METHOD FOR PRODUCING AN APERTURE PLATE

Abstract

An aperture plate is manufactured by plating metal around a mask of resist columns having a desired size, pitch, and profile, which yields a wafer about 60 μm thickness. This is approximately the full desired target aperture plate thickness. The plating is continued so that the metal overlies the top surfaces of the columns until the desired apertures are achieved. This needs only one masking/plating cycle to achieve the desired plate thickness. Also, the plate has passageways formed beneath the apertures, formed as an integral part of the method, by mask material removal. These are suitable for entrainment of aerosolized droplets exiting the apertures.

Claims

1. A method of manufacturing an aperture plate wafer, the method comprising providing a substrate of conductive material, applying a mask over the substrate in a pattern of columns having top surfaces, electroplating around the columns, removing the mask to provide a wafer of the electroplated material with aerosol-forming holes, wherein, the electroplating step partially over-plates the top surfaces of the columns while leaving aerosol-forming apertures of a desired size, the columns have a height in the range of 40 μm to 70 μm.

2. The method as claimed in claim 1, wherein the columns have a height in the range of 55 μm to 65 μm.

3. The method as claimed in claim 1, wherein the column width dimension is in the range of 20 μm to 40 μm.

4. The method as claimed in claim 1, wherein the column width dimension is in the range of 25 μm to 35 μm.

5. The method as claimed in claim 1, wherein the combined aperture plate wafer thickness achieved by the column height and the height of over-plating is in the range of 50 μm to 70 μm.

6. The method as claimed in claim 1, wherein the aperture size is in the range of 2 μm to 6 μm.

7. The method as claimed in claim 1, wherein the over-plating is controlled and the column dimensions are chosen to also achieve a desired slope of wafer material towards the aerosol-forming apertures to achieve a funnelling effect for liquid in use.

8. The method as claimed in claim 1, wherein the over-plating is controlled and the column dimensions are chosen to also achieve a desired slope of wafer material towards the aerosol-forming apertures to achieve a funnelling effect for liquid in use; and wherein the wafer is formed into a dome shape which is concave on the side of the apertures, and the extent of curvature and the shape of the over-plated metal is chosen to provide a funnelling effect for liquid towards the apertures.

9. The method as claimed in claim 1, wherein the top surfaces of at least some columns (are generally convex.

10. The method as claimed in claim 1, wherein the columns are configured so that when the masking material is removed they form passageways aligned with the apertures and being shaped for entrainment of droplets form the apertures.

11. The method as claimed in claim 1, wherein at least some of the columns have a configuration widening towards the substrate so that after removal of the masking material they form passageways which widen in a direction away from the apertures.

12. The method as claimed in claim 1, wherein at least some of the columns have a configuration widening towards the substrate so that after removal of the masking material they form passageways which widen in a direction away from the apertures; and wherein the passageways are gradually tapered with a consistent slope.

13. The method as claimed in claim 1, wherein the columns are configured so that when the masking material is removed they form passageways aligned with the apertures and being shaped for entrainment of droplets form the apertures; and wherein the passageways have a length in the range of range of 40 μm to 70 μm.

14. An aperture plate comprising a body of metal configured with aerosol-forming apertures in a top surface and passageways aligned with and beneath the apertures, wherein the metal forms convex shapes around the apertures to provide a funnel-shaped entrance to the apertures.

15. The aperture plate as claimed in claim 14, wherein said passageways have a length in the range of 40 μm to 70 μm.

16. The aperture plate as claimed in claim 14, wherein the passageways widen towards a lower side of the plate.

17. The aperture plate as claimed in claim 14, wherein the passageways have a length of 55 μm to 65 μm, and the aperture plate has a thickness in the range of 50 μm to 70 μm; and wherein the passageways have a width in the range of 20 μm to 40 μm.

18. The aperture plate as claimed in claim 14, wherein the passageways have a length of 55 μm to 65 μm, and the aperture plate has a thickness in the range of 50 μm to 70 μm; and wherein the passageways have a width in the range of 20 μm to 40 μm; and wherein the passageways have a width in the range of 25 μm to 35 μm.

19. An aerosol-forming device comprising an aperture plate drive and an aperture plate support supporting an aperture plate comprising a body of metal configured with aerosol-forming apertures in a top surface and passageways aligned with and beneath the apertures, wherein the metal forms convex shapes around the apertures to provide a funnel-shaped entrance to the apertures.

