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Design007-May2019

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20 DESIGN007 MAGAZINE I MAY 2019 ity and efficiency. What I do is predictive engi- neering, which is to reuse circuits that they've already used. If they are a repeat customer, they already know it works, and now sudden- ly it saves them in fabrication, assembly, tests, and debug. They save a boatload of money and end up with fewer spins. Our process is to create reusable modules. This allows us to use parts that you've already used, and if it's a new part, we go ahead and do a module for it; just substitute the old one for the new one after we've modified it. So, from that point on, after it has been proved to work, it works for us. First, we have them define stackups ahead of time. We sit down with the customer and their fabrication shop and determine whatever layer count they feel with this particular com- pany works best. We build in all of the fabri- cation capabilities that their fabrication house has because they usually have more than one fabrication house. We're just trying to define everything ahead of time so that it now be- comes predictable. Then, you place and replicate as much as you can. That's really what it comes down to. When the placement is done, you do place- ment verification. Then, once that's all done, approved, and cleaned up, you route all of the differential pairs and high-speed clocks. Next, you send that to engineering for them to re- view and route the remaining signals, which are pretty much single-ended nets, matched groups, etc. That last step is final verification. When we get to that, we send them a final board to review. We can do it in two weeks when we have all these pieces in place because it's already designed. "At least I know that the replication process or reuse process is very good. It works, and people that have experienced it like it. And now the tools are better." The process is as follows, using clusters, templates, and bundles: • Auto-cluster from schematics • Auto-place for complex parts • Place • Replicate and/or reuse templates • Placement verify (refine) • Fabrication and assembly review • Cluster nets into bundles and route • Complete routing with constraints • Engineering review for SI, PI, and power distribution network (PDN) • Rest of routing • Validation (DFM and DFT) • Create a template for future use • Customer review • Deliverables Visit I-007eBooks.com to download The Printed Circuit Designer's Guide to… Executing Complex PCBs as well as other free, education- al titles. DESIGN007 Words of Advice for New PCB Designers In a recent survey, we asked the following question: What do you think is the most important thing a designer should remember when planning a new PCB design? Here are a few answers, edited slightly for clarity. 1. Have a good music selection. 2. Don't panic. It's almost always possible to complete a complicated design if you go step by step. 3. How will the board be fabricated and how will it be assembled? Both of these will affect cost and reliability. 4. Place with flow planning for routing in mind. 5. Each design has its own restriction and requirements. And each design is a new challenge. Communicate with the team and gather all information (mechanical, environmental, SI, PI).

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