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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 printing process, and the variables involved when selecting the type of solder to use for specific applications.
Stephen Las Marias: What are the biggest challenges that your customers face when it comes to solder paste printing?
Mitch Holtzer: One issue that comes up frequently 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 process, some customers are able to manage this issue, but many struggle.
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 process?
Holtzer: The combination of flux and powder are key to a solder paste recommendation. 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.
Las Marias: What other industry trends are affecting the solder paste printing process?
Holtzer: The desire to eliminate wave soldering and less expensive components and laminate material has forced many end users to use lower melting lead-free solder alloys, using pin-in-paste processing.
Editor's Note: This article originally appeared in the June 2016 issue of SMT Magazine.