Description

DESCRIPTION OF THE EMBODIMENTS

[0052] Referring to FIGS. 1 to 4, the following are the main steps to manufacture an aperture plate in one embodiment.

[0053] An aperture plate is manufactured by plating metal around a mask of resist columns 2 having a height of about 45 μm, a diameter of about 30 μm and a separation of about 30 μm. The plating is continued so that the metal 3 overlies the top surfaces of the columns until the desired apertures 4 are achieved. This provides the benefits of both photo-defined technology (by reducing the aspect ratio near the aperture region during electroforming) and aperture density by enabling more closely patterned resist islands, with need for only one masking/plating cycle to achieve the desired plate thickness.

[0054] In more detail, non-conductive photo-resist 2 is laid on to a mandrel 1 substrate. This is developed to leave the upstanding columns 2 where holes are required. The tops of the columns 2 are approximately convex. The mandrel is placed in an electroforming tank. As the plating continues, the space between the columns 2 of developed photo resist is in-filled with the plating material. This is typically a PdNi alloy matrix, or it could alternatively be Nickel or a Nickel Cobalt alloy matrix.

[0055] The plating is initially to the extent shown in FIG. 2 and is continued so that over-plating occurs as shown in FIG. 3. This plating is stopped just in time to create 2 to 6 μm holes 4 as shown also in FIG. 3.

[0056] The diametrical size accuracy of these holes can be improved by slowing down the plating deposition activity as the holes are being formed. This prevents ‘overshoot’ resulting in smaller or occluded holes with the possibility of a thicker than desired wafer construction. The 45 μm column height is so chosen such that when the plating is stopped (FIG. 3) the holes are typically 2 to 6 μm and preferably 2 to 5 μm, which is required to produce droplets in the inhalable range for nebulisation, and concurrently the wafer thickness is in the range of 60 to 62 μm in one embodiment.

[0057] The convex shape of the entry surfaces to the apertures in addition to the concave shape of the overall domed shaped aperture plate (FIG. 7) provides effective funnelling of the liquid towards the aerosol-forming apertures 4, thereby minimising the residual volume of the drug in the nebuliser. When the photo-resist 2 is removed using an appropriate dissolving solvent, the full wafer cross-section is evident as depicted in FIG. 4. The cross-sectional profile under the hole 4 forms passageways directly under and aligned with the apertures. Because they are formed by removal of the column resist they have the same length as the heights of the columns 2. In use, these passageways under the apertures encourage entrainment of the aerosol towards the outlet of the nebuliser, thereby reducing coalescence with the resultant undesirable effect of larger droplets being formed.

[0058] In an alternative embodiment (FIG. 5), photo-resist columns 11 have flat top surfaces over which the metal (12) is plated.

[0059] As evident from FIG. 6, in a plate 20 the remaining metal may form outlet hole or passageway 24 sides that are tapered towards the aerosol outlet direction. This drawing shows the wafer metal 21 forming aerosol-forming apertures 22. The liquid 23 is aerosolized through the apertures 22 to exit as droplets through the entrainment openings or passageways 24 aligned with and below the apertures 22. Clearly, choice of geometry of the resist columns decides the geometry of the passageways.

[0060] FIG. 7 shows an aperture plate 30 with metal 31 forming apertures 32 and droplet entrainment openings 34, after being formed into a dome shape. As noted above, this dome shape together with the convex shape of the metal between the apertures 32 helps to effectively funnel the liquid 33 towards the apertures 32 in order to form droplets, which exit via the entrainment openings 34.

[0061] These much larger holes 34 in comparison (to the aperture diameter) can entrain the aerosol, almost into a laminar flow pattern. This reduces turbulence and consequential coalescence which can lead to an undesirable increase in droplet size. These openings may be tapered (FIGS. 6 and 7) or not (FIGS. 1-4).

[0062] The resultant wafer 10 has a greater number of holes, greater than 44,100 per 650 mm.sup.2 (square inch, Mesh 210), than the prior art and yet maintains the same aperture plate thickness (approximately 61 μm) as many commercially available products. This ensures that the existing drive controllers (128 kHz) already in situ in many hospitals can be used for the aperture plate, alleviating the cost and considerable time required to be expended to develop a bespoke drive controller to ensure that the correct frequency is available to achieve optimum aerosol output. It is also more conducive for meeting and exceeding the fatigue life requirements. As there is single-layer plating it incorporates a fine equiaxed microstructure.

