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82 SMT Magazine • August 2015 we're seeing that being a much more important criteria: Ensuring it's a cleanroom-ready prod- uct before you take it out of the box. Matties: what sort of life expectancy should some- body expect from a stencil? Weissmann: In most cases, customers will change their designs more often than a stencil wears out. Sometimes you have some things that are very high runners and then they'll wear out. We have a customer that makes a set-top box, and they make about 40,000 a week and go through a couple of stencils a week to do that. Matties: it's important to take good care of every part of it— good housekeeping brings good product. Weissmann: Right, and to be careful with it. Stencils can be thin—some of them we make now are less than 1 mil thick. It's pretty easy in handling to drop those stencils and break them. Matties: how does the cleaning process work? Weissmann: There are two ways of cleaning stencils: One is during the use of the stencil; the underside cleaning is per- formed by the printer. The other is to clean the stencil afterward. We test our stencils with the different cleaners that are out there, the clean- ing solutions and so forth, to make sure that they're durable. The one caution I would give is that some customers have tried to turn up the heat on their cleaning solutions, and that can adversely affect the lifetime of a stencil. Matties: another variable, right? Weissmann: Right. Matties: it's all about the variable controls. Do you bring the internet of things to this part of the process, where you're measuring the wear of the blade or the surface of the stencil? Because this is where we're talking about going. this is the kind of thing that your customers would love to have, because it's going to save them from defects. even when you're talking about cleaning, it could mea- sure the temperature of the cleaning process and give all that feedback instantly. Weissmann: Or why not clean when you need to clean, instead of just randomly? Matties: exactly. Weissmann: Well, maybe we'll have a discussion about that at the next trade show. There's so much opportunity in the smart factory. We say SMT printing is as much art as sci- ence. That just means we need more science. I think one other thing I'd like to touch on is in compar- ing different stencil products, and it probably applies to any product, but we're most inter- ested in helping with stencils. If we look a little bit below the hood, what does a speci- fication mean? What does the thickness of a stencil mean? Is that the thickness at the edge of an aperture, the average thickness across, and exactly how positional accuracies are mea- sured, and so forth? So we would look at what it means to have each of these things, and we are planning to publish a set of open source specifications for different attributes of stencil measurement. By open source I mean that the design of the test stencil will be public, that anybody can extend it, like open source software. It can become an evolving standard faster than a standards body could evolve it; that would help customers de- cide what certain things mean. They'll be able to say, "Well, we want one that's measured this way." Once they determine their critical perfor- mance characteristics, they can specify that spec measured that way, as opposed to the way that a STENCILS: WHY THEY STILL MATTER continues IntervIeW the one caution I would give is that some customers have tried to turn up the heat on their cleaning solutions, and that can adversely affect the lifetime of a stencil. " "

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