Spring-loaded test probes: definition and classification

A test probe is the contact medium used in electrical testing, applied to high-end precision electronic components. Spring-loaded probe families include test probes, semiconductor probes, ICT probes, high-frequency probes, high-current probes and battery contact probes.

Classification by testing application

Bare-board test probes detect open and short circuits on circuit boards before components are installed; most domestic products can replace imported equivalents. In-circuit test probes test boards after the components are fitted, but the core technology for the high-end products is still held by foreign companies, although some domestic probes have been developed successfully and can replace imported ones.

Microelectronic test probes perform wafer testing or chip (IC) detection. Here too the core technology is mainly in foreign hands; domestic manufacturers are active in research and development, but only a small part of their output has reached successful production. The main probe types are cantilever probes (blade type and epoxy type) and vertical probes.

Probe families by specification

ICT series probes are generally 2.54 mm to 1.27 mm in diameter, matching the industry-standard 100 mil, 75 mil and 50 mil centres; some special probes are as small as 0.19 mm. They are used for in-circuit test (ICT) and functional test (FCT). Interface probes are non-standard parts customised for the small number of customers who build large test machines, such as Teradyne and Agilent. Micro series probes have a centre distance of 0.25 mm to 0.76 mm between the two test points.

Switch probes route two current paths through a single probe. High-frequency (coaxial) probes test high-frequency signals: with a shielding ring they work up to 10 GHz, and up to 500 MHz without one. Rotary probes have generally low elasticity because their penetration is already strong, and they are typically used for testing OSP-treated PCBs.

High-current probes are 2.54 mm to 4.75 mm in diameter with a maximum test current of 39 A. Semiconductor probes are 0.50 mm to 1.27 mm, with a bandwidth above 10 GHz and a 50 Ω characteristic impedance. Battery and connector contact probes are used to optimise contact quality, stability and service life. Automotive wiring-harness test probes specialise in on/off detection of automotive harnesses, with diameters of 1.0 mm to 3.5 mm and currents of 3 A to 50 A. Temperature probes, Kelvin probes and similar types are also available but are used relatively rarely.