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The I-Connect007 editorial team spoke with GreenSource Fabrication’s Alex Stepinski, VP and officer, and Rick Nichols, product engineer, about plating capabilities, new equipment developments, and how best to create more plating flexibility in a shop.
Barry Matties: Let’s start with today’s plating challenges that people face.
Alex Stepinski: It starts with the end-user. In copper plating, from our end-users, the most feedback that we see is associated with the ability to plate shut higher aspect ratio structures. The higher the aspect ratio—whether it is a blind microvia or a through-hole—gives that more design latitude. That’s one driver. Another driver is the stacked microvias that increase density and the ability to do any layer. All of the plating processes required to support both of these design approaches seem to be the biggest needs that the market brings to us to address.
Rick Nichols: There’s a very strong thermal management drive. People are asking more and more for vias. Not only that, but this is linked in with a higher density circuitry, and then they also need to use verticals—the fluid dynamics and plating vertical through-hole in the vertical mode conflict. You need to have special equipment and—to a lesser extent— special electrolytes. That’s the challenge.
Matties: Happy, what do you think are some of the challenges that are out there today?
Happy Holden: They’ve always been uniformity and throwing power. We wanted specialized plating baths that would throw more into the hole than on the surface because we’re going through sequential lamination, and we still have to etch the circuitry on the surface of the board. Aspect ratio and ductility are important, but the big thing in the last 20 years has been plating vias solid so that it was easier to stack, and we didn’t have to use resins to fill them and then cap plate. But it has always been one of the hearts of making a PCB. It’s relatively easy to drill all kinds of aspect ratios, but it’s not so easy to metallize them reliably.
Matties: Alex, in one of our last conversations, you talked about reaching what I would describe as record-setting aspect ratio achievements in your system. What are some of the aspect ratios that you’re hitting now?
Stepinski: It depends on the diameter. It’s a gradual curve, so the larger the diameter, the easier it is to do the aspect ratios, while the smaller the diameter, the harder. But on through-holes, we can metallize 40:1 on blind microvias depending on the diameter. If it’s really, really tiny, it’s around 1:1. If it’s larger, we were doing 10:1, 15:1, or things like that with slots. On through-hole filling, we’ve demonstrated up to 8:1.
One of the challenges is that the suppliers present a strategy to do these things, and it doesn’t work on the higher aspect ratios. It was kind of like the bridge-plating strategy that’s common with through-hole fill. You have to do things a little bit differently. It’s hard to get things done with one electrolyte. You may need two or three electrolytes in a row to shape the structure the way you want.
As Happy indicated before, throwing more in the hole than on the surface is okay. However, what generally happens is if you throw more in the hole than on the surface, the solutions that are on the market tend to compromise the knees of the hole, and you have to come back and do something about the knee. Then, you also have a situation where if you bridge plate, you can plate the knee shut before you finish filling from the bottom in four sequences.
You have to analyze each electrolyte, see what the possibilities are with it, and then find out, “I’m going to use this electrolyte for Step A, and this electrolyte for Step B.” It’s a multistep approach in plating. It’s different than what it’s been traditionally where people just want to drop it in one or two baths and are done. As you go toward these higher aspect ratios, this is where we find ourselves now—until the time that people develop new electrolyte formulations that are more sophisticated to do it in one step or two.
To read this entire interview, which appeared in the November 2020 issue of PCB007 Magazine, click here.