PCBA Tech - About the principle of SMT patch function tester

Although a variety of new inspection technologies emerge in endlessly, such as AOI, X-ray inspection, and online testing of electrical properties based on flying probes or needle beds, etc., they can effectively find various defects and failures that occur during the SMT assembly process, but they cannot be evaluated. Whether the system composed of the entire circuit board can operate normally. The functional test can test whether the entire system can achieve the design goals. It takes the unit under test on the circuit board as a functional body, provides input signals to it, and detects output signals according to the design requirements of the functional body. This kind of test is to ensure that the circuit board can work normally according to the design requirements. Therefore, with the development of various advanced detection technologies, functional testing is still the main method to detect and ensure the final functional quality of products. The functional tester usually includes 3 units: adding stimulus, collecting response and evaluating the response of the tested component based on the response of the standard component. Most functional tests have diagnostic procedures that can identify and determine faults. The price of functional testers is relatively expensive. The simplest functional test is to connect the surface mount circuit board to the corresponding circuit of the device, and observe the operating status of the device after power-on. This method is simple and requires less investment, but it cannot automatically diagnose faults.

1. Functional test principle

The functional test is generally to test the board under test through its external interface. The principle of the test is that the test equipment itself provides various excitation signal sources, stimulates the board under test through the interface, and the test equipment receives the response signal of the board under test and responds. The signal is compared with the expected result, and finally the function is judged. UUT is the tested object, which may be a single board or motherboard; Input is the input signal of the tested board; Output is the output signal of the tested board; Stimulator is the analog part, which provides power, slot number, clock, control signal, and status for the UUT Signals, etc. Controller is the control part, which can be a serial port, expansion bus, etc., used to control the UUT; Detector is the detection part, used to test the output signal of the UUT; Fixture is a flexible fixture, used to fix the UUT.

SMT patch processing010

2, Features of functional testing

The function test is mainly for mass production. Its purpose is to test the hardware function from the external interface of the single board, rather than test the right and wrong, good and bad of the single board design, all branches of the software and the single board. Overall performance. The prerequisite for the function test is that the design of the default single board is successful, but some single boards are damaged due to various reasons during the production process, resulting in failure to work normally, and the function test can eliminate these bad boards. The functional tester generally only needs to make the connector or fixture corresponding to the tested object. As long as the external interface remains unchanged, the original tester can be used for the new tested board, and only the software needs to be upgraded, so the functional tester The ability to adapt to the changes of the tested board is strong. The function tester generally simulates the whole machine environment, after allowing the single board to work normally, test its input and output signals, comprehensively detect the quality of its hardware, and have high test reliability. However, because the test is performed at the interface, the fault location is vague, and only the quality of certain functions of the board can be judged. If you want to locate a specific chip, further analysis is needed.

About SMT patch function tester

3. The difference between functional test and online test

The test system generally includes an online test system and a functional test system. Online testing is generally to find out the faults of the components and connections of the tested single board, and the purpose of functional testing is to test whether the whole machine or single board can work normally and whether the various functional indicators meet the requirements. The online test system and the functional test system complement each other's strengths and complement each other to jointly complete product testing tasks. In the production system, the finished board must be tested online. Finished boards are aged at high temperature and then put into storage after functional testing. Before shipment, each single board has to go through the environment test of the whole machine. Generally speaking, it is necessary to determine whether to use online testing or functional testing according to the complexity, yield, output and maturity of the product. For some boards with very simple functions, you can generally consider only using function tests. If the product is more complex, the output is high, the yield is high and mature, both online testing equipment and functional testing equipment are needed. Regardless of whether or not it has undergone online testing and functional testing, the product must be commissioned by the whole machine before shipment to ensure the performance of the whole machine.