EP0741839B1 - Micro-diaphragm pump - Google Patents

Description

The invention relates to a micro diaphragm pump according to the preamble of claim 1, as from R. Rapp, W. K. Schomburg, P. Bley, "Concept, Development and Realization a micromembrane pump using LIGA technology ", KfK report no. 5251, (1993). This pump is from an external pneumatic actuator and is able to to promote gaseous media. The pump has a pump membrane made of titanium and valves consisting of a titanium and a Polyimide membrane exist. The pump membrane can reach the bottom the pump chamber can be deflected and in this way a high compression ratio. For the deflection of the Pump diaphragm, however, becomes a relatively high pressure required that is not generated by an integrated actuator can be. In addition, all pumps must be manufactured individually be glued, which requires a lot of effort. The Manufacturing this pump requires many in a row individual steps to be carried out.

Various other micromembrane pumps are known e.g. two differently driven pumps, which in H.T.G. van Lintel, F.C.M. van de Pol, "A piezoelectric micropump based on micromachining of silicon ", sensors and Actuators, 15 1988 153-167 and H.T.G. van Lintel, H.T.G. van Lintel, M. Elwenspoek, J.H.J. Fluitman, "A thermopneumatic pump based on micro-engineering techniques ", sensors and Actuators, A21-A23 1990, 198-202. The first Pump has a pump membrane with glued-on piezoceramic, the second pump has one above the pump membrane thermopneumatic drive in the form of a heat supply expanding air volume. Both pumps have integrated intake and exhaust valves.

Another micropump is in Roland Zengerle, Axel Richter, "Micropumps as components for microsystems", physics in our Time / 24. Year 1993 / No. 2, the also has integrated valves and their pump diaphragm is deflected by electrostatic forces.

The fixed and moving parts of the mentioned micro diaphragm pumps, that represent the current state of the art, are essentially made of the basic materials silicon and Made of glass. The elastic parts of the pumps described, these are primarily the pump and valve membranes thinly etched using different etching processes. The smallest membrane thicknesses are of the order of magnitude 20 mm. The thickness of the membranes and the material properties of glass or silicon provide the pumping power for these pumps essentially restrictive constraints. It are only small deflections with relatively large membrane diameters possible. As a result, such pump membranes can be used not those necessary to extract gases Achieve compression ratios. Furthermore, the diameter The valves are chosen very large for flexibility of the valve membranes and thus the pressure loss in the forward direction to keep small.

US-A-3 606 592 and GB-A-2 088 965 show the possibility via a grid embedded in the membrane to allow increased temperature and thus heat generation, one or more interconnected cavity systems are however not available.

The object of the invention is to provide a pump of the e. G. Way of designing that with just a few work steps you can do a simple one Construction can be built.

This object is achieved by the features of patent claim 1 solved.

The sub-claims describe advantageous refinements the pump.

A particular advantage of the pump is that the simultaneous, parallel production of many pumps with few Manufacturing steps made possible with as little effort becomes. The lowest possible manufacturing effort relates doing both on the manufacture of the individual components of the pump such as pump housings, pump diaphragms and valves as well as on the simultaneous and exact bonding of many micro components in one step. Furthermore, by designing the membrane minimized pressure losses in the area of the actuator chamber.

The invention is described below using an example Help of the figures explained in more detail.

Fig. 1 shows a schematic cross section through a pump and FIG. 2 shows a molding tool for the production thereof.

3, 4 and 5 show valves as used in the pump will.

6, 7 and 9 to 12 explain the adhesive technology for production the pump and Fig. 8 shows an example of the manufacture a membrane with a heating coil.

