Reducing Defects with Embedded Sensing

Gerry Padnos
Juki Automation Systems, Inc., Morrisville, NC USA

Tim Skunes, Thang Huynh
CyberOptics Corp., Golden Valley, MN USA

Typical SMT production lines are a collection of disconnected machines performing various tasks. Errors can occur at any step during this process, but often go undetected until the PWB is completed and soldered and it is too late to do anything other than re-work or scrap it. New tools with better integration are required to support the demand for increased yields and improved efficiency.

To prevent defects from simply passing from one machine on to the next, it is necessary to have inspections throughout the line.

Better yet, sensing at different points should be linked to form a complete solution. This is especially critical in the placement phase of assembly due to the wide variety of inputs (components) and movements. The assembly system has to take up to hundreds of different components and individually place them at different locations on the PCB. This complicated task requires more thorough oversight to ensure defects are not created or passed on. Optical sensors can provide this oversight into the assembly process and offer the benefits of being fast, accurate, and non-contact.

Some of the challenges of integrating these sensing technologies are cost and space. It would be too expensive to have a complete inspection machine before and after each assembly system and take up far too much space. New generations of optical sensors, however, are also compact enough such that they can be embedded at key locations within the PCB assembly process. These sensors can be integrated to form a complete web of error prevention.

This paper discusses the new integrated optical sensing technologies that make it possible to virtually guarantee that only good PCBs will pass through the assembly process, reducing costly rework or scrapped PCBs and improving efficiency

New generations of optical sensors such as On-the-fly Laser Centering, Embedded Micro-cameras, and Strobed Imaging Modules can provide cost effective, real-time, continuous process monitoring throughout the assembly process. Catching defects early can increase yields and improve efficiencies. Costs can be reduced by not allowing errors to propagate through the assembly process where they become increasingly more expensive to correct.

Of course the monitoring system should be simple to use and not create a big additional overhead, so the embedded optical sensor technologies capitalize on the component and solder paste data already available during the assembly process to reduce or eliminate additional programming. Finally, an embedded sensor network distributed at multiple locations in the assembly process dramatically improves the likelihood that only good PCBs pass through the assembly process