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34 The PCB Design Magazine • May 2014 have coverlay film within rigid sections of the board, caused by the size constraints of the de- sign and its mechanical form factor. They actu- ally advised the designer about the problems, and the risk, but in this case the designer was out of time and really could not easily redesign for better assembly yield and maintain the nec- essary product form factor. This falls into the age-old trade-off between form (a largely mar- keting driven design aspect) and manufactur- ing cost (i.e., scrap). In this case, the prototypes were needed quickly, so the designer requested production in spite of the associated risk. Sierra is an example of what I call an edu- cator fab—these are the guys who will tell you what is wrong with your design so that you can try to get it right next time. But there is still a level of frustration for them, as it seems like the designers rarely perform comprehensive DFM checks on their designs. I'm told that it is still most common that designs are at first rejected for DFM issues when the fab runs their own DFM checks using their own CAM/DFM tools. Another type of fab, such as Hughes, in San Marcos, California, is just as likely to request the original source documents from the PCB designer in the native CAD format. I refer to these guys as a fix-it fab. You could say part of their service is to make the changes necessary to your design to improve the manufacturing yield and lower costs—optimizing your design to their processes and equipment. Most high- volume fabs would want to work with the de- signer in similar ways to ensure low waste, but if you're working with fabs on distant shores this may not be desirable. As an example, I asked Hughes how they need masks to be generated in the CAD software; their response was a firm, "Don't; let us do that for you in CAM." From all the PCB fabs I've talked with, there is an overwhelmingly common message: Even though PCB designers have access to DFM checks and tools, there's no easy industry stan- dard way for the PCB designer to fully run DFM Figure 2: White acrylic adhesive layers are added to the lamination book. feature CLOSING THE GAP BETWEEN DESIGN AND FAB continues