Structure of the micropump, naming of the components

Figure 1 shows schematically the basic structure of the micropump. A polyimide membrane 3 with a thickness of 2 mm is on it Top with the pump housing upper part 1 and on its underside glued to the pump housing lower part 2. The pump housing contain the non-movable functional components of the Pump. These are the actuator chamber in the pump housing upper part 1 17, various flow channels 6, the valve chamber 8 and the Valve seat of the intake valve 10, the valve chamber of the exhaust valve 13, fluid inlet 5, fluid outlet 7, a coherent Cavity system 19 for filling with adhesive, and Filling openings 20 and outlet openings for filling with glue. Also not shown are openings for the electrical contacting of the pump available. The functional components are the pump chamber 16 in the lower part of the pump housing, the flow channels 6 between valves and pump chamber, the Valve chamber of the intake valve 9, the valve seat of the exhaust valve 14, a cavity system 18 for filling with adhesive, Glue inlet 22 and glue outlet 23. Cavities 18, 19 for the filling process and the cavities 6, 8, 9, 12, 13, 16, 17 are delimited from one another by webs 24, with the help of which the lateral structures are formed and the structure height is exact To be defined. The polyimide membrane 3 is characterized by high elasticity and forms in the area of the actuator chamber 17 the pump membrane. In the area of the inlet valve 8, 9, 10 and the exhaust valve 12, 13, 14 are each one Holes 11 and 15 in the polyimide membrane 3. The valve action arises from the fact that the hole in the membrane through the plan Valve seat is closed, provided there is overpressure on the Valve seat opposite side prevails, or that the Diaphragm with reverse pressure from the valve seat takes off that the hole in the membrane is released and a flow arises. The micromembrane pump is driven due to the thermal expansion of a fluid which is located in the actuator chamber 17 and through a on the polyimide membrane applied metallic heating coil 4 heated becomes.

How the micropump works:
A short current pulse is applied to the heating coil 4. This heats up and gives off heat both to the medium in the actuator chamber 17 and to the medium in the pump chamber. If there are gaseous media in the actuator chamber 17 and pump chamber 16, the resulting from the heating directs
Pressure increase of the actuator gas from the pump membrane. The deflection of the pump membrane 3 reduces the volume of the pump chamber 16 and, together with the simultaneous heating of the pump gas, leads to an increase in pressure in the pump chamber 16. By using a liquid medium which boils at low temperature in the actuator chamber 17, the expansion of the medium is reduced by the latter Evaporation reached, which can generate very high actuator pressures. The consequence of the pressure increase in the actuator chamber 17 is again the deflection of the pump membrane 3 in the direction of the pump chamber 16. In both cases, the resulting pressure increase of the fluid to be pumped continues via the flow channels to the valves and leads to the membrane becoming larger in the area of the inlet valve 11 bears on the valve seat 10 and closes the valve, while the membrane in the area of the outlet valve 15 lifts off the valve seat 14 and opens the opening in the valve membrane. The pump medium is pushed out.

After the end of the current pulse, the cooling of the medium begins in the actuator chamber 17 by heat conduction and heat radiation. In the case of the gaseous medium in the actuator chamber pressure and volume decrease inside the actuator chamber according to the gas laws, in the case of the vaporized liquid returns condensation to its original state. The Pump diaphragm moves back to its original position and thus creates as a result of the pump medium previously ejected a negative pressure in the pump chamber 16 and on the valves. Closes according to the valve function described above now the exhaust valve while the intake valve opens and Pump medium enters into the pump chamber. Repeat these operations each pump cycle.

The heating coil attached directly to the pump membrane has in addition to the resulting simple manufacturing process other significant advantages. On the one hand is the heat transfer minimized on the pump housing in the heating phase. The second is when using a low boiling liquid the recondensation of the actuator medium as the actuator medium initiated by the pumped medium at the location of the heating coil. This ensures that at the beginning of the next Heating phase the heating coil in optimal thermal contact with the Actuator liquid is standing.

Valves

Figure 3 shows an embodiment of a valve. The Valves are characterized in that they consist of a flexible, free spanned membrane 3, which in the central Area has a microstructured opening 11. The outline the valve opening 11 and the membrane clamping 25 can, as shown by way of example in FIG. 4, round, oval or through a Polygon be writable. Figure 3 explains the principles Structure of a valve as manufactured in the Pumping is implemented. Located on one side of the membrane a flat, fixed valve seat 10, which the opening of the Valve membrane by at least the width of the required Sealing surface between diaphragm and valve seat covered. Of the The valve seat is part of one of the two pump bodies that are connected to the Membrane are connected. The tightness of the valves in the blocking direction is determined by the degree of coverage, the surface roughness of valve membrane and valve seat and essential determined by the flexibility of the valve membrane. By a very thin polyimide membrane can also work under unclean conditions the sealing effect can be maintained as it is able is to nestle around small dirt particles.

