Fingerprint Sensor Metal Bump Interconnects
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Solution Overview
Problem
Conventional capacitive fingerprint sensors face challenges with increased sensing distance due to lead-out wires, leading to reduced sensing accuracy and higher costs, while attempts to reduce this distance through hole digging in protection glass increase material costs and fabrication complexity, compromising yield and durability.
Innovation Solution
The use of metal bumps to connect sensing electrodes directly to an integrated circuit chip, reducing the sensing distance and eliminating the need for lead-out wires, thereby enhancing sensing accuracy and reducing packaging complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lead-out wires are used to connect sensing electrodes to the IC chip, then electrical connection is achieved, but the sensing distance increases by tens of micrometers reducing sensing accuracy
Solution Approach 1:
The patent extracts and removes the lead-out wires from the connection path between sensing electrodes and IC chip, replacing them with metal bumps that directly connect the sensing electrodes to the IC chip, thereby eliminating the unnecessary distance h1 and improving sensing accuracy
Solution Approach 2:
The patent introduces metal bumps as an intermediary connection element between the sensing electrodes and IC chip, replacing the lead-out wires. These metal bumps provide a much shorter and more direct electrical connection path, reducing the sensing distance from tens of micrometers to minimal height
2Reliability
If sapphire protection film is used to fill the area along height h1, then the lead-out wires are protected, but the cost increases due to expensive material
Solution Approach 1:
The patent extracts and removes the expensive sapphire protection film from the structure by eliminating the lead-out wires that required such protection. The metal bump connection method inherently protects the connection path without requiring additional expensive protective layers
Solution Approach 2:
The patent replaces expensive sapphire protection film with a simpler, cheaper protection approach using standard sealing resin that adequately protects the metal bump connections, significantly reducing material cost while maintaining sufficient protection
3Length of stationary object
If holes are dug in protection glass to embed the IC chip, then the sensing distance is reduced, but material cost and fabrication complexity increase while yield and durability decrease
Solution Approach 1:
The patent extracts and removes the complex hole-digging process from the fabrication sequence by using metal bumps that can be directly connected to the sensing electrodes on the IC chip surface, eliminating the need to modify the protection glass structure
Solution Approach 2:
Instead of modifying the protection glass by digging holes to reduce sensing distance, the patent inverts the approach by using metal bumps that naturally provide a short connection path without requiring any modification to the protection glass structure
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 effectively minimizes the sensing distance, enhances measurement sensitivity, and lowers production costs while maintaining high performance and durability, making the fingerprint recognition apparatus more efficient and cost-effective.
Implementation Method 1
The capacitive fingerprint sensor integrates the sensing electrodes and the sensing circuit into one integrated circuit (IC). The conductive pads of the fingerprint recognition IC are electrically connected to the corresponding conductive pads on the package substrate through the lead-out wires. To protect the lead-out wires, a sealing resin is used to encapsulate the lead-out wires. However, the distance between the finger and the sensing electrodes will be increased by the height h1 (in the order of tens of micro meters)
Data Source
AI summary
A fingerprint recognition apparatus includes an electrode-and-wiring substrate having two main surfaces opposite to each other, where one main surface is in proximity to user finger and the electrode-and-wiring substrate has a plurality of sensing electrodes on the other main surface. The fingerprint recognition apparatus further includes an integrated circuit (IC) chip having a fingerprint sensing circuit and a plurality of metal bumps. At least part of the metal bumps are electrically connected to the fingerprint sensing circuit and corresponding sensing electrodes on the electrode-and-wiring substrate, whereby the fingerprint sensing circuit is electrically connected to the sensing electrodes.