EP1894248A2

EP1894248A2 - Semiconductor package with transparent lid

Info

Publication number: EP1894248A2
Application number: EP06779754A
Authority: EP
Inventors: Jos c/o MELEXIS NV RENNIES; Appolonius Jacobus c/o MELEXIS NV VAN DER WIEL
Original assignee: Melexis NV
Current assignee: Melexis NV
Priority date: 2005-06-22
Filing date: 2006-06-22
Publication date: 2008-03-05
Also published as: WO2006136935A2; WO2006136935A3; GB0512732D0

Abstract

In an optical integrated circuit device a transparent element (106) is mounted over at least the optically active elements (102) in order to provide protection for the integrated circuit during use. The transparent element 106 is retained in position by adhesive (105). The adhesive (105) is deposited between and maintained in position by a pair of ridges (104) provided around the optically active element or elements. The ridges (104) are formed from an organic photolithographic gel.

Description

Semiconductor package with Transparent Lid

The present invention relates to an optically active integrated circuit device, particularly an optically active integrated circuit device for use in a DVD system including blue light DVD systems and further to a method of manufacture of such devices.

On a DVD, data is encoded in a spiral track on the DVD surface. DVD reading apparatus operates by directing a narrow beam of light, typically generated by an LED, VCSEL, or laser diode, at the spiral track of a spinning DVD. Sections of the track have varying reflective properties, such that a light sensing means provided in a particular position will detect a series of variations (or pulses) in the intensity of the reflected light. The light sensing means thus generates an electrical output signal corresponding to the data stored on the DVD. Typically the electronics for both detecting and decoding the reflected light are implemented on a single integrated circuit.

For protection during use, DVD reading devices are usually packaged.

Known packaging techniques for DVD reading devices comprise glass lidded packages wherein the glass lid covers the light sensitive portion of the integrated circuit and is secured by epoxy adhesive means. For DVD readers using blue light rather than red light, such packages have some disadvantages. The additional step of fitting a glass lid to the package can be expensive and may cause operational problems. For instance: the atmosphere trapped between the light sensing means and the lid may contain moisture or contaminants that may affect the performance or reliability of the assembled device; and/or the glass lid may not be aligned with or parallel to the sensitive surface of the light sensing means which may affect the focussing of incident light reflected from the DVD surface.

It is therefore an object of the present invention to provide a method of manufacturing an integrated circuit device which overcomes or alleviates at least some of the above problems.

According to a first aspect of the present invention there is provided a method of manufacturing optical integrated circuit devices comprising the steps of: providing a die, said die comprising an integrated circuit provided within a pair of encompassing ridges, said integrated circuit having at least one optically active element, said pair of ridges having a gap provided therebetween; dispensing adhesive material into the gap between said pair of ridges; and placing a transparent element over said integrated circuit, said transparent element being secured in position by said adhesive material.

This thus provides an optical integrated circuit device wherein a transparent element provides protection for the optically active elements and wherein the transparent element may be readily and accurately mounted relative to the optically active elements. This minimises adverse effects on the focussing of incident or emitted light.

Said optically active elements may comprise emitting means and/or sensing means. Emitting means may be operable to emit light at visible, infra red or ultraviolet wavelengths as desired. Similarly, said sensing means may be operable to sense light of visible, infra red or ultra violet wavelengths as desired. In some preferred embodiments said sensing means may comprise an array of individual light sensing elements.

Preferably, said transparent element is placed over said integrated circuit using pick and place technology. Pick and place technology is well known and accurate and thus allows the transparent element to be mounted with a high degree of accuracy.

The ridges may be formed of a flexible material. In such embodiments, the transparent element may be placed in such a manner that it compresses the inner ridge of the ridge pair.

The adhesive may be dispensed in such a manner as to substantially fill the gap between the ridges. In some embodiments, the adhesive may project above the top of the ridges. In such embodiments, the transparent element may be adapted to fit within the outer ridge but not within the inner ridge. In this manner, when the transparent element is placed in position, adhesive material is displaced outwards. This prevents the adhesive obscuring the optically active elements and helps to improve the seal between the adhesive and the transparent element.

