How much do you know about PCB flying probe?

flying probe is the latest solution to some main problems in electrical testing. It replaces the needle bed with probes, and uses a plurality of electric probes driven by motors and capable of moving quickly to contact the pins of the device for electrical measurement.

In the production process of PCB, electrical defects such as short circuit, open circuit and electric leakage are inevitable due to external factors,In addition, PCB circuit boards are constantly evolving towards high density, fine spacing and multi-level,If defective boards are not screened out in time and allowed to flow into the manufacturing process, more cost waste will inevitably result,Therefore, in addition to the improvement of manufacturing process control, improving testing technology can also provide PCB manufacturers with solutions to reduce scrap rate and improve product yield.

The electrical test methods are:?Dedicated, Universal?Grid, Flying?probe, E-beam, conductive cloth, capacitive and ATG-Scanman. There are three kinds of commonly used devices:?They are special testing machine (PCB automatic universal testing?machine), high quality universal testing machine and flying needle testing machine.

What is the difference between flying probe?and test stand? What are their respective advantages?

flying probe: four probes are used to test the circuit board for high voltage insulation and low resistance conduction (open circuit and short circuit of the test circuit) without making a test jig,It is very convenient to directly install the PCB board to run the test program, which saves the test cost, reduces the time for manufacturing the test rack, improves the delivery efficiency, and is suitable for testing small batches and samples.

The test rack is a special test fixture for the on-off test of mass-produced PCB boards, which has high production cost, but good test efficiency, and there is no charge for returning orders.

First of all, in terms of the applicable purpose of testing technology, flying probeing is an electrical testing equipment suitable for small-scale production and samples at present,However, if it is applied to large-scale production, the testing cost will be greatly increased due to the slow speed measurement and high equipment price,No matter what level of PCB boards the general-purpose and special-purpose type are used for, as long as the output reaches a certain number, the testing cost can reach the standard of economies of scale, and only accounts for about 2~4% of the selling price, which is why it is universal.

Working Principle of flying probing：

?The flying probe is an improvement of the traditional on-line automatic high-voltage PCB testing machine, which replaces the needle bed with probes.

The unit under test (UUT) is transported to the tester by belt or other UUT transmission system, and then the probe of the tester is fixed to contact the TESTpad and via, so as to test the single element of the UUT. Test probes are connected to drivers and sensors through multiplexing systems to test components on UUT. When one component is being tested, other components on UUT are electrically shielded by probe to prevent reading interference.

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The flying probe?can check short circuit, open circuit and component value. A camera is also used in the flying probe?to help find the missing components. Use a camera to check the shape of directional components, such as polar capacitors.

With the positioning accuracy and repeatability of the probe reaching the range of 5-15 microns, the flying probe?can accurately detect UUT. Flying pin test solves a lot of existing problems in PCB assembly: for example, it may take 4-6 weeks to test and develop; Can not economically test small batch production; And that prototype assembly of the prototype cannot be test?quickly.

Flying pin test is a method to check the electrical function of PCB (open short circuit test). Flying tester is a system for testing PCB in manufacturing environment. Instead of using all the traditional bed-of-nails interfaces on the traditional online testing machine, the flying probe?uses four to eight independently controlled probes to move to the component under test. UUT,?unitunder?test (UUT) are transported to the tester through belts or other UUT transmission systems. Then fixed, the probe of the tester contacts the test?pad and via to test the single element of the UUT. Test probes are connected to drivers (signal generator, power supply, etc.) and sensors (digital multimeter, frequency counter, etc.) through multiplexing system to test components on UUT. When one component is being tested, other components on UUT are electrically shielded by probe to prevent reading interference.

1,Charge/discharge time method The charge/discharge time (also called network value, net value) of each network is certain. If there are networks with equal values, there may be short circuits between them, so it is only necessary to measure the short circuits in the networks with equal values. Its test steps are as follows: first board: full open circuit test → full short circuit test → network value learning; The second back plate: full open circuit test → network value test, and then test with resistance method where short circuit is suspected. The advantages of this test method are accurate test results and high reliability,Disadvantages are that the test time of the first board is long, the number of back tests is high, and the test efficiency is not high. The most representative is the SPEEDY machine of MANIA Company.

