Issue link: https://iconnect007.uberflip.com/i/1038326
44 PCB007 MAGAZINE I OCTOBER 2018 medium build, after which you can either pat- tern plate, put dry film on it, or go to a copper- strike or full-panel plating. Johal: This line also has the latest generation of electroless copper specially designed for blind microvias—a direction more customers are pushing us. With current HDI PCB blind microvias, fabricators are paying attention to how much electroless copper is on the surface versus how much is in the bottom of the capture pad of the BMV; this is becoming more critical for blind microvia reliabil- ity. Customers are asking to have >80% throw in the blind microvia at a minimum, and that's an abso- lute thickness measurement—not by weight gain, but by focused ion beam (FIB) cross-sections. Foley: True values. The name of the electroless copper bath is Prin- toganth T1. Holden: Is that T1 bath formalde- hyde-free? Foley: No, it has formaldehyde. Holden: Do you do anything spe- cial to stabilize it, keep it from generating nodules, or extend its life? Foley: It has stabilizers in it just like any other electroless copper bath, and if you look behind the bath, every fluid head in the bath has filtration on it. Typically, at the end of the production week, the operator will press one but- ton to go into service mode. Ser- vice mode performs electroless cleaning. For example, this line was their production line last week. Now they are running the other line, but you can see it's time for a cleanout; there's a lit- tle bit of copper plate in the fil- ter pipe. The operator will call up service mode and start the electroless copper clean process. That will automatically pump it from here to the holding tank, bring the etch from the other holding tank in, run a cycle for probably three or four hours at temperature, etch out all the copper, and then it will fill it with water, rinse it, dump it, and it should be ready to bring your electroless back and start again. Figure 7: GreenSource operators control the Atotech lines from service kiosks like this one. Figure 8: Atotech tank transfer plumbing automates chemistry change-over and maintenance.