Wafer bonding with BCB and SU-8 for MEMS packaging

In this paper, intermediate layer bonding technologies using SU-8 and BCB are successfully demonstrated. The bonding process, which consists of only several simple steps such as material deposition, exposure and development, as well as contact and bonding, can be carried out in a bonder at low temperature, e.g., somewhere between 120°C and 350°C Benefits from this, integration of metal electrodes and wires between the bonding interfaces becomes possible. Moreover, since adhesive bonding does not necessitate extremely smooth contact surface, nor does it rely on the cleanliness of ambient environment, it is possible to carry out this process in a standard chemistry lab, and join different substrates without any pre-treatment. Initial inspection results showed that this method has a satisfactory yielding rate of more than 90%, and an acceptable bonding strength of above 2 MPa. The minimal thickness of the adhesive layer, which should retain the chips together after dicing, can be reduced to values between 6-10m. For low-cost capacitive transducers, this is an attractive packaging technology. On the other hand, because SU-8 epoxy is an innovative building block for polymer devices, this method can also be used to construct complex micro systems.