Reinforced Isolation Current Sensor Using Polyimide Insulation Structure
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Solution Overview
Problem
Current integrated circuit (IC) current sensors with magnetic field sensing elements face challenges in achieving double or reinforced insulation levels required for safety isolation, relying on basic insulation within the package assembly and external supplemental insulation, which can be costly and complex.
Innovation Solution
A current sensor design incorporating a lead frame with a magnetic field sensing circuit and an insulation structure featuring two layers of thin sheet material, such as polyimide film, and a molding compound to provide reinforced insulation, eliminating the need for external opto-isolators and ensuring compliance with UL 60950-1 standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If basic insulation is used within the package assembly, then the current sensor can be simpler and less costly, but it does not provide sufficient safety isolation for user-accessible secondary circuits
Solution Approach 1:
The patent combines basic insulation and supplemental insulation into a single integrated insulation structure within the package assembly. The insulation structure includes a first insulation layer (basic insulation) and a second insulation layer (supplemental insulation) that are integrated together, eliminating the need for separate external opto-isolators and providing reinforced insulation in one unified component.
Solution Approach 2:
The insulation structure is nested within the package assembly, with the first insulation layer positioned between the current conductor and the magnetic field transducer, and the second insulation layer positioned between the magnetic field transducer and the package substrate. This nested arrangement provides multiple levels of insulation protection within the compact package structure.
2Reliability
If external opto-isolators are used to provide supplemental insulation, then safety isolation requirements are met, but the device becomes more complex and costly
Solution Approach 1:
The patent merges the function of external opto-isolators into the integrated insulation structure by incorporating both basic and supplemental insulation layers within the package assembly. This integration eliminates the need for separate external components and simplifies the manufacturing process while maintaining safety isolation compliance.
Solution Approach 2:
The insulation structure serves multiple functions simultaneously: it provides basic insulation between the current conductor and magnetic field transducer, supplemental insulation between the magnetic field transducer and package substrate, and achieves reinforced insulation overall. This multi-functionality replaces what would otherwise require multiple separate components.
3Measurement precision
If the magnetic field transducer is positioned close to the current conductor, then sensitivity is improved, but achieving reinforced insulation becomes more difficult
Solution Approach 1:
The patent applies different insulation layers at different locations: the first insulation layer is positioned between the current conductor and magnetic field transducer where close proximity is needed for sensitivity, and the second insulation layer is positioned between the magnetic field transducer and package substrate to provide supplemental insulation. This localized insulation approach maintains both sensitivity and safety isolation.
Solution Approach 2:
The patent achieves reinforced insulation by adding the second insulation layer in a different spatial dimension (between the magnetic field transducer and package substrate) rather than increasing the separation distance between the current conductor and magnetic field transducer. This dimensional approach maintains close proximity for sensitivity while providing additional insulation protection.
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
The design achieves reinforced insulation in a single package, enhancing safety isolation and reducing costs by eliminating the need for external components, while maintaining high sensitivity and accuracy of the magnetic field sensing.
Implementation Method 1
The magnetic field transducer generates an output signal having a magnitude proportional to the magnetic field induced by a current that flows through the current conductor
Implementation Method 2
the magnetic field induced by a current that flows through the current conductor
Implementation Method 3
The insulation structure is disposed between the current conductor and the die, and includes a first insulation layer and a second insulation layer
Data Source
AI summary
A current sensor packaged in an integrated circuit package to include a magnetic field sensing circuit, a current conductor and an insulator that meets the safety isolation requirements for reinforced insulation under the UL 60950-1 Standard is presented. The insulator is provided as an insulation structure having at least two layers of thin sheet material. The insulation structure is dimensioned so that plastic material forming a molded plastic body of the package provides a reinforced insulation. According to one embodiment, the insulation structure has two layers of insulating tape. Each insulating tape layer includes a polyimide film and adhesive. The insulation structure and the molded plastic body can be constructed to achieve at least a 500 VRMS working voltage rating.