ICT (In-circuit testing) is a method of white box testing for PCBs. It checks shorts, opens and other basic components of the board like resistance and capacitance. ICT may be performed with electronic test fixture (bed of nails), or with a fixtureless in-circuit test setup.
Importance of ICT
ICT is used for testing the PCB where a bed of nails in-circuit test equipment can test parameters like resistance, capacitance, etc. along with the operation of analogue. Most faults of the PCB usually arise out of manufacturing stage and can consist of short circuits, open circuits or faulty components. ICT form of testing can detect most of the problems of the board. Provided accessibility to all the nodes on the board, ICT has the ability to detect around 98% of faults.
ICT test equipment consists of different elements:
In circuit tester:which is a matrix of drivers and sensors to perform the measurements.
Fixture: which acts as a physical interface between the board and the in circuit tester.
Software : which is specifically written for each board type to be tested.
The tester is generic, while the fixture and software can be assembly specific.
Advantages and disadvantages of ICT
Ease of detection of manufacturing defects
Easy program generation
Fast test time and ease of interpretation
Fixtures are expensive
Fixtures are difficult to adjust
Difficulty of test access for some boards
Back-driving or damage to components
Types of In-Circuit Testing
The main types of ICT machines that are commonly used include the following:
The Standard ICT machine
Flying probe tester: which has a simple fixture for holding the board while contact is made using a few probes that can be moved around the board to make the required contact as required. These probes are moved using software control, so any board updates can be accompanied with changes to the software program.
MDA (Manufacturing defect analyzer): This tester is used for detecting manufacturing defects like short circuits across tracks and open circuit connections. It offers a basic In-circuit test of components like resistance, continuity and insulation.
Cableform tester: This test form is used for testing cables and uses the same basic functions as an MDA. The operation is adjusted for testing cables, however some form of high voltages may need occasional application to test for insulation.