Issue link: https://iconnect007.uberflip.com/i/1276973
AUGUST 2020 I DESIGN007 MAGAZINE 47 ity in creating the type of documentation you need to convey the specifications. That's what a fabrication drawing is. It's a specification for the PCB component—how it's supposed to look, how it gets finished, how it should per- form, and what type of manufacturing issues or deviations you can take during the manu- facturing process. They're all part of it, and they all go together. Matties: You mentioned people may start with templates, and my understanding is, when you start with the template, you often wind up with conflicting notes on a particular job. That creates additional confusion and delay. Almeida: Right, and think of it, too. It's just not writing notes to tell somebody else what to do. The fabrication documentation is just as important for the company creating it as it is for the manufacturer who has to read it. The more information you give them, the better chance they have to meet your requirements. But it's also the company's record of how this thing is supposed to be built, and not just today, but 10–15 years from now. Matties: I had not heard it from that point of view. That's an interesting angle to consider. Almeida: PCB documentation is not the glam- orous side of the design process. We tend to look at it and complete it, including all the manufacturing outputs, as quickly as possible, but it's the form, fit, and finish specification of that end-product; it's the record of the prod- uct. The design file is just the enabler to that. Matties: What advice would you give designers on this topic? Almeida: Don't assume it's going to get built the way it looks on your screen. You need to verify that what you translated out of that database matches what the database says for the first step. If you're not familiar with simple things like netlist compare, that is just a small effort that could have huge returns on the quality and accuracy of the design. Fugitt: Let me just jump in for one second, Rick. I call it a sanity check. It is the single most important thing I think a designer can do before sending their data off—a simple netlist comparison. It was the '90s when it became required, and people would say, "What is it?" Then, I started with DownStream in the 2000s and would tell people, "You need to do this." They would look at me with blank stares, but now we see some real progress there. It has become a standard part of the process, and it is a sanity check. Shaughnessy: Let's talk about IPC-2581 and ODB++. How does that change the fab notes situation? Almeida: It's also a translation. For example, when we design a board, you have layers, vias, and components, and they all have intelligent interrelationships between each other. This trace on the top layer knows it's connected to these traces on the inner layer and the bottom layer, and they know what components they go to. When we create Gerber information, we strip all that intelligence away, and we create different files. What these intelligent formats do is take that ambiguity away because they give you a manufacturing file that is a direct correspondence to that intelligent database. Fugitt: One of my favorite classes at PCB West a few years ago was presented by Mike Tucker. He was a fabricator and showed the cleanup that has to be done on the data incoming to fab. He spent the first 30 minutes of that pre- I call it a sanity check. It is the single most important thing I think a designer can do before sending their data off—a simple netlist comparison.