KR20220034437A - Optical filter carrier, image sensor package having optical filter, and method of fabricating the same - Google Patents

Abstract

According to an embodiment of the present invention, an optical filter module includes: an optical filter; and a molding member surrounding the top, bottom, and sides of the optical filter along an edge of the optical filter, wherein the molding member includes a light blocking material. The present invention provides an image sensor package capable of reducing a planar area.

Description

OPTICAL FILTER CARRIER, IMAGE SENSOR PACKAGE HAVING OPTICAL FILTER, AND METHOD OF FABRICATING THE SAME

The present invention relates to a camera system for optical imaging and sensing, and more particularly to an image sensor package having an optical filter, a method of manufacturing the same, and an optical filter carrier used for manufacturing the same.

Various optical filters and image sensors are used in camera systems for optical imaging and sensing in various fields such as automobiles, mobile phones, and CCTVs. An optical filter is an optical element that transmits light in a selected wavelength range and blocks other light in VR (Virtual Reality), AR (Augmented Reality), autonomous vehicles, drones, face recognition, iris recognition, gesture recognition, etc. The field of application continues to expand.

The image sensor is disposed downstream of the optical filter to sense light transmitted through the optical filter. Image sensors generally include CCD or CMOS image sensors, which are manufactured using a silicon substrate. As the area of the silicon substrate increases, recently, an image sensor using a 12-inch silicon substrate is being manufactured.

The image sensor includes pixels, and each pixel detects incident light and converts it into an electrical signal. The image sensor is mounted on a printed circuit board, and bonding wires are generally used to electrically connect the image sensor to the printed circuit board. The bonding wire electrically connects the pad formed around the pixel area and the pad on the printed circuit board. The pad for bonding the wire increases the area of the image sensor in addition to the pixel area required for light sensing. An increase in the area of the image sensor increases the size of a front camera module such as a mobile phone, making it difficult to display a full screen, for example.

Furthermore, since the image sensor using the bonding wire is not freely movable, there is a limit in applying the sensor movement OIS (Optical Image Stabilization) module to achieve optical image stabilization by moving the image sensor.

On the other hand, the conventional camera module adjusts the focal length by moving the lens using an actuator including a voice coil motor (VCM). In these camera modules, the optical filter is usually mounted on an actuator and placed near the image sensor. Accordingly, the process of manufacturing the optical filter module and the process of manufacturing the image sensor package have been separated from each other.

An object of the present invention is to provide an image sensor package having an optical filter.

Another problem to be solved by the present invention is to provide an image sensor package capable of reducing a planar area.

Another problem to be solved by the present invention is to provide an optical filter carrier that can be used for manufacturing an image sensor package using a large-area substrate.

Another problem to be solved by the present invention is to provide a method for manufacturing an optical filter carrier and an image sensor package.

An optical filter carrier according to an embodiment of the present invention includes: a substrate having a plurality of aligned holes; a plurality of optical filters disposed to correspond to the plurality of holes; and a bonding layer disposed between the optical filter and the substrate to couple the optical filter to the substrate.

The optical filter carrier may further include an anti-reflection layer disposed on inner side surfaces of the plurality of holes.

The light reflection prevention layer may be a light absorption layer.

In one embodiment, the bonding layer may be a glass frit.

A plurality of bonding layers may be disposed to correspond to each optical filter, and each bonding layer may be disposed to surround the hole of the substrate.

Each of the bonding layers may be disposed inside a region surrounded by an edge of each optical filter.

The optical filter may be an infrared cut-off filter.

The substrate may have a diameter of at least 12 inches.

An image sensor package according to an embodiment includes: a semiconductor chip having an image sensing pixel disposed on an upper surface and solder balls formed on a lower surface for electrical connection; an optical filter disposed on the semiconductor chip; a spacer disposed between the optical filter and the semiconductor chip; and a bonding layer coupling the optical filter to the spacer, wherein the spacer is disposed in a ring shape along an edge of the semiconductor chip, an outer surface of the spacer is parallel to a side surface of the semiconductor chip, and the optical filter A width of is smaller than a width of the semiconductor chip, and the optical filter is located in an upper region of the semiconductor chip.

The image sensor package may further include a light absorbing layer disposed on an inner side surface of the spacer.

