GB2518212A

GB2518212A - A mould and a method of moulding

Info

Publication number: GB2518212A
Application number: GB1316344.9A
Authority: GB
Inventors: Bissacco Giuliano; Hans Norgaard Hansen; Christian Holme; Per Ibsen; Jesper Nissen
Original assignee: Danmarks Tekniskie Universitet; Kaleido Technology ApS
Current assignee: Danmarks Tekniskie Universitet; Kaleido Technology ApS
Priority date: 2013-09-13
Filing date: 2013-09-13
Publication date: 2015-03-18
Also published as: GB201316344D0

Abstract

There is provided an apparatus, a moulding base plate, and moulding inserts for wafer-based precision glass moulding that alleviate the stresses place upon the apparatus and glass wafer, the apparatus comprising a moulding base plate having a body, one or more recesses extending into the body for receiving one or more moulding inserts, and one or more retaining means; and one or more moulding inserts each having an upper portion with a moulding feature for shaping an optical component, and a lower portion having latching means; wherein the one or more retaining means of the base plate are arranged to be engaged by the latching means of the lower portion of the one or more moulding inserts to enable at least one moulding insert to be loosely retained in one of the recesses. Also disclosed is a method of moulding an optical component.

Description

A Mould and A Method of Moulding The present invention relates to a mould and a method of moulding In embodiments, the present invention relates to an apparatus for wafer-based precision glass moulding, a moulding base plate for the apparatus, and moulding inserts for the apparatus. In particular, the present invention relates to a mould with moulding inserts for manufacturing optical components.

1 0 High precision smalllmicro optical components are characterized by extremely smooth surfaces and extremely small form errors. Typically, such optical components are made of optical glass materials in order to achieve high optical performance and can have spherical or aspherical surface geometries.

Large volume production of low-cost glass optical components such as lenses can be achieved by precision moulding, where a glass preform of suitable geometry is pressed between two mould surfaces of optical quality in precisely controlled conditions. For example, for glass materials with a high glass transition temperature (Tg, the processing temperature can be as high as 973K and the average pressure can reach up to 2OMPa. Due to such high temperature and pressure, as well as the accuracy and the optical surface quality required, the process is extremely demanding on the mould. Therefore, moulds used in the process must be characterized by high temperature resistance and tight tolerances. In addition, the mould must be able to maintain a high surface quality over a large number of moulding cycles if the mould is 2 5 to be re-used. Also of concern when designing moulds for the process is the thermal shrinkage of the glass during the cooling process and thermal deformation of the mould.

These must be taken into account in order to avoid form errors and damages in the final product.

In wafer-based precision glass moulding of high quality optical components, a structured mould with a large number of identical features is used for the net-shape moulding of an optically flat glass wafer. Typically, the features are casts (i.e. negative geometries) of the optical components to be produced, which may be concave or convex and may be rotationally symmetric. In this way, both spherical and aspherical small/micro lens structures can be produced in large numbers from a single moulding cycle.

Typically, a mould with an array of suitable casts is heated together with or separately from a glass wafer formed from a suitable glass material to a sufficiently high temperature to soften thc glass wafer for moulding. the mould is then prcssed onto the heated glass wafer so that individual optical components can take shape within each cast. Thereafter, whilst maintaining the press, the glass wafer and the mould are cooled 1 0 to allow the glass to harden. Once moulding is complete, the glass wafer may then be cut and ground to form individual optical components.

With wafer-based precision moulding, it is also possible to stack and align individual lenses at wafer level to produce lens modules. This is particularly advantageous for fabricating lens modules in portable electronic devices such as mobile telephones, laptops, and tablet computers, where a module typically comprises several different lenses. For example, double-sided glass wafers carrying the required lens types may be stacked, aligned, and bonded before dicing into separate individual lens stacks such that several hundreds of lenses would be aligned in a single operation.

Spacers between the lenses can be embedded in the moulded optics at wafer level, or could be added in between the wafers to be stacked. Quality control of the stacked lens modules can then be performed automatically by means of functional testing, after which dicing of the individual lens modules is carried out. As a result, very compact lens modules may be obtained whilst reducing the number of alignment operations by a 2 5 factor equal to the number of lenses per wafer.

