Image sensor device

An image sensor device is made using an ultra-thin substrate so that the overall device height is less than 1.0 mm. The image sensor includes a flexible circuit substrate having first and second opposing sides, the first side having a central area and an outer, bonding pad area including bonding pads. A sensor integrated circuit (IC) is attached to the central area of the first side of the circuit substrate. The IC has an active area and a peripheral bonding pad area including bonding pads. Wires are wirebonded to respective ones of the IC bonding pads and corresponding ones of the circuit substrate bonding pads to electrically connect the IC and the circuit substrate. A wall having a first end with a step and a second end has its second end attached to an outer portion beyond the outer bonding pad area of the first side of the flexible circuit substrate. The wall at least partially surrounds the sensor integrated circuit. A transparent cover is located above the IC such that light can pass through the cover onto the IC active area. Opposing edges of the cover are secured within the step of the wall. Solder balls are attached to the second side of the circuit substrate. The circuit substrate provides for electrical interconnect between the solder balls and the bonding pads on the first side of the circuit substrate.

BACKGROUND OF THE INVENTION

The present invention relates generally to the packaging of electrical components, and more particularly, to a method of packaging an imaging sensing circuit.

There has been a constant demand for smaller and smarter industrial and consumer electronic products such as digital cameras, camcorders, audio players, etc. Such miniaturization and increased functionality has benefited from advances in the design and manufacturing of semiconductor circuits and wafers. There has also been a marked increase in the use of optical and image sensors in electronic products. At present, all of the available optical and image sensors are packaged in conventional, rigid base carriers such as ceramics or organic substrates. Rigid organic substrates are generally made from BT (bismaleimide-triazine) resin, ceramics, or FR-4.

For example, U.S. Pat. No. 6,268,231 discloses a CCD package having a plastic base structure, a flexible plastic circuit board mounted on the base structure, a plastic rim mounted on the circuit board, a CCD sensor mounted on the circuit board and inside the rim, and a glass cover mounted on the rim. The CCD sensor is wire bonded to the circuit board. The plastic base structure, circuit board and rim, not to mention the glass cover, make for a relatively thick package. U.S. Pat. Nos. 6,034,429, 6,268,654 and 6,143,588 also disclose a CCD package including an IC die mounted on and wire bonded to a first side of a BT substrate, a bead or dam formed in varying manners around the IC die, a glass lid attached to the bead, and solder balls attached to a second side of the BT substrate. All of these packages are relatively thick. Thus, although the package size of image sensors has decreased, there is still room for improvement, as lower cost and smaller package footprint and height are critical in assuring that more intelligence and functionality are incorporated into new electronic devices.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of the presently preferred embodiments of the invention, and is not intended to represent the only forms in which the present invention may be practiced. It is to be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the invention.

Certain features in the drawings have been enlarged for ease of illustration and the drawings and the elements thereof are not necessarily in proper proportion. However, those of ordinary skill in the art will readily understand such details. In the drawings, like numerals are used to indicate like elements throughout.

The present invention provides an image sensor device made using an ultra-thin substrate so that the overall device height is less than about 1.0 mm. In one embodiment, the present invention provides an image sensor including a flexible circuit substrate having first and second opposing sides, the first side having a central area and an outer, bonding pad area including bonding pads. A sensor integrated circuit (IC) is attached to the central area of the first side of the circuit substrate. The IC has an active area and a peripheral bonding pad area including bonding pads. Wires are wirebonded to respective ones of the IC bonding pads and corresponding ones of the circuit substrate bonding pads to electrically connect the IC and the circuit substrate. A wall having a first end with a step and a second end has its second end attached to an outer portion beyond the outer bonding pad area of the first side of the flexible circuit substrate. The wall at least partially surrounds the sensor integrated circuit. A transparent cover is located above the IC such that light can pass through the cover onto the IC active area. Opposing edges of the cover are secured within the step of the wall. Solder balls are attached to the second side of the circuit substrate. The circuit substrate provides for electrical interconnect between the solder balls and the bonding pads on the first side of the circuit substrate.

