Issue link: https://iconnect007.uberflip.com/i/1481368
16 DESIGN007 MAGAZINE I OCTOBER 2022 and buried vias. It's a sequential process. If you have five lam cycles sequentially, and you screw up the last one, you just burned up two to four weeks of work and you have to start over. Shaughnessy: Now, much of this wouldn't have been possible even 10 to 15 years ago because these enabling technologies didn't exist, right? Snogren: Direct imaging is a big one. at has helped with registration and feature size capa- bilities. When we were using film in the past, we had registration issues because the film moved, and we had to register it manually. It expanded and contracted with temperature and humidity. We had to pin it and the pinning wasn't always perfect. Now we can have much smaller annular rings, much smaller feature sizes. With film, typically we had a really hard time getting down to 2-mil lines and spaces consistently when we were using a phototool. Not that it can't be done because they use phototools for ICs, but they're tiny and they use stepper cameras. ey're not doing panels on a single sheet of film. Direct imaging is probably the biggest example. Any- body can buy a direct imaging system that can go down to 12 microns and maybe even less if you want to spend the money. If you get the right resist, you can resolve 20-micron lines and spaces fairly easily. at was unheard of 10 years ago. You couldn't even think about it. Shaughnessy: Where are the bottlenecks in this whole process? Where do we need to innovate? Snogren: It's just adopting the thin foils. Design- ers need to understand what the manufactur- ing process is like so they can design around it, whether it be using thin foils or semi-addi- tive process with electroless copper. It's about understanding what the copper thicknesses will be, what the feature size capabilities are. For the fabricator, it's about getting the sys- tems in place: the direct imaging system, AOI, electrical test, differential etch, the proper via fill and laser drill capabilities. HDI manufac- turers already have these, so it's just a matter of adapting them to a slightly different process flow and adding a few other processes. Shaughnessy: I keep hearing about the Asian companies doing UHDI well and for fairly cheap. What do we need to learn from them? Snogren: ey've already adopted modified semi-additive processing and semi-additive processing. With the modified semi-additive processing, which gets you down to 20- or 25-micron lines and spaces relatively com- fortably, we must copy what they're doing. Remember, when they do this in Asia, it's in a factory that was designed to do nothing but that. ey're not building a wide variety of products; they're only doing ultra HDI. Shaughnessy: ose are all greenfield facilities. Snogren: It's what they do all day, so it's a fairly standardized well-controlled process where they build things that are within a narrow design feature range. Shaughnessy: What percentage of ultra HDI now is mSAP or A-SAP?