SMT007 Magazine

SMT-Nov2014

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56 SMT Magazine • November 2014 abstract With increasing demand for the use of Pb- free solder materials coupled with an increasing requirement for halogen-free solder paste for- mulations, some market sectors are experienc- ing several challenges using standard SnAgCu (SAC) halide-free solder materials, especially in electronic assemblies for automotive products experiencing harsh operating environments such as high operating temperatures, increased thermal cycling conditions, high levels of vibra- tion and contact with liquids such as moisture and lubricants. For example, in automotive 'un- der the hood' conditions, temperatures easily exceed 125°C and can cycle lower than -20°C. The reliability required to survive these harsh conditions is often greater than standard SAC solders can provide. In this paper, the perfor- mance of a specifically designed Pb-free solder alloy for increased reliability in high tempera- ture thermal cycling is discussed. Reliability can also be impacted by no-clean post reflow residues adjacent to solder joints. These may potentially interact with other sur- face materials causing corrosion issues or lower insulation resistance. With halogen-free elec- tronic assemblies arguably becoming more fa- vourable than halide-free—even within some automotive manufactures—solder paste manu- factures are now faced with the challenge of formulating halogen-free fluxes which can also demonstrate high reliability. While removing the halogen from a material is not difficult, re- placing it with an activator set that can deliver a wide reflow process window whilst retaining or increasing reliability is a significant challenge. The paper also documents the challenges and breakthroughs in developing halogen-free or zero-halogen solder fluxes that are compatible with the Pb-free alloy specifically designed for higher reliability. introduction Reliability testing of standard SAC-based al- loys as a direct comparison to Pb-containing materials as a response to the implementation of the RoHS directive during the mid-2000s has been well documented [1,2,3] . The results of the testing broadly concluded that little differences High-Reliability, Pb-free, Halogen-free Solder arTiCle by ian J. wilding & gavin J. Jackson heNKel lTD, uNiTeD KiNGDoM

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