Lens laminate and method

An optical lens laminate has an adhesive member with at least one aperture, an optical member with an optical feature; and another optical member with an optical feature. The lens laminate may be made by positioning the at least one adhesive member between the optical members, with the apertures aligned with the lens features, and pressing the optical members together.

FIELD OF THE INVENTION

The present invention pertains to lens construction and to a multi-layer laminate lens construct.

BACKGROUND OF THE INVENTION

Wafer, or multi-layer, lens constructs may include various components such as optical members, filters, spacers, image sensors, and the like. Multiple layers are coupled during manufacture to create a module array. Manufacturing compact lens structures for portable devices continues to present a number of still unsolved challenges because the lens structures must be small in size, capable of mass manufacturing with great precision, and of suitable cost.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention can be practiced without these specific details. In other instances, methods, structures and devices are shown in block diagram form in order to avoid obscuring the invention.

It is highly desirable to fabricate multiple-layer lens constructs from a stack of sheets having a plurality of laterally spaced lens features. Fabricating such multiple-layer lens constructs can include dispensing liquid adhesive patterned around each of the multitude of individual lens features on each sheet, or wafer. There are three major challenges presented when employing such techniques for the assembly of the array lens stack. These challenges include: overflow of liquid dispensed adhesive into the optical area between lenses upon assembly, resulting in distorted images when the lens stack is used with an imager; inconsistent wafer-to-wafer spacing making consistent optical performance unlikely; and incomplete bonding and resulting separation between the layers of the stack due to inconsistent adhesive deposition. These failures can lead to delamination of the stack, also referred to as separation of the layers, or chipping during the dicing process in singulation of lens stacks from the wafer, as well as an opportunity for the introduction of contaminants into the incompletely sealed stack. These problems with existing lens constructs are avoided by consistency of placement and thickness of adhesive.

An exploded view a lens stack100is shown inFIG. 1. The example lens stack100includes seven layers. A lens sheet102, also referred to as a lens wafer, an optical member, or an optical sheet, is shown as the top of the stack. An adhesive layer110, also referred to herein as an adhesive member, is positioned between the top lens sheet102and an intermediate lens sheet120, also referred to herein as a lens wafer, an optical member, or an optical sheet. An adhesive layer130, also referred to herein as an adhesive member, is positioned between intermediate lens sheet120and a spacer140. An adhesive layer150, also referred to herein as an adhesive member, is positioned between spacer140and lens sheet160, which is the bottom of the stack. More or fewer layers may be employed in the stack to achieve the desired optical construct.

An optical member102is illustrated by example to include four optical features104, and may be a lens sheet102including lenses or lens features104. The lens sheet102can include any number of optical features. Each optical feature104in the illustrated example of a laminate lens stack is for a respective optical path. The lens sheet, or wafer, may be manufactured by any suitable means and of any suitable material for manufacture of optical lenses. For example, the lens sheet may be manufactured from glass, a polycarbonate, a composite, or any other suitable material for use in an optical lens. Each of the lens features104in the sheet102may be molded, grounded, or polished, or a combination thereof, to the precise desired shape in the sheet to provide the optical properties desire for the lens stack. The lens features may be different, formed to have different optical properties, or identical. In the illustrated example, a plurality of optical features104are lenses formed at uniformly laterally spaced locations in a planar sheet body103. The lens elements are preferably uniformly spaced in the planar sheet body such that when diced, or cut, along planes108and109, each respective lens is positioned in a corner of the resulting square or rectangular block, and adjacent the edges of the block. The planar sheet body103provides a planar surface for affixing to an adjacent layer as part of the construct of a multi-layer laminate lens stack. The dicing planes108and109are illustrated along sides of the lenses104to permit the positioning of four lenses in juxtaposition when the four lenses are assembled together for use with a single array imager (not shown).

As shown inFIGS. 1 and 2, the adhesive layer110includes four apertures112in planar body114, adhesive layer130includes four apertures132in planar body134, and adhesive layer150includes four apertures152in planar body154. The apertures112,132, and152are spaced uniformly at the same lateral spacing as lenses104in layer102, for precise alignment with the four lenses104when the laminate lens stack is formed. The adhesive layers110,130, and150, are preferably a pre-formed adhesive film constructed of materials such as, but not limited to, a B-staged thermosetting material or cross-linkable thermoplastic, a film with embedded spacers, such as rigid spheres (not shown) either alone or with a dimensionally stable carrier such as an internal polyimide layer to provide stable layer-to-layer thickness necessary to support the tight tolerances in the optical path. The apertures112,132,152in the adhesive film may be constructed via punching. Alternatively, and more preferably, the apertures112,132,152are advantageously laser cut from the body to remove the circular aperture cut-out from the adhesive sheet. The laser cutting process is advantageous as the laser locally cures the adhesive at the edge of the aperture, and thus the cured perimeter edge of the aperture creates a stop or dam that reduces or eliminates resin flow into the optical path of the lens stack during the lamination process. Other methods of sealing the aperture perimeter can be employed. Another optional process that can be employed during assembly is to apply a low energy surface treatment that is printed or sprayed onto the surfaces of the lenses104in the imager optical path so as to prevent wetting by the adhesive, further reducing potential for contamination by the deposited adhesive during lamination.

