In SMT chip processing, two or more groups of probes that can move in a certain test area are used to replace the non moving needle bed. At the same time, a movable probe driving structure is added. Motors of various structures are used to drive the flying needle tester for horizontal positioning and vertical test point contact.
The Flying Probe Tester usually has 4 heads and 8 test probes in total, with a minimum test gap of 0.2mm. During operation, the test probe is moved to the test point according to the pre arranged coordinate position program and contacted with it. Each test probe carries out open circuit short circuit or component test on the assembled components according to the test program. This method can effectively and accurately find all kinds of defects and obstacles in SMT assembly process.

(1) The basic composition of the flying needle tester.
① Computer system: the computer system is usually equipped with a special instrument card, image and moving card for the test system on the basis of a personal computer. Network hub or workstation system may also be used in case of high functional requirements. The operating system and testing software of the flying pin debugging system of European and American Series mostly use the current popular Microsoft Windows, while the Japanese series online testing system basically uses DOS system, testing software interface and operation is relatively simple and applicable.
② Instrument and measurement module: most of the instrument and measurement modules are located at the bottom of the test system, basically including two types of test excitation signals and measurement devices, which are programmable DC voltage and current sources, multi-functional waveform (sine, triangle, square wave) generators, clock generators, voltmeters, counters, pull-up and pull-down resistors, etc. corresponding to this, in the instrument interface The card integrates a switch system, which is used to connect different excitation signals or measuring devices with the test program for testing.
③ Motion and driving system: for the basic flying needle motion, there are two types of horizontal and vertical movements relative to the working area. For the horizontal movement of rectangular coordinate system, there are two types: X and y. The main purpose of X and Y driving is to find and locate the test point through the digital camera. When moving, the lead screw drive system drives the arm of the rack to move; while the driving purpose of vertical movement is relatively single, which is to contact the probe with the vertical direction of the test point. Generally, the contact angle between the probe and the test point of the flying probe test system will be inclined to a certain extent, and the angle between the probe and the vertical direction is usually about 5 °. The probe motion system is required to have fast and high-precision positioning capability. The probe arm and probe operation are driven by motor. Generally, the x-axis and y-axis are driven by the brushless motor with the precision lead screw of integrated encoder, and some manufacturers use the air suspension, linear motor and other mechanisms. The z-axis servo device of the probe is generally based on the linear motor or precision stepping motor.
④ Test area: This is the specific test area of the flying pin online test system. Generally, an operation panel will be equipped near it. In addition to the mechanical positioning device of the circuit board to be tested, in order to expand the ability of flying pin online test, auxiliary access devices will be added at the bottom side to access the power supply, test excitation signal, non vector test device, etc. for general test The test area also has a protective cover to protect the safety of the test personnel.
（2） The difference between flying needle tester and online needle bed tester
According to the testing needs of different products, the on-line needle bed tester makes a special fixed needle bed fixture. It has the characteristics of rapid testing of all testing points in sequence at the same time. The on-line testing ability and speed are good, and it is suitable for the testing application of mass production and single variety production. However, the manufacturing cycle of the needle bed fixture is long, the number of probes is large, the test programming cycle is long, the price is expensive, and it can not be reused. In addition, the needle bed fixture needs to be arranged in strict accordance with the industrial standard grid pitch, which has a test "breeding point" for the test of many complex and high-density circuit components.
The flying needle tester is an improvement of the on-line needle bed tester. The flying needle tester uses the movable probe instead of the fixed needle bed fixture. At the same time, the probe driving device is added. The test program can be obtained directly from the CAD software of the circuit board. It has greatly improved the test accuracy and the minimum test clearance. It is convenient to use and is most suitable for the assembly and production of many kinds and small batches of circuits On line test and prototype verification. But the on-line testing ability and speed of the flying needle tester are not as good as that of the needle bed tester. Taking the on-line test of medium circuit module as an example, the needle bed type may only need 305 tests, while the flying needle type may take 8-10min, which is not conducive to the formation of on-line test mode with SMT processing plant.