Diffusion bonding has been widely used within microlamination architectures for the fabrication of Micro Energy and Chemical Systems (MECS). MECS are microsystems with the ability to process bulk amounts of fluid within highly-parallel microchannel arrays capable of accelerated heat and mass transfer. Thus far, diffusion bonding of the microchannel arrays is commonly done in a vacuum hot press system. The use of the hot press greatly restricts the production rate due to vacuum pump-down time and heating-up and cool-down periods. Furthermore, larger substrates are gaining interest
in the system design of MECS devices and it is not apparent that uniaxial pressing within a hydraulic vacuum hot press will provide the bonding pressure uniformity necessary for large substrate bonding.
This thesis presents a novel fabrication approach for the high-volume thermal bonding of MECS devices with the use of controlled thermal expansion. A thermal bonding fixture based on the principle of differential thermal expansion was developed with focus on controlling the bonding pressure magnitude, the pressure timing and its sensitivity. The application of such a fixture within a conveyorized furnace system could be the key to a continuous thermal bonding approach for the mass production of MECS devices. The conceptual design and the feasibility of such a device was validated and explored by building a finite element model. Subsequently, a fixture prototype was fabricated. Functionality of the prototype △CTE-fixture was confirmed at low temperatures (180°C) with the use of pressure sensitive film. An experimental comparison of at the diftusion bonding quality of the fixture versus the hot press was
conducted under various bonding conditions. A 2⁴ full factorial experimental design with one replicate was conducted with mode (fixture/hot press), bonding pressure
(3MPa/6MPa), bonding temperature (500°C/800°C) and bonding time (3Omin/6Omin) as
experimental factors. The metallurgical examination of void fraction at the bond line
(pressure magnitude) and the amount of measured fin warpage (pressure timing) were
used to compare the bonding quality of the two approaches. An analysis of variance
(ANOVA) revealed that there is no statistically significant difference in the levels of
warpage found within samples prepared in the zCTE-fixture compared to samples
processed in the hot press indicating no major issues in pressure timing. The
comparison of void fractions has shown that there was a difference in the level of
pressure reached within the △CTE-fixture although the bonding quality of the △CTE-fixture was found to be satisfactory, especially at higher temperatures.
Recommendations for design improvements were made to eliminate current issues with
the level of pressure reached.
This study has shown that diffusion bonding conditions can be controlled using a static
△CTE bonding fixture. Results obtained conclude that the investigated concept is a
plausible approach towards the high-volume microlamination of diffusion-bonded MECS
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