Comparative Compliance of Representative Lead Designs for Surface Mounted Components

The long-term solder attachment reliability of leaded surface mounted (SM) devices is controlled in part by the lead compliance. Lead stiffness characterization is then an essential feature of any program aimed at surface mount solder joint reliability evaluation. Structural models have been developed for common lead designs, including the straight J-lead, dimpled J-lead, gull-wing lead, butt-lead (I-lead), and S-bend lead configurations. Elastic strain energy methods were then applied to determine the effective flexural and torsional spring constants for each representative lead design. 

SM device solder attachment reliability assessment is typically accomplished through accelerated temperature, powered, or mechanical cycling of test vehicles. Lead stiffness evaluation has been performed for different SM components tested using accelerated functional cycling and circuit-board dynamic bending. Comparative compliance data are provided for the PLCC 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.