Figure 1 illustrates an example of a commonly used mould for wafer-based precision glass moulding. The mould 10 is typically of a cylindrical disc shape with multiple moulding features 12 each corresponding to a cast for an optical component on one of the circular sides and is typically made from binderless sintered tungsten carbide, for its extreme hardness even at elevated temperatures, by means of ultra-precision milling/grinding. The moulding features 12 may be recesses for forming convex optical elements or protrusions for forming concave optical elements. The fabrication of the mould 10 is often a very slow process due to the fact that very smooth and precise moulding features 12 are required in order to produce high quality optical components and that the material for forming the mould 10 is necessarily hard in order to cope with the demands of the moulding process. For a typical mould 10, 100mm in diameter and carrying 250 moulding features 12, approximately 720 hours of machining time would be required.

Furthermore, materials suitable for forming the mould 10 typically have different coefficients of thermal expansion (CTEs) than the materials they would be 1 0 used to mould. Generally, the mould material would have a CTE in the order of 5x106K'. In contrast, many of the optical glass materials suitable for forming optical components would have a much higher CTE. For example, the CTE of optical glass materials in the temperature range of 293K to 573K can be in the order of 13x10K', and can reach much larger values at the glass transition temperature (Tg). The consequence of the disparity of the CTE of the mould 10 and the glass wafer is that, during the moulding process where the mould 10 and the glass wafer are allowed to cool, the glass wafer will contract by a much greater amount than the mould 10.

Therefore, during the cooling stage of the moulding process, the moulded components on the glass wafer, in particular those on the periphery of the glass wafer, would have a greater tendency to shift than the moulding features 12 within which the moulded components are formed. As such, the movement of each moulded component would be restricted by the moulding features 12. This restriction of movement in turn induces stress on the moulded components, causing unwanted residual stresses, breakages, or even cracking of the wafer.

In order to limit residual stresses, breakages, or cracking, the rate at which the wafer and the mould 10 are heated/cooled maybe reduced to lower the stress load at the contact between the glass surface and the surface of the moulding features 12.

However, this inherently slows down the moulding process, thereby reducing the efficiency. Moreover, if a moulding feature 12 of the mould 10 is damaged, repair by re-machining is extremely complicated and may be impossible in certain cases. In the worst ease, a replacement mould may be required.

There is therefore a need for an improved mould for forming optical components when using the wafer-based precision glass moulding process.

According to an aspect of the present invention, there is provided a moulding base plate for wafer-based precision glass moulding, the base plate comprising a body; one or more recesses extending into the body for receiving one or more moulding inserts, and one or more retaining means arranged to be engaged to loosely retain at least one moulding insert in one of the recesses.

The moulding base plate of the present invention is therefore able to thermally expand and contract independently of the moulding inserts, thereby reducing the stresses placed on a glass wafer caused by a different amount of expansion/contraction to that of the glass wafer during the moulding process. The ability to expand and contract independently also means that less stress is placed on the moulding base plate.

Alleviating stresses reduces the probability of damaging the glass wafer during the moulding process and enables each moulding insert to be replaced separately, eliminating the need for complex repairs if the mould is damaged.

In an embodiment, the base plate is formed of a material having a coefficient of thermal expansion between 6xlOK1 to 3Oxl06K' at a temperature in the range of 323K to 1173K.

In another embodiment, at least one of the recesses has at least a portion that is frusto-conically shaped and subtends a cone angle in the range of 60° to 170°.

According to another aspect of the present invention, there is provided a moulding insert for a moulding base plate for wafer-based precision glass moulding, the moulding insert comprising an upper portion having a moulding feature for shaping an optical component; and a lower portion having latching means that are arranged to be engaged to enable the moulding insert to be loosely retained in a recess of the moulding base plate.

In an embodiment, the moulding feature is concavely shaped to correspond to the shape of an optical component. In another embodiment, the moulding feature is convexly shaped to correspond to the shape of an optical component.

Optionally in somc cmbodimcnts, thc cxterior of thc uppcr portion is frusto-conically shaped and subtends a cone angle in the range of 60° to 170°.

According to yct another aspect of the present invention, there is provided an apparatus for wafer-based precision glass moulding, the apparatus comprising a 1 0 moulding base plate having a body, one or more recesses extending into the body for receiving onc or more moulding inserts, and onc or more rctaining means; and onc or more moulding inserts cach having an upper portion with a moulding fcature for shaping an optical component, and a lower portion having latching means; wherein the one or more retaining means of the base plate are arranged to be engaged by the latching means of the lower portion of the one or more moulding inserts to enable at least one moulding insert to be loosely retained in one of the recesses.

