Multi-layered, complex mmWave Device Interface Boards (DIBs) are becoming more common as devices start to utilize the 5G millimeter-wave frequency bands and the full capabilities of Teradyne’s microwave extension instrumentation. This complexity causes even the slightest manufacturing variations to result in mmWave performance degradation. A Vector Network Analyzer (VNA) checks to see if this performance degradation exists but does not reveal where the degradation occurs or what could be causing it. Because of this, a need for more diagnostic tools has surfaced. Luckily, a tool often used for high-speed digital trace analysis can help solve this issue: Time-Domain Reflectometry (TDR). By incorporating TDR into your mmWave DIB evaluation process, impedance discontinuities can be precisely found quickly and cost-effectively. This presentation will discuss the benefits and limitations of Time Domain Reflectometry in the context of examining mmWave structures.