Flying probe test to detect the electrical performance of PCB boards

可乐zzZ

Flying probe test to detect the electrical performance of PCB boards [Copy link]

Flying probe test: Use probes to replace the bed of nails, and use multiple motor-driven, fast-moving electrical probes to contact the pins of the device and perform electrical measurements.

During the production process of PCB boards, it is inevitable that electrical defects such as short circuits, open circuits and leakage will occur due to external factors. In addition, as PCB circuit boards continue to evolve towards high density, fine pitch and multi-layer, if defective boards are not screened out in time and allowed to flow into the process, it will inevitably cause more cost waste. Therefore, in addition to improving process control, improving testing technology can also provide PCB board manufacturers with solutions to reduce scrap rates and increase product yields.

The methods of electrical testing include: dedicated, universal grid, flying probe, non-contact electron beam (E-Beam), conductive cloth (glue), capacitance (Capacity) and brush test (ATG-SCANMAN). Among them, there are three commonly used equipments, namely dedicated tester (PCB automatic universal tester), high-quality universal tester and flying probe tester.

What is the difference between flying probe test and test stand? What are the advantages of each?

Flying probe test: It uses 4 probes to perform high-voltage insulation and low-resistance continuity tests on the circuit board (testing the open circuit and short circuit of the circuit) without the need for test fixtures. The test can be performed by directly installing the PCB board and running the test program. It is extremely convenient, saving test costs, reducing the time for making test fixtures, and improving delivery efficiency. It is suitable for testing small batches and samples.

The test frame is a special test fixture designed for conducting continuity tests on mass-produced PCB boards. It has a high production cost, but has good test efficiency and is free of charge for return orders.

First of all, in terms of the applicable purpose of testing technology, flying probe testing is currently suitable for electrical testing equipment used in small-scale production and samples. However, if it is used in medium-to-large-scale production, the testing cost will be greatly increased due to the slow test speed and expensive equipment. Regardless of the level of PCB boards used for general-purpose and special-purpose testing, as long as the output reaches a certain amount, the testing cost can reach the standard of economies of scale, and it only accounts for about 2~4% of the selling price. This is the main reason why general-purpose and special-purpose testing machines are currently the main types of mass production testing machines.

Working Principle of Flying Probe Test

The flying probe tester is an improvement on the traditional bed-of-nails online automatic high-voltage dedicated PCB board tester. It uses probes instead of the bed-of-nails.

During operation, the unit under test (UUT) is transported to the tester through a belt or other UUT conveying system, and then the probe of the fixed tester contacts the test pad (TESTpad) and the via hole (via) to test the single component of the unit under test (UUT). The test probe is connected to the driver and sensor through a multiplex transmission system to test the components on the UUT. When a component is being tested, other components on the UUT are electrically shielded by the probe to prevent interference with the reading.

The flying probe tester can check for shorts, opens and component values. A camera is also used on the flying probe tester to help find missing components. The camera is used to check for component shapes that have a clear direction, such as polarized capacitors.

With the probe positioning accuracy and repeatability reaching the range of 5-15 microns, the flying probe tester can precisely detect the UUT. Flying probe testing solves a lot of existing problems seen in PCB circuit board assembly: such as the test development cycle that may be as long as 4-6 weeks; the inability to test small batch production economically; and the inability to quickly test prototype assembly.

Flying probe testing is a method of checking the electrical functionality of a PCB (open and short circuit testing). A flying probe tester is a system for testing PCB circuit boards in a manufacturing environment. Instead of using the traditional bed-of-nails interface found on traditional online testers, flying probe testing uses four to eight independently controlled probes that move to the component under test. The unit under test (UUT) is transported to the tester via a belt or other UUT transport system. Then fixed, the tester's probe contacts the test pad and via to test a single component of the unit under test (UUT). The test probes are connected to drivers (signal generators, power supplies, etc.) and sensors (digital multimeters, frequency counters, etc.) through a multiplexing system to test components on the UUT. While one component is being tested, other components on the UUT are electrically shielded by the probe to prevent interference with the readings.