By providing moulding inserts separately of the moulding base plate, the apparatus of the present invention greatly increases flexibility by allows the same moulding basc plate to be used with moukiing inscrts designed for different optical components. Loosely retaining the moulding inserts enables the base plate to expand by a different amount during the moulding process, thus allowing the moulding inserts to manoeuvre independently of the base plate, thereby reducing the stresses place upon the various parts of the apparatus.

In an embodiment, the moulding feature of at least one moulding insert is concavely shaped to correspond to the shape of an optical componenL In another embodiment, the moulding feature of at least one moulding insert is convexly shaped to correspond to the shape of an optical component.

Preferably in some embodiments, the coefficient of thermal expansion of the base plate is greater than the coefficient of thermal expansion of at least one moulding insert. Alternatively or additionally, the base plate is formed of a material having a coefficient of thennal expansion between 6x104IC' to 30x1O4K) at a temperature in the range of 323Kto 1173K.

Optionally in some embodiments, at least one of the recesses is frusto-conically shaped and subtends a cone angle in the range of 60° to 170°.

Optionally in some other embodiments, the upper portion of at least one moulding insert is frusto-conically shaped and subtends a cone angle in the range of 60° to 1700.

According to yet another aspect of the present invention, there is provided a method of moulding an optical component, the method comprising providing an apparatus for wafer-based precision glass moulding, the apparatus comprising: a moulding base plate having one or more recesses for receiving one or more moulding inserts, and one or more moulding inserts provided in the base plate; and pressing the apparatus against an optical wafer so as to mould optical components through the interaction of the moulding inserts and the wafer.

According to a yet further aspect of the present invention, there is provided an apparatus for wafer-based precision moulding, the apparatus comprising: a moulding base plate including one or more recesses for receiving one or more moulding inserts, and one or more moulding inserts provided in the one or more recesses, wherein the coefficient of thermal expansion of the base plate is greater than that of the moulding inserts.

Providing an apparatus such as this enables the material from which the base plate is made to be selected to match closely the CTE of a material to be moulded such that the bulk size of the apparatus and material to be moulded will expand and contract in a similar manner with temperature changes during moulding or subsequent cooling steps. Additionally, the moulding inserts can be selected to have a different CTE and thus the material fitm which they are made can be selected so as to optinñse the moulding characteristics without concern for stresses that would otherwise occur in the moulded material or mould itself.

Preferably, the recesses and moulding inserts are shaped such that as the temperature of the apparatus varies causing different amounts of expansion due to the difference in coefficients of thermal expansion of the base plate and the moulding inserts, the moulding inserts slide in the recesses in a direction dependent on temperature.

Embodiments of the present invention will hereinafter be described byway of examples, with references to the accompanying drawings, in which: Figure 1 is an illustration of a typical mould used in wafer-based precision glass moulding of smal I/micro optical components, Figure 2 is an illustration of an apparatus for wafer-based precision glass moulding having a moulding base plate and several moulding inserts, Figure 3 is an illustration of a moulding base plate of an apparatus for wafer-based precision glass moulding, Figure 4 is a trans-planar cross-sectional view of a recess of a moulding base plate of an apparatus for wafer-based precision glass moulding, Figure 5 is an illustration of a moulding insert of an apparatus for wafer-based precision glass moulding, Figure 6 is a bottom view of an apparatus for wafer-based precision glass moulding, Figure 7 is a plan view of an apparatus for wafer-based precision glass moulding.

Referring to Figure 2, an example of an apparatus 100 for wafer-based precision glass moulding in accordance with an embodiment of the present invention is shown. In general, the apparatus 100 comprises a moulding base plate 200 (hereinafter referred to as base plate 200 for brevity) and one or more moulding inserts 300 (hereinafter referred as inserts 300 for brevity). As will be explained in more detail, each insert 300 is effectively an individual mould for an optical component such that, when the base plate 200 is fully loaded with inserts 300, a large number of high quality optical components may be fabricated from an optical glass wafer in a single moulding cycle by using the apparatus 100.

