Pulse Reverse Plating for Blind Micro Via Filling
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Solution Overview
Problem
Current copper electroplating methods for printed circuit boards and IC substrates require multiple process steps, leading to high costs, low yields, and inadequate copper thickness for fine line etching, especially due to incomplete blind micro via filling and excessive copper layer thickness on the top surface.
Innovation Solution
A method using an aqueous acidic copper plating bath with specific concentration ranges of ferrous and ferric ions, brightener additives, and leveller additives, combined with pulsed plating parameters, allows for one-step filling of blind micro vias and conformal plating of through-holes in horizontal equipment, reducing process steps and improving alignment and yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conformal plating of through-holes and filling of blind micro vias are performed simultaneously using known methods, then both structures are plated in one step, but the copper layer thickness on the top surface becomes too thick for fine line etching
Solution Approach 1:
The patent applies different current densities to different areas: high current density (10-50 A/dm²) is applied to blind micro vias to ensure complete filling, while low current density (0.1-2 A/dm²) is applied to the top surface to minimize copper deposition. This local differentiation allows simultaneous plating of through-holes and filling of blind micro vias while controlling top surface copper thickness to remain suitable for fine line etching (≤75 μm copper line width)
Solution Approach 2:
The patent employs pulsed current plating with dynamic current density variation. The current density is dynamically adjusted between high (10-50 A/dm²) and low (0.1-2 A/dm²) levels during the plating process, allowing precise control over copper deposition patterns. This dynamic approach enables complete blind micro via filling while maintaining thin top surface copper layers appropriate for subsequent fine line etching operations
2Manufacturing precision
If separate process steps are used for through-hole plating and blind micro via filling, then each structure receives optimized treatment, but the number of process steps increases leading to higher costs and lower yields
Solution Approach 1:
The patent merges the plating of through-holes and the filling of blind micro vias into a single simultaneous electroplating process step. By applying differentiated current densities within one plating operation, the method achieves optimized plating quality for both structures while reducing the total number of process steps, thereby lowering production costs and improving yields
Solution Approach 2:
The patent makes a single electroplating process perform multiple functions: it simultaneously plates through-holes conformally and fills blind micro vias completely. The electroplating bath and process parameters are optimized to handle both functions in one operation, eliminating the need for separate plating steps and reducing overall process complexity
3Reliability
If higher current density is applied to ensure complete blind micro via filling, then via filling is improved, but excessive copper is deposited on the top surface making fine line etching difficult
Solution Approach 1:
The patent applies high current density (10-50 A/dm²) specifically to blind micro vias to ensure complete filling, while simultaneously applying low current density (0.1-2 A/dm²) to the top surface to minimize copper deposition. This localized differentiation of current density ensures reliable via filling while maintaining top surface copper thickness suitable for fine line etching (≤75 μm copper line width)
4Manufacturing precision
If multiple registration systems are used for blind micro via formation and through-hole formation, then each can be optimized independently, but alignment between them deteriorates and production yields decrease
Solution Approach 1:
The patent combines blind micro via formation and through-hole formation into a single registration system and one simultaneous electroplating process step. This unified approach ensures precise alignment between blind micro vias and through-holes while maintaining the ability to optimize plating parameters for both structures, thereby improving both alignment accuracy and production yields
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 enables complete blind micro via filling, sufficient copper thickness within through-holes, and a thin top surface copper layer suitable for fine line etching, while reducing process complexity and costs, and improving production yields by using a single registration system.
Implementation Method 1
A method for combined through-hole plating and via filling utilizing horizontal plating equipment comprises the steps of a) TH and BMV formation, b) flash plating, c) electroplating in one and the same plating step of the THs conformally and of the BMVs with copper
Implementation Method 2
The process parameters utilized in step c. comprise distinct concentration ranges for certain ingredients of the aqueous acidic copper plating bath... and current settings for pulsed plating including forward and reverse peak currents as well as pulse time setting
Data Source
AI summary
The present invention relates to a method for copper electroplating in the manufacture of printed circuit boards, IC substrates and the like. Said method is suitable for a combined conformal through-hole (5) filling and filling of blind micro vias (6). The method utilizes a metal redox system and pulse reverse plating and involves a multilayer laminate comprising a dielectric core layer (1) having an inner copper layer (3), a dielectric outer layer (2) and an outer copper layer (4). A first copper layer (7) is formed by flash plating then copper (8) is electroplated by pulse reverse plating.