Candor: UHDI Under Development

Estimated reading time: 3 minutes

Candor Industries is a PCB fabricator investing in UHDI fabrication capabilities in Canada. To support advanced packaging, as well as the current pace of IC process shrinks, PCB fabrication capabilities must shrink to keep up. Sunny Patel, Candor’s technical sales manager, brings us up to speed on what Candor has learned in their journey to add UHDI. What we gain from this interview is that, while certainly not insignificant, the stretch to add UHDI may be not as far as one might think.

Nolan Johnson: Sunny, is Candor officially stepping into the realm of UHDI?

Sunny Patel: We’re starting to get there. The first dabbling in UHDI has been these direct on-chip boards that some of our customers are trying to do. Every layer seems sequentially drilled with 2-mil line and space, or 2-mil line with 1.5-mil spacing. We haven’t done a lot of it, but we have seen some demand for it.

Johnson: Where do you draw the line between UHDI and HDI? When does it become UHDI to you?

Patel: For us, UHDI is when it becomes more than sub-drilling and sequential blind vias; it’s a mixture of that, plus sub-3-mil lines/spaces, from my perspective. It becomes case-by-case specific on how to process these boards. I suppose that is the limitation of our equipment, but also our understanding of how things etch differently in that space. The basic tools that you have, the direct imaging, and the really tight registration of your layers are all important. But then you start getting into etch factor adjustments in different areas, like the horns or making sharper square pads, and extreme reduction of copper on the surface becomes very important.

Johnson: Do you need clean room facilities?

Patel: Most board shops use a clean room already or at least the ones I’ve seen; we all have a clean room. On the imaging side, that’s very important, but it’s more than that. It’s a whole new ball game. We’ve done the sequential blind vias, but how do we plate those areas but also limit the copper surface and make sure the etching is still perfect every time for every layer set? The processes are very involved now. You need someone who can look at the data. Based on experience, you know how things are going to etch in that sub-2-mil space and adjust here and there.

Johnson: Is there more custom tuning to get that ready to go?

Patel: Yes, and everyone in that space is experienced with semiconductor-level tolerances. There seems to be a big learning curve for those designers because they’re usually designing with that in mind. There seems to be a bit of a knowledge gap on learning how a circuit board factory works and the limitations of it all.

Johnson: Yes, the dimensions on the silicon 20 years ago weren’t much smaller than the dimensions we’re putting on the boards now. At that point for ICs, we were doing silicon in clean room environments and a great deal of standardization and process work and precision in that which doesn’t seem to have migrated over into the printed circuit board manufacturing industry until now. How close are we to needing to have a clean room environment throughout the facility?

Patel: I’m not entirely sure if we need a clean room for every system. But we need more control. Obviously, the imaging has always been a clean room setup, but the control of the plating and the control of the drilling becomes so much more critical. There doesn’t necessarily need to be a clean room throughout the whole department. For example, with a laser drill you need that vacuum system and the enclosed ventilation system in that kind of equipment whenever you’re doing the actual process.

With plating, it becomes more about chemistry control. The fluid dynamics must be fine-tuned to make sure that you’re even across the panel. That’s what people are transitioning toward, like the knife edge movement vs. the traditional rack movement of plating, enclosed vertical plating lines. So, the systems are becoming more controlled. I don’t know if the whole line must be in a clean room, but it has to be less open to the environment.

To read this entire conversation, which appeared in the November 2022 issue of PCB007 Magazine, click here.