The testability concept of PCB Design
The testability of the product design (De sign for testability. OFT) Product manufacturability is also the main content from the production point of view is also one of the design process. It refers to the design of the product performance can be considered difficult to detect, that is, design products should consider how to use the simplest method of product performance and processing quality testing, or product design as far as possible to make products easily according to the specified method of its performance and quality Testing. In particular, the design of electronic products, product performance testing is essential. DFT Good product design, can simplify the production process inspection and product final inspection preparation, improve testing efficiency, reduce testing costs, and easy to identify product defects and failures, to ensure product quality stability and reliability. The poor design of DFT not only increases the time and cost of testing, but also can not guarantee the quality and reliability of the product because it is difficult to test. Therefore, the design and testing methods and equipment compatible with the testability designed, electronic product design must consider one of the important content.
The testability of printed circuit board design
The testability and manufacturability of the printed pole design are the same as the technical design of the printed board, which also includes the manufacture of printed boards and finished printed boards (light plates). Testability and the testability of PCB assemblies two parts. The test methods and content of these two parts are completely different, but to be reflected in the design of the same piece of printed circuit board, it is necessary for designers to understand the performance and method that need to be tested on the printed circuit board, and to understand the installation test requirements and methods of the printed board assembly. Test method and performance for printed board plates Requires a uniform standard of regulation, Just check the relevant printed circuit board standards can be found. For PCB assembly test, according to the circuit and the structure of the characteristics and requirements of the overall consideration by the designers, in the layout and cabling to take appropriate measures to properly set the test point or the test decomposition in the installation process. Especially with the miniaturization of electronic products, the pitch of components is getting smaller and more There are fewer circuit nodes available for testing, so the online testing of PCB assemblies is becoming more difficult, so design should fully consider the electrical conditions and physical and mechanical conditions for the testability of printed boards, as well as the use of appropriate mechanical and electronic equipment.
Second, the printed circuit board test
The board test of printed boards is an important means to ensure the quality of the printed circuit board, and it is also a powerful measure to ensure the quality of the printed board assembly and reduce the cost of rework, rework and scrap. The quality of the test plate is guaranteed, which can improve the efficiency of PCB installation, Reduce costs. If the quality of the board can not be guaranteed, to the PCB after installation and then found that the quality problems need to remove the components, not only maki time-consuming and may be damaged components, the cost of the times and the economy is greater. Therefore, in the domestic and foreign electronics industry attaches great importance to the performance of the printed board testing, developed a number of Testing, testing of physical and chemical properties, and reliability (environmental adaptability). There are many test items for the printed board, but there are few restrictions on the design.
Inspection is generally on the finished printed circuit board through the visual inspection or the appropriate optical instruments for testing, mainly to check the quality of manufacturing, visual inspection of the design of the testability requirements are not many. In these performance tests, printed circuit board design and layout of the impact of the strong is the electrical performance test, which includes voltage resistance, insulation resistance, characteristic impedance, Circuit-breaking test items and test points should be designed to meet the test requirements. The most testable relationship with design is the circuit pass-through test, which is the key to ensure the quality of the printed board to l00% each printed board The logical pass-through test. Therefore, the design of the printed circuit board should be considered when testing the test device may be used in the test probe and test circuits physical dimensions of the matching problem. Otherwise it will be due to the position and size error of the measured point on the printed board. The problem of the error of the test or the poor repeatability of the test. For destructive Chemical performance measurements are generally taken from the same batch of product sampling or design-specific test board or attached test board according to standards for testing and evaluation. Design should be familiar with Test board and attached test board design and test requirements and methods.
Third, the test of printed circuit board assembly parts
The test of the printed circuit board assembly is the electrical and physical testing of the printed circuit board after the component is installed. It is much more difficult to test the PCB assembly, and its detection method is more complicated than that of the printed circuit board. The testability design of the assembly should include the testability of the system. The testability function of the system should be submitted to the concept of the overall design of the machine to evaluate Test. The testability of printed board assemblies must be compatible with the integrity of the design integration, testing and maintenance.
The testability of the PCB assembly is before the design begins. The production, installation and testing of printed boards should be reviewed. To ensure the effectiveness of testability. The content of the review should relate to the visual degree of Circuit graphics, installation density, test operation method, test area division, special test requirements and test specifications.
There are two main types of PCB assembly-level tests, one is functional testing of an assembly with independent electrical functions, and a predetermined excitation signal is applied at the input end of the assembly. Verify that the design and installation are correct by monitoring the results of the output. Another test is the assembly of optical inspection and on-line testing, optical inspection of the design has no clear constraints, as long as the circuit has a certain degree of visibility can be detected, the method is mainly to check the quality of installation and welding. The test point should be designed on the coordinate grid to Where the test needle bed is matched, and can be tested at the weld surface. If the flying needle test, it is necessary to ensure that the test point is located on the coordinate grid, but also in the layout to maintain enough space to make the probe (flying needle) hit the test point, the Flying needle test can be carried out on both sides of the board, the main detection of
Commonly used test methods are manual testing and automatic testing of instruments. Manual testing by means of multimeter, digital voltmeter, insulation resistance tester and other instruments to detect, low efficiency, record and data processing complex, and limited by the density of the assembly, miniaturization of high-density assembled printed boards difficult to rely on manual testing. Automatic instrument detection with high precision, The characteristics of good reliability, good repeatability and high efficiency, and some instruments also have the ability to automatically determine, record, display and automatic fault analysis.
Common automated testing techniques include automatic optical inspection (AOD), automatic X-ray building (AX I), on-line testing (ICT) and functional testing. The test compatibility of printed circuit board assemblies should be considered in the design of the PCB, if the test method and the necessary test mechanical rules are not taken into account, even if the electrical aspects of a good testability circuits on the printed board assembly is also more difficult to test, such as the location of the test point, The size and the pitch of the test point match the test probe or the needle bed. The problem of the electrical condition setting, preventing the damage of the test to the component in the online test are the problems that should be considered and solved.
The testability concept of PCB Design
