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Stretchable electronics based on Ag-PDMS composites.

Larmagnac A, Eggenberger S, Janossy H, Vörös J - Sci Rep (2014)

Bottom Line: For the last decade, research on improving the stretchability of circuits on elastomeric substrates has made significant progresses but designing printed circuit assemblies on elastomers remains challenging.Silver epoxy was used to bond commercial electrical components and no mechanical failure was observed after hundreds of stretching cycles.We also demonstrate the fabrication of a stretchable clock generator.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biosensors and Bioelectronics, Institute for Biomedical Engineering, ETH Zurich, CH-8092, Switzerland.

ABSTRACT
Patterned structures of flexible, stretchable, electrically conductive materials on soft substrates could lead to novel electronic devices with unique mechanical properties allowing them to bend, fold, stretch or conform to their environment. For the last decade, research on improving the stretchability of circuits on elastomeric substrates has made significant progresses but designing printed circuit assemblies on elastomers remains challenging. Here we present a simple, cost-effective, cleanroom-free process to produce large scale soft electronic hardware where standard surface-mounted electrical components were directly bonded onto all-elastomeric printed circuit boards, or soft PCBs. Ag-PDMS tracks were stencil printed onto a PDMS substrate and soft PCBs were made by bonding the top and bottom layers together and filling punched holes with Ag-PDMS to create vias. Silver epoxy was used to bond commercial electrical components and no mechanical failure was observed after hundreds of stretching cycles. We also demonstrate the fabrication of a stretchable clock generator.

No MeSH data available.


Related in: MedlinePlus

Fabrication of soft electrical circuits on PDMS integrating commercially available electrical components.(a) Picture of a ribbon cable with 8 conductors clamped on both ends by a commercial ZIF connector. (b) Picture of a custom-made miniature connector with 12 contacts. (c) Pictures of chip resistors bonded on conductive tracks (from left to right: 0805, 0603 and 0402 packages). (d) Picture of a large array of SMD LEDs bonded on a soft PCB. (e) Picture of a 2 kHz clock generator produced on a 0.2 mm thick soft single-sided PCB that conforms to a plastic brain. (f) Picture of a 1 Hz clock generetor with LEDs to display the output levels and produced on a 0.7 mm thick double-sided soft PCB (that shows less conformability on the plastic brain than the single-sided PCB) with vias and connected to a power supply with a ZIF connector.
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f4: Fabrication of soft electrical circuits on PDMS integrating commercially available electrical components.(a) Picture of a ribbon cable with 8 conductors clamped on both ends by a commercial ZIF connector. (b) Picture of a custom-made miniature connector with 12 contacts. (c) Pictures of chip resistors bonded on conductive tracks (from left to right: 0805, 0603 and 0402 packages). (d) Picture of a large array of SMD LEDs bonded on a soft PCB. (e) Picture of a 2 kHz clock generator produced on a 0.2 mm thick soft single-sided PCB that conforms to a plastic brain. (f) Picture of a 1 Hz clock generetor with LEDs to display the output levels and produced on a 0.7 mm thick double-sided soft PCB (that shows less conformability on the plastic brain than the single-sided PCB) with vias and connected to a power supply with a ZIF connector.

Mentions: Interconnecting electrical circuits can be done in a reversible manner using mechanical clamping or in an irreversible way using solder bonding. Zero Insertion Force (ZIF) connectors were used to interconnect soft PCBs to rigid standard PCBs. A stretchable ribbon cable with 8 leads was produced using stencil printing and was clamped between two ZIF connectors as shown in Fig. 4a. The ZIF connectors provided good electrical contacts even when the ribbon cable underwent large strains as high as 40% (see Supplementary Movie 1) but mechanically damaged the printed tracks after repeated manual stretching cycles due shear stress exerted by the metallic contacts on the soft Ag-PDMS leads. To solve this problem, the local stress can be delocalized by reinforcing the terminals with a sheet of polyimide or additional clamping on the PDMS. Novel designs of ZIF connectors including a second clamping system could significantly improve the reliability of the connector. Another way of interconnecting was to use Ag epoxy to bond the soft ribbon cable onto a rigid double-sided PCB. Figure 4b shows the interconnection between a stretchable ribbon cable with 12 conductors and a miniature custom-made connector. This solution allowed for smaller contact area and miniaturized interconnections but the bond is permanent. The Ag epoxy bonding technique was also used to mount SMD components onto the soft PCB. Chip resistors of various sizes were bonded between two tracks with different widths. Figure 4c shows 0406, 0603 and 0805 chip resistors after bonding. The samples were stretched to 20% over a thousand of cycles several cycles at 1 mm/s and the bond did not fail mechanically. When chip resistors were manually removed from the circuit by pulling on them some Ag-PDMS came off with the components suggesting good adhesion. High yield of the bonding was demonstrated with 6 × 7 arrays of LEDs = 84 contacts (see Fig. 4d). A soft astable circuit generating a 2 kHz clock was produced using the described method and is visible in Fig. 4e. Finally, a stretchable clock generator assembled on a double-sided PCB including vias with LEDs flashing every second and a ZIF connector is showed in Fig. 4f. The frequency of the clock determined by the values of the resistor and capacitor remained stable during manual bending and stretching (see Supplementary Movies 2 and 3).


