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
Read more about this topic: Adhesive Bonding