What are Flexible Printed Circuits?

Flexible printed circuits, also known as flex circuits, are sometimes regarded as a printed circuit board (PCB) that can bend, when in reality there are significant differences between PCBs and flex circuits when it comes to design, fabrication and functionality. One common mistake that designers make is to design a flexible circuit using the same rules as a PCB. Flex circuits require a unique set-up and have their own set of design rules. The Hemeixin team has termed this process “flex-izing,” and we have worked hard to perfect it over the last 30+ years.

Flex PCB can be defined as a patterned printed circuitry arrangement. It also refers to components that use flexible based materials that either have a flexible overlay or those that don’t. Components used in the fabrication for rigid printed circuit boards can equally be used in Flex PCB. This is possible if the board conforms to the desired flexible shape. Flex PCB is a day to day procedure used in common technologies and in particular, high-end electronics use the concept.

Electronics like desktop printers and hard disk drives use this knowledge. Flex PCB is used in a wide area of technology ranging from; automotive, medical, communication, consumer electronics, transportation, military, aerospace and in industries. They are highly preferred in the transport industry due to their capacity to withstand high vibrations. There are various types of Flex PCB; Double-Sided and Multi-layer flex which is mostly used in high-speed applications with a desire for flexibility. Double-sided Flex PCB is designed in various shapes to meet the demand of the user. They can also be designed using “Bling and Buried Vias” with Plated through Holes. Secondly, there is the Heavy Copper Flex Circuit Boards and they can be coupled with a flexible and thin copper layer that is designed to carry heavy currents. Flex PCB has a number of benefits. It helps in the reduction of wiring errors. With the traditional cabling boards, it is common to have issues with the wires. Flex PBC provides room for a high level of circuit density. It can carry heavy circuit with no setbacks. It eliminates mechanical connectors and provides a range for more robust temperatures. Flex PCB gives a strong signal quality thus enhancing the quality of the end result. This system provides an improved impedance control and reliability, lastly, Flex PCB reduces the weight and size of the board.

A flexible printed circuit consists of a metallic layer of traces, usually copper, bonded to a dielectric layer, usually polyimide. Thickness of the metal layer can be very thin (<.0001″) to very thick (> .010″) and the dielectric thickness can vary from .0005″ to .010″. Often an adhesive is used to bond the metal to the substrate, but other types of bonding such as vapor deposition can be used to attach the metal.

Because copper tends to readily oxidize, the exposed surfaces are often covered with a protective layer; gold or solder are the two most common materials because of their conductivity and environmental durability. For non-contact areas a dielectric material is used to protect the circuitry from oxidation or electrical shorting.

Each of the materials used in the development of Flex PCB must meet the demands that are aimed at making it better and long-lasting. Its base is made of a polymer film that provides the foundation for a laminate. This base material acts as the foundation on which the whole PCB is built. For bonding, adhesives are used in the creation of a laminate. Different polymer families are used to helping in the withstanding of high temperatures. A metal foil is used as a conductor and it creates the circuit paths. Copper foil is most common due to its friendly cost and high capacity in conducting currents. Flex PCB is what modern electronic technology is riding on.

Hemeixin has been a market leader in this field for many years and is manufacturing flex circuits with a layer-count of 1 to 8. We are working with polyimide foils as thin as 12.5 µm (0.5 mil) and adhesive bond plys starting at a thickness of 12.5 µm (0.5 mil). Our state of the art equipment is enabling us to produce FPCs with high output, reliability and repeatability. Depending on the dielectric thickness, laser drilled blind vias can be as small as 35 µm (1.4 mil) in diameter, and can be filled with copper in the subsequent plating process. This plating technology is enabling the use of stacked vias and via-in-pad structures.

In an effort to better serve all of our clients, Hemeixin offers a wide arrange of flexible circuit board options. Hemeixin stocks Adhesive-less FPC for our Flex PCBs. Our standard material list includes; Panasonic R-F775, ShengYi SF305, ShengYi SF201, ShengYi SF202. If you require adhesive FPC material, there may be some additional lead time for material procurement.

The number of material combinations that could go into a flexible printed circuit are nearly endless; current, capacitance, chemical and mechanical resistance, temperature extremes and type of flexing are just some of the criteria that impact the material selections to best meet functional needs. An experienced Hemeixin design engineer takes the critical requirements into consideration when designing a circuit to meet your needs.