Due to the height of the valve seats, the opening and Specify the closing behavior of the valves, see Figure 5. Figure 5a shows the relationships of the executed example. Membrane clamping and valve seat are on one level. Figure 5b shows the embodiment of a high valve seat, which in no-load condition the membrane bulges upwards. Here is for Opening the valve requires a considerable pressure difference the valve remains until this pressure difference is reached closed in the forward direction. The pressure drop at a given Flow and therefore the drop in performance is higher than in Figure 5a. However, the reflux decreases Load changes through the smaller stroke volume and through the less flexibility of the free, more tense Membrane. This configuration is advantageous if Small volume flows rectified under large pressure differences should be or if the load change frequencies are high are. In Figure 5c the height of the valve seat does not reach that Level of membrane clamping, the membrane is in the no load Case freely stretched over its entire surface. The valve has in the forward direction a lower flow resistance than in case a, closes in the blocking direction only after reaching a barrier pressure. This interpretation of valve seat and Membrane is advantageous when large volume flows are below small pressure differences should be rectified.

glue

Are the individual parts of the upper pump housing, membrane and lower Pump housing glued in a conventional manner, d. H. glue is applied to the individual parts using techniques such as dispensing, Screen printing or pad printing applied, then one is created Adhesive layer, the thickness of about 10 microns with the Order of magnitude of the microstructures themselves can be compared can. High tolerances of the adhesive joint thickness are not too avoid what mainly negatively affects the function of the microvalves because the desired distance between Valve membrane and valve seat are not adhered to exactly can. Another disadvantage of conventional gluing techniques is the additional positioning of the lateral distribution of the Adhesive to the microstructures because different areas so z. B. the valve seats and channel structures, not with adhesive may be wetted. Finally, is the glue applied, then the exact positioning of the adhesive partners to each other and the subsequent smear-free Put together very high handling requirements Rehearse. So two positioned operations are necessary.

The adhesive technology mentioned in claim 5 overrides all of these Disadvantages and is due to their simplicity and low Number of steps for the parallel bonding of Microstructures ideally suited. Already in Design of the microstructures the prerequisites for successful Gluing created. The basic idea is that itself on a substrate that has a large number of microstructures may contain concave structures around the microstructures are around that are contiguous or partially contiguous can be and from the functional areas the microstructures separated by bars of constant height are. The concave structures have the task, in fact Adhesive step to take up the adhesive so that after gluing the adhesive, separated by the webs, round around the microstructures. The adhesive takes over the function of the mechanical linkage of the joining partners, the Sealing of individual microstructures and the joining partners with each other and contributes to degradation through internal relaxation processes of residual stresses, e.g. B. by temperature changes arise between the adhesive partners, at. The bridges have them Task, due to their height, an exactly reproducible reference height to specify for the setting of the adhesive joint thickness and while the adhesive flows into the microstructures to avoid the gluing process.

FIG. 6 explains the conditions on the basis of a supervision of the Lower part of the housing of the micropumps as they were manufactured. 18 means the concave structure in which adhesive is filled 24, the webs that delimit the adhesive area, 16, 9, 6, 14 are the functional areas pump chamber, valve chamber, Flow channels of the pump and valve seat that are free of Have to stay glue. 22 is the opening into which the adhesive flows in and 23 is the opening from which excess Adhesive can leak out or into another microstructure can occur.

Figure 12 shows in detail the cross section through a concave Structure to hold the adhesive between two microstructures. It means 24 the webs that cover the adhesive area of delineate the actual microstructures, 26 and 31 are the locally involved adhesive partners. Figure 12a shows the case that the adhesive layer thickness corresponds to the height of the webs (= reference height). The concave structure is shown in FIG. 12b of the adhesive in areas of great structural height 36, which are primarily serve the adhesive feed, and in areas low structural height, which is adapted to the adhesive exact adjustment of the actual adhesive thickness allowed.

