Almost all technological marvels owe their existence to PCBs or printed circuit boards. Without them, electricity will never be harnessed to its full use. In case you don’t know or forget, a PCB’s purpose is to hold electrical components together to maintain a stable connection at all times.
The boards are also economical solutions since there will be fewer wires used and lesser interference and resistance incurred. As innovative ideas come up, there’s a need for PCBs to be flexible in order not to compromise the designs. Fortunately, useful materials like Kapton are developed to create flexible PCBs.
What Is Kapton Flexible PCB
Kapton flexible PCBs, as the name suggests, are flexible PCBs made from Kapton. To be specific, Kapton is the backbone of the said PCB. You may have been wondering what are flexible PCBs in the first place. Before we proceed, let’s have a brief understanding of the types of boards.
Types Of PCBs
- According To Layering
PCBs generally have 2 layers – one that is conductive and one that is not. Electrical components have legs for getting soldered to a specific connection. In “single-sided” PCBs, the electrical components are placed on the non-conductive side and their legs go straight through a hole towards the other side which has the conductive material (commonly copper).
In “double-sided” PCBs, both sides have conductive material. The components will have to rely on areas that are etched (a process undergone to remove the conductive material or copper) for placements. This type is used to utilize small compartments and limited wire length.
There are also what we call the “multi-layered” PCBs. For a much simpler explanation, it is a PCB over a PCB. These are used for very complicated circuits wherein multiple components need to process without lagging, such as those boards used in tablets or TVs.
- According To Structure
There are 2 types of PCBs according to structure: the rigid PCB and the flexible PCB. Rigid PCBs are the general purpose type of PCBs used in electronics which are used from a simple light switching circuit to the more complicated motherboard of a personal computer. The conductive layer is on a surface of a sturdy PVC board.
On the other hand, flexible PCBs are used for special purposes wherein folding dynamics are essential to the design of a particular system. The conductive layer is laid out on a polymer film. One of the most commonly used is Kapton. Note that both rigid and flexible PCBs can be single-sided, double-sided, or multi-layered.
What Is Kapton
As mentioned, Kapton is a type of polymer, specifically a polyimide film, used for creating flexible PCBs. Its development during the 1960s is credited to DuPont Corporation, one of the world’s leading companies in producing chemicals and materials for industrial use. The motivation for developing Kapton is the need for PCBs that can withstand high heat.
During the production process, it was found that Kapton remains stable from temperatures of -452 to 752 degrees Fahrenheit. It was also determined that the material can withstand various forms of mechanical stresses. One could argue that thanks to Kapton, we have foldable gadgets, portable appliances, and compact electrical systems today.
How Are Kapton Flexible PCBs Made
To make Kapton flexible PCBs, the first thing to do is to develop polyimide. It all starts by having dianhydride and diamine monomers react to each other under condensed conditions. There can be many types of Kapton made and each of them has specific applications.
The standard variant is the “Kapton HN.” Other variants are “FN” for applications that require heat sealability, “HPP-ST” for situations that need utmost stability and adhesion, and “CR” for conditions that need to withstand the impacts of corona (not the virus, but the radiation emitted by solar flares).
Now that the Kapton is ready, the next process is to bond it with a conductive material. Assuming that the PCB has to be a single-sided type, the conductive material is on one side and the Kapton is on the opposite. Note that Kapton is a polymer at its core, which is also the core of plastics. Therefore, Kapton is an insulator. It is thermally conductive, but not electrically.
When etching a flexible PCB, the conventional way used for etching rigid PCBs is not applicable. A special printing machine typically uses a stencil to etch the flexible PCB. Kapton is safe for public use since it complies with the ASTMD-5213-07 standard, which is a specification for polymer resin film applications on electronics.
When Is Kapton Flexible PCB Used
Kapton flexible PCBs are used in many different applications due to their wide range of thermal resistance and durability against mechanical stress. For any device wherein heat and stress are part of the operation, the Kapton flexible PCB has to be used.
