Advantages of Flexible PCB and Rigid-Flex PCB

According to the IPC 6013 standard, flexible boards are classified into single-sided, double-sided, multilayer, and rigid-flex boards.

The manufacturing process of rigid-flex boards includes material preparation, forming, etching, drilling, plating, flexible board cutting, and electrical testing.

The manufacturing process of rigid-flex boards is an ideal choice for constructing circuits in the medical, aerospace, military, and telecommunications industries.

Due to their advantages such as lightweight, high assembly density, and miniaturization, the demand for such PCBs is increasing. Flexible PCBs also have advanced mechanical design and excellent electrical and thermal performance. The popularity of flexible PCBs has driven the development of other related products, such as HDI flexible PCBs, embedded flexible PCBs, and rigid-flex PCBs.

Among these derivative products, rigid-flex PCBs are commonly used in the automotive, medical, military, and aerospace industries. The manufacturing of rigid-flex boards is a time-consuming process, involving steps such as material preparation, etching, drilling, and plating, followed by final product manufacturing. This article will explore flexible PCBs and understand the rigid-flex manufacturing process.

Flexible PCBs Advantages

A circuit board made of flexible base materials is called a flexible PCB. Flexible PCBs (or flex boards) are flexible and adaptable, capable of being shaped to meet the requirements of various applications. Compared to traditional rigid boards, flex boards have many advantages, including:

• Small size, lightweight
• Thin
• Miniaturization of circuits, high assembly density
• Fewer wiring errors
• Flexibility, suitable for constructing bendable circuits
• No need for mechanical connectors
• Compatible with 3D interconnects
• High degree of mechanical and electronic design freedom
• High signal integrity and circuit reliability
• Good impedance control
• Wide range of operating temperatures
• Strong shock resistance
• Suitable for harsh environments

Despite possessing all these advantages, flexible PCBs have higher material costs compared to rigid or rigid-flex boards. Rigid-flex boards combine the advantages of rigid and flexible PCBs, making them a boon for circuit manufacturing. The following content will introduce rigid-flex boards and the rigid-flex manufacturing process.

Rigid-flex boards are commonly used in the automotive, medical, military, and aerospace industries.

What is Rigid-Flexible Boards

According to the IPC 6013 standard, flexible boards are classified into different types, including single-sided, double-sided, multilayer, and rigid-flex boards. Type 4 under IPC 6013 mentions rigid-flex boards, which combine the advantages of flexible and rigid boards. They can be described as hybrid boards or rigid-flex boards. Rigid-flex boards are divided into two categories:

1. Flexible Mounting Type – This type can only be bent once during installation or maintenance.
2. Dynamic Flexible Type – This type can be bent multiple times during use.

Rigid-flex boards are suitable for applications that require a small size, i.e., the need to incorporate more components in a smaller area. Designed in 3D space, rigid-flex boards have higher spatial efficiency; they can be dynamically bent or folded, facilitating the formation of the required shape in the final product packaging; they do not require many interconnections, require less maintenance, and are widely recognized for their reliability; rigid-flex boards are most commonly used in the medical, telecommunications, and aerospace industries.

Rigid-flex boards are suitable for applications that require a small size, i.e., the need to incorporate more components in a smaller area.

Rigid-flex Manufacturing Process

Before the rigid-flex manufacturing process begins, the PCB design layout needs to be done. Once the layout is determined, the rigid-flex manufacturing process can begin.

The rigid-flex manufacturing process combines the manufacturing techniques of rigid and flexible boards. Rigid-flex boards stack rigid and flexible PCBs layer by layer. Components are assembled in the rigid areas and interconnected to adjacent rigid boards through the flexible areas. Connections between layers are introduced through plated through-holes.

The rigid-flex manufacturing process includes the following steps:

1. Prepare the substrate: The first step in the rigid-flex manufacturing process is to prepare or clean the laminate. Whether or not there is an adhesive coating, laminates with copper layers need to be pre-cleaned before being put into other manufacturing processes.
2. Pattern generation: Done through screen printing or photo imaging.
3. Etching process: Both sides of the laminate with the circuit pattern are immersed in an etching tank or sprayed with etching agent solution for etching.
4. Mechanical drilling process: Precision drilling systems or technical drilling are used to drill the required circuit holes, pads, and through-hole patterns in the production panels. For example, laser drilling technology.
5. Copper plating process: The focus of the copper plating process is to deposit the required copper inside the plated through-holes to establish electrical interconnections between layers of the rigid-flex board.
6. Apply cover layer: The cover layer material (usually polyimide film) and adhesive are printed on the surface of the rigid-flex board through screen printing.
7. Cover layer lamination: Lamination is carried out at specific temperatures, pressures, and vacuum limits to ensure proper adhesion of the cover layer.
8. Apply reinforcement ribs: Additional reinforcement ribs may be applied before additional lamination processes, depending on the design requirements of the rigid-flex board.
9. Flexible board cutting: Use hydraulic punching methods or specialized punching knives to cut the flexible board from the production panel.
10. Electrical testing and validation: Rigid-flex boards are electrically tested according to IPC-ET-652 guidelines to confirm the insulation performance, interconnection, quality, and performance of the circuit board meet the requirements of the design specifications. Testing methods include flying probe testing and grid testing systems.

The rigid-flex manufacturing process is an ideal choice for constructing circuits in the medical, aerospace, military, and telecommunications industries because these circuit boards have excellent performance and precise functions, especially in harsh environments.