Aperture plate for a nebulizer

Abstract

A photo-resist (21) is applied in a pattern or vertical columns having the dimensions of holes or pores of the aperture plate to be produced. This mask pattern provides the apertures which define the aerosol particle size, having up to 2500 holes per square mm. There is electro-deposition of metal (22) into the spaces around the columns (21). There is further application of a second photo-resist mask (25) of much larger (wider and taller) columns, encompassing the area of a number of first columns (21). The hole diameter in the second plating layer is chosen according to a desired flow rate.

Claims

1. An aperture plate wafer comprising: a bottom layer with tapered aerosol-forming through holes; and at least one top layer having spaces, in which said spaces overlie a plurality of the tapered aerosol-forming through holes, wherein the at least one top layer directly contacts the bottom layer so as to completely occlude and inter-fill some of the tapered aerosol-forming through holes in the bottom layer.

2. The aperture plate wafer of claim 1, wherein the tapered aerosol-forming through holes are funnel-shaped.

3. The aperture plate wafer of claim 1, wherein the tapered aerosol-forming through holes are tapered toward a bottom surface of the bottom layer, the bottom surface being opposite a surface that directly contacts the at least one top layer.

4. The aperture plate wafer of claim 1, wherein the spaces are tapered.

5. The aperture plate wafer of claim 4, wherein the spaces are tapered toward the tapered aerosol-forming through holes.

6. The aperture plate wafer of claim 4, wherein the spaces are funnel-shaped.

7. The aperture plate wafer of claim 1, wherein a material of the bottom layer is the same as a material of the at least one top layer.

8. The aperture plate wafer of claim 1, wherein the tapered aerosol-forming through holes have a width dimension in the range of 1 μm to 10 μm.

9. The aperture plate wafer of claim 1, wherein the aperture plate wafer thickness is in the range of 45 μm to 90 μm.

10. An aperture plate wafer comprising: an outlet layer with aerosol-forming outlet holes; and at least one reservoir layer having tapered reservoir holes, in which said reservoir holes overlie the plurality of the aerosol-forming outlet holes, wherein the at least one reservoir layer directly contacts the outlet layer so as to completely occlude and inter-fill some of the aerosol-forming outlet holes in the outlet layer.

11. The aperture plate wafer of claim 10, wherein the reservoir holes are funnel-shaped.

12. The aperture plate wafer of claim 10, wherein the aerosol-forming outlet holes are tapered toward a bottom surface of the outlet layer, the bottom surface being opposite a surface that directly contacts the at least one reservoir layer.

13. The aperture plate wafer of claim 10, wherein the reservoir holes are tapered toward the aerosol-forming outlet holes.

14. The aperture plate wafer of claim 10, wherein the aerosol-forming outlet holes are funnel-shaped.

15. The aperture plate wafer of claim 10 wherein the outlet layer is a bottom layer and the reservoir layer is a top layer, and wherein a material of the bottom layer is a metal and is the same as a material of the top layer.

16. The aperture plate wafer of claim 15, wherein the material of the bottom layer and the top layer is a plated metal.

17. The aperture plate wafer of claim 10, wherein the aerosol-forming outlet holes have a width dimension in the range of 1 μm to 10 μm.

18. The aperture plate wafer of claim 10, wherein the aperture plate wafer thickness is in the range of 45 μm to 90 μm.

19. An aperture plate wafer comprising: an outlet layer with tapered aerosol-forming outlet holes having a width dimension in the range of 1 μm to 10 μm; and at least one reservoir layer having tapered reservoir holes that are tapered toward the tapered aerosol-forming outlet holes, in which said reservoir holes overlie the plurality of the aerosol-forming outlet holes, wherein the at least one reservoir layer directly contacts the outlet layer so as to completely occlude and inter-fill some of the tapered aerosol-forming outlet holes in the outlet layer.

