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8 SMT Magazine • April 2015 heat activation/decomposition of the chemicals in the flux, commonly known as "activators." The latter is generally known in the industry, but is rarely taken into consideration for reflow profiling in SMT assembly. Optimization of a reflow profile often fo- cuses on mitigating defects such as voiding, tombstoning, graping, slumping/bridging, etc. However, little thought is given to the reflow profile's effect on the electrical reliability of the no-clean flux residue. Because of the wide varia- tion in size and thermal density of SMT com- ponents and PCBs, achieving a reflow profile that equally heats the entire assembly can be challenging and often impossible. The tempera- ture under a large component, such as a BGA, An estimated 80% of all SMT assembly in the world is performed with a no-clean solder- ing process, largely due to the predominance of consumer electronics. The continuing trend of increasing miniaturization that dominates modern electronics devices requires no-clean flux residues to be as benign and electrically resistive as possible. Solder pastes with an IPC J-STD-004 [1] classification of ROL0 or ROL1 rely heavily on two basic mechanisms to render the flux residue as "no-clean": (1) the encapsulating properties that the rosin provides and (2) the by Eric Bastow indiuM corp. reflow Profiling on the electrical reliability of no-clean Solder Paste Flux residues FeAture

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