function test (FT)
Functional test( FT) is used to test the functionality of chips and assembled boards. It is about whether a circuit fulfills the predefined functions. This test procedure, which has been used for many years, can detect defective electrical components, as well as press-fit errors, SMT and THT assembly errors, soldering errors and solder bath errors.
The preparations for a functional test are extremely time-consuming and can take several months, depending on the complexity of the board. In addition, troubleshooting is associated with high costs, as it must be performed by qualified personnel and is relatively time-consuming. Since the functionalities of modern boards are extremely diverse, testing all functions is practically impossible.
In practice, functional testing is supported by automatic test pattern generation( ATPG). There are corresponding tools for test pattern generation for digital logics and analog circuits. For digital circuits, bit pattern generation aims to generate as many bit patterns as possible to simulate faults in the circuits or in the components. Functional tests include the in-circuit test and the boundary-scan test.
The International Electronics Manufacturing Initiative (iNEMI) has developed evaluation criteria for functional tests, the so-called FAM metrics. The acronym stands for Feature (F), At-Speed (A) and Measurement (M). According to this evaluation, it is recognized whether a feature is present or absent, whether the pins and features are tested with a low, medium or maximum speed, and with which measurements can be carried out with certain bit error rates or other criteria.
In addition to the hardware test explained here, there is also a software function test.