Time:2026-04-10Reading:547Second
ICT (Online Circuit Testing) is the core link in electronic manufacturing for detecting PCB open/short circuits and component virtual soldering. As the "last millimeter" of signal transmission, the selection of ICT probes directly determines the stability and yield of testing. Many manufacturers suffer from issues such as stuck pins, broken pins, poor contact, and PCB damage due to mismatched selection.
This article explains the selection of ICT probes from four dimensions: structural classification, needle and sleeve installation, selection of core parameters, and probe maintenance. Even beginners can directly copy and use them.
ICT probeMainly used for online circuit testing and functional testing, detecting the electrical performance of online components on the board and the connection status of the circuit network. It can quantitatively measure and perform functional testing on the components.
Usually, ICT online testing needles are used together with their matching size needle sleeves, which are fixed on the PCB board for easy replacement of probes at any time.
ICT probes are generally composed of needles, needle tubes, and springs, each of which is indispensable and plays its own role
1. Needle:The "front-end contact" between the probe and the PCB test point is the core component that determines the stability of the contact. The shape, material, and coating of the needle should be adapted according to the characteristics of the testing point. Common head types include pointed heads (strong penetration, suitable for test points with oxide layers on the surface), round heads (moderate contact area, strong versatility), flat heads (large contact area, suitable for large solder pads), etc; The material is generally chosen as beryllium copper、SK4The surface is often treated with gold plating on nickel, which can improve conductivity and wear resistance, and prolong uselife.
2. Spring:The 'power core' of the probe is responsible for providing stable contact pressure. The spring material is generally made of piano steel wire or stainless steel wire, and its elasticity coefficient and fatigue strength directly affect the life of the probe. High quality springs can ensure that the probe maintains stable pressure after tens of thousands of compressions, avoiding problems such as poor contact and needle breakage. This is also one of the key indicators to distinguish the quality of the probe.
3. Needle tube:As the main body shell of the probe, it plays a role in fixing the internal structure, conducting current, and protecting the spring.
1. Instructions for using needles and sleeves:
First, install the sleeve into the mold hole, and then install the needle.
2. Selection and matching of needles and sleeves:
For example, based on a center distance of 2.54mm, drill a suitable mold hole of 1.75, and select a needle sleeve with an outer diameter ofφAbout 1.70mm, the outer diameter of the protrusion isφAround 1.80mm, the inner diameter of the needle sleeve is determined by the outer diameter of the needle tube, which is around 1.36.
3. Needle installation method:
a. Use a suitable insertion tool to press the needle into the mold hole, ensuring that the opening is level with the mold hole. Be careful not to pull the adhesive thread with excessive force to prevent it from falling off.
b. When pressing the needle into the sleeve hole, pay attention to protecting the needle tip to avoid pressure damage. Determine the exposed size of the needle according to the design size. As the sleeve has a meter position, a certain amount of force is required when pressing it in (the service life of the sleeve is to be pulled out three times).
The selection of ICT probes is essentially a precise match between parameters and requirements. By specifying the following six parameters, the compatible model can be quickly identified to avoid blind selection. Among them, contact resistance, lifespan, and needle diameter are the most basic and easily overlooked key indicators that require special attention.
1. Contact resistance: the "lifeline" for testing accuracy
Contact resistance is the resistance value when the probe comes into contact with the test point, which directly affects the accuracy of the test data. The smaller the value, the better. It should be noted that some manufacturers have parameter false labeling issues, such as claiming "contact resistance<50m Ω", but actual measurements far exceed the standard, especially in high temperature environments where performance degradation is severe. Manufacturers can be required to provide reports.
The contact pressure is provided by the spring, not necessarily the greater the better: too little pressure can easily lead to poor contact and signal interruption; Excessive pressure may damage the PCB test points.
The needle diameter (probe outer diameter) needs to be selected based on the spacing and size of the PCB testing points: the closer the points to be tested on the PCB board are, the thinner the outer diameter of the selected probe will be to ensure testing accuracy and avoid short circuits.
The rated current refers to the maximum test current that the probe can withstand. The rated current of conventional ICT testing probes is usually between 1A and 3A. When selecting, it is necessary to ensure that the rated current of the probe is greater than the maximum current requirement in the testing plan, otherwise it may cause the probe to heat up or even burn out.
Mechanical lifespan refers to the number of times a probe can be inserted and removed normally, which directly determines the frequency of replacement and maintenanceCost, the mechanical lifespan of ordinary ICT probes needs to be ≥ 100000 times, and the lifespan is mainly determined by the quality of the spring and the coating process，It should be noted that the nominal mechanical life is obtained under ideal testing conditions, and may be reduced in actual use due to factors such as dust, overpressure, and lateral forces. Therefore, choosing probes with wear-resistant coatings and good spring fatigue resistance, although the single cost is slightly higher, the comprehensive downtime and labor cost for needle replacement are actually more cost-effective.
The choice of needle tip shape directly affects the testing effect. Different head shapes have their own applicable scenarios:
Although probes are consumables, proper maintenance can significantly extend their service life and play an important role in cost control.
The main factors affecting the lifespan of probes include whether the probe's travel is overvoltage, whether there is lateral force intervention, and whether the test current passing through is greater than the rated value.
Daily maintenance suggestions:
1. Regular cleaning:Regularly clean the probe needle and needle tube to remove surface dust, oxide layer, and solder residue. Alcohol can be used to wipe to avoid poor contact caused by impurities.
2. Ensure the cleanliness of the measuring points:Ensure that there are no excessive residues of rosin, flux, or other contaminants at the PCB testing points. These contaminants can enter the probe body during movement and adhere to the spring, which can cause severe corrosion or jamming of the spring.
3. Proper use of itinerary:The probe should be used according to the recommended travel and should not be over pressurized. Excessive compression can exacerbate needle tip wear and accelerate probe failure.
4. Avoid lateral forces:Ensure that the probe extends and retracts vertically on the device, as lateral forces can cause the needle to wear off or even be damaged.
5. Control the test current:Ensure that the test current does not exceed the rated value of the probe to prevent overheating and damage.
6. Use dust cover:For vacant or unused fixtures, using dust covers can effectively prevent dust and dirt from falling onto the test needle.
