3D-IC is a solution to achieve lower cost and higher performance as the transistor density doubles every 18 months following Moore's law. In recent years, Integrated Fan-Out Wafer-Level Chip-Scale Packaging (InFO WLCSP) is one of the most promising packaging technologies for 3D-IC. In InFO WLCSP, there are some inter-die interconnects. We cannot access these interconnects directly. Therefore, it causes 1-2% test coverage loss. As a result, a built-in self-test (BIST) or other design-for-test (DFT) methodology is necessary to test these interconnects. It is easy to detect open defects and short defects leading to large leakage currents with conventional test methods. However, defects leading to small leakage currents are hard to detect, so we focus on these defects in this work. In this paper, we propose a scheme to measure the small leakage current of these inter-die interconnects. The scheme uses IEEE 1149.1 boundary scan interface. Because boundary scan is a well-adopted standard, the scheme can be integrated into any electronic product easily. Beside four mandatory terminals, we add a reference current input. Users can apply current to compare it with the leakage current. For the input EBSC, two OR gates, a MUX, and a current digitizer are added and it is compared with the conventional BSC. A test chip is implemented to verify our design, which uses the one-polynine-metal (1P9M) 90nm CMOS technology. Measurement results show that the proposed scheme is able to measure the leakage current of the interconnect. In addition, with the dynamic range of 128nA, the current digitizer has 6-bit resolution.