Issue link: https://iconnect007.uberflip.com/i/1507822
14 PCB007 MAGAZINE I SEPTEMBER 2023 your planes, and areas of the power layer which should be free of copper. It becomes harder to fill and remain thin. All these "planets" are lining up and they're pulling at each other. It's easy to fill, just make it thicker. But if your board is already 5 milli- meters thick, how much thicker can you get and still plate your vias reliably? Johnson: What's your take on the blurring line between boards and substrates? ere is a blurring between the materials tradi- tionally used on substrates, and those used on PCBs. In some design cases, we may be look- ing at a substrate material even being used in a PCB factory, or as a PCB material. In general, those designs don't get pushed to the substrate factories because of the differences in re- quirements. On the substrate side, they require the highest quality, meaning low defect rate, and very thin materials. Whereas the PCB side generally has cost pres- sures that are higher than the substrate side. at creates an opportunity for a big trade-off. Usually, the trade-off means different choices during development of a substrate material than for a PCB mate- rial. Holden: Does this come down to the type of OEM, a general one like aerospace or military wanting traditional boards, or is this a semiconductor OEM? They each adhere to different standards. If one PCB factory can figure out how to use the material, another one can. But the bigger difference comes in the substrate sites. e capital costs are very different, for one thing. With some of these technologies, like modified semi-additive plating (mSAP) or some of these high-end cleanrooms, extremely thin prepregs the substrate factory, and that line is ever changing. As substrate technology advances so does the PCB factory technology. Johnson: Would you provide some back- ground on fillers and the challenges those materials present on the PCB side? e main filler in the market continues to be silica. ere are also fillers related to the flame retardants, but we're moving away from bro- minated flame retardants. To have a fire you need a fuel source and oxygen. e brominat- ed ones remove the oxygen, and they're quite effective at it. e halogen-free flame retar- dants are trying to cover up the fuel, creating a charred layer. at layer covers up the fuel so the fire will go out. In addition to silica and halogen- free flame retardants, other fillers balance electrical, mechanical, and thermal performance. But we still need to drill it without burning through drill bits because of the fillers. A lot of things that go into these material systems are more filler. Johnson: That affects the manufacturability? Yes, definitely. It's the ability of the resin to fill in-between the voids, for example. As BGA packages get larg- er, that is a void in your plane. If you have a package that is, say, 100 millimeters square, you have less than 50% copper in that large area, which affects the planes. Let's narrow down the focus to an infra- structure board; I call them the big, thick, and ugly boards. ese are the 20-, 30-, 40-, 50-layer boards, a lot of plated through-hole vias with increasingly more HDI in the stack- up. ese boards are using the very low-loss resins that are heavily filled, making it harder to fill up the space le by anti-pads, gaps in There is a blurring between the materials traditionally used on substrates, and those used on PCBs.