PCB Transmission Line Layout Using Smooth Copper Interfaces
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Solution Overview
Problem
High frequency circuits in printed circuit boards (PCBs) experience significant transmission line losses due to conductor surface roughness, which is exacerbated by the skin effect at millimeter-wave frequencies, leading to inconsistent signal transmission and poor efficiency.
Innovation Solution
The method involves manufacturing PCBs with smooth conducting layers by using PCB cores with unabraded copper laminate surfaces and prepreg insulator layers to reduce surface roughness, thereby minimizing signal path length and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conductor layers are abraded to improve adhesion between conducting and dielectric layers, then adhesion strength is improved, but conductor surface roughness increases leading to higher surface resistivity and transmission line losses at high frequencies
Solution Approach 1:
The invention applies different surface treatments to different conductor layers based on their function. Signal carrying layers maintain smooth surfaces to minimize transmission losses, while ground planes and power layers are abraded to ensure good adhesion. This local differentiation resolves the contradiction by optimizing each layer's surface properties according to its specific electrical function.
Solution Approach 2:
The invention performs adhesion preparation (abradation) only on conductor layers that require it for structural integrity, rather than uniformly treating all layers. By preliminarily identifying which layers need adhesion enhancement versus which need smooth surfaces for signal integrity, the process avoids unnecessary roughening of signal paths while ensuring adequate bonding where required.
2Reliability
If conductor surface roughness is increased to improve adhesion, then bonding between layers is enhanced, but skin effect losses increase at millimeter-wave frequencies
Solution Approach 1:
The invention selectively applies surface roughening only to ground planes and power layers where adhesion is critical, while keeping signal carrying layers smooth. This local quality differentiation ensures that bonding reliability is enhanced where structurally necessary without compromising signal transmission efficiency at millimeter-wave frequencies.
Solution Approach 2:
The invention changes the surface roughness parameter differently for different conductor layers. Signal layers maintain low roughness parameters to minimize skin effect losses, while ground and power layers are treated to achieve higher roughness parameters that maximize adhesion. This parameter optimization resolves the contradiction between bonding reliability and energy loss.
3Ease of manufacture
If uniform abraded surfaces are used on all conductor layers, then manufacturing process is simplified, but transmission line losses increase due to elongated current paths
Solution Approach 1:
The invention implements a differentiated manufacturing approach where signal carrying layers are kept smooth and ground/power layers are abraded. This requires additional process steps to selectively treat different layers, but the increase in manufacturing complexity is justified by the significant reduction in transmission line losses and improved high-frequency performance.
Solution Approach 2:
The invention applies different surface roughness parameters to different conductor layers based on their electrical function. This parameter differentiation requires modified manufacturing processes but results in optimal electrical performance by minimizing current path elongation on signal layers while maintaining adequate adhesion on support layers.
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 reduces transmission line losses by approximately 20% and enhances high frequency signal transmission efficiency by maintaining smooth signal and ground paths throughout the PCB manufacturing process.
Implementation Method 1
The surface resistivity of metals at high frequency is dominated by the 'skin effect ', meaning that the currents flow on outermost layer of the metal only.
Data Source
AI summary
Systems and methods for improving high frequency transmission in printed circuit boards use the smooth internal interfaces between the conducting laminate and dielectric substrates of PCB cores to serve as signal carrying lines and ground planes in transmission lines. Flanking PCB cores may be mounted to a central dielectric layer including a stripped PCB core providing structural integrity of the PCB.