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ers that they come to me at initial startup of a product before they even bother to route any circuitry, because designs get so complicated that it's very challenging for them to go back and make changes if they've violated standard fabrication design guidelines. It's really stress- ful to explain to an engineer why his design isn't suitable for mass production, so I prefer to avoid that like the plague. The information I request from the designer includes: • Initial prototype and final volume production region/sites • Material type • Overall thickness • Layer count • Layer copper thicknesses • Layer designations (signal, plane, mixed) • Smallest component, connector, or BGA pitch • Smallest expected lines/spaces for plated and non-plated layers • Drill structures and traces required for fan-out • Controlled impedance requirements • Special requirements (require non-standard materials, additional processes, or tighter tolerances) – High speed, low Df materials – Plugged or filled vias-in-pad (VIPPO) – Back-drills – High voltage or current – Optical routing – Dual finish plating – Edge plating – Castellations – Cavities – Thermal management – Press-fit holes I always ask what the minimum BGA pitch is if there's a BGA, because the most difficult component establishes the level of technical capability required. And I can provide basic design guidelines per device pitch. With a 0.4- mm pitch BGA, if a customer is trying to run one trace between the pads on internal lay- ers, those traces and spaces can only be 2.36 volume site or sites. TTM calls this Seamless Global Transfer, and it works best when imple- mented in the planning stages of a new design. I also review designs for cost savings. For ex- ample, in Asia, materials are 40 to 50% of a fabricator's cost, compared to less than 20% in the United States. When we get into high-vol- ume manufacturing, optimizing material utili- zation can save a customer several percent on the final assembly if we can keep a lowered cost on the PCB by planning the PCB dimen- sions to fit very well on a fabrication panel. If the circuit board is small, TTM often works with our customers to calculate the best mul- tiple-up array with rails for assembly that can still fit optimally on the fabrication panel. The most common fab panel size is 18" x 24", but we also mass-produce 21" x 24" panels at many sites. Shaughnessy: Sometimes, I get the feeling that the designers don't realize how much control they have over the final product. What are some of the common errors that you see com- ing in that you wish that you could just tell the designer, "If you just did this...?" Ellis: If you just…came to me for your stack- up and design rules first, I wouldn't h ave to tell you that nobody can fabricate this design in mass production. I request of my custom- 18 DESIGN007 MAGAZINE I JUNE 2019 Julie Ellis

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