Polyimides, also known as polyamides, are polymers consisting of imide monomers. This diverse group of polymers includes various materials, both natural and synthetic. For example, natural polyamides include silk and wool. In manufacturing PCBs, however, the polyamides used for board bases are synthetically mass-produced.
Synthetic polyimides are produced by polymerizing various chemistries that contain imide structures. Most commonly, the process uses bismaleimides and maleic anhydride. The different chemicals and additives used in the process can produce varied results, creating various types of polyimides that offer various advantages. Some examples are listed below:
- Pure Polyimides: Pure Polyimides, also known as 2nd generation polyimides, are produced without brominated flame retardants and other additives. As a result, they are more thermally stable and temperature resistant than many of today’s alternatives.
- 3rd Generation Polyimides: These polyimides include additives that improve flammability resistance, which can help prevent electrical fires. While these types of polyimides tend to be less thermally stable, they offer improved production times due to the lower temperatures and times needed for curing.
- Filled Polyimides: Filled polyimide systems consist of polyimide and a filler. The polyimide produces the thermal resistance and flexibility needed, but the filler helps reduce resin shrinkage, which helps minimize the formation of cracks during the curing and drilling processes.
- Low-Flow Polyimides: These polyimides consist of various resins and flow restrictors that reduce the flexibility of the material.
With time, more polyimide variations are expected to become popular. For example, 4th Generation polyimides are currently under development, which would improve copper foil adhesion and moisture sensitivity, as well as overall stability.
When should it be used?
Polyimide products are in high demand across the industry, most notably due to the material’s flexibility and strength. However, this isn’t the only reason that polyamides are favored.
When choosing a PCB base material, it’s essential to pick the material that is best suited to the application. Polyamide may be your best choice if your application requires the following PCB characteristics:
- Excellent Flexibility: Polyimide material is most commonly used to produce flexible and rigid-flex printed circuit boards because the material is exceptionally flexible.
- Excellent Tensile Strength: Despite its flexibility, polyimide materials are very strong and resistant to warping. This makes it an excellent choice for any application that may require some amount of physical durability.
- Very Thermally Stable: Polyimides are extremely stable at a wide range of temperatures. They can support operation at normally inhospitable temperatures up to 260 degrees Celsius. Additionally, they have good thermal conductivity and can also resist thermal damage during the manufacturing and repair processes.
- Resistant to Chemicals: Polyimides are chemically stable, meaning that they can be exposed to a variety of corrosive chemicals without negative effects. This is crucial in applications that include exposure to such chemicals.
- Highly Durable: On top of being resistant to heat and chemicals, polyimide PCBs are highly resistant to physical stress. They will retain their shape regardless of the physical and thermal conditions applied to them, making them ideal for applications that involve harsh environments and field repairs.
On top of these properties, polyimide has the electrical properties needed to make for a great PCB base material.
What are the applications of polyimide PCB material?
Polyamides, both natural and synthetic, are used in a wide range of applications. These materials can be found in vehicles, clothing and consumer products. Most notable, however, is their use in printed circuit boards. Specifically, polyamide boards are used to create flexible and rigid-flex PCBs, which have gained popularity within the past several years and are expected to expand in market share between 2017 and 2027.
Polyamide flexible and rigid-flex boards have found a wide range of applications in the PCB industry. Some examples include:
- Computer Electronics: Computer environments, especially laptops, require some amount of flexibility and durability in order to withstand the physical stresses of daily use. In addition, the environments in which computer PCBs operate can become exceptionally hot. Polyamide flexible and rigid-flex PCBs are ideal in these environments, due largely to their flexibility, durability and thermal stability.
- Automotive Electronics: Modern automobiles rely heavily on electronics and commonly use flexible PCBs to handle the vibrations and heat that often occurs within a vehicle.
- Consumer Electronics: Consumer electronics, including smartphones and tablets, are often made with flexible or rigid-flex PCBs due to the stresses of daily use. Flexible PCBs are further being developed for potential future consumer electronics, such as flexible tablets and smart phones.
- Medical Industry Electronics: Many medical applications require some amount of flexibility in the electronics used, especially in the case of implants, prosthetics and imaging technology, which tend to require more movement.
- Military and Aerospace Electronics: Aerospace and military applications tend to prefer polyamide materials for PCBs for their reliability, thermal stability and flexibility. This is both due to the physical stressors involved in these industries as well as the frequent necessity for field repairs, which other materials are less suitable for.
In short, polyamide is highly desirable for a wide range of applications primarily due to its flexibility, strength, durability and thermal capabilities.