In one embodiment, the bonding layer may be a glass frit.

The optical filter may be an infrared cut-off filter.

A method of manufacturing an optical filter carrier according to an embodiment includes forming a plurality of holes in a substrate, and coupling optical filters on the substrate to correspond to each of the holes.

In addition, combining the optical filters includes applying a glass frit surrounding each of the holes, disposing an optical filter on the glass frit, and irradiating a laser beam along the glass frit to melt the glass frit. may include

The method of manufacturing the optical filter carrier may further include forming a light absorbing layer covering inner walls of the holes before applying the glass frit.

The substrate may have a diameter of at least 12 inches.

The method for manufacturing an image sensor package according to an embodiment includes manufacturing an optical filter carrier by the method described above, manufacturing a semiconductor wafer having a plurality of image sensing pixels formed thereon, and attaching the optical filter carrier on the semiconductor wafer, , cutting the semiconductor wafer together with the substrate in a region between the optical filters.

According to embodiments of the present invention, by providing an optical filter carrier in which a plurality of optical filters are combined, an image sensor package having an optical filter can be provided using a large-area semiconductor wafer on which a plurality of image sensing pixels are formed. . Furthermore, by using a spacer, an optical filter can be coupled to an image sensor package employing a ball grid array. In addition, it is possible to reduce the planar area of the camera module by adopting an image sensor package adopting a ball grid array.

1 is a schematic plan view for explaining an image sensor package according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view taken along line A-A' of FIG. 1 ;
FIG. 3 is a schematic cross-sectional view taken along line B-B' of FIG. 1 ;
4 is a schematic plan view illustrating a semiconductor wafer on which a plurality of image sensing pixels are formed.
5A is a schematic plan view for explaining a substrate in which a plurality of holes are formed.
5B is a partially enlarged plan view of FIG. 5A .
Fig. 5c is a schematic cross-sectional view taken along line C-C' of Fig. 5b;
6A, 7A, 8A, and 9A are schematic plan views for explaining a method of manufacturing an image sensor package according to an embodiment of the present invention.
6B, 7B, 8B, and 9B are schematic cross-sectional views taken along line C-C' of FIGS. 6A, 7A, 8A, and 9A, respectively.
10 is a schematic cross-sectional view for explaining a process of individualizing image sensor packages.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. And in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Like reference numerals refer to like elements throughout.

1 is a schematic plan view for explaining an image sensor package according to an embodiment of the present invention, and FIGS. 2 and 3 are schematic cross-sectional views taken along the cut-out lines A-A' and B-B' of FIG. 1, respectively.

1, 2, and 3, the image sensor package according to the present embodiment includes a semiconductor chip 10a for an image sensor, an optical filter 20, a spacer 30a, a first bonding layer 40a, and A second bonding layer 50 may be included.

The semiconductor chip 10a for an image sensor may include a semiconductor substrate 11 and a pixel region 13 . For example, the pixel region 13 may be formed in a semiconductor substrate 11 such as silicon. The pixel region 13 may be formed of CCD or CMOS, and thus a CCD image sensor or CMOS image sensor may be provided. Since the semiconductor chip 10a for a CCD or CMOS image sensor is a well-known semiconductor chip in the art, a detailed description thereof will be omitted.

Micro lenses 15 for forming an image may be arranged on the semiconductor chip 10a for an image sensor. The microlenses 15 may be disposed to image the light passing through the optical filter 20 on the pixel area 13 . Micro-scale lenses may be aligned on the pixel area 13 .

Meanwhile, the solder balls 17 may be disposed on the lower surface of the semiconductor chip 10a for the image sensor. The solder balls 17 are used to supply electricity for operation of the pixel region 13 to the pixel region 13 , or to transmit an electrical signal generated in the pixel region 13 to a printed circuit board. In particular, the solder balls 17 are bonded on the printed circuit board, and thus bonding wires according to the prior art are omitted. Furthermore, since the solder balls 17 are disposed on the lower surface of the semiconductor chip 10a, the area for forming the pads in the prior art can be omitted or significantly reduced. Accordingly, the planar area of the semiconductor chip 10a can be reduced. The image sensor package according to the present embodiment may be particularly suitably used in a camera module for a full-screen display (FSD) due to a reduction in the planar area of the semiconductor chip 10a.

