Microwave bonding of polymer-based substrates for micro-nano fluidic applications

Microwave-based bonding of polymer substrates is presented in this paper to illustrate a promising technique for achieving precise, well-controlled, low temperature bonding. Microwave power is absorbed by a very thin film metal layer already deposited on the polymer (PMMA) substrate surface. The intense thin-film volumetric heating promotes localized melting of refractory metals such as gold. One of the advantages of the process is that PMMA is relatively transparent to microwave energy in the 2.4 GHz regime. This makes it an excellent substrate material for microwave bonding. Selective heating and melting of the thin layers of metal also causes localized melting of the PMMA substrates and improves adhesion at the interface. We have shown that /spl sim/1 /spl mu/m of interfacial layer can be generated which composed of the melted gold and PMMA, and which can hold the substrates together under applied tension greater than 1001b/in/sup 2/. We also used lithographically patterned metal lines on the PMMA substrate to demonstrate that the PMMA remains optically transparent after microwave processing.