Ultrasonic hot embossingCopyright: © KEmikro
The financial effort for the fabrication of micro systems is not limited by the material costs but by the necessary investments and qualified employees. Besides others, this is the reason why corrosion is avoided by conductor paths from gold or platinum instead of covering them by a protection layer.
For low-cost fabrication of micro structures ultrasonic hot embossing has been developed at KEmikro [24, 7, 9, 10, 16, 11, 65, 85]. This process is often also called ultrasonic embossing, ultrasonic imprinting or ultrasonic nanoimprint lithography. For this process just a commercially available ultrasonic welding machine and a tool with the inverse of the desired structures are required. One or more polymer foils are placed onto the tool and pressed down by the sonotrode. On the surface and inside of the polymer friction is generated by the ultrasound which results in heating and softening of the foils. Then, the polymer flows into the tool and adapts to its surface structure. Since the polymer gets warm only where it is in direct contact to the micro structures on the tool, comparatively few energy is required and the polymer is cooled down quickly after ultrasound is switched off again, because the metal tool dissipates the heat immediately. Ultrasonic hot embossing can be done in a cycle time of a few seconds.
Directly afterwards, additional structure levels can be joined to the sample by ultrasonic welding generating several micro structured levels on top of each other. A good example for this is the micro heat exchanger.
The tools required for ultrasonic hot embossing at KEmikro are milled into aluminum. However, other fabrication methods are also possible with which micro structures from materials can be generated withstanding the mechanical and thermal loads of the embossing process . Examples are tools fabricated by the LIGA process.Copyright: © KEmikro
The material flow during ultrasonic hot embossing was demonstrated by embossing a micro structure into a stack of colored foils from polypropylene . In the stack, there were starting from the sonotrode black, red, and yellow foils. The mixture of the different colors shows that the polymer is flowing very much in the few 100 ms of ultrsonic hot embossing. This way, it becomes clear that the foils are joined to a single piece of polymer where there are protruding micro structures on the tool. At the rim of the cut trough the micro structure (upper figure) there is seen that the foils have not been molten and joined aside of the micro structures.
For industrial production ultrasonic hot embossing can be performed in a role to role process if a corresponding machine is mounted to the ultrasonic welding machine .
We welcome everybody interested and show ultrasonic hot embossing at KEmikro.
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