der Pauw” method.
Measurements are taken at a temperature of 5 K (-268.15°C or –450.67°F). Test setup: Contacts are closed at room temperature and the entire specimen holder is cooled down in the cryostat to its low target temperature. The temperature swing ∆T amounts to approx. 300 K. Throughout the entire test process the quality of contacting is maintained on a constant high level – even after a large number of measurement cycles.

Case study for high temperature application:

Spring contact probes for burn-in test of semiconductor devices, continuous temperature approx. 200°C for more than 72 hours, continuously used in shift operations. All contacts perform flawlessly over many thousand test cycles. 

6.2 Non-Magnetic Versions

Some testing tasks require highly non-magnetic behaviour of the used spring contacts. On request, we deliver designs whose parts are all made of non-magnetic CuBe and whose surface treatment is free of nickel.
Our technical staff will be pleased to advise on availability of non-magnetic series and styles.

6.3 Robustness Against Agressive Media

We know areas of application, where the spring contact probe is completely immersed into aggressive liquid during the test procedure. In such cases it’s of vital importance to apply an absolutely pore-free surface coating on all parts. Our XXLonglife nano coating proved helpful here. Similar applications are found in mechanical engineering when e.g. tool changers are equipped with electrical contacts which come in contact with cooling lubricants. The self-cleaning effect of the XXLonglife coating keeps contact surfaces permanently free from contaminations.

6.4 Measurement of Insulation Resistivity Requires Ceramics Instead of FR4 (G10)

Spring contact probes are typically installed into carrier plates made of FR4 or similar materials. Measurement of very high impedance requires plate materials with an insulation resistance far higher than found in typical plastics. The widely adopted FR4 (Hgw 2372.1) e.g. features a resistance between inserts (DIN 53482) of approx. 5x1010 Ω. Laminated fabric like Hgw 2083.5 features a resistance of 107 Ω and special materials like PEEK or machinable glass ceramics, which we are processing in-house, feature a volume resistivity of more than 1016 Ωcm at 20°C. If you need custom made contact carrier plates: we are at your disposal.