The transparent element may be provided with filtering means to limit the incoming radiation to a desired wavelength band, which may be the optical band generally or the blue region of the optical band. Preferably, said filtering means is in the form of a layer of filtering material deposited on one or both surfaces of said transparent element.

One or both surfaces of said transparent element may be pre-etched to define a lens pattern to improve the effectiveness of the optical sensing elements. Additionally or alternatively, one or more surfaces of the said transparent element may be pre- etched to reduce the reflection of optical radiation and/or improve the transmission efficiency of the said transparent element for radiation.

The transparent element may be formed of glass. Preferably, the transparent element has a coefficient of thermal expansion substantially similar to that of the. die.

According to a second aspect of the present invention there is provided a method of manufacturing an integrated circuit die, suitable for use in the method of the first aspect of the present invention, comprising the steps of: providing a wafer; forming an integrated circuit on said wafer, said integrated circuit having at least one optically active element; providing a layer of photolithographic material over said wafer; selectively exposing said photo lithographic material to light; and selectively removing said unexposed areas of photolithographic material to leave said integrated circuit provided within a pair of encompassing ridges.

This method enables a die to be manufactured wherein the ridges are formed to substantially the same level of accuracy as the integrated circuit. This makes the die particularly suited to use in the method of the first aspect of the present invention, not least because the accuracy of the size of the gap between the ridges enables a standard amount of adhesive to be dispensed between the ridges.

The wafer may be a standard CMOS wafer. The wafer may be spun after a known quantity of photolithographic material is deposited on to its surface. This ensures that the layer of photolithographic material has an even thickness. Preferably, the method is adapted so as to form an array of integrated circuits with associated ridge pairs on a single wafer. In such embodiments, the method may incorporate the additional step of making cuts through the array between the integrated circuits and their associated ridges to provide separate individual dies.

The ridges may be formed of a flexible photolithographic material, for example, photoresist. In one preferred embodiment, said flexible photolithographic material is an organic photolithographic Gel such as that manufactured by Dow Corning and known as DC50001a.

Once the transparent element has been placed over said integrated circuit to form a covered assembly, said covered assembly may be mounted onto a lead frame and packaged in a suitable housing. Alternatively of course, the die may be mounted on said lead frame prior to the transparent element being placed over said wafer, the covered and mounted assembly subsequently being packaged in a suitable housing.

Preferably, before the covered assembly is packaged, the method includes the step of making electrical connections between the integrated circuit and the periphery of the lead frame either using bond wires and bond pads provided on the die or otherwise. The packaging may be achieved by placing the covered assembly into the cavity of a mould tool and encapsulating all of said covered assembly other than the periphery of the lead frame and the area of transparent element aligned with said optically active means in a suitable mould compound. The transparent element may be kept free of mould compound during the packaging process by means of a suitable pin or projection of the moulding tool or by means of the Boschmann film in mould process.

According to a third aspect of the present invention there is provided an optical integrated circuit device manufactured in accordance with the method of the first and/or second aspects of the present invention.

The optical integrated circuit device according to the third aspect of the present invention may incorporate any of the features of the first and/or second aspects of the present invention as desired or appropriate.

According to a fourth aspect of the present invention, there is provided a DVD reader incorporating an optical integrated circuit device according to the third aspect of the present invention.

The DVD reader according to the fourth aspect of the present invention may incorporate any of the features of the first and/or second and/or third aspects of the present invention as desired or appropriate. In order that the invention is more clearly understood, it will now be described further herein, by way of example only and with reference to the following drawings in which:

Figure 1 is a cross-sectional view of a first stage in manufacturing an integrated circuit device according to the present invention;

Figure 2 is a cross-sectional view of a further stage in manufacturing an integrated circuit device according to the present invention;

Figure 3 is a cross-sectional view of a later further stage in manufacturing an integrated circuit device according to the present invention;

Figure 4 is a cross-sectional view of a an integrated circuit device according to the present invention; and

Figure 5 is a cross-sectional view of an alternative embodiment of an integrated circuit device according to the present invention.

Referring to the figures, an integrated circuit is provided on a semiconductor wafer 101. The integrated circuit comprises one or more optically active elements, 102, and control and interface means. The integrated circuit typically also comprises bond pads (not shown) enabling connections to be made to external circuitry. The optically active elements may be radiation emitting and/or radiation sensing means. In one embodiment, the integrated circuit may be an integrated circuit adapted to be suitable for use as a DVD reader.

