Development of a Low-Cost, Rapid-Cycle Hot Embossing System for Microscale Parts

Abstract

Hot embossing is an effective technology for reproducing micro-scale features in polymeric materials, but large-scale adoption of this method is hindered by high capital costs and low cycle times relative to other technologies, and a general lack of manufacturing equipment. This work details a hot embossing machine design strategy motivated by maximum production speed and quality with minimal capital cost. The approach is to "right-size" the machine for specific product needs while making the design flexible and scalable. Toward this end, a minimal number of components were used, commercially available off-the-shelf components were chosen where possible, system layout was designed to be modular, and system size was scaled for the intended products (in this case microfluidic devices). Innovative design aspects include the use of new ceramic substrate heaters for electrical heating, use of a moveable heat sink to minimize heat load during the heating cycle, and the careful design of the thermal elements to minimize the heating and cooling cycle times. The capital cost and the cost per part produced with this machine are estimated to be an order of magnitude less than currently available hot embossing manufacturing options. The hot embossing machine has been tested extensively to characterize the process variability. The minimum cycle time is two minutes, and microstructures are replicated within a maximum of a 25mm by 75mm area with very low relative variance in dimensions.

A method for the accelerated simulation of micro-embossed topographies in thermoplastic polymers

“…In figure 11 we compare experimentally measured [21] and simulated topographies near the centers of the three gratings for sample-average pressures of 0.5 MPa and 1.5 MPa, applied at 120 • C for 1.5 min. The simulations use the PMMA material model that was calibrated in our earlier work [12].…”

Measurement and Process Control in Precision Hot Embossing

“…Previous work completed by Hale demonstrated that the design and construction of a simple, fast-cycle, low-cost embossing machine was feasible (14). However, this work also demonstrated a need for enhanced control over forming parameters and for mechanical precision and repeatability.…”

“…Given sufficiently high temperatures and pressures, the micro-features will form to a high degree of fidelity, and any increased force or temperature will not significantly improve quality. However, excessively high temperatures and pressures will cause the polymer substrate to exhibit bulk flow, distorting the substrate and preventing subsequent registration for further finishing steps (14).…”

A research factory for polymer microdevices: muFac

“…For this process a novel approach was taken to achieve both rapid cycle times and an overall low capital cost machine. The details of this approach can be found in [4]. The key features are a simple actuation system with limited travel, but precise force control.…”

“…An earlier paper [17] highlights the factory's inception, with a team of more than 10 research assistants and 4 faculty members. The basis of our work is detailed in a number of papers including those on deformation properties of polymers [1][2], novel machine and process design for hot micro embossing and PDMS Casting [3][4][5] , tooling production and de-molding analysis [6][7][8], bonding methods [9] and methods for measurement and control of the resulting processes [10][11][12][13].…”