A flying probe test PCB is an essential tool for electronics engineers. It allows them to quickly test their designs before they build anything.
For many manufacturers, PCB production focuses on on-time delivery and quality. If you have a PCB design in hand, PCB testing becomes equally important. Currently, flying probe testing can effectively detect production quality problems. It is also seen as proving to be a particularly cost-effective way of raising board standards.
If you also have the following questions:
What is flying probe test?
What affects the cost of flying probe testing?
I will seriously answer and supplement your questions at the same time.
WHAT IS FLYING PROBE TEST?
Flying probe testing uses multiple independent probes and operates without fixed test points.
We need to understand that the probe is electromechanically controlled and moves according to software instructions.
The interface in the probe moves rapidly in XY coordinates. The purpose of this is obvious, check:
- capacitance
- component value
- Component polarity
- Inductance of parts
Maybe you will say, “Price is very important.” Let me answer How much is the price of flying probe test.
WHAT AFFECTS THE COST OF FLYING PROBE TESTING?
- volume
- test location
- Complexity
- Testing frequency
WHAT ARE THE TEST METHODS
Charge/discharge time method
The charging/discharging time (also called network value, net value) of each network is certain. If there are nets with equal values, there may be a short circuit between them, and it is only necessary to measure the short circuit on the nets with equal net 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 advantage of this test method is that the test result is accurate and the reliability is high; the disadvantage is that the first board test takes a long time, the number of retests is large, and the test efficiency is not high. The most representative one is the SPEEDY machine of MANIA Company.
Inductance measurement
The principle of the inductance measurement method is to use one or several large networks (usually the ground network) as antennas, and apply signals to them, and other networks will induce a certain inductance. The testing 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 perform a short circuit test.
This test method is only suitable for the test of the board with the ground layer, and the reliability of the test for the double-sided board (without the ground grid) is not high; when there are multiple large-scale networks, since more than one probe is used to apply Signal, but 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 ones are ATG’s A2 and A3 machines. In order to make up for the number of probes, this machine is equipped with 8-pin and 16-pin to improve test efficiency.
Capacitance measurement method
This method is similar to the charge/discharge time method. According to the 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 there is an open circuit, the area of the conductive pattern decreases, and the corresponding capacitance decreases, indicating an open circuit; if two parts of the conductive pattern are connected together, the capacitance response increases, indicating a short circuit. In the open circuit test, the capacitance values of the terminals of the same network should be equal, if not equal, there is an open circuit, and record the capacitance value of each network as a comparison of the short circuit test.
The advantage of this method is that the test efficiency is high, but the disadvantage is that it is completely dependent on the capacitance, and the capacitance is affected by many factors, and the test reliability is lower than that of the resistance method, especially the measurement error caused by the associated capacitance and the secondary capacitance. Smaller networks, such as single point networks, are less reliable for testing. At present, there are flying probe testers from HIOKI and NIDEC READ that use this test method.
Phase difference method
This method is to add a sine wave signal to the ground layer or electrical layer, and obtain the angle of phase lag from the circuit layer, so as to obtain the capacitance value or inductance value. The test procedure is to first test the open circuit of the first board, then measure the phase difference of other networks, and finally measure the short circuit;
For the second or more boards, first test the open circuit, then measure the network phase difference, and then use the resistance method to test and verify the possible short circuit. The advantage of this method is that the test efficiency is high and the reliability is high; the disadvantage is that it is only suitable for testing boards with more than 4 layers, such as measuring double-sided boards, only the resistance method can be used. A company currently using this testing method is MicroCraft.
Adaptive testing method
The adaptive test method is that each test application process is completed once the test is completed. According to the specific situation of the wrench and the test specification, the device selects an appropriate test process by itself. For example, the network value of a network (charging time or capacitance, etc.) is less than the device test error , the device will automatically use resistance test and electric field test. This method of testing is the fastest and produces the best results.
With the improvement of the positioning accuracy of the flying probe test probe, 5-15 microns can perfectly detect the UUT.
MORE QUESTIONS?
The price of flying probe test depends on the volume, test location and complexity of PCB. While ICT is a good approach, it is not the only one.
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