2,Inductance measurement The principle of inductance measurement is to use one or several large networks (generally ground networks) as antennas, and apply signals on them, and other networks will induce certain inductance. The tester measures the inductance of each network, and compares the inductance values of each network,If the network inductance values are the same, it may be short-circuited. This test method is only suitable for the test of boards with ground electrical layer, but the reliability of double panels (without ground grid) is not high; When there are many large-scale networks, because there are more than one probe for applying signals, the number of probes for testing is reduced, and the testing efficiency is low,The advantages are high testing reliability and low number of back tests. The most representative ones are A2 and A3 machines of ATG Company,In order to make up for the number of probes, this machine is equipped with 8 needles and 16 needles to improve the testing efficiency.

3,Capacitance measurement This method is similar to the charge/discharge time method. According to the law relationship between conductive pattern and capacitance, if a reference plane is set, the distance from the conductive pattern to it is l, and the area of the conductive pattern is a, then C=εA/L .. If there is an open circuit, the conductive pattern area decreases and the corresponding capacitance decreases, it means that there is an open circuit; If two conductive patterns are connected together, the capacitance response increases, indicating a short circuit. In the open circuit test, the capacitance values of each end point of the same network should be equal, if they are not equal, there will be an open circuit, and the capacitance value of each network should be recorded as a comparison of short circuit tests. The advantage of this method is that it has high testing efficiency, but its disadvantage is that it depends entirely on capacitance, which is affected by many factors, and its testing reliability is lower than that of resistance method, especially the measurement error caused by associated capacitance and secondary capacitance, and the testing reliability of networks with few endpoints (such as single-point networks) is lower. At present, the flying probes of HIOKI and NIDEC READ are used in this test method.

4,Phase difference method This method is to add the signal of a chord wave to the stratum or electric layer, and obtain the phase lag angle from the circuit layer, so as to obtain the capacitance value or inductance value. The test step is to measure the open circuit of the first board, then measure the phase difference of other networks, and finally measure the short circuit; First, measure the open circuit of the second or more boards, then measure the network phase difference, and then test and verify the possible short circuit by resistance method. The advantages of this method are high test efficiency and high reliability,The disadvantage is that it is only suitable for testing boards with more than 4 layers,For example, the resistance method can only be used for testing double panels. At present, companies adopting this test method have Micro?Craft.

5,Adaptive test method Adaptive test method means that after each test application process is completed, according to the specific conditions and test specifications of the wrench, the equipment chooses the appropriate test process by itself,If the network value (charging time or capacitance, etc.) of a network is less than the test error of the equipment, the equipment will automatically adopt resistance test and electric field test. This test method has the fastest speed and the best test effect. However, up to now, there is no contact with the testing machine using this testing method.

The flying probe?is an improvement on the traditional on-line tester of needle bed, which can replace the needle bed with probes,The X-Y mechanism is equipped with 4 heads and 8 test probes which can move at high speed respectively, and the minimum test gap is 0.2 mm. In operation, UUT (unit under test) is transported into the testing machine by belt or other UUT transmission system, and then the probe of the testing machine is fixed to contact the test pad and via, so as to test the single element of UUT. Test probes are connected to drivers (signal generator, power supply, etc.) and sensors (digital multimeter, frequency counter, etc.) through multiplexing system to test components on UUT. When one component is being tested, other components on UUT are electrically shielded by probe to prevent reading interference.

The flying probe?can check short circuit, open circuit and component value. A camera is also used in the flying probe?to help find the missing components. Use a camera to check the shape of directional components, such as polar capacitors. With the positioning accuracy and repeatability of the probe reaching the range of 5-15 microns, the flying probe?can accurately detect UUT.?