20. The aperture plate wafer of claim 19, wherein a material of the outlet layer is the same as a material of the at least one reservoir layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:—

(2) FIGS. 1 to 3 are cross-sectional diagrams outlining a prior art process as described above;

(3) FIGS. 4(a) and 4(b) are cross-sectional views showing masking and plating steps for a first stage of the method, and FIG. 5 is a part plan view of the wafer for this stage;

(4) FIGS. 6(a) and 6(b) are cross-sectional views showing a second masking and plating stage, and FIG. 7 is a plan view;

(5) FIG. 8 is a cross-sectional view after resist removal;

(6) FIG. 9 shows the wafer after punching to form the final aperture plate shape;

(7) FIG. 10 is a plot of particle size vs. flow rate to illustrate operation of the aperture plate;

(8) FIGS. 11(a), 11(b) and 12 are views equivalent to FIGS. 4(a), 4(b), and 5 for a second embodiment, in which the holes are tapered; and

(9) FIGS. 13(a) and 13(b) are views equivalent to FIGS. 6(a) and 6(b), and for the second embodiment, and FIG. 14 is a plan view in the region of one large upper hole after removal of the photo-resist mask.

(10) Referring to FIG. 4(a) a mandrel 20 has a photo-resist 21 applied in a pattern of vertical columns having the dimensions of holes or pores of the aperture plate to be produced. The column height is preferably in the range of 5 μm to 40 μm height, and more preferably 5 μm to 30 μm, and most preferably 15 μm to 25 μm. The diameter is preferably in the range of 1 μm to 10 μm, and most preferably about 2 μm to 6 μm diameter. This mask pattern provides the apertures which define the aerosol particle size. They are much greater in number per unit of area when compared to the prior art; a twenty-fold increase is possible, thus having up to 2500 holes per square mm.

(11) Referring to FIGS. 4(b) and 5 there is electro-deposition of metal 22 into the spaces around the columns 21.

(12) As shown in FIG. 6(a) there is further application of a second photo-resist mask 25, of much larger (wider and taller) columns, encompassing the area of a number of first columns 21. The hole diameter in the second plating layer is between 20 μm and 400 μm and more preferably between 40 μm and 150 μm. To ensure higher flow rates this diameter is produced at the upper end of the range, and to assure lower flow rates it is produced at the lower end of the range to close more of the smaller openings on the first layer.

(13) Referring to FIGS. 6(b) and 7 the spaces around the photo-resist 25 are plated to provide a wafer body 26 on the mandrel 20. When the photo-resist 21 and 25 is cleaned with resist remover and rinsed away the plated material 22 and 26 is in the form of an aperture plate blank or mask 30, as shown in FIG. 8, having large top apertures 32 and small bottom apertures 33. In this embodiment all of the resist 21 and 25 is removed together, however, it is envisaged that the resist 21 may be removed before the subsequent cycle of masking and plating. In this case the subsequent plating is more likely to at least partly in-fill some of the aerosol-forming apertures.

(14) As shown in FIG. 9 the wafer 30 is punched into a disc and is formed into a dome shape to provide a final product aperture plate 40.

(15) At this stage the doming diameter may be selected to provide a desired spray angle and/or to set the optimum natural frequency for the drive controller. The dome shape provides a funneling effect, and the particular shape of the domed plate affects the spray characteristics.

(16) In an alternative embodiment the aperture plate is not domed, but is left planar, suitable for use in a device such as a passive plate nebulizer. In this type of nebulizer a sonotrode or horn is placed in contact with the medication on the plate. A piezo element causes rapid movement of the transducer horn, which forces a wave of medication against the aperture plate causing a stream of medication to be filtered through the plate to the exit side as an aerosol.

(17) The majority of the benefits of the aperture plate manufacture of the invention are applicable to either vibrating or passive devices.

(18) In more detail, the mandrel 20 is coated with the photo resist 21 with a column height and width equal to the target hole dimension. This coating and subsequent ultraviolet (UV) development is such that columns 21 of photo-resist are left standing on the mandrel 20. These columns are of the required diameter and are as high as their rigidity will support. As the columns are only less than 10 μm, and preferably less than 6 μm in diameter it is possible to get many more columns and resulting holes per unit of area than in the prior art. It is expected that there may be as many as twenty times more holes than in the prior art electroplating approach. This creates potential for a substantial increase in the proportion of open area and resultant nebulizer output.

