Issue link: https://iconnect007.uberflip.com/i/1207026
FEBRUARY 2020 I SMT007 MAGAZINE 23 tems, while analyzing trends to optimize the process and identify trends. The connected systems can automatically define correlations between the processes. For instance, the PCBA industry has many studies and documentation detailing how the solder reflow process can help position sur- face-mount components normally on the pads, even if component placement is off pad. How- ever, the trend to shrink components to 0.3-mm bumps or 0201M microchips is opening doors to explore how process controls can improve yields in high-density placements. Enter advanced process control (APC), a proven control and optimization technology delivering measurable and sustainable improve- ments in production yield. Most engineers will agree that stabilizing control loops, with under- utilized or ineffective process time and strong process interactions is exceedingly difficult. APC has become a standard solution for realiz- ing stable control processes, and, quite simply, it is the added value upgrade to a process automa- tion system. APC collects and analyzes solder and component location data from an inspec- tion system and then sends the recommenda- tions across the line to printers or mounters for automatic implementation (Figure 2). Manufacturers want to monitor and adapt the process to achieve zero defects by access- ing all the data, anytime, anywhere. They must also cope with shorter life cycles, so inspection solutions should be able to collect and analyze a large amount of data to produce traceable results. Advanced Process Control Methodology Reliable AOI methods have become pow- erful, economical complements to traditional test strategies. AOI can be used successfully as a process monitoring tool for measuring print- ing, placement, and reflow performance. Some advantages include: • Detecting and correcting SMT defects during process monitoring is less expen- sive than after final test and inspection, where repairs are typically 5–10 times more costly • Detect trends in process behavior, such as placement drift or incorrect mount- ing, earlier in the overall process. Without early inspection, more boards with the same defect could be rejected during functional test and final inspection • Identify missing, skewed, or misplaced components with incorrect polarity earlier in the assembly process when component placement is verified before reflowing Yet, a single inspection system has limita- tions, especially when there is limited or no communication with the balance of the line. In this setup, it simply cannot optimize a PCBA process. Equipment suppliers must cooperate to achieve communication for a zero-defect future. M2M connectivity can optimize the process by exchanging real-time SPI and AOI measurement data with other machines in the production line. This real-time feedback includes measurement data such as offset, vol- ume, height, area, and warnings to other sys- Figure 2: Theoretical SMT lines using APC active feedback between solder paste printer, SPI, component mounter, and AOI systems.