Journal of SMT Article
Pb-Free Flux: A Chemical View of Reliability
Company: IBM Corporation
Date Published: 1/31/2015 Volume: 28-1
In light of these developments, we studied the board assembly process for high end server technology applications in detail, and focused on the increasingly important role that flux plays during the reflow of solder. As it relates to electronic assembly flux is simply defined as a reducing agent which prevents oxide formation on the surface of a molten metal (viz. solder). Recognizing that both 50 plus years of electronics research and development, and the use of eutectic SnPb solder will become obsolete as current exemptions to Restriction of Hazardous Substances, RoHS, and other legislations expire, we focused our efforts on Pb-free solders which are subject to increased temperatures and smaller process windows. The chemistry of flux and its affect on the flow of solder during joint formation will be evaluated using several analytical techniques including Differential Scanning Calorimetry, DSC, Thermogravimetric Analysis, TGA, and Surface Insulation Resistance, SIR, as we seek further understanding on how flux can sufficiently remove oxide formation during solder reflow. We will also examine what occurs after the redox reaction to render no-clean, NC, flux reaction residue acceptable and of no consequence to reliability.
Pb-free, No clean flux, flux activation and flux residue
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