As described above, the difference between the coefficient of thermal expansion (CTE) of many glass materials suitable for use as a glass wafer and the CTE of a typical mould such as the mould 10 of Figure 1 gives risc to different amount of thermal expansion/contraction between the mould 10 and the glass wafer. This difference in the amount of thermal expansion/contraction places stress on the glass wafer during the cooling stage of the moulding process when the mould 10 would be pressed against the glass wafer, causing damage to the moulded components or cracking of the glass wafer.

In embodiments of the present invention, the base plate 200 is formed from materials with CTE values that are more comparable to that of the optical glass material to be moulded, and the inserts 300 are formed from materials characterized by hot hardness (i.e. high values hardness at elevated temperatures). When in use, the base plate 200 is able to expand and contract more readily so that, during the cooling step of the moulding process, the base plate 200 and the glass wafer contract by a similar amount such that each insert 300 remains aligned with the moulded optical component on the glass wafer, thus reducing the stresses placed on the glass wafer.

Referring to Figure 3, an example of a base plate 200 for wafer-based precision glass moulding of a wide variety of optical components is shown. The base plate 200 can generally be considered as having a platform-like body In the example of Figure 3, the body of the base plate 200 is a generally circular disc shape with a single continuous side surface 206 and is provided with a number of recesses 208. Each recess 208 has an opening at least at a top surface 202 of the body of the base plate 200 and extends through into the body in a general direction from the top surface 202 to a bottom surface 204 of the body of the base plate 200. Each recess 208 of the base plate 200 is shaped and arranged to receive an insert 300, which will be described in more detail below.

As shown in the example of Figure 3, five recesses 208 are provided within the base plate 200, which is ofa cylindrical disc shape. In this example, the five recesses 208 are arranged generally in a circumferential manner. However, it will be appreciated that the base plate 200 may be of any suitable size and may be provided with any suitable number of recesses 208 arranged in any suitable manner. It will also be appreciated that, as an alternative to a cylindrical disc, the base plate 200 may be of any other suitable shape. For example, the base plate 200 may be square shaped with the recesses 208 arranged in a regular array or other suitable pattern.

Figure 4 shows a vertical cross-section of an example of a recess 208 of the base plate 200. In this example, the recess 208 extends generally in the direction from the top surface 202 of the base plate 200, through into the body of the bas plate 200, to the bottom surface 204 of the base plate 200. The recess 208 includes a top portion 210 having an opening at the top surface 202. In some embodiments, the recess 208 additionally includes a bottom portion 212, which may have an opening at the bottom surface 204, and may also include a depression 214 at the bottom surface 204. The recess 208 is shaped and arranged so that an insert 300 can be received therein. In the particular example shown in Figure 4, the top potion 210 of the recess 208 is arranged with one or more sides 210a sloping inwardly towards the centre of the recess 208 in the direction of an axis defined generally from top surface 202 to the bottom surface 204.

Such an arrangement provides the top portion 210 with an in-plane, transaxial cross-sectional area that decreases in a generally axial direction so that an insert 300 can be received in the recess 208 from the opening at the top surface 202. Preferably, the top portion 210 is shaped such that the in-plane cross-sectional area is rotationally symmetric. For example, the top portion 210 of the recess 208 may be frusto-conically shaped so that an insert 300 can be easily received or removed. However, it will be appreciated that the top portion 210 may be of any other suitable shape.

In some embodiments, retaining means 400 may be provided, within the depression 214 for example, for retaining an insert 300 that is received in the recess 208. The retaining means 400 (not shown in Figure 4) may be, but are not limited to, a clip, hook, sprung grip, or friction grip. The retaining means 400 are then arranged to -10 -retain an insert 300 in the recess 208 so that, when the base plate 200 is inverted, the insert 300 remains in the recess 208. More particular, the recess 208 is arranged so that the insert 300 is loosely retained in the recess 208 and is able to have limited movement when the base plate 200 is not used in the moulding process.

