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Due to increasing integrated circuit design complexity, engineering change orders (ECOs) have become a necessary technique to resolve late-found functional errors and/or performance deficiencies. To fix timing violations, gate sizing and buffer insertion are commonly used in postmask ECO. These techniques, however, may not be powerful enough, especially when spare cells are inserted to balance between functional and timing repair capabilities. We propose a postmask ECO technique, called TRECO, to remedy timing violations based on technology remapping, which also supports functional ECO. Unlike conventional technology mapping, TRECO performs technology mapping with respect to a limited set of spare cells and confronts dynamic changes of wiring cost incurred by selection of different spare cells. With a precomputed lookup table of representative circuit templates, TRECO iteratively performs technology remapping to restructure timing critical subcircuits until no timing violation can be further removed. Experimental results on five industrial designs show the effectiveness of TRECO in ECO timing optimization and in timing-aware functional ECO.