compression to improve the alignment accuracy. The degree of polymerization should not be over 50%, so it is robust enough to be patterned and still sufficiently adhesive to be bonded. If the BCB is hard-baked (far over 50%), it loses its adhesives properties and results in an increased amount of void formation. But also if the soft-curing is above 210 °C the adhesive cures too much, so that the material is not soft and sticky enough to achieve a high bonding strength. The substrates with the intermediate layer are pressed together with subsequent curing results in a bond. The post-bake process is applied at 180 to 320 °C for 30 to 240 min usually in a specific atmosphere or vacuum in the bond chamber. This is necessary to hard-cure the BCB. The vacuum prevents air trapped in the bond interface and pumps out the gases of the out-gassing residual solvents during annealing. The temperature and the curing time are variable, so with a higher temperature curing time can be reduced based on a quicker cross-linking. The final bonding layer thickness depends on the thickness of the cured BCB, the spinning speed and the shrink rate. Examples Adhesive bonding using a BCB intermediate layer is a possible method for packaging and sealing of MEMS devices, also structured Si wafers. Its use is specified for applications that does not require hermetic sealing, i.e. MOEMS mirror arrays, RF MEMS switches and tunable capacitors. BCB bonding is used in the fabrication of channels for fluidic devices, for transfer protruding surface structures as well as for CMOS controller wafers and integrated SMA microactuators. Technical specifications References Electronics manufacturing Packaging (microfabrication) Semiconductor technology Wafer bonding