Conductive Pillar Solder Element CTE Mismatch Stress
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Solution Overview
Problem
Conventional die-to-die electrical interconnections in microelectronic devices often lack sufficient compliance, leading to stress and cracking due to coefficient of thermal expansion (CTE) mismatch during assembly and operation.
Innovation Solution
The use of electrically conductive pillars with a solder element, such as a Tin alloy, sandwiched between traditional conductive materials like Cu or Ag alloys, which becomes compliant during reflow to absorb stress caused by CTE mismatch, reducing the likelihood of die cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional rigid conductive materials (Cu, Ag alloys) are used for electrical interconnections, then electrical conductivity is maintained, but stress from CTE mismatch causes die cracking
Solution Approach 1:
The patent uses a composite interconnection structure consisting of a solder element (Sn, SnAg, SnCu, or SnAgCu alloy) combined with traditional conductive materials (Cu or Ag alloy). This composite structure provides both the electrical conductivity needed and the compliance to absorb CTE mismatch stresses, preventing die cracking while maintaining functional performance.
Solution Approach 2:
The patent changes the material parameter of the interconnection from rigid (traditional Cu/Ag alloys) to compliant (solder materials with lower melting points and higher ductility). The solder element can undergo plastic deformation and phase changes during reflow, allowing it to absorb thermal expansion stresses that would otherwise cause die cracking in rigid structures.
2Strength
If high stiffness materials are used in die packages, then structural support is provided, but CTE mismatch stress increases during assembly
Solution Approach 1:
The compliant interconnection structure acts as an intermediary element between the first die package (with high stiffness materials) and the second die package. This intermediate structure absorbs the stress generated by CTE mismatch during assembly and thermal cycling, protecting the rigid die packages from cracking while maintaining structural integrity.
3Reliability
If compliant interconnection structures are used, then CTE mismatch stress is absorbed, but manufacturing complexity increases
Solution Approach 1:
The patent applies compliance selectively at the interconnection level rather than throughout the entire die package structure. The solder elements are placed specifically at the electrical interconnection points where stress absorption is most critical, while the bulk die package materials can remain rigid for structural support. This localized approach provides stress absorption without requiring complex changes to the overall device architecture.
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 solution effectively reduces the risk of die cracking and other CTE-related failures by providing a compliant interconnection structure that can absorb thermal expansion mismatch stresses during assembly and operation.
Implementation Method 1
Electrical interconnections with improved compliance due to stress relaxation
Implementation Method 2
coefficient of thermal expansion (CTE) mismatch between and within microelectronic devices
Data Source
AI summary
According to various embodiments of the present disclosure, an electrically conductive pillar having a substrate is disclosed. The electrically conductive pillar can comprise a first portion, second portion and a third portion. The first portion and/or third portion can be formed of an electrically conductive material that can be the same or different. The second portion can be intermediate and abut both the first portion and the third portion. The second portion can comprise a solder element formed of a second electrically conductive material that differs from the electrically conductive material and has a second stiffness less than a stiffness of the electrically conductive material.