Comparative compliance of representative lead designs for surface-mounted components

The author provides equations for the directional spring constants for common compliant lead designs on surface-mounted (SM) components. The lead configurations include the straight J-lead, dimpled J-lead, gull-wing lead, butt-lead, (I-lead), and S-bend lead designs. Elastic strain energy methods were applied to determine the effective flexural and torsional spring constants for each representative lead design. Lead stiffness evaluation was performed for different SM components tested using accelerated functional cycling and circuit-board dynamic bending. Comparative compliance data are provided for the chip-carrier J-lead designs in the Phase A IEEE Compliant Lead Task Force mechanical cycling test program. The solder joint cycles-to-failure statistics indicate that significant differences in attachment fatigue performance can be correlated with disparate lead compliance between the tested SM components. The structural models and strain energy formulation presented provide a generalized method for quantifying the compliance of common lead configurations. The resultant spring constants represent mechanical properties of the particular lead design and are independent of the SM package geometry and PCB (printed circuit board) interconnection details.<
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