Issue link: https://iconnect007.uberflip.com/i/989774
18 SMT007 MAGAZINE I JUNE 2018 are some instances when jet printing is used, depending on the design of the flex circuit and the different thicknesses of the flex circuit. "There are times where we used the tradi- tional printing and then in addition we would use jet printing. A combination of both," says Matt Kan, EMS manager at Lenthor Engineer- ing. "For example, you have double-sided components close to a stiffener, and that area, the stiffener or the rigid portion, is higher than the pads. So, you can print everything else traditionally. But in those areas where it's so close to the stiffener, you can't bend the flex, so you would have to opt to your jet printing. Or, if you don't have a jet printer, you may have to deploy hand soldering." Kan adds that the speed of jet printing will impact flex circuit assembly from the paste printing standpoint, but he says he doesn't see jet printing taking over the whole process any time soon. "From an equipment standpoint, the options are very limited," says Wettermann. "Mydata [Mycronic] certainly is one of the drivers there, ASYMTEK has a version. Making it more ubiq- uitous will allow you to use different kinds of either solder paste or conductive inks, and not just specific ones. That's a whole differ- ent engineering problem, but that would be advantageous for flex assembly if that printing problem were to be solved, and inkjet might be one of the ways. "The only other thing I would add to that part of the discussion is that we do a lot of syringe dispensing using robotics, and then we do some pin transfer when the devices are very small. We seem to be able to control solder paste volume a little bit better than syringe printing, when that's the case." Depanelization Another topical area that is considered a big challenge when it comes to flex circuit assem- bly is depanelization. According to Wettermann, most of these circuits are not the typically large such as 8" x 12" or 12" x 14" rigid boards. "Most of the time, they're multiple up flex circuits on a panel, part of one assembly. And the customer at the end of the day needs to put it into a housing, or we're putting it into a little hous - ing, or doing some other secondary operation to it. But now, how do we depanelize—which is also a misnomer when you talk about flex, but how do you get individual circuits out of the multiple up panel? There are many cases where you have multiple kinds of mate - rial that we need to cut through or separate from the skeleton to singulate the individ- ual assemblies. It's not just simply Kapton; it could be Kapton and copper, it could be Kapton, copper, and a laminate of some sort; the list goes on. Again, we're trying to depan - elize essentially a giant noodle, and turn it into little noodles. This depanelizing opera- tion on its own is very challenging; whereas in the rigid world, there are lots and lots of options for depanelization—breakouts and routing and laser scribing, etc.—while in the flex world, there are fewer options. In addi - tion to the other problems that we already talked about—the three-dimensional nature, the multiple types of materials, and the lack of rigidity—singulating the circuits is also very challenging." To address this issue, Wettermann says lasers are commonly used to depanelize. "We have five lasers here at Lenthor," says Kan. "We determine how we depanel- ize upstream where, depending on the design, for rigid areas we pre- score both sides, leaving about 12-, 16-mils mate- rial thickness. There are times when we do a flex tab, leaving just the mate- rial of the flex circuit, and then we can just come in