Issue link: https://iconnect007.uberflip.com/i/1116895
42 PCB007 MAGAZINE I MAY 2019 ences and seminars helps you keep up to date on the materials world because there's a lot going on. And it's our job as material suppliers to spread the word on what we're working on. OEMs have to seek it out, but material sup- pliers need to ensure that the information is available for them. We're trying to get people to realize that things that have been introduced in the flex world could maybe be used in the rigid world, which Jon mentioned earlier. We have exam- ples of people using our flexible materials in- side of circuit boards for reducing the thickness or other electrical improvements. Companies are using more like mixed constructions; it's not a pure package anymore. Instead of all lay- ers being one material, it could utilize multiple material sets to try to accomplish everything at the right cost performance. Matties: When an OEM comes to you, what ad- vantages are they looking for in materials in addition to cost? Andresakis: Each OEM has their own hot but- ton. In the infrastructure world—telecommu- nications and internet—they want to reduce loss and skew because that's becoming a much bigger issue at the higher data rates. With ev- erything being done at the package level for making things denser, they still need to have more layers on the circuit boards. Some of these boards have gone out of control with thickness. That's where materials that are film- based, like what we make, have an advantage because we can make very reliable layers. It's hard for fiberglass to get below two mils reli- ably, and we can do that day in and day out. Happy Holden: I'd like to hear your thoughts on five materials, and the first one is liquid crystal polymer (LCP), which has been turned into material but can also be made into a film. Especially for 5G, what's your opinion on the LCP? Weldon: LCP is an excellent material if convert- ed to a film properly. As a standalone material, LCP has some isotropy concerns, meaning its dielectric properties are variable in certain di- mensions. If converted to a proper film, which I think most manufacturers available now are producing a film that's relatively isotropic, LCP does perform well. It has a relatively low loss tangent around 0.001–0.002, a dielectric constant around 3–3.1, and an extremely low moisture uptake. It's almost hermetic in its properties, but it does pose some challenges and has some process issues. If you try to use it as a self-bonding method (i.e., using LCP to bond to other LCPs), you hit the melting point of the material to do the bonding. Making a multilayer circuit, which most flex circuits would be, it creates a swimming trace problem that we've seen in past type materials as well, which is pretty classic of a thermoplastic. Then, there are some adhesion issues of very smooth coppers to the base substrate. As I mentioned earlier, conductor losses and rough- ness can play as much or more of a role in the dielectric loss, especially in thin flex laminates. You may end up losing some of the benefits of having a low-loss material by using a non- or un-optimized copper type. So, LCP is great, depending on how you're using it and where you're using it, but it's certainly not the only material out there that will meet the needs for 5G and other sorts of high-frequency flex. Holden: Second, is there any chance that some- thing like THERMOUNT® can come back as a low-loss material? Andresakis: THERMOUNT® was more of a re- inforcement than a resin system. It was a kind Copper foil rolls.