Contactless inductive transmission systems for high power ...
High-Speed Contactless Electrical Evaluation of Printed Electronics using Inductive Sensors
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© Queen’s Printer and Controller of HMSO, 2016. 11563/0116 www.npl.co.uk Samples Six paste formulations were printed onto PET substrates as shown in the figure (5 mm wide tracks). Prior to testing, the tracks were characterised in terms of height and sheet resistivity. The height was measured using a TalySurf PXI1000. The sheet resistivity was measured using a Keithley 4200. These values are given in the table. Inductive Sensor The sensor was based on a radial inductor. This was prepared by removing the protective ferrite cap, an image of the sensor can be seen in the figure. • Coil inductance: 100 µH. • Coil diameter: ~7 mm. • Resonant frequency: ~10 MHz. High-Speed Contactless Electrical Evaluation of Printed Electronics using Inductive Sensors Adam Lewis, Chris Hunt, Owen Thomas and Martin Wickham National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK [email protected] Photograph of screen printed tracks on PET substrate. Track Height (μm) Sheet Resistivity (Ω/square) T1 18 1.6 T2 12 0.5 T3 21 7.8 T4 15 2.0 T5 11 82.1 T6 8 1.0 Measured properties of printed tracks. Introduction • We use inductive sensors to evaluate the resistivity of a range of printed tracks which can work at high speed. • Using a rotating cylinder, we are able to simulate a roll-to-roll system at high speed. • To ensure high yield it is important to monitor print quality of printed electronics. • Market growth of conductive inks for flexible/printed electronics is predicted to increase from $2.3 billion to $3.2 billion by 2025 1 . • Quality/functionality monitoring is typically optical. Our approach measures conductivity by monitoring generation of eddy currents with a good signal-to-noise ratio. 1. Stationary Measurement For each of the tracks, using an impedance analyser, the frequency response (impedance and phase) of the sensor between 8.5 to 11 MHz (this range covers the resonant frequency of the inductor) was monitored with an air gap between the sensor and tracks of ~20 µm. Around the resonant frequency we can see that the impedance and phase response gave the largest variation for the tracks. The relationship between the maximum impedance measured within this frequency range has been plotted against the sheet resistivity. To measure the higher resistivity tracks, a coil with a higher resonant frequency would be required. 2. High Speed Measurement The tracks (on the PET substrate) were placed on a rotating cylinder ~ 500 µm from the inductive sensor. As the tracks moved past the sensor at high speed (to simulate a roll- to-roll system) the sensor was monitored at a single frequency (15.9 MHz). After passing the signal through a voltage rectifier, the signal was sampled using a data acquisition card with a sampling frequency of 250 kHz. In the results shown, the tracks were travelling at 147.5 mm/s (8.85 m/min) which corresponds to a distance between samples of 0.59 mm. The resolution can be increased by decreasing the sample speed or increasing the sampling rate. There is a clear relationship between the peak height and the resistivity. Track 2, which has the lowest sheet resistivity can be seen to give the largest response. Tracks, 1, 4 and 6 show that with an increase in sheet resistivity, there is a decrease in the eddy currents produced and hence a decrease in the response measured. For tracks with a sheet resistivity greater than 2 Ω/sq, (tracks 3 and 5) it was not possible to identify them. Conclusions • Inductive sensors can be used to monitor conductivity of printed electronics. • The value of measured impedance can be related to the sheet resistivity. • Our results show that tracks with values sheet resistivity below 3.3 Ω/sq* could be detected. • Analysis of samples with higher/lower values of sheet resistivity could be achieved by coils with higher/lower resonant frequencies. • The measurement can be made at high speed and compatible with roll- to-roll manufacturing techniques. *normalised to a print thickness of 25 µm. Acknowledgements The authors would like to thank Gwent Electronic Materials Ltd. for providing the pastes. Reference [1] D. Savastano, “Conductive Inks Drive Growth in Flexible and Printed Electronics”, Printed Electronics Now, March 2015 Track 20 μm Illustration of sensor above track. Impedance and phase responses of sensor measured for each track. Relationship between sheet resistivity and maximum amplitude of impedance signal for measured tracks. Tracks Cylinder Sensor Experimental setup with coil above samples attached to rotating cylinder. Response from inductive sensor as samples pass under coil. Photograph of inductive sensor. Introduction Samples Inductive Sensor 1. Stationary Measurement 2. High Speed Measurement Conclusions Acknowledgements
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Transcript of High-Speed Contactless Electrical Evaluation of Printed Electronics using Inductive Sensors
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SamplesSix paste formulations were printed onto PET substrates as shown in the figure (5 mm wide tracks). Prior to testing, the tracks were characterised in terms of height and sheet resistivity. The height was measured using a TalySurf PXI1000. The sheet resistivity was measured using a Keithley 4200. These values are given in the table.
