Issue link: https://iconnect007.uberflip.com/i/310350
May 2014 • The PCB Design Magazine 35 checks before hand-off. This common com- plaint from the fabs is that designers still largely don't hand over manufacturing-ready designs. In response, it would be easy to ask, "What about constraint-driven design?" It's a good question. I think that a designer having a good understanding of the constraints and then be- ing able to run design rule checks against the fabrication constraints is an essential part of the solution. The problem with this, however, is that you often have one design, but multiple fabricators who may use different equipment. Of course, the answer to that problem appears to be well-accepted transfer data formats such as IPC-2581 or ODB++. IPC-2581 has promise for streamlining the data handoff, but it still doesn't address the basic problem that, from the outset, designs often begin with too little awareness of how the boards will actually be made once the design is finished. When discussing these issues with Sierra, Hughes and others, I received a surprisingly overwhelming response that "ECAD tools don't have proper DFM checks in them." Frankly, the first time I heard that I was taken aback. Real- ly? Yet when I probed deeper, I discovered that the DFM checks referred to are available in the ECAD tool's design rule check engine. The real problem is actually that the designer either does not apply them, or applies them without prop- erly defining the constraints according to their fab's capabilities. For example, let's consider silkscreen ink being allowed to print over bare copper. As a test, I sent a design that had a small bit of silk- screen designator text over an untented via (a via with no soldermask over the copper lands) to three different fabs: an educator fab, a fix-it fab, and a broker for offshore fabs. The educator fab immediately informed me that I had silk- screen over a mask opening and it had to be fixed in my design. The fix-it fab asked for the files in the native (Altium Designer or Protel) format, and the broker simply sent the Gerbers to a fab, which eventually emailed me inform- ing me that some silkscreen items would be re- moved because of overlap with mask openings. In all three cases, at a minimum, the produc- tion date would be delayed. So what are the op- tions for a solution? Figure 3: The usual PCB design-to-fab flow looks connected, but there's plenty of room for error. feature CLOSING THE GAP BETWEEN DESIGN AND FAB continues