Once upon a time, there was some truth to this. Flexible copper clad laminates were made with one grade of polyimide film that came with restrictive limitations, such as susceptibility to lower Tg (glass transition temperature), higher loss tangent, lower copper peel strength, etc.
Today, modern polymide materials overcome these obstacles, offering exceptional signal integrity, higher glass transition temperatures, and real-world performance. In fact, materials available today in flexible circuit manufacturing offer capabilities not available in rigid manufacturing. A few examples:
- DuPont AP for high reliability applications such as automotive, space and medical.
- DuPont HP for high-speed applications and offers very good signal integrity performance.
- DuPont MT+ for applications requiring very high thermal conductivity such as LEDs and efficient Heater flexes.
- DuPont RS heating materials offer completely flexible and consistent heat output.
Perhaps a better way to think about the question of material availability in flex circuit manufacturing is in the context of Applications Engineering. Applications Engineering goes beyond Design for Manufacturability, and involves correct material selection based on the application environment. These steps help ensure that your finished product will work as intended for years to come in its real-world application.
When faced with a choice between designing for rigid or flexible circuitry, instead of considering, “which one supports rolled-annealed copper” as a deciding factor, think instead, “which one offers better support for my real-world product requirements over the life of the finished product.”
In flexible circuit manufacturing, materials and their capabilities can be layered as needed. In the image at the top of this post, you can visually see materials added to support the LED and surface mounted components, leaving the rest of the finished circuit to retain greater flexibility. There is also an LPI, or Liquid Photo Imageable solder mask, a durable solution for controlling solder flows in your circuits.
A specific material choice is usually a means to a real-world performance requirement, and not a requirement itself. Today, Design Engineers can find more than enough options in flexible circuit manufacturing to meet their real-world, applications engineering needs.
When in doubt, the best thing to do is to work with your manufacturer to understand what materials are available to you, and how they can solve your applications engineering requirements.