Furthermore, the thickness of the semiconductor chip 10a may be reduced before the solder balls 17 are formed. The thickness of the semiconductor chip 10a can be reduced by polishing a substrate such as silicon using a technique such as grinding. By reducing the thickness of the semiconductor chip 10a, an increase in the height of the package due to the formation of the solder balls 17 may be alleviated.

By reducing the thickness of the image sensor package, it is possible to prevent the overall height of the camera module from being increased, and in particular, to reduce the camera module size in a camera for 3D image sensing, for example, a Time of Flight (ToF) camera. can

The optical filter 20 transmits light of a wavelength band required in various camera systems for imaging or sensing, and blocks light in an unnecessary region. The optical filter 20 may be various depending on the use, for example, may be an infrared cut-off filter that blocks infrared rays in an imaging system, and may be an infrared transmission filter that blocks visible light and transmits infrared rays in a three-dimensional image sensing system can

The optical filter 20 may include a filter laminate disposed on a substrate, and may include a blocking laminate or an anti-reflective coating under the substrate. The optical filter 20 may be any filter manufactured using a conventional technique, and a detailed description thereof will be omitted. However, to withstand high temperatures, the optical filter 20 may use a glass substrate as a substrate, and the filter laminate, blocking laminate, or anti-reflection coating is formed using inorganic layers.

The spacer 30a is disposed between the semiconductor chip 10a and the optical filter 20 . The spacers 30a may be arranged in a ring shape along the edges of the semiconductor chip 10a. 1 , the spacer 30a may have a rectangular ring shape, but is not limited thereto.

Meanwhile, the outer surface of the spacer 30a may be parallel to the side surface of the semiconductor chip 10a. The thickness of the spacer 30a may be greater than the thickness of the substrate 11 . In particular, the thickness of the spacer 30a is greater than the height of the lenses 15 , thus spacing the optical filter 20 from the lenses 15 .

The spacer 30a is formed of a material that can withstand the mounting temperature when the image sensor package is mounted on a printed circuit board using the surface mounting technology using the solder balls 17 . In particular, the image sensor package may be surface mounted using a reflow process, wherein the mounting temperature may exceed 220°C at most. The spacer 30a is formed of a material that can withstand high temperatures in the reflow process. Furthermore, the spacer 30a may be formed of a material similar to the substrate of the optical filter 20 or an inorganic layer disposed thereon, for example, glass.

The first bonding layer 40a couples the optical filter 20 and the spacer 30a. In one embodiment, the first bonding layer 40a may be, for example, a double-sided adhesive such as a die-adhesive film (DAF). In this embodiment, the first bonding layer 40a may be formed of a material that can withstand the mounting temperature when the image sensor package is mounted on the printed circuit board using the surface mounting technology using the solder balls 17. there is. In another embodiment, the first bonding layer 40a may be a glass frit. The glass frit is particularly advantageous for sealingly bonding the glass spacer 30a and the optical filter 20 . The first bonding layer 40a using the glass frit may be located inside the lower region of the optical filter 20, as shown in FIGS. 1, 2, and 3, and has a ring shape on the spacer 30a. can be partially placed.

The second bonding layer 50 couples the semiconductor chip 10a and the spacer 30a. The second bonding layer 50 may be a double-sided adhesive such as a die adhesive film (DAF). The second bonding layer 50 may also be formed of a material that can withstand the temperature at which the image sensor package is mounted by using a surface mounting technique such as a reflow process.

Meanwhile, the light reflection prevention layer 31 prevents light from being reflected from the spacer 30a and incident on the pixel region 13 . The light reflection prevention layer 31 may be formed on the inner side surface of the spacer 30a to prevent reflection of light incident to the spacer 30a. The light reflection prevention layer 31 may cover the upper surface of the spacer 30a.

Light passing through the optical filter 20 or light reflected from the microlens 15 or the semiconductor chip 10a may be reflected by the spacer 30a to be incident on the pixel region 13 . The light reflected from the spacer 30a causes problems such as flare, resulting in image defects. The light reflection prevention layer 31 may block the reflection of light from the inner side of the spacer 30a to prevent flare.

