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24 DESIGN007 MAGAZINE I MAY 2023 Columnist Kelly Dack has had a pretty wide range of experiences. As a PCB designer, he has sat behind the desk at an NPI company, an OEM, a fabricator, and now an EMS provider. We asked him to share a few thoughts on the materials selection process and how it could be improved. Kelly also explains how overly zealous PCB designers make things too complicated by over-specifying their materials, which leads to confusion once the board goes to volume pro- duction overseas. Are you over-constraining your material choices? Andy Shaughnessy: Kelly, what is your process for material selection? Walk us through it. Sure. I actually wrote a guideline for our cus- tomers that explains the material selection Stop Over-specifying Your Materials process. As mentioned, over-specification in the EMS realm is rampant and problematic from the standpoint of scaling products to volume overseas. is guide has a section on laminated materials that includes a simple, tried-and-true material specification. It says, "Materials: laminated glass epoxy resin type FR-4 series or equivalent per IPC-4101 with a Tg of greater than or equal to xxx." This is a number that we can modif y. We say, for instance, 170°C, and a Td (time to delami- nation) temperature of greater than 3XX°C. ose are all movable numbers that designers can edit. at's how we specify our laminate materi- als for printed circuit boards, unless the per- formance criteria dictates that it needs to go further and get more specific—for example, high-performance signal integrity constraints, impedance control, or exotic materials. But Feature Interview by the I-Connect007 Editorial Team