Reverse Treated Copper Foil for High Speed PCB Signal Integrity
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Solution Overview
Problem
Conventional copper foils experience significant signal loss when transmitting high-frequency electrical signals above 100 MHz due to the skin effect, where current is forced to follow the surface profile, increasing path length and resistance, and the irregular surface roughness of the deposit side exacerbates this issue.
Innovation Solution
A 'reverse treated' copper foil is developed with nodules deposited on the drum side, which becomes the lamination side, and the deposit side is treated as the resist side, achieving a surface roughness of 1.5 to 3.1 μm and a 15% to 30% difference in light reflection between 570 nm and 610 nm, ensuring a random nodule distribution to minimize signal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If nodules are added to the deposit side to aid adhesion, then adhesion strength is improved, but signal loss increases due to increased surface roughness and skin effect
Solution Approach 1:
The patent inverts the conventional approach by depositing nodules on the drum side instead of the deposit side. This reversal allows the nodules to be positioned on the side that will become the inner surface after lamination, thereby reducing their impact on signal transmission while maintaining adhesion benefits.
Solution Approach 2:
The patent applies different surface characteristics to different sides of the copper foil. The drum side receives nodule treatment for adhesion, while the deposit side maintains smoothness for optimal signal transmission. This localized differentiation resolves the contradiction between adhesion requirements and signal integrity.
2Strength
If surface roughness is increased to improve adhesion, then adhesion strength is improved, but electrical resistance increases due to skin effect
Solution Approach 1:
By inverting which side receives the nodule treatment, the patent ensures that surface roughness is concentrated on the drum side rather than the deposit side, thereby improving adhesion without significantly increasing the electrical resistance path for high-frequency signals.
Solution Approach 2:
The patent creates localized surface roughness only where needed for adhesion (drum side), while keeping the signal transmission surface (deposit side) smooth. This spatial separation of functions resolves the contradiction between adhesion strength and electrical resistance.
3Productivity
If current flows through the body of copper foil at low frequency, then signal transmission is efficient, but at high frequency the skin effect forces current to the surface increasing path length
Solution Approach 1:
The patent inverts the conventional nodule placement strategy, positioning nodules on the drum side rather than the deposit side. This inversion creates a smoother signal transmission surface that minimizes skin effect impacts on high-frequency current flow.
Solution Approach 2:
The patent applies surface treatment locally to the drum side only, leaving the deposit side smooth for optimal electrical performance. This localized approach allows the copper foil to maintain low electrical resistance at high frequencies while still providing adequate adhesion through the nodule-treated drum side.
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 significantly reduces signal loss by maintaining a low surface roughness and random nodule distribution on the drum side, enhancing the transmission of high-frequency signals through the copper foil and printed circuit boards.
Implementation Method 1
When an electrical current is applied through the bath, utilizing an insoluble metal anode, with the drum acting as a cathode, the copper in solution plates upon the outer surface of the drum
Implementation Method 2
when the frequency of the electrical signal is increased to 100 MHz or greater, the influence of the skin effect in which current flows only through the surface of the conductor becomes remarkable
Data Source
AI summary
Surface treated copper foils for use in high speed circuits on the order of 100 MHz or greater contain a reverse treated layer of copper nodules on the drum side of the electrolytically deposited copper foil to form a lamination side to be laminated to a dielectric material to form a copper clad laminate. Methods of forming the surface treated copper foil, and printed circuit boards (PCB) from the copper clad laminates are also described. The surface treated copper foils, copper clad laminates and PCBs can be incorporated into various electronic devices in which high speed signals are employed, including personal computers, mobile communications, including cellular telephones and wearables, self-driving vehicles, including cars and trucks, and aviation devices, including manned and unmanned vehicles, including airplanes, drones, missiles and space equipment including satellites, spacecraft, space stations and extra-terrestrial habitats and vehicles.