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Process Considerations for QFN Voiding in SMT Electronics Assembly (1/3)

Phil Zarrow: This is part one of a three-part series. This video is for anyone interested in design of experiment aspect of Avoid the Void™. 
 
Brook, with all the discussion regarding Avoid the Void™, what about setting up the design of experiment? For example, what are some of the potential variables?
 
Brook Sandy-Smith: I would break the potential variables up into three different families: material variables, process variables, and then design variables. For material variables these would be things like Flux Type, the alloy that's chosen, and the powder size, and then metal load can also have an effect. For process variables, this like your printing parameters, how you place the component, and your reflow profile. Your design parameters are usually a little more solid. It's less likely you'll be able to change them, but those would be things like your pad design, whether you have vias and how they're treated, your board finish, or your stencil design and thickness.
 
Phil Zarrow: Right. In practice when you're doing an evaluation, how do you limit it to, say, two variables?
 
Brook Sandy-Smith: Well, for instance with the materials since we're a solder paste company we're always testing lots of different materials and solder pastes. We try to test one flux, maybe, with lots of different alloys to see how the alloy plays a role, or if we're testing the powder size, we use different types of powder and then also vary the metal loading to keep the same rheological properties. Or, it would be the same alloy and lots of different fluxes. There are lots of different combinations. When testing process variables, you might choose one or two benchmark materials or three benchmark materials, and then change your process variables to see how that affects the voiding overall. We also use commercially available test vehicle, so we're always keeping the board the same, it's always an OSP finish, and we always have the same kind of component so that we can go back and compare previous studies to current studies.
 
Phil Zarrow: Brook, you've done a lot of extensive work in this area. Where can we find more information, papers, and videos on the subject?
 
Brook Sandy-Smith: You can contact us at www.indium.com or you could contact me directly at bsandy@indium.com.
 
Phil Zarrow: Great. Brook, thank you so very much.
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