Guide to Wearable Flexible Printed Circuit Boards

Overview

This research guide aims to help you review and understand the knowledge related to wearable flexible printed circuit boards (hereinafter referred to as wearable FPCBs), their manufacturing methods, and their applications in smart devices. The core content revolves around a novel wearable FPCB described in the patent document and its technical characteristics.

Core Concepts

The main innovation of this wearable FPCB lies in its substrate. Unlike traditional FPCBs based on polyimide films, the substrate of this new FPCB is composed of a fiber web formed by electrospinning technology. This fiber web endows the wearable FPCB with unique physical properties, making it suitable for future wearable smart devices.

Main Components

1. Substrate: A fiber web formed by the accumulation of fibers with a diameter of less than or equal to 3 μm through electrospinning technology. This fiber web can have various micro-pores or be in a non-porous state. The fiber web can consist of single or multiple layers, including a middle layer with fine fibers or a non-porous state, as well as upper and lower layers. The thickness of the substrate can be adjusted according to the conduction requirements of the circuit pattern (non-conductive on both sides or conductive on both sides).
2. Conductive Circuit Pattern: The conductive pathways formed on the aforementioned fiber web substrate. The circuit pattern can be formed by printing conductive pastes (such as Ag paste or Cu paste). The conductive paste can fill the fibers and pores of the fiber web or only form on the fibers.
3. Strength Reinforcing Support (Optional): When the strength of the fiber web is insufficient, a support material such as non-woven fabric can be used, and the fiber web can be layered on one or both sides to form a multi-layer structure.

Key Features

• Flexibility: Due to the fiber web structure, the wearable FPCB exhibits excellent bending characteristics.
• Recovery: It can return to its original flat state even after being folded or wrinkled.
• Breathability: The fiber web substrate with multiple micro-pores allows gases to pass through, making it suitable for breathable wearable devices.
• Waterproofness: The fine pores can prevent liquids from passing through while allowing gases to pass.
• Ultra-thin: Electrospinning technology can produce extremely thin fiber webs, resulting in ultra-thin printed circuit boards.

Manufacturing Method

The main steps in manufacturing wearable FPCBs include:

1. Forming the Substrate: Using a spinning solution of mixed polymers and solvents for electrospinning, fibers are accumulated to form a fiber web substrate with multiple pores. The fiber morphology can be influenced by controlling the humidity environment (high humidity produces wrinkled fibers, while low humidity produces straight fibers).
2. Forming the Circuit Pattern: Printing conductive paste on the fiber web substrate to form the circuit pattern.
3. Curing: Curing the printed conductive paste. The curing temperature depends on the melting point of the conductive paste and the polymer fibers used.

Wearable Smart Devices

Wearable smart devices utilize the aforementioned wearable FPCB as a base and install various electronic components. These electronic components can include:

• Sensor Unit: Biosensors (for detecting body states such as heart rate, respiration, blood sugar/blood pressure) and environmental sensing sensors (for sensing surrounding environments such as gas, illumination, infrared).
• Short-range Communication Module: For short-range wireless communication (such as NFC, Bluetooth, RFID, etc.).
• Antenna Pattern: For wireless communication, which can be directly formed on the wearable FPCB using conductive paste.
• Control Unit: For executing signal processing functions.
• Heater Pattern: For generating heat based on the external environment, which can also be directly formed on the wearable FPCB using conductive paste.

These electronic components can be directly installed on the wearable FPCB, which can be embedded between the inner and outer layers of clothing or layered on the inner side of the lining.

Quiz

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

1. What unique physical properties does the fiber web substrate used in this invention have compared to traditional flexible printed circuit board substrates (such as polyimide films)?
2. Why is the wearable flexible printed circuit board of this invention considered breathable?
3. How is the conductive circuit pattern formed on the fiber web substrate?
4. How does the thickness of the fiber web substrate affect the conductivity of the circuit patterns on both sides?
5. How is electrospinning technology used to manufacture the fiber web substrate for wearable flexible printed circuit boards?
6. How can the morphology of the fibers be controlled to be either wrinkled or straight during the electrospinning process?
7. What potential applications does the wearable flexible printed circuit board have in smart clothing?
8. Besides traditional electronic components, what functional patterns can be directly formed on the wearable flexible printed circuit board by printing conductive paste?
9. If the strength of the wearable flexible printed circuit board is insufficient, what methods can be used to reinforce it?
10. How is the waterproofness of the wearable flexible printed circuit board achieved?