FigureS shows an example of an insert 300 for wafer-based precision glass moulding. In general, the insert 300 includes at least an upper portion 302 having a moulding feature that is exposed when the insert 300 is retained in the base plate 200, and a lower portion having latching means that can be engaged to enable the insert 300 to be loosely retained in the recess 208 of the base plate 200. In the particular example shown in FigureS, the insert 300 has an upper portion 302 with a top end 302a and a base end 302b, and is shaped correspondingly and proportionally to the recess 208 as described above so as to be received and retained in the recess 208 when in use. As described above, the recess 208 is arranged such that the transaxial cross-sectional of the area of the top portion 210 decreases in the direction from the top surface 202 to the bottom surface 204. Accordingly, the upper portion 302 of the insert 300 is shaped such that the transaxial cross-sectional area of the upper portion 302 decreases in the direction from the top end 302a to base end 302b so as to correspond to the particular recess 208 in which the insert 300 is to be received. In the embodiment in which the top portion 210 of the recess 208 is frusto-eonically shaped, the upper portion 302 of the insert 300 to be received therein is also frusto-conically shaped. In other embodiments, the recess 208 may be any other suitable shape and it will be appreciated by the skilled person that the insert 300 to be received therein is correspondingly shaped to complement the shape of the recess 208.

In general, the upper portion 302 of the insert 300 is provided with a moulding feature 306, which when pressed against a heated glass wafer, moulds the heated glass into a desired shape. The moulding feature 306 may be concave or convex depending on the shape of the optical component required. For example, the moulding feature 306 is a convex protrusion for moulding concaved lenses and a concave cavity for moulding convex lenses. In the example shown in Figure 5, the upper portion 302 of the insert 300 is further provided with moulding feature 306 in the form of a cavity having an opening at the top end 302a of the upper portion 302. The cavity 306 is generally

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shaped and arranged such that the interior shape of the cavity 306 corresponds to an optical component that is to be fabricated. For example, the cavity 306 of embodiments of the insert 300 may be shaped suitably for, but not limited to, forming lenses, micro-lenses, mirrors, beam-splitters, and may include other concave or convex features within thc void of thc cavity. Shaping thc cavity 306 of thc uppcr portion 302 in such a manner enables each insert 300 to function as separate moulds, each capable of fabricating an individual optical component.

As shown Figure 5, the insert 300 further includes a lower stem portion 304 in addition to the upper portion 302. The stem portion 304 extends from the base end 302b of the upper portion 302. In embodiments in which the recess 208 includes a top portion 210 and a bottom portion 212, the stem portion 304 of the insert 300 to be received in the recess 208 is shaped correspondingly to the bottom portion 212. In some embodiments, the end 308 of the stem portion 304 may be shaped and arranged to engage externally so as to enable the insert 300 to be retained in the recess 208 by the retaining means 400. As shown in Figure 5, the end 308 includes a groove 310 for engaging with the retaining means 400. For example, as shown in Figure 6, the stem portion 304 may be arranged to extend through the opening of the recess 208 at the bottom surface 204 such that the end 308 protrudes out of the depression 214. The retaining means 400, which are preferably arranged and shaped correspondingly to the end 308, may then be disposed in the depression 214. In such an arrangement. the end 308 is able to engage the retaining means 400 to enable the insert 300 to be retained in the recess 208.

2 5 As described above, the base plate 200 is able to expand and contract more freely as compared to the inserts 300 during the heating and cooling stages of the moulding process due to the higher CTE of the base plate 200 To accommodate for the higher CTE, the base plate 200 and the inserts 300 are arranged so that the inserts 300 are loosely retained in the recess 208. In such an arrangement, the inserts 300 are provided with a limited degree of movement so that the volume of the recess 208 increases by a greater amount relative to the size of the insert 300 when the base plate heated during the moulding process. The increase in the volume of the recess 208 relative to the size of the insert 300 would then allow the insert 300 to recede into the -12 -recess 208. In embodiments, the base plate 200 is formed from materials that have a CTE ranging from 6x1OK' to 30 x10K1 at temperatures ranging from 293K to 1173K and, optionally the one or more inserts 300 are formed from materials that remain sufficiently hard in this temperature range. The materials for forming the one or more inserts 300 may also enable surfaces of optical quality to be achieved and maintained. For example, the inserts 300 may be formed from, but not limited to, bindcrless sintcred tungsten carbide, silicon carbidc, silicon nitride, molybdenum, or sapphirc. Such matcrials arc typically characterized by having a high value of hardness at high temperatures. By forming the inserts 300 from these materials, each insert 300 is able to maintain its shape, size, and general integrity during the heating and cooling stages of the moulding process. The base plate 200 may, in examples of some embodiments, be formed from austenitic chromium-nickel steels, beryllium copper, or nickel alloys. These materials are typically characterized by a CTE closer to that of optical glass materials commonly used for forming optical components than to that of typical materials used to form the inserts 300. It will be appreciated that, as alternatives to the materials given above, the one or more inserts 300 and the base plate 200 may be formed from other suitable materials having characteristics described herein.

