Experimental measurements of surface mount component lead stiffness

An approach to the experimental determination of lead stiffness (the straddle board method) has been used to assess surface-mount package leads of actual service dimensions. Correlation was observed between the experimental data and trends of predicted values from the linear elastic beam model. However, the simplified model cannot be used to predict actual performance. Current 3D finite-element analysis shows good correlation and predictive capability. Lead stiffness values of PLCC (plastic leaded chip carrier), cerquad (ceramic quad flat pack), and PQFP (plastic quad flat pack) packages have been measured. Transverse values exceed lateral for PLCC and cerquad packages. Cerquad packages exhibit lower stiffness than PLCC. This behavior can be attributed to the longer shoulder length of the cerquad lead and thinner lead thickness, which offsets the effect of the elastic modulus. PQFP leads are in order of magnitude more compliant than the 50-mil pitch J-lead configuration due to the smaller lead cross section and the gull-wing configuration. The board-level solder-joint reliability of PQFP packages is expected to exceed that of the established PLCC component because of the increased lead compliancy.<
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