Issue link: https://iconnect007.uberflip.com/i/1511130
62 DESIGN007 MAGAZINE I NOVEMBER 2023 The fully additive process is a pretty old pro- cess, and I remember back when they were making print and etch boards with 15-mil line width and space. What's the difference between additive and semi-additive? Semi-additive is similar, but it's not. With that old additive process, those processes would run in plating for 24 hours or more to get the right plating thickness, but in this process, we are putting down a very thin layer of electro- lytic copper as a base metal, rather than using an ultra-thin foil or something like that. Once that's defined, then we go down with a photoresist and image trace patterns, which are actually trenches in the resist. en we plate those up and strip away the resist, and there we go. We'll just flash-etch the base elec- trolytic copper so it's not touching the circuit walls at all. It really looks like an additive-type trace, but it's plated up inside that trench. You then get perfectly straight sidewalls and a lot of benefits toward signal integrity. Talk a little bit about chemistries and what kind of applications this process typically is made for? is process works well for anyone trying to define a very thin-lined trace, and it works for ultra-high density cir- cuit boards. In fact, that's what we call our program: ultra-high density intercon- nection. If you look at any h i g h - p e r f o r m a n c e H D I circuit boards, they can benefit from this technol- ogy where you have something sub-75-micron trace and space—the old 3-mil lines and spaces. If you have a 2-mil and, let's say, via-in-pad plated over with multiple plating steps, this technology can help; it's a pretty broad range for packaged substrates and interposers. ere are many buzzwords floating around in the U.S. because they're bringing this technology back here to support the supply to critical indus- tries like defense and aerospace. is allows us to not be so dependent on the Far East. But it requires traces that are sub-25 microns (sub-1 mil), so this chemistry works well for that as well as passives like inductors and capacitors inside the boards. e technology for embed- ded capacitors and resistors is not new, but certainly, this can be done in a different way where you're building traces that are very tall and narrow, meaning that your aspect and spacing ratios are tight. For antennas and wave- Figure 1. John Johnson