Patent Application
20160336370
1. Field of the Invention
The present disclosure relates to focal arrays, and more particularly to infrared focal plane arrays and packaging therefor.
2. Description of Related Art
A variety of devices and methods are known in the art for infrared focal plane array (FPA) image sensors. Traditional FPA image sensors include a photodiode array (PDA) packaged with a read out integrated circuit (ROIC). The package containing the FPA is generally electrically coupled to the topside of the ROIC via bond wires and bond pads such that circuitry on the ROIC can be electrically accessed.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved FPA devices and packaging therefor. The present disclosure provides a solution for this need.
A focal plane array (FPA) includes a read out integrated circuit (ROIC) having a circuit side. A photodiode array (PDA) defines an optical axis and has a backside electrically connected to the circuit side of the ROIC. A plurality of conductive through-vias extend from the circuit side of the ROIC through to input/output (I/O) bondpads on the backside of the ROIC, e.g., for the purpose of making the I/O bondpads accessible from the back-side of the ROIC die to facilitate surface mount packaging configurations not currently possible with traditional top-side wirebond pad schemes.
The backside of the PDA can include pixel circuitry, and the topside of the PDA can be free from wire bond connections. In addition to or in lieu of the topside of the PDA being free from wire bond connections, the circuit side of the ROIC can be free from wire bond connections. The FPA can include a window directly abutting the topside of the PDA. A perimeter of the ROIC in a plane perpendicular to the optical axis can be equal to a perimeter of the PDA in another plane perpendicular to the optical axis. Optionally, the circuit side of the ROIC can be covered entirely by the PDA. The conductive through-vias can extend in a direction parallel to the optical axis.
In another aspect, a package assembly includes a package body and a FPA within the package body. The FPA is similar to the FPA described above. A window is operatively connected between the FPA and the package body. The window can be defined in an opening of the package body. The package body can be electrically connected to the conductive through-vias on the backside of the ROIC. A perimeter of the ROIC in a plane perpendicular to the optical axis can be equal to perimeters of the PDA and the window in other respective planes perpendicular to the optical axis.
These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a package assembly in accordance with the disclosure is shown in
The ROIC I/O contact pads are typically physically located in the surrounding peripheral edge of the ROIC. This is to facilitate, for example, placement of the infrared FPA (IRFPA), e.g., a PDA or sensor chip array, or other image sensor with a plurality of pixels, in an interior two-dimensional array. These edge contact I/O pads are the functional electrical connections, made for power, ground, clocks, analog and/or digital signals, or the like. The ROIC interfaces with camera electronics, or the like, by these connections typically through wirebond contacts made from the ROIC I/O pads to some printed circuit board assembly (PCBA), ceramic substrate, or the like, designed for said purpose.
The systems and methods disclosed herein make application of insulated through vias at these I/O pad locations, thus facilitating reduced package area by use of surface mount (using back-side contacts), reduction or elimination of wirebonds, improved optical path by reduced lens backworking distance, improved path to chipscale packaging, improved design freedom with respect to I/O layout and placement within the ROIC die, as well as improved design freedom with respect to PDA size constraints typically brought about by the need to accommodate top-side electrical connections.
As shown in
With continued reference to
Respective perimeters of ROIC 108, PDA 114 and window 106 in respective planes perpendicular to the optical axis A are equal one another. Those skilled in the art will readily appreciate that with backside contacts by way of through-vias 116, wire bond pads on circuit side 110 of ROIC 108 are not required. This enables PDA 114 to be sized up to the extent of ROIC 108, facilitating wafer-to-wafer bonding.
As shown in
During manufacture, a portion 117 of backside 112 of ROIC 108, indicated schematically by dashed lines, is ground away to expose the conductive through-vias 116 before assembling into package 100, as shown in
By removing all topside in-put/out-put considerations on ROIC 108 and PDA 114, fewer challenges are placed in the optical path, thus the optics can be designed with fewer limitations. Such challenges in traditional configurations include wirebonds and required mechanical clearances, and any top-side electrical contact would necessarily prevent optical elements from being butted to the surface of the FPA without incorporating electrical traces in those optical elements. Thus, common, traditional package design includes some clearance distance between the FPA and the optical mount, thus adding back-working distance, and making the total package, including lens diameter, necessarily larger than would be with a reduced backworking distance. Other optical considerations include reflections or scattering sources for light, which are presented by the mechanical considerations mentioned above. Those skilled in the art will readily appreciate that optionally some topside contacts can still be present on ROICs in accordance with this disclosure, e.g., for testing purposes or the like.
A method for forming a FPA, e.g. FPA 104, includes forming a plurality of conductive through-vias, e.g. conductive through-vias 116, extending through a ROIC, e.g. ROIC 108, starting from a circuit side, e.g. circuit side 110. The method includes grinding a portion, e.g. portion 117, of the ROIC from a backside, e.g. backside 112, to expose the conductive through-vias. Those skilled in the art will readily appreciate that the method can include electrically connecting circuitry on a circuit side, e.g. circuit side 110, of the ROIC to a PDA, e.g. PDA 114. It is also contemplated that the method can include electrically connecting the through-vias from the backside of ROIC 108 to a package, e.g. package 100, e.g., with bump bonds.
The methods and systems of the present disclosure, as described above and shown in the drawings, provide for focal plane arrays and packaging therefor with superior properties including reduced size, increased manufacturability, and increased mitigation ability for artifacts such as light scattering. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.
This invention was made with government support under contract number HR0011-13-C-0068 awarded by DARPA. The government has certain rights in the invention.
