Issue link: https://iconnect007.uberflip.com/i/1498723
26 DESIGN007 MAGAZINE I MAY 2023 otherwise, FR-4 laminates cover 85–95% of our customers' design requirements. Shaughnessy: Where do designers typically go to find this information? What documents or guidelines should they use? Many designers use their company's docu- mentation template or go to their elders and learn through knowledge that has been passed down. I just went through a bunch of our cus- tomers' designs and fabrication drawings, and I found plenty of examples of customer mate- rial specification. Many of them call out a spe- cific IPC-4101 slash number, and it's usually the same slash number each time. It's either 4101/26 or /21. Shaughnessy: IPC has said that slash sheets were not ever meant for designers to use; they're mainly a way for PCB supplier pur- chasing and marketing departments to communicate with buyers. I'm glad to hear that confirmation as it was my understanding as well. is all came from the MIL-S-13949 spec back in the mil-spec days, most of which has been replaced by IPC stan- dards. But we are seeing some of our custom- ers' designs specifying laminates by using slash numbers and I get the feeling it's just because of tribal knowledge. If you look at most of the designs, they appear to be basic, not really requiring a specific material. e board would work fine with a generic glass-epoxy laminate because it has no impedance control or per- formance criteria. We just print and etch some copper onto it, create a circuit, and it moves electrons. It's usually only when we get into the super high-speed design in the gigahertz range where we have to start thinking about loss tan- gents and permittivities. Here's the challenge: How much do you constrain? If you're build- ing your PCB design down at the local proto- type shop, which will build a board any way you want, everybody seems fat and happy. But when you want to build 1 million boards, you must introduce a low-cost constraint because you can't pay $1,000 a board and make a profit. You scale to volume to get cost savings. To real- ize maximum cost savings, this has always been done offshore. But designers must realize that offshore suppliers don't have access to all the materials and capabilities that U.S. prototype companies have. Over-specification of lami- nate materials by composition, performance characteristics, or a trademarked source cre- ates a terrible, but avoidable ordering situa- tion, putting quotes on hold every single day. e simple fact is that it causes our offshore PCB suppliers to request and obtain approval for material substitutions before they can pro- ceed. Shaughnessy: How can our PCB designers re-think material specification for low-cost volume production? I like to use a hamburger analogy. If I go to In- N-Out Burger, I know within a small margin of error how my hamburger will taste, and how Kelly Dack