Through Wiring Adhesion Layer for Thermal Expansion Mismatch
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Solution Overview
Problem
Conventional methods for forming through wiring in silicon substrates face issues with conductive failure due to thermal expansion differences between silicon and copper, leading to copper removal from inner side surfaces of through holes, and also result in defects like seams and voids, especially at high aspect ratios.
Innovation Solution
A wiring board structure featuring a substrate with through holes, where a first metal layer is formed on one side of the inner surface, a first wiring layer covers it, a second metal layer is formed on the other side, and a second wiring layer covers that, with both layers being electrically connected via the second metal layer, using adhesion layers to enhance copper adherence and reduce defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is deposited in a through hole using electrolytic plating process with a conductive layer as seed layer, then the through wiring is formed, but the copper does not adhere to the inner side surface of the through hole, causing conductive failure due to thermal expansion differences
Solution Approach 1:
An adhesion layer is introduced as an intermediary between the copper wiring layer and the inner side surface of the through hole. This adhesion layer has good adhesion to both the copper and the substrate, preventing copper from detaching during thermal cycling while maintaining electrical conductivity.
Solution Approach 2:
A composite structure is formed by combining multiple materials with different properties: the conductive layer (seed layer), the adhesion layer (with intermediate thermal expansion properties), and the copper wiring layer. This composite structure resolves the thermal expansion mismatch between copper and the silicon substrate.
2Reliability
If an insulating layer is formed on the surface including the inner side surface of the through hole with a seed layer having good adhesion, then the pumping phenomenon of copper is suppressed and conductive failure is reduced, but the likelihood of generation of defects such as seams and voids in the through wiring is increased
Solution Approach 1:
The adhesion layer is applied selectively only to the inner side surface of the through hole where copper deposition occurs, rather than covering the entire substrate surface. This localized application ensures good adhesion where needed while avoiding interference with the plating process and reducing defect formation.
3Length of moving object
If the aspect ratio of the through hole becomes high, then the through wiring can connect opposite surfaces, but the likelihood of generation of defects such as seams and voids becomes high
Solution Approach 1:
The adhesion layer serves as a mediator that promotes uniform copper deposition along the entire length of the through hole, including the difficult-to-reach regions in high aspect ratio holes. This ensures continuous wiring without seams or voids even in deep through holes.
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 suppresses conductive failures and defect generation, such as seams and voids, even at high aspect ratios, by ensuring strong adhesion and reduced copper removal due to thermal expansion, while maintaining high-intensity bonding between the wiring layers.
Implementation Method 1
the difference between coefficients of thermal expansion of silicon and copper
Implementation Method 2
a seed layer whose adhesion to the insulating layer is good is formed
Implementation Method 3
copper (Cu) is deposited in a through hole provided in the silicon substrate by electrolytic plating process using the conductive layer as a seed layer
Implementation Method 4
the through wiring is formed in the through hole by filling plating
Data Source
AI summary
A wiring board includes a substrate body provided with a through hole penetrating the substrate body from one surface to another surface; and a through wiring formed in the through hole and including a first metal layer formed on a part of an inner side surface of the through hole at the one surface side, a first wiring layer that covers the first metal layer to fill a part of the through hole at the one surface side, a second metal layer continuously formed on the rest part of the inner side surface of the through hole at the other surface side and on an end portion of the first wiring layer at the other surface side, and a second wiring layer that covers the second metal layer to fill a part of the through hole at the other surface side.