Introduction to Single-Sided Flexible Circuit Boards

Product Overview

In the flexible circuit board (FPC) family, the single-side panel is an entry-level core member by virtue of its simple structural design. Its overall construction is characterized by distinct layers: the core conductive layer is formed by a precision chemical etching process of conductive lines, which, like a carefully planned “traffic network” in accordance with the needs of electronic signal transmission, are able to accurately guide the flow of current. Below the line layer is a flexible insulating substrate, the most commonly used basic substrate for PI polyimide, this material not only has excellent insulating properties, but also provides a stable support carrier for the line. Conductive lines used in the copper skin material after rigorous screening, calendered copper skin has better flexibility and bending resistance, suitable for frequent bending application scenarios; electrolytic copper skin is more advantageous in terms of conductivity, according to the different needs of the use of flexible choice.

Core features

Insulation substrate selection: 

PI polyimide: as the industry's first choice of substrate, with high and low temperature resistance (-269 ℃ to 400 ℃), chemical resistance, high mechanical strength, even in extreme environments, but also to maintain stable insulation properties even in extreme environments, making it an ideal choice for high-end electronic equipment.

PET polyethylene terephthalate: outstanding cost performance, with good insulation and a certain degree of flexibility, suitable for cost-sensitive and mild use of the environment of the civilian electronic equipment.

aramide fiber ester: with superb tensile strength and aging resistance, it is often used in industrial control fields that require high reliability.

PVC Polyvinyl Chloride: good plasticity and insulation, low cost, suitable for some simple electronic circuit connection scenarios.

In terms of substrate processing form, the adhesive substrate realizes the close combination of the copper skin and the substrate through the pre-coated high-temperature-resistant adhesive, which has a high bond strength and is suitable for use in complex environments; the non-adhesive substrate relies on the close combination of copper and substrate. The non-adhesive substrate relies on the direct attachment of copper to the substrate, and has a thinner thickness and better flexibility to meet the demand for extreme thinness and lightness.

Types of copper skin

As a conductive core material, the performance of copper skin directly affects the efficiency of circuit transmission:

Calendered copper skin: Produced by rolling process, the copper molecules are arranged in a tight and orderly manner, with excellent ductility and resistance to bending, and still maintains good electrical conductivity after many bending tests, especially suitable for wearable devices, folding screens, etc. It is especially suitable for wearable devices, folding screens and other products that require frequent deformation.

Electrolytic Copper Skin: Made by electrolytic deposition process, it has high surface flatness, better conductivity than calendered copper skin, low signal transmission loss, and is widely used in high-precision electronic instruments.

Thickness Specification

The thickness control of the single panel reflects the level of precision manufacturing, which can be flexibly adjusted according to the space constraints and performance requirements of different devices:

Ultra-thin specification (0.05-0.07 mm): the thickness is equivalent to only 3-4 hair strands superimposed, which can be easily embedded into the small space of micro-electronic components, such as the internal wiring connection of a smartwatch and a medical micro-sensor.
Regular specification (0.1-0.13 mm): balancing flexibility and structural strength, it is the mainstream choice in the field of consumer electronics, and is widely used in scenarios such as cell phone camera modules and laptop computer wiring.

Thickened specification (0.16 mm): with better mechanical impact resistance, it can work reliably in industrial equipment and other environments that require high structural stability.

Processing

The processing process of single panel is a set of interlocking precision manufacturing system, and each process plays a decisive role in the quality of the final product：

Cutting: According to the size requirements of the design drawings, use high-precision cutting equipment to cut large rolls of substrate into standard-size veneer, with the error controlled within ±0.1 mm, to provide an accurate processing basis for subsequent processes.

 Drilling: CNC drilling machines are used to process positioning holes and connection holes at specified locations with a hole diameter accuracy of up to 0.1 mm. These small holes are not only used for positioning and calibration between processes, but also provide a physical channel for the subsequent soldering of electronic components and circuit connections.

Dry Film Lamination: A layer of light-sensitive dry film is uniformly laminated to the surface of the substrate. The thickness of the dry film is usually 25-50 microns, which closely covers the surface of the copper skin and forms a temporary protective barrier to prevent non-line areas from being eroded by the etching solution.

Exposure and development: The film with the line pattern is precisely aligned with the substrate to which the dry film is applied, the dry film is sensitized and solidified by ultraviolet light exposure, and the unexposed areas are dissolved in the developer solution, thus forming a protective layer of dry film on the surface of the substrate that is consistent with the line pattern.

 Etching: the substrate into the acid etching solution, not protected by the dry film will be chemically corroded to remove the copper skin, retained copper skin that is the formation of the required conductive line, etching process requires strict control of the temperature and time, to ensure that the line edges are smooth and burr-free.

de-filming: the use of alkaline de-filming solution to remove the residual dry film, so that the conductive line is completely bare, after the de-filming of the line surface is clean and tidy, ready for the subsequent surface treatment.

Surface treatment (first): chemical cleaning to remove the line surface oil, oxide layer and other impurities, while forming a layer of microscopic roughness, to enhance the bonding strength of the subsequent cover film.

Applying covering film and pressing curing: the covering film is made of the same insulating material as the substrate, with welding windows opened in advance, and then cured by hot pressing equipment at 160-180℃ and 0.5-1MPa pressure after applying, so as to make the covering film and the substrate tightly bonded to form a permanent insulating protection.

Surface treatment (second time): Clean and activate the exposed soldering area to improve the bonding of the plating with the copper skin.

Nickel-gold plating: electrolytic plating process is used to deposit a nickel layer (thickness 5-10 microns) and a gold layer (thickness 0.05-0.2 microns) in the soldered area in sequence. The nickel layer prevents the oxidation of the copper layer, while the gold layer has excellent electrical conductivity and antioxidant properties, which ensures the reliability of the soldering and the stability of the long-term use.

Printing Character: Use high temperature resistant ink to print product model, specification, production date and other identification information in the specified position, after high temperature curing the ink is firmly adhered to facilitate product traceability and installation identification.

 Edge Cutting: Remove excess material from the edge of the board by means of mold or laser cutting equipment, so that the product shape meets the design requirements.

Electrical testing: Special test probes are used to connect with the lines, and the conductivity, insulation resistance and voltage resistance of the lines are detected by high-precision instruments to ensure that there are no defects such as short-circuits and circuit-breaks.

Punching: According to the shape requirements of the final product, the circuit boards are punched and cut into the required shapes using precision punching dies, with a punching accuracy of ±0.05 mm.

Final Inspection and Packaging: Quality inspectors eliminate defective products through optical inspection and appearance inspection, and qualified products are sealed and packaged with anti-static packaging materials to prevent static damage and physical contamination during transportation.

Founded in 2009, our company has been deeply engaged in the production of various types of circuit boards, focusing on building the electronic foundation and providing key support for the development of different industries. Whether you are electronic manufacturing, intelligent equipment development, or other industries have circuit board needs, you can communicate with us through the mailbox sales06@kbefpc.com, look forward to answering your questions, customized solutions, and sincerely invite partners from all walks of life to consult and cooperate, and explore new possibilities in the industry.