In another embodiment, the present invention provides an image sensor device including a flexible circuit substrate having first and second opposing sides, the first side having a central area and an outer, bonding pad area including bonding pads. A sensor integrated circuit (IC) is attached to the central area of the first side of the circuit substrate. The IC has an active area and a peripheral bonding pad area including bonding pads. A plurality of wires are wirebonded to respective ones of the IC bonding pads and corresponding ones of the circuit substrate bonding pads, thereby electrically connecting the IC and the circuit substrate. A wall is attached to an outer portion beyond the outer bonding pad area of the first side of the flexible circuit substrate. The wall at least partially surrounds the sensor integrated circuit. A transparent cover is disposed above the sensor integrated circuit such that light can pass through the cover onto the IC active area. The circuit substrate includes a polyimide layer having top and bottom surfaces, and a thickness of about 50 um, an adhesive layer having a thickness of about 12 um overlying the top surface of the polyimide layer, a conductive trace layer having a thickness of between about 12 um to about 30 um overlying the adhesive layer, and a mask layer having a thickness of about 30 um overlying the conductive trace layer. A top surface of the mask layer forms the first side of the circuit substrate and the bottom surface of the polyimide layer forms the second side of the circuit substrate.

In yet another embodiment, the present invention provides a method of making an image sensor device, comprising the steps of:providing a multi-layer circuit substrate including a polyimide layer having a thickness of about 50 um, an adhesive layer having a thickness of about 12 um overlying a first side of the polyimide layer, a conductive metal trace layer having a thickness of between about 12 um to about 30 um overlying the adhesive layer, and a solder mask layer having a thickness of about 30 um overlying the conductive metal trace layer;forming a wall along an outer perimeter of the circuit substrate;attaching a sensor integrated circuit (IC) to the circuit substrate within the walls, wherein the IC has an central active area and a peripheral bonding pad area including bonding pads;electrically connecting wires to the bonding pads of the IC and corresponding bonding pads of the circuit substrate via wirebonding;attaching a transparent cover to the wall such that the cover is over the IC, whereby light may pass through the cover onto the IC active area; andattaching solder balls to a second side of the polyimide layer opposing the first side, wherein the circuit substrate provides for electrical interconnect between the solder balls and the wires, and wherein the image sensor device has a height of less than about 1.3 mm.

In a further embodiment, the present invention provides a method of making a plurality of image sensor devices, comprising the steps of:providing a multi-layer circuit substrate including a polyimide layer having a thickness of about 50 um, an adhesive layer having a thickness of about 12 um overlying a first side of the polyimide layer, a conductive metal trace layer having a thickness of between about 12 um to about 30 um overlying the adhesive layer, and a solder mask layer having a thickness of about 30 um overlying the conductive metal trace layer;attaching a plurality of sensor integrated circuits to the circuit substrate at spaced intervals, wherein each of the integrated circuits has a central active area and a peripheral bonding pad area including bonding pads;electrically connecting wires to the bonding pads of the integrated circuits and corresponding bonding pads of the circuit substrate via wirebonding;forming walls on the circuit substrate around each of the integrated circuits;attaching a transparent cover to the walls such that the cover extends over all of the integrated circuits, wherein light may pass through the cover onto the integrated circuits active areas;attaching solder balls to a second side of the polyimide layer opposing the first side, wherein the circuit substrate provides for electrical interconnect between the solder balls and the wires; andsingulating the covered integrated circuits at the walls, thereby forming individual image sensor devices, wherein the image sensor devices have a height of less than about 1.3 mm.

