Printed Wiring Board Substrate With Local Palladium for Fine-Pitch Vias
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Solution Overview
Problem
Conventional printed wiring boards face challenges in forming wiring lines at a fine pitch while ensuring reliable conduction between lines on different surfaces.
Innovation Solution
A substrate for printed wiring boards is designed with a base film having controlled palladium distribution, where the palladium content is lower on the main surfaces and higher on the inner wall surfaces of through holes, allowing for the formation of conductive layers that enable fine pitch wiring with reliable connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional substrate structures are used, then manufacturing is simpler, but wiring lines cannot be formed at fine pitch with reliable conduction
Solution Approach 1:
The base film is designed with non-uniform palladium distribution, where the inner wall surface of through holes has higher palladium content than the main surfaces. This local quality variation enables electroless copper plating to form reliable conductive paths in through holes while maintaining fine pitch wiring capability on the main surfaces, resolving the contradiction between fine pitch manufacturing precision and conduction reliability.
2Ease of manufacture
If uniform palladium distribution is used in the base film, then manufacturing is easier, but undercut occurs during electroless copper plating
Solution Approach 1:
Instead of uniform palladium distribution, the invention implements localized palladium enrichment at the inner wall surfaces of through holes. This non-uniform distribution compensates for the geometry-induced plating non-uniformity, preventing undercut formation during electroless copper plating while maintaining manufacturing feasibility through controlled palladium application processes.
3Reliability
If higher palladium content is used throughout the base film, then electroless copper plating is more effective, but cost increases and manufacturing complexity increases
Solution Approach 1:
The invention applies palladium selectively at the inner wall surfaces of through holes rather than uniformly throughout the entire base film. This localized application reduces the total palladium quantity required, lowering cost and simplifying manufacturing, while still achieving effective electroless copper plating where it is most needed for conduction reliability.
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
The substrate enables the formation of wiring lines at a fine pitch with reduced undercut, ensuring reliable electrical connections between layers.
Implementation Method 1
a third electroless copper plating layer disposed on an inner wall surface of the through hole
Data Source
AI summary
A substrate for a printed wiring board comprises: a base film having a first main surface and a second main surface; a first conductive layer disposed on the first main surface; a second conductive layer disposed on the second main surface; a first electroless copper plating layer disposed on the first conductive layer; a second electroless copper plating layer disposed on the second conductive layer; and a third electroless copper plating layer. In the base film, a through hole extending through the base film along a thickness direction of the base film is formed. The third electroless copper plating layer is disposed on an inner wall surface of the through hole. An amount of palladium in the base film at each of the first main surface and the second main surface is smaller than an amount of palladium in the base film at the inner wall surface.