Conductive Back-Layer for High-Frequency Substrate Reflection Control
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Solution Overview
Problem
High-frequency wave semiconductor devices face issues with reflection of high-frequency waves at the interface between the substrate and air or soft magnetic materials, leading to signal interference and increased manufacturing costs due to the need for thick soft magnetic materials.
Innovation Solution
A conductive layer, such as NiCr, TaN, or ITO, is directly applied to the back face of the substrate, with a thickness that matches or is a fraction of the substrate's impedance, to effectively limit high-frequency wave reflection and reduce manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a soft magnetic material layer is provided on the back face of the substrate to limit high frequency wave reflection, then the reflection is reduced, but the manufacturing cost increases and the layer thickness must be several hundreds of μm
Solution Approach 1:
The patent changes the material parameter from soft magnetic material to conductive material (such as gold, copper, or aluminum), and optimizes the thickness parameter to 1 μm to 10 μm, achieving both reflection limitation and cost reduction
Solution Approach 2:
The patent replaces expensive soft magnetic material with cheaper conductive materials that can be applied as thin films, significantly reducing manufacturing cost while maintaining the reflection limitation function
2Reliability
If a soft magnetic material layer is provided on the back face of the substrate to limit high frequency wave reflection, then the reflection is reduced, but the layer thickness must be several hundreds of μm
Solution Approach 1:
The patent changes the material type and optimizes the thickness parameter from several hundreds of μm to 1 μm to 10 μm, achieving the same reflection limitation effect with much thinner layers
Solution Approach 2:
The patent uses thin conductive film layers (1 μm to 10 μm) on the back face of the substrate to limit high frequency wave reflection, replacing the need for thick soft magnetic material layers
3Device complexity
If the substrate interface is left without a conductive layer to reduce manufacturing complexity, then the device structure is simpler, but high frequency wave reflection occurs at the substrate-air interface
Solution Approach 1:
The patent introduces a conductive layer as an intermediary between the substrate back face and the air, which limits high frequency wave reflection and improves signal isolation without significantly increasing device complexity
Solution Approach 2:
The conductive layer is formed on the back face of the substrate during the semiconductor manufacturing process before packaging, preliminarily preventing reflection issues before the device is assembled into the final package
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 conductive layer significantly reduces high-frequency wave reflection at the substrate interface, improving signal isolation and reducing manufacturing expenses by allowing for thinner, easier-to-form layers.
Implementation Method 1
the conductive layer having a sheet resistance Rsh which satisfies the following relationship: 1/4 Zo≤Rsh≤4 Zo (where Zo represents a resistance component of an impedance of the substrate)
Data Source
AI summary
An electronic device has a substrate, a conductive layer and a substrate mounted portion. The substrate has a circuit portion used from 60 GHz to 80 GHz. The conductive layer is provided directly on a face of the substrate that is opposite side of the circuit portion. The face having the circuit portion of the substrate is mounted face down on the substrate mounted portion. A thickness of the conductive layer is a thickness where a sheet resistance of the conductive layer is ¼ to 4 times of a resistance component of an impedance of the substrate.