Image sensor package with transparent adhesive covering the optical sensing circuit

An integrated circuit package includes a support substrate having a front side and a back side and an optical integrated circuit die having a back side mounted to the front side of the support substrate and having a front side with an optical sensing circuit. A glass optical element die has a back side mounted to the front side of the optical integrated circuit die over the optical sensing circuit. The mounting of the glass optical element die is made by a layer of transparent adhesive which extends to the cover the optical sensing circuit and a portion of the front side of the optical integrated circuit die peripherally surrounding the optical sensing circuit. An encapsulation material body encapsulates the glass optical element die and the optical integrated circuit die.

TECHNICAL FIELD

Embodiments herein relate to the packaging of integrated circuits and, in particular, to the packaging of image sensor integrated circuits.

BACKGROUND

Image sensor integrated circuit packages typically include a supporting substrate to which an image sensor integrated circuit die is mounted. The die includes an optical sensing circuit. A transparent optical element is mounted over the optical sensing circuit. It is important that thermal cycling of the package, for example in the context of solder reflow operations, not cause damage to the package.

SUMMARY

In an embodiment, an integrated circuit package comprises: a support substrate having a front side and a back side; an optical integrated circuit die having a back side mounted to the front side of the support substrate and having a front side with an optical sensing circuit; a glass optical element die having a back side mounted to the front side of the optical integrated circuit die over the optical sensing circuit; wherein the mounting of the glass optical element die is made by a film layer of transparent adhesive which extends to the cover the optical sensing circuit and a portion of the front side of the optical integrated circuit die peripherally surrounding the optical sensing circuit; and an encapsulation material body which encapsulates the glass optical element die and the optical integrated circuit die.

The optical sensing circuit may include an array of microlenses provided over a corresponding array of photosensitive elements. The film layer of transparent adhesive is provided to extend over and in contact with the array of microlenses.

The film layer of transparent adhesive comprises a transparent die attach film have a suitable thickness to cover and encapsulate the array of microlenses.

It will be noted that the drawings are not necessarily presented to scale, and some exaggeration of sizes, shapes, thicknesses, etc., has been made in order ease understanding of the illustrated structures.

DETAILED DESCRIPTION

FIG.1shows a cross sectional view of an embodiment of an image sensor integrated circuit package10.

An insulating support substrate12includes a front side12fand a backside12b. First conductive pads14are located on the front side12fand second conductive pads16are located on the back side12b. Although not specifically illustrated, electrically conductive lines forming a redistribution network may be included on the front side12fand/or the backside12band connected for signal and power routing to the pads14and16, as needed. An electrical interconnection network17within the insulating support substrate12electrically connects the first conductive pads14to the second conductive pads16. The insulating support substrate12may comprise a multi-layer structure, and in such a case the electrical interconnection network17includes a plurality of electrically conductive lines18and electrically conductive vias20located on and/or in the various layers of the multi-layer structure. In a single layer insulating support substrate12, only the vias20are used to make electrical connections between the front side12fand backside12bof the insulating support substrate12. Although not specifically illustrated, the front side12fand backside12bof the insulating support substrate12may be coated with a protective insulating layer (such as a passivation or solder mask layer) with an opening provided at the locations of each pad14,16.

The back side of an image sensor integrated circuit die24is mounted to the front side12fof the insulating support substrate12using a thin layer of adhesive material25(for example, using a suitable die attach adhesive film). The front side of the image sensor integrated circuit die24includes a plurality of die pads26and an optical sensing circuit28. Bonding wires30electrically connect the die pads26of the image sensor integrated circuit die24to the first conductive pads14of the insulating support substrate12. The optical sensing circuit28may, for example, be formed by an array of photosensitive elements (for example, photodiodes).

To protect the optical sensing circuit28, an optical element40is mounted to the front side of the image sensor integrated circuit die24by a ring42of adhesive material. The adhesive material used for the ring42is typically a glass attach glue such as a UV-light cured epoxy. The optical element40may, for example, comprise a transparent glass die having one or more surfaces coated with an anti-reflective material. This mounting scheme leaves a hermetically sealed cavity44, laterally delimited by the ring42of adhesive material, between a bottom of the optical element40and the front side of the image sensor integrated circuit die24over the optical element40.

An encapsulation material is then dispensed around the optical element to form a package body50encapsulating the optical element40, the image sensor integrated circuit die24and the bonding wires30. Use made be made, for example, of suitable dam and fill process with a needle dispensing the encapsulation material constrained by a surrounding dam of resin and with a volume sufficient to cover the bonding wires and reach the peripheral top edge of the optical element.

A solder ball56is mounted to each of the second conductive pads16.

