Multilayer Substrate Via Bonding Through Selective Ni Layer Removal
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Solution Overview
Problem
The existing method of manufacturing multilayer substrates often results in low bonding strength between conductor patterns and vias due to insufficient diffusion layers, which can be inhibited by surface metal layers like the Ni layer on the insulating substrate.
Innovation Solution
A method that involves preparing an insulating substrate with a conductor pattern on one side and a surface metal layer of higher activation energy than the via forming material and Cu, removing the surface metal layer at the via hole bottom before filling, and then sintering to form diffusion layers between the conductor patterns and vias during the stacking and heating process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ni layer is formed on the conductor pattern surface to prevent Cu diffusion into solder, then soldering reliability is improved, but diffusion layer formation between conductor pattern and via is inhibited
Solution Approach 1:
The surface metal layer is segmented into two functional zones: it is removed from the via hole bottom area to allow diffusion layer formation, while being retained on the conductor pattern surface to prevent Cu diffusion into solder. This spatial segmentation resolves the contradiction by allowing both functions to coexist in different locations.
Solution Approach 2:
The surface metal layer is treated differently in different locations: absent at the via hole bottom where diffusion is needed, and present on the conductor pattern surface where diffusion prevention is needed. This local differentiation allows the same material to serve opposing functions in different spatial contexts.
2Ease of manufacture
If the via forming material is heated to form vias, then via formation is achieved, but insufficient diffusion layers are formed between conductor patterns and vias
Solution Approach 1:
The surface metal layer is removed in advance before via formation, preparing the via hole bottom surface to receive the via forming material and enable subsequent diffusion layer formation during heating. This preliminary action ensures that when heating occurs, diffusion can proceed without barrier.
Solution Approach 2:
The heating parameters are optimized to achieve both via formation and sufficient diffusion layer formation. The heating process is controlled to provide adequate temperature and time for diffusion to occur between the via forming material and conductor pattern, transforming the material state to enable atomic-level mixing and bonding.
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 ensures the formation of sufficient diffusion layers, enhancing the bonding strength between conductor patterns and vias, thereby reducing the occurrence of multilayer substrates with low attachment strength.
Implementation Method 1
the stacked body is heated while being subjected to pressure
Implementation Method 2
the stacked body is heated while being subjected to pressure
Implementation Method 3
The via forming material is then heated. As a result, vias are formed, constituted of an alloy
Implementation Method 4
the plurality of insulating substrates become integrated, while the plurality of metal particles are sintered to form vias
Implementation Method 5
diffusion layers are formed between the conductor patterns and the vias by mutual diffusion of the Sn element in the via forming material and the Cu element in the conductor patterns
Implementation Method 6
The Ni layer functions as a diffusion barrier layer that prevents this diffusion of the Cu element
Data Source
AI summary
In a preparatory process of a method of manufacturing a multilayer substrate, an insulating substrate is prepared, with a conductor pattern formed only on one surface of the insulating substrate. At that time, the conductor pattern is constituted of the Cu element, a Ni layer is formed on the surface of the conductor pattern that is on the side of the insulating substrate. In a first forming process, a via hole having the conductor pattern as the bottom thereof is formed in the insulating substrate. At that time, the Ni layer that is in the area of the bottom is removed. In a filling process, a conductive paste is filled in the interior of the via hole. In a second forming process, a stacked body is formed by stacking a plurality of the insulating substrates. In a third forming process, the stacked body is heated while being subjected to pressure.