The interaction between the base plate 200 and the one or more inserts 300 during a moulding cycle will now be described.

Referring to Figure 7, the base plate 200 may be fully loaded with inserts 300 or partially loaded with one or more inserts 300, each insert 300 received and preferably retained in a recess 208, to form the apparatus 100. As described above, the difference in CTEs between the base plate 200 and the one or more inserts 300 gives rise to different amounts of thermal expansion/contraction for the base plate 200 and the inserts 300. When the apparatus 100 is heated to the temperatures required for moulding, typically between 673K and 1073K, the base plate 200 and the inserts 300 would expand by different relative amounts. Therefore, to ensure that base plate 200 and the inserts 300 are in their optimal shape at the moulding temperature, the recesses 208 of base plate 200 and the inserts 300 are arranged in some embodiments so that top end 302a of the upper portion 302 of the insert 300 is flush with the top surface 202 of the base plate 200 when the apparatus 100 is at the desired moulding temperature. For -13 -example, the apparatus 100 is arranged so that the volume of the recess 208 is less than the size of the insert 300 to be received therein. In such an arrangement, at room temperature or when not at the moulding temperature, each insert 300 protrudes partially out of the recess 208 in which it is received and is loosely retained in the recess 208 in a floating manncr whcrcby thc inscrts 300 arc provided with a suitablc dcgrcc of freedom of movement whilst prevented from detaching completely from the base plate 200.

When the apparatus 100 is heated, the base plate 200 expands, leading to each 1 0 recess 208 to expand such that the volume within each recess 208 increases whilst each inscrt 300 expands by a relatively smaller amount. The expanded volume of the recess 208 then allows the insert 300 to recede into the recess 208 in which it is received. In a preferred embodiment, each of the one or more recesses 208 is arranged such that, when the apparatus 100 is at the moulding temperature, each of the one or more inserts 300 fits tightly in one of the one or more recesses 208 so that the one or more inserts 300 no longer protrude from top surface 202.

When the apparatus 100 is cooled, such as when cooled from the moulding temperature after the moulding stage of a wafer-based precision glass moulding process, the base plate 200 contracts such that the volume within each recess 208 decreases whilst the inserts 300 contract by a relatively smaller amount. As the volume of each recess 208 decreases, the insert 300 retained in the recess 208 is effectively forced out of the recess 208 by the constricting motion of the sides 210a of the top portion 210 of the recess 208. As the sides 210a contract inwardly, the insert 300 slides against the side 21 Oa and is displaced outwardly from the recess 208. In some embodiments where the upper portion 302 is frusto-conically shaped, the insert 300 is arranged such that the exterior of the upper portion 302 subtends a cone angle in the range between 60° and 170° so as to facilitate the sliding displacement of the insert 300. In a preferred embodiment, the cone angle subtended by the exterior of the upper portion 302 is in the range between 90° and 150° When in use, the apparatus 100 and a glass wafer are heated to the moulding temperature. As the apparatus 100 is heated, the recesses 208 of the base plate 200 -14 -expands, allowing the inserts 300 to recede into the recesses 208 such that the top end 302a of each insert 300 is substantially flush with the top surface 202 of the base plate 200. Once moulding temperature is reached, the apparatus 100 is pressed onto the glass wafer so that individual optical components are formed within the cavity 306 of each insert 300. When the moulding stage is complete, the apparatus 100 and the glass wafer are cooled, typically to temperatures sufficiently below the glass transition temperature (f and well above room temperature, whilst the apparatus 100 remains pressed onto the glass wafer. As the apparatus 100 and the glass wafer cools, the base plate 200 of the apparatus 100 and the glass wafer contract by a similar extent. The contraction of the base plate 200 forces the inserts 300 out of the recesses 208, causing the base plate to detach and "risc" from the glass wafer, typically by a distance in the order of 3x106m to 8x10m, whilst the inserts 300 remain in contact with the glass wafer.

During this cooling stage, the recesses 208 of the base plate 200, and hence the inserts 300, remain aligned with the optical component formed within the cavity 306 of the inserts 300. The alignment between the optical components formed on the glass wafer and the recesses 208 of the base plate 200 reduces the stress placed on the glass wafer and therefore reduces the probability of damaging the glass wafer.

