PCB News - Circuit board manufacturers: a must-read for FCT functional testing

Circuit board manufacturers: a must-read for FCT functional testing

To put it simply, FCT is an online test, which mainly detects whether the circuit board components are inserted incorrectly after the PCBA processing is completed, and whether the original price parameters are normal; FCT is an online function test, which mainly detects whether the circuit board functions are normal, and the two tests have their own focus., After passing the FCT test, you can confirm that the circuit board is OK and can be used normally.

Professionally speaking, FCT refers to the simulated operating environment (stimulus and load) provided to the test target board (UUT: Unit Under Test) to make it work in various design states, so as to obtain the parameters of each state to verify the UUT The function of the test method is good or bad. Simply put, it is to load a suitable stimulus to the UUT and measure whether the response of the output end meets the requirements. Generally refers to the functional test of PCBA.

Basic overview
The full name of FCT in English is: FunctionalCircuitTest, which is functional test, generally refers to the functional test after PCBA is powered on, including: voltage, current, power, power factor, frequency, duty cycle, position determination, LED brightness and color recognition, LCD characters And color recognition, voice recognition, temperature measurement and control, pressure measurement and control, precision micro-motion control, FLASH and EEPROM online burning and other functional parameters measurement. It refers to a test method that provides a simulated operating environment (stimulus and load) for the test target board (UUT: UnitUnderTest) to make it work in various design states, so as to obtain the parameters of each state to verify the function of the UUT. Simply put, it is to load a suitable excitation and load on the UUT, and measure whether its output end response meets the design requirements.

Classification of functional tests
According to the different control modes, it can be divided into:

(1) Manual control function test

(2) Semi-automatic control function test

(3) Fully automatic control function test

The earliest functional tests were mainly manual and semi-automatic. Even now, for some simple functional tests of the tested boards, manual or semi-automatic testing schemes are sometimes used based on simplifying the design and reducing production costs. With the rapid development of science and technology, in order to save production costs and improve production efficiency, most of the current functional tests use fully automated test solutions.

According to the controller type, it can be divided into:

(1) MCU control method

The MCU control method can be regarded as a simple embedded control. The characteristics of MCU and embedded CPU control methods are:

a Fast test execution speed

b Test operation is simple and clear

c Data display and output require dedicated circuits and programs

d The test plan is highly pertinent

e Test software is easy to modify

(2) Embedded CPU control mode

(3) PC control mode

The PC control method is currently the most widely used FCT test method, mainly because:

a PC technology has become the basic general technology of today's society

b PC is cheap

c The data output and file processing of the test results can be easily realized on the PC operating system

d The operation of the test software is closer to the user's operating habits

e There is a dedicated test program development software

(4) PLC control mode

The PLC control method is also a commonly used FCT development method at present, and its focus is mostly on controlling the sensing part, and the measurement function for the tested board is weak. This is because PLC is professionally used in industrial control.

The composition of the functional test system
The system components of PCBA functional testing are mainly divided into:

(1) System Control Center

(2) Control execution part

(3) Parameter measurement part

(4) Data processing and output part

System control center: This part is generally composed of small or medium-sized central processing units such as PC, MCU, ARM, etc., and is the core component of the entire test system. Its main function is to control the running status of the entire test process, and to control the operation of each step. The test content and results are judged and recorded, and the test results are finally obtained.

Control execution part: The control execution part is mainly composed of I/O components. It is the sensing and executing mechanism of the logic action of the test process. The system uses it to build various test environments and realize test functions.

Parameter measurement part: The measurement part is mainly composed of special measurement boards and meters. It mainly completes the collection of various analog or digital quantities during the test. Sometimes we call it the data collection part.

Data processing and output part: each step and the final test result are the purpose of our entire test. How to store and output these results and data is more convenient for us to effectively control the quality of PCBA products. This is the responsibility of the data processing and output part.

Causes of FCT
PCBA in Chinese is called a mounted circuit board. In the mass production process of PCBA, due to the operating state of the equipment and the human factors of the operator, it is impossible to guarantee that all the PCBAs produced are intact. This requires adding various components at the end of the production. A variety of test equipment and test tools to ensure that all the actual circuit boards shipped out of the factory are completely consistent with the specifications and parameters of the design, which has produced various tests such as ICT, AOI, X-Ray, Boundary-Scan, FCT, etc. means.