Referring now toFIG. 1, an enlarged, cross-sectional view of an optical sensor device10in accordance with the present invention is shown. The image sensor device10includes a flexible circuit substrate12, a sensor integrated circuit (IC)14attached to the circuit substrate12, a plurality of wires16that electrically connect the IC14to the substrate12, a wall18having a step or notch20formed in an outer end thereof, and a transparent cover22located above the sensor IC14. The edges of the cover22are secured within the step20of the wall18, for example, with an adhesive. The image sensor device10further has solder balls24attached to a bottom or underside of the circuit substrate12. The circuit substrate12provides for electrical interconnect between the solder balls24and IC14. The solder balls24allow the sensor device10to be connected to other electrical devices and circuits (not shown).

Referring now toFIG. 2, an enlarged, cross-sectional view of an optical sensor device26in accordance a second embodiment of the present invention is shown. The sensor device26includes the flexible circuit substrate12, the sensor integrated circuit (IC)14attached to the circuit substrate12, the plurality of wires16that electrically connect the IC14to the substrate12, a wall28formed on the substrate12that surrounds the IC14, and a transparent cover30located above the sensor IC14. The cover30is secured to a top side of the wall28, preferably with an adhesive. The image sensor device26further has solder balls24attached to a bottom or underside of the circuit substrate12. The circuit substrate12provides for electrical interconnect between the solder balls24and IC14. The solder balls24allow the sensor device10to be connected to other electrical devices and circuits (not shown). The sensor devices10and26have a very low profile because the substrate12is very thin.

Referring now toFIG. 3, an enlarged, cross-sectional view of the circuit substrate12is shown. The circuit substrate12includes a polyimide layer32having top and bottom surfaces. An adhesive layer34overlies the top surface of the polyimide layer32, and a conductive trace layer36overlies the adhesive layer34. A solder mask layer38overlies the conductive trace layer36for protection. A top surface of the mask layer38forms the first side of the circuit substrate12and the bottom surface of the polyimide layer32forms the second side of the circuit substrate12. As will be understood by those of skill in the art, the circuit substrate12provides an electrical interconnect layer for routing signals. However, as opposed to the interconnect layer used in prior art devices, the substrate12is very thin.

The polyimide layer32has a thickness of about 50 um and preferably less. The adhesive layer34has a thickness of about 12 um. The conductive layer36, which may be formed of a conductive material, such as a conductive metal like copper, has a thickness of between about 12 um to about 30 um. As will be understood by those of skill in the art, the conductive layer36forms electrical distribution paths. Finally, the solder mask layer38has thickness of about 30 um. Depending on the applications, the substrate12may include a layer of metallic interposer (not shown) that acts as a stiffener that is about 150 um thick.

Referring again toFIGS. 1 and 2, the substrate12has first and second opposing sides. The first side has a central area and an outer, bonding pad area including bonding pads. The IC14is attached to the central area of the first side of the circuit substrate12, preferably with an adhesive layer40having a thickness of about 12 um. The IC14has an active area and a peripheral bonding pad area. The peripheral bonding pad area includes bonding pads that are electrically connected to the substrate bonding pads with the wires16via wirebonding. Wirebonding is generally accepted to mean the interconnection, via wire, of chips and substrates. The most frequently used methods of joining the wires to the pads are thermosonic and ultrasonic bonding. Ultrasonic wirebonding uses a combination of vibration and force to rub the interface between the wire and the bond pad, causing a localized temperature rise that promotes the diffusion of molecules across the boundary. Thermosonic bonding, in addition to vibration, uses heat, which further encourages the migration of materials. The various types of wirebonding are well known by those of skill in the art. The wires16may be formed of any electrically conductive metal or combination of metals, such as are known by those of skill in the art. Suitable bond wires typically comprise copper or gold and may be either fine wires (<50 um in diameter) or heavy wires (>50 um in diameter).

The IC14is of a type known to those of skill in the art, and may comprise, for example, a Charge Coupled Device (CCD), a CMOS image sensor, or even a memory device like an EPROM, etc. The active area receives radiation that passes through the transparent cover22and converts the radiation to a digital signal. As previously discussed, the IC14is preferably attached to the substrate12with an adhesive40. An underfill (not shown) may be disposed between the IC14and the substrate12to strengthen the device10.

