INTEGRATED FILTER OPTICAL PACKAGE

Abstract

An integrated filter optical package including an ambient light sensor that incorporates an infrared (IR) filter in an integrated circuit (IC) stacked-die configuration is provided. The integrated filter optical package incorporates an infrared (IR) coated glass layer to filter out or block IR light while allowing visible (ambient) light to pass through to a light sensitive die having a light sensor. The ambient light sensor detects an amount of visible light that passes through the IR coated glass layer and adjusts a brightness or intensity of a display screen on an electronic device accordingly so that the display screen is readable.

Claims

1. A method of making a light sensor comprising: attaching a light sensitive die to a die pad; bonding wire bonds from the light sensitive die to electrical terminations arranged in a lead frame; applying an optical film on a surface of the light sensitive die; attaching a glass infrared (IR) filter to the optical film opposite the light sensitive die; molding a molding compound around the light sensitive die, the die pad, the wire bonds, the glass infrared (IR) filter, and the optical film to encapsulate the light sensitive die, the die pad, the wire bonds, the glass infrared (IR) filter, and the optical film leaving an exposed surface of the glass infrared (IR) filter exposed to ambient light; and curing the molding compound.

2. The method of claim 1, wherein the molding compound includes a film assist to prevent bleeding on a surface of the glass filter.

3. The method of claim 2, further comprising: deflashing the molding compound to remove molding compound residue.

4. The method of claim 1, wherein prior to attaching the glass infrared (IR) filter to the optical film, the method includes dividing the glass filter into even pieces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGS. 1A and 1B are block diagram representations of example ambient light sensors in a stacked-die configuration.

[0009] FIG. 2 is an example of an ambient light sensor having a stacked-die configuration.

[0010] FIG. 3 is another example of an ambient light sensor having a stacked-die configuration.

[0011] FIG. 4 is another example of an ambient light sensor having a stacked-die configuration.

[0012] FIG. 5 is a block diagram illustration describing a process of manufacturing an ambient light sensor having a stacked-die configuration.

DETAILED DESCRIPTION

[0013] Optical mold compounds mentioned above have several drawbacks. First, the optical mold compound has a high coefficient of thermal expansion (CTE) as compared to the silicon. Thus, as the temperature of the IC changes, the optical mold compound expands/contracts at a much different rate than the SiO.sub.2, which in turn can damage the IC and/or snap internal wire bonds. Second, in order to more closely match the CTE between the optical mold compound and the silicon, fillers (e.g., fused silica) are added to the optical mold compound. The fillers however, are not optically clear and thus, attenuate the visible light traveling through the optical mold compound to the internal light sensor, which compromises the performance of the ambient light sensor. Finally, optical mold compounds are more expensive than non-optical mold compounds used in a stacked-die configuration.

[0014] Disclosed herein is an integrated filter optical package and more specifically, an ambient light sensor that incorporates an infrared (IR) filter in an integrated circuit (IC) stacked-die configuration (e.g., quad flat no-lead (QFN) package, dual flat no lead (DFN) package, chip-on lead (COL) package, etc.) that utilizes a non-optical mold compound. The ambient light sensor, which can be used in an electronic device (e.g., mobile, wearable, tablets, smart thermostats, etc.), incorporates an IR coated glass layer to filter out or block IR light while allowing visible (ambient) light to pass through to a die having a light sensor. The ambient light sensor detects an amount of visible light that passes through the IR glass filter and adjusts a brightness or intensity of a display screen on the electronic device accordingly so that the display screen is readable. Some attenuation may occur to the visible light as it passes through the IR glass filter, but the attenuation is negligible since the IR glass filter blocks all of the IR light.

[0015] FIGS. 1A and 1B are block diagram representations of example integrated filter optical packages (e.g., ambient light sensor) 100A, 100B in an IC stacked-die configuration that incorporates an IR filter 102 to block out IR light. The IR filter 102 is incorporated with a homogeneous glass layer (e.g., borosilicate glass) 104. More specifically, the IR filter 102 is coated on one or both opposite surfaces of the glass layer 104, as illustrated in FIGS. 1A and 1B. In another example, the IR filter 102 can be comprised of a film having IR properties that is attached to one or both surfaces of the glass layer 104. In the example where the IR filter 102 is applied to both opposite surfaces of the glass layer 104, the IR light is filtered or blocked from passing through the glass layer 104 by either reflecting the IR light and/or absorbing the IR light where it is converted to heat. In another example, the IR filter 102 can be comprised of a material that is embedded into the glass layer 104.

