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76 SMT Magazine • March 2015 Now that we're well into 2015, we can take a look back at the 2014 stencil market and explore our expectations for 2015. In general, 2014 was a solid year with year-over-year growth in vol- ume. Component sizes continued to get smaller, with 01005 components no longer a rarity, but a regular occurrence. Shrinking components have been accompanied by shrinking spaces between the components. This combination of small components and spacing constraints has con- tinued to challenge stencil manufacturers. Com- bine that with boards that contain both 01005 components and standard size components, and the stencil manufacturers have had to head back to the lab to find ways to accommodate these challenging parameters. In the solder paste printing process, the squeegee blade delivers solder paste into the stencil aperture as it travels across the stencil sur - face. When the board separates from the stencil the solder paste in the stencil encounters a com- peting process: solder paste will either transfer to the pad on the PCB or it will stick to the inside of the aperture walls. The smaller the area ratio (the area of the aperture opening divided by the area of the inside aperture wall; the generally ac- cepted guideline is area ratio > .45, depending on technology), the more difficult it is to achieve complete paste release. To achieve good paste release with apertures small enough to accommodate 01005 compo- nents, manufacturers have experimented with different stencil materials and technologies. The material the stencil is made from determines the size of the aperture and the smoothness and ex- actness of the aperture walls. The need to satisfy the more rigorous printing requirements of finer pitch components leads to a natural hierarchy of stencil technologies based on the applica- tion. The hierarchy advances through the tech- by rachel miller-Short phoTo STenCil llC ThE ShOrT ScOOP adapting Stencils to manufacturing challenges in 2015 ColuMn

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