Referring toFIG. 1, the wall18of the device10is formed on the surface of the substrate12and at least partially surrounds the IC14and the wires16. In the preferred embodiment, the wall18completely surrounds the IC14and the wires16. The wall18extends upwards from the surface of the substrate12. The wall18has a first end with a step20and a second end, which is attached to an outer portion, beyond the outer bonding pad area, of the first side of the substrate12. The wall18is preferably formed of a hard or stiff material, such as a metal or BT, that is strong enough to support the cover22. The transparent cover22is located above the sensor integrated circuit14and has its opposing edges secured within the step20of the wall18, preferably with a clear expoxy. The cover22allows light to pass therethrough onto the active area of the IC14. The cover22is formed of a transparent material that allows light or radiation to pass therethrough and in order to provide a thin device, the cover22should be relatively thin, yet at the same time, should be formed with a relatively stiff material. In the presently preferred embodiment, the cover22comprises borosilicate glass having a thickness of about 0.4 mm. However, it will be understood by those of skill in the art that other materials that allow radiation to pass therethrough and can be made thin may also be used. The cover22may be treated with an anti-reflective coating and an IR block.

Referring toFIG. 2, the wall28of the device26is similar to the wall18of the device10shown inFIG. 1except that the wall28does not include the steps20for receiving the cover22. Rather, a cover30that is longer than the cover22is attached to the top surface of the wall28in a conventional manner. The cover30, like the cover22preferably comprises borosilicate glass having a thickness of about 0.4 mm.

Referring toFIG. 8, a transparent cover50is shown in which the edges thereof have been etched to form channels52. When the cover50is attached to the walls28of the device26shown inFIG. 2, the walls28are received within the channels52so that the device has a lower profile. It is noted that the cover50shown inFIG. 8is sized for two devices prior to singulation. Thus, the center channel52has a double width.

Referring again toFIGS. 1 and 2, the image sensor devices10and26have solder balls24attached to a bottom or underside of the circuit substrate12. The solder balls have a height of less than about 400 um. By using a very thin substrate12, the final device10,26has a very low profile. The thickness of the device, as shown by A, is in the range from about 0.9 mm to about 1.3 mm. The preferred device has a thickness of less than 1.0 mm.

Referring now toFIG. 5, two of the devices10are shown prior to singulation. In this case, an adhesive, such as epoxy, is dispensed on the steps20or is preformed on the edges of the covers22prior to placing the covers22over the ICS14. Similarly,FIG. 6shows two of the devices26prior to singulation. Note that the cover50(FIG. 4) may be substituted for the cover30in FIG.6. The grooves or channels etched or formed in the cover50aid in alignment of the cover50.FIGS. 5 and 6illustrate that multiple devices can be formed in parallel, as will be discussed in more detail below.

Referring now toFIGS. 7-10, alternate embodiments of image sensor devices of the present invention are shown.FIG. 7shows an image sensor device70that is similar to the sensor device26shown inFIG. 2except that the device70does not have the same cover30. Rather than a glass cover, a cover72of the device70is formed of a clear material, such as epoxy, that is globbed over the IC14and wires16, and within the wall28surrounding the IC14and wires16.FIG. 8shows an image sensor device80in which a cover82thereof comprises a clear material, such as epoxy, that is molded over the over the IC14and wires16, and within a wall84surrounding the IC14and wires16. The wall84is preferably shorter than the wall28of the devices26(FIG. 2) and70(FIG.7).FIG. 9shows an image sensor device90having a cover92that is attached over the active area of the IC14, preferably with a clear adhesive94. A clear material96, such as epoxy, is then used to fill the area between the IC14and the wall28, and cover the wires16. The cover92preferably comprises glass and the clear adhesive94an epoxy.FIG. 10shows an image sensor device100having a cover102that is attached over the active area of the IC14, preferably with a clear adhesive104. A clear material106, such as epoxy, is then used to fill the area between the IC14and a wall108, and cover the wires16. The cover102preferably comprises glass and the clear adhesive104an epoxy. The wall108is this example is formed of a soft material, such as epoxy, that has been hardened, such as by curing. Each of the devices shown inFIGS. 7-10has a height or thickness of less than 1.3 mm and preferably less than 1.0 mm.

