Flying probe test is the latest solution to some major problems in electrical testing. It uses probes to replace the needle bed, and uses multiple electrical probes driven by a motor that can move quickly to contact the pins of the device and perform electrical measurements.

 

 

Introduction

This kind of instrument was originally designed for bare boards, but also requires complex software and programs to support it; now it can effectively perform analog online testing. The advent of flying probe testing has changed the testing methods for low-volume and quick-turn assembly products. The test that used to take several weeks to develop can now take a few hours, greatly shortening the product design cycle and time to market.

 

Structural features

The flying probe tester is an improvement of the traditional needle bed online tester. It can use probes to replace the needle bed. The XY mechanism is equipped with 4, 6 or 8 test probes that can move at a high speed. The minimum test gap is 0.2mm. When working, the unit under test (UUT) is transported to the test machine through a belt or other UUT transmission system, and then the probe of the test machine is fixed to contact the test pad and via hole, so that the test is A single component of the UUT. The test probe is connected to the driver (signal generator, power supply, etc.) and 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 prober to prevent reading interference.

The flying probe tester can check short circuits, open circuits and component values. A camera was also used in the flying probe test to help find missing components. Use a camera to check the shape of components with clear orientations, such as polar capacitors. With the probe positioning accuracy and repeatability reaching the range of 5-15 microns, the flying probe tester can accurately detect UUTs.

Flying probe testing solves a large number of existing problems seen in PCB assembly: for example, a test development cycle that may be as long as 4-6 weeks; fixture development costs of approximately US$10,000-50,000; small batch production cannot be tested economically; and The prototype assembly cannot be tested quickly.

The flying probe test is an invaluable production resource because of its ability to closely contact the shielded UUT and the ability to bring new products to the market faster (time-to-market). In addition, since there is no need for experienced test and development engineers, the system also has the advantages of saving manpower and saving time.

 

Development and debugging

The programming of the flying probe tester is easier and faster than the traditional ICT system. Taking the GRPILOT system of GenRad as an example, the test developer converts the CAD data of the design engineer into usable files. This process takes 1-4 hours. Then the new file is run through the test program to generate a .IGE and .SPC file, and then put it into a directory. Then the software runs in the directory to generate all the files that need to be tested UUT. The short-circuit test type is selected from the option page. The reference point used by the tester on the UUT is selected from the CAD information. The UUT is fixed on the platform. After the software development is completed, the program is "screwed in" to ensure that the best possible test location is selected. At this time, add various component "protection" (component test isolation). The time spent on test development of a typical 1000-node UUT is 4-6 hours.

After the software development and loading are completed, the test and debugging of the typical flying probe test process begins. Debugging is the next job of the test developer and needs to be used to obtain the best possible UUT test coverage. During the debugging process, check the upper and lower test limits of each component, confirm the contact position of the probe and the value of the part. A typical 1000-node UUT debugging may take 6-8 hours.

The development of flying probe tester is easy and the debugging cycle is short, which makes UUT test program development quite few requirements for test engineers. The short time between receiving the CAD data and the UUT being ready for testing allows the greatest amount of flexibility in the manufacturing process. In contrast, traditional ICT programming and fixture development may require 160 hours and debugging 16-40 hours.

 

shortcoming

Due to the ease of programming, the ability to test prototype assembly within a few hours, and test low-volume UUTs without the typical fixture development costs, flying probe testing can solve many problems in the production environment. But not all production test problems can be solved by using flying probe test.

Like anything, flying probe testing has its drawbacks. Because the test probe makes physical contact with the solder on the via hole and the test pad, small pits may be left on the solder. For some OEM customers, these small pits may be considered as cosmetic defects, causing rejection. However, some high-end flying probe test equipment manufacturers have already developed new technologies. The use of "soft landing" can avoid leaving obvious pits on the solder, and even test on ceramic chips.

In addition, because sometimes the probe touches the component pins where there is no test pad, it may miss loose or poorly soldered component pins.

In addition, the probe tester also limits the size of the circuit board: it cannot exceed 16" 24".

Flying probe test time is another major factor. Where a typical bed of needle tester may take 30 seconds to test the UUT, a flying probe tester may take 8-10 minutes.

 

advantage

Despite these shortcomings, flying probe testing is still a valuable tool. Its advantages include:

Rapid test development; lower cost test methods; flexibility for rapid conversion; and rapid feedback for designers in the prototype stage.

The 8-pin flying probe tester can use double-sided testing, saving time for turning the board.

Therefore, compared with traditional ICT, the time required for flying probe testing can be more than compensated by reducing the total testing time.

The advantages of using a flying probe test system outweigh the disadvantages. For example, in the assembly process, such a system provides that production can begin within a few hours after receiving the CAD file. Therefore, prototype circuit boards can be tested within a few hours after assembly. Unlike ICT, high-cost test development and fixtures may delay the process by days or even months.

In addition, due to the simplicity and speed of setting, programming and testing, in fact, ordinary technical assemblers, not engineers, can perform testing. Flying probe testing also has flexibility, enabling rapid test conversion and rapid feedback of process errors. Also, because flying probe testing does not require fixture development costs, it is a low-cost system that can be placed in front of the typical testing process. And because the flying probe tester has changed the low-volume and quick-change assembly test method, the test that usually takes a few weeks to develop is now available in a few hours.