Typical Thickness of a Flex PCB
The typical thickness of a flex pcb depends on the circuit’s intended use. Thinner flex circuits are lighter, but they can also be more susceptible to stress failure. Thicker flex circuits are more sturdy and durable, but they can also be more expensive. As such, it is important to understand the thickness of a flex circuit before making a purchase.
Several factors determine the thickness of a flex circuit, including the number of layers, base material, copper foil layer thickness, coverlay, and stiffener. In general, thinner flex circuits are more flexible and space saving, while thicker ones offer better durability and electrical performance. It is important to note that a flex circuit’s thickness must not exceed a threshold that will cause it to break when bending, since doing so would interfere with the device’s function and safety.
The most common base materials for flex circuits are PI and PET films. Other options include thin glass fiber and epoxy substrates. These base materials vary in thickness, but they all provide a rigid platform for the layers of the flex circuit. The conductor layer is the layer that contains the actual circuit patterns. This can be single-layered, double-sided, or multilayer. Conductor layer thickness ranges from 0.5 mm to 7 mm, with higher levels offering greater resilience and current carrying capacity.
What is the Typical Thickness of a Flex PCB?
Coverlay is the dielectric protective coating that covers the conductor layer and insulates it from corrosion, damage, and soldering. It is usually laminated on top of the base material and conductors with adhesives such as thermally cured acrylic or pressure-sensitive adhesives. Some manufacturers are even using a liquid photo-imaged polyimide that adheres directly to the copper without any additional adhesives.
Stiffeners are optional rigid sections that a manufacturer can laminate to specific areas of the flex circuit. They are useful for relieving strain, balancing weight, and improving abrasion resistance. They are often made of aluminum or stainless steel and can be attached with thermally cured acrylic, pressure-sensitive, or a liquid photo-imaged polyimide.
The thickness of a flex circuit also depends on the type of copper used. Rolled annealed copper is more resilient and less susceptible to work-hardening than unannealed copper, making it ideal for flex circuits that will be subjected to repeated creasing and movement. It is possible to use a lower-grade copper to reduce overall circuit thickness, but this will compromise the device’s reliability.
It is vital for designers to select a flex circuit that will withstand the expected amount of bending that the device will experience in its lifetime. This is especially important if the device is designed for outdoor use, such as an electric bike controller. To maximize a flex circuit’s bending capability, designers should stagger the traces across each bend radius and use tear guards to prevent stress and cracking. The conductors should also be routed perpendicular to the overall bending radius, which minimizes I-beaming and eliminates stress points that can cause trace copper breakage. In addition, they should avoid discontinuities such as vias, cut-outs, slits, and holes in the bend area.