The shift to ball grid arrays and flip chips has made X-ray inspection a common check for both chip makers and assemblers, but techniques that automatically  inspect every solder ball are still rare. Intel has developed a system that automatically looks at every ball, removing the need to manual inspect every image.

Intel's system can be used to examine solder ball connections between the silicon die and its substrate, as well as connections at the printed board level. In all of them, it scans for voids in the solder balls or joints. Many scanning systems exclude solder balls or joints that are obscured by shadows from the IC and other components including the die bumps. In contrast, the Intel approach images all the solder balls, including those that are obscured using other systems.

"We look at each ball and process all suspect areas within the ball. We haven't seen anyone else who does that," said Bonnie Bennett, an Intel researcher whose job title is pathfinding technologist. She will provide full details with a number of photos during IPC APEX Expo 2010 in Las Vegas, Nevada, April 6-8, 2010. Her paper is entitled A Robust Automated Method for Void Detection in Solder Balls and Joints.

The system accurately identifies each ball in the image, thus removing the x-ray effects. It then locates all the suspect areas within each ball. 

Once the suspect areas have been identified, the algorithm created by Intel's research team automatically classifies and measures each void. It can be used to inspect both chips and boards. "The algorithm is applicable to both post ball attach IC packages and post surface mount assemblies," Bennett said.

Though the system does a lot of processing, it doesn't require expensive computers. "This runs on an off-the-shelf PC. For large images, we use a PC with a quad core processor, one that would be considered a gaming type machine," Bennett said.