Issue link: https://iconnect007.uberflip.com/i/806706
16 SMT Magazine • April 2017 inkjet printing or solder mask printing in the PCB area. I don't have a lot of experience with it, but any kind of jetting like that, be it inkjet, solder mask, or solder, really has not met the needs of volume manufactures to be cost-effec- tive, not yet. It's for the prototype or high mix. Las Marias: Does solder paste selection or qualifi- cation still matter today despite the standard sol- der types used in certain applications? Holden: Yes, because they're constantly improv- ing solder paste and things like that. You're kind of always evaluating tweaks and minor im- provements to see what it does, especially when one of our focuses in the past has been voiding and the micro-voiding you had with lead free. We haven't rejected products but we'd liked to eliminate it. Those are constantly minor tweaks in the formulation of the solder paste and the refill profile. Las Marias: I understand solder voiding is still a big issue in the industry. Cathy, how do you tack- le voiding? Cox: We go with Indium solder paste. We have a really good connection with them. They help us through a lot of our issues with inci- sions, voids, stuff like that. We have been try- ing a few things here in our shop with chang- ing the amount of paste that we put on a sten- cil, removing the mask around the pads so that the air can actually escape between the compo- nent and the solder pad. We've seen some suc- cess with that. The IPC standard keeps getting more and more vague on voiding under QFNs or even in through-hole components. We took it upon ourselves to kind of set our own stan- dards, making sure that we have anything un- der 25% under a component or within a barrel fill. With our window pane and with reducing the solder mask around the pads, we've been successful in minimizing voiding to about 25% with our QFNs, BGAs. Our biggest struggle is making sure that if you call a component out, your footprint should actually meet what the manufacturer of the component recommended. We do run into quite a few times here where the customer will call out a part, and it doesn't quite fit, which means that you don't get proper solder joints, you don't get the heel fillet that you want, or the side joints that you want. Then they don't meet IPC standards. It's a struggle to keep going back and forth between the customer and the manu - facturer trying to make sure the component still functions. So verifying that you're setting your board up for success with proper pad size would be a good thing for customers to know. Las Marias: What else do you think should the readers know more about when it comes to solder- ing? Holden: Some of the effects that different for- mulations of lead-free solder paste has when it's reflowed, in terms of interacting with final fin- ish and interacting with land size, is that they don't spread like tin lead, and we find smaller pad sized footprints because it's a stronger joint than tin lead. We've always watched very close- ly the Japanese and the JPCA standards, because they've been using lead free for 10 years longer than North America. Since a third of all of our output goes to Japanese automakers, we've got a lot of cooperation with Nissan, Honda, and Toyota about what they recommend. Las Marias: Standardization is still an issue? Holden: It's all a point of view. Like I said, we're such as big industry that I've been talking about automotive electronics, which were going for a 15-year useful life—and that's a lot different than a mobile phone. We virtually test 100% of every lot because the Japanese or the German THE COMPLEX WORLD OF SOLDERING