Function test of smt assembly quality inspection
Although a variety of new detection technologies emerge endlessly, such as optical and X-ray inspection, electrical performance testing based on flying probes or needle beds, etc., functional testing is still the main method to detect and ensure the final functional quality of products. At present, there are more and more applications of technologies such as built-in self-test (BIST). These technologies can reduce the cost of functional testing, but they cannot completely replace functional testing. Especially for products that are used in important fields such as military, aviation, automobiles, transportation, and medical care, or products with very high cost and complexity (such as applications in telecommunications networks, power stations, etc.), it is often necessary to ensure that the product itself and other systems It works reliably when integrated, and functional testing will be necessary at this time.
The functional test is actually to treat an electronic device or a circuit component as a black box, use the external connection port of the circuit as the input and output port of the excitation or test signal, and turn on the power according to the normal working state of the tested circuit. By adding a variety of prescribed input signal combinations to the input port, the response signal of the output port is detected in time to determine the working condition of the circuit. The hardware equipment required for a dedicated functional test system is relatively easy to obtain, and the programming language is generally C/C++, Visual Basic and other high-level languages. During testing, one device can be used to connect multiple circuits under test at the same time by polling or interruption, so as to realize the whole process monitoring of multiple circuit modules during the detection and test process (such as “aging” test, etc.).
Functional testing involves analog, digital, memory, RF, and power circuits, and different testing strategies need to be used in a targeted manner. The test content includes important functional path, structure, circuit dynamic function verification, determining whether there are circuit hardware errors, etc., to make up for the parts that were not detected in the online test process performed before. This requires analog and digital excitation signals to be applied to the circuit module under test according to the test requirements. At the same time, the measurement device in the system must be able to monitor the same number of analog and digital response signals, and be able to control their execution timing and process. Functional testing can be implemented at different stages of the product manufacturing life cycle. The first is the engineering development stage, where the new product functions are confirmed before the system production verification; then in the production process, as part of the entire process, the defect discovery cost (missing cost) is reduced through system testing; finally, it is also not available in the delivery stage. What’s missing, it can reduce the cost of on-site maintenance in the application, and ensure that the function is normal and will not be returned.
The online test program and the functional test program each have their own advantages and disadvantages. Generally, you can choose which program to apply according to your needs. For products with high product quality requirements, two solutions can be used for testing at the same time, online testing first, and functional testing later to ensure product quality. The functional test system is generally rarely used in a certain part of the circuit assembly production line, and is usually put into use at the finished product inspection stage.
As mentioned above, functional testing is used to assemble circuit modules, but now highly integrated electronic equipment puts circuit boards and modules in a replaceable module, which ultimately constitutes the electronic equipment or system as a whole. For different test objects, although the structure of the tester is similar, the test procedure, the transportation process of the test object, and the test location are quite different. For this reason, there are many types of functional tests. These forms have their own advantages and disadvantages in terms of cost, time, effect and maintainability. The following is an introduction to the four basic types of characteristics of model test system, test bench, dedicated test equipment (STE), and automatic test equipment (ATE).