Different types of defects caused by the printed circuit board (PCB) manufacturing process or faulty components are detected by in-circuit testing (ICT).
Checking for shorts, opens, resistance, capacitance and other basic quantities in the SMT line, right after the assembly and soldering of components.
Typically, a bed of nails type of test fixture is used in ICT testers. The tested product is pressed against the test fixture populated with hundreds or even thousands of test probes. Every test probe is in contact with its own test point enabling electrical measurement. Prior to contacting, the product is guided with tooling pins. Different contacting methods are used, like servo-driven, pneumatic and vacuum contacting. Most ICT test points are at the bottom side but double-sided ICT contacting is also doable.