Introduction of several PCB testing techniques
First, the introduction of several PCB testing techniques
1.1 Online Test ICT (1n-CircuitTester)
Basic PCB test equipment is used in circuit tester (ICT), the traditional measurement circuit tester beds and the use of specialized needles have a good welding contact with the circuit board components, and with hundreds of millivolts and 10 mA division within the current of isolation tests to accurately measure the loaded resistors, inductors, capacitors, diodes, transistors, SCR, FET, integrated block and other general and specific components of the drain installation, the wrong equipment, parameter deviation, solder joints with welding, short circuit, open circuit board failure, and failure is short-circuit in which components or open tell the user exactly which point. PCB Assembly Needle bed line tester is to test the speed advantage for civilian-type appliances in a single species and large-scale production of PCB circuit board test, and the host the price is cheaper. But with the increased density of circuit board assembly, especially in fine pitch SMT assembly and new product development and production cycles are getting shorter, more and more varieties of circuit boards, circuit tester needle bed, there are some insurmountable problems: test the production of needle-bed fixture, debug cycle is long, expensive; for some high-density SMT Assembly circuit board precision problem since the test can not be tested.
Basic ICT technologies in recent years with advanced technology to overcome the limitations of the technology improvements. For example, when integrated circuits became too big to not provide coverage for the equivalent circuit detection target, ASIC engineers developed a boundary-scan technology. Boundary Scan (boundary scan) provides an industry standard method to identify the component parts of the probe does not allow connections. Additional circuit design to IC inside, allowing the components to a simple way to communicate with the surrounding elements to a format easy to check the test results.
Another non-vector technology (Vectorlesstechnique) AC (AC) signal is applied through the needle into the test bed components. A sensor board positioned against the surface to suppress the test components, and component lead frame to form a capacitor coupling the signal to the sensor board. Coupling signal that spot is not open.
For large complex boards artificially generated test program is very time consuming, but the automatic test program generation (ATPG, automated testprogramgeneration) software solves this problem occurs, the software based on CAD data and assembly of PCB Assembly and component specifications of the library board , automatic fixture design requirements and testing procedures. While these technologies help to reduce simple program generation time, but the high number of nodes in the demonstration test program was time-consuming and technically challenging.
Flying Needle needle bed tester is an improved circuit tester, it is replaced with a probe needle bed, in the XY body is equipped with high-speed mobile respectively a total of eight 4-head test probe, the minimum test gap is 0 .2 mm. Work coordinates based on pre-programmed mobile test probes to the test program point, contact with them, the test probe assembly according to the test program components for open / short circuit or component testing. Needle bed with the line tester compared to the measurement precision, the minimum testing space and so on are more substantial increase, and the needle bed without making a special fixture, the test program directly from the circuit board CAD software available, but the test speed The biggest deficiency is its relatively slow.
1.2 Functional Test (FunctionalTester)
ICT can effectively find the SMT assembly process occurs in a variety of defects and malfunctions, but it can not evaluate the whole system consisting of circuit boards in the clock speed performance. The functional test to test the whole system design goals can be achieved, it will test the circuit board unit as a function of the body, it provides the input signal, in accordance with the functional design requirements of the body detection output signal. This test is to ensure that the board can work in accordance with design requirements. So the easiest way functional test is to a certain electronic devices assembled a dedicated circuit board connected to the appropriate circuit of the device, then the applied voltage, if the device is working properly, to show that the circuit board qualified. This method is simple, low investment, but it does not automatically diagnose the problem.
1.3 Automated Optical Inspection AOI (AutomaticOpticallnspection)
With the components of the circuit board assembly increased density, to the electrical contact testing increased the difficulty, the AOI technology into the field of SMT production line testing is also a general trend. AOl not only to examine the quality of welding, but also light board, solder paste printing quality, patch quality to be checked. The emergence of the AOI process almost completely replace manual operation, to improve product quality and production efficiency are promising. When the auto-detection (A01) when, AOI through the camera automatically scans PCB, capture images, the test spot with the database to compare the parameters of qualified, through image processing, check out the PCB, defects, and through the monitor or automatically mark the defects show / marked for maintenance personnel repaired.