AOI (Automated Optical Inspection)
can check part numbers and solder quality, but can’t test anything electrically.
AXI (Automated X-ray Inspection)
can even check solder quality under BGAs, but again can’t test electrically.
ICT (In-Circuit Test or Bed of Nails)
is quick and gets good coverage including power rails, but is expensive to set up and requires test points.
FPT (Flying Probe Test)
is slower to test and requires test points, but is cheaper to set up and more flexible.
BST (Boundary Scan or JTAG Test)
can test connections the previous systems will miss and is low cost and quick but requires power to be in place.
FCT (Functional Circuit Test)
can check the circuit at full speed and under real-world conditions, but has high development costs.

To compare key PCB testing methods by setting different requirements, check out:

Interactive Test Method Finder widget

ICT vs Flying Probe vs Boundary Scan – Which is best for PCB fault diagnosis?

ICT, flying probe and boundary scan all test electrical connectivity, but they have different strengths.

Flying Probe is easy to set up for an individual design, but the individual tests take a long time to run and require expensive hardware, making it well suited to prototypes.
ICT is the opposite – the NRE (non-recurring engineering) costs are high, but once set up, each individual board test is much faster, making it a good choice for production.
Boundary Scan works very differently and can test hidden nets which the other two can’t reach, but it can have limited access to power or analogue nets. Boundary scan is cheap to set up and fast to run, making it an ideal starting point after testing the power rails that can be expanded with one of the other systems if necessary.

ICT vs Boundary Scan

ICT tests boards from the outside in, applying signals to test points and seeing how the board responds. Boundary scan uses JTAG devices on the board to apply the signals directly, giving a different type of coverage. It requires all devices on the JTAG chain to be working properly, however it can give much better coverage around BGA and fine-pitched devices. On the other hand, ICT can access any net with a test point, including analogue and power nets which might not have direct connections to JTAG devices.

Boundary Scan vs Functional Test

Boundary scan and functional test both use hardware on the board to run the tests, rather than connecting to test points, however functional test runs actual code on the board’s processors or FPGAs directly, whereas boundary scan bypasses the core functionality to set pin states, under control of an external PC. This means that functional test can run the circuit at full speed and test many components in near real world conditions, however it’s more time consuming to produce the required code, requires the board to be largely functional and often doesn’t pinpoint errors; tests will fail, but you won’t be told why.