WO2005053940A1

WO2005053940A1 - Method of manufacturing a mould for use in the manufacture of a lens array

Info

Publication number: WO2005053940A1
Application number: PCT/IB2004/052572
Authority: WO
Inventors: Marinus J. J. Dona; Johannes M. M. Swinkels; Johannes C. Van De Ven; Raymond J. W. Knaapen
Original assignee: Anteryon BV; Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV; Anteryon BV
Priority date: 2003-12-05
Filing date: 2004-11-26
Publication date: 2005-06-16
Anticipated expiration: 2006-06-05

Abstract

A method of manufacturing a mould (10) for use in the manufacture of a lens array comprises the following consecutive steps: arranging cavities (12) in the mould (10) by means of a milling device or the like; and deforming a surface (13) of the cavities (12) by imprinting a die (40) in the cavities (12). The shape of a die surface (41) corresponds to the shape of lenses of the lens array to be manufactured. By arranging cavities (12) before the mould (10) is processed by the die (40), it is achieved that the shape of one cavity (12) is not altered when the die (40) is pressed in an adjacent cavity (12), as the amount of mould material which needs to be displaced is relatively small. In this way, a mould (10) having sharp boundaries between adjacent cavities (12) for forming the lenses of the lens array is obtained.

Description

Method of manufacturing a mould for use in the manufacture of a lens array

The present invention relates to a method of manufacturing a mould for use in the manufacture of an optical element provided with mutually adjoining optical sub-elements arranged relative to one another in accordance with a pattern, by which method the mould is given a mould shape which is complementary to the pattern of sub-elements, wherein the mould is manufactured from a ductile material and is given the mould shape by means of a die which is provided with a die surface corresponding to a shape of the optical sub-element and which is imprinted in the mould with a predetermined force at consecutive positions in accordance with the pattern. A method as described in the preceding paragraph is known from WO 96/07523. The known method is disclosed in the context of manufacturing a mould for use in the manufacture of a two-dimensional array of microlenses, wherein the microlens array is to be regarded as the optical element, and wherein the microlenses are to be regarded as the sub- elements. A microlens is a lens having a relatively small diameter, for example a diameter of 1 mm, or even 0.1 mm or smaller. According to the known method, a die having a die surface which corresponds to a shape of a single microlens is pressed into a mould with a predetermined force at consecutive positions in accordance with the pattern of the microlenses. The material of the mould and the applied force are chosen such that as a result of this pressing the die into the mould, a mould shape which is complementary to the pattern of the microlenses is obtained. In particular, the material of the mould is a ductile metal, comprising for example silver, copper, aluminium, or zinc. The fact that the die is imprinted in the mould at consecutive positions in accordance with the pattern implies that a number of times the die is imprinted in the mould corresponds to a number of microlenses of the microlens array. Once the mould has been provided with the mould shape, the mould is ready for use in the manufacture of the microlens array. In the process, the imprints are filled with for example a synthetic resin material, and an optical substrate is positioned such as to cover the imprints. Once the synthetic resin material has cured, the entirety of the optical substrate and the cured synthetic resin material is removed from the mould. In this way, a lens array is obtained, wherein the lenses comprise the cured synthetic material that has been inside the imprints of the mould. Application of the known method of manufacturing a mould yields good results in the context of manufacturing microlens arrays. However, this appears not to be the case in the context of manufacturing arrays of lenses which are larger than microlenses, wherein the diameter and/or a depth of the lenses may be comparatively large. In this context, it appears that no sharp boundaries between adjacent imprints arise in the mould, as a result of which the individual lenses of the lens array manufactured by means of the mould merge fluently into one another, and an optically useful surface area of the lens array is limited by vague boundaries between the lenses of the lens array. It is an objective of the present invention to provide a method of manufacturing a mould for use in the manufacture of an optical element such as a lens array, which yields good results in case of being applied for the purpose of manufacturing a mould for use in the manufacture of an array of lenses larger than microlenses. This objective is achieved by means of a method such as known from WO 96/07523, further comprising the step of providing the mould with cavities at positions in accordance with the pattern, wherein the die is imprinted in the mould with a predetermined force at consecutive positions in alignment with the positions of the cavities. According to the present invention, mould material is removed at positions where the die is to be imprinted in the mould in order to form imprints which are complementary to the sub-elements of the optical element to be manufactured by means of the mould. In this way, the mould is provided with cavities, wherein the positions of the cavities are in accordance with a pattern of the sub-elements. In comparison with a situation in which no cavities are present in the mould, less mould material is displaced under the influence of the die, as a result of which the shape of an already formed imprint is not disturbed by an imprinting process taking place in the vicinity of that imprint. In this way, sharp boundaries between adjacent imprints are obtained. Therefore, in a situation in which the mould manufactured by means of the method according to the present invention is applied, sharp boundaries between individual lenses of a lens array manufactured by means of the mould are obtained, and an optically useful surface area of the lens array is comparatively large. In a preferred way of carrying out the method according to the present invention, a surface of the cavity is given a spherical shape. In this way, it is possible to arrange the cavities in the mould by using a conventional cutting device, which is controlled in a relatively simple manner. The cutting device may for example be a milling device. A cavity having a spherical shape may very well serve as a basis for various types of lens shapes. The die surface of the applied die may have any suitable shape, depending on the desired shape of the sub-elements of the optical element to be manufactured by means of the mould.

