The present invention refers to (a) thermoplastic plastic (thermoplastic) after the oxidized the surface of the substrate consisting of introducing into amino group ; (b) modified with epoxy and a silicon material and said substrate surface and the reacting including combusting the materials to form coating layer, substrate for joining substrate surface treating method and said substrate surface treating method comprising at the following formula 1. method for joining substrates. According to the present invention, ambient temperature and atmospheric an amine-epoxy linkage forming reagents under conditions thermoplastic plastic on a surface of a substrate through low molecular weight PDMS coating the potential of the output terminal by thermoplastic plastic irrespective of the kind of a robust design which is irreversible reproducible a bonding a thermoplastic plastic-PDMS substrate assembly, the substrate assembly or thermoplastic plastic-thermoplastic plastic substrate assembly, the substrate assembly can be produced. In particular, the present invention according to substrate assembly, the substrate method using microfluidic device when is to be produced, substrate before bonding to reduce corner rounding of a micro channel types of the profile and the without affecting the, the plastic substrate real estate can be conserved as the dusk light projection micro which, secure fit by clutch process a sample of a mass has (high pressure resistance) purpose : a pretreatment of samples (high-throughput) processing capacity (pre-treatment) device portable and useful to design a platform can be used.