Single axis accelerometer fabricated using printed circuit board techniques and laser ablation

Sensors and Actuators A: Physical, Volume 192, 1 April 2013, Pages 119-123.
A. Luque, G. Flores, F. Perdigones, D. Medina, J. García, J.M. Quero

 

Department of Electronics Engineering, University of Seville, E.S. Ingenieros, Av. Descubrimientos, s/n, 41092 Seville, Spain.

 

Abstract

 

Low-cost accelerometers could be used in applications where extremely good characteristics are not a requirement. This paper presents an accelerometer fabricated using printed circuit board (PCB) processing techniques, and laser ablation. Laser is used to remove part of the PCB substrate, releasing a mass suspended by copper beams. The structure is easily bonded to another PCB, creating a variable parallel-plate capacitor with a small gap, which capacitance varies with the movement of the mass, caused by external acceleration. The fabricated accelerometer has been compared to a commercial silicon one, showing good agreement in the measurements. The measured sensitivity was 81 fF/g.

 

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Additional Information:

The fabrication of MEMS devices using Printed Circuit Board techniques leads to novel ways of creating sensors. An accelerometer can be fabricated using laser ablation or other etching techniques and bonding of two standard printed circuit boards (PCBs) made of FR4 and copper. The working principle is a suspended mass connected to a fixed frame by copper beams which deflect with acceleration. As the proof mass moves, the gap between it and the other PCB changes, causing a variation in capacitance that can be easily measured. The performance characteristics are comparable to some commercial silicon-based accelerometers, which makes this design ideal for low volume applications or rapid prototyping, as the cost is several orders of magnitude smaller than that of silicon processing for small quantities. The fabrication process is a mixture of standard PCB techniques for copper patterning, and laser ablation for copper releasing. Two PCBs are used: one which contains the fixed electrode and is fabricated completely using the standard copper patterning in PCB, and another one which contains the movable electrode and it is released using laser ablation. The only non-standard process used is indeed laser ablation, but this can be replaced by traditional micro-machining with high precision numerical control (CNC) if needed. If using laser ablation, care must be taken in using a low frequency and low power, because a higher one could cause deformations in the structure due to thermal stress created by the laser. Another critical step is the bonding of both PCBs using tin/lead alloy. After bonding, calibration needs to be done for every device in order to correct the deviations that can appear in the resulting gap.

 

Single axis accelerometer fabricated using printed circuit board techniques and laser ablation

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