Fingerprint Sensing Circuit Package With Back-Lapped Substrate
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Solution Overview
Problem
Fingerprint sensor circuitry requires protection from physical and electrical damage, and existing solutions often compromise on cost, size, and reliability.
Innovation Solution
A fingerprint sensing circuit package with a two-substrate architecture, where the top side is a sensing side for fingerprint swiping and the bottom side contains fingerprint sensing circuitry, including an image sensor structure, velocity sensor structure, and sensor IC, with protective measures such as back-lapping to reduce thickness and enhance sensing performance, and stud-based or cavity-based packaging with polymer fillers for added protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If barrier materials are used to protect fingerprint sensor circuitry, then reliability is improved, but cost and size increase
Solution Approach 1:
The package structure is segmented into distinct functional layers: a substrate housing the sensor circuitry, a separate barrier layer for protection, and a lens structure. This segmentation allows each component to be optimized independently for its specific function while maintaining overall system reliability without excessive complexity.
Solution Approach 2:
The lens structure serves multiple functions: it protects the sensor circuitry from physical damage, focuses light onto the sensor, and acts as a structural element of the package. This multi-functionality reduces the need for separate protective components, thereby reducing overall package complexity while maintaining reliability.
2Measurement precision
If substrate thickness is reduced through back-lapping, then sensing performance is enhanced, but mechanical strength decreases
Solution Approach 1:
The substrate is constructed as a composite structure combining multiple materials with complementary properties. The substrate housing uses a material that provides both the necessary mechanical strength and the optical transparency required for fingerprint sensing. This composite approach allows the substrate to be thinned for improved sensing performance while maintaining adequate mechanical strength through material selection and structural design.
3Reliability
If protective layers are added to cover sensor circuitry, then reliability is improved, but package height increases
Solution Approach 1:
The sensor control circuit package is nested within the substrate housing structure. The protective barrier layer and lens are integrated into the housing in a nested configuration, where each protective element is positioned within the overall package footprint rather than adding external height. This nesting approach provides comprehensive protection while minimizing the increase in package height.
Data Source
AI summary
Fingerprint sensing circuit packages and methods of making such packages may comprise a first substrate having a top side and a bottom side; the top side comprising a fingerprint image sensing side over which a user's fingerprint is swiped; the bottom side comprising a metal layer forming a fingerprint sensing circuit image sensor structure; and a sensor control circuit housed in a sensor control circuit package mounted on the metal layer. The sensor control circuit may comprise an integrated circuit die contained within the sensor control circuit package. The fingerprint sensing circuit package may also have a second substrate attached to the bottom side of the first substrate having a second substrate bottom side on which is placed connector members connecting the fingerprint sensing circuit package to a device using a fingerprint image generated from the fingerprint sensing circuitry contained in the fingerprint sensing circuitry package.