Guide to Learning Circuit Board Technology

Guide to Learning Circuit Board Technology

Overview

This learning guide aims to help you review and consolidate your understanding of the circuit board technologies introduced in the source material. The source material discusses various types of Printed Circuit Boards (PCBs), their applications, key steps in the manufacturing process, and connection methods. It also covers different bending applications of flexible PCBs and the challenges related to reliability, particularly connection failures. Furthermore, the source material elaborates on rigid-flex PCBs as a solution and how redundancy design can enhance reliability.

Main Concepts

• Basic Functions of Printed Circuit Boards (PCBs): Serving as mechanical support and electrical interconnection layers for electronic components.
• Types of PCB Substrates: Rigid, flexible, and rigid-flex.
• Applications of PCBs: Almost all electronic products, including consumer electronics, industrial, automotive, and medical devices.
• Key Technologies in PCB Manufacturing: Photolithography, developing, and etching.
• Types of Photoresists: Positive and negative photoresists and their opposite reactions to light.
• Interconnection Methods: Connections between rigid PCBs, with flexible PCBs serving as connectors.
• Connection Failure Modes: Disconnection of plugs and sockets, and connection failures between ribbon cables and plugs.
• Bending Applications of Flexible PCBs: Frequent bending, occasional bending, and seldom bending.
• Advantages and Disadvantages of Rigid-Flex PCBs: No need for plug and socket connections, but issues arise from mechanical performance differences between rigid and flexible layers.
• Redundant Connections: Using multiple conductive paths simultaneously to enhance system reliability.
• Current Distribution in Distributed Networks: Current is automatically redistributed to available paths.
• Grid Structure: Used in flexible PCBs to enhance bending and tearing strength.
• Applications in Medical and Wearable Devices: Using flexible PCBs to create electronics that conform to human curves, as well as sensor arrays and energy-emitting devices.

Review Questions

1. What are the two main roles of Printed Circuit Boards (PCBs) in electronics?
2. What three different types of PCB substrates are mentioned in the source material?
3. Describe how positive and negative photoresists react differently to light during the PCB manufacturing process.
4. Besides serving as component substrates, what other functions do PCBs provide?
5. What common failure modes might plug and socket connections face in applications involving repeated movement and bending?
6. According to the source material, how many layers do flexible PCBs typically include when operating purely as “flexible connectors”?
7. Give an example of an application for a flexible connector that experiences “frequent” bending.
8. What is the main advantage of rigid-flex PCBs over rigid PCBs that use plug and socket connections?
9. What is electrical redundancy? How does it enhance system reliability?
10. Besides traditional rectangular or linear patterns, what other patterns can grid structures take in flexible PCBs to enhance strength?

Key Points for Answers

1. PCBs play a dual role in electronics: mechanically providing support as component substrates and electrically providing interconnections between components.
2. The source material mentions three types of PCB substrates: rigid, flexible, and rigid-flex.
3. Positive photoresist is washed away where exposed to light due to bond breakage, while negative photoresist cross-links and remains where exposed to light.
4. In addition to serving as component substrates, PCBs also provide multilayer interconnections between these components and electrical connectors.
5. Common failure modes include plugs disconnecting from sockets and connection failures between ribbon cables and plugs.
6. Flexible PCBs operating purely as “flexible connectors” typically include one to four layers.
7. An example of a “frequent” bending application is a flexible connector connected to the print head in an inkjet printer.
8. The main advantage of rigid-flex PCBs is that they do not require plugs and sockets to facilitate electrical connections between rigid printed circuit boards.
9. Electrical redundancy refers to using multiple conductive paths simultaneously. If one or more interconnections fail, current is redistributed to available paths, thus maintaining system operation to some extent.
10. Grid structures can take patterns formed by diagonal elements, basket weave patterns, fishbone or herringbone shapes, etc.

Suggested Essay Questions

1. Compare and contrast the structures, application scenarios, and respective advantages and disadvantages of rigid, flexible, and rigid-flex printed circuit boards in detail.
2. Analyze the three key steps in the PCB manufacturing process described in the source material: photolithography, developing, and etching, explaining how positive and negative photoresists work and how they affect the final conductive layer pattern.
3. Discuss the reliability challenges faced by plug and socket connections in applications requiring frequent movement and bending, and how rigid-flex PCBs can overcome these issues through their structural design.
4. Explain the role of redundant connections in enhancing the reliability of circuit board systems, and provide examples from the source material to illustrate how redundant connections are applied in distributed networks.
5. Explore the specific roles of flexible PCBs in wearable electronics and medical applications, and analyze how grid structures contribute to enhancing the mechanical performance of flexible PCBs in these applications.

Glossary of Key Terms

• Printed Circuit Board (PCB): A substrate and interconnection carrier for electronic components.
• Rigid Printed Circuit Board: PCB using a non-flexible substrate.
• Flexible Printed Circuit Board (Flexible PCB): PCB using a flexible substrate.
• Rigid-Flex Printed Circuit Board: A hybrid PCB that laminates rigid and flexible layers together.
• Substrate Laminate: The insulating material that makes up the PCB substrate.
• Photoresist: A light-sensitive material used in photolithography.
• Developing: The chemical process of removing exposed or unexposed parts of the photoresist after photolithography.
• Etching: The process of removing metal layers not protected by the photoresist.
• Photomask: A patterned layer used to selectively expose the photoresist during photolithography.
• Plug and Socket Connection: A separable electrical connection method.
• Ribbon Cable: A flat cable composed of multiple wires arranged side by side.
• Surface Mount Technology (SMT): A technique for soldering components directly onto the surface of a PCB.
• Frequent Flexing: The repeated alternation of flexible PCBs between bent and unbent states.
• Occasional Flexing: The infrequent change between bent and unbent states of flexible PCBs.
• Seldom Flexing: The shape of flexible PCBs remains unchanged after being bent into position during manufacturing.
• Via: A hole that connects traces on different layers of a PCB.
• Redundant Connection: Using multiple parallel connection paths to enhance reliability.
• Redundancy Factor (RF): Indicates the degree of redundancy in connections.
• Grid: A repetitive structure or pattern used in flexible PCBs to enhance mechanical strength.
• Sensor Array: A system of multiple integrated sensors.
• Energy Emitting Devices: Devices used to emit energy (such as light, electricity, sound waves, etc.).