flexible PCB fabrication techniques vary by industry
The fabrication process for flexible PCBs varies by industry due to the different requirements of each sector. These industries include consumer electronics, automotive, aerospace and medical devices. The type of product, the design and the materials used to produce the flexible circuits also vary by sector.
The first step in the flexible pcb fabrication manufacturing process is procuring the raw materials. These include polyimide films, coverlay, bondply, copper foils and soldermask. These materials are laminated together using a heat or thermocompression bonding method to form the multilayer stackup. A solder mask is printed on top to protect the conductive paths from corrosion. Drilling of precise holes for vias and through-holes follows. These holes are then plated with copper to create the conductive pathways. This is followed by an imaging and etching process to transfer the design onto the surface of the PCBs. The image is then etched to remove the copper and leave behind the desired circuit pattern.
Stiffeners are then applied to prevent warpage of the flex PCB during soldering, bending and high-speed inserts. The stiffeners can be placed on both or one side of the flex PCB and can be either spring-loaded or non-spring-loaded. This will depend on the application and the structural needs of the flex circuit.
How do flexible PCB fabrication techniques vary by industry?
Next, the flex PCB undergoes visual inspection to verify all components are positioned correctly and that the solder joints look good. The flex circuit is then subjected to electrical testing and verification of connectivity. The testing methods may be flying probe, bed of nails or automated optical inspection. After electrical tests, the flex circuits are cut into individual boards or arrays. The fabricated flex circuits are then shipped to customers for assembly.
The flex circuits are assembled by hand or machine into the final PCB assembly. Smaller components with SMT leads are inserted into the plated through holes and reflow soldered. Larger components are bonded to the flex circuit with solder, conductive epoxy or mechanical attachment. Careful handling is required since flex PCBs are more fragile than rigid PCBs.
However, component placement on a flexible PCB requires special consideration. Components should be positioned in such a way that they are not directly on bending areas to avoid stress-related damage. The use of stiffeners—rigid sections added to support specific areas—can help maintain structural integrity where components are placed.
Failure points in flex circuits can be the result of material expansion or shrinkage, misregistration or poor assembly techniques. Typical defects include pad cratering, solder beading and shadowed joints. Keeping track of these defects can help to improve flex PCB reliability. The right assembly processes and regular inspection can minimize these defects. Other defects include stress cracks in the plated through hole barrels and contamination of the PCB from foreign particles lodged under components or blocking solder flow. Ensure proper design and engineering for a successful end-product.
