US EPA

2171052 

Journal Article 

COMPLIANCE METRICS FOR THE INCLINED GULL-WING, SPIDER J-BEND, AND SPIDER GULL-WING LEAD DESIGNS FOR SURFACE MOUNT COMPONENTS 

Kotlowitz, RW; Taylor, LR 

1991 

Yes 

IEEE transactions on components, hybrids, and manufacturing technology
ISSN: 0148-6411 

14 

4 

771-779 

WOS:A1991GR72800018 

Lead compliance is a critical parameter in the optimized design and interconnection reliability of surface mount (SM) leaded components. Compliance metrics have been developed for the inclined gull-wing, spider J-bend, and spider gull-wing lead designs commonly used on active SM components. A wide variety of plastic and ceramic SM devices have compliant gull-wing leads for circuit board interconnection. Thermocompression (TC) bonded circular cross section wire leads are currently used to convert SM leadless ceramic chip carriers to leaded packages with improved solder attachment reliability margin on organic substrates. The so-called "spider" J-bend and "spider" gull-wing leads represent innovative options for TC-bonded wire lead designs, and can provide an alternative to relatively high compliance soldered clip leads. Prior work by the principal author analytically characterized the directional compliance for a variety of SM component lead designs with rectangular and circular cross section. Effective flexural and torsional spring constants were developed by elastic strain energy deformation analysis of representative structural models. The diagonal lead stiffness measures the flexural compliance of the SM component corner-most leads in the package diagonal direction; the component half-diagonal extends from the neutral center to the device corner. The long-term SM interconnection reliability during operational thermal cycling is controlled in part by the diagonal lead stiffness. The newly developed stiffness metrics for the inclined gull-wing lead, spider J-lead, and spider gull-wing lead designs substantially add to current capabilities in lead compliance evaluation. The directional spring constants are given an algebraic format suitable for computer and spread sheet evaluation. The generalized structural models and resultant spring constants provide an effective means to compare and optimize SM component lead designs based on overall direction compliance. The overall lead height is well recognized as a critical dimensional parameter controlling lead compliance and SM component standoff. The inclination angle in the gull-wing lead design determines the overall lead height, as well as the overall lead footprint on the circuit board. Compliance evaluation has been performed for a representative gull-wing lead for various lead inclination angles. A 25-degrees variation in the inclination angle can nominally double the diagonal lead stiffness, compared to the vertical gull-wing lead design. The lead compliance metrics for a commercial TC-bonded spider J-bend wire lead have been parametrically evaluated over a wide range of typical lead heights. As the overall lead height is reduced from 185 to 135 mil, the corresponding diagonal lead stiffness increases to nominally 2.3 times the value for the tallest lead configuration. Comparative compliance evaluation has been performed for the spider J-bend wire lead and a commercial S-bend clip lead with rectangular cross section. The diagonal spring constants for the 185- and 135-mil tall spider J-leads are, respectively, comparable to and nominally double the diagonal lead stiffness for the 153-mil tall S-lead. Depending on the SM interconnection reliability and PCB assembly requirements, the TC-bonded spider J-bend wire leads can provide a design alternative to relatively high-compliance soldered clip leads. The diagonal stiffness of TC-bonded and clip-type lead designs can be tailored using lead compliance analysis to optimize the contour, dimensions, and material.