Abstract

An innovative method of thermal fusion bonding (TFB) using a pressure assisted boiling point (PABP) control system was characterized to determine the optimum parameters for bonding thermoplastic components containing microchannels and thin cover sheets. The PABP TFB system enables precise control of the temperature and the pressure boundary conditions by immersing a bag containing the components being bonded in boiling water and varying the vapor pressure. The original system used a human operator to manually adjust a pressure relief valve and maintain the system temperature, which introduces time delays. A closed loop control system was developed to automatically control the temperature in the pressure vessel. Test structure geometries containing microchannels of two depths, 5μm and 10μm, and four different aspect ratios were designed: 1:10, 1:50, 1:100, and 1:200. Microchannels were hot embossed in polymethyl methacrylate (PMMA) using micro-milled brass mold inserts. Results of bonding with the closed loop systems were evaluated. Mean rupture pressures decreased with increasing AR and were higher for shallower channels for the automated closed loop system. For a given aspect ratio, the rupture pressures ranged from 5%–19% higher for 5 mm channels and increased by 5%–10% in 10 mm channels with the automated closed loop system.

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