j 39 balaji an antha suresh

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Electro-magnetically Actuated Minute Polymer Pump

Fabricated using Packaging Technology

G Balaji, A Singh and G K Ananthasuresh

Mechanical Engineering, Indian Institute of Science, Bangalore 560012, India

{gbalaji, aksingh, suresh}@mecheng.iisc.ernet.in

Abstract. Design, fabrication and preliminary testing of a flat pump with millimetre thicknessare described in this paper. The pump is entirely made of polymer materials barring the magnetand copper coils used for electromagnetic actuation. The fabrication is carried out using widelyavailable microelectronic packaging machinery and techniques. Therefore, the fabrication ofthe pump is straightforward and inexpensive. Two types of prototypes are designed and built.

One consists of copper coils that are etched on an epoxy plate and the other has woundinsulated wire of 90 m diameter to serve as a coil. The overall size of the first pump is 25 mm 25 mm 3.6 mm including the 3.1 mm-thick NdFeB magnet of diameter 12 mm. It consistsof a pump chamber of 20 mm 20 mm 0.8 mm with copper coils etched from a copper-clad

epoxy plate using dry-film lithography and milled using a CNC milling machine, two passivevalves and the pump-diaphragm made of Kapton film of 0.089 mm thickness. The secondpump has an overall size of 35 mm 35 mm 4.4 mm including the magnet and the windings.A breadboard circuit and DC power supply are used to test the pump by applying an alternatingsquare-wave voltage pulse. A water slug in a tube attached to the inlet is used to observe andmeasure the air-flow induced by the pump against atmospheric pressure. The maximum flowrate was found to be 15 ml/min for a voltage of 2.5 V and a current of 19 mA at 68 Hz.

1. Introduction

Miniature pumps are important components of micro-fluidic systems such as lab-on-a-chip, micro-

total-analysis systems, implantable drug-delivery devices, etc. Several transduction principles,materials and fabrication methods have been used to develop proof-of-concept miniature pumps. Laser

and Santiago [1] recently reviewed the developments from the first reported micro pump in 1986 to

2004. They noted that there are no micro pumps that best suit certain applications despite the rapiddevelopment in this field. Flow rates, pressure against which pumping is to take place, precision of the

delivered volume, packaged size, power consumed, bio-compatibility, etc., are some of the

characteristics that help choose a pump for a given application. The cost of the fabrication and

packaging are also equally important. In this paper, we report on a millimetre-thick flat pump that is

made of polymer materials (except the magnet and coils) and fabricated using electronic packaging

machinery and techniques. Consequently, the cost of fabrication is low.

There are a few earlier attempts of polymer micro pumps. One of them was reported by Bohm et al.

[2] who used conventional techniques such as punching, milling and injection-molding. They used

both piezoelectric and electromagnetic actuation. Boden et al. [3] used paraffin-actuation for plastic

pump of about 0.15 cm3size that gave a flow rate 74 nl/min. Xia et al. [4] used electroactive polymer

material for their micro pump. In comparison to the large number of reported micro pumps (more than

Institute of Physics Publishing Journal of Physics: Conference Series 34(2006) 258263doi:10.1088/1742-6596/34/1/043 International MEMS Conference 2006

258 2006 IOP Publishing Ltd


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260), there are relatively very few polymer pumps. Polymer materials are attractive for many reasons,

which include fabrication without the need for the expensive clean room environment, amenability to

use inexpensive macro-machining techniques, bio-compatibility for implantable applications, etc. The

strength-stiffness ratio is also very high for polymers when compared with silicon, metals and

ceramics. This implies that less power is consumed for the diaphragm-based positive-displacement

type pumps for desired change of volume in the pump-chamber. While piezo-actuation is a

predominantly used technique for micro pumps, electromagnetic actuation has its own advantages.

Unlike piezo-actuation, electromagnetic actuation does not require very high voltages. The powerconsumed by the pump alone may be more in electromagnetic actuation but when one takes the overall

system including the power electronics, it may be even competitive with other actuations [5]. One of

the significant advantages is that electromagnetic actuation does not need special materials: a simple

permanent magnet and coils will suffice. It is particularly well suited for an all-polymer pump such asthe one presented here. The micro pumps reported in [6-8] also use electromagnetic actuation. The

pumps in [7] and [8] use Kapton diaphragm integrated with a Low Temperature Co-fired Ceramic

(LTCC) tapes. These designs used coil on the diaphragm and had the magnet fixed to the substrate.

This was found to be slightly disadvantageous due to the over-heating of the diaphragm and the

consequent thermally induced deformation effects.

The remainder of the paper is organized as follows. In Section 2, the constructional features of the

pump are given along with two different designs that differ in the types of coils used. Section 3

describes the fabrication procedures in detail. Testing and results are in Section 4. Concluding remarks

are in Section 5.

