Fingerprint Sensor Package with RDL Electrodes for Lower Interference
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Solution Overview
Problem
Conventional fingerprint sensors face interference issues due to the close proximity of sensing electrodes to the circuits in the sensor die, limiting the accuracy and quality of fingerprint image capture.
Innovation Solution
The formation of sensing electrodes in Redistribution Layers (RDLs) rather than on the surface of the sensor die, which increases the distance between the electrodes and the circuits, reducing interference and allowing for a larger sensing area without sacrificing sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If sensing electrodes are placed on the surface of the sensor die, then the sensing area can be maximized, but the proximity to circuits causes interference and reduces measurement precision
Solution Approach 1:
The sensing electrodes are moved from the horizontal surface of the sensor die to the vertical sidewalls of the encapsulating material. This dimensional transition from 2D surface mounting to 3D sidewall integration increases the distance between electrodes and circuits while maintaining or expanding the effective sensing area through vertical electrode arrangements.
Solution Approach 2:
The encapsulating material serves as an intermediary structure that provides sidewalls for mounting the sensing electrodes. This intermediary structure physically separates the electrodes from the circuits on the sensor die, reducing electromagnetic interference while still allowing the electrodes to function as capacitor plates for fingerprint sensing.
2Device complexity
If sensing electrodes are placed close to circuits on the sensor die, then device complexity is reduced, but circuit interference increases and reduces reliability
Solution Approach 1:
The electrode mounting location is changed from the horizontal plane to the vertical dimension by utilizing the sidewalls of the encapsulating material. This spatial reconfiguration reduces circuit interference and improves sensing reliability without significantly increasing device complexity, as the sidewall structure is inherent to the encapsulation process.
3Area of stationary object
If the sensing area is increased, then more fingerprint detail can be captured, but the proximity to circuits causes more interference
Solution Approach 1:
By transitioning electrode placement to the vertical sidewalls of the encapsulating material, the design enables larger sensing areas to be implemented without proportionally increasing proximity to circuits. The vertical arrangement allows electrodes to be positioned farther from circuit planes while maintaining large horizontal footprint for capturing detailed fingerprint patterns.
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 configuration enhances the sensitivity and durability of fingerprint sensor packages by minimizing circuit interference and enabling a larger sensing area, improving the quality and accuracy of fingerprint image capture.
Implementation Method 1
capacitance sensors use principles associated with capacitance in order to form fingerprint images. Each of the sensing electrodes in a sensor array acts as one plate of a parallel-plate capacitor. The dermal layer (which is electrically conductive) of the finger to be sensed acts as the other plate
Data Source
AI summary
A package includes a sensor die, and an encapsulating material encapsulating the sensor die therein. A top surface of the encapsulating material is substantially coplanar with or higher than a top surface of the sensor die. A plurality of sensing electrodes is higher than the sensor die and the encapsulating material. The plurality of sensing electrodes is arranged as a plurality of rows and columns, and the plurality of sensing electrodes is electrically coupled to the sensor die. A dielectric layer covers the plurality of sensing electrodes.