PCB Tech - Overview of PCB flying pin test technology

China PCB development began in 1956 and gradually expanded to form the PCB industry from 1963 to 1978. More than 20 years after the reform and opening up, due to the introduction of foreign advanced technology and equipment, single panel, double-sided board and multilayer board have developed rapidly, and the domestic PCB industry has gradually developed from small to large. Due to the concentration of downstream industries and relatively low labor and land costs, China has become a region with strong development momentum. In 2002, it became the third largest PCB producer. In 2003, PCB output value and import and export volume exceeded US $6 billion, surpassing the United States for the first time and becoming the second largest PCB producer in the world. The proportion of output value also increased from 8.54% in 2000 to 15.30%, nearly doubling. In 2006, China has replaced Japan as a PCB production base with output value and a country with active technology development. China's PCB industry has maintained a high growth rate of about 20% in recent years, which is much higher than the growth rate of PCB industry.

Flying pin testing is the solution to some main problems in PCB testing. It uses a probe to replace the needle bed, and uses a plurality of fast-moving electrical probes driven by a motor to contact the pins of the device and make electrical measurements. This instrument was originally designed for bare board, and it also needs complex software and programs to support it; Now it can effectively carry out simulation online test. The appearance of flying needle test has changed the test method of low yield and quick turn assembly products. Tests that used to take weeks to develop can now be developed in a few hours, greatly shortening the product design cycle and the time to market.

1. Structural characteristics of flying needle test system

The flying needle tester is an improvement of the traditional needle bed on-line tester. It uses a probe to replace the needle bed. The X-Y mechanism is equipped with 4 heads that can move at high speed, a total of 8 test probes, and the test gap is 0.2mm. During operation, the unit under test (UUT) is transported to the testing machine through belt or other UUT transmission system, and then the probe of the testing machine is fixed to contact the test pad and via hole, so as to test a single element of the unit under test (UUT). The test probe is connected to the driver (signal generator, power supply, etc.) and sensor (digital multimeter, frequency counter, etc.) through the multiplexing system to test the components on the UUT. When a component is being tested, other components on the UUT are electrically shielded through the probe to prevent reading interference. The flying needle tester can check short circuit, open circuit and component value. A camera is also used in the flying needle test to help find missing components. Use the camera to check the shape of components with clear direction, such as polar capacitance. With the probe positioning accuracy and repeatability reaching the range of 5-15 microns, the flying needle tester can accurately detect UUT. Flying pin test solves a large number of existing problems seen in PCB assembly: for example, the test and development cycle may be as long as 4-6 weeks; Fixture development costs of approximately $10000 - $50000; Cannot test small batch production economically; And the inability to quickly test prototype assembly. Because of the ability of close contact shielded UUT and the ability to make new products put into the market faster, flying needle test is an invaluable production resource. In addition, because there is no need for experienced test and development engineers, the system also has the advantages of saving manpower and time.

2. Test development and debugging

The programming of flying needle tester is easier and faster than the traditional ICT system. Taking the grpilot system of GenRad company 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 into a directory. Then the software runs in the directory to generate all the files that need to test UUT. The test type of short circuit is selected from the options page. The reference point used by the tester on UUT is selected from CAD information. UUT is fixed on the platform. After the software development is completed, the program is "screwed in" to ensure that the test position is selected as far as possible. At this time, various components "protection" (component test isolation) are added. The test and development time of a typical 1000 node UUT is 4-6 hours. After the completion of software development and loading, start the test and debugging of the typical flying needle test process. Debugging is the next work of test developers, which needs to be used to obtain UUT test coverage as much as possible. During commissioning, check the upper and lower test limits of each element and confirm the contact position of the probe and part value. Typical UUT debugging of 1000 nodes may take 6-8 hours. The development of flying needle tester is easy and the debugging cycle is short, which makes the development of UUT test program have very few requirements for test engineers. The short time between receiving CAD data and UUT ready for testing allows flexibility in the number of manufacturing processes. In contrast, the programming and fixture development of traditional ICT may take 160 hours and 16-40 hours of debugging.

3. Flying needle test advantages

Despite these shortcomings, flying needle test is still a valuable tool. Its advantages include: rapid test development; Lower cost test methods; Flexibility of fast conversion; And provide rapid feedback to designers in the prototype phase. Therefore, compared with traditional ICT, the time required for flying needle test is sufficient to make up for by reducing the total test time. The advantages of using flying needle test system outweigh the disadvantages. For example, during assembly, such a system provides that production can begin a few hours after receiving CAD files. Therefore, the prototype circuit board can be tested several hours after assembly. Unlike ICT, the high-cost test development and fixture may delay the process for several days or even months. In addition, due to the simplicity and speed of setting, programming and testing, in fact, the general technical assembler, not the engineer, can operate the test. Flying needle test also has flexibility to achieve rapid test conversion and rapid feedback of process errors. In addition, because flying needle test does not require fixture development cost, it is a low-cost system that can be placed in front of the typical test process. And because the flying needle tester changes the test method of low production and rapid conversion assembly, the test that usually takes several weeks to develop can now be obtained in a few hours.

4. Characteristics and software support of flying needle test

Test scope and software characteristics the flying needle tester of our company is the A3 tester of German AGT company, with a test area of 550 * 430mm, plate thickness 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, etc. IGI is a software for processing data required by A3 test player, which processes Gerber data. Define the layer name, arrange the sequence, check the properties of the pad and the coordinates of the drawing, and optimize the hole. The important thing is to extract the net list and output A3 test files. When optimizing the hole, it should also be noted that the ring width is too small, and large holes (such as positioning holes) should be optimized manually to prevent needle breakage. DPS is a software used to output the position coordinates, panel, number of test holes and scanning points of printed boards. From the OUTPUT folder into the *.les file, the software will be prompted, according to the prompts Select pads to be used for scanning into the scan point, the top and bottom each layer plus 4. If the printed board is too large and dense during the test, it shall be divided into several areas and added with several scanning points in the software, but it shall be noted that the isolation line shall not be pressed on the graphic elements to prevent the machine from giving wrong instructions and failing to work normally. If DPS software cannot generate test program, there may be the following reasons:

a) The figure in the IGI software is not in the quadrant, which leads to a large test range. It should be moved to the normal use area

b) If the antenna point is not selected correctly, repeat the test and exchange the antenna points up and down to achieve the purpose

c) When selecting an antenna, you should not select a network that is too small, which cannot be used as a standard for testing the whole board

A3 debugger is the software to calibrate the flying needle tester. After a certain period of testing, 8 test heads of the tester will produce errors, so the machine should be calibrated regularly to ensure the accuracy of the test. Browser is used to correct errors. When there is an open or short circuit on the printed board, it is used to find the exact position and mark it there. A3 test player is the test software, which is used to select the test mode (mostly supervisor mode), test type, probe pressure, strokes and height. Also determine how to select scanning points, including manual and automatic. The scanning points given by the DPS shall be manually defined during the test, and the automatic scanning points shall be used for the test in the future. When the A3 system is closed, the bracket shall be returned to the zero point first to prevent the collision and folding test when the 8 test heads bounce off.

At present, China PCB testing is still in the development stage. As a PCB manufacturer, ipcb has advanced automatic production lines and testing equipment at home and abroad. The company has 2 fully automatic sinking copper wires, 4 exposure machines, 60 flying needle testing machines and 4 AOI optical testing machines. In February 2012, half of the testing services were cancelled and replaced with all testing services, all free of testing fees.