PCB News - Overview of PCB Flying Probe Testing Technology

My PCB development work started in 1956, and gradually expanded to form the PCB industry from 1963 to 1978. After more than 20 years of reform and opening up, due to the introduction of foreign advanced technology and equipment, single-sided, double-sided and multi-layer boards have achieved rapid development, and the internal PCB industry has gradually developed from small to large. Due to the concentration of industries in the middle and lower reaches and the relatively low cost of labor and land, it has become a region with strong development momentum. In 2002, it became the top three PCB output. In 2003, PCB output value and import and export value both exceeded US$6 billion, surpassing the United States for the first time and becoming the world's second largest PCB output. The proportion of output value also increased from 8.54% in 2000 to 15.30%, an increase of nearly double. In mid-2006, it replaced Japan and became a PCB production base with a large global output and an active home for technological development. Our PCB industry has maintained a rapid growth of about 20% in recent years, which is far higher than the growth rate of the global PCB industry.

Flying probe testing is a new solution to some major problems of PCB 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. 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.

1. Structural characteristics of flying probe test system

The flying probe tester is an improvement of the traditional needle bed online tester. It uses probes to replace the needle bed. The XY mechanism is equipped with 4 heads that can move at a high speed and a total of 8 test probes. The small test gap is 0.2mm. When working, the unit under test (UUT, unit under test) is transported to the testing machine through a belt or other UUT transmission system, and then the probe of the testing machine is fixed to touch the test pad and the via hole, so as to test the 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. (smtsh.cn/ target=_blank class=infotextkey>Shanghai PCB) 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. Because of its ability to closely contact shielded UUTs and the ability to bring new products to market faster (time-to-market), flying probe testing is an invaluable production resource. 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.

2. Test 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 a large amount of flexibility in the manufacturing process. In contrast, traditional ICT programming and fixture development may require 160 hours and debugging 16-40 hours.

3. Advantages of flying probe test

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. 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, (smtsh.cn/ target=_blank class=infotextkey>Shanghai PCB) high-cost test development and fixtures may delay the process for 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.

4. Feature and software support of flying probe test

Test range and software characteristics The company's flying probe tester is the A3 type tester of German AGT Company, with a large test area of 550*430mm and a large plate thickness of 6mm. The operating system is WINNT4.0, and the required software mainly includes A3 TEST PLAYER, A3 DEBUGGER, DPSwinzard, VIEW2000, IGI (Launch EXT6.58), Browser and so on. IGI is the software that processes the data required by the A3 TEST PLAYER, and it processes the GERBER data. Define the layer name, arrange the layer sequence, check the attributes of the pads, the coordinates of the graphics, and optimize the holes. The important one is to extract the netlist and output the A3 test file. When optimizing the holes, pay attention to the fact that the ring width is too small and the large holes (such as positioning holes) should be optimized manually to prevent needle breakage. DPS is a software used to output the position coordinates of the printed board, the puzzle, the number of test holes, and the scanning point. Import the *.les file from the OUTPUT folder, the software will prompt, follow the prompt Select pads to be used for scanning to enter the scanning point, add 4 more for each layer of the top and bottom layers. If the printed board is too large and dense during the test, it should be divided into several areas in the software, and several scanning points should be added. However, it should be noted that the isolation line should not be pressed on the graphic element to prevent the machine from giving wrong instructions. Work. If the test program cannot be generated after the DPS software, there may be the following reasons:

a) The graphics in the IGI software are not in one quadrant, so the test range is too large, and it should be moved into the normal use area

b) The antenna point is incorrectly selected. Repeated trials and swapping the antenna point up and down can achieve the goal.

c) When choosing an antenna, you should not choose a network that is too small, so that it cannot be used as a standard for testing the entire board

A3 DEBUGGER is the software to calibrate the flying probe tester. The eight test heads will produce errors after a certain period of testing. Therefore, the machine must be calibrated regularly to ensure the accuracy of the test. BROWSER is used for error correction. When the printed board has an open circuit or a short circuit, use it to find the exact position, and then mark it there. A3 TEST PLAYER is the test software. Use this software to select the test mode (Supervisor mode is often used), test type, probe pressure (pressure), movement speed (strokes), and height. Also determine how to select the scan point, there are two kinds of manual (MANUAL) and automatic (AUTOMATIC). When you test once, you must first manually define the scan points given in the DPS, and then use automatic when you test. When shutting down the A3 system, the bracket should be returned to the zero point first to prevent the eight test heads from collapsing and testing when they bounce off.