Understanding Smart Sensors - Nomads.usp

Packaging, Testing, and Reliability Implications of Smarter Sensors 235Molding compoundGold-plated die attachSolder maskDieDie attach epoxyBT resin epoxyCopper foilSolder ballSolder maskcovering thermal viaThermal via:copper-plated through holeFigure 10.5 Plastic BGA package.dissipate heat from the package. The solder bumps reflow during the surfacemountassembly process to attach the package to a printed circuit board.10.4 Packaging for Monolithic SensorsThe highest volume semiconductor packaging techniques utilize molded plasticpackages with form factors that include SIPs, DIPs, quad flat packs, and a varietyof surface-mount devices (SMDs). The leadframe and molding techniquesused in plastic packages provide the lowest cost semiconductor packages.Recent improvements include improved capability to withstand autoclave testingfor improved hermeticity and the use of improved, low-stress mold compoundsfor surface-mount applications. However, a sensor that must physicallyinterface with a mechanical system, such as a pressure sensor, presents additionalpackaging challenges.Cylindrical TO-5 and TO-8 metal-can semiconductor packages havebeen adapted for usage as sensor packages. For pressure sensors, the lid and theheader of the package usually have a hole to allow the pressure source to beapplied to the die and provide a pressure reference to atmosphere. The leadsextend through the base of the package through glass mounting seals. The useof gold plating material and hard die attachment to the glass substrate of thesensor provides one of the most media-compatible sensors. The metal lid is