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F E AT U R E Q & A w i t h F i l b e r t A r zo l a , Ra y t h e o n SAS S etting design constraints is one of the most critical parts of the PCB design process. The PCB designer must balance performance, manu- facturability, and cost while addressing issues such as component function, signal integrity, thermal management, and EDA tool idiosyncrasies. Filbert Arzola is a principal electrical engineer at Raytheon SAS and an instructor who teaches one of the few classes (that we know of) that focuses on setting design constraints. We asked Fil to share his thoughts on design constraints: the fac- tors involved, the various trade-offs, and his best practices for optimizing constraints for your partic- ular design. As Fil says, "Everything about a PCB is a constraint." Getting Our 'Fil' of Design Constraint Techniques What sort of pre-layout analysis should be per- formed before you begin setting constraints? Filbert Arzola: When starting a new PCB board design, one must set up initial routing and clear- ance constraint settings to enable a good start to engineer your board design. However, one must first review and settle on the initial mechanical model that will house your board design. I highly advise every PCB board engineer to fully under- stand and confirm the mechanical aspects of the housing, including the outline, the amount and size of the mounting hole clearances, the type and size of the bolt and washer hardware, and most of all, if there are any 3D interferences. A nice DXF file that details all this information com- pletes the electronic model to pre-analyze the mechanical aspect of the board design. One must understand why we constrain our designs and what doing so will give us in return. Having a solid, well-designed, and engineered mechani- cal model is a must to constrain a successful PCB model database. Designers often say that setting constraints cor- rectly is a delicate balance of trade-offs. What are some of these trade-offs? The most important trade-offs in modern PCB design engineering mainly surround what can go wrong and cause delays and overrun costs in fab- rication, assembly, manufacturing, having to re- spin the design, poor electronic circuit design and most of all, poor signal and power integrity electrical models that cause poor trade-offs with the mechan- ical model. Yes indeed, a lot of bad stuff. One must understand the good, the bad, and the ugly that can happen with board design engineering. Under- standing what could go wrong/bad and using engi- neered constraint management methodologies will help to overcome and balance out all those bad things and give you a balanced design that has Fil Arzola