(19) The mandrel 20 with the selectively developed photo resist in the form of upstanding columns 21 is then placed in the plating bath and through the process of electro-deposition containing the metals Palladium Nickel (PdNi) in liquid form typically is then imparted to the surface. The plating activity is stopped when the height of the columns is reached. No over-plating is allowed as the plating is stopped just as it reaches the height of the columns of photo resist. The plating solution is chosen to suit the desired aperture plate dimensions and operating parameters such as vibration frequency. The Pd proportion may be in the range of about 85% to 93% w/w, and in one embodiment is about 89% w/w, the balance being substantially all Ni. The plated structure preferably has a fine randomly equiaxed grain microstructure, with a grain size from 0.2 μm to 2.0 μm for example. Those skilled in the electro-deposition field art will appreciate how plating conditions for both plating stages may be chosen to suit the circumstances, and the entire contents of the following documents are herein incorporated by reference: U.S. Pat. Nos. 4,628,165, 6,235,117, US2007023547, US2001013554, WO2009/042187, and Lu S. Y., Li J. F., Zhou Y. H., “Grain refinement in the solidification of undercooled Ni—Pd alloys”. Journal of Crystal Growth 309 (2007) 103-111, Sep. 14, 2007. Generally, most electroplating solutions involving Palladium and Nickel would work or Nickel only or indeed Phosphorous & Nickel (14:86) or Platinum. It is possible that a non-Palladium wafer could be plated at the surface (0.5 to 5.0 μm thick, preferably 1.0 to 3.0 μm thick) in PdNi to impart more corrosion resistance. This would also reduce the hole sizes if smaller openings were desired.

(20) When removed from the plating bath, the wafer thickness is typically 5-40 μm depending on the height of the columns. Peeling off the wafer at this point would yield a very thin wafer in comparison to the standard 60 μm thickness of the prior art. A wafer of this thickness would lack rigidity, be very difficult to process, and would require complex and expensive changes to the mechanical fabrication of the nebulizer core to achieve a natural frequency equivalent to the state of the art such that the existing electronic control drivers would be useable, which in some cases are integrated into ventilators. Use of a different drive controller would be a significant economic barrier to market acceptance due to the costs involved.

(21) This problem is overcome by offering the plated mandrel to the second photo resist deposition process. In one embodiment, the photo resist thickness is placed to a depth equal to that required to bring the overall wafer thickness to approximately 60 μm (similar to the prior art wafer thickness). The second mask height is preferably in the range of 40-50 μm for many applications. It is then developed to allow larger columns to stand on the plated surface. These are typically of a diameter between 40-100 μm but could be larger or smaller. The additional height from the second plating aids removal from the mandrel, but importantly it also achieves a particular thickness which is equivalent to the prior art aperture plate thickness to allow the end product aperture plate 40 to be electrically driven by the existing controllers on the market. This creates a natural frequency matching to achieve correct vibration to generate an aerosol. In general, the second plating stage provides a thickness more suited to the nebulizer application for rigidity, flexibility and flexural strength. Another aspect is that it occludes some of the smaller holes, thereby achieving improved control over flow rate. Hence, the second masking and plating stage can be used to “tune” the end product aperture plate according to desired flow rate. Also, it may be rapidly changed between small batches to enable a wide range of differently tuned plates.

(22) The wafer is then carefully peeled from the substrate without the aid of any subsequent processes such as etching or laser cutting. This ease of peeling has the advantages of not imparting additional mechanical stresses into an already brittle wafer. The wafer is then washed and rinsed in photo-resist remover prior to metrology inspection.

(23) In the aperture plate blank or mask 30 the holes 33 have a depth equal to the first plating layer and the final wafer thickness will be equal to the sum of both plating layers, see FIGS. 8 and 9. It is then ready for annealing, punching and doming to form the vibrating plate 40 shown in FIG. 9.