[0016] The glass layer 104 is attached, via an optical film (e.g., optical die attach film (ODAF), film over wire material (FOW)) 106, to a light sensitive die (e.g., light sensor) 108 that senses light traveling through the glass layer 104. The optical film 106 is a clear film that allows light to pass through to the light sensitive die 108. In the example in FIG. 1A, the light sensitive die 108 is attached, via a die attach film (DAF) 110, to a die pad (e.g., thermal die pad) 112 in a QFN or DEN type IC package. In the example in FIG. 1B, the light sensitive die 108 is attached, via the die attach film (DAF) 110, to electrical terminations 114 in the COL type package. The stacked-die configuration portion of the light sensor 100A, 100B is packaged (more specifically embedded) in an epoxy non-optical molding compound 116. Wire bonds 118 are provided to electrically connect the light sensitive die 108 to the electrical terminations 114.

[0017] Several benefits of the integrated filter optical package include, the epoxy non-optical molding compound employed in the integrated filter optical package can be manufactured such that the CTE can be tuned to closely match the CTE of the other components of the filter, especially the lead frame. The epoxy non-optical molding compound is less expensive than the optical mold compound used in the prior art. Attenuation of the light signal traveling through the filter is mitigated. The glass layer including the IR filter(s) and the optical film can be assembled separately and then attached to the light sensitive die. This leads to broader material selection choices, which leads to better stress performance, better optical performance, increased reliability, and less cost since the size of the IR coated glass layer is no longer tied to the size of the die or wafer. This allows the IR coated glass layer to be mass produced in a single process, which reduces production costs.

[0018] FIG. 2 is an example of an ambient light sensor 200 packaged in an IC stacked-die configuration (e.g., QFN, DFN, etc.). The sensor 200 includes a package 202 made from a molding compound (e.g., epoxy non-optical molding compound (EMC)) 204. The package 202 includes a mounting (first) surface 206 and a non-mounting (second) surface 208. The mounting surface 206 of the package 202 is the surface of the package 202 that faces a printed circuit board (PCB) when the light sensor 200 is mounted to the PCB. The stacked-die configuration is embedded in the molding compound 204 and includes a die pad (e.g., thermal die pad) 210 adjacent to the mounting surface 206 of the package 202. Electrical terminations 212 are embedded in the molding compound 204 in a lead frame around a perimeter 214 of the package 202 (or alternatively on opposite sides of the perimeter) and adjacent to the mounting surface 206 of the package 202. The stacked-die configuration also includes a light sensitive die (e.g., a die having a light sensor) 216 attached to the die pad 210 via a die attach film (DAF) 218. Wire bonds 220 are attached to the light sensitive die 216 at one end and to the electrical terminations 212 at an opposite end. The wire bonds 220 are attached to the light sensitive die 216 via a bonding process (e.g., ball bonding, wedge bonding, compliant bonding, etc.). The wire bonds 220 form electrical connections between the light sensitive die 216 and the electrical terminations 212.

[0019] The stacked-die configuration further includes a homogenous glass layer (e.g., borosilicate glass) 222 attached to the light sensitive die 216 via an optical film (e.g., optical die attach film (ODAF)) 224. In this example, the glass layer 222 has a smaller footprint than the light sensitive die 216. The glass layer 222 is coated (via sputtering) with an infrared (IR) filter 226 on a first (top) surface 228 and/or on a second (bottom) surface 230. The first surface 228 is adjacent to the non-mounting surface 208 of the package 202 and is exposed to ambient light. The second surface 230 is the surface that attaches to the light sensitive die 216 via the optical film 224. The IR filter 226 disposed on the first and/or second surfaces 228, 230 of the glass layer 222 filters or blocks IR light directed at the light sensor 200. In addition, because the glass layer 222 is embedded in the molding compound 204, the molding compound 204 blocks light from entering sides of the glass layer 222 that are normal to the first surface 228 of the glass layer 222.

[0020] As mentioned above, the optical film 224 is a clear film that allows light to pass through to the light sensitive die 216. The optical film 224 also mitigates attenuation of the visible light that passes through the filter to the light sensitive die 216 as opposed to a light sensor incorporating the optical mold compound described above. In one example, the optical film 224 can be a film attached to the glass layer 222. In another example, the optical film 224 can be a dispensed material where the glass layer 222 is pressed into the dispensed material and then cured.

