Flex printed circuit board (Flex PCB), in contrast to inflexible and Rigid PCB or HDI, forms a distinct material characteristic of flex and rigid, which is common in today's electronic product equipment. The product characteristics of flex printed circuit boards are not only flexible materials, but also lightweight structures with very thin and light configurations. The materials can be bent frequently without the breaking of insulation material of Rigid PCB. The flexible plastic substrate and wire layout of flex boards prevent them from high conduction currents and voltages. Therefore, flex board design is almost invisible in high-power electronic circuit applications, and the usage of flex boards is quite large in low current and low-power consumer electronic products.
The main materials and characteristics of Flex printed circuit board
A flex printed circuit board is a type of circuit board made of flexible materials that can be bent and folded while maintaining electrical performance. Its basic structure includes an insulation layer, a binder, a conductive copper foil layer, and a covering film or solder mask ink.
Insulation substrate for Flex PCB materials
Flex printed circuit board substrate material is highly insulating in nature and the commonly used ones are polyimide and polyester. Polyimide and polyester have their own advantages and disadvantages.
PI (Polyimide): Polyimide materials are great because they offer high heat resistance, good chemical stability and electrical properties for use in reliable electronic products of superior performance.
PET (Polyester): Polyester materials are suitable for general electronic devices as it has plasticity, durability, low cost.
Adhesive for Flex PCB materials
To make a flex printed circuit board, adhesives are needed to bind different layers of covering layers rolled copper, substrate. Typically, two types of adhesives can be applied here; acrylic acid or epoxy resin. In production structure, thickness of adhesive equals 20-40 μm out of overall thickness.
Acrylic Adhesive: It is flexible and transparent which makes it ideal for applications that require frequent bending. The adhesive is suitable for wearable devices, consumer electronics and transparent appearance demanding applications.
Epoxy Adhesive: This type has excellent adhesion quality and chemical stability so that it can be used well in various difficult environments. It can be used widely in industries such as automotive industry or industrial electronics.
Conductive copper foil for Flex PCB materials
Conductive copper foil is the core material of flex printed circuit boards. And common types include electrolytic copper foil, rolled copper foil, and high annoyed copper foil.
ED Foil (Electrolytic Copper Foil): Electrolytic copper foil is manufactured by electrolytic deposition process, which is characterized by rough crystal particles but high electrical conductivity. It is suitable for high frequency applications and occasions requiring high electrical conductivity. It has low manufacturing cost, relatively poor flexibility and it is not suitable for frequent bending applications.
RA Foil (Rolled Annealed Copper Foil): It is manufactured by mechanical rolling process, with finer crystal particles, smooth surface, good flexibility and fatigue resistance. And it is suitable for applications requiring frequent bending. But It has a higher production cost compared to ED foil and its conductivity is slightly lower than that of the former.
HA Foil (High Annoyed Copper Foil): HA foil is a high-performance copper foil, which is characterized by a very smooth and flat surface, and a high flatness of the pad. Through a special annealing process, this copper foil the copper foil has excellent flexibility and fatigue resistance, so that it can withstand multiple bending without fracture or performance degradation. It is mainly used in high-end flexible circuit boards, especially suitable for high-frequency and high-speed signal transmission of electronic devices.
Solder resist ink for Flex PCB materials
During the manufacturing process of Flex printed circuit board, solder mask ink is very important. It not only protects the copper line on the circuit board to prevent oxidation and short circuit, but also plays a role in isolating the pad and non-pad areas during welding
Thermosetting Solder Mask Ink: It has good adhesion and heat resistance because it is made through heating and curing processes. It is suitable for high-temperature welding processes such as reflow soldering or wave soldering.
UV Curing Solder Mask Ink: Cured by UV light, it has a fast curing speed and high production efficiency. It is suitable for flex printed circuit board that needs quick curing in manufacturing processes.
Photo-imageable Solder Mask Ink: Formed through exposure and development processes, it is suitable for flex printed circuit board with high-precision and high-density wiring. And it is suitable for high-precision electronic products, such as smartphones and tablets.
How to choose the most suitable Flex PCB material for your product? Flex Plus suggests prioritizing specific application environments and requirements, including working temperature, mechanical strength, flexibility requirements, and electrical performance. When we are selecting, it is important to balance the cost-effectiveness and performance advantages of materials to ensure the stability of the final circuit board.
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