It will be appreciated that the above-described process can be applied to both sides of a glass wafer. It will also be appreciated that as an alternative to pressing the apparatus 100 onto the glass wafer in the process described above, the glass wafer may be pressed onto the apparatus 100 in the moulding stage. In this alternative, as the glass wafer and the apparatus 100 cool, the apparatus 100 contracts such that the inserts 300 may "rise" out of the base plate 200 whilst remaining aligned with the optical component formed within the cavity 306 of each insert 300.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the appending claims.

Claims

-15 -Claims: 1. A moulding base plate for wafer-based precision glass moulding, the base plate comprising: a body; one or more recesses extending into the body for receiving one or more moulding inserts; and one or more retaining means arranged to be engaged to loosely retain at least one moulding insert in one of the recesses.
2. A moulding base plate as claimed in claim 1, wherein the base plate is formed of a material having a coefficient of thermal expansion between 6x106Ki to 30xl061C' at a temperature in the range of 323K to 1173K.
3. A moulding base plate as claimed in claims 1 or 2, wherein at least one of the recesses has at least a portion that is frusto-conically shaped and subtends a cone angle in the range of 60° to 1700.
4. A moulding insert for a moulding base plate for wafer-based precision glass 2 0 moulding, the moulding insert comprising: an upper portion having a moulding feature for shaping an optical component; and a lower portion having latching means that are arranged to be engaged to enable the moulding insert to be loosely retained in a recess of the moulding base plate.
5. A moulding insert as claimed in claim 4, wherein the moulding feature is concavely shaped to correspond to the shape of an optical component.
6. A moulding insert as claimed in claim 4 or 5, wherein the moulding feature is convexly shaped to correspond to the shape of an optical component.
7. A moulding insert as claimed in any of claims 4 to 6, wherein the exterior of the upper portion is frusto-conically shaped and subtends a cone angle in the range of 60° to 170°.

-16 -
8. An apparatus for wafer-based precision glass moulding, the apparatus comprising: a moulding base plate having a body, one or more recesses extending into the body for receiving one or more moulding inserts, and one or more retaining means; and one or more moulding inserts each having an upper portion with a moulding feature for shaping an optical component, and a lower portion having latching means; wherein the one or more retaining means of the base plate are arranged to be engaged by the latching means of the lower portion of the one or more moulding inserts to enable at least one moulding insert to be loosely retained in one of the recesses.
9. An apparatus as claimed in claim 8, wherein the moulding feature ofat least one moulding insert is concavely shaped to correspond to the shape of an optical component.
10. An apparatus as claimed in claims 8 or 9, wherein the moulding feature of at least one moulding insert is convexly shaped to correspond to the shape of an optical component.

2 0
11. An apparatus as claimed in any of claims 8 to 10, wherein the coefficient of thermal expansion of the base plate is greater than the coefficient of thermal expansion of at least one moulding insert.
12. An apparatus as claimed in any of claims 8 to 11, wherein the base plate is formed of a material having a coefficient of thermal expansion between 6x10K' to 30 xl06K1 at a temperature in the range of 323K to 1173K.
13. An apparatus as claimed in any of claims 8 to 12, wherein at least one of the recesses is frusto-eonically shaped and subtends a cone angle in the range of 600 to 170°.
14. An apparatus as claimed in any of claims 8 to 13, wherein the upper portion of at least one moulding insert is frusto-eonically shaped and subtends a cone angle in the range of 60° to 1700.

-17 -
15. A method of moulding an optical component, the method comprising: providing an apparatus for wafer-based precision glass moulding, the apparatus comprising: a moulding base plate having one or more recesses and one or more moulding inserts rcccivcd in thc onc or morc rcccsscs; and pressing the apparatus against an optical wafer so as to mould optical components through the interaction of the moulding inserts and the wafer.
16. A moulding base plate for wafer-based precision glass moulding substantially as 1 0 described hereinbefore with reference to the accompanying drawings.
17. A moulding insert for wafer-based precision glass moulding substantially as described hereinbefore with reference to the accompanying drawings.
18. An apparatus for wafer-based precision glass moulding substantially as described hereinbefore with reference to the accompanying drawings.
19. A method of moulding an optical component substantially as described hereinbefore with reference to the accompanying drawings.