Fusion Bonded LCP Circuit Structure for High Density Signal Integrity
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Solution Overview
Problem
Traditional printed circuit boards face challenges in achieving high-speed, high-density circuitry due to limitations in feature size, line spacing, and signal integrity, particularly with rigid and flexible circuits, which are prone to reliability issues like taper, carbon contamination, and impedance mismatch.
Innovation Solution
The use of liquid crystal polymer (LCP) as a dielectric material in fusion-bonded circuit structures, processed with conventional equipment, allows for the creation of fine line and high-density circuits with solid metal vias, enabling signal integrity beyond 40 GHz and reducing line and space requirements below 50 microns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional rigid or flexible PCB materials are used, then manufacturing process is simple and cost is low, but circuit density is limited and signal integrity deteriorates at high frequencies
Solution Approach 1:
The patent changes the material parameter from traditional PCB substrates (FR-4, polyimide) to liquid crystal polymer (LCP), which has fundamentally different electromagnetic properties including lower dielectric constant (2.9-3.2) and loss tangent (0.004-0.008), enabling high-frequency signal integrity while supporting fine-line circuitry
Solution Approach 2:
The patent uses composite construction combining LCP dielectric material with metal cladding layers (copper, aluminum, or other conductors) to create a hybrid structure that leverages the low-loss properties of LCP for signal transmission while using traditional metal layers for circuit patterning and connectivity
2Quantity of substance
If feature size and line spacing are reduced to increase circuit density, then circuit capacity increases, but manufacturing precision deteriorates due to laser ablation limitations
Solution Approach 1:
The patent replaces the mechanical laser ablation process with electrochemical etching using ammonium persulfate solution, which provides isotropic, uniform material removal without the taper, carbon contamination, and registration errors inherent in laser drilling, enabling precise via formation at sub-50-micron pitch
Solution Approach 2:
The patent changes the manufacturing process parameter from laser-based thermal ablation to chemical etching, fundamentally altering the material removal mechanism to achieve superior dimensional control and surface quality for fine-pitch via structures
3Ease of manufacture
If conventional PCB lamination is used, then manufacturing is straightforward, but impedance control and signal performance are insufficient for high-speed applications
Solution Approach 1:
The patent changes the dielectric material parameter to LCP with controlled thickness (0.002-0.006 inches) and optimized copper cladding thickness (0.0003-0.001 inches), achieving precise impedance control (50 ohms single-ended, 100 ohms differential) through material and geometric parameter optimization
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 enhances circuit density and signal performance, providing a cost-effective method for producing high-density circuits with improved reliability and reduced impedance issues, applicable to both rigid and flexible circuits, and semiconductor packaging.
Implementation Method 1
A first layer of LCP is fusion boned to the first major surface of the substrate, to encapsulate the first conductive traces in an LCP material
Data Source
AI summary
A method of making a fusion bonded circuit structure. A substrate is provided with a seed layer of a conductive material. A first resist layer is deposited on the seed layer. The first resist layer is processed to create first recesses corresponding to a desired first circuitry layer. The first recesses expose, portions of the seed layer of conductive material. The substrate is electroplated to create first conductive traces defined by the first recesses. The first resist layer is removed to reveal the first conductive traces. The substrate is etched to remove exposed portions of the seed layer adjacent the first conductive traces. A portion of the seed layer is interposed between the first conductive traces and the substrate. A first layer of LCP is fusion boned to the first major surface of the substrate to encapsulate the first conductive traces in an LCP material. The first LCP layer can be laser drilled to expose the conductive traces.