Silicon Interposer Through-Hole Electrodes Thermal Stress Relief
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Solution Overview
Problem
The difference in thermal expansion coefficients between copper-filled through-hole electrodes and silicon oxide insulating films in semiconductor devices leads to thermal stress and cracking issues, while using alternative materials like iron or nickel alloys compromises high-frequency characteristics and density requirements.
Innovation Solution
A silicon interposer with through-hole electrodes featuring a base section and a buffer section made of conductive materials, where the buffer section has a lower elastic coefficient than the base section, primarily using solder as the buffer material to absorb thermal stress, and is formed using electrolytic plating or paste injection methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used for through-hole electrodes, then electrical conductivity and density requirements are met, but thermal stress and cracking occur due to significant difference in thermal expansion coefficient with silicon oxide insulating film
Solution Approach 1:
The through-hole electrode is constructed as a composite structure with multiple material layers: a copper base section for electrical conductivity and a solder buffer section for thermal stress relief. This composite configuration allows the electrode to simultaneously achieve good electrical properties and thermal stress resistance by combining materials with different characteristics.
Solution Approach 2:
A solder buffer section is introduced as an intermediary layer between the copper electrode and the silicon oxide insulating film. This intermediate layer has a thermal expansion coefficient intermediate between copper and silicon oxide, serving as a transition zone that gradually relieves thermal stress and prevents direct contact between the two materials with vastly different expansion coefficients.
2Strength
If iron or nickel alloy is used for through-hole electrodes to match thermal expansion coefficient with insulating film, then thermal stress is reduced, but high frequency characteristics deteriorate due to high electric resistance and magnetic properties
Solution Approach 1:
Different sections of the through-hole electrode have different material properties optimized for their specific functions: the base section uses copper for electrical conductivity, while the buffer section uses solder for thermal stress relief. This local differentiation allows each part to have the quality needed for its specific role without compromising overall performance.
3Strength
If insulating film material is changed to solve thermal expansion mismatch, then thermal stress is reduced, but density requirements cannot be met as silicon oxide is required for high density wiring patterns
Solution Approach 1:
The through-hole electrode is segmented into multiple sections with different materials: the base section (copper) and the buffer section (solder). This segmentation allows the electrode to fulfill multiple functions - electrical conductivity from the copper base and thermal stress relief from the solder buffer - without requiring changes to the insulating film material that would compromise density.
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 effectively relieves thermal stress at the connection sections between through-hole electrodes and insulating films, preventing cracks and maintaining high electrical reliability even under repeated thermal loads, while allowing for the use of copper and silicon oxide materials that meet density and frequency requirements.
Implementation Method 1
the buffer section is formed of a conductive material having an elastic coefficient lower than that of the conductive material of the base section
Implementation Method 2
after through-hole electrodes are formed in a silicon board, a first metal layer is formed on one face side of the silicon board and a protective tape is attached, and the first metal layer is filled into the through-hole electrodes from the other face side of the silicon board by carrying out electrolytic plating
Data Source
Figure 1A~1D
Figure 2A~2D
Figure 3A~3D
AI summary
A silicon interposer 30 being held between a wiring board 40 and a semiconductor element 60 to electrically connect the wiring board 40 to the semiconductor element 60, wherein through-hole electrodes 17 for electrically connecting the wiring board 40 to the semiconductor elements 60 are each formed of a base section and a buffer section, and the buffer section is formed of a conductive material having an elastic coefficient lower than that of the conductive material of the base section, and a semiconductor device package 50 and a semiconductor device 70 incorporating the silicon interposer 30.