What methods are used for manufacturing flexible circuits?
manufacturing flexible circuits
A flexible circuit is a conductor circuit printed onto a thin insulating polymer film. These are used in applications with limited space or complex shapes that can’t be accommodated by rigid PCBs. They’ve been in use since the 1950s and are one of the most important technologies in modern electronic devices. They’re used in many different fields from industrial to consumer electronics to aerospace and military applications. Flex circuits offer multiple advantages compared to rigid PCBs including compact size, reduction in weight, better impedance control and the absence of mechanical connectors.
They’re also able to adapt to small or irregularly shaped spaces, providing greater freedom of design and operation. Moreover, they take up less space than rigid boards, which helps save on the cost of material and assembly labor. They also provide superior thermal management, dissipating heat faster and more effectively.
The structure of a flexible circuit is made up of an insulating substrate, such as polyimide, and a copper layer. The copper is typically bonded to the substrate using an adhesive. However, a newer method uses vapor deposition to bond the metal to the dielectric substrate. This technique is known as dry film stack technology and is gaining popularity for its quality and performance.
What methods are used for manufacturing flexible circuits?
When a PCB is built with both rigid and flex sections, the layer stack must be carefully designed to meet the requirements of each section. This includes determining how much flexing will be needed up front, and whether it will be continuous or static (such as when a handheld ultrasound device is being used). Choosing the right materials for the flex sections can also help reduce the cost of production by reducing the number of layers required for each sub-stack and selecting cheaper rigid-flex substrates like FR-4 or MCPCB.
Another challenge is ensuring that the flex sections can support the vertical connections that may be required by the circuit. This is particularly true for flex circuits that use through-hole components. To do this, the pads on the flex section must be plated to ensure they can hold the component pins while also allowing the solder fillet to be placed around them. In addition, pad and trace layout must be carefully designed to reduce the chances of stress cracking the material during bending.
Lastly, it’s essential to apply a cover lay or laminate on the top and bottom of the flex circuit to prevent moisture, dust, or other environmental contaminants from corroding or oxidizing the copper. For example, tin finishing can be used to protect exposed traces while soft gold covering is ideal for protecting through-hole pads from damage during assembly processes.