[0063] It will be appreciated that the method provides the benefits of both photo-defined technology, partially decoupling the dependence of wafer thickness to resist island patterning distance and increased aperture density, with the process simplicity of electroforming, because it needs only one masking/plating cycle to achieve the desired plate thickness.

[0064] Those skilled in the electro-deposition field will appreciate how the plating conditions 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 (1-3 microns thick) in PdNi to impart more corrosion resistance. This would also reduce the hole sizes if smaller openings were desired.

[0065] The resist geometry, such as height, width, and shape, is configured in such a way as to increase the number of holes while maintaining the desired wafer thickness. Further increase of hole density is also possible. For example, the invention in one embodiment achieves an aperture plate of about 4 times the density (moving from 210 to 420 holes per 25 mm (linear inch) or from 44,100 to 176,400 holes per 650 mm.sup.2 (square inch), while still maintaining the typical 60 to 62 μm thickness range.

[0066] Adjusting the dimensions in FIG. 1, by reducing the column 2 diameter (30 μm) and dimensions between the columns 2 to say 15 μm has the potential to increase the number of holes to 700 to 850 per 25 mm (linear inch).

[0067] The invention avoids need for two-layer photo defined technology to increase the number of holes while maintaining the same wafer thickness. It also solves the problem of using standard plating defined technology as referred to in the Prior Art Discussion with a greater number of holes which will result in a lower thickness wafer, thus requiring significant changes to the core construction, or more typically the drive controller, to find the optimum drive frequency.

[0068] The invention finds particular application where faster nebulisation treatment times are required. This is usually required for hand-held devices when aerosol is administrated through the mouth or nasal passages in fully mobile patients. These are typically patients who administer nebulised drugs in a non-hospital setting.

[0069] This is in contrast to intubated hospital patients who are typically on mechanical ventilation where treatment times are less important as long as the patient gets the full prescribed dose.

[0070] Techniques for vibrating the aperture plates are described generally in U.S. Pat. Nos. 5,164,740; 5,586,550; and 5,758,637, which are incorporated herein by reference. The aperture plates are constructed to permit the production of relatively small liquid droplets at a relatively fast rate. For example, the aperture plates of the invention may be employed to produce liquid droplets having a size in the range from about 2 μm to about 10 μm, and more typically between about 2 μm to about 5 μm. In some cases, the aperture plates may be employed to produce a spray that is useful in pulmonary drug delivery procedures. As such, the sprays produced by the aperture plates may have a respirable fraction that is greater than about 70%, preferably more than about 80%, and most preferably more than about 90% as described in U.S. Pat. No. 5,758,637.

[0071] In some embodiments, such fine liquid droplets may be produced at a rate in the range from about 2 μl (microliters) per second to about 25 μl per second per 1000 apertures. In this way, aperture plates may be constructed to have multiple apertures that are sufficient to produce aerosolized volumes that are in the range from about 2 μl to about 25 within a time that is less than about one second. Such a rate of production is particularly useful for pulmonary drug delivery applications where a desired dosage is aerosolized at a rate sufficient to permit the aerosolised medicament to be directly inhaled. In this way, a capture chamber is not needed to capture the liquid droplets until the specified dosage has been produced. In this manner, the aperture plates may be included within aerosolisers, nebulizers, or inhalers that do not utilise elaborate capture chambers.

[0072] The aperture plate may be employed to deliver a wide variety of drugs to the respiratory system. For example, the aperture plate may be utilized to deliver drugs having potent therapeutic agents, such as hormones, peptides, and other drugs requiring precise dosing including drugs for local treatment of the respiratory system. Examples of liquid drugs that may be aerosolized include drugs in solution form, e.g., aqueous solutions, ethanol solutions, aqueous/ethanol mixture solutions, and the like, in colloidal suspension form, and the like. The invention may also find use in aerosolizing a variety of other types of liquids, such as insulin.

[0073] It will be appreciated that the invention allows the production of a wafer from which nebuliser aperture plates are punched in one single plating step and facilitates the creation of a larger number of holes than that known today (typically up to 400%). Also, it facilitates the use of aperture plates which are 60 to 62 μm thick. Also, it allows an increase in the number of holes per unit of area while still being able to control the plating thickness to a predetermined dimension.

[0074] The above in combination allows the creation of a higher output nebuliser while still maintaining the standard drive controller and core construction all of which is accomplished in a very economical manner.