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10 SMT Magazine • June 2016 Las Marias: From your perspective, how do the tighter tolerances and even narrower PCB lines and spacing impact the solder paste printing process? Holtzer: Modern solder paste formulations and smaller particle size powder has been able to keep up with features like 0.3 mm pitch BGAs and 01005 components down to an area ratio of 0.5. Reflowing large and tiny deposits of paste can be a bigger issue than printing. Las Marias: What about solder pastes? What are the variables involved when it comes to selecting the appropriate solder paste for the printing pro- cess? Holtzer: The combination of flux and pow- der are key to a solder paste recommenda- tion. Sometimes customers ask for type 5 and type 6 powder when they don't really need the fine feature print capability afforded by these PSDs. by Stephen Las Marias I-CONNECT007 Mitch Holtzer, Alpha Assembly Solutions' global director of customer technical support, and expert columnist at SMT Magazine, talks about the impact of solder pastes on the print- ing process, and the variables involved when selecting the type of solder to use for specific applications. Stephen Las Marias: What are the biggest chal- lenges that your customers face when it comes to solder paste printing? Mitch Holtzer: One issue that comes up fre- quently is managing the paste bead height. Too large of a diameter roll can cause paste to get hung up in the squeegee holding mechanism, and customers mistake this for paste rheology issues. Depending on the paste delivery pro- cess, some customers are able to manage this issue, but many struggle. The Solder Paste Factor in Printing FEATU RE I NTE RVI EW

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