Copper Via Grain Structure for Wiring Board Electromigration Resistance
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Solution Overview
Problem
Electromigration in wiring boards, which occurs due to the movement of conductor atoms induced by current application, leads to vacancies in conductors, reducing the reliability of electronic devices and modules, especially near openings in through-holes where current direction changes and concentrates.
Innovation Solution
A wiring board design featuring an insulation substrate with through-holes filled with a through-conductor and surface wiring conductors, where the average size of Cu crystal grains in the through-conductor is larger than in the wiring conductors, improving electromigration resistance by reducing grain mobility and stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wiring structures with uniform Cu crystal grain size are used, then manufacturing is simpler, but electromigration resistance is poor due to grain mobility and stress concentration near through-hole openings
Solution Approach 1:
The patent applies local quality by creating different Cu crystal grain sizes in different regions: larger grains in the through-conductor and smaller grains in the wiring conductor. This spatial variation in microstructure optimizes electromigration resistance locally where current concentration occurs at through-hole openings, while maintaining manufacturability through selective process control.
Solution Approach 2:
The patent changes the physical parameter of Cu crystal grain size to resolve the contradiction. By controlling the average grain size to be larger in the through-conductor than in the wiring conductor, the invention reduces grain mobility and stress concentration effects, thereby improving electromigration resistance without requiring complete redesign of the manufacturing process.
2Reliability
If Cu crystal grain size is reduced to improve electromigration resistance, then grain mobility decreases, but manufacturing precision requirements increase to control grain size distribution
Solution Approach 1:
Instead of uniformly reducing grain size throughout the entire conductor structure, the patent applies local quality by specifying different grain size requirements for different components: the through-conductor has larger grains while the wiring conductor has smaller grains. This localized approach reduces electromigration risk at critical interfaces without imposing uniform high precision requirements across all manufacturing steps.
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 enhances electromigration resistance by maintaining a small difference in Cu crystal grain size across boundaries, reducing the likelihood of grain movement and improving reliability near through-hole openings, thereby enhancing the durability of electronic devices and modules.
Implementation Method 1
Electromigration is a phenomena in which the movement of conductor atoms induced by current application causes vacancies in conductors of wiring boards
Data Source
AI summary
A wiring board includes an insulation substrate, a through-conductor, and a wiring conductor. The insulation substrate includes a first surface, a second surface opposite to the first surface, and a through-hole extending from the first surface to the second surface. The through-conductor is located in the through-hole and on an opening of the through-hole on a first surface side. The wiring conductor is located on the first surface and connected to the through-conductor. The through-conductor and the wiring conductor contain copper as a main component. The average size of Cu crystal grains in the through-conductor is larger than the average size of Cu crystal grains in the wiring conductor.