In one embodiment, the light reflection prevention layer 31 may be a light absorption layer. For example, the light absorbing layer may be formed using an ink including a light absorbing agent such as black ink.

In one embodiment, as shown in FIGS. 2 and 3 , the light reflection prevention layer 31 covers the inner surface of the spacer 30a, and the first bonding layer 40a and the second bonding layer 50 are do not cover In another embodiment, the light reflection prevention layer 31 may cover the inner surface of the first bonding layer 40a. In addition, the inner surface of the second bonding layer 50 may also be covered with the light reflection preventing layer 31 .

According to the present embodiment, an image sensor package capable of surface mounting is provided by combining the optical filter 20 with the semiconductor chip 10a for an image sensor by adopting the spacer 30a formed of a material that can withstand high temperatures such as glass. can do.

Meanwhile, in the present exemplary embodiment, the outer surface of the spacer 30a may be parallel to the outer surface of the semiconductor chip 10a. That is, the lateral width T1 and the longitudinal width T2 of the spacer 30a may be the same as the lateral width T1 and the longitudinal width T2 of the semiconductor chip 10a, respectively. In contrast, the lateral width W1 and the longitudinal width W2 of the optical filter 20 have values smaller than the lateral width T1 and the longitudinal width T2 of the semiconductor chip 10a, respectively. Furthermore, as shown in FIGS. 1, 2, and 3 , the optical filter 20 is disposed inside the upper region of the semiconductor chip 10a.

Hereinafter, an image sensor package manufacturing method will be described in detail. The image sensor package is manufactured by manufacturing a semiconductor wafer having a pixel for an image sensor and an optical filter carrier, respectively, and then bonding the optical filter carrier to the semiconductor wafer and unifying the image sensor packages. Hereinafter, each manufacturing process will be described with reference to the drawings.

(Semiconductor Wafer Manufacturing)

4 is a schematic plan view for explaining the semiconductor wafer 10 on which a plurality of image sensing pixels are formed.

Referring to FIG. 4 , the semiconductor wafer 10 includes a plurality of image sensing pixels 13 formed on a substrate 11 . Pixels 13 for image sensing are arranged in the substrate 11 . Microlenses 15 as described with reference to FIGS. 2 and 3 may be formed on each image sensing pixel 13 .

The substrate 11 may be, for example, a silicon substrate. The image sensing pixel 13 may be formed on the silicon substrate 11 using a conventional technique. Here, the size of the silicon substrate 11 is not particularly limited, but may have a diameter of, for example, at least 8 inches, and further, at least 12 inches. By using the large-area substrate 11 , a plurality of image sensor packages may be manufactured through a single manufacturing process. Although the present invention does not specifically limit the size of the substrate 11, it is more useful when the substrate 11 is relatively large.

(manufacture of optical filter carrier)

5A, 5B, 5C, 6A, 6B, 7A, 7B, 8A, and 8B are schematic plan views and cross-sectional views illustrating a method of manufacturing an optical filter carrier according to an embodiment. Here, FIG. 5B is a partially enlarged plan view of FIG. 5A, and FIGS. 5C, 6B, 7B, and 8B are schematic views taken along the cut-off line C-C' of FIGS. 5B, 6A, 7A, and 8A, respectively. are cross-sections.

First, referring to FIGS. 5A , 5B and 5C , a plurality of holes 30h are formed in the substrate 30 . The plurality of holes 30h are aligned to correspond to the image sensing pixels 13 of the semiconductor wafer 10 described above. The substrate 30 may have substantially the same size as the semiconductor wafer 10 . For example, when the diameter of the semiconductor wafer 10 is 8 inches, the diameter of the substrate 30 may also be 8 inches, and when the diameter of the semiconductor wafer 10 is 12 inches, the diameter of the substrate 30 is also It may be 12 inches. The diameter of the substrate 30 may exceed 12 inches.

The substrate 30 may be, for example, a glass substrate, and the plurality of holes 30h may be formed through, for example, laser processing. For example, an ultraviolet laser having a wavelength of about 355 nm may be used, and as shown in FIG. 5B , a plurality of holes 30h may be formed in the substrate 30 by partially removing the substrate 30 in a rectangular shape. can

The holes can be spaced equally spaced from each other, and the spacing between the holes is precisely controlled. The spacing between the holes may be, for example, 500 um or more. Meanwhile, the size of the hole may be adjusted according to the size of the pixel region 13 .

