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Fluxless Reflow Technology for Combination Fine-Pitch and SMT-Level Component Attach
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Authored By:Evan Griffith, MEM Indium Corporation NY, USA Xike Zhao, Phil Lehrer, David Heller Heller Industries NJ, USA SummaryMiniaturization continues to be a challenge for the electronics industry. One of the challenges in assembling ultra-fine pitch devices is the challenge of remaining flux residue after reflow; the decreasing standoff height of flip-chip devices makes residue cleaning difficult which can result in dendritic growth and poor compatibility with underfill materials. One solution to the residue cleaning problem is the removal of flux from the soldering process, referred to as fluxless soldering. Fluxless soldering alleviates many of the problems caused by using flux as a soldering agent, such as the residue problems, as well as eliminating voids caused by outgassing. There are a few common reducing agents which can be used in place of flux for oxide removal, one of these is formic acid vapor (CH2O2). While formic acid can act as a reducing agent in this process, there still exists a material need to hold devices in place during the reflow process. This paper will introduce a novel fine-pitch soldering material compatible with the formic acid reflow process. Fine-pitch device soldering in a formic acid environment is possible with the combination of reflow equipment and soldering materials. The objective of this study to be discussed in this paper is to determine a solution for component attach in a formic acid environment with the appropriate combination of soldering material and equipment. A particular focus will be placed on a material and equipment combination which will provide acceptable soldering using a low-residue solder paste for large components and a novel formic acid adhesive for fine-pitch flip chip components. Post-reflow residue, SIR performance, and solder joint cross sections will be discussed. In addition, the performance of the novel material will be discussed as a solution for the BGA ball attach process. ConclusionsIn this paper, a novel tacking agent for fine-pitch chip attach was introduced, and a combination of material and in-line formic acid reflow equipment was presented, showing equivalent performance when compared to a similar performance in pure nitrogen. A BGA sphere attach application was also presented. This combination of low-residue solder paste and tacky agent can prove a promising solution to customers wishing to assemble fine-pitch components or achieve a true no-clean build. Further development work is planned on a one-step fluxless solder paste solution for formic acid reflow, as well as a tacky agent with an activation temperature below SAC305 and other mid-temperature alloy reflow peaks. Initially Published in the SMTA Proceedings |
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