material selection play in PCB flex
A pcb flex is a flexible printed circuit board designed to handle multiple bends. Its elasticity makes it more reliable than traditional PCBs and helps manufacturers produce complex products in small packages. To ensure your pcb flex is as durable as possible, you must consider the environment it will operate in, assembly requirements, and manufacturing processes when choosing its materials.
A key component of a flex circuit is the copper-clad laminate (CCL). Professionals choose to use polyimide resin, as it has superior thermal control and retains its flexibility even in harsh environments. This makes it a preferred choice for military and aerospace applications. However, despite its resilience, it is important to remember that CCL can be susceptible to stress and tension. During the design phase of your project, it is important to minimize stress by designing a large bending radius and keeping conductors away from plated through-holes and components. It is also crucial to stagger conductors in multi-layered flex circuits, and avoid putting too much strain on the copper by using gradual and large bending angles.
Another important consideration when choosing your flex material is its dielectric constant and dissipation factor. These factors determine how well your pcb flex conducts signals and handles noise. For best results, choose a flex material with a low dielectric constant and high dissipation factor to reduce signal loss and improve the speed at which your flex circuit can transmit information.
What role does material selection play in PCB flex
Once the conductive material has been etched on the flex circuit, a coverlay is then applied to protect the layers from moisture, dirt, and damage. This layer can be made of a variety of materials, but the most common are polyester and polyimide. The coverlay must be adhered to the copper traces in a way that will prevent them from being lifted during mechanical stress, as this can cause shorts. This is often accomplished by creating a rough surface on the traces or by using anchor points to hold the flex circuit in place.
During production, the etching process creates tiny holes in the flex. Small amounts of copper are then deposited on these holes, and this process is known as panel plating. Alternatively, the copper can be plated only on the pads and vias, which is known as button plating. This allows manufacturers to better control the copper thickness and provides a more uniform appearance for the circuit. Regardless of the method used, it is critical to have a drill-to-copper distance of at least 8 mil to prevent stress on the circuit during manufacturing.
Once the pcb is drilled and has been plated, it will then be covered with a solder mask to protect the copper from corrosion and oxidation during the soldering process. The solder mask is typically made of photo-imageable epoxy or acrylic. Finally, the flex circuit is coated with a tin or soft gold finish to make it more resistant to chemicals and environmental elements. This is a vital step in the assembly process, as it ensures that the finished product will be able to work as expected.