Split Lead Frame Magnetic Sensor with Integrated Ferromagnetic Mold

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Solution Overview

Problem

Magnetic field sensors with back bias magnets face performance variations due to mechanical positioning tolerances and high costs associated with hard magnetic materials used in these magnets, while existing packaging techniques like molding can introduce stress and cost inefficiencies.

Innovation Solution

A magnetic field sensor design featuring a split lead frame with non-conductive mold material and integrated passive components, where the semiconductor die is attached to multiple leads, and a ferromagnetic mold material can function as a concentrator or back bias magnet, reducing mechanical stress and costs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If mechanical means (adhesive) are used to hold back bias magnet and concentrator in place, then the sensor can be assembled, but performance variations occur due to position tolerances

Engineering Contradiction:

Improveassembly capabilityVSAvoidposition tolerance

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent merges the back bias magnet and concentrator into a single integrated magnetic component structure. This integration eliminates the need for separate mechanical positioning of multiple components, thereby removing position tolerance issues while maintaining assembly capability. The unified structure ensures consistent magnetic field generation and concentration without variability from mechanical alignment.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The integrated magnetic component serves multiple functions simultaneously: it acts as both the back bias magnet and the concentrator. This multi-functionality eliminates the need for separate positioning mechanisms for two distinct components, resolving the contradiction between ease of manufacture and manufacturing precision by consolidating positioning requirements into a single structural element.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If hard magnetic materials are used for back bias magnets, then magnetic field generation is achieved, but cost increases significantly

Engineering Contradiction:

Improvemagnetic field generationVSAvoidcost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent changes the material parameter from hard magnetic materials to soft magnetic materials for the back bias magnet. Soft magnetic materials are more cost-effective while still achieving the required magnetic field generation through alternative design configurations. This parameter change resolves the contradiction between reliability and manufacturing cost.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The integrated magnetic component may utilize composite material structures that combine different magnetic material properties. This allows achieving reliable magnetic field generation and concentration functions using cost-effective material combinations rather than expensive hard magnetic materials throughout.

Inventive Principle:

Principle #40Composite materials

3Reliability

If molding is used to enclose the semiconductor die, then protection is provided, but stress is introduced to the device

Engineering Contradiction:

Improvedevice protectionVSAvoiddevice stress

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent segments the encapsulation into two distinct portions: a first encapsulant material that directly contacts and protects the semiconductor die, and a second encapsulant material that provides external protection. This segmentation allows each material to be optimized for its specific function, providing protection while minimizing stress transmission to the sensitive die through appropriate material selection and interface design.

Inventive Principle:

Principle #1Segmentation

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 design enhances sensor sensitivity and reduces cost by eliminating mechanical positioning variations and utilizing cost-effective materials, while maintaining the sensitivity and reliability of magnetic field detection.

Implementation Method 1

a magnetically permeable concentrator or magnetic flux guide is sometimes used to focus the magnetic field generated by the target on the magnetic field transducer, thus increasing the sensitivity of the sensor

Methodology Applied

Scientific EffectMagnetic flux concentration: Magnetic Field

Implementation Method 2

in which the ferromagnetic target is not magnetic, a permanent magnet, sometimes referred to as a back bias magnet, may be used to generate the magnetic field that is then altered by movement of the target

Methodology Applied

Scientific EffectMagnetic field generation: Magnetism

Implementation Method 3

Magnetic field sensors including a magnetic field sensing element, or transducer, such as a Hall Effect element or a magnetoresistive element, are used in a variety of applications to detect aspects of movement of a ferromagnetic article

Methodology Applied

Scientific EffectMagnetic field detection: Hall Effect

Data Source

PatentUS9494660B2Integrated circuit package having a split lead frame

Publication Date: 2016.11.15 ALLEGRO MICROSYSTEMS LLC

AI summary

A magnetic field sensor includes a lead frame having a plurality of leads, at least two of which have a connection portion and a die attach portion. A semiconductor die is attached to the die attach portion of the at least two leads. In some embodiments, at least one passive component is attached to the die attach portion of at least two leads.