The main advantage of flexible circuit boards (FPCBs) is their flexibility and portability, allowing them to adapt to various complex shapes and dynamic movements. However, this flexibility also comes with certain weaknesses in its structure. Typically, FPCB is made of multilayer films and conductive materials that can get damaged due to mechanical stress when they are bent or stretched repeatedly causing break of their conductive lines or delaminate interlayers. This susceptibility is usually observed during high-frequency usage and under high-stress condition which may lead to equipment malfunction and performance deterioration.
Common Stiffener Material and their Comparison
The FR4 (Flame Retardant) is one example of these commonly used choices among others like Polyimide (PI), Polyester (PET), etc. in the reinforcement process. The most common stiffener, FR4, has excellent mechanical and electrical properties. Unlike many other materials, FR4 has higher strength and better electrical insulation performance, which can maintain stable performance over a wider temperature range. PI, although more flexible, are more expensive and are mainly used in high-end applications. PET is cheaper, but its heat resistance and mechanical properties are relatively poor. Therefore, in most application scenarios, FR4 becomes the first choice for stiffeners.
The role and advantage of stiffener
To improve durability and reliability of the FPCB, stiffener has become a necessary means. Stiffener materials can increase the mechanical strength of the circuit board to prevent damage caused by bending and stress. By using stiffener in critical areas, stress can be effectively dispersed and the impact of mechanical fatigue on circuit boards can be reduced. Furthermore, stiffener also enhances thermal stability of a PCB and prevents material deformation and performance degradation at high temperature. On the whole, it can significantly extend the service life of flex PCBs and improve their reliability in harsh environments.
Properties and applications of FR4 material
What is FR4?
FR4 is a fiberglass reinforced epoxy resin laminate widely used in the manufacturing of PCB. The "FR" means "Flame Retardant", which is one of its most notable properties.
Properties of FR4 material
Mechanical strength: The FR4 has extremely high mechanical strength and rigidity, making it excellent in a variety of applications. Due to its superior mechanical properties, it ensures that the flexible PCB can withstand physical stress in production, assembly and use without any damages.
Thermal stability: FR4 materials have the ability to endure high temperature without any distortion or decay making them suitable for multiple welding cycles and high-temperature operating environments. Generally, its glass transition temperature Tg is 120℃ or above with some types of high-performance reaching as much as 170°C.
Electrical insulation: FR4 materials exhibit excellent electrical insulation properties which help in preventing short circuits and signal interference. Due to its high dielectric strength, FR4 can effectively isolate conductive paths in high-density circuits.
Fire Retardance: The “FR” in FR4 stands for “Flame Retardant” (flame retardant), meaning it will not easily burn when exposed to a fire source. This is necessary to protect electronic devices from catching fire.
Moisture resistance: FR4 material’s epoxy matrix enables great resistance to humidity as well as covers PCBs from corrosion and other moisture related destruction.
Chemical resistance: It is chemically resistant to most acids, bases and solvents. This allows FR4 to work stably in a variety of complex and demanding environments without degradation or failure due to chemical reactions.
Common applications of FR4 material in electronic products
FR4 is widely used in electronic products because of its excellent performance. The most common application is the substrate for printed circuit boards (PCBs), and almost all modern electronic devices use FR4 as the substrate. Other examples include computers, mobile devices, home appliances, industrial control equipment and so on. Additionally, FR4 is employed in the manufacturing of insulating layers for different electronic components like transformers and motors insulators. Moreover, it is used in high reliability requirement zones such as aerospace and military products due to its high heat resistance and flame retardancy.
Why choose FR4 as flex PCB stiffener?
The choice of FR4 as a stiffener was based on its unique performance advantages. Firstly, one of the reasons is that it possesses remarkable mechanical strength; thus can efficiently strengthen the structural stability of flexible circuit board preventing it from being broken or damaged by mechanical stresses. Secondly, the excellent electrical insulation property possessed by FR4 ensures that a reinforced circuit board can still work stably in high pressure and high frequency. Furthermore, FR4 possesses heat resistant properties and flame retardant ability making it perfect for applications that may experience extreme temperatures or fire hazards which further enhance the safety and reliability of boards.
Advantages of FR4 stiffener
There are several advantages to using FR4 as flexible PCB stiffeners. The first is cost effectiveness. The price of FR4 materials is moderate, and the processing process is mature. So we can greatly improve the performance of the board under the premise of controlling the cost. Secondly, FR4 materials are easy to process and can be processed by conventional PCB manufacturing processes, simplifying the production process of stiffener. In addition, the stable performance of FR4 stiffener enables it to maintain good performance under various environmental conditions and is suitable for a wide range of application scenarios.
By understanding the properties of FR4, we can better select the right materials to meet specific board design and manufacturing needs.
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