The gluing process begins with the adjustment of the gluing partners to each other (Figure 7a) and the subsequent fixing of the joining partners by a tensioning device (Figure 7b). The tension ensures that the webs 24 of a joining partner be pressed onto the second joining partner, creating a closer Contact is guaranteed. This close contact enables the exact adherence to the desired structural distance between the two Joining partner and offers adequate sealing during the actual gluing process. The process of adjustment and tensioning happens without the presence of glue, which has the advantage that the problems of adhesive handling do not negatively affect the precision of the bond can. In the actual gluing step (Figure 7c) Glue into the hollow structures created by joining them together filled. Either microstructures, which have a Kleeinein 20 and outlet 21, individually filled (see Figure 6), or a large number of microstructures, the about appropriately prepared cavities have a channel system (see Figure 9), or there can be a number of microstructures over a complete Cavity system are filled (see Figure 10). The sequence the filling process depends on the fluid dynamic properties of the adhesive used. To control the filling The glue can be applied through a cannula that is tight on the glue inlet is put on, fed. Depending on the viscosity and wettability of the adhesive, as well as the desired Inflow rate, the adhesive is with Overpressure is conveyed into the microstructures until it reaches the exit opening exit. Adhesive flow and distribution controlled by the geometry of the cavity system. A further control of the flow process can be achieved by Outlet openings 21 are subjected to negative pressure. This may be necessary especially when designing complex channel systems meet the fluid dynamic requirements not sufficiently precise for even filling could be taken into account. After filling the The adhesive is cured according to its specification.

Suitable for this technology, all adhesives are more satisfactory Adhesion that occurs in the microchannels and microvoids Have them transported in with reasonable pressures. The surface tension of the Adhesive and the resulting capillary behavior in the Interaction with the joining partners. Highly wetting adhesives have the property of penetrating the smallest gaps. This can cause adhesive to work as described into the adhesive parts due to roughness in the nanometer range under the webs pressed onto the adhesive partner creeps what u. U. undesirable for the function of the micro component can be. In general, this effect does not lead to a malfunction of the microcomponent, provided the adhesive not over the edge of the webs that define the adhesive cavities are turned away, flows over and wets the microstructures, which should remain free of glue. Should flow into it of the adhesive under the webs are completely prevented, so the gluing process can be done by a non-adjusted intermediate step expand that for a complete seal below the webs. To do this, the microstructures, which contain the webs, in the stamp process with a highly viscous, chemically stable layer, which on a flat Substrate with constant thickness was applied in contact brought. It can be z. B. is an industrial fat, which after the gluing with a solvent can be rinsed out without residue. Become the bridges now pressed onto the adhesive partner (see Figure 7b), so seals the applied in the order of the surface roughness Layer the adhesive cavities completely from the adhesive-free Functional areas. Penetration of the glue as a result of the capillary action no longer takes place.

The use of hot melt adhesives is also conceivable, provided that whose processing temperature does not destroy the joining partners or impaired. This is where the adhesive partners have to be the filling process to the processing temperature of the adhesive to be brought.

It is also possible that more than two adhesive partners on one Bonding are involved. This is e.g. B. the case when as shown in Figure 11 using an example, an auxiliary structure 32 is used to form a first structure 28, 26 with a to glue the second structure 31. The auxiliary structure 32 provides for a separation of the areas that should contain adhesive from the areas that must remain free of glue and ensures the exact maintenance of a desired distance between the adhesive partners. It can consist of one or more Share exist, it can be inserted discretely or it can have been built on one of the adhesive partners.

The manufacture of the individual components of the micropump is described using an exemplary embodiment:
Each of the three individual components pump housing upper part 1, pump membrane 3 with an applied metal structure 4, pump housing lower part 2 in FIG. 1 of the micropump was produced independently. The individual components can thus be checked before assembly.

Body, use of form, workflow

Upper 1 and lower pump body 2 were microstructured using a Impression tool by methods of plastics processing Injection molding and vacuum stamping. FIG. 2 exemplifies the structure of a Impression tool for the upper housing part of Figure 1. One for prepared for use in the plastic impression apparatus, ground and polished semi-finished product from the impression surface Brass was cut with the help of a carbide micro milling cutter (diameter: 300 µm) structured. It's both the structures included for the valve seats according to claim 2, as well as the Structures for separating the adhesive area from the functional area the micropump according to claim 1. The mold inserts could by the fact that the pump housing only constant from webs Width (= milling cutter width) and a few valve seats with little machine time in the form of grooves of simple geometry be milled. On a first impression tool the structures for twelve pump tops 1, on one second mold insert the structures for twelve pump lower parts

