Glass frit bonding

Glass frit bonding, also referred to as glass soldering or seal glass bonding, describes a <a href="/facts/Wafer_bonding/aW5sSa4t">wafer bonding</a> technique with an intermediate <a href="/facts/Glass/hezRsAGf">glass</a> layer. It is a widely used <a href="/facts/Electronic_packaging/42DmcQFc">encapsulation</a> technology for surface <a href="/facts/Microelectromechanical_systems/TkhEzDpm">micro-machined structures</a>, e.g., <a href="/facts/Accelerometer/xxrXzrlI">accelerometers</a> or <a href="/facts/Gyroscope/UjXGsfMq">gyroscopes</a>. The technique utilizes low melting-point glass ("glass solder") and therefore provides various advantages including that <a href="/facts/Viscosity/QLVfrdCz">viscosity</a> of glass decreases with an increase of temperature. The <a href="/facts/Viscous_flow/48pQugEa">viscous flow</a> of glass has effects to compensate and planarize surface irregularities, convenient for bonding wafers with a high roughness due to <a href="/facts/Plasma_etching/VEHxRdLI">plasma etching</a> or <a href="/facts/Vapor_deposition/n8Lu88Sw">deposition</a>. A low viscosity promotes <a href="/facts/Hermetic_seal/N4W2PQnS">hermetically sealed</a> encapsulation of structures based on a better adaption of the structured shapes. Further, the <a href="/facts/Coefficient_of_thermal_expansion/BP2vjX0N">coefficient of thermal expansion</a> (CTE) of the glass material is adapted to <a href="/facts/Silicon/cgWx0hdr">silicon</a>. This results in low <a href="/facts/Stress_(mechanics)/ErAXDbbd">stress</a> in the <a href="/facts/Wafer_bonding/aW5sSa4t">bonded wafer</a> pair. The glass has to flow and wet the soldered surfaces well below the temperature where deformation or degradation of either of the joined materials or nearby structures (e.g., metallization layers on chips or ceramic substrates) occurs. The usual temperature of achieving flowing and wetting is between 450 and 550 °C (840 and 1,020 °F).
Glass frit bonding can be used for many surface materials, e.g., silicon with <a href="/facts/Hydrophobic/Ifya0CXQ">hydrophobic</a> and <a href="/facts/Hydrophilic/k8p95WYu">hydrophilic</a> surface, <a href="/facts/Silicon_dioxide/A3WILp6J">silicon dioxide</a>, <a href="/facts/Silicon_nitride/58X9QPQJ">silicon nitride</a>, <a href="/facts/Aluminium/7wmR8jYE">aluminium</a>, <a href="/facts/Titanium/53ArnDoy">titanium</a> or <a href="/facts/Glass/hezRsAGf">glass</a>, as long as the CTE are in the same range. This bonding procedure also allows the realization of metallic <a href="/facts/Feedthrough/H8eLWw3R">feedthroughs</a> to contact active structures in the hermetically sealed cavity. Glass <a href="/facts/Frit/cFGeCd78">frit</a> as a <a href="/facts/Dielectric_material/PnVt9P2G">dielectric material</a> does not need additional <a href="/facts/Passivation_(chemistry)/tPADJj5G">passivation</a> for preventing <a href="/facts/Leakage_current/Nd6PNxhV">leakage currents</a> at process temperatures up to 125 °C (257 °F).
The process begins with the deposition of glass paste onto the surfaces to be treated. It is then heated to burn out additives and fire it in order to form the glass layer. The bonding process reconfigures the sintered glass into the desired state. Finally, the reconfigured glass is cooled down.
Glass frit bonding is used to encapsulate surface <a href="/facts/Microelectromechanical_systems/TkhEzDpm">micro-machined sensors</a>, i.e. <a href="/facts/Gyroscope/UjXGsfMq">gyroscopes</a> and <a href="/facts/Accelerometer/xxrXzrlI">accelerometers</a>. Other applications are the sealing of absolute <a href="/facts/Pressure_sensor/ccQINerP">pressure sensor</a> cavities, the mounting of <a href="/facts/Optical_window/ur52Kl8b">optical windows</a> and the capping of thermally active devices.

Glass frit bonding open-in-new

Glass frit bonding