Charge /discharge time method

The charge/discharge time (also called network value, net value) of each network is certain. If there are equal network values, there may be a short circuit between them. It is only necessary to measure the short circuit in the network with equal network values. Its test steps are: the first board: full open circuit test → full short circuit test → network value learning; the second and subsequent boards: full open circuit test → network value test, and then use the resistance method to test where there is a suspected short circuit. The advantages of this test method are accurate test results and high reliability; the disadvantages are that the first board test time is long, the number of retests is large, and the test efficiency is not high. The most representative is MANIA's SPEEDY machine.

Inductance measurement method

The principle of the inductance measurement method is to use one or several large networks (usually ground grids) as antennas, apply signals to them, and other networks will sense a certain inductance. The test machine measures the inductance of each network and compares the inductance values of each network. If the network inductance values are the same, there may be a short circuit, and then a short circuit test is performed. This test method is only suitable for testing boards with ground layers. If the test reliability of double-sided boards (without ground grids) is not high; when there are multiple large-scale networks, since there is more than one probe used to apply signals, the number of probes provided for testing is reduced, and the test efficiency is low. The advantage is that the test reliability is high and the number of retests is low. The most representative are ATG's A2 and A3 machines. In order to make up for the number of probes, the machine is equipped with 8-pin and 16-pin to improve test efficiency.

Capacitance measurement

This method is similar to the charge/discharge time method. According to the law relationship between the conductive pattern and the 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 an open circuit occurs, the area of the conductive pattern decreases, and the corresponding capacitance decreases, indicating that there is an open circuit; if two parts of the conductive pattern are connected together, the capacitance response increases, indicating that there is a short circuit. In the open circuit test, the capacitance values of each end of the same network should be equal. If they are not equal, there is an open circuit, and the capacitance value of each network is recorded as a comparison for the short circuit test. The advantage of this method is high test efficiency, and the disadvantage is that it is completely dependent on capacitance, and capacitance is affected by many factors, and the test reliability is lower than the resistance method, especially the measurement error caused by the associated capacitance and secondary capacitance. The test reliability of networks with fewer endpoints (such as single-point networks) is low. Currently, the flying probe testers of HIOKI and NIDEC READ use this test method.

Phase Difference Method

This method is to add a sine wave signal to the ground layer or electrical layer, and use the line layer to obtain the phase lag angle, thereby obtaining the capacitance value or inductance value. The test steps are to first test the open circuit of the first board, then measure the phase difference of other networks, and finally measure the short circuit; the second and subsequent boards are first tested for open circuits, then the network phase difference, and the possible short circuits are tested and verified by the 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 to test double-sided boards. Companies that currently use this test method include MicroCraft.

Adaptive Testing

The adaptive test method is that after each test application process is completed, the device selects the appropriate test process according to the specific situation and test specifications. For example, if the network value (charging time or capacitance, etc.) of a network is less than the device test error, the device will automatically use resistance test and electric field test. This test method is the fastest and has the best test effect. However, I have not come across a test machine that uses this test method so far.

The flying probe tester is an improvement on the traditional needle bed online tester. It can use probes to replace the needle bed. There are 8 test probes with 4 heads that can move at high speed on the XY mechanism, and the minimum test gap is 0.2mm. When working, the unit under test (UUT) is transported to the tester through a belt or other UUT conveying system, and then the probe of the fixed tester contacts the test pad and the via to test the single component of the unit under test (UUT). The test probe is connected to the driver (signal generator, power supply, etc.) and the sensor (digital multimeter, frequency counter, etc.) through a multiplexing system to test the components on the UUT. When a component is being tested, other components on the UUT are electrically shielded by the probe to prevent reading interference.

The flying probe tester can check for shorts, opens, and component values. A camera is also used on the flying probe test to help find missing components. The camera is used to check for well-defined component shapes, such as polarized capacitors. With probe positioning accuracy and repeatability in the 5-15 micron range, the flying probe tester can precisely probe the UUT.

丨 The article is organized to spread related technologies, the copyright belongs to the original author丨
丨 If there is any infringement, please contact us to delete丨

qwqwqw2088

Flying test aircraft with camera identification?

So how can we use the camera to identify the phase difference capacitance measurement method?

EFT

I feel like I need a picture to explain this thing more clearly. After looking at it, I feel like I understand it, but it seems like some details are missing.