Compliance metric for the S-bend lead design for surface mountcomponents, with application to clip-leads

摘要

New stiffness metrics have been developed from an upgraded S-leadstructural model that extends compliance evaluation capabilities to awide variety of commercial S-lead designs. By selectively eliminatinglead members, the generalized S-lead structural model can be used torepresent a broad range of common lead forms for SM (surface mount)components. The S-lead directional spring constants are given in aneasy-to-apply, algebraic format suitable for computer and spread-sheetevaluation. Compliance evaluation has been performed for a commercialS-bend clip-lead specifically developed for high-reliability SMinterconnection of CCCs (ceramic chip carriers) on organiccircuit-boards. Accelerated powered cycling of clip-leaded CCCs onepoxy-glass circuit-boards has shown that leads with diagonal stiffnessin the nominal range of 10-40 lb/in provide a comparatively high marginfor SM attachment reliability. The diagonal stiffness of S-bend leaddesigns can be tailored by using the upgraded compliance formulation tooptimize the contour and critical dimensions