Introduction to Flexible PCB Basics

In the 21st century, technology has become ubiquitous, permeating every aspect of our daily lives. As keen observers, we have likely noticed the trend of electronic devices becoming increasingly compact and even foldable, with implantable applications on the rise. To accommodate this shift in consumer preferences, traditional rigid PCB is no longer sufficient, necessitating the adoption of flexible PCB. In this article by TechSparks, we will provide a comprehensive introduction to this innovative PCB type that is ideal for three-dimensional spaces.

What is a Flexible PCB

Flexible printed circuit board as known as FPCB, is a specialized type of PCB that is designed to connect electronic components. This circuit board is typically made of polyimide or polyester film and is highly adept at dealing with three-dimensional space design. While rigid circuits dominated the electronics industry in its early days, the concept of flexible circuits was proposed in the 1950s and has since become a key component of most electronic devices.

flexible pcb

In order to reduce wiring, flexible PCB manufacturers use advanced electrical interconnection technology to save 70% of wiring in circuits. Although these PCB are not inherently rugged, they are designed to withstand large temperature changes, making them ideal for use in industries such as oil and gas, where borehole measurement equipment must operate in harsh environments. Additionally, it has the ability to resist radiation and ultraviolet radiation, and when combined with multi-layer lamination technology, they become highly useful in the development of aviation industry.

Features & Applications of Flexible PCB

True to its name, “flexible” is the defining feature of Flexible PCB, allowing them to bend and fold. If traditional PCB can be likened to steel, then flexible PCB are akin to paper—light and thin. This characteristic provides significant advantages in electronic devices. For instance, breaking free from the constraints of complex and compact internal spaces within devices by bending and folding. Furthermore, it fosters the development of portable and foldable devices. Moreover, it contributes to more effective solutions for weight-sensitive applications like aerospace.

For users unfamiliar with Flexible PCB, the assumption that their lightweight and thin nature implies low reliability and susceptibility to damage might arise. In reality, Flexible PCB employ high-performance substrate materials, enabling stable operation in extreme environments and withstanding temperatures of up to 200°C. These materials exhibit low sensitivity to chemical components, resisting threats from corrosion, acidity, or alkalinity. Additionally, in applications dealing with vibrations and impacts, such as automotive electronic systems, the superior flexibility of Flexible PCB allows them to absorb and mitigate physical threats.

While the cost of Flexible PCB is relatively high due to raw materials and manufacturing complexities, it is generally considered worthwhile. Through flexible circuit boards, we can establish connections with other electronic components through bending and folding, eliminating the need for additional mechanical connectors. This not only reduces the number of physical connection points but also lowers the potential risk of wiring errors, thereby enhancing the overall stability of the equipment. This is particularly advantageous in applications with higher quality requirements, such as the medical field. Hence, during project planning, it is advisable to focus on optimizing the overall project rather than solely fixating on the manufacturing cost of individual boards.

Flexible PCB Substrate Materials

With a multitude of flexible substrate materials available, having a comprehensive understanding of their properties is essential in making an informed choice. The following information on various aspects of the substrate, including peel and tear strength, flexibility, processability, chemical stability, electrical performance, and cost, will provide valuable insight. It is important to note that the values provided are generalizations and may differ depending on the specific application.

PropertiesMaterials
PolyimidePolyesterPolyamidePTFELCP
Temperature(℃)-200 to +350-40 to +125-200 to +200-65 to +200-40 to +80
Peel Strength(N/cm)15010-201.5-3.5>51-2
Tear Strength(N/cm)140100-20070-130>50100
FlexibilityBestExcellentGoodGenerallyBest
ChemicalBestExcellentGoodBestExcellent

Rigid vs Flexible vs Rigid-Flex

AspectRigid PCBFlexible PCBRigid-Flex PCB
Conductive MaterialsRigid Electrolytic CopperBendable Annealed Copper Foil/Silver Paste/Carbon Fiber
SizeLarge, thickSmall, thinCombination of both to reduce device size
ManufacturingSolder maskCover filmFlex board to rigid board
CostInexpensive for single boards, not cost-effective for projectsModerate cost for both prototyping and productionExpensive for single boards, but can reduce overall project cost
ApplicationsWide range of applicationsWearable, medical, and small electronicsBoth rigid mechanical strength and flexible bending properties for specialized applications

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