mmWave frequency range, not only coax cable, but also RF trace on board characteristics is affected to measurement performance and accuracy. Typical DUT circuit in RF, one side is with RF connector, another side is open-ended. Simple way of RF path loss in DIB is, measuring double length of RF trace and calculation of Bisect, simple scalar math is no issue, however if calculation on vector level, having magnitude error at closing 0 or +/-Pi range in phase. RF instruments of UltraFLEX and UltraFLEX plus have OSL (Open-Short-Load) is as standard calibration. However, OSL calibration is difficult to measure RF trace on DIB, especially, one side open-ended line. When measuring this kind of RF trace line on DIB, customized OSL calibration standard kit is required for each device and package type. TRL (Thru-Reflect-Load) calibration does not require precision calibration standard as like OSL calibration. TRL calibration is consist of some different length RF trace line and a reflect (open or short) line is made in DIB. This calibration standard is able to be made by DIB at same time. In same DIB or separately as coupon board. This paper will cover topics which are about fundamentals, what is advantage, evaluation result and also challenging parts will be explained as well as issues that arose during design and testing.