Particle-filled Through Silicon Vias for Thermal Expansion Control
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Solution Overview
Problem
The mismatch in coefficients of thermal expansion (CTE) between copper and silicon in through silicon vias leads to mechanical stress and failures such as delamination and die cracking due to temperature excursions, which can degrade integrated circuit performance and increase costs by requiring larger die sizes or reduced via density.
Innovation Solution
The use of particle-filled through silicon vias with a composite bulk material having a reduced CTE, achieved by embedding particles with a lower CTE than copper within a copper matrix, which reduces thermal expansion and stress, while maintaining electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used to fill through silicon vias, then electrical conductivity is improved, but thermal expansion mismatch causes mechanical stress and reliability degradation
Solution Approach 1:
The patent applies composite materials by filling the through silicon via with a composite material consisting of copper particles embedded in a solder matrix, rather than using pure copper. This composite structure allows the via material to have both good electrical conductivity (from copper particles) and reduced thermal expansion mismatch (from the solder matrix with lower CTE than pure copper), thereby resolving the contradiction between conductivity and thermal expansion compatibility
Solution Approach 2:
The patent changes the physical and chemical parameters of the via fill material by using a composite composition with controlled particle size, volume fraction, and material properties. By adjusting the copper particle concentration and solder matrix composition, the effective CTE of the via material can be tuned to better match silicon, while maintaining adequate electrical conductivity, thus resolving the thermal expansion mismatch problem
2Reliability
If via size is reduced to maintain stress below critical levels, then thermal stress is reduced, but die density and productivity decrease
Solution Approach 1:
By using composite via fill material with tailored CTE properties, smaller via sizes can be used without exceeding critical stress levels. The composite material's reduced thermal expansion allows higher via density on the die while maintaining stress control, thereby improving die density and productivity without sacrificing reliability
3Reliability
If via spacing is increased to reduce thermal stress, then mechanical failures are prevented, but die area increases and density decreases
Solution Approach 1:
The composite via fill material with reduced CTE allows smaller spacing between adjacent vias while preventing thermal stress-induced failures. This enables higher via density within the same die area, reducing the overall die area required for a given functionality and improving area utilization
4Reliability
If copper volume fraction is increased to improve conductivity, then electrical performance is enhanced, but thermal expansion mismatch increases
Solution Approach 1:
The patent optimizes the copper particle volume fraction within the solder matrix to achieve a balance between electrical conductivity and thermal expansion compatibility. By controlling the copper content and distribution in the composite, adequate conductivity is maintained while the solder matrix provides CTE buffering to reduce thermal expansion mismatch with silicon
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 approach significantly reduces mechanical stress and enhances the reliability of integrated circuits by minimizing thermal expansion mismatch, allowing for higher density and smaller via sizes without compromising performance.
Implementation Method 1
Many materials may undergo a physical expansion or contraction resulting from a change in temperature. A coefficient of thermal expansion (CTE) may represent a change in unit volume of a bulk material for a unit change in temperature.
Implementation Method 2
The use of particle-filled through silicon vias with a composite bulk material having a reduced CTE, achieved by embedding particles with a lower CTE than copper within a copper matrix
Data Source
AI summary
A method, apparatus and system with an electrically conductive through hole via of a composite material with a matrix forming a continuous phase and embedded particles, with a different material property than the matrix, forming a dispersed phase, the resulting composite material having a different material property than the matrix.