[0021] FIG. 3 is another example of an ambient light sensor 300 packaged in an IC stacked-die configuration (e.g., QFN, DFN, etc.). The sensor 300 includes a package 302 made from a molding compound (e.g., epoxy non-optical molding compound (EMC)) 304. The package 302 includes a mounting (first) surface 306 and a non-mounting (second) surface 308. The mounting surface 306 of the package 302 is the surface of the package 302 that faces the PCB when the light sensor 300 is mounted to the PCB. The stacked-die configuration is embedded in the molding compound 304 and includes a die pad (e.g., thermal die pad) 310 adjacent to the mounting surface 306 of the package 302. Electrical terminations 312 are embedded in the molding compound 304 in a lead frame around a perimeter 314 of the package 302 (or alternatively on opposite sides of the perimeter) and adjacent to the mounting surface 306 of the package 302. The stacked-die configuration also includes a light sensitive die (e.g., a die having a light sensor) 316 attached to the die pad 310 via a die attach film (DAF) 318. Wire bonds 320 are attached to the light sensitive die 316 at one end and to the electrical terminations 312 at an opposite end. The wire bonds 320 are attached to the light sensitive die 316 via a bonding process (e.g., ball bonding, wedge bonding, compliant bonding, etc.). The wire bonds 320 form electrical connections between the light sensitive die 316 and the electrical terminations 312. The stacked-die configuration further includes a homogenous glass layer (e.g., borosilicate glass) 322 attached to the light sensitive die 316 via an optical film (e.g., a film over wire material) 324 that adheres, via heat, the glass layer 322 to the light sensitive die 316. In this example, the glass layer 322 has a footprint that is equal to or larger than a footprint of the light sensitive die 316. As above, the glass layer 322 is coated (via sputtering) with an infrared (IR) filter 326 on a first surface 328 and/or on a second surface 330. The first surface 328 is adjacent to the non-mounting surface 308 of the package 302 and is exposed to ambient light. The second surface 330 is the surface that attaches to the light sensitive die 316 via the optical film 324. The IR filter 326 disposed on the first and/or second surfaces 328, 330 of the glass layer 322 filters or blocks any IR light directed at the light sensor 300. In addition, because the glass layer 322 is embedded in the molding compound 304, the molding compound 304 blocks all light from entering sides of the glass layer 322 that are normal to the first surface 328 of the glass layer 322.

[0022] The optical film 324 is a clear film that allows light to pass through to the light sensitive die 316, but has a thickness larger than the optical film 224 described above and illustrated in FIG. 2. The optical film 324 also mitigates attenuation of the visible light that passes through the filter to the light sensitive die 316 as opposed to a light sensor incorporating the optical mold compound described above. The optical film 324 has liquidous properties and is a B-stage cured material when applied to the glass layer 322. When the glass layer 322 is attached to the light sensitive die 316, the optical film 324 heats up and spreads over a surface 332 of the light sensitive die 316 filling in spaces/voids in the surface 332 while contemporaneously encapsulating the end of the wire bonds 320 that are bonded to the surface 332 of the light sensitive die 316.

[0023] FIG. 4 is yet another example of an ambient light sensor 400 packaged in an IC stacked-die configuration (e.g., COL). The sensor 400 includes of a package 402 made from a molding compound (e.g., epoxy non-optical molding compound (EMC)) 404. The package 402 includes a mounting (first) surface 406 and a non-mounting (second) surface 408. The mounting surface 406 of the package 402 is the surface of the package 402 that faces the PCB when the light sensor 400 is mounted to the PCB. Electrical terminations 412 are embedded in the molding compound in a lead frame around a perimeter 414 of the package 402 (or alternatively on opposite sides of the perimeter) and adjacent to the mounting surface 406 of the package 402. The stacked-die configuration is embedded in the molding compound 404 and includes a light sensitive die (e.g., a die having a light sensor) 416 attached at opposite ends to the electrical terminations 412 via a die attach film (DAF) 418. Wire bonds 420 are attached to the light sensitive die 416 at one end and to the electrical terminations 412 at an opposite end. The wire bonds 420 are attached to the light sensitive die 416 via a bonding process (e.g., ball bonding, wedge bonding, compliant bonding, etc.). The wire bonds 420 form electrical connections between the light sensitive die 416 and the electrical terminations 412.

