5D solder paste inspection—merits beyond 3D technology
5D solder paste inspection—merits beyond 3D technology
Henk Biemans, Marantz Business Electronics, Eindhoven, Netherlands
With 3D SPI becoming more and more established and offered by multiple suppliers,
it is often
assumed that this is the final stage in solder paste inspection. A closer look as to what 3D-only systems can and—specially—cannot detect shows that there is room for fur- ther yield improvement. By looking at the traditional characteristics of advanced 3D and 2D imaging, strengths of both can be utilized, especially if combined within the same measurement cycle. With the introduction of “5D” SPI, all types of print process errors can be reli- ably identified and prevented. Two dimensions (X and Y) are needed to measure area parameters, such as offset,
smearing, shape and
bridging. The third dimension (Z) adds additional height and volume information. Combining the best techniques to identify anomalies in each axis clearly improves the ROI for SPI equipment and enables a next generation of closed loop pro- cess control.
Figure 1. Assembly defect analysis. Source: SMTA Post-print solder paste
Keywords: Solder Paste Inspection, 2D Techniques, 3D Techniques, Moiré Topography, Laser, SPC
Dual Multisampling 8 – Global SMT & Packaging – February 2011
inspection (SPI) Many process engineers and quality man- agers still question the value of solder paste inspection (SPI). Tough it has been agreed for years that high percent- ages of end-of-line defects can be traced back to the print process, SPI has not been deployed in a significant percentage of SMT lines. Many still question the ROI analysis. Others consider the need for SPI critical during the new product introduc- tion (NPI) phase or production ramp-ups, but not beneficial for mature, established processes. For them, the information pro- vided by the SPI doesn’t bring any relevant product quality improvements, or they perhaps are unable to usefully apply the improvements. Nonetheless, research done at IBM in Austin almost two decades ago clearly identified solder paste volume as the most important characteristic contributing
to good solder joints. Unlike the “random number generators” (to quote the late Dr Steve Case, a pioneer in 3D SPI) that no doubt impacted the attitudes of many pro- duction engineers, today’s technologies can provide reliable volumetric data as well as crucially important X-Y data. Structural test verification technol-
ogy clearly identifies the value of adding SPI, and while typically the need for inline solder paste inspection is driven by main- taining production line stability and pro- viding notification of process deviation, frequent change over and smaller run sizes demand special performance capabilities to properly serve such manufacturing envi- ronments: • Printer verification, even on first time builds
• 30 minute or less CAM to board test time
• Minimal false calls
www.globalsmt.net
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