Introduction of several PCB testing techniques-2
Now the AOI system uses an advanced vision system, the new way to light, increased magnification and complex algorithms, which can be obtained at high test speed high defect capture rate. AOI system can detect the following error; components missing paste, the polarity of the error tantalum capacitors, solder pin positioning error or deviation, the pin bent or folded, excessive or insufficient solder, solder bridges or cold solder joint and so on. AOI addition to checking out the visual pcb inspection of the defects can not be identified, AOI in thepcb production process but also the quality of the work process and the emergence of the type of defects, etc. collection, back to the company for process control analysis and management personnel. But the AOI system is also deficient, if not an error detection pcb circuit, while the detection of invisible solder joints can not do anything.
1.4 Automatic X-ray examination AXI (AutomaticX-raylnspection)
AXI is only in recent years the rise of a new testing technology. When the assembled circuit board (PCB Assembly) along the rail into the apparatus, the circuit board side in the X-Ray has a launch tube, the emission of X-ray after being put through the circuit board beneath the detector (usually cameras) to accept, because you can spot contains a large number of X-ray absorption of lead, and is therefore through the glass fiber, copper, silicon and other materials than X-ray irradiation on the spot by a large number of absorbed x-ray, while the black spots were produce good images, makes the analysis of solder joints become very intuitive, so simple image analysis algorithm can automatically and reliably test solder joint defects. 2D AXI technology test method from the past to the current 3D test method. The former X-ray transmission test, the single-sided board soldered joints can produce a clear video, but for the widely used double-sided circuit board mounting, the effect will be poor, will make both sides of the video spot overlapping is extremely difficult to distinguish. The 3D test method using layering technology, will focus the beam to any image projected onto the corresponding layer and high-speed rotation of the acceptance of a surface, the receiving surface at high speed rotation so that the image in focus is very clear, but the image on the other layers were eliminated, so the 3D test method can separate circuit board solder joints on both sides of imaging.
3DX-Ray technology in addition to mount double-sided circuit board inspection, but also for those who are not visible solder joints such as BGA (BallGridArray, ball grid array) and other multiple layers of image "slices" test, that is, the junction of BGA solder top, middle and bottom of a thorough inspection. While taking advantage of this method can also be measured through-hole (PTH) solder joints, check whether the substantial hole in the solder, thereby greatly enhancing the quality of solder connections.
Second, the future prospect of SMT Assembly Testing
Predict that the next two decades the success of a testing technology will be eliminated or not a simple task, because not only need to sum up the past, you also need a clear understanding of the application of the future. From the development trend in recent years, the use of a variety of testing techniques, in particular, AXI and ICT combined tests will soon become the preferred test in this area.
Increasingly complex due to the current board, the traditional circuit-contact test has been greatly restricted by ICT and functional testing is difficult to diagnose defects. With most of the complex increasing the density of circuit boards, the traditional testing methods can only increase the test line tester access points. However, with the increase in access points, testing, programming and the cost of needle-bed fixture increased exponentially. Development test program and fixture usually takes a few weeks, more complex circuit board may be even more than a month. In addition, the increase in the number of ICT Contact ICT test will result in errors and increase the number of re-testing. AXI technology is not subject to the above factors, the high coverage of process defects, usually up to 97%. The process defects are generally accounted for 80% -90% defects, and inspection of solder joints are not visible, but the AXI technology can not test circuit electrical performance deficiencies and failure.
Detection of the AXI technology and traditional methods of combining ICT online test, you can learn from each other, so that SMT detection technology to achieve the perfect combination, because each technology has the shortcomings of compensation to another technology. X-ray focus on the quality of solder joints. It also confirmed the existence of components, but can not confirm whether the correct component, orientation, and values are correct. On the other hand, ICT may determine the direction and value components, but can not decide whether the weld is acceptable, especially the joints in the bottom of the package components such as BGA, CSP and so on. Figure 2 shows the AXI and ICT test method to check complement the range map. Specifically, with the AXI technology development, ICT systems AXI system and can "talk to each other", which is known as "AwareTest''technology to eliminate duplication between the test section. By reducing the ICT / AXI redundant test coverage can greatly reduce the number of ICT contacts. This simplified the original test ICT test only 30% of access points can maintain the current high test coverage, and reduce the ICT access points can be shortened ICT test test time, speed up the ICT programming and reduce costs of ICT fixture and programming.