Inductive SensorThe sensor was based on a radial inductor. This was prepared by removing the protective ferrite cap, an image of the sensor can be seen in the figure.
• Coil inductance: 100 µH.
• Coil diameter: ~7 mm.
• Resonant frequency: ~10 MHz.
High-Speed Contactless Electrical Evaluation of Printed Electronics using Inductive Sensors
Adam Lewis, Chris Hunt, Owen Thomas and Martin Wickham National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, UK
Photograph of screen printed tracks on PET substrate.
Track Height (μm)
Sheet Resistivity (Ω/square)
T1 18 1.6T2 12 0.5T3 21 7.8T4 15 2.0T5 11 82.1T6 8 1.0
Measured properties of printed tracks.
Introduction• We use inductive sensors to evaluate the resistivity of a range of printed tracks which can work at high speed.• Using a rotating cylinder, we are able to simulate a roll-to-roll system at high speed.• To ensure high yield it is important to monitor print quality of printed electronics.• Market growth of conductive inks for flexible/printed electronics is predicted to increase from $2.3 billion to $3.2 billion by 20251.• Quality/functionality monitoring is typically optical. Our approach measures conductivity by monitoring generation of eddy currents with a good
signal-to-noise ratio.
1. Stationary MeasurementFor each of the tracks, using an impedance analyser, the frequency response (impedance and phase) of the sensor between 8.5 to 11 MHz (this range covers the resonant frequency of the inductor) was monitored with an air gap between the sensor and tracks of ~20 µm.
Around the resonant frequency we can see that the impedance and phase response gave the largest variation for the tracks.
The relationship between the maximum impedance measured within this frequency range has been plotted against the sheet resistivity.
To measure the higher resistivity tracks, a coil with a higher resonant frequency would be required.
2. High Speed MeasurementThe tracks (on the PET substrate) were placed on a rotating cylinder ~ 500 µm from the inductive sensor.
As the tracks moved past the sensor at high speed (to simulate a roll-to-roll system) the sensor was monitored at a single frequency (15.9 MHz). After passing the signal through a voltage rectifier, the signal was sampled using a data acquisition card with a sampling frequency of 250 kHz.
In the results shown, the tracks were travelling at 147.5 mm/s (8.85 m/min) which corresponds to a distance between samples of 0.59 mm. The resolution can be increased by decreasing the sample speed or increasing the sampling rate.
There is a clear relationship between the peak height and the resistivity. Track 2, which has the lowest sheet resistivity can be seen to give the largest response. Tracks, 1, 4 and 6 show that with an increase in sheet resistivity, there is a decrease in the eddy currents produced and hence a decrease in the response measured. For tracks with a sheet resistivity greater than 2 Ω/sq, (tracks 3 and 5) it was not possible to identify them.Conclusions
• Inductive sensors can be used to monitor conductivity of printed electronics.
• The value of measured impedance can be related to the sheet resistivity.• Our results show that tracks with values sheet resistivity below 3.3 Ω/sq*
could be detected.• Analysis of samples with higher/lower values of sheet resistivity could be
achieved by coils with higher/lower resonant frequencies.• The measurement can be made at high speed and compatible with roll-
to-roll manufacturing techniques.*normalised to a print thickness of 25 µm.
AcknowledgementsThe authors would like to thank Gwent Electronic Materials Ltd. for providing the pastes.
Reference[1] D. Savastano, “Conductive Inks Drive Growth in Flexible and Printed Electronics”, Printed Electronics Now, March 2015
Track
20 µm
Illustration of sensor above track.
Impedance and phase responses of sensor measured for each track.
Relationship between sheet resistivity and maximum amplitude of impedance signal for measured tracks.
Tracks
Cylinder
Sensor
Experimental setup with coil above samples attached to rotating cylinder.
Response from inductive sensor as samples pass under coil.
Photograph of inductive sensor.
Introduction
Samples Inductive Sensor
1. Stationary Measurement 2. High Speed Measurement
Conclusions
Acknowledgements
