IEC 61188-6-2-2021 pdf Circuit boards and circuit board assemblies – Design and use – Part 6-2: Land pattern design – Description of land pattern for the most common surface mounted components (SMD)

The assumption is that the following dimensions have the necessary and sufficient accuracy: a) component tolerance; c) printed board fabrication tolerance; d) placement tolerance. NOTE Further information on the effect of the above dimensional tolerance on the land pattern can be found in Annex A of IEC 61188-6-1:2021. There are two classes of land pattern relating to the assembly limitations of components and the intended soldering process: • land pattern for wave soldering – For low density product applications, land patterns are designed to accommodate several types of wave soldering applicable to surface mounted components. • land pattern for reflow soldering – The land patterns generated for all device families shall provide a robust solder attachment condition for reflow soldering. 6 Requirements 6.1 General requirements The calculated land pattern geometry for an electronic component can be different depending upon the type of soldering process to be used. Wherever possible, land patterns should be defined in such a manner that are transparent to the attachment process being used. Land pattern designers can use the information contained herein to establish standard configurations not only for manual designs but also for computer-aided design systems. Whether parts are mounted on one side or both sides of the board, subjected to wave soldering, reflow soldering, or other type of soldering, the land pattern and part dimensions should be optimized to insure proper solder joint and inspection criteria. Although patterns are dimensionally defined and since they are a part of the circuit board geometry, they are subject to the reducibility levels and tolerances associated with plating, etching, assembly or other conditioning process.
6.2.3 Courtyard excess Since courtyard excess is influenced by equipment performance, part size accuracy, provision for rework, etc., it should be desirable for the user to decide it. Therefore, in this document, courtyard excess is indicated as a reference value in Annex C. 6.2.4 Rounding factor The rounding factor of the land pattern dimension should be 0,01 mm in general. However, if the rounding factor exceeds 10 % of the dimension, the rounding factor can be decreased to 0,005 mm.