Issue link: https://iconnect007.uberflip.com/i/1471044
16 PCB007 MAGAZINE I JUNE 2022 out there in terms of adjustments, in terms of anodes, anode distance, and then solution impingement. I've gone to all eductor plating. I don't use air agitation anymore. I'm basically using solution movement in what I call laminar flow as opposed to air agitation, which causes a number of problems including air bubbles, which gives you turbulent flow. It doesn't give you a good movement across that diffusion layer. You must go across that cathode diffu- sion layer so the ions have a smooth path to the board. Holden: Pete Pellegrino was the king of the flow motion plating with his 200 horsepower pumps on each side of the board. Fundamen- tally, I'd have to use refrigeration to cool the bath because there's so much energy being put in by those pumps, to create turbulent agita- tion. Carano: Yeah, he did, but again, let me tell you, that's 20 years ago and I did a lot of work with Micro-Plate in the early '80s. e equipment was set up to process boards vertically using high current density plating. ln those days they were using high-impingement (solution move- ment) plating at 100 or 125 ASF, and getting boards done in 10 minutes through a conveyor. We spent a lot of time optimizing the plating of high-aspect or medium-aspect ratio boards, but also at 100 ASF, 125 ASF. You don't do that today. Again, you can't violate Faraday's Law. ere are certain laws to the universe that you need to learn that you can't violate. Feinberg: If you want to increase your plating rate, are you increasing the amount of copper sulfate? Carano: Yes. Feinberg: So those are your choices— increase the copper sulfate level vs. the power consumption? Carano: Whenever you increase your cathode current density, you are forc- ing the ions to move from the bulk solution to the cathode to be reduced. You achieve what is good or bad, it's called the limiting current density. It means, if you don't have enough concentration, you'll reach a limit to where no matter how high you go, you're not going to get any better plating. You're actually going to get terrible plating. So you must have a higher concentration of ions in bulk solution to meet with and work with that higher cathode cur- rent density. But there's a caveat here. e higher the cath- ode current density, you favor the surface vs. the hole. You might say, "I'll plate at 40 ASF." at's great, raise the copper to double. en you end up with two mils in the surface and six tenths in the hole. Is that what you want? No, I don't think so. ose are the trade-offs. Feinberg: It's a cost and balance thing. Holden: It's more than that, because you also have to think of the boundary layer. Agitation plays a big role in getting those fresh cations onto the surface of the cathodes. Carano: at's the cathode diffusion layer which we just talked about. It's the finite thick- ness that builds up in front of the cathode and it becomes an area where the ions are either going to move faster or going to move slower depending on a number of factors like agita- tion and concentration. You have to remem- ber, when you're plating, you have two types