The present invention will now be explained in greater detail with reference to the figures, in which similar parts are indicated by the same reference signs, and in which: figures 1 and 2 diagrammatically illustrate consecutive steps of a process of manufacturing a mould for use in the manufacture of a lens array; figure 3 diagrammatically shows a top view of the mould which is obtained as a result of the process as illustrated by means of figures 1 and 2; figures 4 and 5 diagrammatically illustrate consecutive steps of a process of manufacturing a lens array, wherein the mould as shown in figure 3 is applied; figure 6 diagrammatically shows a side view of a lens array which is obtained as a result of the process as illustrated by means of figures 4 and 5, and of an optical substrate for supporting the lens array; and figure 7 diagrammatically shows a top view of the optical substrate and the lens array as shown in figure 6.

Figure 1 diagrammatically shows a sectional view of a mould 10 and a milling device 20 for processing a mould surface 11 of the mould 10. The milling device 20 comprises a driven shaft 21, and a cutting member 22 arranged at a free end of the shaft 21. The cutting member 22 may for example comprise a diamond milling cutter. The mould 10 is supported by a table 30, which is displaceable in an X- direction and a Y-direction which is perpendicular to the X-direction, wherein both the X- direction and the Y-direction are parallel to the mould surface 11. For the sake of clarity, the X-direction and the Y-direction are indicated in figure 1. Table positioning means 35 are provided for controlling the positions and the displacements of the table 30. The mould 10 is fixed on the table 30 in a suitable way, for example through clamping means (not shown). The milling device 20 is movable in the X-direction, the Y-direction and a Z- direction, wherein the Z-direction is perpendicular to both the X-direction and the Y- direction. For the sake of clarity, the Z-direction is also indicated in figure 1. Milling device positioning means 25 are provided for controlling the positions and the displacements of the milling device 20. During a milling process, the milling device 20 is activated, wherein the cutting member 22 is rotated about a central axis of the shaft 21. At positions where the rotating cutting member 22 is put in contact with the mould surface 11, material of the mould surface 11 is cut from the mould 10. In the shown example, the cutting member 22 is moved with respect to the mould 10 in such a way that at the end of the milling process a preformed cavity 12 in the mould 10 is obtained, which has a spherical surface 13, i.e. a surface 13 which is suitable for encompassing a portion of a sphere. The milling device 20, the milling device positioning means 25, the table 30 and the table positioning device 35 may be part of a conventional CNC-milling machine. For the purpose of manufacturing a mould 10 which is suitable to be applied in the manufacture of a lens array comprising a plurality of lenses, the mould 10 needs to be provided with a plurality of preformed cavities 12, wherein mutual positions of the preformed cavities 12 correspond to predetermined mutual positions of the lenses. The table positioning means 35 and the milling device positioning means 25 are programmed such as to accurately position the table 30 and the milling device 20 with respect to each other, so that the preformed cavities 12 are arranged in the mould surface 11 at positions which are determined by positions of the lenses in the lens array. It will be clear that the preformed cavity 12 may be obtained by another suitable cutting process than a milling process. However, a milling process is advantageous, as it is possible to obtain a smoothness of the surface 13 of the preformed cavity 12 of optical quality which is desired for the lens array. Further, it will be clear that it is also possible to obtain a preformed cavity 12 having another shape than a spherical shape. As soon as all preformed cavities 12 are provided in the mould 10, the mould 10 is ready to be processed by a die 40 having a die surface 41 for contacting the surface 13 of the preformed cavities 12. The die 40 is diagrammatically shown in figure 2. In the process, the mould 10 is still supported on a table 30, which is preferably the same table 30 as the table 30 supporting the mould 10 during the milling process. A shape of the die surface 41 corresponds to the shape of the lenses of the lens array to be manufactured. In the shown example, the mould 10 is intended to be applied in a process for manufacturing a lens array comprising aspherical lenses. Therefore, the shown die surface 41 has an aspherical shape. That does not alter the fact that the die surface 41 may have another shape, depending on the shape of the lenses of the lens array to be manufactured. The mould 10 is manufactured from a ductile material, preferably a ductile metal such as, for example, silver, copper, aluminium, zinc, or an alloy comprising these metals. The die 40 is movable in the Z-direction (the X-direction, Y-direction and Z- direction are indicated in figure 2). In order to process the mould 10 such as to be suitable for use in the manufacture of a lens array, the die 40 is imprinted in the mould 10 with a predetermined force at consecutive positions in alignment with the positions of the preformed cavities 12, i.e. consecutive positions in accordance with the pattern of the lenses of the lens array to be manufactured. In view of obtaining a mould 10 which is suitable for forming a lens array in an accurate manner, it is important that the table positioning means 35 are programmed such as to position the table 30 with respect to the die 40 in an accurate manner, so that the die 40 is aligned with the preformed cavities 12. In this way, it is ensured that the mould 10 is shaped such as to be capable of forming a lens array comprising lenses which are positioned in accordance with a predetermined pattern. While the die 40 is being imprinted in a preformed cavity 12, the ductile material of the surface 13 of the preformed cavity 12 is plastically deformed, so that said surface 13 of the preformed cavity 12 assumes a shape complementary to the shape of the die surface 41, i.e. to the shape of the lens to be formed by means of a definitive version of the cavity 12. In the process, the smoothness of the surface 13 of the cavity 12 is maintained. As soon as the surfaces 13 of all cavities 12 in the mould 10 have been shaped complementary