flexible PCB fabrication support multi-layer designs
Several layers of copper are etched onto flexible polyimide substrates in PCB fabrication to create conductor traces. These conductive pathways make up the flexible circuitry in single- and multilayer flex PCBs, allowing for advanced design capabilities and higher component density. Single-layer flex circuits feature access points on one side of the polyimide substrate, while multilayer flex PCBs offer multiple access points on both sides.
Unlike rigid PCBs, flexible pcb fabrication can be made with either adhesive-based or non-adhesive-based materials. The type of material used depends on the product’s end use and manufacturing process. In addition, different fabrication techniques may be necessary depending on the thickness of the flex circuits. For example, thinner flex circuits require high-performance adhesives with low shrinkage and stress crack resistance. For thicker flex circuits, acrylic thermally-cured and pressure-sensitive adhesives can be used.
Flex PCBs are also fabricated with stiffeners to support the mechanical integrity of a product. Localized rigid materials like FR4, Kapton, or aluminum can be used to strengthen the board and prevent deformation or failure. Stiffeners can also be used to reduce stress and weight balance, improve abrasion resistance and heat dissipation, and increase solder joints strength and durability.
How does flexible PCB fabrication support multi-layer designs?
Another consideration is how a flexible PCB will be bent and handled over time. To reduce stress, the flex circuit should be designed with tight trace spacing and no discontinuities or sharp bends. It is also important to keep the flex material free of pad or via drills, cutouts, slits, and holes. These discontinuities can lead to stress and cracks, which are often the cause of PCB failure or malfunction.
For reliable flex circuits, it’s important to work closely with the manufacturer during the design phase. A skilled manufacturer can provide design for manufacturability (DFM) guidance, technical feedback, and prototyping support. They can help ensure the flex circuit will be manufactured with appropriate materials, adhere to proper design rules, and meet all required test specifications.
When it comes to the actual production of a flex circuit, there are several processes that can be performed to achieve high-quality results. For example, the etching of the copper can be done using panel plating or button plating. Panel plating involves the deposition of copper across the entire surface of the board, while button plating deposits copper only on pads and vias. Button plating reduces etching time and helps achieve more precise copper deposit widths and depths, which can help to create more consistent conductor traces with regulated impedance.
Another important step in the production process is lamination, which is when the etched, plated, and coverlayed flex circuits are combined with a glass-epoxy rigid panel. For high-volume flex circuits, this is often done with a hydraulic punch and die set, which requires significant investment in tooling. For smaller runs, a blanking knife is used. This method is more affordable, but it doesn’t provide the same level of precision as a hydraulic press.
