This document summarizes the design, fabrication process, and experimental results of a capacitive pressure sensor made using printed circuit board microelectromechanical systems (PCBMEMS) technology. The sensor consists of two FR4 circuit boards with a small separation that varies with applied pressure, changing the capacitance. Photolithography is used to etch copper patterns on the boards. Experimental results show the sensor's output frequency varies linearly with increasing applied pressure up to 3,000 mbar. The low-cost PCBMEMS fabrication process could enable integration with electronics for pressure sensing in various industries.

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3. This presentation includes ,
INTRODUCTION.
DESIGN.
FABRICATION PROCESS.
EXPERIMENTAL RESULTS.
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4. This presentation includes ,
Figures included
Process flow diagram. Photolithography.
+ve & -ve photo resist. Fabricated sensor.
Root principle. Exp. Setup.
Relaxation oscillator. Results.
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5. Introduction
PCBMEMS Technology.
FR4.
Photo resist.
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6. PCBMEMS Technology
1. Micro Electro Mechanical Systems (MEMS)
The technology of very small mechanical devices
Made up of components between 1-100 m in size
Consist of a central unit, the P and Micro sensors.
Basic techniques are Deposition, Patterning & Etching
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7. PCBMEMS Technology
2. Materials used
Silicon
Polymers
Metals
Ceramics
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8. PCBMEMS Technology
Photo Exposed remaining
Copper sensitive to materials
covering uv rays etched off
Process Block Diagram
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9. FR4
What is..?
Popular And Versatile High Pressure Thermoset.
With zero water absorption.
Retains insulating qualities in dry & humid conditions.
Made of woven fiberglass cloth with an epoxy resin
binder
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10. FR4
Properties
Parameter Value
Specific gravity/Density 1850 kg/m³
Water Absorption -.125" < .10 %
Temperature Index 140 °C
Bond Strength > 1000 kg
Dielectric strength 20 kV/mm
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11. FR4
Applications
Printed circuit boards
Relays
Switches
Transformers
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12. Photo resist
What is..?
A light sensitive material to form patterned coating on
a surface.
Classified as Positive and Negative Photo resist.
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13. Photo resist
What is..?
Positive photoresist: the light exposed portion
becomes soluble while the unexposed remains
insoluble.
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14. Photo resist
What is..?
Negative photoresist: the light exposed portion
becomes insoluble while the unexposed is dissolved.
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15. Photo resist
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16. Photo resist
CHARACTERISTIC
POSITIVE NEGATIVE
S
Adhesion to Silicon Fair Excellent
Relative Cost More expensive Less expensive
Developer Base Aqueous Organic
Minimum Feature <-0.5 m ± 2 μm
Step coverage Better Lower
Wet chemical
Fair Excellent
resistance
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17. Design
Principle: Variation in capacitance b/w 2 PCB substrates.
Solder paste applied keeps the 2 plates together.
Small separation in between yields a large capacitance.
Capacitance obtained is converted to frequency.
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18. Design
Principle
Substrates etched with copper.
Applied pressure deforms the gap.
The circuits provided, reads the capacitance.
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19. Design
Capacitance-frequency conversion
Capacitance is converted to frequency.
Relaxation oscillator is used.
Equation:
Square wave obtained.
Here R=1M
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20. Fabrication process
Photolithography
Selectively remove parts of a thin film.
Uses light to transfer geometric pattern.
Affords exact control of shape & size of the objects.
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21. Fabrication process
Photolithography
Cleaning
Preparation
Photo resist application
Exposure and developing
Etching
Photo resist removal
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22. Fabrication process
Step 1
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23. Fabrication process
Step 2
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24. Fabrication process
Step 3
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25. Fabrication process
Step 4
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26. Experimental Results
Fabricated sensor
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27. Experimental Results
AIM : To obtain the relation b/w applied pressure & output frequency
A metal chamber gas was glued on the top PCB.
Connected it with a regulated pressure source through.
A manometer is used to measure the applied pressure.
Pressure was varied & the frequencies obtained were
read on an oscilloscope
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28. Experimental Results
Experimental Setup
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29. Experimental Results
Pressure was varied & waiting time was given after
each.
The pressure was varied in the range from 0-3000 mbar.
Result is plotted as a function of the applied pressure.
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30. Experimental Results
Measured freq. vs applied pressure
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31. Experimental Results
Calculated capacitance b/w the 2 electrodes as a fn. of applied pressure.
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32. Advantages
Low cost.
Ease of integration with electronics.
Manufactured in large volumes.
Wide range of applications.
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33. Conclusion
Inexpensive fabrication.
Relying only on PCB techniques & automated
soldering.
Applicable in industries.
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34. Future Scope
This process along with some modifications may be used
to fabricate other sensors like accelerometers and micro
fluidic detectors.
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36. Photograph of a PCBMEMS Fabricated Accelerometer
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37. Cross sectional view
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38. References
IEEE Electron Device Letters 2009, v.30 n.12, p.1293-
1295
A Thesis on Design, Fabrication, and Dynamic
Modeling of a PCBMEMS Accelerometer by John E.
Rogers.
Soldering techniques-UNC Dept. of Chemistry
An introduction to thermosets R.Bruce. Prime IBM
(retired) / consultant www.primethermosets.com
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39. References
Mask less Lithographic PCB/Laminate MEMS for a
Salinity Sensing System D. Fries et al. University of
South Florida.
Applications of High-Performance MEMS Pressure
Sensors Based on Dissolved Wafer Process by
Srinivas Tadigadapa and Sonbol Massoud-Ansari
Integrated Sensing Systems (ISSYS) Inc.,387 Airport
Industrial Drive, Ypsilanti, MI 48198
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40. References
Soldering techniques for PCB-Min Chen, student
member IEEE.
Photolithography written by Scotten.W.Jones.
Capacitive pressure sensor design Version 8/PC
Part Number 30-090-101 March 2006
©IntelliSense Software Corporation 2004, 2005, 2006
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41. References
www.primethermosets.com
www.sensorcontrolsindia.com
www.seminar projects.com
Wikipedia
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