Through-Hole Copper Plating Void Reduction via Current Density Cycling
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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, especially in thicker substrates, due to incomplete filling and undesirable conformal deposition, which affects the reliability and electrical properties of the devices.
Innovation Solution
A direct current electroplating method is applied with a high current density for a predetermined period followed by a pause and then a lower current density for a longer period, reducing voids and dimples, and inhibiting nodule formation, while using a single copper electroplating bath to improve through-hole filling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional direct current plating is used to fill through-holes, then the process is simple and continuous, but voids and dimples form in the copper deposit
Solution Approach 1:
The patent applies periodic action by cycling the current density through high and low phases. High current density (1.5-4 ASD) is applied initially to promote copper deposition, then reduced to low current density (0.5-3 ASD) to allow proper filling without voids. This periodic variation in current density resolves the contradiction by maintaining process continuity while improving fill quality.
Solution Approach 2:
The patent changes the current density parameter dynamically during the plating process. By transitioning from high current density to low current density, the process achieves both efficient copper deposition and complete hole filling without voids. This parameter change resolves the contradiction between manufacturing simplicity and fill quality.
2Productivity
If high current density is applied continuously to fill through-holes quickly, then productivity increases, but voids and dimples form due to incomplete filling
Solution Approach 1:
The patent uses periodic action with high current density applied initially for rapid deposition, then switched to low current density for complete filling. This two-phase approach maintains high productivity while ensuring complete filling without voids, resolving the contradiction between speed and completeness.
Solution Approach 2:
The patent applies preliminary high current density to deposit copper quickly and establish a good foundation, then transitions to low current density to complete the filling. This preliminary action ensures both speed and completeness, resolving the contradiction.
3Productivity
If a single copper electroplating bath is used for through-hole filling, then process efficiency and cost are improved, but conformal copper deposition occurs instead of complete filling
Solution Approach 1:
The patent changes the current density parameter during the plating process to achieve both efficient filling and uniform deposition. By switching from high to low current density, the single bath process achieves complete filling without conformal deposition, resolving the contradiction between efficiency and uniformity.
4Ease of operation
If conventional constant current density plating is used, then the process is simple to control, but dimple depth increases with substrate thickness
Solution Approach 1:
The patent applies periodic variation in current density to control dimple formation. By cycling between high and low current density, the process maintains simple control while preventing dimple depth increase, even in thicker substrates up to 200 µm or greater.
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 significantly reduces dimple formation and voids, achieving a uniform copper layer with minimal nodule formation, enhancing the filling of through-holes in substrates with thicknesses up to 200 µm or greater, and improving throwing power for consistent copper deposition.
Implementation Method 1
immersing the substrate in a copper electroplating bath; and filling the through-holes with copper by a direct current cycle
Implementation Method 2
applying a first current density ranging from 1.5-4 ASD for a first predetermined period of time followed by turning off direct current
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 a pause in electroplating and then turning on the current to electroplate at a lower current density to fill through-holes.