Wafer-level BCB bonding using a thermal press for microfluidics

Abstract

Benzocyclobutene (BCB) is a thermosetting polymer that can form microfluidics and bond top and bottom layers of the microfluidics at the same time, and yields high repeatability and high bonding strength. This paper reports using photosensitive BCB to fabricate microfluidics and to bond with a thermal press for 4 in. wafers. By optimizing the parameters for pattern development and using a three-stage temperature and pressure increment BCB bonding, we realize the whole wafer glassSi or glass-glass bonding in thermal press without any crack. The wafer-level bonding shows a bonding percentage above 70%, a tensile stress above 4.94 MPa, and a bonding repeatability over 95%. Furthermore, the bonding is compatible with thick electrode integration, that microfluidics with 380 nm thick electrodes underneath can be well-bonded. Our bonding method much reduces the cost compared with bonding BCB in a wafer bonding machine.

Void-free BCB adhesive wafer bonding with high alignment accuracy

“…among the commonly-used bonding adhesives like SU-8 (Iliescu et al 2006), polyimide (Bayrashev andZiaie 2003), and photoresist (Su et al 2001), benzocyclobutene (BcB) has emerging as a widely-used bonding adhesive in the applications of three-dimensional (3-D) integration (Kwon et al 2008;Zhang et al 2006;Kim et al 2013;Ohba et al 2010;lu et al 2003) and MeMS/microsensors (Dragoi et al 2008;Seok et al 2012;Zhou et al 2009;McMahon et al 2008). In MeMS/microsensor applications, BcB has been used as a permanent or temporary bonding material for wafer transfer or heterogeneous integration of MeMS/microsensors and integrated circuits (Brault et al 2010;lapisa et al 2011).…”

Room-temperature intermediate layer bonding for microfluidic devices

“…12 In order to create a hermetic seal between two substrates via an intermediate, a thermal or photo curable resin (thickness at least several microns) is dispensed on one substrate, contacted with another substrate after pre-curing, and cured at temperatures below 300 C. Although spin-on sodium silicate solution (spin-on-glass; SOG) yields good bonds at temperatures in the range 90-200 C, [13][14][15] polymers are mostly used as an intermediate layer, because most polymer-based materials can be patterned photolithographically, which allows localized adhesive bonding. Voidfree, low-temperature adhesive silicon-silicon, glass-glass and silicon-glass bonds are realized with polydimethylsiloxane (PDMS) or its precursor at 60-65 C, 16,17 Nafion (a perfluorinated ion exchange polymer) at 120 C, 18 polyimide, SU-8 and cyclic perfluoropolymer (Cytop) at 150-160 C, [19][20][21][22] and benzocyclobutene (BCB) at 180-270 C, [23][24][25] whereas roomtemperature glass-glass adhesive bonding is possible with UV curable epoxy resins. [26][27][28][29] The quality of the adhesive bond, i.e.…”

3-D Integration and Through-Silicon Vias in MEMS and Microsensors

“…The main disadvantages of adhesive bonding are low heat transfer capability, and large post-bonding alignment errors. Due to the low thermal conductivities of polymers, the bonding adhesives significantly lessen the heat transfer and thermal dissipation across the thickness of the bonded chip pairs [142]. Some approaches like CNT doping can improve thermal conductivity [143], but the effect is still far from satisfactory.…”