The parameters were used to manufacture the plastic pump body both the vacuum embossing device and the Injection molding machine chosen so that the total thickness of the molded Parts lmm. The plastics were used as materials Polysulfone (PSU) (in the injection molding machine) and polyvinyl diflouride (PVDF) (used in the vacuum embossing machine). The materials mentioned are characterized by high chemical Resistance, optical transparency and temperature resistance out. An unfavorable material property for pump operation of all plastics is their compared to metals and semiconductors low thermal conductivity. The consequence of the use of plastic pump housings is that when operating the Pump dissipated heat output in relation to pump housings Metal of the same thickness is small and the pump as a result only may be operated at low power to prevent overheating to avoid. The disadvantage can be overcome by the total thickness of the pump housing is chosen to be very small and an intensive thermal contact with a basic substrate with high thermal conductivity possibly heatsink is produced. A decrease the layer thickness can be selected by choosing the impression parameters, by post-processing with the help of an ultra-milling machine or be carried out by a plasma etching step. The Bores for fluid inlet and outlet (5, 7 in FIG. 1), Adhesive feed and ventilation (20, 21, 22, 23 in Fig 1), as well as the holes for electrical through-plating not yet considered in the design of the mold inserts, but subsequently with twist drills with a diameter of 0.45 mm and drilled 0.65 mm.

Manufacturing process PI, Ti

The core of the micropump is a polyimide film with direct applied heating coil. The polyimide film that is used for a large number of single pumps with a single mask lithographically is structured, takes on both the task of individual pump membranes as well as the valve membranes. On the polyimide film was made using thin-film technology an electrically conductive layer applied in the area of the individual pump membranes was structured into heating coils. The contact surfaces for the electrical connection of the heating coils were each outside of the pump membrane. The manufacturing process the structured polyimide film and the Heating coils will now take a closer look at the pumps manufactured be explained (see Figure 8). As a carrier substrate for the thin film processes was a silicon wafer with a wafer Diameter of 100mm used. Since the slide after the first Bonding has to be separated from the wafer thin gold separating layer 27 sputtered onto the wafer Figure 8a. An edge 33 of 5 mm was created during the sputtering process covered around the wafer to ensure adhesion there of the polyimide to maintain the silicon substrate and thereby prevent premature detachment of the polyimide film from the wafer. A polyimide layer 28 was then formed (FIG. 8b) of the photo-structurable polyimide Probimide 408 from CIBA-GEIGY spun to a thickness of 3 µm with a spin coater and dried in one step. The dried one Paint layer was then in the contact process with UV light 34 exposed. Because the polyimide used is a negative varnish the chrome mask 29 used for this an exposure of the areas where a polyimide film obtained should stay and for coverage of the areas that should be extracted during development. Latter are the holes of the valves 15 and different alignment marks. This was followed by the development of the polyimide and a postbake in the Vacuum oven Figure 8c.

After structuring the polyimide was a titanium layer 30 applied by magnetron sputtering in a thickness of 2 µm., to structure heating coils 15, the one have good adhesion to the polyimide. The titanium layer 30 was lithographically through the positive lacquer AZ4210 and through a subsequent etching process in a solution containing hydrofluoric acid structured. The exposure of the photoresist used was adjusted using the alignment marks in the polyimide layer and using alignment marks on the mask for structuring made of the titanium layer. Figure 8e shows the finished membrane structure located on the auxiliary substrate.

The sputtering parameters were used in the production of the titanium layer (Temperature, bias voltage, gas flow and the plasma generating electrical power) set so that a internal tension in the titanium. The heating coils stood therefore after the titanium layer also under tension. After the detachment of the heating coil 4 and polyimide membrane 3 pulled the titanium from the silicon wafer 26, which has a much higher modulus of elasticity than polyimide together with the polyimide film. The polyimide film was upset. By the shape of the applied Heating coils were achieved that not only the pump membrane was tension-free but sagging. For the deflection such a slack pump membrane almost needs no energy to be spent. If you design them Heating coil as a double spiral, this leads to the voltage reduction the heating coil after detaching from the substrate for reduction their length, which according to geometric laws leads to the fact that the inner areas of the polyimide membrane in the Large radial ratio in relation to the elastic material expansions Experience shift towards the center. This shift leads to the curvature of the membrane. A curvature of a membrane can also be achieved by using any other structures tangential orientation around the membrane or in the Membrane are attached. The structures can be closed or broken circles to closed or interrupted polygons or spirally arranged closed or interrupted traverse lines.

