Issue link: https://iconnect007.uberflip.com/i/1507822
12 PCB007 MAGAZINE I SEPTEMBER 2023 larger, especially in infrastruc- ture, but also in the mobile space. e XY dimensions are growing to accommodate the I/O, plus the pad sizes are getting smaller. is means the surface area with the volume of your solder—the surface area to your BGA pads, both on the package side and on the PCB side—are getting small- er. Meanwhile the adhesion is getting more challenging and the materials more rigid. Sud- denly, CTE mismatch becomes a much bigger challenge. Johnson: And you might be talking about ball grid arrays for most of the packages that have thousands of potential solder failures per package. Yes, the array packages and their increasing density is a challenge on materials. ere are some creative things to be done on the mate- rial side to either absorb the strain between the package and the PCB, or to make them more robust to the stresses that they encounter. Happy Holden: Electric vehicles are challeng- ing. They're using the latest chip technology, but they want subassemblies which are low- cost but high reliability for a longer life. There are the mobile phone requirements for small form factors and power efficiency; that's a real dilemma. at's where substrate-like or near-substrate technology comes into play. It's the space be- tween a substrate or packaging side vs. the traditional PCB side. e line is blurring, and within that blurring is the desire for the density of a substrate but at the cost of a PCB. Johnson: How big is that gap? At one time, there was a gap, but now it's al- most a continuum. Some traditional PCB fab- ricators have factories producing substrates. For those fabricators, there's a continuum; once you get to a certain density, it moves to IPC committee responsible for IPC-4101 industry standard for PCB laminate and prepreg. I'm engaged in the industry consortia with OEMs, fabricators, and raw material suppliers. Nolan Johnson: What's really happening in the industry around those groups? In my SMTA presentation, I talked about the North American market, how the book-to-bill has been doing lately, and then I shied quick- ly into talking about density. At a high level, packaging density drives both PCB density and substrate density. As your packages get more stuff packed in—10 pounds of stuff in a five-pound bag, for example—ev- erything gets smaller and more compact, and there's more I/O. at drives the packaging technology, which in turn, drives the PCB technology. Johnson: Which then drives the materials? Yes. From a materials perspective, they're get- ting thinner. e electrical drivers are making for a lower dielectric constant, but that's not the primary driver. e primary driver is the desire to get lower dissipation factor, or loss tangent. e next driver is to get the copper smoother. e copper challenge is adhesion; as your resin systems become lower and lower loss, it's difficult to get them to stick to anything. At the same time, copper is getting smoother, which makes it harder to adhere to resin systems. ose are some of the emerging challenges for both copper and the resin system. As you con- tinue to add filler, you have increasingly lower percentages of the resin in that system, which challenges adhesion. Glass transition temper- atures in newer materials are getting higher, which makes them more brittle. e fillers make them brittle, too. At the same time, the packaging is adding I/O, and the sizes of the packages are getting Darren Hitchcock