Quiz Answers

1. Compared to traditional polyimide films, the fiber web substrate of this invention has better flexibility, recovery, breathability, and waterproofness. These properties make it more suitable for wearable applications.
2. The fiber web substrate of this invention has multiple micro-pores formed by the accumulation of nano-sized fibers. These pores allow gases such as water vapor to pass through, thus providing breathability to the printed circuit board.
3. The conductive circuit pattern is formed by printing conductive paste (such as Ag paste or Cu paste) on the fiber web substrate. The conductive paste can fill the fibers and pores or only form on the fibers.
4. When the substrate thickness is between 20μm and 100μm, the circuit patterns on the upper and lower sides are electrically isolated. When the substrate thickness is between 5μm and 20μm, the printed conductive paste can conduct electricity from one side to the other, achieving through connection.
5. By electrospinning a spinning solution of mixed polymers and solvents, ultra-fine fibers are accumulated on a collector to form a non-woven fiber web substrate.
6. By controlling the humidity environment during the electrospinning process. A high humidity environment (60-80%) favors the formation of wrinkled fibers, while a low humidity environment (below 60%) favors the formation of straight fibers.
7. The wearable flexible printed circuit board can be used to connect various electronic components in smart clothing, such as sensors, communication modules, and control units, enabling functions like health monitoring, entertainment interaction, environmental sensing, or military special purposes.
8. Antenna patterns and heater patterns can be directly formed on the wearable flexible printed circuit board by printing conductive paste.
9. If the strength of the wearable flexible printed circuit board is insufficient, non-woven fabric can be used as a strength reinforcing support, layering the fiber web on one or both sides to form a multi-layer structure.
10. The waterproofness of the wearable flexible printed circuit board is achieved by controlling the size of the pores in the fiber web. The accumulation of nano-sized fibers forms micro-pores that allow gases to pass while preventing liquids from passing.

Suggested Essay Topics

Here are five essay topics that can help you further explore and elaborate on your understanding of the source material:

1. Compare and contrast the wearable flexible printed circuit board described in this invention with traditional flexible printed circuit boards based on polyimide films in terms of substrate structure, physical properties, and application fields.
2. Detail the specific process and importance of using electrospinning technology in this invention to manufacture the substrate for wearable flexible printed circuit boards, and discuss how controlling fiber morphology (wrinkled vs. straight) affects the characteristics of the final product.
3. Explore the specific application scenarios of the wearable flexible printed circuit board in smart clothing, and analyze how its waterproofness, breathability, and flexibility enhance the functionality and comfort of smart clothing.
4. Analyze how the wearable flexible printed circuit board achieves through connection and discuss the advantages of this design in specific applications (such as medical drug patches).
5. In addition to the electronic components mentioned in the source material, envision and discuss what other types of electronic functions or components could be integrated into the wearable flexible printed circuit board to expand its application range in future devices.

Glossary

• Wearable Flexible Printed Circuit Board (Wearable FPCB): A printed circuit board designed for wear, characterized by flexibility, recovery, waterproofness, and breathability, with a substrate made of a fiber web.
• Fiber Web: A mesh structure formed by the accumulation of fibers obtained through electrospinning technology, used as the substrate for wearable FPCBs.
• Electrospinning: A technique for producing ultra-fine fibers from polymer solutions or melts using electrostatic force.
• Conductive Circuit Pattern: Conductive pathways formed on the fiber web substrate for connecting electronic components.
• Conductive Paste: A paste-like substance containing conductive particles (such as Ag or Cu) and a binder, used for printing circuit patterns.
• Flexibility: The ability of a material to bend without damage.
• Recovery: The ability of a material to return to its original shape after deformation.
• Breathability: The ability of a material to allow gases to pass through.
• Waterproofness: The ability of a material to prevent liquids from passing through.
• Porosity: The ratio of the volume of voids in a material to its total volume.
• Strength Reinforcing Support: Materials used to increase the strength of the fiber web substrate, such as non-woven fabric.
• Wearable Smart Device: Devices that integrate electronic components using wearable FPCBs, designed for wear.
• Sensor Unit: Electronic components including biosensors and environmental sensing sensors.
• Short-range Communication Module: Electronic components for enabling short-range wireless communication.
• Antenna Pattern: Conductive patterns for wireless communication.
• Heater Pattern: Conductive patterns for generating heat based on the external environment.
• Control Unit: Electronic components for executing signal processing functions.
• Through Connection: Refers to conductive pathways that extend from one side of the printed circuit board to the other.

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