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26 SMT Magazine • December 2017 EQUIPMENT MATTERS IN SOLDER PASTE PRINTING small parts, and you don't have to order sten- cils," says Stone. "But at the same time, there's a cost involved in getting the equipment to start. You could buy a lot of stencils for the difference in cost from a good automatic printer to a jet- type printer. The other thing is the jet printer is going to require a lot more maintenance, and it's going to require that you use the higher cost solder paste rather than the typical Type 4 or Type 5. You're going to be up there in Type 5 or Type 6 solder pastes, so your cost of those goods is also going to go up." O'Neill agrees. "Then, we have the reflow is- sues downstream, so there are a lot of consider- ations. Matt mentioned the possibility of it be- ing one to one with screen printing, and I don't see it being a one to one any time soon." Essential to Success As mentioned earlier, solder paste printing is the source of the majority of defects in the SMT process. One very important factor to ad- dress the issue is selecting a very good stencil printer that's going to match the types of chal- lenges that users are going to have in the assem- bly process, according to Stone. "The printer is not the part where you want to go cheap," he says. "A good printer is essential to success, as well as having a good reflow oven." SMT Scientists at the National Institute of Standards and Technology (NIST) have taken a new step for- ward in the quest to build quantum photonic cir- cuits. The quantum circuit architecture devised by the team is among the first to combine two dif- ferent types of optical devices, made from differ- ent materials, on a single chip—a semiconductor sour ce that efficiently generates single particles of light (photons) on demand, and a network of "waveguides" that transports those photons across the circuit with low loss. Maximizing the number of photons, ideally having identical properties, is critical to enabling applica - tions such as secure commu- nication, precision measure- ment, sensing and computa- tion, with potentially greater per formance than that of ex- isting technologies. Developed by Marcelo Da- vanco and other NIST research- ers along with collaborators from China and the U.K., the ar- chitecture employs a nanome- ter-scale semiconductor struc- ture called a quantum dot— made from indium arsenide— to generate individual photons on the same chip as the optical waveguides—made from sili- con nitride. Such hybrid circuit architectures could become building blocks for more com- plex systems. Hybrid Circuit Combines Single-Photon Generator and Efficient Waveguides on One Chip