Direct Current Electroplating Through-Hole Filling
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Solution Overview
Problem
The challenge in filling through-holes in printed circuit boards with copper plating is the formation of voids and dimples due to incomplete filling, which affects the reliability and electrical properties of the devices, especially in thicker substrates, and the inefficiency of using multiple electroplating baths for this process.
Innovation Solution
A direct current electroplating method involving a high current density for an initial period followed by a lower current density for a prolonged period, applied to substrates with a layer of electroless copper, to inhibit dimple and void formation, and improve uniformity of the copper layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional direct current plating is used to fill through-holes, then the process is simple and fast, but it results in incomplete filling with voids and dimples forming
Solution Approach 1:
The patent applies periodic action by using pulsed direct current plating with alternating high and low current density cycles. The high current density phase promotes copper deposition into through-holes, while the low current density phase allows diffusion and reduces void formation. This periodic variation in current density achieves complete through-hole filling with minimal voids and dimples, resolving the contradiction between filling completeness and process simplicity.
2Productivity
If high current density is applied continuously, then copper deposition speed increases, but voids and dimples form due to uneven deposition
Solution Approach 1:
The patent uses periodic action by alternating between high current density phases (which provide fast deposition speed) and low current density phases (which ensure uniform deposition and prevent void formation). This periodic cycling allows the system to achieve both high productivity and high deposition uniformity, resolving the contradiction between these two parameters.
Solution Approach 2:
The patent applies dynamics by making the current density variable rather than static. The system dynamically adjusts current density between high and low phases during the plating process, allowing optimal deposition conditions to be maintained throughout the through-hole filling process. This dynamic approach enables both fast deposition and uniform coverage.
3Length of stationary object
If substrate thickness increases beyond 100 μm, then more applications are needed for complete filling, but void area increases to 10-15%
Solution Approach 1:
The patent applies periodic action with multiple cycles of high and low current density phases. Each cycle promotes copper deposition while the alternating phases prevent void formation. This periodic approach allows complete filling of thick substrates (200 μm and greater) while maintaining low void area, resolving the contradiction between substrate thickness and void prevention.
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 method reduces dimple depth and void area, ensuring complete filling of through-holes with minimal defects, enhancing the throwing power and uniformity of the copper layer, and preventing nodule formation, even in substrates with thicknesses up to 300 µm.
Implementation Method 1
immersing the substrate in a copper electroplating bath; and filling the through-holes with copper by a direct current cycle comprising applying a current density for a first predetermined period of time followed by applying a lower direct current density
Implementation Method 2
providing a substrate with a plurality of through-holes including a layer of electroless copper, copper flash or combinations thereof on a surface of the substrate and walls of the plurality of through-holes
Data Source
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AI summary
Direct current plating methods inhibit void formation, reduce dimples and eliminate nodules. The method involves electroplating copper at a high current density followed by electroplating at a lower current density to fill through-holes.