Angled Interconnect Pillars for Thermal Stress Relief
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Solution Overview
Problem
The coefficient of thermal expansion (CTE) mismatch between integrated circuit (IC) chips and packaging materials leads to stress and potential crack formation in interconnect joints, particularly in flip chip processing, due to the use of solder bumps and other materials, which are insufficiently addressed by existing corrective designs.
Innovation Solution
The implementation of IC structures with angled interconnect elements, such as conductive pillars and springs, extending from the IC chip surface, where a first plurality is oriented perpendicularly and a second plurality is oriented non-perpendicularly relative to a radial centerline axis, providing stress relief and accommodating thermal expansion mismatches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder bumps are used to connect IC dies to packaging, then electrical connection is achieved, but stress and crack formation occur due to CTE mismatch
Solution Approach 1:
The interconnect structure is segmented into multiple functional layers: conductive pillars extending from the die, solder bumps at the packaging interface, and optional intermediate structures. This segmentation allows each layer to handle specific stress types, with the pillars providing rigid support and the solder providing compliant stress relief, thereby resolving the contradiction between connection reliability and joint strength.
Solution Approach 2:
The interconnect structure uses composite materials combining different metals with complementary properties: copper or tungsten pillars for high strength and low CTE matching the die, tin-silver-copper solder for ductility and stress absorption, and optional nickel or palladium diffusion barriers. This composite approach enables the structure to simultaneously achieve reliable electrical connection and resistance to stress-induced cracking.
2Stress or pressure
If CTE-matching materials are used to reduce stress, then stress relief is improved, but manufacturing complexity increases due to material constraints
Solution Approach 1:
Different materials with optimized CTE properties are assigned to specific locations: low-CTE copper or tungsten pillars at the die interface to match silicon thermal expansion, medium-CTE nickel or palladium barrier layers in the intermediate region, and high-CTE tin-silver-copper solder at the packaging interface. This local quality approach reduces thermal stress while avoiding the need to constrain the entire structure to a single CTE value, thereby reducing material selection complexity.
Solution Approach 2:
The invention changes the CTE parameter gradient through the interconnect structure height, creating a progressive transition from low-CTE materials near the die to high-CTE materials near the packaging. This parameter change strategy allows each material layer to accommodate its local thermal expansion requirements, reducing overall stress while using commercially available materials with standard CTE values, thus avoiding excessive manufacturing complexity.
3Duration of action of stationary object
If angled interconnect elements are used to provide stress relief, then fatigue life is extended, but manufacturing precision requirements increase
Solution Approach 1:
The interconnect structure incorporates dynamic characteristics through the angled pillars and compliant solder joints that can deflect and rotate under thermal stress. This dynamic behavior allows the structure to adapt to thermal expansion mismatches in real-time, extending fatigue life. The manufacturing precision requirement is reduced because the structure self-adjusts during operation, tolerating reasonable variations in pillar angle and position.
Solution Approach 2:
The invention transitions from traditional vertical (one-dimensional) interconnect pillars to angled pillars with radial orientation (adding angular dimension). This dimensional change allows stress relief in multiple directions simultaneously, extending fatigue life. The radial orientation pattern provides isotropic stress distribution, reducing sensitivity to precise manufacturing angles compared to fixed-orientation angled pillars.
4Stress or pressure
If radial orientation of conductive pillars is used to align with thermal expansion, then stress relief is improved, but interconnect density is reduced
Solution Approach 1:
The radially oriented conductive pillars serve multiple functions simultaneously: providing electrical connection, mechanical support, and thermal stress relief in all radial directions. This multi-functionality allows fewer pillars to achieve the same stress relief effect that would require more densely packed isotropic pillars, compensating for the reduced interconnect density with enhanced per-pillar efficiency.
Solution Approach 2:
The radial orientation of conductive pillars is specifically designed to align with the radial thermal expansion pattern of the circular IC die during heating. As the die expands radially outward from its center, the pillars oriented in radial directions naturally accommodate this expansion, reducing shear stress. This thermal expansion alignment provides efficient stress relief with moderate pillar density, as each pillar optimally handles stress in its specific radial direction.
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
This configuration reduces strain and extends the fatigue life of IC chip-to-packaging components by aligning stress relief with thermal expansion directions, effectively mitigating the risks of crack formation and material strain during temperature changes.
Implementation Method 1
due to the coefficient of thermal expansion (CTE) differences between the IC die and the packaging
Implementation Method 2
provide stress relief and accommodating thermal expansion mismatches
Data Source
AI summary
Aspects of the present disclosure include integrated circuit (IC) structures with angled interconnect elements. An IC structure according to the present disclosure can include: an IC chip interconnect surface including a radially inner region positioned within a radially outer region; and a plurality of conductive pillars extending outward from the radially inner region of the IC chip interconnect surface, relative to a radial centerline axis of the radially inner region of the IC chip interconnect surface, wherein the radially inner region of the IC chip interconnect surface is free of conductive pillars thereon.