LCOS Imager Backside Bonding Via Interconnects
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Solution Overview
Problem
Conventional liquid crystal on silicon (LCOS) imager packaging configurations with input and output bond pads on the top-side are not convenient for assembly and system integration, deviating from modern electronic system packaging frameworks, and the manufacturing process is inefficient.
Innovation Solution
A liquid crystal imager design with a transparent front plane plate, a planar liquid crystal cell, and a backplane plate, where the conductive seal ring electrically connects the transparent conductive coating to the transmit cell connection pad, and the active matrix driving circuitry is connected to both the reflective pixel electrodes and input-output pads routed onto the backside, allowing for efficient wafer-level packaging and thru-substrate via interconnects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If input and output bond pads are placed at edge on top-side of backplane substrate, then wiring of bond pads is facilitated, but assembly and system integration convenience deteriorates
Solution Approach 1:
The patent inverts the conventional bond pad placement from top-side edge to backside of the substrate. This inversion allows the bond pads to be accessible from the back, enabling backside bonding configurations similar to BGA packages, which improves assembly and system integration convenience while maintaining manufacturing feasibility through adjusted wiring routes
2Ease of manufacture
If backplane substrate is die sawed asymmetrically, then wiring of ITO underneath glass cover is made easier, but manufacturing efficiency and process standardization deteriorates
Solution Approach 1:
The patent employs asymmetric die sawing configuration where the glass cover extends beyond the backplane substrate on one side. This asymmetric design facilitates wiring of ITO underneath the glass cover while the patent compensates for manufacturing efficiency loss by integrating this asymmetric cut into the standard manufacturing process flow
Solution Approach 2:
The asymmetric die sawing configuration serves multiple functions: it facilitates ITO wiring, enables access to bond pads, and allows for standardized packaging. By making this asymmetric configuration part of the standard process, the patent achieves multi-functionality without sacrificing manufacturing efficiency
Data Source
AI summary
The disclosed LCOS device comprises a transparent composite plate, a planar liquid crystal cell, a base plate which contains an active matrix driving circuitry. In the basic embodiment, the planar liquid crystal cell comprises a conductive seal ring which encloses liquid crystal filling and connects the transparent conductive layer underneath the transparent composite plate with the base plate and the active matrix driving circuitry. In the extended embodiment, the base plate further incorporates a set of thru-substrate via and backside bond pads. The set of thru-substrate via electrically connect a set of input-output pads of the active matrix driving circuitry to the bottom bond pads underneath the base plate. In addition, the conductive seal ring electrically connects the transparent conductive film placed underneath the transparent front plane plate, preferably made of glass, to the active matrix driving circuitry on the base plate. Electrostatically charged between the transparent conductive coating and an electrode array layer including a planar array of reflective pixel electrodes on top of the base plate, planar liquid crystal cell is operated to produce spatial light modulation to incident illumination. The method of wafer level process and packaging of the disclosed LCOS imagers is further disclosed.