Manufacture Flex Circuit Boards
The process of fabricating a flex circuit board can seem complex and daunting. But, if you have the right resources and support, you can produce a high-quality and reliable product. The first step in the process is to work closely with your PCB fabricator. They should be familiar with flexible materials and be able to guide you along the learning curve of designing with them. You can also choose to have them do a test run on your design using their fabrication tools to determine if the final product will be successful.
The basic components of a flex circuit board include copper traces, the PCB substrate layer, and a solder mask layer. In addition, there are often silk screen areas for component labels and other important information. Some flex circuit boards have special features such as a stiffener to relieve strain, balance weight, and improve heat dissipation. Other options include adding a protective surface finish for etching and to prevent copper corrosion.
To create a flex circuit board, the copper traces are first printed on the substrate layer with an epoxy or acrylic adhesive material. Then, a photomask is aligned over the printed circuit board and UV light is used to expose the photoresist pattern. This enables the etching of the substrate and removal of the exposed copper to reveal the desired circuit patterns.
Once the etching process is complete, the metal foil is added either by lamination to the adhesive or by chemical plating directly on the copper seed layer. Some newer fabrication processes by materials vendors are offering an alternative to copper lamination through the use of adhesiveless lamination of rolled annealed copper.
How to Manufacture Flex Circuit Boards
A coverlay is then applied to the exposed copper to protect it from damage during assembly and operation of the flex circuit board. The coverlay is an additional layer of polyimide or polyester and can be deposited in either an adhesive or non-adhesive process.
The next step is to add solder mask and any other required protective layers. The solder mask is a black epoxy material that covers the conductive copper traces and prevents them from being exposed to moisture or contaminants during the assembly and reflow soldering process. It also helps to improve signal integrity and reduce noise and EMI.
After the solder mask and other protective layers are added, the flex circuit is laminated to the rigid PCB sections in the appropriate stack-up configuration. This can be a two-layer flex circuit laminated to rigid boards with the flex section in between or a three-layer rigid-flex board.
Depending on the complexity of your flex circuit board, it may be necessary to perform electrical testing and inspection before shipping to ensure that all the elements of your design are functioning properly. This can help to catch any issues that might be encountered during manufacturing, which could result in a short circuit or other failures that would not be detectable by visual inspection. This is an important step in the fab process and should be taken seriously to avoid costly mistakes.