to the lenses of the lens array by means of the die 40 and the die surface 41, the mould 10 is ready for use in the manufacture of the lens array. It is noted that on the basis of a suitable choice of the force with which the die 40 is pressed in the mould 10, it is possible to ensure that the ductile material of the mould 10 is plastically deformed exclusively in the vicinity of a contact surface between the die surface 41 and the surface 13 of a preformed cavity 12. Furthermore, the size and shape of the preformed cavity 12 play an important role in preventing situations in which a surface 13 of a cavity 12, which has already been shaped by means of the die 40, is partially deformed when the die 40 is applied for shaping the surface 13 of an adjacent preformed cavity 12. Due to the fact that the preformed cavities 12 have been provided first, the amount of material which is pushed away by the die 40 during the process of shaping the surface 13 of a cavity 12 is relatively small. In fact, a major portion of the material which should be displaced by the die 40 in a situation in which no preformed cavities 12 are provided has already been removed by means of the milling process. In figure 3, an example of a mould 10 is shown, which is obtained after the preformed cavities 12 have been arranged in the mould surface 11, and the cavities 12 have been given their final shape by means of the die 40. In the example, the mould 10 comprises sixteen cavities 12. It will be clear that this number of cavities 12 is arbitrary; the mould 10 may be provided with less or more cavities 12, depending on the number of lenses of the lens array to be manufactured. Figure 4 illustrates a first step of a process of forming a lens array using the mould 10. In this first step, the cavities 12 are filled with material such as a synthetic resin material. It will be understood that the material is in a liquefied state, to such an extent that the material is capable of flowing and completely filling the cavities 12. The material is for example 2p-lacquer. In figure 4, a flow of the material is diagrammatically depicted and indicated by reference numeral 51, and supplying means 50 for supplying the material to the mould 10 are diagrammatically shown. At the end of the first step, separate portions of material are obtained, which are present in the cavities 12. These portions are shown in figure 5, and are hereinafter referred to as lens portions 52. Figure 5 illustrates a second step of the process of forming a lens array using the mould 10. In this second step, an optical substrate 53 is positioned on top of the mould surface 11, wherein the optical substrate 53 contacts the lens portions 52 of material, which are present in the cavities 12. Subsequently, the lens portions 52 are hardened. In the shown example, the lens portions 52 are cured by subjecting them to UV light (ultraviolet light). In figure 5, the UV light is diagrammatically depicted by means of arrows UV. As soon as the lens portions 52 are hardened, a lens array 55 supported by an optical substrate 53 is obtained. The lenses 52 of the lens array 55 are constituted by the hardened lens portions 52. The entirety of the optical substrate 53 and the lens array 55 is shown in figures 6 and 7, wherein figure 6 shows a sectional view of said entirety, taken along line A-A in figure 7. The shape of the lenses 52 corresponds to the shape of the die surface 41 of the die 40 which has been applied during the manufacturing process of the mould 10. Therefore, in the shown example, the lenses 52 have an aspherical shape. Sharp boundaries are present between the lenses 52, due to the fact that sharp boundaries are present between the cavities 12 of the mould 10, as during the manufacturing process of the mould 10, the shape of the surface 13 of the cavities 12 has exclusively been determined by the shape of the die surface 41. The presence of the preformed cavities 12 is an important factor in preventing situations in which the shape of a surface 13 of a cavity 12, which has been given the final shape by means of the die 40, is disturbed when the die 40 is pressed in an adjacent preformed cavity 12. The obtained lens array 55 may for example be used in the manufacture of an array of small cameras for mobile phones. Usually, a practically useful lens array 55 comprises more than sixteen lenses 52, for example 40 rows of 40 lenses 52, which makes a total of 1,600 lenses 52. In the process of manufacturing the camera array, electronics of the cameras are manufactured on a wafer, after which the lens array 55 is assembled on the wafer. In this way, an array of complete cameras is obtained. A collection of separate cameras is obtained by dicing the camera array, for example through sawing. It will be understood that manufacturing an array of cameras, which is diced in order to obtain separate cameras, is advantageous with respect to manufacturing cameras separately, as the first way of manufacturing is considerably less time-consuming than the latter way of manufacturing. An important aspect of the method according to the present invention of manufacturing a mould 10 is that the process of imprinting the mould 10 by means of the die 40 is performed after the mould 10 has been provided with preformed cavities 12. Thus, said process is not performed on a planar mould surface 11, and the amount of mould material which needs to be displaced by means of the die 40 is comparatively small. Preferably, the surface 13 of the preformed cavities 12 has an optical quality. As has already been described, it is possible to obtain such quality by forming the cavities 12 by means of a milling process. During contact of the surface 13 of the preformed cavities 12 with the die surface 41, the quality of the first surface 13 is not affected. Instead, the optical quality of the surface 13 of the cavities 12 is maintained, and there is no need for subjecting the surface 13 to a post-treatment process aimed at increasing the surface quality. It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the present invention as defined in the attached claims. The present invention is especially intended for application in the field of manufacturing lenses which are larger than microlenses, but that does not mean that the present invention may not be applied in the field of manufacturing microlenses as well. Summarizing, the method according to the present invention of manufacturing a mould 10 for use in the manufacture of a lens array 55 comprises the following consecutive steps:

