Automated vision inspection is a key feature of most advanced stencil printing machines used for printing solder paste onto PCBs. In some PCB assembly camps, vision inspection, whether it be 3D or 2D, is not used and reasons vary. Sometimes, a stencil printer has vision inspection, but an operator simply ignores it. Other times, it’s not put into use due to poor operator training. A third reason is small contract manufacturers (CMs) avoid vision inspection system as an option due to its high cost.

Regardless of the reason, several problems can occur if a vision inspection isn’t deployed, especially on highly dense and complex PCBs. Among them: Solder bridging, insufficient solder paste deposited or being dispensed, missing solder, and print mis-registrations.

Here are some tips you can follow to assure your EMS provider or CM is applying not only vision inspection, but knows how to effectively perform stencil printing on your PCB projects.

• Verify to determine if in fact a vision inspection is programmed into your stencil printing PCB project.
• Find out if the SMT line operator is well trained and qualified on getting the best results from the stencil printer being used.
• Have your EMS provider or CM explain how they can best apply vision inspection to your PCB project.
• Question whether or not operators or process engineers know to properly apply support pins to avoid uneven sqeegee pressure.
• Learn how often your EMS provider or CM experiences assembly personnel turnover, especially stencil printer operators? Valuable experience may have left out the door and the new hire doesn’t have it.
• Ask questions when a new stencil operator comes on the assembly floor to determine if he or she been fully trained on the machine.
• Find out if a newly hired process engineer at your EMS provider or CM has the same level of assembly and stencil printing experience as the one he or she is replacing.

In most cases, OEM customers rely on and have confidence in their EMS providers and CMs to accurately perform the required PCB assembly and stencil printing functions on their projects. Sometimes, operators and process engineers are not properly trained on critical process steps. Unfortunately, the consequences of this lack of proper training appear after PCBs are built and are in the field experiencing latent problems. It is always a good idea to have a handle and a say so on these important assembly procedures to avoid extra costs.