Molded Capsule Magnet Retention for Magnetic Field Sensors

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Solution Overview

Problem

Conventional magnetic field sensors, particularly proximity detectors, face challenges due to their dependence on the air gap between the magnetic field sensing element and the object being sensed, which affects sensitivity and leads to increased costs when the sensor fails during manufacturing, as the magnet is often irreversibly integrated and cannot be reused.

Innovation Solution

A packaging scheme for magnetic field sensors that includes a molded capsule with a cavity to house a magnet and a liquid encapsulant, allowing for the magnet to be reused if the sensor fails during testing, and optionally using ferromagnetic particles within the encapsulant to generate or concentrate magnetic fields, thereby maintaining sensitivity and avoiding excessive air gaps.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the magnet is irreversibly integrated into the sensor during manufacturing, then the sensor structure is simplified and production is easier, but the magnet cannot be reused if the sensor fails during testing, increasing costs

Engineering Contradiction:

Improvemagnet integrationVSAvoidmagnet reuse

Core Design Contradiction:

Ease of manufactureVSLoss of substance

Solution Approach 1:

The patent divides the sensor assembly into separable components: the magnet is placed in a cavity within the molded capsule but is not permanently bonded to the sensing element. This segmentation allows the magnet to be removed and reused if the sensor fails during manufacturing testing, while still providing a simplified integrated structure during normal operation.

Inventive Principle:

Principle #1Segmentation

2Measurement precision

If the air gap between the magnetic field sensing element and the magnet is reduced to maintain sensitivity, then the sensor becomes more sensitive, but the sensor is more vulnerable to environmental factors and mechanical damage

Engineering Contradiction:

ImprovesensitivityVSAvoidenvironmental protection

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent places the magnet and sensing element within a molded capsule that encloses both components. This nesting structure maintains a small air gap for high sensitivity while the capsule provides environmental protection. The cavity within the capsule further organizes the components in a protected space.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The molded capsule acts as an intermediary structure between the magnet and the external environment. It allows the magnetic field to pass through while protecting the components from environmental factors such as moisture, dust, and mechanical damage.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If the magnet is placed close to the magnetic field sensing element to maintain sensitivity, then the sensor performance is improved, but the manufacturing process becomes more complex and costly

Engineering Contradiction:

Improvesensor performanceVSAvoidmanufacturing process

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent combines the magnet placement and environmental protection functions into a single molded capsule structure. The capsule is molded with an integrated cavity that holds the magnet in the optimal position close to the sensing element, eliminating the need for separate mounting structures and simplifying the manufacturing process.

Inventive Principle:

Principle #5Merging (Combining)

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 ensures reliable protection from environmental factors, maintains sensitivity by keeping the magnetic field sensing element close to the magnet, and allows for the reuse of the magnet, reducing waste and costs associated with failed manufacturing tests.

Implementation Method 1

Proximity detectors typically include a permanent magnet to generate a magnetic field and also include a magnetic field sensing element, for example, a Hall effect element, to detect changes in the strength of the magnetic field

Methodology Applied

Scientific EffectHall effect: Hall Effect

Implementation Method 2

placing a liquid encapsulant into the cavity proximate to the magnet. The method also includes curing the liquid encapsulate to a solid condition to retain the magnet

Methodology Applied

Scientific EffectCuring: Photopolymerisation

Implementation Method 3

optionally using ferromagnetic particles within the encapsulant to generate or concentrate magnetic fields

Methodology Applied

Scientific EffectFerromagnetism: Ferromagnetism

Data Source

PatentUS8486755B2Magnetic field sensors and methods for fabricating the magnetic field sensors

Publication Date: 2013.07.16 ALLEGRO MICROSYSTEMS LLC

AI summary

Magnetic field sensors and associated methods of manufacturing the magnetic field sensors include molded structures to encapsulate a magnetic field sensing element and an associated die attach pad of a lead frame and to also encapsulate or form a magnet or a flux concentrator.