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Fixed-outline floorplanning, which enables hierarchical design, is considered more and more important nowadays. In this paper, a novel SA-based Fixed-outline Floorplanner with the Optimal Area utilization named SAFFOA is introduced to improve the total wirelength. The basic idea is to build and solve a group of four quadratic equations in four variables iteratively, which can handle the fixed-outline constraint of any aspect ratio. A new topological representation called Ordered Quadtree is then custom-made for this basic idea to facilitate its integration into SA iterations. After the fixed-outline constraint with 100% area utilization is achieved, we will solve the tradeoff between the chip area and wirelength and thus concentrate on the latter in SA process. Experimental results show that the chip wirelength is decreased by about 16.8% and 8.6% on average, compared with two previous fixed-outline floorplanners on soft modules, which are both proved to be better than Parquet. Besides, our method is still competitive on the wirelength, even if compared with some leading-edge outline-free floorplanners. At last, Local Refinement is also adopted to guide the SA process and reshape soft modules to meet the constraint on their aspect ratios (ARs). With its help, SAFFOA can still generate feasible floorplans with no deadspace under a strict AR constraint such as [0.5,2].