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50 SMT Magazine • May 2015 Feature Fine pitch/fine feature solder paste print- ing in PCB assembly has become increasingly difficult as board geometries have become ever more compact. The printing process itself, tra- ditionally the source of 70% of all assembly de- fects, finds its process window narrowing. The technology of metal blade squeegees, with the aid of new materials, understanding, and set- tings such as blade angle, has kept pace with all but the smallest applications. Enclosed media print head technology has existed, and has been under increasing develop- ment, as an alternative to metal squeegee blade printing. Until recently, the performance of en- closed print heads had been comparable to the very best metal squeegees, but advances in en- closed print media technology have now made it a superior alternative to squeegee blades in virtually all applications. by michael L. martel SpEEDlinE TECHnologiES inC. Enclosed Media Printing as an Alternative to Metal Blades Introduction Solder paste printing through stencils has long been achieved using metal blades, or squeegees, which replaced polymer squeegee blades due to performance issues years ago. The move from screens to stencils, and then to smaller apertures and fine pitch land patterns, necessitated the change to metal, which offered superior printing performance characteristics. The evolution of PCBs in terms of the minia- turization of assemblies, components, and ever- finer feature print patterns has not slowed, and as a result continues to present ever-increasing challenges to the makers of assembly equip- ment and solder paste printing technology, nar- rowing the process window. Fine pitch and fine feature printing applications, e.g., 200µ–.50 area ratio (AR) and 150µ–.375 AR, have been pushing blade printing technology to its limits. Skilled printer operators using superior metal blade alloys, varying angle of attack, etc., can achieve acceptable results against the most challenging printing applications, but there are

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