Low-k Buffer Layer for Plastic Encapsulated Semiconductor Die
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Solution Overview
Problem
Plastic encapsulated semiconductor devices suffer from significant capacitive coupling and power loss due to the high dielectric constant and loss tangent of traditional plastic encapsulants, which degrade performance at high frequencies and voltages, and existing solutions like Faraday shields or vacuum packages are either complex or costly and not as rugged.
Innovation Solution
A semiconductor device with a low dielectric constant and loss tangent buffer layer is introduced between the semiconductor die and the plastic encapsulation, using materials like Sol-Gels, Aero-Gels, or low-loss organic materials to reduce fringing electric fields and minimize cross-talk and power loss, while maintaining a solid, rugged structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional plastic encapsulation is used to protect the semiconductor die, then mechanical protection and ruggedness are improved, but capacitive coupling and power loss increase due to high dielectric constant and loss tangent
Solution Approach 1:
The encapsulation structure is segmented into multiple layers: an inner buffer layer with low dielectric constant and loss tangent in direct contact with the die, and an outer plastic encapsulation layer providing mechanical protection. This segmentation allows each layer to perform its specialized function - the buffer layer minimizes electromagnetic losses while the outer layer provides ruggedness.
Solution Approach 2:
The buffer layer acts as an intermediary between the die and the plastic encapsulation. It mediates the interaction by providing a low-loss dielectric interface that reduces fringing electric field effects while still allowing the outer plastic layer to provide mechanical protection.
2Strength
If plastic encapsulation is used to provide mechanical protection, then device ruggedness is improved, but capacitive cross-talk increases due to high dielectric constant
Solution Approach 1:
The encapsulation is divided into functional segments: the inner buffer layer specifically addresses capacitive cross-talk by having low dielectric constant, while the outer plastic layer provides mechanical protection. This functional segmentation resolves the contradiction between protection and electromagnetic performance.
Solution Approach 2:
Different regions of the encapsulation have different properties optimized for their specific functions. The inner buffer layer has low dielectric constant and loss tangent to minimize cross-talk, while the outer layer has high mechanical strength for protection. Each region's quality is tailored to its local requirement.
3Loss of energy
If Faraday shield is used to constrain fringing fields, then capacitive coupling is reduced, but device complexity increases due to additional conductor and masking layers
Solution Approach 1:
The buffer layer serves as an intermediary dielectric material that naturally constrains fringing fields through its low dielectric constant properties, eliminating the need for active Faraday shields with their complex conductor and masking layer structures.
Solution Approach 2:
The buffer layer is a simple, thin dielectric coating that can be applied during wafer fabrication using standard deposition techniques. It is much simpler and more cost-effective than Faraday shields, requiring no additional complex structures.
4Loss of energy
If hollow ceramic or metal packages with air or vacuum space are used, then capacitive loss is minimized, but manufacturing cost increases and mechanical ruggedness decreases
Solution Approach 1:
Instead of using air or vacuum (extreme parameter values), the invention uses a solid buffer layer with optimized dielectric parameters (low constant and loss tangent) that provides similar electromagnetic performance while enabling solid-state manufacturing and better mechanical properties.
Solution Approach 2:
The encapsulation uses a composite structure combining a buffer layer material with specific low-loss dielectric properties and an outer plastic encapsulation material. This composite approach achieves the electromagnetic benefits of air/vacuum packages while maintaining the manufacturing and mechanical advantages of solid encapsulation.
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 low dielectric constant and loss tangent buffer layer effectively reduces capacitive coupling and power loss, improving the performance of semiconductor devices at high frequencies and voltages without increasing complexity or cost, and can be integrated into existing manufacturing processes.
Implementation Method 1
plastic encapsulation having dielectric constant εe and loss tangent δe... buffer layer of lower dielectric constant εbl and/or loss tangent δbl than εe and δe, respectively, of the plastic encapsulation
Data Source
AI summary
Structure and method are provided for plastic encapsulated semiconductor devices having a buffer layer of low dielectric constant and/or low loss tangent material separating the die surface from the plastic encapsulation. Semiconductor wafers with substantially completed SC die are coated with the buffer layer. The buffer layer is patterned to expose the die bonding pads but leave the buffer layer over some or all of the other die metallization. The die are then separated, mounted on a lead-frame or other support, wire bonded or otherwise coupled to external leads, and encapsulated. The plastic encapsulation surrounds the die and the buffer layer, providing a solid structure. The buffer layer reduces the parasitic capacitance, cross-talk and loss between metallization regions on the die. An optional sealing layer may also be provided at the wafer stage between the buffer layer and the plastic encapsulation to mitigate any buffer layer porosity.