1) arranging cavities 12 in the mould 10 by means of a milling device 20 or the like; and

2) deforming a surface 13 of the cavities 12 by imprinting a die 40 in the cavities 12. The shape of a die surface 41 corresponds to the shape of lenses 52 of the lens array 55 to be manufactured using the mould 10. By arranging cavities 12 in the mould 10 before the mould 10 is processed by the die 40, it is achieved that the shape of one cavity 12 is not altered when the die 40 is pressed in an adjacent cavity 12, as the amount of mould material which needs to be displaced is relatively small. In this way, a mould 10 having sharp boundaries between adjacent cavities 12 for forming the lenses 52 of the lens array 55 is obtained.

Claims

CLAIMS:

1. Method of manufacturing a mould (10) for use in the manufacture of an optical element (55) provided with mutually adjoining optical sub-elements (52) arranged relative to one another in accordance with a pattern, by which method the mould (10) is given a mould shape which is complementary to the pattern of sub-elements (52), wherein the mould (10) is manufactured from a ductile material and is provided with cavities (12) at positions in accordance with the pattern, and wherein the mould (10) is given the mould shape by means of a die (40) which is provided with a die surface (41) corresponding to a shape of the optical sub-element (52) and which is imprinted in the mould (10) with a predetermined force at consecutive positions in alignment with the positions of the cavities (12).

2. Method according to claim 1, wherein a surface (13) of the cavities (12) is given a spherical shape.

3. Method according to claim 1 or 2, wherein the surface (41) of the applied die

(40) has an aspherical shape.

4. Method according to any of claims 1-3, wherein the cavities (12) are arranged in the mould (10) by means of a milling process.

5. Method according to any of claims 1-4, wherein a surface (13) of the cavities (12) is given a smoothness desired for the optical element (55) to be manufactured, before the die (40) is imprinted in the mould (10).

6. Method according to any of claims 1 -5, wherein the ductile material comprises a ductile metal such as silver, copper, aluminium, or zinc.

7. Optical element, manufactured by applying a mould manufactured according to the method as claimed in any of claims 1-6, comprising an array (55) of lenses (52).

8. Lens (52), separated from the array (55) of lenses (52) as claimed in claim 7.

9. Array of cameras, provided with an array (55) of lenses (52) according to claim 7, wherein said array (55) of lenses (52) is arranged on a wafer provided with electronics of the cameras.

10. Camera, separated from the array of cameras as claimed in claim 9.

11. Method for manufacturing a collection of separate cameras, comprising the following steps: - manufacturing an array of cameras by providing a wafer, manufacturing an array of camera electronics on the wafer, and assembling an array (55) of lenses (52) as claimed in claim 7 on the wafer, wherein each lens (52) is associated with the camera electronics of a single camera; and - dicing the array of cameras.