Flexible interconnect in 2.5D ICs to minimize the interposer's metal layers

In 2.5D ICs, the number of metal layers in the interposer contributes strongly to its manufacturing costs. Many systems implemented as 2.5D ICs include component dies, e.g. FPGA dies, that have flexible interconnect that increase connectivity options within the 2.5D IC. We present the first work to leverage flexible interconnect in FPGA dies within a 2.5D IC to decrease routing metal layers in the interposer. This is done by performing 3D global routing and reassigning flexible pins in the FPGA dies. In our experiments, we reduce the number of metal layers by up to 33% versus the number of layers required before reassigning flexible pins.