AOI, automated optical inspection, images a board with cameras and lighting from several angles and compares the result with the design data and programmed rules, flagging missing, wrong, shifted, rotated or tombstoned parts, bridges and poor fillets. It usually runs after reflow and sometimes after placement, while a companion 3D system, solder paste inspection (SPI), checks the printed paste. It cannot see hidden joints such as BGA balls, which need X-ray, and its false call rate depends on how well the program is tuned.
AOI is flagging every 0201 on the board, tighten the library before the operators start ignoring real calls.
Also heard as
- automated optical inspection
Related terms
Tombstoning
Defect where a small two-terminal chip stands up on one end during reflow, leaving the other end unsoldered.
Bridging
Solder defect in which solder joins two pads or leads that should be separate, creating a short.
Bed of nails
Test fixture with an array of spring-loaded pins that touch every test point on a board at once.
IPC class
Reliability class 1, 2 or 3 under IPC standards, setting the acceptance criteria a board is built to.