flexible PCB fabrication done
The fabrication of a flexible PCB is an intricate process with multiple steps. The process starts with the design of the circuit using a CAD program. The design will include the placement of components and any flexing or bending requirements. Once the design is complete it will undergo optimization for production. This will ensure that the final product meets the original design criteria and can withstand flexing or bending. The conductive material used for the circuit must be flexible to allow for movement of the PCB. Typically copper is the preferred conductive material due to its high electrical conductivity and ability to resist flexing. Other conductive materials may be used, such as silver ink, carbon ink, and conductive polymer, depending on the specific needs of the circuit.
The next step in the flexible pcb fabrication process is material preparation. This includes selecting high-quality polyimide films and copper foils that meet industry standards for durability and performance. The conductive material is then cut to create the desired flex PCB shape using precision male/female punch and die sets, mechanical routing, steel rule dies or chemically milled. The holes required for the flex PCB are then drilled with a machine that ensures precise hole size and location. The board then goes through the imaging process where a photomask is aligned to the substrate and UV light is used to transfer the circuit pattern to the copper surface. The board then goes through the etching process which removes the unneeded copper from the board leaving behind the desired circuit pattern.
Once the conductive pattern is formed on the substrate, it is covered with an adhesive film. The adhesive can be made from a variety of different materials such as epoxy, acrylic, or silicone. The coverlay is designed to protect the conductive material from environmental factors such as moisture and dust. It is also designed to be able to withstand the flexing and bending of the flex PCB during its lifetime.
How is flexible PCB fabrication done?
Prior to lamination the flexible PCB must be cleaned with isopropyl alcohol to remove any contaminates that could cause damage during the manufacturing process. Once the cleaning is complete the layers of the flexible PCB are stacked together in the correct order and bonded with the application of heat and pressure. Lamination helps to prevent the flex PCB from warping or tearing during assembly and use.
After the flex PCB is fabricated it must be assembled with all of the components. This can be done by a variety of methods, including surface mount adhesive placement – where an adhesive paste or film is screen printed on the surface of the board and the component placed on top – or dispensed liquid adhesive – where a syringe or needle dispenses a small amount of liquid adhesive onto the component, which sticks to the PCB upon placement.
The finished flex PCB is then attached to any additional mechanical parts that are needed for the product to be complete such as stiffeners or mounting holes. It is then ready for shipping and use. Proper flex circuit assembly requires careful planning and excellent workmanship to avoid common defects that can affect the function and reliability of the resulting product.
These include solder beading – where the solder builds up unevenly along the edges of the flex PCB – misregistration – where SMT components are not properly aligned on the flex and rigid sections of the PCB – tombstoning – where the SMT components stand up vertically during solder reflow – adhesive oozing – where excess adhesive is coming out from under the component – fold damage – cracks or broken traces along flex fold lines – via cracks – stress fractures in plated through holes – contamination – foreign particles lodged under the components – and shorts – where electrical connections are compromised.
