Functional test (FCT) is used as a final manufacturing step. It provides a pass/fail determination on finished PCBs before they are shipped. An FCT’s purpose in manufacturing is to validate that product hardware is free of defects that could, otherwise, adversely affect the product’s correct functioning in a system application.
In short, FCT verifies a PCB’s functionality and its behavior. It is important to emphasize that the requirements of a functional test, its development, and procedures vary widely from PCB to PCB and system to system.
Functional testers typically interface to the PCB under test via its edge connector or a test-probe point. This testing simulates the final electrical environment in which the PCB will be used.
The most common form of functional test simply verifies that the PCB is functioning properly. More sophisticated functional tests involve cycling the PCB through an exhaustive range of operational tests.
Customer Advantages of Functional Test:
Functional test simulates the operating environment for the product under test thereby minimizing the expensive cost for the customer to provide the actual testing equipment
It eliminates the need for expensive system tests in some cases, which saves the OEM lots of time and financial resources.
It can check the functionality of the product anywhere from 50% to 100% of the product being shipped thereby minimizing the time and effort on the OEM to check and debug it.
Prudent testing engineers can extract the most productivity out of functional test thereby making it the most effective tool short of system test.
Functional test enhances the other types of tests such as ICT and flying probe test, making the product more robust and error free.
A functional test emulates or simulates a product’s operational environment to check its correct functionality. The environment consists of any device that communicates with the device under test (DUT), for example, the DUT’s power supply or program loads necessary to make the DUT work properly.
The PCB is subjected to a sequence of signals and power supplies. Responses are monitored at specific points to ensure functionality is correct. The test is usually performed according to the OEM test engineer, who defines the specifications and test procedures. This test is best at detecting wrong component values, functional failures and parametric failures.
Test software, sometimes called firmware, allows production line operators to perform functional test in an automatic way through a computer. To do this, the software communicates with external programmable instruments as a digital multi-meter, I/O boards, communication ports. The software combined with the fixture interfacing the instruments with the DUT make it possible to perform a FCT.