With continued reference toFIGS. 1 and 2, an optical member120, which may be a lens sheet120, is illustrated to include four optical features122. The lens sheet can include any number of optical features, such as lenses, and each illustrated lens feature122in the example can be a single optical path for a respective single lens laminate stack. The lens sheet may be manufactured by any suitable means and of any suitable material for manufacture of optical lenses. For example, the lens sheet may be manufactured from glass, a polycarbonate, a composite, or any other suitable material for use in an optical lens. The lenses122in the sheet120may be molded, grounded, and polished, or a combination thereof, to the precise desired shape in the sheet to provide the optical properties desire for the lens stack. The lens features need not be identical, but the can be identical if desired. In the illustrated example, a plurality of lenses122are formed at uniformly laterally spaced locations in a planar sheet body120. The lenses122are spaced uniformly on the sheet body124at the same spacing as lenses104in layer102, for precise alignment with the four lenses104when the laminate lens stack is formed and may for example be axially aligned. The lens sheet body124provides a planar body for bonding with the adjacent lens body102and spacer body134in the lamination process.

The spacer140is illustrated to include four apertures142. The spacer can include any number of apertures, each aperture in the illustrated example of a lens stack being for a respective single optical path of the lens laminate stack. The lens sheet may be manufactured by any suitable means and of any suitable material. For example, the lens sheet may be manufactured from glass, a polycarbonate, a composite, or any other suitable material that will withstand the lamination process and provide precise spacing for optical assembly. The apertures may be formed, cut, or punched in the spacer sheet. The apertures142are spaced uniformly on the sheet at the same lateral spacing as lenses104in layer102, for precise alignment with the four lenses104when the laminate lens stack is assembled. The spacer body144provides a planar body for bonding with the adhesive layer to join adjacent lens sheets in the lamination process.

The optical member160is illustrated to include four optical features162in planar body164. The lens sheet can include any number of features, and is illustrated to include four lens features, each illustrated lens feature162in the example of a lens stack being for a respective single lens laminate stack. The lens sheet may be manufactured by any suitable means and of any suitable material for manufacture of optical lenses. For example, the lens sheet may be manufactured from glass, a polycarbonate, a composite, or any other suitable material for use in an optical lens. The lenses, or lens features, or optical features,162in the sheet160may be molded, grounded, or polished, or a combination thereof, to the precise desired shape in the sheet to provide the optical properties desire for the lens stack. In the illustrated example, a plurality of lenses104are formed at uniformly spaced locations in a planar sheet body103. The lenses162are spaced uniformly on the sheet body164at the same spacing as lenses104in layer102, for precise alignment with the four lenses104when the laminate lens stack is assembled. The lens sheet body164provides a planar body for bonding with the adhesive layer to join adjacent lens sheets in the lamination process.

The adhesive and spacer thicknesses are critical to control both consistent spacing and resin flow. A preferred embodiment employs a preformed adhesive film. This preformed adhesive allows for the deposition of the adhesive in a single operation, greatly reducing the cycle time and number of opportunities for defects significantly. Increased precision is achieved by the dimensional control to meet critical tolerances across all aspects of the assembly.

Each of the layers has features with the same lateral spacing to permit alignment of respective optical paths when the lamination is made, and may for example have axial alignment throughout the stack.

The lamination of the pre-form adhesive to the glass wafers and spacer can be accomplished through a thermal and pressure exposure, with temperatures in the range of 25 C to 200 C and pressures ranging from 5-500 psi, dependent upon the specific adhesive chosen. This technique is applicable to both lens-to-lens bonding as well as lens-to-optical spacer, should such a standoff in the optical path be required or desired.

In addition, to protect against the film adhesive pre-form composition lacking sufficient initial tack to hold the parts in alignment prior to or during assembly bonding, a supplemental process may be added to insure alignment is maintained throughout manufacture of the complete construct. One optional process employs a secondary adhesive, also referred to herein as an alignment adhesive. One or more additional holes are provided in the pre-formed adhesive layer, which holes are in addition to the apertures for the optical path through the lens stacks. The additional holes, which are spaced laterally from the optical path, provide an opening for a second compressible adhesive to be dispensed. A material such as, but not limited to, a low durometer UV-curable adhesive can be dispensed into the additional adhesive holes. Once the lens components are aligned, the secondary adhesive is cured to hold the lens wafers in X-Y alignment during handling and throughout curing. The primary lens assembly adhesive layers,110,130,150, are then cured according to their bonding requirements, compressing the alignment adhesive and relieving the alignment adhesive of its temporary function. An alternative to the addition of an alignment adhesive is to use localized spot curing of the primary adhesive through use of a spot cure mechanism. For example, a laser output may be applied to spots of the primary adhesive, generating a thermal process which will allow the primary adhesive, layers110,130,150, to hold the in alignment during handling and throughout curing. The adhesive is then cured according to its bonding requirements to achieve the final cure, providing adhesion, sealing of the optical cavity, and maintaining dimensional control for the optimal optical path.

The structure and process described herein permits precise spacing of optical features in multiple layers of an optical stack. The construct enables reliable production of a plurality of lenses with precision and uniformity for the resulting optical paths.