Embedded Chip Interconnects Using Thixotropic Epoxy Underfill
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Solution Overview
Problem
Traditional methods for embedding chips in dielectric substrates result in gaps that complicate the connection of chip pads to the substrate, leading to issues like short circuits and limited material choices for gap filling, and require process pauses for filling and planarization.
Innovation Solution
Using conductive epoxy with adhesive and thixotropic properties to create interconnects across the gap, followed by a dielectric liquid underfill to encapsulate and form a dielectric layer, allowing for multilayer structures with additional embedded chips through direct print additive manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conductive ink is used to draw interconnects across the gap, then electrical connection is achieved, but the ink flows into the gap causing short circuits and vulnerability to subsequent dielectric layer printing
Solution Approach 1:
The patent changes the physical and chemical parameters of the conductive material by using thixotropic conductive epoxy instead of regular conductive ink. The thixotropic property causes the material to become less viscous under shear stress (during printing) and more viscous at rest (preventing flow into gaps), while the epoxy formulation provides adhesion and gap-filling capability without causing short circuits
Solution Approach 2:
The patent uses a composite material system combining thixotropic conductive epoxy with dielectric underfill material. The conductive epoxy provides electrical connection while the dielectric underfill encapsulates and protects the interconnects, creating a composite structure that simultaneously achieves electrical connectivity and prevents short circuits
2Ease of manufacture
If gap filling with dielectric material is performed, then material selection flexibility is limited and manufacturing process must be paused for filling and planarization
Solution Approach 1:
The patent merges the gap-filling function with the underfill material application step. The dielectric underfill material simultaneously fills the gap between chip and substrate and provides the encapsulation layer, eliminating the need for separate gap-filling and planarization steps that would interrupt manufacturing continuity
Solution Approach 2:
The dielectric underfill material serves multiple functions: it fills the gap, provides mechanical support, enables thermal management, and creates the dielectric layer for subsequent interconnect printing. This multi-functionality eliminates the need for separate processing steps
3Device complexity
If traditional chip embedding in milled cavity is used, then a gap is created between chip and substrate, but this gap complicates interconnect formation and requires additional processing steps
Solution Approach 1:
The patent changes the approach to gap management by using thixotropic conductive epoxy that can be printed directly across the gap. The material's rheological properties allow it to be deposited in a controlled manner and then remain stationary without flowing, maintaining precise interconnect geometry despite the presence of the gap
Solution Approach 2:
The thixotropic conductive epoxy acts as an intermediary material that bridges the gap between chip and substrate. It provides both mechanical bridging for electrical connection and self-supporting structure that doesn't require the gap to be eliminated or precisely controlled
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 method ensures stable interconnects without short circuits and provides a continuous manufacturing process, enabling the creation of complex integrated circuit packages with multiple layers and vertical interconnects.
Implementation Method 1
The chosen epoxy is adhesive and thixotropic so that it sticks well
Implementation Method 2
The chosen epoxy is adhesive and thixotropic so that it sticks well and won't lose its volume after a drying process
Implementation Method 3
a dielectric liquid is used as an underfill material to not only fully refill the gap underneath and surrounding the embedded integrated circuit chip
Data Source
AI summary
Methods and techniques are provided for using a conductive epoxy to create interconnects across a gap between an embedded integrated circuit chip and a dielectric substrate. The chosen epoxy is adhesive and thixotropic so that it sticks well and won't lose its volume after a drying process. Further, a liquid dielectric ink is used as an underfill material to not only cover and protect the interconnects but also act as a dielectric layer. This allows as for additional dielectric layers with corresponding interconnects and vias to form a multilayer structure with additional embedded chips. The disclosed methods and techniques can be implemented using direct print additive manufacturing processes.