I circuiti stampati (PCB) sono sempre più complessi e diversificati. Con un'ampia gamma di applicazioni, l'unico requisito comune a tutti i tipi di PCB è che devono funzionare in conformità ai parametri di progettazione, senza errori e guasti. In breve, i PCB devono funzionare in modo impeccabile.

Complex PCBs can have hundreds of components with thousands of solder connections and that gives innumerable opportunities for failure. The Printed circuit boards manufacturing industry makes sure all their PCBs meet the above challenge of flawless working through a battery of inspection and testing procedures to ensure the quality of their products.

Assemblers detect circuit board faults before assembly through various inspection methods. After assembly is over, they employ another set of inspection and test methods to solve PCB errors.

Evolution of PCB Inspection and Test Methods

Simple circuit boards with a handful of components needed only manual visual inspection (MVI) methods to ensure solder problems and placement errors were weeded out. With increasing complexity and growing production volumes, MVI systems were found to be inadequate, as humans soon grew tired, and could not be relied upon to carry out the task of inspection repeatedly for long hours. As a consequence, inspectors missed defects and faulty boards reached later stages where it was more expensive to solve PCB errors.

This brought up the next step in inspection systems—Automated Optical Inspection (AOI) methods—now a widely accepted inline process. Assemblers effectively use AOI to inspect PCBs before and after reflow soldering to check for a variety of possible faults. Now, even pick-and-place machines incorporate AOI capabilities, allowing them to check for misalignment and faulty component placements.

With the advancement of surface mount technology, components became smaller, and this increased the board complexity along with PCBs becoming double sided and even multi-layered. Additionally, introduction of fine-pitch SMDs and BGA packages brought out the limitations of AOI, forcing assemblers to implement even better inspection methods such as the Automated X-ray Inspection (AXI) systems.