Ultrasonic hot embossing

  Prinziple of ultrasonic hot embossing Copyright: © 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.

 
Movie on ultrasonic hot embossing and ultrasonic welding
Movie on ultrasonic hot embossing and ultrasonic welding and on milling of the aluminum tool
 

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 [61]. Examples are tools fabricated by the LIGA process.

The feasibility has been proven by fabricating a variety of micro systems such as flow sensors, lab-on-chip devices, heat exchangers, RFID-antennas, thin-film key pads, and micro whistles.

  Cut through and birds view of a micro structure fabricated by ultrasonic hot embossing of a stack of colored polymer foils. Copyright: © KEmikro

The material flow during ultrasonic hot embossing was demonstrated by embossing a micro structure into a stack of colored foils from polypropylene [85]. 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.

 
Roll to roll fabrication by ultrasonic hot embossing
Roll to roll fabrication by ultrasonic hot embossing into five polymer stripes
 
Role-to-role fabrication of polymer chips by ultrasonic hot embossing
Role-to-role fabrication of polymer chips by ultrasonic hot embossing
 

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 [56].

We welcome everybody interested and show ultrasonic hot embossing at KEmikro.

 
 

References

[24] W.K. Schomburg, K. Burlage, C. Gerhardy, ”Ultrasonic hot embossing”, Micromachines 2 (2011) 157 – 166, ISSN 2072-666X, doi:10.3390/mi2020157.

[7] P. Khuntontong, T. Blaser, W.K. Schomburg, ”Ultrasonic micro hot embossing of polymers exemplified by a micro thermal flow sensor”, Proc. Smart Systems Integration 2008, Barcelona, Spain, 9th - 10th April (2008) 327 - 334, ISBN 978-3-8007-3081-0.

[9] P. Khuntontong, T. Blaser, W.K. Schomburg, ”Ultrasonic micro hot embossing of thermoplastic polymers”, Proc. 24th Annual Meeting of the Polymer Processing Society, PPS24, Salerno, Italy, June 15-19 (2008) page II.364.

[10] P. Khuntontong, T. Blaser, D. Maas, W.K. Schomburg, ”Fabrication of a polymer micro mixer by ultrasonic hot embossing”, Proc. 19th MicroMechanics Europe Workshop, MME 2008, 28. - 30. September (2008) 259 - 262, ISBN 978-3-00-025529-8.

[16] P. Khuntontong, T. Blaser, W.K. Schomburg, ”Fabrication of Molded Interconnection Devices by Ultrasonic Hot Embossing on Thin Polymer Films”, IEEE Transactions on Electronics Packaging Manufacturing 32 (2009) 152 - 156.

[11] P. Khuntontong, “Fabrication of polymer micro devices by ultrasonic hot embossing”, Dissertation an der RWTH Aachen (2008), (http://darwin.bth.rwth-aachen.de/opus3/volltexte/2008/2581/).

[56] B. Memering, C. Gerhardy, W.K. Schomburg, “Roll-to-roll-production of micro structures in polymer foils by ultrasonic hot embossing”, Publikation “Microsystems Technology in Germany 2014”, trias consult (2014) 40-41, ISSN 2191-7183.

[65] J. Sackmann, K. Burlage, C. Gerhardy, B. Memering, S. Liao, W.K. Schomburg, “Review on ultrasonic fabrication of polymer micro devices”, Ultrasonics 56 (2015) 189-200, ISSN: 0041-624X, DOI: 10.1016/j.ultras.2014.08.007.

[61] S. Liao, C. Gerhardy, J. Sackmann, W.K. Schomburg, „Tools for ultrasonic hot embossing“, Microsystem Technologies (2014), DOI: 10.1007/s00542-014-2232-6.

[85] J. Kosloh, J. Sackmann, R. Šakalys, S. Liao, C. Gerhardy, W.K. Schomburg, “Heat generation and distribution in the ultrasonic hot embossing process”, Microsyst Technol (2016), doi: 10.1007/s00542-016-2836-0.