2. Design

Two different embodiments of the pump are considered in this work. These are shown in figures 1 and

2. Both designs have a stationary coil and a moving magnet mounted on a Kapton diaphragm. Thedifference between the two lies in the way coils are practically realized. In the first design (see figure

1a), a copper-clad epoxy plate is chosen as the main substrate. This plate is 1.2 mm thick and had

copper layer of 17.5 m on one side. A square spiral coil is etched on the copper side of this plate.

There exists a milled cavity on the other side. A spacer plates with a square window cutout in the

middle along with the milled cavity forms the pumps chamber. Figure 1a shows this along with inlet

and outlet passive valves and Kapton diaphragm, which is attached between the first spacer plate and a

second spacer plate glued on the top side. A permanent magnet of diameter of 12 mm and thickness of

3.1 mm is attached at the center of the square diaphragm. Passive inlet and outlet check valves were

made using strips of Kapton film placed over 1 mm-diameter holes drilled into the pump-chamber

plate.

Figure 1.Features of the first embodiment of the pump

In the second design, coils are wound in an annular recess made in the epoxy plate. For the coil, we

used 43-gauge enamel-coated copper wire of 90 m diameter is used. Approximately 400 turns of this

wire were manually wound into a coil of average diameter of 9 mm and a height of 2 mm. This coil isburied under the pump chamber. The Kapton diaphragm, the magnet, passive valves and the top-

Bottom epoxy plate

with milled cavity

Spacer plate 1

Spacer plate 2MagnetKapton diaphragm

Inlet valveEtched

copper coilsOutlet valve

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spacer plate are the same as in the previous design. Compared to the etched spiral coil of the first

design, the wound coil has the advantage that its constant radius can be chosen to be the optimum

radius that has the largest magnetic field near to the magnet. This helps in reducing the electrical

power needed to actuate the pump and also helps in preventing undue heating of the pump

Figure 2.Features of the second embodiment of the pump

3. Fabrication

The fabrication procedures for the first and second types of pumps are slightly different although

many of the steps are common to both. The procedure for the first design consists of the following

steps.

(i) A lithography mask (figure 3a) is made using photo-plotting on a transparency sheet from a

Gerber file. The minimum spacing of the 17.5 m thick and 200 m wide coils was 100

m. Using this mask, the image is transferred onto the copper side of the epoxy plate of

size 30 mm 30 mm 1.2 mm. The image-transfer can be done using wet or drylithography methods. In the wet-lithography method, the epoxy sheet is spin-coated with a

positive photoresist for one minute. It is then pre-baked and exposed to UV light through

the mask followed by photoresist-development and post-baking. In the dry-lithography, the

epoxy sheet is laminated with a dry photoresist film. It is then exposed to the UV light for

10 s through the mask. After that it is passed through a developer spraying machine for 10

s.

(ii) The patterned copper layer can be etched using ferric chloride solution (250 g of FeCl3in

one litre of DI water and 10% of HCl) in a beaker. Or, the patterned epoxy plate can be

passed through a copper etchant (CuCl 2 + HCl + H 2 O 2 )-spraying, conveyerized machine.

Then, the photoresist is stripped using acetone or peeled off in NaOH. The etched copper

coil is shown in figure 4.

(iii) After patterning the copper coating, a pocket was milled into the epoxy plate (figure 3b) toa depth of 0.8 mm. Two holes of 1 mm diameter were drilled to serve as inlet and outlet at

the bottom of the milled cavity.

(iv) A small strip of 1 mm wide Kapton film was carefully glued on the inside of the milled

cavity over the inlet hole. The strip should be movable when the pressure inside the

chamber is less than the outside pressure.

(v) Another Kapton film was cut to size and glued on top of the first spacer plate which in turn

is over the epoxy plate with the coil. It is important to ensure that the Kapton film is in a

stretched condition to be effective as the diaphragm. Although it is not imperative, adding a

second spacer plate on top of the Kapton diaphragm helps in securing the diaphragm in the

taut condition.

(vi) The next step is to attach the magnet at the centre of the diaphragm.

(vii) A small strip of Kapton film was affixed over the outlet hole on the outer side of the epoxyplate with the coil. This serves as the outlet check valve.

(viii) Plastic tubing is epoxy-glued over the inlet and outlet holes.

Bottom epoxy plate

with milled cavity

Spacer plate 1

Spacer plate 2MagnetKapton diaphragm

Inlet valve

Wound

copper coils Outlet valve

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(ix) The last step is to solder the electrical wires to the ends of the coil. The wires are connected

to the breadboard circuit that supplies the required electrical power to the pump.

The fabrication of the second design consists of fewer steps. It begins with Step (iii) wherein a

cavity and an annular recess are milled into the epoxy plate and inlet and outlet holes are drilled.

The wound coil of enamel-coated 43-gauge wire is placed into the annular recess (figure 5). The

inlet check valve is glued as in Step (iv). The remaining steps, i.e., (v)-(ix), are the same as they

were for the first design. The prototypes of the two pumps are shown in figures 6a-d.

(a) (b)

Figure 3.(a) Photo-mask showing the square spiral (b) the CNC-milled cavity in the epoxy plate.

