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74 SMT Magazine • December 2015 by Steven Grabey HERAEuS ElECTRoniCS New technologies in the printed electronics industry have fostered an increased interest in low-temperature polymer thick film products. Industry expectations are demanding that low- temperature products perform at the same level as their high-temperature counterparts, includ- ing high reliability, strong adhesion, and sol- derability with lead-free solders. Much of the shift to lead-free solders is due to environmental concerns and legislation that has surfaced over the past 15 years. Tradition- ally, it has only been possible to use leaded sol- ders for soldering to polymer-based thick film conductors. While using lead-free solders is beneficial both to the industry and the environ- ment, they pose challenges during processing. The high temperatures required for lead-free soldering generate a harsh environment that is too severe for polymer thick film pastes to sur- vive. Using new Substrates As the electronic industry moves towards flexible electronics, they are realizing the bene- fits in using substrates such as treated glass and aluminum that require a low-temperature-pro- cessing, polymer thick film. These materials not only offer a cost-effective approach to building complex, integrated circuits, they also provide a viable option to manufacturers dealing with the new demands of substrates that cannot handle temperatures higher than 500°C. Polymer thick film materials have the ver- satility to be engineered depending on sub- strate and preferred application method such as screen printing, stencil printing, dispens- ing, dipping, and roll-to-roll printing. For tra- ditional thick film materials, additive process- ing has always offered benefits including ease of use, simple design changes, and the ability to manufacture patterns from simple circuits to intricate designs. The addition of polymer thick film to this category not only continues to have these listed advantages but also brings new gains such as: low temperature processing, quick-curing steps, and the ability to offer many of the same ben- efits as high-temperature thick film material without the need for the traditional firing step. Despite the known advantages for polymer thick film materials, they are not as widely ac- cepted in the industry as equivalent alternatives to their standard high-temperature thick film Low-temperature thick Film Pastes Permit Lead-Free soldering ArTiCle

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