Issue link: https://iconnect007.uberflip.com/i/1002143
54 PCB007 MAGAZINE I JULY 2018 and thick was good; the thicker the better. And now, you have the DI machines that are really bogged down; the differential in the thickness of the solder mask makes them much slower. Now the driving force is to make that solder mask as thin and as consistent as possible, be- cause it speeds up the direct imaging step. Matties: In terms of cycle time for the solder mask process, curing probably takes the great- est amount of time. Are there any improve- ments in cycle time in solder mask? What sort of advancement or reductions in cycle time are you seeing? Meeker: There have been a lot of attempts to reduce the cycle time in solder mask by de- creasing the time in the oven. A standard pan- el is tack-baked for about 45 minutes, and there have been a lot of attempts with infra- red, which could reduce that dramatically. IR has been only marginally successful, for a lot of reasons. A lot of people came out with in- frared drying systems, to try to speed up the bake. It's not been particularly successful in a lot of application sizes and thicknesses and types. You know, if you have 100,000 of the exact same panels then that makes it easier to do. But especially in the North American mar - ket where it's five of this panel type, and 10 of that one, it's really hard to adjust an infrared system to be successful; whereas, a thermal, convection-based system doesn't really care. That would be a challenge to come up with something faster in the oven. Matties: I was going to say, back in early days, systems like True Cure came out. They had reci- pes, but the variations were so many and so deep, that it wasn't a practical piece of equipment. Meeker: Yeah. True Cure is a good example, but there were 20 of them out there. I don't think any of them are still in operation. Matties: No, I don't think so. But today, with the IoT and the quantity of sensors and, look- ing at what GreenSource is doing with a lot size of one, it seems to me there may be oppor- tunities to reexamine that and see what's pos- sible. In a quick-turn environment, an hour or two in an oven is a lot of time. Meeker: That is true. And especially, if you look at the two processes, it's about a 45-min- ute tack-dry and about an hour final cure, so a two-hour cycle time. It's much easier to achieve something for the final cure because you're not trying to hit a target window. Tack dry, you've got to go 85°C plus or minus two degrees, or something. In final bake, it's just got to get hot enough to cure it. There's a much wider pro- cess latitude for final curing in solder mask, and I see that there's some new technology on the horizon that is somewhat promising. It's a much easier application. Matties: Is this something that the fabricators are asking for, or do they just accept the pro- cess as is? Meeker: No, they would like it. Saving any amount of cycle time is great. Most people, especially if you look in the North American market, are in the quick turnaround business, so if you can save an hour or two in cycle time, that's a huge thing. Matties: If a fabricator came to you and asked for the best advice you could give about sol- der mask, or the process of solder mask, what would that be? Lindland: Test the available options out there, which are probably spray, flatbed, and obvi- ously double-sided screen printing. Talk to the existing shops out there, see what they're do- ing, and then talk to us and we'll make the best recommendation based on what your needs are. You know, if you have 100,000 of the exact same panels then that makes it easier to do.