Comparison of predicted and measured lead stiffnesses of surface mounted packages

A comparison was made of predicted and measured values of lead stiffness for selected surface-mounted packages. Excellent agreement was found in all cases: 68- and 44-lead plastic leaded chip carriers (PLCCs) and cerquads (pressed ceramic quad flat pack); and 100-lead plastic quad flat packs (PQFPs). Predictions were based on the 3D elastic beam finite-element option of ANSYS, with lead geometries taken from design drawings and lead elastic properties from material specifications. Measured values were taken from straddle board test data. In these tests, the board is straddled on both sides by packages surface mounted by only their lateral or transverse leads so that lateral and transverse bending effects can be measured independently. The results point out the importance of low stiffness lead design in minimizing solder-joint deformation. >