Stretchable electronics based on Ag-PDMS composites.

Larmagnac A, Eggenberger S, Janossy H, Vörös J - Sci Rep (2014)

Fabrication of soft electrical circuits on PDMS integrating commercially available electrical components.(a) Picture of a ribbon cable with 8 conductors clamped on both ends by a commercial ZIF connector. (b) Picture of a custom-made miniature connector with 12 contacts. (c) Pictures of chip resistors bonded on conductive tracks (from left to right: 0805, 0603 and 0402 packages). (d) Picture of a large array of SMD LEDs bonded on a soft PCB. (e) Picture of a 2 kHz clock generator produced on a 0.2 mm thick soft single-sided PCB that conforms to a plastic brain. (f) Picture of a 1 Hz clock generetor with LEDs to display the output levels and produced on a 0.7 mm thick double-sided soft PCB (that shows less conformability on the plastic brain than the single-sided PCB) with vias and connected to a power supply with a ZIF connector.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4248267&req=5

f4: Fabrication of soft electrical circuits on PDMS integrating commercially available electrical components.(a) Picture of a ribbon cable with 8 conductors clamped on both ends by a commercial ZIF connector. (b) Picture of a custom-made miniature connector with 12 contacts. (c) Pictures of chip resistors bonded on conductive tracks (from left to right: 0805, 0603 and 0402 packages). (d) Picture of a large array of SMD LEDs bonded on a soft PCB. (e) Picture of a 2 kHz clock generator produced on a 0.2 mm thick soft single-sided PCB that conforms to a plastic brain. (f) Picture of a 1 Hz clock generetor with LEDs to display the output levels and produced on a 0.7 mm thick double-sided soft PCB (that shows less conformability on the plastic brain than the single-sided PCB) with vias and connected to a power supply with a ZIF connector.
Mentions: Interconnecting electrical circuits can be done in a reversible manner using mechanical clamping or in an irreversible way using solder bonding. Zero Insertion Force (ZIF) connectors were used to interconnect soft PCBs to rigid standard PCBs. A stretchable ribbon cable with 8 leads was produced using stencil printing and was clamped between two ZIF connectors as shown in Fig. 4a. The ZIF connectors provided good electrical contacts even when the ribbon cable underwent large strains as high as 40% (see Supplementary Movie 1) but mechanically damaged the printed tracks after repeated manual stretching cycles due shear stress exerted by the metallic contacts on the soft Ag-PDMS leads. To solve this problem, the local stress can be delocalized by reinforcing the terminals with a sheet of polyimide or additional clamping on the PDMS. Novel designs of ZIF connectors including a second clamping system could significantly improve the reliability of the connector. Another way of interconnecting was to use Ag epoxy to bond the soft ribbon cable onto a rigid double-sided PCB. Figure 4b shows the interconnection between a stretchable ribbon cable with 12 conductors and a miniature custom-made connector. This solution allowed for smaller contact area and miniaturized interconnections but the bond is permanent. The Ag epoxy bonding technique was also used to mount SMD components onto the soft PCB. Chip resistors of various sizes were bonded between two tracks with different widths. Figure 4c shows 0406, 0603 and 0805 chip resistors after bonding. The samples were stretched to 20% over a thousand of cycles several cycles at 1 mm/s and the bond did not fail mechanically. When chip resistors were manually removed from the circuit by pulling on them some Ag-PDMS came off with the components suggesting good adhesion. High yield of the bonding was demonstrated with 6 × 7 arrays of LEDs = 84 contacts (see Fig. 4d). A soft astable circuit generating a 2 kHz clock was produced using the described method and is visible in Fig. 4e. Finally, a stretchable clock generator assembled on a double-sided PCB including vias with LEDs flashing every second and a ZIF connector is showed in Fig. 4f. The frequency of the clock determined by the values of the resistor and capacitor remained stable during manual bending and stretching (see Supplementary Movies 2 and 3).

Bottom Line: For the last decade, research on improving the stretchability of circuits on elastomeric substrates has made significant progresses but designing printed circuit assemblies on elastomers remains challenging.Silver epoxy was used to bond commercial electrical components and no mechanical failure was observed after hundreds of stretching cycles.We also demonstrate the fabrication of a stretchable clock generator.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biosensors and Bioelectronics, Institute for Biomedical Engineering, ETH Zurich, CH-8092, Switzerland.

ABSTRACT
Patterned structures of flexible, stretchable, electrically conductive materials on soft substrates could lead to novel electronic devices with unique mechanical properties allowing them to bend, fold, stretch or conform to their environment. For the last decade, research on improving the stretchability of circuits on elastomeric substrates has made significant progresses but designing printed circuit assemblies on elastomers remains challenging. Here we present a simple, cost-effective, cleanroom-free process to produce large scale soft electronic hardware where standard surface-mounted electrical components were directly bonded onto all-elastomeric printed circuit boards, or soft PCBs. Ag-PDMS tracks were stencil printed onto a PDMS substrate and soft PCBs were made by bonding the top and bottom layers together and filling punched holes with Ag-PDMS to create vias. Silver epoxy was used to bond commercial electrical components and no mechanical failure was observed after hundreds of stretching cycles. We also demonstrate the fabrication of a stretchable clock generator.

No MeSH data available.


Related in: MedlinePlus