The heating coil applied directly to the heating coil has two essential advantages. Firstly, the heat transfer to that Pump housing minimized during the heating phase. The second is when using a low-boiling liquid as an actuator medium the recondensation of the actuator medium by the funded Medium introduced at the point of the heating coil. Thereby is achieved at the beginning of the next heating phase the heating coil in optimal thermal contact with the actuator fluid stands.

Instead of polyimide as membrane material, others can also Plastics or metals are used, with metal membranes an additional electrically insulating layer between Membrane and heating coil must be provided.

Assembling the micropumps

The individual components of the upper part of the pump housing, Pump housing lower part and polyimide membrane with titanium heating coils could be examined for errors and were now available Ready to glue. The three individual components were through two adhesive processes (Figure 7) of the type described together glued. For this purpose, a simple device 35 was created, in which the adhesive partners are inserted, adjusted to each other and then connected were braced against each other. In the first gluing process became the polyimide film on the silicon substrate 26 with the pump housing upper part 1, which i.a. the Contains actuator chamber and all pump connections, glued (Figure 7a-c). To further reduce voltage in the free membrane areas of the micropumps were obtained Adjustment, bracing and adhesive filling at about 100 ° C. Since the pump housing made of PSU or PVDF a much higher coefficient of thermal expansion than the silicon substrate, the lateral ones were already Dimensions of the adhesive partners matched so that it is only complete after it has been heated to 100 ° C are a perfect fit. At room temperature the structure dimensions are the membrane and the heating coils on the substrate 26 larger than the corresponding dimensions of the pump housing. Cool the adhesive partners again after bonding to room temperature, then the contraction of the plastic Pump housing for compressing the membranes.

After the adhesive has fully hardened at 150 ° C the wafer with the connected, glued-on pump housing upper part 1 of the clamping device 35 and cut the polyimide film around the rectangular plastic part. As the cooling progressed, the dissolved Polyimide film starting from the cut edge and supported due to the contraction of the plastic part due to cooling 1 independently of the silicon wafer (Figure 7d).

In the second gluing step, the same was finally done Way the pump housing lower part 2 glued to the membrane side (Figure 7e and 7f). To start up the pumps, the necessary electrical and fluid connections attached and the pumps isolated.

The pumps were operated with an electrical voltage of 15 V and operated at a frequency of 3 Hz. The tension was there for each 58 ms applied. The average input power was 0.27 W. There was a delivery rate for air of 26 ml / min measured. The deflection of the pump membrane was clear 3 recognized to the bottom of the pump chamber 16 with the naked eye be synchronized with the movement of the pump membrane Opening and closing the valve membranes in the microscope be observed.

Claims (6)

1. Micromembrame pump consisting of the upper and the lower part of the pump housing with membranes being arranged between both parts, thus making up a pump chamber, two valves and flow channels, with the membrane in the range of the pump chamber acting as a pumping membrane and the membranes in the range of the valves taking over part of the valve function, as well as of the driving unit for the pump membrane, characterized by a heating element (4) connected to the pump membrane (3) and by one or several connected trench systems in each part of the pump housing (1, 2) which are open towards the membrane and completely filled with a bonding material.
2. Micromembrane pump according to claim 1, characterized by the heating element (4) being an electrically heatable heating spiral.
3. Micromembrane pump according to claim 1 or 2, characterized by the pump membrane and the valve membranes being parts of a single complex structure.
4. Micromembrane pump according to one of the claims 1 to 3, characterized by the valves consisting of valve seats (10, 14) which are structured into both parts of the pump housing (1, 2) and of holes (11, 15) in the membrane.
5. Process for the production of micromembrane pumps according to one of the claims 1 to 4, characterized by both parts of the pump housing accommodating one or several connected trench systems which are open towards the membrane, including the following process steps:

   a) Adjusting of one or both parts of the pump housing (1, 2) and the membrane (3) and pressing of the adjusted parts together such that the trench systems and the membranes form complex, tight cavity systems, and

   b) complete filling of the cavity systems with a bonding material.
6. Process according to claim 5, characterized by several pumps being produced simultaneously.

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