Segmented Lead Frame Layout for Robust Magnetic Sensor Dies
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Solution Overview
Problem
Existing lead frame designs for semiconductor packages, particularly those with magnetic field sensing elements, suffer from die cracking during handling and testing due to inadequate mechanical support and induced eddy currents, which affect the sensitivity and accuracy of the magnetic field sensors.
Innovation Solution
The design incorporates a lead frame with strategically positioned openings and discontinuities that create mechanical support for the die while minimizing eddy currents, ensuring no lead frame coverage over magnetic field sensing elements and reducing the size of current loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the lead frame provides continuous mechanical support to the die, then die strength and support are improved, but eddy currents are induced that reduce magnetic field sensor accuracy
Solution Approach 1:
The lead frame is segmented into discrete support regions separated by openings, rather than providing continuous support. This segmentation allows mechanical support at critical locations while creating gaps that interrupt eddy current paths, resolving the contradiction between die strength and sensor accuracy
Solution Approach 2:
The lead frame provides differentiated support qualities at different locations - solid support under the die for mechanical strength, and openings in regions where magnetic field sensing occurs to eliminate eddy currents. This local variation in support quality addresses both requirements simultaneously
2Strength
If the lead frame covers the magnetic field sensing elements, then mechanical support is maximized, but sensor sensitivity and accuracy deteriorate due to eddy current interference
Solution Approach 1:
The lead frame material is extracted or removed from regions directly overlying the magnetic field sensing elements, creating openings that eliminate the source of eddy current interference. This extraction preserves mechanical support through strategic placement of remaining lead frame sections while removing harmful electromagnetic effects
3Measurement precision
If the lead frame is designed with openings to reduce eddy currents, then magnetic field sensor accuracy is improved, but mechanical support and die robustness are reduced
Solution Approach 1:
The lead frame is divided into segmented support structures that provide mechanical reinforcement at critical locations while maintaining openings for electromagnetic performance
Solution Approach 2:
The support function is enhanced by adding vertical dimension features such as raised support pads or three-dimensional structural elements that provide mechanical strength without requiring continuous planar coverage, thus maintaining openings for sensor accuracy
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 die robustness by minimizing cracking and improving the sensitivity and accuracy of magnetic field sensors by reducing mechanical stress and eddy current interference.
Implementation Method 1
induced eddy currents, which affect the sensitivity and accuracy of the magnetic field sensors
Implementation Method 2
a magnetic field sensing element, or transducer, such as a Hall Effect element
Data Source
AI summary
A magnetic field sensor comprises a die, first and second magnetic field sensing elements supported by the die, at respective spaced apart positions, and a lead frame supporting the die. The lead frame comprises a die attach segment having first and second openings formed therein, where there is no lead frame covering either magnetic field sensing element. The die attach segment includes a horizontal support portion disposed between the first and second openings, having a size configured to provide die support along a predetermined portion of at least one predetermined horizontal axis of the die. In other aspects, the lead frame comprises multiple die attach segments separated by slots, where at least one of the multiple die attach segments supports the die along its horizontal axis. At least one of the slots mitigates a current loop arising from operation of at least one of the magnetic field sensing elements.