6A and 6B , the light reflection prevention layer 31 is formed on inner surfaces of the holes 30h. The light reflection prevention layer 31 may be formed by applying an ink including a light absorber, such as black ink, to the inner surfaces of the holes and drying the ink.

The light reflection prevention layer 31 may be formed by, for example, spraying black ink using a spray coater. In particular, a nanojet spray coater capable of spraying micro- or nano-sized water droplets may be used. The size of the water droplets may be approximately 200 nm to 5 μm, and the light reflection prevention layer 31 , for example, a light absorption layer, may be formed on the inner surfaces of the holes by adjusting the spray angle. The light reflection prevention layer 31 may be heat-treated at, for example, about 80° C. for 1 hour.

The light reflection prevention layer 31 may be formed not only on the inner surface of the holes 30h but also on the upper surface of the substrate 30 . The thickness of the light reflection prevention layer 31 may be substantially uniform, but is not limited thereto, and may become smaller as it moves away from the upper surface of the substrate 30 .

7A and 7B , a glass frit 40 is coated on a substrate 30 . The glass frit 40 may be formed before the light reflection prevention layer 31 is formed.

A glass frit 40 is applied to surround the hole 30h for each hole 30h. The glass frit 40 may be applied in a liquid form. The glass frit 40 may be formed with a generally uniform width and thickness using, for example, screen printing techniques. The glass frit 40 may be formed to a thickness of, for example, about 5 μm. The glass frit 40 may further include a light absorber.

8A and 8B , the optical filter 20 is disposed on the substrate 30 with the glass frit 40 interposed therebetween. A plurality of optical filters 20 may be disposed to be spaced apart from each other to correspond to the holes 30h. Thereafter, the glass frit 40 is melted by irradiating a laser beam. The laser beam may be continuously irradiated along the glass frit 40 , and accordingly, the optical filter 20 and the substrate 30 may be bonded by the glass frit 40 .

The laser beam may be, for example, an infrared laser of about 1064 nm, and the diameter of the laser beam may be greater than the width of the glass frit 40 . Accordingly, the sealing process can be completed by continuously melting the glass frit 40 arranged in a ring shape by one laser beam irradiation. The melted glass frit 40 is solidified to form a first bonding layer 40a for bonding the optical filter 20 to the substrate 30 .

The laser beam may be irradiated from the optical filter 20 side or the substrate 30 side. In an embodiment, when the optical filter 20 is an infrared cut-off filter and the laser is an infrared laser, the laser beam may be irradiated from the substrate 30 side. Accordingly, the optical filter 20 and the substrate 30 may be coupled to each other by the first bonding layer 40a formed of the glass frit 40 . Accordingly, the optical filter carrier to which the optical filters 20 are combined is completed.

In this embodiment, although it is described that the first bonding layer 40a is formed using the liquid glass frit 40, the first bonding layer 40a may be formed using, for example, a double-sided tape. That is, a double-sided tape may be attached on the substrate 30 or under the optical filter 20 and the substrate 30 and the optical filter 20 may be coupled using the double-sided tape.

(Combination of semiconductor wafer and optical filter carrier)

9A is a plan view showing the semiconductor wafer 10 and the optical filter carrier are combined, and FIG. 9B is a schematic cross-sectional view taken along line C-C' of FIG. 9A.

Referring to FIGS. 9A and 9B , an optical filter carrier is coupled to the semiconductor wafer 10 on which pixels for image sensing are formed. Specifically, the substrate 30 may be attached to the semiconductor wafer 10 using the second bonding layer 50 . The second bonding layer 50 may be a double-sided tape such as a die attach film (DAF).

The semiconductor wafer 10 and the substrate 30 may have a similar size, for example, a diameter of 12 inches, and the optical filters 20 are aligned to correspond to the image sensing pixels on the semiconductor wafer 10 .

Meanwhile, as described with reference to FIGS. 1 to 3 , micro lenses 15 may be formed on the pixel region for image sensing, so that the micro lenses 15 face the optical filter 20 . The wafer 10 and the substrate 30 are coupled.

