Magnetic Sensor Perimeter Opening Design for Moisture Ingress Control
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Solution Overview
Problem
Magnetic sensors employing magnetoresistive elements face challenges in maintaining high performance in harsh environments due to moisture ingress through stress relief openings, leading to variability in durability and sensor characteristics.
Innovation Solution
The magnetic sensor design incorporates a protective film with open portions along the perimeter of the magnetoresistive body, where the separation distance between the open portion's inside wall and the magnetoresistive body is greater than the alignment margin, and optionally includes dam portions between the insulator and protective film to further prevent moisture ingress, thereby extending the path for moisture entry and minimizing durability variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If stress relief openings are formed in the protective film, then stress on the magnetoresistive film is relieved, but moisture can ingress through the openings causing performance degradation
Solution Approach 1:
The protective film is segmented by forming open portions that run along at least a portion of the perimeter of the magnetoresistive body. This segmentation allows stress relief while maintaining protective coverage in critical areas, preventing moisture ingress pathways that would otherwise compromise reliability.
Solution Approach 2:
The open portions are positioned to run along the perimeter of the magnetoresistive body rather than uniformly across the entire film. This local quality approach provides stress relief where needed at the edges while maintaining continuous protection over the central magnetoresistive body, balancing stress relief with moisture protection.
2Reliability
If the separation distance between the open portion and magnetoresistive body is increased, then moisture ingress is suppressed, but the alignment margin requirement becomes more difficult to satisfy
Solution Approach 1:
The open portions are configured to run along the perimeter in a linear arrangement rather than positioning isolated openings at critical distances. This dimensional change from point-based to line-based configuration provides continuous moisture barrier protection while maintaining adequate separation from the magnetoresistive body, satisfying both reliability and manufacturing precision requirements.
Data Source
AI summary
A magnetic sensor includes a magnetoresistive body that is disposed over a surface of an insulator, a protective film that is provided over a surface of the insulator, including over the magnetoresistive body, and an open portion that runs along at least a portion of a perimeter of the magnetoresistive body and penetrates the protective film in a thickness direction of the protective film. In the magnetic sensor, a separation distance between an inside wall of the open portion and the magnetoresistive body, this being a minimum distance with respect to the magnetoresistive body, is configured so as to be longer than an alignment margin dimension of the open portion with respect to the magnetoresistive body.