Figure 4.Copper coil etched on the epoxy plate. Thin strip of Kapton acting as the outlet valve is

also shown in the figure.

Figure 5.The wound coil of 43-gauge enamel-coated copper wire

4. Testing and resultsIn order to test the pumps for air-flow rate, a breadboard circuit was developed to supply the electrical

power to the pump. The circuit amplifies the small-amplitude square or sinusoidal signal of the HP

33220A function generator by using two transistors connected in a cascade (Darlington pair)

arrangement. The biasing voltage is supplied by HP 34410A DC power supply. The frequency of the

signal can be varied over a range of 0 100 Hz. The range of the voltage is from 1.5 5 V. The

current drawn can be measured using the same power supply unit.

In order to measure the flow rate, we attached a long plastic tube in which a colored water slug is

introduced. The tube is set against a ruler so that the movement of the slug can be timed. This is shown

in figure 7. The frequency of the signal is varied at different voltage levels. The measured flow rate

against frequency is plotted in figure 8 for pump 2. As it can be seen, it has a maximum flow rate of

4.8 ml/min at a frequency of 68 Hz. The voltage and current for this measurement were 2.5 V and 19

mA respectively. Pump 1 requires much higher voltage, draws more current and consequently suffers

from the heat-induced effects and consumes more power for the same performance as pump 2.

Outlet check valve

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(a) (b) (c) (d)

Figure 6.(a) Pump 1 with etched coils (b) Side-view of pump 1 (c) Pump 2 with wound coils (d)

Side-view of pump 2

Figure 7.The test setup for the pump along with the water slug arrangement to measure the flow

rate against atmospheric pressure.

10 20 30 40 50 60 700

2

4

6

8

10

12

14

16

Frequency (Hz)

FlowRate(ml/min)

2.5 V

2.0 V

1.5 V

Figure 8.Air-flow rate of pump 2 at different frequencies and voltages

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5. Closure

The design, fabrication and testing of an electromagnetically actuated minute pump are described in

this paper. The key feature of this pump is that it is flat with a thickness of 4 mm that could be reduced

even further with design improvements. It is made entirely of polymer materials excepting the magnet

and the coil. The measure flow rate was 15 ml/min for a pump of size 5.39 cm3. The fabrication

procedure does not need clean room environment and uses mostly electronic packaging machinery. As

shown in pump 2, the lithography step may also be avoided. Currently, the winding of the coil in

pump 2 is done manually but it too can be automated for a batch-fabrication process. The performanceof the pump can be improved further through modeling and design, which will be taken up in our

future work. This may help reduce the lateral size as well as thickness of the overall pump. The pump

has not yet been tried with the liquids which is our next step.

Acknowledgments

This work was supported by a grant from the National Program on Smart Materials (NPSM) by the

Government of India (Grant # NPSM PARC 5.8). The authors would like to thank Center for

Electronics Devices and Technology (CEDT) and Microfabrication Laboratory of the Indian Institute

of Science for allowing us to use their facilities and equipment. Technical help by Mr. Anthony

Swamy (CEDT) and Mr. Dwarakanath (Microfab) is gratefully acknowledged.

References

[1] Laser, D. J. and Santiago, J. G., A Review of Micropumps, Journal of Micromechanics and

Microengineering, Vol. 14 (2004), pp. R35-R64.

[2] Bohm, S., Olthuis, W., and Bergveld, P., A Plastic micropump constructed with conventional

techniques and materials, Sensors and Actuators A, 77 (1999), pp. 223-228.[3] Boden, R., Lehto, M., Simu, U., Thornell, G., Hjort, K. and Schweitz, J.-A., A Polymeric

Paraffin Actuated High-Pressure Micropump, Sensors and Actuators A, 2006 (article in

press).[4] Xia, F., Tadigadapa, S., and Zhang, Q. M., Electroactive Polymer Based Microfluidic Pump,

Sensors and Actuators A, 125 (2006), pp. 346-352.

[5] Busch-Vishniac, I. J., The Case for Magnetically Driven Microactuators, Sensors and

Actuators A, 33 (1992), pp. 207-220.

[6] Gong, Q., Zhou Z., Yang, Y., Wang, X., Design, optimization, and simulation on

electromagnetic pump, Sensors and Actuators A, 83(2000), pp. 200-207.

[7] Kim, M., Ananthasuresh, G. K., and Bau, H. H., Electromagnetic Pump Fabricated with Low-

temperature Co-Fired Ceramic Tapes and Kapton polyimide Film, IMECE 2000, MEMS

2000 Symposium Proceedings, pp. 249-254, 2000.[8] Bau, H. H., Ananthasuresh, G. K., Santiago-Aviles, J., Zhong, J., Kim, M., Yi, M,. Espinoza-

Vallejos, P., and Sola-Laguna, L., Ceramic Tape Based Meso systems Technology,Micro-Electro-mechanical Systems, 1998 Int. Mechanical Eng. Conf. and Exp., pp. 491-498,

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