(24) There may be additional steps to improve the membrane properties for certain applications. For example, the membrane may be of an electroformed Ni substrate material that is over-plated with corrosion-resistant materials such as Copper, Silver, Palladium, Platinum and/or PdNi alloys. Copper and silver advantageously have bacteria-resistant properties.

(25) It will be appreciated that the invention provides an aperture plate having a first layer of electroformed metal with a plurality of aerosol-forming through holes which defines the droplet size being ejected and a second top layer of similar or dis-similar electroformed material with larger diameter holes or spaces above the aerosol-forming holes and the plating material of which occlude some of the first layer holes.

(26) In various embodiments, the second layer has a number of holes or spaces with diameters chosen such that a pre-determined number of droplet size forming first layer holes are exposed, which determines the number of active holes and thus defines the quantity of liquid being aerosolised per unit of time

(27) The size and number of holes in both layers can be independently varied to achieve the desired ranges of droplet size and flow rate distribution, which is not possible with the prior art plating defined technology.

(28) It will also be appreciated that the invention provides the potential for a much greater number of holes per unit of area when compared to the prior art. For example a twenty-fold increase is possible, thus having up to 2500 holes per square mm.

(29) Also, in various embodiments the second layer at least completely or partly inter-fills some of the aerosol-forming holes in the first layer, thus forming mechanical anchorage of both layers to help achieve endurance life requirements.

(30) The following is a table of examples of different hole configurations for aperture plates (“AP”) of 5 mm diameter:

(31) TABLE-US-00001 Large Hole Diameter (mm) 0.10 0.08 0.06 0.04 Number Large Holes/AP 815 1085 1464 2179 Small Holes/Large Hole 12 7 4 1 Small Holes/AP 9780 7595 5856 2179

(32) Advantageous aspects of the invention include: (i) Greater number of holes per unit of area are possible (ii) Smaller and more diametrically accurate hole sizes are possible. (iii) Similar thickness to existing commercially available wafers, which alleviates the onerous need to re-design the nebulizer to match the correct frequency for the existing controllers to activate the aerosol generator. (iv) Only two plating layers or plating steps are required (v) Still easy to carefully peel the wafer from the mandrel substrate. (vi) Possible to use existing electronic controllers to drive the aperture plate as the natural frequencies are matched, having achieved similar aperture plate thickness. (vii) Possible to get smaller and more controllable particle sizes (2-4 μm). (viii) Possible to achieve higher flow rates (0.5 to 2.5 ml/min, more typically 0.75-1.5 ml/min) (ix) Possible to achieve flow rates and particle size more independent of each other when compared to the prior art as described. (Typically in the prior art, the increasing flow rate usually requires increasing particle size and vice versa). These advantages are illustrated in the plot of FIG. 10.

(33) Referring to FIGS. 11 to 14 in a second embodiment the processing is much the same as for the above embodiment. In this case however, both of the sets of photo-resist columns are tapered so that the resultant holes are tapered for improved flow of aerosol liquid. There is a mandrel 50, first mask columns 51 and in-between plating 52. The second mask comprises tapered columns 55, and the spaces in-between are plated with metal 56. Greater care is required for the plating steps to ensure that there is adequate plating under the mask overhangs. FIG. 14 shows a plan view, in this case after removal of the photo resist. It will be seen that there are several small holes 61 for each large top hole 65 in the PdNi body 56/52. The top hole 65 has the effect of a funnel down to the small holes 61, which themselves are funnel-shaped.

(34) The invention is not limited to the embodiments described but may be varied in construction and detail. For example, it is envisaged that the second cycle of masking and plating may not be required if the wafer can be removed from the mandrel, either due to the required wafer depth being achieved in the first stage or due to improved wafer-removal technologies being available. In addition, a third layer could be applied to provide more mechanical rigidity to the aperture plate. Also, in the embodiments described above the layers are of the same metal. However it is envisaged that they may be different, and indeed the metal within each hole-forming layer may include sub-layers of different metals. For example the composition at one or both surfaces may be different for greater corrosion resistance and/or certain hydrophilic or hydrophobic properties. Also, there may be an additional plating step for the top 1 to 5 μm or 1 to 3 μm surface layer.