In order to provide protection for the integrated circuit during use without compromising the operation of the optically active element or elements, a transparent element 106 is mounted over at least the optically active elements 102 of the integrated circuit. The transparent element 106 is retained in position by adhesive 105. The adhesive 105 is deposited between and maintained in position by a pair of ridges 104 provided around the optically active element or elements.

In order to manufacture such a protected assembly, an array of integrated circuits is provided on a semiconductor wafer 101. A layer of photolithographic material, such as photoresist or an organic photolithographic gel, is then provided over the surface of the wafer 101. The wafer 101 is spun to ensure that the layer is of even thickness. The photolithographic layer is then selectively exposed to light

(typically ultraviolet light). The unexposed areas of the photolithographic layer are then washed away to leave ridge pairs 104 around each optically active element of each integrated circuit in the array.

As the ridges 104 are formed by the above process their position, height and separation can be accurately controlled, hi particular, the ridges may be positioned at the same level of accuracy as the individual integrated circuits. Typically, one pair of ridges will be provided around each optically active element 102, however if desired, two or more like or unlike optically active elements 102 may be provided within each ridge pair 104.

After the ridges 104 are formed the wafer 101 is cut along scribe lines provided between the integrated circuits and associated ridges 104 to provide individual dies comprising an integrated circuit and a ridge pair, as is illustrated in figure 2.

Each individual die containing optically active elements 102 and a pair of ridges 104 is mounted onto the centre portion of a lead frame 108 using pick and place means and electrical connections 110 made between the die and the external portions of the lead frame 109.

The next steps in the process are to dispense a known quantity of adhesive material 105 between the ridges 104, as shown in figure 3, and then to place a transparent element 106 in position over the optically active element 102 as shown in figures 4 and 5. The transparent element 106 is placed in position by pick and place means. The accuracy of placing the transparent element 106 over the integrated circuit 102 is of the same order of that of placing the die on the lead frame 108. Pick and place technology is well known in the semiconductor industry and can be used cheaply and conveniently for both purposes whilst achieving the required accuracy.

The transparent element 106 is retained in position by the adhesive 105. As the volume of the space between the ridges 104 can be very accurately controlled, it is relatively simple to ensure that a correct amount of adhesive 105 is dispensed. In the embodiment of figure 4, the transparent element 106 is pressed on to the top of the adhesive 105. If necessary, the adhesive 105 is free to deform outward, away from the integrated circuit 102, through the gap between the outer ridge 104 and the end of the transparent element 106. This stops the adhesive 105 from obscuring the optically active element or elements. It also improves the sealing between the adhesive 105 and the transparent element 106.

hi the alternative embodiment of figure 5, the transparent element is pressed down harder, so as to partially compress the inner ridge 107. As before, there is a gap between the outer ridge and the end of the transparent element 106 through which the adhesive 105 can deform which prevents the optically active element or elements being obscured and improves the seal between the adhesive 105 and the transparent element 106.

In any of these embodiments, the transparent element may be etched or otherwise adapted to improve focusing or transmission of light radiation through the transparent element 106. The element 106 may also be provided with a suitable filter means.

The die and transparent element 106, together comprising a covered assembly, would typically be housed in a suitable package for protection during use. The package may be manufactured by inserting the covered assembly and lead frame 108, 109 into the cavity of a moulding tool and encapsulating the covered assembly and lead frame 108, 109 in a suitable moulding compound in such a manner that the peripheral portions of the lead frame 109 and the upper surface of the transparent element 106 are exposed.

To ensure that the upper surface of the transparent element 106 is exposed the moulding tool may be adapted to have a projection or pin in contact with the upper surface of the transparent element 106 or with a gel blob applied to the upper surface of the transparent element 106. Additionally or alternatively, the Boschmann film in mould process may be used to ensure the surface of the transparent element 106 remains free from encapsulant.

It is of course to be understood that the invention is not to be limited to the details of the above embodiment which is described by way of example only.

Claims

1. A method of manufacturing optical integrated circuit devices comprising the steps of: providing a die, said die comprising an integrated circuit provided within a pair of encompassing ridges, said integrated circuit having at least one optically active element, said pair of ridges having a gap provided therebetween; dispensing adhesive material into the gap between said pair of ridges; and placing a transparent element over said integrated circuit, said transparent element being secured in position by said adhesive material.

