Flip Chip Assembly with Interposer for High Frequency Performance
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Solution Overview
Problem
The use of underfill materials in flip chip assemblies can impair the performance of monolithic microwave integrated circuits (MMICs) operating at high frequencies due to differences in permittivity and dissipation factor compared to air, causing performance degradation in RF characteristics and parasitic changes.
Innovation Solution
Relocating the underfill away from the flip chip by using an interposer that matches the footprint of the flip chip, allowing a space free of underfill material between the flip chip and the interposer, and incorporating passive components on the interposer to improve electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If underfill material is used between flip chip and carrier substrate, then mechanical strength and CTE mismatch compensation are improved, but RF performance and electrical characteristics deteriorate due to permittivity differences
Solution Approach 1:
The underfill material is extracted and removed from the space between the flip chip and carrier substrate. This eliminates the harmful dielectric effects of the underfill on RF signals while the interposer provides alternative mechanical support and CTE compensation functions without compromising electrical performance.
Solution Approach 2:
An interposer is introduced as an intermediary component between the flip chip and carrier substrate. The interposer serves as a mediator that provides mechanical strength and CTE mismatch compensation through its structural properties, while allowing the flip chip to operate in an air environment for optimal RF performance.
2Object-affected harmful factors
If underfill material is used between flip chip and carrier substrate, then moisture protection is improved, but electrical performance and signal integrity worsen
Solution Approach 1:
The underfill material is removed from the critical RF path between flip chip and carrier substrate, eliminating its harmful dielectric effects on signal integrity while alternative moisture protection methods are employed that do not compromise electrical performance.
Solution Approach 2:
Different regions of the assembly have different properties: the space between flip chip and carrier substrate is kept air-filled for optimal RF performance, while moisture protection is provided locally through conformal coatings or encapsulation layers that do not interfere with electrical signals.
Data Source
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AI summary
A system for improving flip chip performance is provided. In one embodiment, the invention relates to an assembly configured to improve performance of a flip chip device, the assembly including a semiconductor die having an active surface and a back surface, the active surface including a plurality of conductive pads, an interposer substrate having a first surface in electrical contact with the active surface of the semiconductor die and a second surface, a space between the active surface of the semiconductor die and the first surface of the interposer substrate, where the space is essentially free of underfill material, and a carrier substrate having a top surface in electrical contact with the second surface of the interposer.