Optical Sensor Package Stacked Die Assembly
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Solution Overview
Problem
Current optical sensor packaging solutions are complex, costly, and unreliable, with high tooling expenses and integration challenges due to the need for visually exposed sensor dies and expensive materials.
Innovation Solution
A low-cost optical sensor package is fabricated using a stacked die assembly process with an optical overlay and adhesive, encapsulated in a mold layer, employing interconnection techniques like flip chip and through-silicon via technology to connect optical devices to a substrate, avoiding custom tooling and ensuring high reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional optical sensor packaging methods are used, then the sensor die can be visually exposed, but the packaging becomes complex and costly with high tooling expenses
Solution Approach 1:
The patent combines the optical overlay and sensor die into a single stacked die assembly, eliminating the need for separate packaging steps and tooling. The overlay is directly bonded to the sensor die using chip-scale packaging techniques, merging multiple components and processes into one integrated structure that reduces complexity while maintaining sensor exposure functionality
Solution Approach 2:
The stacked die assembly serves multiple functions simultaneously: the optical overlay provides both protective coverage and optical filtering, while the chip-scale bonding process provides both mechanical attachment and electrical interconnection. This multi-functionality eliminates the need for separate protective windows, filters, and bonding steps, reducing packaging complexity and tooling requirements
2Reliability
If expensive materials and custom tooling are used for optical sensor packaging, then integration reliability improves, but manufacturing cost increases
Solution Approach 1:
The patent employs standard, commercially available optical overlay materials and adhesive films instead of expensive custom-engineered materials. The chip-scale packaging process uses conventional bonding equipment rather than custom tooling, significantly reducing material and equipment costs while maintaining sufficient reliability for the application
Solution Approach 2:
The patent changes the bonding parameters by using chip-scale bonding at lower temperatures and smaller bond areas compared to traditional packaging methods. This allows the use of standard adhesive materials that are cheaper than high-performance specialty materials, while the controlled bonding parameters ensure adequate mechanical and thermal reliability
3Ease of manufacture
If optical overlays are stacked on optical devices using adhesive, then assembly process simplifies, but optical isolation and electrical connectivity must be maintained
Solution Approach 1:
The patent performs preliminary alignment of the optical overlay with the sensor die before bonding, using alignment marks or features that are pre-formed on both components. This preliminary positioning ensures correct optical alignment is achieved before the adhesive sets, maintaining manufacturing precision while keeping the assembly process simple and sequential
Solution Approach 2:
The adhesive layer serves as an intermediary that not only bonds the overlay to the sensor die but also provides optical coupling between the two components. By selecting adhesives with appropriate optical properties (transparency, refractive index), the bonding medium itself contributes to maintaining optical precision while enabling the simplified stacked assembly process
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the assembly process, reduces tooling costs, and enhances the reliability of optical sensor packages by exposing the optical overlay while maintaining optical isolation and electrical connectivity, making it suitable for various package types and configurations.
Implementation Method 1
One or more optical overlays are disposed (e.g., stacked) on the active side of the optical device(s), and mounted to the device(s) using an adhesive
Data Source
AI summary
Optical sensor packages include a substrate assembly such as a leadframe or semiconductor substrate. One or more optical devices are mounted to the substrate assembly. One or more optical overlays are disposed (e.g., stacked) on the active side of the optical device(s), and mounted to the device(s) using an adhesive layer. In embodiments, the optical devices may comprise optical sensors (e.g., photodetector such as phototransistors or photodiodes), light sources (e.g., light emitting diodes (LED), combinations thereof, and so forth. A mold layer is formed over the substrate assembly, proximate to the optical device and optical overlay so that an outer surface of the optical overlay is exposed.