Heterogeneous reconfigurable platforms with tensor cores, suchas AMD ACAP, are increasingly adopted for deep neural network(DNN) inference due to their high throughput and flexibility. How-ever, their suitability for microsecond-scale inference on small prob-lem sizes remains underexplored. In jet-tagging applications inhigh-energy physics, inefficient on-chip communication and largeinter-layer latency prevent existing frameworks from meeting the1-𝜇s latency budget. Moreover, hardware overheads such as syn-chronization and VLIW processor prologue are often overlooked,making it infeasible to optimize accelerators correctly. To addressthese problems, we propose µ-ORCA, a customized heterogeneousaccelerator framework for ultra-low-latency model inference. µ-ORCA enables direct inter-layer communication between DNN lay-ers on the AIE array, instead of using shared memory tiles or FPGAfabric. Moreover, a 512-bit/cycle cascade connection is applied in-stead of a 32-bit/cycle DMA connection. µ-ORCA also provides anoverhead-aware performance model that adapts to different NNlayer sizes, and conducts design space exploration to optimize end-to-end latency. µ-ORCA supports MLP and DeepSets models withnon-MM kernels, including bias, ReLU, and global aggregation onAIE. We evaluate µ-ORCA on the AMD ACAP VEK280 platform.Experimental results show that µ-ORCA achieves average latencyreduction of >1.70× and >1.83× compared with different state-of-the-art ACAP frameworks, and achieves 0.93 𝜇s latency for a 6-layerreal-world DeepSets model, satisfying the latency budget. We opensource µ-ORCA at https://github.com/arc-research-lab/u-ORCA.