201305.pdf 43279KB May 08 2013 11:07:04 PM

the DFM issues that provide the highestgains.The role of packagemodeling in dfm ofelecTronic devicesSiva P Gurrum and ManuPrakuzhy, Design for Manufacturing,Semiconductor Packaging,Texas InstrumentsSemiconductor packaging is evolvingfrom an enabling role to a differentiatorin today’s electronic devices.Identifying a manufacturable designwithin the bounds of performance, reliability,and cost requirements is becomingever more challenging. Advances inpackage modeling are providing meansto predict a multitude of parametersrelated to performance, reliability, andcost.Predictions from package modelingcan be broadly categorized into performanceand reliability. The cost of apackaging solution is typically derivedfrom the design specification and manufacturingprocess flow. Performanceparameters include thermal, such asthermal resistance values, and electrical,such as parasitics. In reliability,predictions typically cover risks andtrends for the identified fail modesin a package family or package lifetimebased on some of the fail modes.Predictions of both performance andreliability require correlations betweenmodel values and physical evaluations(Figure 1).Modeling correlations are typicallyempirical relations between outputparameters resulting from a model andphysical parameters. Examples include:(a) the relationship between a modelevaluation of the fatigue damage insolder joint and the physical numberof temperature cycles to electrical failure,and (b) the relationship betweenelectrical model prediction for the currentdensity profile in a trace and theelectromigration lifetime from physicaltests. In some cases, physical parametersare directly predicted by a model,such as the junction-to-air thermalresistance of the package, or bond wireelectrical parasitics. In these instances,correlations serve as a validation of thechosen approach for derivative designs.For good modeling correlation, it isessential to incorporate the best modelingtools and techniques, accuratePACKAGE DESIGNPERFORMANCERELIABILITYCOSTMODELING TOOLSAND TECHNIQUESSIMULATIONMETHODOLOGYPHYSICALANALYSIS TOOLSCAD TOOLSAND CONVERTERSproperties from material characterization,and the wealth of data fromphysical evaluations. Analysis tools arematuring, with customized tools nowavailable for thermal and electrical,whereas the majority of mechanicaltools are more general purpose, withlonger cycle times. Material characterizationmust include bulk propertiesas well as properties sensitive to thephysical structure and assembly of apackage, such as the interfacial thermalresistance of a die attach materialor the adhesion strength betweeninterfaces. Also important is packagecharacterization to bound manufacturingtolerances on critical parameters.An example is the die attach bondline thickness in a leadframe package,which critically affects delaminationrisk. Physical evaluations needed tocomplete a correlation include thermalresistance measurements, electricaltesting on evaluation boards, andreliability testing according to standardspecifications.Some examples of design for manufacturingin packaging are:• Bond wire pattern to eliminateshorts during mold flow for high wiredensity molded packages• Lead finger design to minimizeMODELING CORRELATIONSTHERMAL, THERMO-MECHANICAL, ELECTRICALMATERIAL/PACKAGECHARACTERIZATIONFUNDAMENTALPROPERTIESSIMPLIFIEDLAB TESTSMANUFACTURABILITYINPUTSPHYSICAL PACKAGEEVALUATIONSTHERMALPERFORMANCEELECTRICALPERFORMANCERELIABILITYTESTINGFigure 1 Building blocks of modeling correlations enable package design formanufacturing.[ www.edn.com]MAY 2013 | EDN 29