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24 SMT Magazine • December 2017 over. In my recent discussion with a jet print- er manufacturer, he said that while jet printers are not yet comparable to screen printers when it comes to volume, however, removing certain process steps in a jet printing environment will somehow make the overall cycle time near that of screen printing. But, in our recent survey on solder paste printing, majority of the assemblers who re- sponded said they are not using jet printers in their process. Among the key reasons highlight- ed are the cost of the printer, speed, as well as the need for a special solder paste, which is sig- nificantly more expensive and only have a few types to choose from. "As technology evolves, it may get there, but I don't know if it's going to be a one to one ratio where screen printing versus jet printing is going to be equal," says Kan. "I go to the IPC APEX EXPO show every year, and the technol- ogy improves each year. Everything's evolving, and things are getting smaller. The electronics manufacturing world is very competitive. In my opinion, it's good to have both in one envi- ronment. In our environment, we'll definitely take the advantages of both where, if we don't have a flat surface board, we can go ahead and use the inkjet, and if we do have a flat surface that we can tool up, we'll use the screen printer or a combination of both. For O'Neill, inkjet printing represents the next evolution of solder deposition technolo- gy. "It's certainly not there yet, in my opinion, but it could serve several very meaningful roles in a surface mount line, not necessarily displac- ing traditional stencil printing, but augment- ing it. In my opinion, you'll see SPI and jetting working in combination to provide addition- al volume and eliminate the need for steps and fancy stencils. So, you can manipulate the vol- ume of the solder paste on a board and make real-time corrections to solder past volume de- ficiencies, and that's a pretty exciting. Imagine now that you've got a jet printer on the SPI, it sees the missing solder deposit, and goes over and fixes it. That, to me, is where jet printing probably holds the most promise in the rela - tive short term, because it's very difficult to do a point-to-point solder application that can re- place the swipe of a stencil that can throw down ten thousand deposits in a single pass. I see jet- ting going in that direction, but I'm one voice in the world in this and one perspective, but I think it' s a viable technology that will definite- ly find its way into everybody's surface mount line over time." According to Kan, jet printing works very well in the flex and rigid-flex world because the thickness of the solder mask to pads varies. You have to 3D your fixture in a way that you get a flat level printing surface. "But sometimes, you can't get away with that. In some areas, you'll have 10 mils-thick of a flex circuit, and then in some areas, you'll have 62 mils thick rigid," he says. "It doesn't matter how you fixture your board, the different thicknesses that's in play that will prevent you from having a flat surface to print. Having jet printing can give you a lot of advantages, because jet printing is basically a nozzle depositing the solder paste onto individ- ual pads. Jet printing has it challenges as well when dealing with small pad size and aperture counts." For Stone, one of the problems with a jet printer is that it is cost prohibitive for a lot of customers. "People are talking about how they want a line to do low volume. If you think about it, the jet technology is awesome. It gives you an incredible amount of flexibility, it's ca- pable of doing the very fine pitch, the very EQUIPMENT MATTERS IN SOLDER PASTE PRINTING