2. A method as claimed in claim 1 wherein said optically active elements comprise emitting means and/or sensing means.

3. A method as claimed in claim 2 wherein said sensing means comprise an array of individual light sensing elements.

4. A method as claimed in any preceding claim wherein said transparent element is placed over said integrated circuit using pick and place technology.

5. A method as claimed in any preceding claim wherein the ridges are formed of a flexible material.

6. A method as claimed in any preceding claim wherein the transparent element is placed in such a manner that it compresses the inner ridge of the ridge pair.

7. A method as claimed in any preceding claim wherein the adhesive is dispensed in such a manner as to substantially fill the gap between the ridges.

8. A method as claimed in any preceding claim wherein the adhesive projects above the top of the ridges.

9. A method as claimed in any preceding claim wherein the transparent element is adapted to fit within the outer ridge but not within the inner ridge.

10. A method as claimed in any preceding claim wherein the transparent element is provided with filtering means to limit the incoming radiation to a desired wavelength band.

11. A method as claimed in claim 10 wherein said filtering means is in the form of a layer of filtering material deposited on one or both surfaces of said transparent element.

12. A method as claimed in any preceding claim wherein one or both surfaces of said transparent element are pre-etched to define a lens pattern to improve the effectiveness of the optical sensing elements.

13. A method as claimed in any preceding claim wherein one or more surfaces of the said transparent element are pre-etched to reduce the reflection of optical radiation and/or improve the transmission efficiency of the said transparent element for radiation.

14. A method as claimed in any preceding claim wherein the transparent element is formed of glass.

15. A method as claimed in any preceding claim wherein the transparent element has a coefficient of thermal expansion substantially similar to that of the die.

16. A method of manufacturing an integrated circuit die, suitable for use in the method of the first aspect of the present invention, comprising the steps of: providing a wafer; forming an integrated circuit on said wafer, said integrated circuit having at least one optically active element; providing a layer of photolithographic material over said wafer; selectively exposing said photolithographic material to light; and selectively removing said unexposed areas of photolithographic material to leave said integrated circuit provided within a pair of encompassing ridges.

17. A method as claimed in claim 16 wherein the wafer is a standard CMOS wafer.

18. A method as claimed in claim 16 or claim 17 wherein the wafer is spun after a known quantity of photolithographic material is deposited on to its surface.

19. A method as claimed in any one of claims 16 to 18 wherein the method is adapted so as to form an array of integrated circuits with associated ridge pairs on a single wafer.

20. A method as claimed in claim 19 wherein the method incorporates the additional step of making cuts through the array between the integrated circuits and their associated ridges to provide separate individual dies.

21. A method as claimed in any one of claims 16 to 20 wherein the ridges, are formed of a flexible photolithographic material.

22. A method as claimed in claim 21 wherein said flexible photolithographic material is an organic photolithographic Gel.

23. A method as claimed in any one of claims 16 to 22 wherein once the transparent element has been placed over said integrated circuit to form a covered assembly, said covered assembly is mounted onto a lead frame and packaged in a suitable housing.

24. A method as claimed in claim 23 wherein the die is mounted on said lead frame prior to the transparent element being placed over said wafer.

25. A method as claimed in claim 23 or claim 24 wherein before the covered assembly is packaged, the method includes the step of making electrical connections between the integrated circuit and the periphery of the lead frame using bond wires and bond pads provided on the die.

26. A method as claimed in any one of claims 23 to 25 wherein packaging is achieved by placing the covered assembly into the cavity of a mould tool and encapsulating all of said covered assembly other than the periphery of the lead frame and the area of transparent element aligned with said optically active means in a suitable mould compound.

27. A method as claimed in claim 26 wherein the transparent element is kept free of mould compound during the packaging process by means of a suitable pin or projection of the moulding tool.

28. A method as claimed in claim 26 wherein the transparent element is kept free of mould compound during the packaging process by means of the Boschmann film in mould process.

29. An optical integrated circuit device manufactured in accordance with the method of any preceding claim.

30. A DVD reader incorporating an optical integrated circuit device according to claim 29.