Flexible Printed Circuits

26 Jul.,2022

 

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 PCB’s 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 that the All Flex team has termed “flex-izing” and have worked hard to perfect over the last 25+ years.

The word “printed” is somewhat of a misnomer as many of the manufacturing processes today use photo imaging or laser imaging as the pattern definition method rather than printing.

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.

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 impacts the material selections that best meet the functional needs. An experienced All Flex design engineer takes the critical requirements into consideration when designing a circuit to meet your needs.