FIGS. 11A-11G, enlarged side views illustrating the steps of forming sensor devices in accordance with the present invention are shown. More particularly,FIGS. 11A-11Gillustrate the capping of image sensor devices in the case where a vacuum or inert gas is used within the IC cavity. Referring now toFIG. 11A, a multi-layer circuit substrate110is provided. The substrate110includes a polyimide layer having a thickness of about 50 um, an adhesive layer having a thickness of about 12 um overlying a first side of the polyimide layer, a conductive metal trace layer having a thickness of between about 12 um to about 30 um overlying the adhesive layer, and a solder mask layer having a thickness of about 30 um overlying the conductive metal trace layer. A plurality of sensor integrated circuits (IC)112are attached to the circuit substrate110with a die attach adhesive at spaced intervals. Each of the integrated circuits112has a central, active area for receiving light and a peripheral bonding pad area including bonding pads. The integrated circuits112are electrically connected to the substrate110via wires114, which are wirebonded to the bonding pads to the bonding pads on the integrated circuits and corresponding bonding pads on the substrate110.

Referring now toFIG. 11B, a wall116is formed around each of the integrated circuits112. The wall116may be formed by dispensing a dam material, such as an epoxy, a metal, or an organic material like BT, in a grid-like pattern such that each of the intergrated circuits112is surrounded by the wall116. In the cases where the wall116is formed of metal or BT materials, the top surface of the wall116has a thin coat of suitable adhesive applied thereto. The thin coat of adhesive will hold the top glass plate and essentially seal the IC therein. An outer wall118, which is larger (higher) than the wall116is then formed around the outer perimeter of the substrate110such that the outer wall118surrounds all of the integrated circuits112, wires114and the wall116. The outer wall118may be formed of a soft material such as dam epoxy.

As shown inFIG. 11C, a transparent cover120is then placed over the integrated circuits112and wires114, preferably using first suction pads122and second suction pads124. The second suction pads124have a central bore or hole126that is aligned over a hole128in the transparent cover120. The hole128in the cover120is aligned such that it is located just inside of the outer wall118. The suction pads122may hold the cover120via vacuum force. While the cover120is being moved and placed over the integrated circuits112, the suction pads122have a vacuum on and the suction pads124have a vacuum off. The cover120preferably comprises borosilicate glass having a thickness of less than about 0.4 mm.

Referring toFIG. 11D, the cover120is pressed into contact with the outer wall118. After the cover120contacts the outer wall118, a suction or vacuum force is applied to the second suction pads124such that air is removed from the space130formed by the substrate110, the outer wall118, and the cover120via the holes126and126. In one embodiment of the invention, after vacuuming air out of the space130, the space130is filled with an inert gas by way of the holes126and128. As shown inFIG. 11E, the cover120is then pressed into contact with the wall116, such that the cover120is attached to the wall116.FIG. 11Fshows the vacuum forces being turned off such that the cover120is released by the suction pads122and124, andFIG. 11Gshows a step of singulating the covered integrated circuits by sawing along the wall116, thereby forming individual image sensor devices130. Either before or after the singulation step, solder balls (not shown) may be attached to the underside of the substrate110. The finished devices have a height of less than about 1.3 mm, and preferably less than about 1.0 mm.

As can be seen, the present invention provides an image sensor device with a very low package height. The structure of the device provides for a very short optical path and thus, very low diffraction. The description of the preferred embodiments of the present invention have been presented for purposes of illustration and description, but are not intended to be exhaustive or to limit the invention to the forms disclosed. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but covers modifications within the spirit and scope of the present invention as defined by the appended claims.