(Unification of image sensor package)

10 is a schematic cross-sectional view for explaining unification of an image sensor package according to an embodiment.

Referring to FIG. 10 , the image sensor package as described with reference to FIGS. 1 to 3 is completed by cutting the substrate 30 and the semiconductor wafer 10 . The substrate 30 and the semiconductor wafer 10 may be cut through a sawing process. Sawing can be performed, for example, using a laser. The substrate 30 becomes the spacer 30a in the individual image sensor package, and the semiconductor wafer 10 becomes the semiconductor chip 10a in the individual image sensor package. By cutting the substrate 30 and the semiconductor wafer 10 together, the outer surface of the spacer 30a may be formed parallel to the side surface of the semiconductor chip 10a.

Meanwhile, before cutting the substrate 30 and the semiconductor wafer 10 , the thickness of the semiconductor wafer 10 may be reduced by grinding the lower surface of the semiconductor wafer 10 . For example, the thickness of the semiconductor wafer 10 may be polished to be smaller than the thickness of the substrate 30 . Also, the solder balls 17 as described with reference to FIGS. 1 to 3 may be formed on the lower surface of the semiconductor wafer 10 to correspond to each image sensing pixel. In FIG. 10 , the microlenses 15 and the solder balls 17 are omitted to simplify the drawing.

According to the present embodiment, by providing an optical filter carrier in which a plurality of optical filters 20 are individually coupled to a substrate 30 having a relatively large size, image sensor packages are formed using a large-area semiconductor wafer 10 . It can be manufactured in large quantities.

Although various embodiments have been described above, the present invention is not limited to these embodiments, and various modifications may be made without departing from the scope of the invention.

Claims (17)

a substrate having a plurality of aligned holes;
a plurality of optical filters disposed to correspond to the plurality of holes; and
and a bonding layer disposed between the optical filter and the substrate to couple the optical filter to the substrate. The method according to claim 1,
The optical filter carrier further comprising an anti-reflection layer disposed on the inner side of the plurality of holes. 3. The method according to claim 2,
The light reflection prevention layer is an optical filter carrier that is a light absorption layer. The method according to claim 1,
The bonding layer is a glass frit optical filter carrier. 5. The method according to claim 4,
A plurality of the bonding layers are disposed to correspond to each optical filter,
and each bonding layer is disposed to surround a hole in the substrate. 6. The method of claim 5,
wherein each bonding layer is disposed inside a region surrounded by an edge of each optical filter. The method according to claim 1,
wherein the optical filter is an infrared cut-off filter. The method according to claim 1,
The substrate is an optical filter carrier having a diameter of at least 12 inches. a semiconductor chip on which an image sensing pixel is disposed on an upper surface, and solder balls for electrical connection are formed on a lower surface thereof;
an optical filter disposed on the semiconductor chip;
a spacer disposed between the optical filter and the semiconductor chip; and
a bonding layer coupling the optical filter to the spacer;
The spacers are arranged in a ring shape along an edge of the semiconductor chip,
A side surface of the spacer is parallel to a side surface of the semiconductor chip,
The width of the optical filter is smaller than the width of the semiconductor chip,
and the optical filter is located in an upper region of the semiconductor chip. 10. The method of claim 9,
The image sensor package further comprising a light absorbing layer disposed on the inner side of the spacer. 10. The method of claim 9,
The bonding layer is a glass frit image sensor package. 10. The method of claim 9,
wherein the optical filter is an infrared cut-off filter. forming a plurality of holes in the substrate;
and coupling optical filters on the substrate to correspond to each of the holes. 14. The method of claim 13,
Combining the optical filters is
Applying a glass frit surrounding each of the holes,
placing an optical filter on the glass frit,
and melting the glass frit by irradiating a laser beam along the glass frit. 15. The method of claim 14,
and forming a light absorbing layer covering inner walls of the holes before applying the glass frit. 14. The method of claim 13,
wherein the substrate has a diameter of at least 12 inches. 17. To manufacture an optical filter carrier by the manufacturing method of any one of claims 13 to 16,
Manufacturing a semiconductor wafer on which a plurality of image sensing pixels are formed,
attaching the optical filter carrier onto the semiconductor wafer;
and cutting the semiconductor wafer together with the substrate in a region between the optical filters.

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