Phase Shift Pulse Plating for High Aspect Ratio Through-Hole Filling
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Solution Overview
Problem
Filling high aspect ratio through-holes in substrates with copper plating is challenging due to the formation of voids and defects, as conventional DC and pulse plating methods fail to achieve complete and defect-free filling, especially in printed circuit boards.
Innovation Solution
A method involving phase shift pulse plating, where a partial copper bridge is formed in the through-holes by applying DC current and offset pulse-trains on both sides of the substrate, followed by complete filling using pulse plating reverse, allowing for defect-free filling with reduced surface copper.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC plating is used to fill through-holes, then the plating process is simple and continuous, but voids form and filling is incomplete in high aspect ratio through-holes
Solution Approach 1:
The patent applies periodic pulse plating reverse waveforms instead of continuous DC plating. The waveform alternates between forward plating pulses that deposit copper and reverse pulses that dissolve excess copper, creating a periodic action that prevents void formation while maintaining filling completeness in high aspect ratio through-holes
Solution Approach 2:
The patent changes the plating parameters by using phase-shifted pulse waveforms with varying current densities and timing. By adjusting the pulse duration, reverse pulse intensity, and phase shift between opposite sides, the process achieves complete filling without voids in high aspect ratio through-holes where DC plating fails
2Reliability
If conventional phase shift PPR plating is used, then through-holes are filled, but significant voids form in the copper fill
Solution Approach 1:
The patent applies preliminary low-current density plating to form a uniform base layer before applying the main phase-shifted pulse plating reverse waveform. This preliminary action prepares the surface and ensures even current distribution, preventing void formation during the main filling process
Solution Approach 2:
The patent uses feedback control by monitoring the plating progress and adjusting the pulse waveform parameters in real-time. The reverse pulses act as a feedback mechanism to dissolve protrusions and redistribute copper, ensuring uniform filling without voids
3Reliability
If complete copper bridge is formed before filling, then through-holes are filled, but surface copper thickness increases
Solution Approach 1:
The patent applies partial plating action by using controlled pulse durations and current densities that deposit exactly the required amount of copper for complete filling without excess. The reverse pulses remove any excessive deposition, achieving complete filling with minimal surface copper thickness
4Productivity
If higher current density is used to fill through-holes faster, then productivity increases, but voids and defects increase
Solution Approach 1:
The patent uses periodic pulse waveforms with optimized duty cycles that deliver high current density during forward pulses for fast deposition, followed by reverse pulses that prevent void formation. This periodic high-current approach achieves both high productivity and high filling quality
Solution Approach 2:
The patent dynamically changes current density parameters during the plating process by using higher current densities during forward pulses for speed and lower effective current density during reverse pulses for quality control, achieving both high productivity and defect-free 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 method effectively reduces the number and size of voids in through-holes and minimizes the total surface copper required for complete filling, ensuring high aspect ratio through-hole filling with improved planarity and reliability.
Implementation Method 1
immersing the substrate in a copper plating bath; plating a partial copper bridge in the through-holes by simultaneously applying a plating cycle to the first side and the second side of the substrate
Implementation Method 2
simultaneously polarizing the first side of the substrate with a rectifier and polarizing the second side of the substrate with the rectifier to generate an electrical current on the first and second side of the substrate
Data Source
AI summary
Through-holes of a substrate are initially plated with copper to form an incomplete bridge in the middle of the through-holes by a phase shift pulse plating process on both sides of the substrate simultaneously. This is followed by pulse plating the entire substrate to complete the filling of the through-holes.