What is Datum Reference
Datum reference refers to a set of features on a part that serves as a reference point or frame of reference for dimensional and positional measurements. It is a crucial concept in geometric dimensioning and tolerancing (GD&T) and is important in ensuring the accuracy and quality of PCB components.
The datum reference frame is established by selecting and specifying certain features on the part, which are used to lock down all degrees of freedom necessary for inspection and assembly. This frame creates a coordinate system and orientation that serves as a consistent and standardized reference point for evaluating the geometric tolerances specified in the feature control frames.
The datum reference frame typically consists of three mutually orthogonal planar datum features, which are carefully chosen and ordered to determine their precedence in controlling the degrees of freedom. These datum features, which can be surfaces or other tangible features on the part, are selected based on their functional significance and their role in the assembly process.
By establishing the datum reference frame, the PCB industry ensures that all measurements and inspections are performed relative to the same reference system, reducing errors and inconsistencies. It provides a reliable basis for evaluating the dimensional and positional tolerances of PCB components, contributing to the overall accuracy and functionality of the final product.