Ceramic Wiring Board Structure to Suppress Silver Electromigration
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Solution Overview
Problem
The adhesiveness between a ceramic substrate and a copper-based conductor pattern is inadequate, and the migration of silver in the conductor pattern leads to unreliable electrical characteristics and potential short-circuits due to electromigration.
Innovation Solution
A wiring board structure is implemented with a base metal layer containing titanium and chromium, along with copper, where the silver content in the metal layer is minimized, and the side surfaces of the base metal layer are covered by a copper-rich metal layer to enhance bonding strength and prevent silver migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If silver is added to the conductor pattern to improve adhesiveness between the ceramic substrate and the conductor pattern, then the adhesiveness is improved, but silver migration occurs leading to unreliable electrical characteristics
Solution Approach 1:
The conductor pattern is segmented into two distinct layers: a base metal layer containing silver for adhesion to the ceramic substrate, and a copper-rich metal layer with minimal silver for electrical conduction. This segmentation isolates the silver to the base layer where it provides adhesion benefits while preventing its migration into the electrical conduction path.
Solution Approach 2:
Different regions of the conductor pattern are assigned different material compositions optimized for their specific functions. The base metal layer has high silver content (5-30 wt%) for maximum adhesiveness to the ceramic substrate, while the metal layer has low silver content (0-5 wt%) to ensure electrical reliability and prevent migration.
2Strength
If a base metal layer containing silver is formed to improve bonding strength, then the bonding strength is improved, but silver migration causes potential short-circuits
Solution Approach 1:
The copper-rich metal layer acts as an intermediary barrier between the silver-containing base metal layer and the electrical conduction path. This intermediate layer allows the base layer to provide bonding strength through silver while the copper layer prevents silver atoms from migrating into the electrical circuit, thus eliminating the harmful effect.
Solution Approach 2:
Silver is extracted and concentrated exclusively in the base metal layer, removing it from the metal layer that performs electrical conduction. This extraction eliminates the source of migration problems in the electrical path while preserving silver's adhesion benefits in the base layer.
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 structure improves the bonding strength between the ceramic substrate and the conductor pattern while effectively suppressing electromigration, ensuring higher electrical reliability and preventing short-circuits.
Implementation Method 1
forming a first base metal layer by firing the first base metal paste
Implementation Method 2
forming a first metal layer by firing the first metal paste
Data Source
AI summary
A wiring board includes a ceramic substrate having an upper surface and a lower surface and a conductor pattern formed on the upper surface of the ceramic substrate. The conductor pattern includes a base metal layer formed on the upper surface of the ceramic substrate and a metal layer formed on the upper surface of the ceramic substrate so as to entirely cover the base metal layer. The base metal layer contains at least one of titanium and chromium in addition to copper and silver. The metal layer contains copper as a main component, and a weight percentage of silver contained in the metal layer is smaller than a weight percentage of silver contained in the base metal layer. Side surfaces of the base metal layer are covered with the metal layer.