flex PCBs handle exposure to UV radiation
The flexible PCB is a crucial part of modern electronic devices, such as calculators and mobile phones. These flexible circuits are designed to conform to the shape of the device and balance performance with aesthetics and size requirements. The flexibility of a flex PCB also makes it more durable in the face of mechanical stress or temperature exposure. However, this flexibility comes with a price: the risk of stress cracking and the occurrence of shorts due to high impedance. Fortunately, designers can protect their flex circuits with a stiffener.
A flex pcbs with a stiffener can be made from a variety of materials, but most use a base raw material that’s similar to the substrate used in standard rigid printed circuit boards (PCBs). The most popular choice is polyimide, which has excellent resistance to humidity and tears. However, a standard PI film has limited resistance to heat, so designers need to choose upgraded versions that can withstand high temperatures.
Stiffeners can be incorporated in many ways, including by adding them to the backside of the flex circuit or placing them in strategic areas on the board. They can be made of a wide range of materials, but they must be compatible with the flex circuit’s thermal and electrical requirements. Additionally, the stiffener must be able to endure the rigors of production and assembly.
How do flex PCBs handle exposure to UV radiation?
The layered structure of a flex circuit requires that holes be drilled in the copper surface for vias and through-holes. These holes connect the layers of the flex circuit and allow for the attachment of components to the board. The drilled holes are then plated with copper. This process is done by submerging the flex circuit in an electrolyte solution that’s loaded with copper ions. When a current is applied, it forces the ions into the walls of the drilled holes and onto uncovered copper surfaces.
Once the vias and pads are plated, the photoresist layer is stripped off. The etched copper is then plated with nickel or gold, which helps prevent corrosion and reduce the risk of shorts. It’s important that the nickel and gold be plated well, because a flaw in either material can undermine the flex circuit’s reliability.
To make sure the flex circuit is robust enough for its intended application, designers must consider factors like etching parameters, trace routing, and the bending radius. Etching parameters refer to the etching solutions and etch rates used to create the desired pad, trace, and through-hole geometries. Trace routing is important, as efficient routing can minimize stress hotspots that may cause damage in the event of a mechanical shock. Finally, the bending radius of the flex circuit is also important to ensure that it can withstand physical stress without causing failure.
The flexibility of a flex circuit can improve its thermal management, signal integrity, and manufacturability. It’s important for engineers to understand the risks associated with a flex circuit’s design, but they can mitigate these issues by following best practices and working closely with a qualified flex manufacturer.