[0024] The stacked-die configuration further includes a homogenous glass layer (e.g., borosilicate glass) 422 attached to the light sensitive die 416 via an optical film (e.g., optical die attach film (ODAF)) 424. In this example, the glass layer 422 has a smaller footprint than the light sensitive die 416. The glass layer 422 is coated (via sputtering) with an infrared (IR) filter 426 on a first surface 428 and/or on a second surface 430. The first surface 428 is adjacent to the non-mounting surface 408 of the package 402 and is exposed to ambient light. The second surface 430 is the surface that attaches to the light sensitive die 416 via the optical film 424. The IR filter 426 disposed on the first and/or second surfaces 428, 430 of the glass layer 422 filters or blocks any IR light directed at the light sensor 400. In addition, because the glass layer 422 is embedded in the molding compound 404, the molding compound 404 blocks light from entering sides of the glass layer 422 that are normal to the first surface 428 of the glass layer 422. In this example, the glass layer 422 has a smaller footprint than the light sensitive die 416. Thus, the wire bonds 420 are attached to the light sensitive die 416 via a bonding process (e.g., ball bonding, wedge bonding, compliant bonding, etc.).

[0025] As mentioned above, the optical film 424 is a clear film that allows light to pass through to the light sensitive die 416. The optical film 424 also mitigates attenuation of the visible light that passes through the filter to the light sensitive die 416 as opposed to a light sensor incorporating the optical mold compound described above attenuating the transmitted light signal in the range of 40%60% based on filler loading. In one example, the optical film 424 can be a film attached to the glass layer 422. In another example, the optical film 424 can be a dispensed material where the glass layer 422 is pressed into the dispensed material and then cured.

[0026] In the above examples, the epoxy non-optical molding compound can be made from fillers and other materials so that the CTE of the epoxy non-optical molding compound can be tuned to closely match the CTE of the other components (e.g., the glass layer, the light sensitive die, the die pad, lead frame). Thus, any expansion/contraction differences between epoxy non-optical molding compound and both the glass layer and the light sensitive die is minimized. CTE values for an unfilled optical mold compound can be in the range of 70 ppm while the typical silica filled mold compounds can be in the range of 10 ppm below glass transition temperature. Since silicon and the copper lead frame is in the range of 3 ppm and 17 ppm respectively, the disparity in CTE value of the optical mold compound will cause much higher stress concentrations across the various structures within the package vs. typical silica filled mold compounds. As a result, it is less likely to snap the wire bonds between the light sensitive die and the electrical terminations in the lead frame. In addition, as mentioned above, the epoxy non-optical molding compound is less expensive than the optical mold compounds used in the prior art.

[0027] Referring to FIGS. 2 and 5, a method 500 of manufacturing an integrated filter optical package will now be described. A stacked-die configuration is assembled at 502, by attaching a light sensitive die (e.g., die with a light sensor 216 of FIG. 2) to a die pad (e.g., thermal die pad 210 of FIG. 2) with a die attach film (e.g., die attach film 218 of FIG. 2). At 504, a curing process is performed to cure the die attach film. At 506, electrical terminations (e.g., electrical terminations 212 of FIG. 2), which are arranged in a lead frame, are bonded via wire bonds (e.g., wire bonds 220 of FIG. 2) to the light sensitive die via a bonding process (e.g., ball bonding, wedge bonding, compliant bonding, etc.). At 508, an IR filter (e.g., IR filter 226 of FIG. 2) is applied to a first surface and/or a second surface of a glass layer (e.g., glass layer 222 of FIG. 2) to form an infrared (IR) glass filter. At 510, an optical film (e.g., die attach film 224 of FIG. 2, film over wire 324 of FIG. 3) is applied to a surface of the light sensitive die. At this stage of the method 500 the optical film is a B-stage cured material, which is a partially cured material. The optical film is fully cured during a final curing process further below. At 512, the glass infrared (IR) filter is divided (e.g., sawed, punched) into pieces, each of which have a same size. At 514, the glass infrared (IR) filter is attached to the light sensitive die via the optical film. At 516, the integrated filter optical package undergoes another curing process to cure the optical film. At 518, a molding compound (e.g., epoxy non-optical molding compound (EMC) 204) is applied to encapsulate the filter components. The molding compound includes a film assist to assist in the prevention of the molding compound from bleeding over into the glass layer. At 520, the integrated filter optical package undergoes a final curing process, at which time the epoxy molding compound undergoes a final cure. At 522, the filter is deflashed to remove any molding residue from the molding compound. In some examples, one or more layers of a red, green, blue, white (RGBW) strip can be applied to increase the performance.

[0028] Described above are examples of the subject disclosure. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the subject disclosure, but one of ordinary skill in the art may recognize that many further combinations and permutations of the subject disclosure are possible. Accordingly, the subject disclosure is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. In addition, where the disclosure or claims recite a, an, a first, or another element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. Furthermore, to the extent that the term includes is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term comprising as comprising is interpreted when employed as a transitional word in a claim. Finally, the term based on is interpreted to mean based at least in part on.