PCB007 Magazine

PCB007-July2018

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24 PCB007 MAGAZINE I JULY 2018 may not see any hot air leveling solder or wave solder, but it's still called a solder mask. Holden: That's what I mean. The solder mask does a lot more than just restrict solder now. Like you said, it's morphed into having all these other properties. Matties: One final question from me. What ad- vice would you give a fabricator regarding sol- der mask, if there's any open-ended advice ad- vice that you might offer? Tibbals: My two would be equipment mainte- nance and process control. Earl: I second that. Pre-clean for solder mask is a key process to give you the best adhesion capability that you can get from your solder mask. And as Shaun said, process control and equipment maintenance—control those pro- cesses, maintain those processes, and they help to look after themselves. Matties: Those were pretty quick answers. Is this a common problem out there? Tibbals: It would be inappropriate for us to walk in to a customer and say, "This piece of equipment is no good, and you need to change this." Even though we may think that, in re - ality that customer may not be able to invest in new equipment for each of those process- es. Our job then is to make sure that they get the best possible out of that equipment. And it is amazing what you can get out of a process provided you maintain a piece of equipment, you control the parameters, and have good monitoring systems. So that's really number one for us. If somebody were coming to us with a blank check and a clean sheet of paper and said, "How do I want to lay out my department and what equipment should I put in?" that would be a different answer. We could sit down and work with a customer within his budget to de- sign the ideal solder mask department. But, I'd never known that happen. It's a case of mak- ing sure we get the most out of what they've got. A lot can be achieved with training, main- tenance, and process control. Matties: It sounds like process discipline. Tibbals: It is. As I answer this question, oth- er factors come to mind. For years now, sol- der mask dams have been getting smaller. And that's because you need the registration toler- ance. The solder dam itself doesn't need to be smaller; you just need to make it smaller so you can allow for movement within the board, film and exposure process. If somebody's gone to direct image, and they've taken a part num- ber which had a 2-mil dam on it because it was being exposed through a piece of film, and now they're doing it with a direct imager, that dam no longer needs to be a 2-mil dam. That can go back to being a 4-mil dam, or possibly even a 5-mil dam because the direct image is going to put it exactly where you want it. It's not going to encroach on the pad. So what does that do? That gives you more process window for your exposure time. It gives you more process window for your developing conditions. Again, it's trying to encourage cus - tomers to re-think, when they put in a new pro- cess, what does that enable them to adjust and adapt which might have an indirect effect of widening your process elsewhere? And those are conversations we have with our custom- ers on a regular basis. Sometimes they can't do that because the end user won't allow them. Matties: Well, this has been very informative, you guys. Thank you so much. Goldman: Yes, thank you, we appreciate your time. Tibbals: Thank you. Earl: Thank you. PCB007 For years now, solder mask dams have been getting smaller.

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