Wire Fence ESD Protection for Fingerprint Sensors
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Solution Overview
Problem
The existing methods for protecting fingerprint sensors from electrostatic discharge (ESD) using a grounded metal bezel are costly and result in assembly yield loss due to mold flash, necessitating a more economical and efficient solution.
Innovation Solution
A wire fence fingerprint sensor package is implemented, featuring a substrate with a wire fence electrically connected to a reference voltage source, fabricated using low-cost wire loops and a standard wire bonding apparatus, which effectively discharges ESD from a finger contacting the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a grounded metal bezel is used to discharge ESD, then the fingerprint sensor is protected from electrostatic damage, but the manufacturing cost increases and assembly yield decreases due to mold flash
Solution Approach 1:
The continuous metal bezel is segmented into discrete wire loops arranged in a fence pattern. This segmentation allows the ESD protection function to be distributed across multiple isolated conductive elements rather than requiring a single continuous metallic structure, enabling simpler manufacturing without mold flash issues
Solution Approach 2:
The patent replaces expensive metal bezel material with inexpensive wire loops that can be easily fabricated and attached. The wire loops serve as disposable-like components that provide effective ESD protection through their simple structure, eliminating the need for costly metal machining and assembly processes
2Object-affected harmful factors
If a metal bezel is attached near the fingerprint sensor, then ESD discharge capability is provided, but assembly complexity and cost increase
Solution Approach 1:
The wire fence structure is integrated directly with the substrate, merging the ESD protection function into the existing sensor assembly rather than adding a separate metal bezel component. This integration eliminates additional assembly steps while maintaining effective ESD discharge capability through the wire loops electrically connected to ground
Solution Approach 2:
The wire loops serve as an intermediary structure between the fingerprint sensor and ground, providing ESD discharge path without requiring direct metal-to-metal contact or complex mechanical attachment. The wires act as flexible conductors that bridge the electrical connection need while simplifying the physical assembly
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
The wire fence package provides an economical and efficient means to discharge ESD, reducing assembly costs and yield loss while effectively protecting the fingerprint sensor, thereby enhancing the reliability and affordability of the device.
Implementation Method 1
The finger placed on the fingerprint sensor may have an electrostatic charge. As the finger nears or contacts the fingerprint sensor, this electrostatic charge is discharged as an electrostatic discharge (ESD).
Data Source
AI summary
A wire fence fingerprint sensor package includes a substrate, a fingerprint sensor mounted to the substrate, and a wire fence mounted to the substrate adjacent the fingerprint sensor. During use, the wire fence is electrically connected to a reference voltage source, e.g., ground. Thus, the wire fence discharges electrostatic discharge (ESD) from a finger contacting the wire fence fingerprint sensor package. The wire fence is formed of low cost wire loops that are fabricated, for example, using a standard and inexpensive wire bonding apparatus. Accordingly, the wire fence fingerprint sensor package is fabricated at a minimal cost.