Circuit Board Copper Traces With Anisotropic Plating for Fine Pitch
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Solution Overview
Problem
The existing additive process for creating thick copper traces on circuit boards is limited by the height and resolution of dry film, leading to mushroom head shapes and restricted pitch and height capabilities.
Innovation Solution
The method involves forming a seed layer and a first copper layer on a substrate, followed by electroplating a second copper layer with anisotropic growth, where the acid-to-copper ratio and additive content in the electroplating solution are adjusted to achieve a thickness-to-pitch ratio greater than 1, allowing for thicker traces with finer pitches without being constrained by dry film limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the additive method is used to create thick copper traces, then the copper layer height can be increased, but the height is limited by the dry film thickness and the mushroom head shape develops making dry film removal difficult
Solution Approach 1:
The copper trace fabrication process is divided into multiple stages: initial copper layer formation, dry film application and patterning, and controlled electroplating. This segmentation allows each stage to be optimized independently, preventing the mushroom head shape by controlling copper deposition in discrete steps rather than continuous thick plating.
Solution Approach 2:
The dry film is applied and patterned before the final copper plating stage. This preliminary action establishes precise trace boundaries that guide subsequent copper deposition, ensuring that copper grows only within defined areas and preventing the spread that causes mushroom head formation.
2Length of stationary object
If the dry film thickness is increased to allow taller copper traces, then the copper layer height can be increased, but the resolution ability of the dry film decreases
Solution Approach 1:
The electroplating parameters are changed and optimized to achieve anisotropic growth characteristics. By controlling current density, temperature, and plating solution composition, the copper grows preferentially in the vertical direction rather than laterally, enabling tall traces with fine pitch without requiring proportionally thicker dry film.
Solution Approach 2:
The solution promotes vertical growth in the height dimension while maintaining control in the lateral dimension. This dimensional differentiation allows the copper traces to achieve greater height without proportionally increasing the dry film thickness, as the growth is directed primarily upward rather than outward.
3Productivity
If the pitch between traces is reduced to increase circuit density, then more traces can be packed, but the risk of short circuits increases
Solution Approach 1:
The electroplating process creates local quality differences in copper grain structure and morphology. By controlling plating conditions, the copper develops a dense, fine-grained structure with vertical orientation that maintains electrical integrity and prevents bridging between adjacent traces, even at reduced pitch spacing.
Solution Approach 2:
The mechanical constraint approach (relying on dry film physical barriers) is replaced with electrochemical control. The electroplating process uses electrical fields and chemical reactions to precisely control copper deposition, creating well-defined trace edges and preventing lateral spread that would cause short circuits, thereby improving reliability without sacrificing density.
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 enables the fabrication of traces with increased thickness and reduced pitch, overcoming the limitations of dry film thickness and resolution, resulting in thicker copper lines with finer spacing.
Implementation Method 1
a second copper layer is formed by electroplating on the surface of the substrate by the conductive leads
Data Source
AI summary
A circuit board and a manufacturing method therefor. The circuit board includes a substrate and a plurality of traces arranged at intervals on the substrate. Each trace includes a seed layer located on one surface of the substrate, a first copper layer located on the surface of the seed layer away from the substrate, and a second copper layer plated on one surface of the substrate. The second copper layer covers the seed layer and the first copper layer. The ratio of the thickness of each trace to the space between any two adjacent traces is greater than 1. The thickness of the second copper layer in the thickness direction of the substrate is greater than the thickness of the second copper layer in a direction perpendicular to the thickness direction of the substrate.