Understanding Smart Sensors - Nomads.usp

Packaging, Testing, and Reliability Implications of Smarter Sensors 241• Solderability;• Backside blow-off (for pressure sensors);• Salt atmosphere.Those tests use accelerated life and mechanical integrity testing to determinethe lifetime reliability statistics for silicon pressure sensors. Potentialfailure mechanisms are determined by the materials, processes, and processvariability that can occur in the manufacturing of a particular sensor. Forexample, the pressure sensor in Figure 10.11 has 10 product-related and 8process-related areas with 73 different items that can affect reliability [14].Other sensors will have reliability test requirements commensurate with theapplication for which the sensor is being used and the type of packaging techniquethat is employed.Sensor Reliability ConcernsBonding wires:StrengthPlacementHeight and loopSizeMaterialBimetallic contamination(Kirkendall voids)Nicking and other damagePackage:General quality and workmanshipIntegrityPlating qualityDimensionsThermal resistanceMechanical resistancePressure resistanceLeads:Materials and finishPlating integritySolderabilityGeneral qualityStrengthContaminationCorrosionAdhesionMarking:PermanencyClarityDie attach:UniformityResistance to mechanical stressResistance to temperature stressWettingAdhesion strengthProcess controlDie orientationDie heightChange in material or processMedia compatibilityCompressibilityGel:ViscosityThermal coefficient of expansionPermeabilityChange in material or processHeightCoverageUniformityAdhesive propertiesMedia compatibilityGel aeriationCompressibilityDesign changesMaterial or process changesFaband assembly cleanlinessSurface contaminationForeign materialScribedefectsDiffusion defectsOxide defectsDie metalization:Lifting or peelingAlignmentScratchesVoidsLaser trimmingThicknessStep coverageContact resistance integrityDiaphragm:SizeThicknessUniformityPitsAlignmentFracturesPassivation:ThicknessMechanical defectsIntegrityUniformityElectrical performance:Continuity and shortsParametric stabilityParametric performanceTemperature performanceTemperature stabilityLong term reliabilityStorage degradationSusceptibility to radiation damageDesign qualityFigure 10.11 Reliability areas in a plastic packaged pressure sensor.