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Rigid PCB vs flex PCB – what is the difference

With the rapid development of electronic products, there are many types of circuit boards, including rigid PCB, flexible PCBs, and rigid-flex PCB. Rigid PCBs are ordinary PCB boards that cannot be bent, and most products use PCBs. The flex PCB is a flexible board (FPC), which can be bent to a certain extent, and is generally used in products that are relatively thin or have bending requirements. But do you know any facts about rigid PCB vs flex PCB?

Table of Contents

What is a rigid PCB?


Rigid PCB (Printed Circuit Board), is the support body of electronic components and the carrier of electrical connection of electronic components. It is a kind of PCB that cannot be bent and folded. In the electronics industry, almost every kind of electronic equipment, ranging from electronic watches and calculators to computers, communication electronic equipment, and military weapon systems, as long as there are electronic components such as integrated circuits, in order to make the electrical interconnection between various components, all of them will utilize PCBs.

What is FPC?


FPC (flexible circuit board) is a type of PCB, also known as “flexible PCB“. FPC is made of flexible substrates such as polyimide or polyester film, which has the advantages of high wiring density, light weight, thin thickness, bendability, and high flexibility, and can withstand millions of dynamic bending without damaging the wires. It can move and expand at will, realize three-dimensional assembly, and achieve the effect of integrating component assembly and wire connection and has advantages that other types of circuit boards cannot match.

Advantages and disadvantages of flexible FPC


1) FPC can be bent, wound, and folded freely, and can be arranged arbitrarily according to the requirements of space layout, and can be moved and stretched arbitrarily in three-dimensional space, so as to achieve the integration of component assembly and wire connection;

2) The use of FPC can greatly reduce the volume and weight of electronic products, which is suitable for the development of electronic products in the direction of high density, miniaturization and high reliability. Therefore, FPC has been widely used in aerospace, military, mobile communications, laptop computers, computer peripherals, PDA, digital cameras and other fields or products;

3) FPC also has the advantages of good heat dissipation and solderability, easy assembly, and low overall cost. The design of the combination of rigid and flex also makes up for the slight deficiency of the flexible substrate in the component’s bearing capacity to a certain extent.

1) High one-time initial cost . Since FPC is designed and manufactured for special applications, the cost of initial circuit design, wiring and photographic plates is relatively high. Unless there is a special need to apply FPC, it is usually best not to use it for a small amount of application;

2) It is difficult to change and repair FPC . Once the FPC is made, it must be changed from the base map or the compiled light-drawing program, so it is not easy to change. Its surface is covered with a layer of protective film, which needs to be removed before repairing and restored after repairing, which is a relatively difficult task;

3)Dimensions are restricted. When FPC is not yet popular, it is usually manufactured by batch process, so limited by the size of production equipment, it cannot be made very long and wide;

4) FPC is easy to be damaged by improper operation. Improper operation of the assembly and connection personnel can easily cause damage to the flexible circuit, and its soldering and rework need to be operated by trained personnel.

Rigid PCB vs flex PCB – what is the difference?

Rigid PCBs, often simply called PCBs, are what most people think of when they imagine circuit boards. These boards connect electrical components using conductive tracks and other elements laid out on a non-conductive substrate. On rigid circuit boards, the non-conductive substrate often contains glass cloth, which reinforces the board and gives it strength and stiffness. A rigid circuit board provides good support for components and provides good thermal resistance.

This type of board uses a flexible substrate such as polyimide (PI), although flex PCBs also have conductive traces on a non-conductive substrate. The flexible base enables the flexible circuit to withstand vibration, dissipate heat and fold into various shapes. Due to their structural advantages, flexible circuits are increasingly used as an option for compact devices such as smart wearables, mobile phones, and cameras.

Rigid PCB vs flex PCB

In recent years, the market of consumer electronic products led by mobile electronic devices such as smartphones and tablet computers has grown rapidly, and the trend of miniaturization and thinning of devices has become more and more obvious. What follows is that the traditional PCB can no longer meet the requirements of the products. For this reason, major manufacturers have begun to study new technologies to replace PCBs. Among them, FPC, as the most popular technology, is becoming the main connection accessory of electronic equipment.

In addition, driven by emerging markets such as 5G and wearable devices, FPC will also usher in new growth space.

Then what is the difference between rigid PCB vs flex PCB? Let’s have a deeper look.

The dielectric layer in FPC is usually a homogenous sheet of flexible polyimide material. The dielectric material in a rigid PCB is usually a composite of epoxy resin and glass fiber woven cloth.

Solder mask
Rigid PCBs have a layer of solder mask on both sides. The soldermask has gaps where SMT pads or PTH holes are exposed to allow assembly of components. FPCs typically use covercoats instead of soldermasks. The overlay is a thin polyimide material that can be drilled or laser cut to make contact with components.

Manufacturing process
Most of the manufacturing steps of FPC and rigid PCB are similar. But we need some tools to hold FPC in a fixed position because of its flexibility.

Flexible FPC does not use solder mask, but uses a process called cover film or overlay to protect the exposed circuit pattern of the flexible PCB.

In terms of price alone, FPC is more expensive than rigid PCB. But FPC has many advantages in improving cost performance, such as saving space, reducing weight and high reliability.

Rigid PCB vs flex PCB – application

Rigid PCB vs flex PCB – application

Application of FPC

Mobile phone
Due to the lightweight and thin thickness of the flexible circuit board, it can effectively save the volume of the product, and easily connect the battery, microphone, and buttons into one.

Computer and LCD screen
By using the integrated circuit configuration of the flexible circuit board and the thin thickness to convert the digital signal into a picture and present it through the LCD screen;

CD player
The three-dimensional assembly characteristics and thin thickness of the flexible circuit board help turn the huge CD into a good companion for carrying;

Disk drive
Both hard disks and floppy disks are dependent on the high flexibility of the FPC and the ultra-thin thickness of 0.1mm to complete the fast reading of data, whether it is a PC or NOTEBOOK;

The latest use of FPC: Bluetooth headsets, VR glasses, phones, watches and drones and other small devices.

Application of rigid PCB

Computer motherboard
A computer motherboard is a perfect example of rigid PCB, which is a multilayer rigid PCB, used to distribute electricity from the power supply and creates a conducting path between CPU, GPU, and RAM.

Electronic products
Some low-cost products use rigid PCBs like toys, electronics gadgets, desktop devices, and solid-state devices.

Rigid PCBs can be also used in applications such as AC/DC power converters, Electronic Computer Units (ECUs), transmission sensors, and power distribution junction boxes.

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