Understanding Smart Sensors - Nomads.usp

Packaging, Testing, and Reliability Implications of Smarter Sensors 233Figure 10.2 Pressure sensor and accelerometer packages compared to microcontrollerpackages.Figure 10.3(a). An MCM-C uses thick-film screening on cofired ceramic substrates.An MCM-D has interconnections formed by the thin-film depositionof metals on dielectrics of polymers or inorganic compounds. An MCM-Si usesa silicon substrate with aluminum or copper interconnections and SiO 2 as theinorganic dielectric media.The yields for MCMs can be lower than for assemblies made using packagedsemiconductors. Recent known good die (KGD) efforts in the semiconductorindustry are directed toward improving yields by improved testing at thewafer level. The same approaches will be required for MCM sensors.10.3.3 Dual-Chip PackagingCustom packages that accommodate a sensor die and its associated signal conditioningcircuit are common for high-volume applications. In those instances,the volume justifies the development and tooling costs. An example of a pressuresensor package developed for automotive manifold absolute pressure sensorsis shown in Figure 10.4 [7]. Thin-film resistors on the control die are lasertrimmed to provide a fully signal conditioned and calibrated pressure sensor.The control die has been used as a building block for other pressure applicationsand with different packaging requirements. The two-chip approach hasproved to be both cost effective and flexible.