Guide to the Structure and Manufacturing Methods of Flexible Circuit Boards

Guide to Flexible Circuit Boards and Their Manufacturing Methods

Overview

This guide aims to help you review and understand the structure of flexible circuit boards and their manufacturing methods as described. The patent discloses a design for flexible circuit boards intended to reduce high-frequency signal transmission losses by introducing air-filled sealed cavities to minimize dielectric losses. The guide will cover key parts of the patent text, including the abstract, claims, background technology, invention content, specific implementation methods, and descriptions of the drawings.

Key Concepts

• Flexible Circuit Board: A circuit board that can be bent, folded, or twisted during use.
• High-Frequency Signal Transmission Loss: Energy loss during signal transmission due to dielectric loss and conductor loss, particularly significant at high frequencies.
• Dielectric Loss: Energy loss caused by polarization and conductive losses when signals pass through insulating materials.
• Conductor Loss: Energy loss due to resistance when signals pass through conductors.
• Sealed Cavity: A closed space formed within the circuit board, used to fill with air or other materials with a low dielectric constant.
• Air Filling: Utilizing air as a medium, which has a low dielectric constant, helps reduce dielectric loss.
• Lamination: The process of bonding different layers of the circuit board together under specific temperature and pressure.
• Via Hole: Holes that connect conductive patterns on different layers of the circuit board.
• Conductive Paste: Material used to fill via holes to form conductive connections.
• Inner Layer Circuit Substrate: The substrate that forms the conductive lines within the circuit board.
• Outer Layer Circuit Substrate: The substrate that forms the conductive lines on the outer surface of the circuit board.
• Bonding Layer: The material layer used to bond different layers of the circuit board together.
• Insulating Layer: The material layer that provides electrical insulation.
• Signal Line: Conductive lines that transmit electrical signals.
• Ground Line: Conductive lines that provide a current return path.
• Protective Layer/Solder Mask: A layer covering the surface of the circuit board, protecting conductive lines and preventing solder short circuits.

Key Points of Claims

• Claim 1 describes the basic structure of the flexible circuit board, including the inner layer circuit substrate, bonding layer, and outer layer circuit substrate, as well as the signal lines in the inner layer circuit substrate and at least two ground lines. The focus is on forming a sealed cavity between the inner layer circuit substrate and the outer layer circuit substrate through the bonding layer.
• Claim 2 emphasizes the correspondence between the projection of the signal lines within the sealed cavity and the position of the cavity opening.
• Claims 3 and 4 relate to the arrangement of ground lines and the first conductive via connected to the ground lines.
• Claims 5 and 6 involve the structure and connections of the second and third conductive layers, insulating layers, and conductive vias.
• Claims 7 and 8 describe the manufacturing method of the flexible circuit board, including providing substrates, bonding layers, and protective layers, forming signal lines and ground lines, and creating an integrated structure through lamination.
• Claims 9 and 10 describe the manufacturing method of the bonding layer, including forming openings and vias, and filling with conductive paste.

Invention Content and Specific Implementation Methods

• The invention provides a flexible circuit board with ultra-low signal attenuation and high transmission performance, along with its manufacturing method.
• By forming sealed cavities within the circuit board and filling them with air, which has a low dielectric constant, dielectric losses are significantly reduced.
• Multiple implementation methods are provided, detailing the structure, materials, and manufacturing steps of different layers (such as inner layer circuit substrate, bonding layer, outer layer circuit substrate).
• The specific implementation methods describe the relative positions and spacing of signal lines and ground lines, as well as how to achieve connections between different layers through openings and vias in the bonding layer.
• The manufacturing method includes a series of steps, such as providing substrates, forming conductive lines, creating bonding layers, laminating, and forming protective layers.

Background Technology

• Introduces the issues of dielectric loss and conductor loss present in high-frequency signal transmission.
• Mentioned existing technologies that use low dielectric constant materials (such as LCP, PTFE) to reduce dielectric losses.
• Pointed out that while existing methods can reduce losses, material costs are high, and signal attenuation in flexible circuit boards remains significant.

