What materials are commonly used in PCB flex construction

PCB flex construction

PCB flex is a type of printed circuit board that can withstand bending and movement. It is used in medical devices, aviation and military equipment, as well as electronic appliances like laptops and smartphones. These devices are often subject to extreme stress and pressure, so they need a special construction to prevent them from breaking or losing their functionality. The materials that go into a flexible circuit board can have a big impact on the way it performs and handles stress.

In a pcb flex, the conductor layer is made up of a copper foil that is sandwiched between insulating and dielectric layers. The copper foil can be either rolled annealed or electro-deposited. The latter offers greater flexibility, while the former is cheaper and more durable. RA copper can also be coated with tin or soft gold for added protection and resistance to corrosion.

The insulating and protective layers are made of Kapton or polyester films. These are bonded to the base substrate by acrylic or epoxy adhesives. In addition to preventing the copper from oxidizing, these materials are also resistant to chemicals and heat. They are able to withstand high temperatures and are a good choice for flex circuits that must be soldered and subjected to thermal cycles.

What materials are commonly used in PCB flex construction

To keep the copper traces on a flexible circuit in place, they must be firmly attached to the conductor layer. A polyimide coverlay is usually used to make this happen. A coverlay is a slim, thin layer that insulates the conductors and protects them from damage. It is also used as a solder mask. It can come in various thicknesses, and it can be a dry film or liquid photo-imaged polymer.

Another important material for a flex circuit is the substrate, which must be highly flexible and tough. The most common option is polyimide, as it is a reliable choice that can withstand harsh environmental conditions and mechanical stress. It is also able to tolerate many solder reflow cycles and is capable of absorbing the expansion and contraction of temperature fluctuations.

The other material commonly used in a PCB flex is glass-epoxy laminate (GEL). It is very flexible, with a high glass transition temperature and low CTE. It also provides excellent shielding against electromagnetic interference (EMI). This material is preferred by manufacturers for military and aerospace applications, as it complies with strict UL requirements.

In the case of a flexible pcb, it is important to choose the right copper. The material should be rolled annealed or electro-deposited (ED) in order to reduce the risk of cracking and damage. In addition to this, the conductive layer should have a smooth surface and an appropriate thickness. A high metallurgy is required for a flex circuit, as it needs to withstand the stresses of bending and movement. It should also have a high density and be suitable for high current applications.