Ultrashort laser welding of PMMA to silicon

Utilization of parts made by combining dissimilar materials, such as different polymers, metals, or semiconductor to polymers, are nowadays highly demanded for the fabrication of electronic, electromechanical, medical micro-devices, and analytical systems (e.g., lab-on-chip). Techniques for joining such hybrid micro-devices, generally based on gluing or thermal processes, remain a challenging task presenting some drawbacks, such as deterioration and contamination of the substrates. Ultrashort laser welding is a non-contact and flexible technique to precisely weld similar and dissimilar materials. In this case, the only constrain is that the upper substrate is transparent to the laser wavelength. This technique has been demonstrated both for welding polymers and polymers to metallic substrates, but never for joining polymers to silicon. In this work, we report on direct femtosecond laser welding of Poly(methyl methacrylate) (PMMA) and silicon. The laser welding was performed in ambient air by focusing ultrashort laser pulses at high repetition rate at the interface between the two, being PMMA transparent to the laser wavelength. A mechanical homogenous pressure was applied on the sandwiched substrates during all the laser process. The Si-PMMA weld strength was evaluated as a function of the laser and processing parameters, e.g., repetition rate, scan speed, and the overlap between adjacent scan lines.