SU-8 is applicable to zero-level packaging technology for low cost MEMS packaging. Metallic feed-throughs can be used for electrically connections to packed elements through the adhesive layer. Also biomedical and micro fluidic devices are fabricated based on SU-8 adhesive layer as well as micro fluidic channels, movable micro-mechanical components, optical waveguides and UV-LIGA components. Benzocyclobutene (BCB) Overview Benzocyclobutene (BCB) is a hydrocarbon that is widely used in electronics. BCB exists in a dry etch and a photosensitive version, each requiring different procedural steps for structuring (compare BCB process flow). It does release only small amounts of by-products during curing which enables a void-free bond. This polymer ensures very strong bonds and excellent chemical resistance to numerous acids, alkalines and solvents. The BCB is over 90% transparent to visible light that enables the use for optical MEMS applications. Compared to other polymers the BCB has a low dielectric constant and dielectric loss. The polymerization of BCB is taking place at a temperature around 250 to 300 °C and it is stable up to 350 °C. Using BCB does not ensure a sufficient hermeticity of sealed cavities for MEMS. Procedural steps The procedural steps for dry etch BCB are: Cleaning Supplying the adhesion promoter Drying of the primer BCB deposition Photosensitive BCB Exposure and development Dry etch BCB Pre-bake/soft-cure Patterning of the BCB layer by lithography and dry-etching Bonding at specific temperature, ambient pressure for specific amount of time Post-bake/hard-cure to form solid BCB monomer layer The wafers can be cleaned using H2O2 + H2SO4 or oxygen plasma. The cleaned wafers are rinsed with DI water and dried at elevated temperature, e.g. 100 to 200 °C for 120 min. The adhesion promoter with a specific thickness is deposited, i.e. spin-coated or contact printed on the wafer to improve the bonding strength. Spray coating is preferable when the adhesive is deposited on free standing structures. Subsequently, the BCB layer is spin or spray coated, usually 1 to 50 µm thick, to the same wafer. To prevent that the patterned layer has a lower bond strength than the unpatterned layer, due to the cross-linking of the polymer, a soft-curing step is applied before bonding. The pre-curing of the BCB takes place for several minutes on the hot plate at a specific temperature ≤ 300 °C. The soft cure prevents bubble formation and unbonded areas as well as the distortion of the adhesive layer during