Issue link: https://resources.pcb.cadence.com/i/1524390
Flex PCB Materials and Challenges Materials Choosing the right material is highly dependent on the requirements of the design. There is no 'favorite stack-up' when it comes to flex PCBs, because some areas may need more or less flexibility, may need no flexing or lots of flexing. In short, every flex stack-up is performed on a case-by-case basis, so understanding what materials you have available is the most important part of choosing the right stack-up for your application. Speak with your manufacturer on specifics, but here is a list of the materials, and when and why you would use them using a systematic approach for any application. Double-sided flex circuit board Coverlay Typically 1-2 mils thick, this protects your conductive materials and essentially replaces the solder mask you'd find on a rigid PCB. Soldermask is not quite as flexible and can crack (however, some soldermasks can still be found in specific flex applica- tions if needed). A common coverlay material is LPI (liquid photoimageable), which offers good flexibility and conformability during manufacturing. Polyimide: Offers excellent flexibility, high-temperature resistance, and good chemical resistance. LCP (Liquid Crystal Polymer): Provides superior dimensional stability and moisture resistance compared to polyimide. Colors: Coverlays can carry various colors. Black is a popular coverlay (or stiffener or shield, depending on the designer's choice) color choice in Apple consumer electronic products. Flex Substrates Coverlay counts as a flex substrate, but in this case of flex PCBs, we're considering internal layers as well. These layers are typically made from flexible polymeric films. Polyimide (PI): Offers excellent flexibility, high-temperature resistance, and good chemical resistance. Suitable for demanding applications and can be used as a mild stiffener (compared to more expensive stiffeners shown later). Adhesive-less polyimide is preferred for high-speed applications due to its consistent electrical properties. Polyester (PET): Provides good flexibility and dimensional stability at a lower cost than polyimide. However, consider the quality and how often the PCB will need to flex or bend. Polyimide is usually a safe bet for better durability. PEN (Polyethylene Naphthalate): More dimensionally stable than PET, with a higher temperature rating. 9 www.cadence.com Rigid Flex Design Guide