Fingerprint Sensor Edge Trench for Flat Surface
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Solution Overview
Problem
Existing fingerprint sensor modules face challenges in achieving a flat sensing surface due to protruding wire bonds, which compromise accuracy, and alternative solutions like through-silicon-via connections are complex and costly.
Innovation Solution
A fingerprint sensor module with a trench at its edge for direct electrical connection to a substrate, eliminating wire bonds and allowing for a minimized distance between sensing elements and the surface, using a flip-chip methodology for assembly and potentially embedding conductive traces for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire bonds are used to connect the sensing chip to the substrate, then electrical connection is achieved, but the wire bonds protrude above the sensing surface causing a non-flat surface that reduces sensing accuracy
Solution Approach 1:
The patent removes the wire bonds from the sensing surface area by providing connection pads at the edges of the sensing chip that connect directly to the substrate without protruding wire bonds. This extraction of the harmful element (wire bonds) from the sensing area eliminates the protrusion problem while maintaining electrical connection functionality.
Solution Approach 2:
The patent transitions from vertical wire bond connections (protruding upward from the chip surface) to edge-based planar connections. By moving the connection interface to the edge dimension of the chip rather than the center surface dimension, the electrical connection is achieved without compromising the flatness of the sensing surface.
2Shape
If a thick top coating layer is added to cover the wire bonds and create a flat surface, then surface flatness is improved, but the capacitive coupling between the finger and sensing elements is weakened reducing accuracy
Solution Approach 1:
The patent extracts the wire bonds from the sensing surface area entirely by using edge-based connection pads. This eliminates the need for a thick top coating layer to cover protruding wire bonds, thereby maintaining strong capacitive coupling between the sensing elements and the finger while achieving surface flatness through the absence of protrusions rather than through thick coating.
3Shape
If through-silicon-via connections are used to eliminate wire bonds, then surface flatness is improved, but the manufacturing process becomes complicated and expensive
Solution Approach 1:
The patent segments the electrical connection function into two separate locations: sensing elements remain on the front surface for capacitive sensing, while connection pads are positioned at the edges for substrate connection. This segmentation allows direct bonding at the edges without requiring through-silicon-via fabrication, simplifying the manufacturing process while maintaining surface flatness.
Solution Approach 2:
Instead of bringing connection pads to the center surface (traditional approach requiring wire bonds or TSVs), the patent inverts the approach by bringing the substrate connection interface to the edge of the chip. This inversion eliminates the need for complex through-silicon-via fabrication while achieving the same goal of surface flatness.
4Shape
If through-silicon-via connections are used, then wire bond protrusion is eliminated, but package warpage increases due to thin silicon requirements
Solution Approach 1:
The patent extracts the connection interface from the thin silicon sensing chip by providing pads at the edge that can be directly bonded to the substrate. This extraction eliminates the need for through-silicon-vias in thin silicon, thereby avoiding the mechanical stress and warpage issues that arise from creating holes through thin silicon substrates.
Solution Approach 2:
The patent inverts the traditional connection approach by moving the connection interface to the edge of the chip rather than through the center. This inversion allows direct bonding without penetrating the thin silicon, avoiding the warpage problems associated with TSV fabrication in thin substrates while maintaining surface flatness.
Data Source
AI summary
There is provided a fingerprint sensor module comprising: a fingerprint sensor device comprising a plurality of sensing elements for acquiring an image of a finger placed on a sensing surface of the sensor module. The sensor device comprises a trench at an edge of the fingerprint sensor device, the trench comprising electrically conductive connection pads for connecting the sensor device to external circuitry. The module further comprises a substrate comprising an electrically conductive trace and an electric component arranged on the substrate and in electrical contact with the conductive trace. The substrate is electrically and mechanically connected to the edge trench such that an electrical connection is formed between the sensor device and the electrical component of the substrate via the conductive trace. There is also provided a method for manufacturing the described module.