Galvanic Through-Hole Filling via Segmented Pulse Current
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Solution Overview
Problem
Current processes for filling through-holes in printed circuit boards are inefficient, leading to inclusions and high process costs, especially in miniaturized circuits with varying drill hole diameters, and fail to provide durable, solvent-free, and thermally conductive fillings.
Innovation Solution
A two-step galvanic process involving a metal-deposition electrolyte with pulse reverse current and phase-shift, where the first step creates blind holes in the center of through-holes and the second step fills these holes with metal, using copper sulfate, sulfuric acid, and specific additives to achieve a pure metal layer with improved adhesion and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional galvanic processes are used to fill through-holes, then the filling process is simple, but inclusions occur and thermal conductivity is insufficient
Solution Approach 1:
The galvanic filling process is divided into multiple sequential steps with different current densities: a first galvanic filling step with a first current density, followed by a second galvanic filling step with a second current density. This segmentation allows each step to optimize for different aspects - the first step establishes basic fill while the second step eliminates inclusions and improves thermal conductivity, thereby resolving the contradiction between filling quality and process complexity.
Solution Approach 2:
The process employs periodic alternation between different current density regimes. By switching between the first current density (for initial filling) and the second current density (for inclusion removal and thermal conductivity enhancement), the process achieves high reliability filling quality through controlled periodic variation, accepting increased process complexity as a necessary trade-off.
2Productivity
If high current density is used to fill through-holes quickly, then productivity increases, but inclusions are formed in the filling
Solution Approach 1:
The filling process is segmented into two distinct phases: the first galvanic filling step uses higher current density to achieve rapid filling and maintain productivity, while the second galvanic filling step uses lower current density to remove inclusions and ensure filling quality. This segmentation allows both high productivity and high reliability to be achieved sequentially.
Solution Approach 2:
The process uses periodic alternation between high current density (for speed) and low current density (for quality). By implementing this periodic action with two sequential steps, the patent resolves the contradiction by ensuring that the quality-critical phase occurs after the productivity-critical phase, achieving both goals.
3Reliability
If multiple galvanic filling steps with different current densities are used, then inclusion-free filling with good thermal conductivity is achieved, but process complexity increases
Solution Approach 1:
The process segments the filling operation into two targeted steps: the first step establishes the fill structure, and the second step optimizes thermal conductivity and removes inclusions. This segmentation achieves high reliability filling quality while maintaining reasonable productivity by avoiding unnecessary additional steps.
Solution Approach 2:
The process changes the current density parameter between two sequential steps. By optimizing each step's current density independently - higher for initial filling, lower for quality enhancement - the patent achieves superior filling quality without excessive process complexity, balancing reliability and productivity.
4Ease of manufacture
If solvent-based fillers are used, then ease of manufacture is improved, but solvent inclusions occur that cause defects under thermal stress
Solution Approach 1:
The process replaces chemical-based solvent fillers with electrochemically deposited metal filling. By substituting the chemical mechanism (solvent evaporation) with an electrochemical mechanism (galvanic deposition), the patent eliminates solvent inclusions and their associated thermal stress defects, achieving high thermal stability while maintaining manufacturing feasibility through controlled electrochemical processes.
Solution Approach 2:
The process changes the fundamental parameter of filling material from solvent-based dielectric to metal deposition. This parameter change eliminates the thermal expansion mismatch and solvent inclusion problems inherent in solvent-based fillers, achieving superior thermal stability. The two-step galvanic process with varying current densities ensures complete, inclusion-free metal filling.
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 process reliably fills through-holes with minimal inclusions, achieving high integration density and electrical properties, reducing process costs and enabling efficient metallization with copper, even in small diameters, while maintaining thermal conductivity and avoiding solvent-related issues.
Implementation Method 1
Bringing in contact the workpiece containing through-holes with a metal-deposition electrolyte and applying a voltage between the workpiece and at least one anode so that a current flow is supplied to the workpiece, wherein the current flow is chosen such that in accordance with FIG. 1 a preferred deposition occurs in the center of the through-holes
Implementation Method 2
A two-step galvanic process involving a metal-deposition electrolyte with pulse reverse current and phase-shift, where the first step creates blind holes in the center of through-holes and the second step fills these holes with metal
Data Source
AI summary
The present invention relates to a galvanic process for filling through-holes with metals. The process is particularly suitable for filling through-holes of printed circuit boards with copper. The process comprises the following steps: (i) formation of a narrow part in the center of a through-hole by electroplating; and (ii) filling the through-hole obtained in step (i) with metal by electroplating.