Automated Optical Inspection or the AOI process is the method of inspection gaining popularity with the increasing usage of microelectronics. Over time, it has become an integral solution for the SMT industry. But what exactly is the AOI process?

As the name suggests, it is an automated visual inspection of the PCB in manufacturing. Post the assembly of components on the PCB, it is important to inspect it for any defects. For this, the AOI machine is used. The Air machine is equipped with a camera system to scan for any defects on the board which could further lead to board failure. It can be used at any stage of manufacturing i.e. pre or post-reflow or during both to ensure a flawless placement of PCB.

AOI inspects the PCB for any area defects. It helps ensure accurate component placement by identifying any component offset, absence or presence of components, component skew, flipped or severely damaged components. It also checks the solder joints for excessive or missing solder joints and ensures that there isn’t any wrong part or foreign element present on the PCB.

Types of AOI Inspection

AOI processors are available in two categories, the 3D AOI which is the latest version and its predecessor i.e. the 2D AOI, which was introduced somewhere in the early 1980s.  Despite being an age-old technology, with regular modifications, the 2D AOI is still very much dominating the market. However, the increasing complexity of PCB and reduced size of the PCBs have put 3D AOI ahead of 2D AOI.

• 2D AOI: It is the most commonly used technology with multiple high-resolution cameras, 10 to 15 MP resolution, and precise lenses equipped to inspect tall devices of more than 5mm. The technology makes use of sophisticated inspection algorithms to detect any possible defects on the PCB. It is highly in demand because of its flexible inspection capabilities and is cost-effective. But it stands incapable of providing volumetric measurement data and true-co-planarity inspection.
• 3D AOI: It is the latest technology that uses laser measurement especially to provide a 3D measurement of height-sensitive devices. Over years, it has been used mostly to inspect solder paste deposition on PCBs right after the screen-printing process. It comes in handy in detecting co-planarity defects that may have been ignored when inspecting through the 2D AOI process. It has a lesser false call rate than the 2D AOI and is capable of providing volumetric measurement data and true-co-planarity inspection. But it is an emerging technology with shadowing issues and high cost.

Whether it is the 2D AOI or the 3D AOI Technology, both aid in ensuring the quality of the PCB by providing incomparable reliability, especially in the case of complex boards with thousands of solder joints and intricate components.