The heat applied during various reflow operations for the solder balls56(for example, during formation of the solder balls on the pads16and during mounting of the image sensor integrated circuit package10to an integrated circuit board) can cause an expansion of the fluid (for example air or other gas) located within the hermetically sealed cavity44. This expansion applies an outward force which, if sufficient in magnitude, results in a delamination of the optical element40from the image sensor integrated circuit die24, a cracking of the optical element40itself, and/or a breaking of the hermetic seal.

FIG.2shows a cross sectional view of another embodiment for an image sensor integrated circuit package110that addresses the foregoing issue.

An insulating support substrate112includes a front side112fand a backside112b. First conductive pads114are located on the front side112fand second conductive pads116are located on the back side112b. Although not specifically illustrated, electrically conductive lines forming a redistribution network may be included on the front side112fand/or the backside112band connected for signal and power routing to the pads114and116, as needed. An electrical interconnection network117within the insulating support substrate112electrically connects the first conductive pads114to the second conductive pads116. The insulating support substrate112may comprise a multi-layer structure, and in such a case the electrical interconnection network117includes a plurality of electrically conductive lines118and electrically conductive vias120located on and/or in the various layers of the multi-layer structure. In a single layer insulating support substrate121, only the vias120are used to make electrical connections between the front side112fand backside112bof the insulating support substrate112. Although not specifically illustrated, the front side112fand backside112bof the insulating support substrate112may be coated with a protective insulating layer (such as a passivation or solder mask layer) with an opening provided at the locations of each pad114,116.

The back side of an image senor integrated circuit die124is mounted to the front side112fof the insulating support substrate112using a thin layer of adhesive material124(for example, using a suitable die attach adhesive film). The front side of the image sensor integrated circuit die124includes a plurality of die pads126and an optical sensing circuit128. Bonding wires130electronically connect the die pads126of the image sensor integrated circuit die124to the first conductive pads114of the insulating support substrate112. The optical sensing circuit128may, for example, be formed by an array of photosensitive elements (for example, photodiodes). The optical sensing circuit128may include a layer including a plurality of microlenses129extending over the array of photosensitive elements (see, detailed cross section ofFIG.3).

To protect the optical sensing circuit128, an optical element140is mounted to the front side of the image sensor integrated circuit die124by a layer142of adhesive material. The adhesive material used for the layer142is a transparent die attach film (for example, Locktite® Ablestik ATB 120U from Henkel) with a thickness in a range of 15-25 μm, and more specifically with a thickness of 20 μm. The film is applied to the front side of the image sensor integrated circuit die124prior to placement and attachment of the optical element140. The use of a film adhesive, rather than a deposited flowable and subsequently cured adhesive, is preferred as the film will present a consistent thickness with no sloppy squeeze out or mess during the assembly process. The optical element140may, for example, comprise a transparent glass die having one or more surfaces coated with an anti-reflective material. The film layer142extends to pass over the optical element140and a portion of the front side of the image sensor integrated circuit die124peripherally surrounding the optical element140. The film layer142attaches to the plurality of microlenses129of the optical sensing circuit128(see,FIG.3). In a preferred implementation, the layer substantially encapsulates the plurality of microlenses129(here, substantially encapsulates means contacts nearly all (if not all) of the convex surface of the microlenses and covers nearly all (if not all) of the portion of upper surface of the image sensor integrated circuit die124peripherally surrounding the optical sensing circuit128). The goal with the coverage of the film layer142is to minimize the size of, if not eliminate entirely, any hermetically sealed cavity or cavities144located underneath the optical element140(such cavities144perhaps being trapped at corners where the microlens meets the upper surface of the image sensor integrated circuit die124, as shown inFIG.3, by example). It will be noted that the total volume of the cavities144, if present, is significantly smaller than the volume of the cavity44.

An encapsulation material is then dispensed around the optical element to form a package body150encapsulating the optical element140, the image sensor integrated circuit die124and the bonding wires130. Use made be made, for example, of suitable dam and fill process with a needle dispensing the encapsulation material constrained by a surrounding dam of resin and with a volume sufficient to cover the bonding wires and reach the peripheral top edge of the optical element. The package body150is in contact with the layer142of adhesive material portion of the front side of the image sensor integrated circuit die124peripherally surrounding the optical element140to form a seal.

A solder ball156is mounted to each of the second conductive pads116.

An advantage of the construction for the image sensor integrated circuit package110is that the use of the film layer142to mount the optical element140to the front side of the image sensor integrated circuit die124minimizes the size of, or eliminates the presence of, any air cavity144(compare to reference44,FIG.1) between the optical element140and the image sensor integrated circuit die124. There is accordingly no concern with a delamination occurrence due to expansion forces resulting from the application of heat during various reflow operations for the solder balls56.