Issue link: https://iconnect007.uberflip.com/i/1116895
16 PCB007 MAGAZINE I MAY 2019 a material that is way over-specified for their needs. As Barry mentioned, the problem is that there's so much choice; it's a minefield. The right question to ask is, "You've shown me 100 different products. Which ones do you really sell and are used in the market?" Once you know that, then you can home in on those and start to be sensible about it. Right now, we're discussing another materials evaluation with the High-Density Packaging User Group (HDPUG). We have a list of materials to test, and there are loads of them. OEMs are trying to decide which ones are interesting and they want to have a look at, and they don't know. They're just given names and some kind of ba- sic properties. They don't know whether these are variations on old themes or if they're brand new, or what the chemistry is. As a designer, I would hate to be in the posi- tion of having to choose. I once heard someone say, "Just use the IPC slash sheets," and that is complete nonsense. The IPC slash sheets define a material based on its chemistry, but that has nothing to do with its performance in the mod- ern context. Anybody trying to design purely based on IPC slash sheets is going to fail from the beginning because it doesn't have any rela- tionship to the final properties of the material, which is a huge challenge. When they were de- signed in the first place, there were three resin systems—phenolic, epoxy, and polyimide— and they were all very different. If you say epoxy, there is no epoxy in the final material. Epoxy is just a chemical structure— the C-O-C three-atom ring structure—that was present when you formed it. It all reacts, so you end up with a single molecule compris- ing many component parts that has little to do with epoxy at all. And let's not forget that it's also full of ceramic fillers, flame-retardants, other fillers, etc. Trying to define a material based purely on chemistry just doesn't work anymore, which has made life more difficult for everybody. Now, the industry is crying out for a performance-based or sector-based clas- sification. For example, automotive people are saying, "I have a requirement for in-cabin for my au- Andy Shaughnessy: I don't think a lot of design- ers worry about the glass weave for most de- signs. I don't hear them talking about that as often. Morgan: Many designers don't even know there's glass inside the material; it's a green thing they put their components on. There are two groups: people who are new to design who don't know these things and we need to tell them, and people who have been design- ing for years who don't know about the latest developments and the things I've been talking about, such as low Dk glass or a spread weave. There's a need to continue the education for experienced designers as well. Matties: For many years, it didn't matter. They could just build the board, and there weren't any consequences. But today, the demands are so high, and these critical variables are now coming into play. Morgan: Right. You could get away with every- thing before. Now, people ask, "What's the best material to use?" There's no such thing as "the best material"; all materials are a compro- mise, and the ultimate compromise is cost. For years, the military has been using polyimide- based materials, which is a very high ther- mally performing material. All designs for the military use polyimide because you can go in the field, use a soldering iron to repair it, and it won't fall apart. And that's great, but there are lots of designs now where you're never go- ing to do that. Many designs you can't repair in the field anymore, so the main reason for using polyimide is gone. But the military still specifies it and pays a huge premium for using Many designers don't even know there's glass inside the material; it's a green thing they put their components on.