Issue link: https://iconnect007.uberflip.com/i/1002143
18 PCB007 MAGAZINE I JULY 2018 Tibbals: That's not an area we've studied. The curing time is between 30 and 60 minutes at 300°F. Currently, that would remain about the same for inkjet. One of the reasons why the time is longer is because ovens take time to ramp up to temperature, particularly if it's a conveyorized process; there's a ramp-up stage and a cool-down stage. So, we have to make sure that we've got adequate time at tempera - ture. It is also critical that we ensure the solder mask meets the demands that are required of it now, but also are required of it in the future. And to achieve that, we need to make sure we get the correct crosslinking to take place. If we try and speed that up, the danger is that the sol - der mask will not hold up well to subsequent chemistry and its field requirements. Trying to reduce the curing time by 15 or 30 minutes be- comes a false economy to a certain extent. Matties: In a meeting earlier, they were report- ing times of an hour and 45 minutes from tack dry to final for curing solder masks in a quick- turn environment. Tibbals: If you look at the solder mask process, then the tack dry time alone could easily be 60 minutes in an oven. With inkjet, we would eliminate that processing time because after jetting, the boards go straight in to final cure. Matties: You eliminate 50% of the cycle time right there. Tibbals: Oh, you've eliminated tack dry, you've eliminated exposure and developing. Overall, theoretically you're eliminating at least an hour from the process. But in reality you save a lot more time. With current photoimageable sol- der mask boards you take them out of the oven but they have to cool down before you can ex- pose them. This means they've got to stabilize in the exposure room. If you're doing conven- tional exposure, then you've got to make sure the film is ready and then wait for existing jobs to be completed to avoid unnecessary set-up changes. After that, they would need to be de- veloped and probably inspected. So what the- oretically could be done in the space of may- be an hour, an hour and a half, generally takes longer than that, even if they're being pushed through for a quick-turn job. Whereas with inkjet, you jet the two sides, and you go straight to final bake. Then de- pending on your ramp-up and your final cure oven, one hour to one and a half hours lat- er, you've got a finished solder mask pro- cess. Some of the inkjet machine suppliers are talking about solder mask and legend be- ing done in the same process. This allows even more cycle time to be taken out of the process. Matties: You'd think there would be a lot more demand for this technology to be online sooner than later, with the benefits you're describing. Figure 2: Left, Clive Landells with Chris Wall: screen print solder mask R&D in the 1980s; right, Clive Landells: inkjet solder mask R&D in 2018. A lot more has changed than the hair colour!