PCB Online Test:
Online testing is used to find manufacturing defects in printed circuit board assembly. The online test is to test the circuit board through a bed of needle fixture, which can be in contact with each node on the circuit board assembly. The assembly test is to directly drive the components on the circuit board one by one. Online testing has fewer restrictions on design, but testing touchpoints must be set to achieve defect analysis and performance inconsistency analysis.
For signals that cannot touch the probe (which is common for pinless components), the problem of fault isolation will increase. Here, it is recommended that each signal to be tested should have pads or other test holes in all parts of the printed circuit board that can be used for signal detection (unless scanning register testing is used). It is also recommended that the pads of the test points should be tested. Place it on the grid so that the probe test can be performed on the second side of the printed circuit board. If it is not possible to detect every signal, only special signals at special detection positions can be used. For fault isolation of a single or a small group of components, it is necessary to increase the test vector or adopt other test techniques.
Many faults are often caused by short-circuits of the pins of adjacent components, short-circuits between the pins of the components and the outer conductors of the circuit board, or short-circuits between the outer conductors of the printed circuit board. In the actual design, the normal production defects should be taken into consideration without affecting the fault isolation (these faults are caused by signal inaccessibility or inconvenience). In order to design an online test plan, the test points of the probe pads must be on the grid to facilitate probe testing.
Due to the requirements of electrical performance, sometimes it is necessary to design by function (such as separation of simulation and digital circuit parts). Separating the tests of different functions at the physical level will improve test efficiency. Separating the test connector or grouping the ferrules in the connector will improve the testability of the circuit. This kind of digital and high-performance simulation signal mixing test solution requires two or more types of test instruments. Signal separation not only facilitates the design and maintenance of test fixtures but also helps operators troubleshoot the printed circuit board assembly.
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