Integrated Ferromagnetic Magnetic Sensor IC for Stable Sensitivity

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Solution Overview

Problem

Existing magnetic field sensors face sensitivity variations due to mechanical positioning tolerances and high costs associated with hard magnetic materials used in back bias magnets, which affect their performance and manufacturing efficiency.

Innovation Solution

The integration of a ferromagnetic mold material with a lead frame and semiconductor die, where the ferromagnetic mold material is secured to a non-conductive mold material, forming a concentrator or bias magnet, and can be tapered to facilitate easier removal from molds, reducing stress and enhancing adhesion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If mechanical means such as adhesive are used to hold back bias magnet and concentrator relative to magnetic field sensing element, then assembly is simplified, but position tolerances cause sensitivity variations from device to device

Engineering Contradiction:

Improveassembly simplicityVSAvoidposition tolerance

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent merges the back bias magnet and concentrator into a single integral ferromagnetic structure that is directly formed on the semiconductor die during fabrication. This eliminates the need for separate mechanical assembly steps using adhesive, and ensures precise positioning without position tolerances, thereby resolving the contradiction between assembly simplicity and positioning precision.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The ferromagnetic structure is preliminarily formed on the semiconductor die during the fabrication process before final assembly. By pre-integrating the magnetic components onto the die, the patent eliminates subsequent positioning issues and adhesive application steps, achieving both manufacturing precision and ease of manufacture.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If hard magnetic material is used to form back bias magnet, then magnetic field generation is improved, but cost increases significantly

Engineering Contradiction:

Improvemagnetic field generationVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the magnetic parameter configuration by using soft ferromagnetic material with high permeability instead of hard magnetic material. The soft magnetic material, when magnetized during operation by the Hall element, provides sufficient magnetic field generation while being significantly less expensive, thus resolving the contradiction between reliability and manufacturing cost.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces expensive hard magnetic material with inexpensive soft ferromagnetic material. Although soft magnetic material cannot retain magnetization permanently, it is magnetized during operation by the Hall element and performs its function effectively, providing a cost-effective solution that maintains magnetic field generation capability.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of manufacture

If ferromagnetic mold material is tapered, then removal from mold is easier, but structural complexity increases

Engineering Contradiction:

Improvemold removal easeVSAvoidstructural complexity

Core Design Contradiction:

Ease of manufactureVSDevice complexity

Solution Approach 1:

The patent applies a taper to the outer surface of the ferromagnetic mold material, creating a curved or angled geometry that facilitates easy removal from the mold cavity. This simple geometric modification achieves the desired ease of manufacture without significantly increasing structural complexity.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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 stabilizes sensor performance by eliminating position-related variations and reduces costs by utilizing less expensive soft ferromagnetic materials for concentrators or hard magnetic materials for bias magnets, improving manufacturing efficiency and sensitivity.

Implementation Method 1

a ferromagnetic mold material secured to a portion of the non-conductive mold material... forming a concentrator or bias magnet

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Implementation Method 2

a magnetic field sensing element, or transducer, such as a Hall Effect element or a magnetoresistance element

Methodology Applied

Scientific EffectHall Effect: Hall Effect

Data Source

PatentUS11828819B2Magnetic field sensor integrated circuit with integral ferromagnetic material

Publication Date: 2023.11.28 ALLEGRO MICROSYSTEMS LLC

AI summary

A magnetic field sensor includes a lead frame, a passive component, semiconductor die supporting a magnetic field sensing element and attached to the lead frame, a non-conductive mold material enclosing the die and at least a portion of the lead frame, and a ferromagnetic mold material secured to a portion of the non-conductive mold material. The lead frame has a recessed region and the passive component is positioned in the recessed region. The ferromagnetic mold material may comprise a soft ferromagnetic material to form a concentrator or a hard ferromagnetic material to form a bias magnet.