How to test PCB？
2024-11-08
1. Manual visual testing
Manual visual testing is one of the most widely used online testing methods to confirm the placement of components on a PCB through human vision and comparison. However, as production increases and circuit boards and components shrink, this method becomes increasingly unsuitable. Its main advantages are low upfront costs and the absence of testing fixtures; Meanwhile, the main drawbacks of this method include high long-term costs, discontinuous defect detection, difficulty in data collection, lack of electrical testing, and visual limitations.
2. Automated Optical Inspection (AOI)
This testing method, also known as automatic visual testing, is usually used before and after reflow. It is a relatively new method for confirming manufacturing defects and has a good inspection effect on the polarity and presence of components. It is a non electrical, fixture free online technology. Its main advantages are easy to follow diagnosis, easy program development, and no fixtures; The main disadvantage is poor identification of short circuits and it is not an electrical test.
3. Functional Test
Functional testing is the earliest principle of automatic testing, which is a basic testing method for specific PCBs or units, and can be completed using various testing equipment. There are two main types of functional testing: Final Product Test and HotMock up.
4. Flying Probe Tester
Flying needle testing machine, also known as probe testing machine, is a commonly used testing method. Due to advances in mechanical accuracy, speed, and reliability, it has been widely welcomed in the past few years. In addition, the current demand for testing systems with fast conversion and fixture free capabilities for prototype manufacturing and low yield manufacturing makes flying needle testing the best choice. The main advantages of the flying needle testing machine are that it is the fastest tool to reach the market time (TimeToMarket), automatically generates tests, has no fixture cost, good diagnosis, and is easy to program.
5. Manufacturing Defect Analyzer (MDA)
MDA is a good tool for diagnosing manufacturing defects only in high-yield/low mixed environments. The main advantages of this testing method are low initial cost, high output, easy follow-up diagnosis, and fast and complete short-circuit and open circuit testing; The main disadvantage is that functional testing cannot be conducted, there is usually no test coverage indication, fixtures must be used, and testing costs are high.
Precautions for Testing
Important! The test points should be evenly distributed on the PCB board, avoiding concentration in a small area to reduce the problem of uneven force on the board during testing.
Arrange all test points on the same side of the PCB as much as possible. If the test points are distributed on the top and bottom layers, it will increase the complexity and cost of making fixtures.
Distance between testing points and key elements:
The testing point should be as far away from the edge of the PCB as possible, and it is recommended to be at least 5 millimeters away from the board edge to prevent damage to the PCB caused by edge stress during the testing process.
The testing point should be kept away from the positioning hole, with a recommended center distance of at least 4 millimeters to avoid interference with the positioning device during testing.
Test points should avoid being close to higher components to prevent mutual interference and ensure the accuracy of test signals.
Distance between testing points:
The distance between two test points should not be too close, and it is recommended that the center distance be at least 2.54 millimeters (100 mil) to ensure that the test probes can accurately contact and do not interfere with each other.
In high-density layout, although the spacing can be reduced, it should be ensured that the test probes can make stable contact to avoid accidental contact or short circuit.
Types and materials of testing points:
Types and materials of testing points:
The test point can be a through hole pad or a surface mount pad (SMT). The positioning of through-hole testing points is accurate and can be tested from both sides of the board, but it will occupy the wiring space of all layers on the PCB. SMT test points are more space saving, but in some cases may not be as stable as through-hole test points.
It is recommended to choose materials with higher conductivity for the testing point, such as electroless gold plating (ENIG). Although the price is slightly higher, it can improve the reliability and accuracy of the testing.
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