Testing is an important part of design and manufacturing PCB board. With the miniaturization of parts, the increasing complexity of products, and the shortening of time to market, testing problems are becoming more and more complicated. The expansion of circuit board functions makes assembly-level assessment and on-site maintenance become the assembly process. Important issues in this article. This article introduces three strategies for circuit board testability design.
Electronic assembly testing includes two basic types: bare board testing and load testing. The bare board test is carried out after the completion of the circuit board production, mainly to check the continuity of short circuits, open circuits, and netlists. There are many other inspection and verification methods in the process. The loading test is carried out after the assembly process is completed, and it is more complicated than bare board testing.
The tests in the assembly stage include production defect analysis (MDA), online testing (ICT), functional testing (to make the product work in the application environment) and a combination of the three. In recent years, automatic optical inspection (AOI) and automatic X-inspection have been added to assembly testing. They can provide static images of circuit boards and layered images of X-ray circuit boards on different planes to determine virtual soldering and solder joint bridging defect.
The purpose of the research test strategy is to find an indispensable combination test plan suitable for a certain product. Before starting the design process, define a simple strategy for implementing the required tests. Consider product testability issues early in the product development cycle, rather than later. This will greatly reduce the test cost of each node from the initial design to the final test, and obtain higher node testability.
There are five types of usual tests, and their main functions are as follows:
1. Bare board test: Check the open circuit and short circuit defects on the circuit board without components.
2. Production defect analysis: Check the short-circuit and open-circuit defects of the solder joints on the circuit board of the installed components.
3. Online test: Certify the operation of each individual component.
4. Functional test: The operation of the functional module of the certification circuit.
5. Combination test: Combination test of online test and function test.
The best testing strategy can ensure that every type of test being performed is indeed feasible. Even though the production test process is well defined at the beginning of the development cycle, it can still be changed after the design is completed. From a common test strategy that has been successfully applied to hundreds of high-density design cases, it can be seen that it affects the following aspects:
1. The layout of the component through holes must be strategic.
2. To provide test contact points for each node in each wiring network.
3. To touch each node on both sides of the circuit board.
4. Layout of grid reference components and through holes.
5. Correct test pad shape and spacing.
Even in the highest-density design, 100% testing of each side of the circuit board, each wiring network and each node can only be achieved when the test strategy is adhered to in each link of the design cycle. To determine what is the best detection and testing strategy, it depends on the feasibility of the testing process, the economic analysis of the testing strategy, the life cycle of the product and the time required to enter the market.
Another way to determine the best test strategy is to evaluate all inspection processes to determine the scope of defects and the cost of testing. Before the product enters the market, these problems are discovered and resolved in the design process.
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