Familiar Use
Most gadgets like smartphones, tablets, and laptops use flexible PCBs on certain portions of their overall designs. Kapton can be used on those gadgets that demand high performance such as when used for gaming, on outdoor adventures, and those that are designed to be water-resistant while submerged in water. Kapton flexible PCBs are also used for labeling.
Special Use
For complicated electrical systems designed to be used in unusual locations such as in mountainous places, cold regions, near geothermal sources, and even in outer space, the Kapton flexible PCBs are undoubtedly very reliable.
The low dielectric constant of the boards contributes to the smooth flow of electrical signals. This is very crucial, especially on systems that need real-time data. Furthermore, Kapton’s resistance to a fair amount of radiation makes it trustworthy to be used for aerospace systems and chemical industries.
The flexibility of a Kapton board is not to be taken for granted. In fact, because of its excellent torsion effect, it can be used on highly dynamic applications such as in automobiles and weapon systems.
Advantage Of Using Kapton Flexible PCB
Kapton flexible PCBs are commonly preferred due to their many advantages. Here are the following:
1. Allows Flexibility
It is important to emphasize that a PCB is made flexible because of a material like Kapton. How flexible can it get? The tensile strength of a Kapton flexible PCB is said to be approximately 231 MPa. In comparison, FR4, another common material used for PCBs, has a tensile strength of approximately 70 MPa only. This means that Kapton PCBs can withstand being stretched more.
If you have observed recently, there are many ‘foldable’ electronic products out in the market. How is that possible? That is because portions of their designs utilize the Kapton boards. A smartphone’s performance stays uninterrupted while the range of controls and its display is being extended more.
Because of the Kapton PCB’s amazing flexibility, reducing the space of electrical systems is now possible. What used to be very bulky decades ago are now slim and stylish, without even compromising anything functional. Moreover, Kapton PCBs are among the select few materials that can function well while being used as multi-layered PCB.
2. Withstands Varying Temperatures
The thermal resistance of Kapton is undoubtedly amazing. It can withstand temperatures as cold as -452 degrees Fahrenheit (or -269 degrees Celsius) to the hellish 752 degrees Fahrenheit (400 degrees Celsius).
Electrical systems that are meant to be used in remote locations for research purposes must use Kapton PCBs. Whether for scientific, military, environmental, or aerospace applications, those flexible PCBs are highly consistent.
3. Endures Stressful Conditions
Since Kapton flexible PCBs can handle mechanical stress well, they can be used on circuits that are exposed to vibrations such as those used on motors. Robots are very good examples wherein highly regarded PCBs can be applied.
Another condition that they can manage well is radiation exposure. They can withstand high levels that even the effects of solar flares can be handled well.
The Pros And Cons Of Using Kapton Flexible PCB
Although you have read great things about Kapton flexible PCBs, there will still be situations or conditions wherein using them are disadvantageous. To guide you clearly, below is a concise list of the pros and cons when using the said PCBs.
Pros:
- Excellent thermal conductivity
- Excellent flexibility, which is helpful when utilizing design area or space efficiently
- Excellent stability against mechanical pressure such as bending and torsion
- The low dielectric constant for improving the electric signal flow
- Resistant to varying levels of radiation
- Contribute to the aesthetics of the design
- Ease of soldering
- The low-cost solution in terms of high-end applications
Cons:
- High initial cost – means that Kapton PCBs can be impractical to use on some common circuits such as those that can be made DIY
- Usage of special equipment – etching of circuits on a Kapton PCB needs a printing machine that can cater to flexible PCBs
- Limited designing area – since Kapton is available as a strip of polyimide film, the circuit designs are limited to the width of the material
- Difficult to repair or revise – when used as a multi-layered PCB, it can be difficult to repair if there will be a damaged component or to revise if there are faults in making connections
Conclusion
Kapton flexible PCBs are highly versatile due to Kapton’s impressive properties. There can be many industrial applications for the said PCBs. Amazing they may be, there are still disadvantages when choosing to use them. In the end, the usage will always depend on the intended purpose of the circuit.
