Hermetic sealing is the encapsulation of electronic components into an airtight metal or ceramic housing using either parallel gap resistance seam welding or opposed electrode projection resistance welding. It is a key manufacturing process utilized in assembling micro-electronic packages for communication, aerospace and medical device manufacturing.
Uses of hermetic sealing
Microelectronic devices are commonly used in industrial commercial communications, transportation, military, and aerospace industries and include optical sensors, pressure sensors, communications devices, thermal and laser imaging and power amplifiers. By sealing these electronic packages, external contaminants – like moisture – are kept out preventing degradation of the electronic components inside and extending lifetime usefulness.
Implantable medical devices, like pacemakers and defibrillators, also require careful hermetic sealing to protect both the device and the patient.
Microelectronic package types
There are two primary types of packages: metallic tub and ceramic.
The preferred material for metallic tub base packages is Kovar, which has a similar Coefficient of Thermal Expansion (CTE) as glass; the use of this material prevents the metal-to-glass seals of the feedthrough connectors of the package from leaking due to material expansion from heat generated during the welding process.
Ceramic packages are made of a ceramic substrate with a brazed metal seal ring. Kovar is also used in ceramic packages; the Kovar is brazed onto the ceramic base as a seal ring to which the lid is welded.
Parallel gap resistance seam welding
Parallel gap seam welding is one way to execute a hermetic seal. A seam welder with rolling wheel electrodes is connected to a power supply, which is responsible for delivering electric current across the electrodes, through the lid and the package. The seam welder delivers multiple overlapping weld spots, thus creating a continuous weld (Figures 2 and 3).