Void-Free Through Hole Plating for Fine Line-Spacing PCBs
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Solution Overview
Problem
Conventional methods for forming copper patterns on core layers face limitations in line-spacing and often result in voids within through holes, which hinder the production of smaller and faster electronic devices and can cause reliability failures.
Innovation Solution
The method involves using a conductive electrolysis seed layer and a dry film resist to electroplate copper on both sides of the core, including the through holes, without voids, allowing for finer line-spacing and reducing core line spacing, thereby enabling the production of void-free vias and more flexible electronic package designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If subtractive patterning of electrolytic copper is used, then copper patterns can be formed on core layers, but the line-spacing is limited to 50/50 for 25 um copper traces
Solution Approach 1:
The patent inverts the conventional subtractive patterning approach by using an additive pattern electroplating process. Instead of starting with a complete copper layer and removing material, the invention builds copper patterns directly through electroplating, enabling finer line-spacing while maintaining manufacturing feasibility.
Solution Approach 2:
The patent changes the fundamental process parameter from subtractive to additive manufacturing. By switching from etching-based subtractive patterning to electroplating-based additive patterning, the invention achieves improved line-spacing capability while preserving ease of manufacture through a different technological approach.
2Manufacturing precision
If pattern electroplating process is used to fill through holes, then finer line-spacing can be achieved, but undesirably large voids form in the through holes
Solution Approach 1:
The patent applies preliminary action by first forming a conductive bridge across the through hole before completing the pattern electroplating process. This preliminary bridge formation ensures that subsequent copper deposition occurs uniformly throughout the through hole, preventing void formation while achieving fine line-spacing.
Solution Approach 2:
The conductive bridge acts as an intermediary element that facilitates uniform copper deposition in the through hole. By introducing this intermediate structure, the patent enables complete void-free filling while maintaining the fine line-spacing capability of pattern electroplating.
3Manufacturing precision
If conventional mSAP is used to pattern core layer, then finer line-spacing can be achieved, but voids in through holes cause reliability failures due to unwanted migration
Solution Approach 1:
The patent extracts and eliminates the void formation problem from the pattern electroplating process by introducing the conductive bridge preliminary action. This removal of the harmful void element achieves both fine line-spacing and reliable, migration-free through holes.
Solution Approach 2:
The patent converts the potential harm of void formation into a benefit by using the conductive bridge to promote uniform copper deposition. The preliminary bridge structure transforms what would be a void-prone process into a void-free, reliable filling method that achieves fine line-spacing.
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 achieves void-free through holes, enhances the reliability of electronic packages, and reduces the cost by minimizing the layer count, while protecting dry film resist from damage and allowing for more flexible design options.
Implementation Method 1
covering both sides of the core with a conductive electroless layer
Implementation Method 2
electroplating the core with a conductive material to fill the through hole without voids
Data Source
AI summary
A method that includes electroplating both sides of a core and the through hole of a core with a conductive material to cover both sides of the core with the conductive material and to form a conductive bridge in the through hole, wherein the core has a thickness greater than 200 microns; etching the conductive material that covers both sides of the core to reduce the thickness of the conductive material to about 1 micron; applying a film resist to the core; exposing and developing the resist film to form patterns on the conductive material on both sides of the core; and electroplating additional conductive material on the (i) conductive material on both sides of the core (ii) conductive material within the through hole; and (iii) conductive bridge to fill the through hole with conductive material without any voids and to form conductive patterns on both sides of the core.