U.S. Tech: Reduce PCB Assembly Defects with ScanCAD Systems
ScanCAD’s multipurpose off-line inspection systems are the world’s leading systems for solder paste stencil, emulsion screen and bare PCB inspection, but can do so much more, including modifying production data to improve processes!
Every process is only as good as the data that was used to set it up. Today, most processes related to PCB Assembly as well as other “recipe”-based multi-step manufacturing processes, use CAD data to program automated equipment.
The common assumption is that all of the parts coming together in these processes exactly match the CAD data. This assumption can be costly, given the fact that every part coming together for a process has additive tolerances and other issues that can dramatically impact throughput and finished piece quality.
The fact is, there are differences between the CAD data and the actual parts in process. Today’s automated machines work hard to compensate for these variances by incorporating on-board vision systems to help take corrective action such as stencil orientation relative to PCB, component placement position, etc. spreading the positional errors across the part. As parts and geometries get smaller, this is becoming more and more difficult, if not impossible.
Simple common sense would be to “confirm” that all of the physical parts coming together do so properly, PRIOR to entering full production. This is easier said than done when considering today’s parts can have up to a million or more 25 um features on something the size of a sheet of notebook paper (i.e., a solder paste stencil for a semiconductor wafer). A 99.99% inspection isn’t acceptable. This means that there are potentially hundreds of errors in the one million features.
Actual Customer Example: The image to the left shows 102 errors in 342,605 features on a wafer bump stencil with 75 um apertures. This seemingly good aperture yield of 99.97% is rendering greater than 80% of the semiconductor ICs defective!
ScanCAD’s systems can look at each of the parts coming together, first to compare the part to the original CAD data, to see if they match and are in tolerance. Following that, we can adjust the CAD data to match the real-life parts to facilitate tighter production, mitigate defects and minimize additive tolerances.
Published studies have shown a decrease in solder paste defects by up to 43% by simply adjusting the data used to fabricate a solder paste stencil to more accurately match the part job lot on which the stencil was to be used. Real parts don’t exactly match CAD data.
The same results are being documented when adjusting automated component placement machine data to better match the part job lots on which they are placing components. More accurate placements dramatically reduce placement defects such as tombstoning, etc. Studies have shown tombstoning reductions of over 60% for 0201/0402 packages.
It’s just common sense!
ScanCAD has successfully integrated low-cost, high-resolution, optical image acquisition platforms with powerful PC-based software to provide easy-to-use reverse engineering, inspection and programming systems used in PCB design, fabrication, assembly and test organizations.