In-circuit testing (ICT) for automatic assembly testing machine is the most robust type of PCB testing in existence. The high price reflects that -- tens of thousands of dollars, though the cost will depend on board and fixture size, among other factors.
An ICT, also known as a bed-of-nails test, powers up and actuates the individual circuitry on the board. In most cases, the test is designed for 100% coverage, but you’ll get closer to 85-90% coverage. The nice thing about ICT is that the 85-90% you get is totally free of human error.
This test involves using fixed probes laid out in a way that matches the design of the PCB. The probes checks the integrity of the solder connection. The bed of nails tester simply pushes the board down on the bed of probes to start the test. There are access points predesigned in the board that allows the ICT testing probes to make connections with the circuit. They put a certain amount of pressure on the connection to make sure it stays intact.
ICT is often performed on bigger connections and ball grid arrays (BGAs).
This test is for a “mature” product with very few revisions expected. If you don’t have design-for-manufacturing as part of your goal, with the proper pads on the board, you may not be able to use an in-circuit test. Unfortunately, you can’t change your mind and move to an ICT strategy halfway through production.