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Adhesive bonding (also referred to as gluing or glue bonding) describes a wafer bonding technique with applying an intermediate layer to connect substrates of different materials. These produced connections can be soluble or insoluble.〔 The commercially available adhesive can be organic or inorganic and is deposited on one or both substrate surfaces. Adhesives, especially the well-established SU-8, and benzocyclobutene (BCB), are specialized for MEMS or electronic component production.〔 The procedure enables bonding temperatures from 1000 °C down to room temperature.〔 The most important process parameters for achieving a high bonding strength are:〔 * adhesive material * coating thickness * bonding temperature * processing time * chamber pressure * tool pressure Adhesive bonding has the advantage of relatively low bonding temperature as well as the absence of electric voltage and current. Based on the fact that the wafers are not in direct contact, this procedure enables the use of different substrates, e.g. silicon, glass, metals and other semiconductor materials. A drawback is that small structures become wider during patterning which hampers the production of an accurate intermediate layer with tight dimension control.〔 Further, the possibility of corrosion due to out-gassed products, thermal instability and penetration of moisture limits the reliability of the bonding process.〔 Another disadvantage is the missing possibility of hermetically sealed encapsulation due to higher permeability of gas and water molecules while using organic adhesives.〔 == Overview == The adhesive bonding with organic materials, i.e. BCB or SU-8, has simple process properties and the ability to form high aspect ratio micro structures. The bonding procedure is based on polymerization reaction of organic molecules to form long polymer chains during annealing. This cross-link reaction forms BCB and SU-8 to a solid polymer layer.〔 The intermediate layer is applied by spin-on, spray-on, screen-printing, embossing, dispensing or block printing on one or two substrate surfaces. The adhesive layer thickness depends on the viscosity, rotational speed and the applied tool pressure. The procedural steps of adhesive bonding are divided into the following:〔 # Cleaning and pre-treatment of substrates surfaces # Application of adhesive, solvent or other intermediate layers # Contacting substrates # Hardening intermediate layer The most established adhesives are polymers that enable connections of different materials at temperatures ≤ 200 °C.〔 Due to these low process temperature metal electrodes, electronics and various micro-structures can be integrated on the wafer. The structuring of polymers as well as the realization of cavities over movable elements are possible using photo-lithography or dry etching.〔 The hardening conditions depend on the used materials. Hardening of the adhesives are possible:〔 * at room temperature * through heating cycles * using UV light * by applying pressure 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Adhesive bonding」の詳細全文を読む スポンサード リンク
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