Quiz

Please answer the following questions briefly in 2-3 sentences:

1. What is the main technical objective of this patent?
2. How does this flexible circuit board reduce high-frequency signal transmission losses?
3. What substance fills the sealed cavity?
4. What role does the bonding layer play in this flexible circuit board?
5. What components primarily make up the inner layer circuit substrate?
6. What are the characteristics of the relative positions of signal lines and ground lines on the inner layer circuit substrate?
7. What is the function of the at least two ground lines mentioned in Claim 1?
8. What role do vias play in this circuit board structure?
9. What does the component marked as 81 in Figure 1 represent?
10. How does the structure of the flexible circuit board shown in Figure 8 differ from that in Figure 7?

Quiz Answer Key

1. The main technical objective of this patent is to provide a flexible circuit board with ultra-low signal attenuation and high transmission performance to address the significant losses in high-frequency signal transmission.
2. This flexible circuit board significantly reduces dielectric losses and thus high-frequency signal transmission losses by forming sealed cavities within the circuit board and filling them with air, which has a low dielectric constant.
3. The sealed cavity is primarily filled with air, which has a low dielectric constant that helps reduce dielectric losses.
4. The bonding layer serves to bond the inner layer circuit substrate and the outer layer circuit substrate together and to form the sealed cavity.
5. The inner layer circuit substrate primarily includes the first conductive line layer, which contains signal lines and at least two ground lines.
6. The signal lines and ground lines are arranged parallel on either side of the signal lines on the inner layer circuit substrate to form an electrical circuit for signal transmission.
7. The at least two ground lines mentioned in Claim 1 work together with the signal lines to form an electrical circuit, which is crucial for signal transmission.
8. The vias serve to connect conductive patterns on different layers of the circuit board, achieving electrical connections between different layers.
9. The component marked as 81 in Figure 1 represents the sealed cavity, which is a key structure for filling air to reduce dielectric losses.
10. The structure of the flexible circuit board shown in Figure 8 is another embodiment, with the main differences from Figure 7 being the number of layers and the specific stacking structure, such as including a second conductive layer and a second insulating layer as mentioned in the claims.

Glossary

• Flexible Printed Circuit Board: A type of circuit board that has the properties of being bendable, foldable, or twistable.
• High-Frequency Signal Transmission Loss: Energy lost during high-frequency signal transmission.
• Dielectric Loss: Energy loss caused by material properties when signals pass through insulating materials.
• Conductor Loss: Energy loss due to resistance when signals pass through conductors.
• Sealed Cavity: A closed space within the circuit board used to fill with low dielectric constant media.
• Inner Layer Circuit Substrate: The substrate that forms the conductive lines within the circuit board.
• Outer Layer Circuit Substrate: The substrate that forms the conductive lines on the outer surface of the circuit board.
• Bonding Layer: The material layer used to bond different layers of the circuit board together.
• Insulating Layer: The material layer that provides electrical insulation.
• Signal Line: Conductive lines that transmit electrical signals.
• Ground Line: Conductive lines that provide a current return path.
• Via Hole: Holes that connect conductive patterns on different layers of the circuit board.
• Conductive Paste: Material used to fill vias to form conductive connections.
• Lamination: The process of bonding different layers of the circuit board together.
• Protective Layer/Solder Mask: A layer covering the surface of the circuit board, protecting conductive lines and preventing solder short circuits.
• Dielectric Constant: A physical quantity that measures a material’s ability to store electrical energy, affecting dielectric loss.
• Embodiment: A specific way of implementing the content of the invention.
• Claims: The part of the patent document that defines the scope of patent protection.
• Background Art: The relevant technology existing prior to the invention.
• Summary of Invention: A brief overview of the technical solution of the invention.
• Detailed Description of Embodiments: A detailed description of the specific implementation methods of the invention.
• Description of Drawings: An explanation of the patent drawings.

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