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PCBD-Apr2017

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April 2017 • The PCB Design Magazine 19 of course, is that those treatments tend to be transitory or time-based. So it basically changes the chemical surface or creates available bond sites on the surface of the material, but if you don't do your coating or laminations or sol- der mask very shortly after that process, it will deactivate in open atmosphere. So you've got a short time window to take advantage of that treatment. Matties: I was talking with Alex Stepinski over at Whelen Engineering. He said by not letting your work queue up, it actually saves so much pro- cess time and, exactly what you're saying, it just makes good sense to not let your boards queue up and sit around. You're making that case too. Andy Shaughnessy: Gerry, we've talked to these laminate suppliers over the years and they've said recently that they're working on the next sort of midway high-speed material, something that has the pros of PTFE without any of the cons as far as manufacturability. Are you all seeing any more of these sorts of high-speed laminates that have the processability of FR-4? Partida: Yes. Megtron 7, Megtron 6, Isola's As- tra, I-Tera and Tachyon. They're being used and they're performing very well. It also has 4000- 20 I think, or 4350-20, that seems to be not as popular as the other ones but it is getting some traction. Shaughnessy: That's good to hear. They were real- ly pushing for this. In the last couple of years, they said they had many people that just automatically would ask for PTFE and would over-constrain and would end up making the boards twice or three times more expensive. Partida: Yeah, that's when you lose big in Bel- lagio. Matties: Go outside and watch the water show. Is there anything else that we should be talking about that we haven't covered yet regarding high- speed materials? Partida: I think one of the things you'll see more in the high-speed materials is a lot more critical GD&T (geometric dimensioning and tolerancing). They'll have very critical etch launches that they line up to tooling for other features. For the internal cut-out for an etch launch they have a very smaller tolerance than you normally see in a printed circuit board so those sometimes can be a challenge. You have to use precision rout machines so you would line up to the etch features before you do an etched, routed feature or a cut-out on a board based on where the etching pattern is at so that you're within a 2-mil window in some cases. That's getting pretty tight. Menning: On the flex side, it's not necessar- ily for high-speed, but a lot of times we'll end up doing extended length circuits north of 100 inches that are flex and obviously regis- tering a traditional coverlay layer that's routed to that image pattern is pretty difficult. One of the tools that we're using more and more often now is we'll lay coverlay over the whole pattern and we'll use a local registra- tion feature near the critical areas of the flex and we'll laser ablate the coverlay off and then use a plasma to plane off the carbon. That way we've basically taken away the need for a scale factor and the coverlay will to match the etched feature, much like Gerr y was talk - ing about. Matties: A lot of moving parts in all of this, that's for sure. Partida: That's the challenge, isn't it? Matties: You know, there are just so many vari- ables that it's hard to think that people can pro- duce quality boards time after time after time. Goldman: I would guess it's also a moving target because you don't get to sit back and say, "Well, we're set for the next year with this particular style of something or other or this material." Every- thing's moving forward all the time. Partida: Right. The usage of RF and the demand for it, especially the military and even commer- cial, it's just going to keep growing in a very big way. FABRICATORS SPEAK OUT ON HIGH-SPEED MATERIALS

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