Common Challenges Faced During Coverlay PCB

Challenges Faced During Coverlay PCB

Flex printed circuit boards (FPCBs) are used in a wide range of electronic devices. Unlike rigid PCBs, flex PCBs need to be able to withstand bending and movement. In order to achieve this, the copper layers are insulated and protected by coverlay. The selection of the correct coverlay and implementing proper processing techniques is vital for a successful flex PCB design.

Coverlay is a flexible dielectric film that is laminated to the top of a flex PCB to provide electrical insulation and protect the copper. It can be made from a variety of materials, such as polyimide or polyester, and can be either conductive or non-conductive. The thickness of the coverlay will determine its level of flexibility and protection, and it should be selected based on the minimum bend radius required by the application.

When deciding on the thickness of the coverlay pcb, it is important to keep in mind that the layer will add to the overall thickness of the flex PCB. Thicker coverlays offer better protection but will reduce flexibility. A good design team will be able to work with the fabricator to find a balance that is acceptable for the application.

The process of adding the coverlay to the flex PCB requires a significant amount of processing. The surface of the flex PCB is treated, the coverlay is applied with an adhesive, and then the entire assembly is laminated under heat and pressure to form a strong bond between the flex PCB and the coverlay. Once the lamination has cured, the edges of the board can be cut to finish the fabrication process.

Common Challenges Faced During Coverlay PCB

Careful process control during the lamination process is vital to prevent wrinkles, bubbles and delamination. Wrinkles or bubbles can result in poor adhesion and reduced conductor reliability, while delamination can cause the underlying copper to become exposed. To avoid these problems, a vacuum or autoclave press is typically used to laminate the coverlay. Alternatively, a CO2 laser can be used to ablate openings in the coverlay to expose specific areas of the flex PCB. This method offers high precision and productivity, but it can be more difficult to maintain precise opening sizes compared to mechanical routing or drilling.

Openings in the coverlay must be large enough to allow for manufacturing tolerances during copper plating, etching, punching and the adhesive squeeze that occurs during coverlay dielectric lamination. The openings also need to be large enough to accommodate the diameter of the mechanical NC drill bit that will be used for making the holes.

When the holes are not sized correctly, it can lead to misregistration between the solder mask and the trace, which can impact the quality of the assembly. Sierra Circuits recommends a distance of at least 4 mils between the trace and the solder mask opening to ensure proper imaging. To avoid this, the CAD/CAM engineering level and fabrication quality of the one-stop FPC manufacturer you choose will need to be considered carefully.