When it comes to fabricating printed circuit boards (PCBs), choosing a sufficient material is vital. This will impact both the final cost and your components’ properties.
Let’s review such a popular material as polyimide/polyamide, its different types, benefits of usage, and the scope of application. Besides, the comparison of polyimide and FR-4 materials will be provided as well.
What is Polyimide PCB Material?
Polymide is a polymer that comprises multiple imide monomers. It can be both synthetic and natural. The latter is silk and wool that may also be used for PCB production. But since they are way less widespread, let’s focus on synthetic polymide more. They are made of substances that have imide monomers — plastics, through the reaction known as polymerizing.
So, polyimide is a flexible but rigid plastic-like substance that is durable enough to serve as a PCB substrate. The PCB Manufacturers widely use it due to its high cost to performance ratio.
Different Types of Polyimide PCBs
There are a total of four types of polyamides used to produce PCBs:
2nd Generation Polyimide or Pure Polyimide
This is extremely simple in production and affordable material type. It is produced without adding flame retardants, meaning that it will continue burning if exposed to open fire. This aspect is considered negative.
On the other hand, a lack of additives makes pure polyimides flexible and stable enough. Due to this feature, they fit microelectronics and small communicating devices. They also can withstand severe temperature fluctuations. These benefits make pure polyimides widespread, though it is the oldest type.
3rd Generation Polyimide
This material is basically a modification of pure polyimides. It has additives that make this type flame-resistant. So, they are unlikely to be a source of electric fires. As a bonus, this polyimide is also easy to produce.
Among the 3rd generation polyimides’ limitations is the lack of thermal stability and excessive rigidity. So, they are less frequently used for microelectronics.
Filled Polyimide
The next type features more than one filler material. For example, additives may make such polyimide flame-retardant, and an extra filler reduces resin shrinkage.
As for the mentioned characteristics, resin shrinkage is the possibility of occurrence of cracks in materials after the drilling and curing proceedings. The reduction of this effect makes PCBs more long-lasting.
Low-Flow Polyimide
The last polyimide type is known as the rigid one. It has extra-low flexibility because of the additives and flow restrictors.
This level of stiffness allows PCBs to withstand physical stresses. It makes low-flow polyimide-based PCBs long-lasting in challenging conditions.
As a rule of thumb, you should guide your selection of a polyimide type based on your electronics’ operating environment
Polyimide vs FR4: What is the Difference?
Let’s compare polyimide to another popular PCB material -FR-4.
| Factors | Polyimide | Fr-4 |
|---|---|---|
| Dimensional stability | Superior dimensional stability overall | Good dimensional stability overall |
| Flexibility | 2nd and 3rd generation polyimides are flexible. Others – don’t | It has mediocre flexibility overall |
| Chemical resistance | Good resistance value to most chemical materials | Good resistance value to most chemical materials |
| Thermal resistance | It is highly resistant to temperature fluctuation. It can be used in operating environments in the range of -200°C to 300°C the 2nd generation polyimide does not withstand open flame though |
It is moderately resistant to temperature fluctuations. It can be used in operating environments in the range of -50°C to 110°C |
| Resistance to physical stresses | Superior resistance of filled and low-flow polyimides, and moderate resistance of 2nd and 3rd generation ones | Good resistance overall |
| Durability | Well durable overall | Well durable overall |
| Tensile strength | It can withstand up to 231 MPa | It can withstand up to 70 MPa |
| Thermal cycling | It has a superior thermal cycling capacity | It has moderate thermal cycling capacity |
| Cost | Low to medium-priced | One of the most affordable materials overall |
Benefits of Using Polyimide PCBs
Polyimide is a versatile material having multiple strengths to offer. Some of its benefits to consider are the following:
-
-
Dimensional stability. The good thing about polyimide PCBs is that they do not change their dimensions under temperature fluctuations. It means that at -100°C and at 100°C, they will have nearly the same sizes. It makes the 2nd and 3rd polyimide types suitable for microelectronics.
-
Flexibility. 2nd generation polyimide comprises flame protection but offers superior flexibility overall. It is also an aspect of making such a material suitable for micro PCBs.
-
Rigidity. Low-flow polyimides have superior rigidity. That makes them suitable for some applications that require electronics to withstand high stresses.
-
Chemical resistance. Polyimide PCBs withstand some inorganic and most organic acids, making them suitable for medical electronic. Polyimide have one of the broadest ranges of temperatures available. So such boards fit most electronics operating in extreme environments.
- Great tensile strength ratio. This property allows polyimide PCBs to withstand high levels of pressure and some forms of physical stresses.
-
Dimensional stability. The good thing about polyimide PCBs is that they do not change their dimensions under temperature fluctuations. It means that at -100°C and at 100°C, they will have nearly the same sizes. It makes the 2nd and 3rd polyimide types suitable for microelectronics.
In essence, the beneficial properties of polyimide PCBs make them high-performance ones.
Versatile Usage of Polyimide PCB
It is difficult to mention an industry that is not a consumer of polyimide PCBs. But let’s outline some spheres which require the largest amounts of electronic devices with such components inside:
- Automotive industry. Great tensile strengths, durability, and resistance make polyimide sufficient for electronics inside vehicles. Transports that operate in summer and winter and require electronics components are cars, farm equipment, trucks, self-powered and other commercial vehicles.
- Medical industry. Since polyimide PCBs also offers great chemical and thermal resistance, they are used for laboratory and pharmaceutical equipment. These include high-tech electronics such as microscopes, ultrasonic water baths, thermostats, incubators, and so on.
- Military and defense industry. Devices that can be exposed to severe physical stresses and even explosions fall within this sphere. Luckily, polyimide PCBs can withstand such conditions to a certain extent. They are used to produce robotic systems, communication and navigation devices, LED lighting systems, and many more.
- Consumer electronics. These are basically any non-computerized devices for everyday use. They do not require PCBs to have specific properties, but polyimide is affordable enough to suit manufacturers’ needs. Consumer electronics include refrigerators, washing machines, LED lights, and so on.
- Computer electronics. These are a broad range of computerized devices. They require from PCBs a certain degree of flexibility and the ability to withstand temperature stresses and fluctuations. Examples of such devices include laptops, mobile phones, tablets, etc.
- Aircraft and aerospace industry. Similar to automotive and military spheres, this one requires PCBs to have durability and great tensile strength. The latter enables polyimide to withstand high pressures. Examples of electronics that fall within this category are planes, aircraft communication systems, radars, and many more.
The only scope of application that polyimide PCBs do not suit are high-frequency ones. These concerns broadcasting and communication electronics. Also, such boards do not show low outgassing meaning that they can contaminate a pure environment like a surgical room.
Final Word
Polyimide PCBs are an excellent option that offers great characteristics at an affordable cost. They have superior durability and tensile strength, can work under extreme temperatures, and fit some types of microelectronics. Some properties vary depending on the type of polyimide PCB.
Compared to FR-4, such boards are a more advanced option. However, it is not completely cost-effective for producing low-priced electronics.