Issue link: https://iconnect007.uberflip.com/i/911509
22 SMT Magazine • December 2017 vast majority of consumer electronics are un- washed, and so no-clean technology is where we, as a paste manufacturer, concentrate our R&D efforts. As such, our goal is to create the lowest possible residue product with the high- est possible electrical properties or highest resis- tivity properties." Beyond that, everything else is product- component specific, he adds. QFNs, in partic- ular, are considered the biggest challenge in terms of voiding. "With water-soluble fluxes, we need to make sure that they're easily removed, because clean- ing under the same low standoff devices is pre- senting real challenges for manufacturers that must clean. There are applications that require cleaning, like RF signal circuitry, where the pres- ence of residue will affect the signal, or the ap- plication of coatings for environmental purpos- es or to contain the environmental robustness. It's all of these no-clean water solubles, the big ones, but then you go downstream from there and there are individual application require- ments that would further refine the product as the best for our customers' given application," says O'Neill. Designer Alloys One of the issues highlighted when it comes to choosing solder pastes is lead-free. Interest- ingly, despite the industry moving into the lead-free world and processes, there are still in- dustries that are using leaded solder, and are continually facing issues when it comes to pro- cess parameters. One industry in particular is the military market, which, according to Kan, accounts for about 40–50% of Lenthor Engineering's cus- tomer base. "I think it's not their choice, and the supply chain drives them into a lead-free world," ex- plains O'Neill. "Some of them will acquiesce, re- luctantly. Others will reintroduce lead into their systems. That's how some of them are address- ing it. In terms of the chemistry, most are clean- ing and most are using some sort of no-clean product or RMA product in combination with a soap or solvent cleaning process after assem- bly takes place, for a variety of reasons. A lot of stuff gets coated, so their concern is over-ad- hesion. They're profoundly impacted, and I've had both cases. I've had guys reballing BGAs. I have guys still buying tin-lead paste. I have guys transitioning over to lead free. A lot of military went to commercial off-the-shelf. My understanding is that in July 2019, unless you have applied for an exemption from the EU to manufacture circuit boards with lead, you must be RoHS compliant. I presume that somebody who is concerned about incorporating lead free into their process will apply for an exemption and will get one, so that's going to represent a very, very small portion of at least the Europe- an market. Now, the challenge becomes differ- ent countries having different regulations. Chi- na, it seems, is adopting more or less the EU regulations. If America was steering the ship, we don't have any regulations for lead-free, you can still use lead. So, if it's a U.S. military inter- est or concern, then they can be leaded, and I expect they'll continue to make leaded stuff." O'Neill says they have every intention to manufacture leaded solder. "But what I expect will happen is a lot like your software upgrades. You can have that old iOS that you were in love with and are afraid to migrate over to the new one, but eventually what happens is stuff starts to evolve around you to a point where stick- ing with the old stuff becomes impractical," he says. "You can't keep reballing forever. I had a customer that had an assembly and had 29 BGAs on it, and the BGAs were warranted by the manufacturer for three reflow cycles. That meant you could remove the lead-free balls, at- tach the leaded balls, reflow the first side, but you couldn't reflow the second side because that would have been four. They actually went lead free. That's kind of an anecdote as to how it sorts itself out." EQUIPMENT MATTERS IN SOLDER PASTE PRINTING " QFNs, in particular, are considered the biggest challenge in terms of voiding. "