by Ava
October 16, 2022
PCB knowledge
(0)
05 mins

Extensive understanding of flex PCB design

What is PCB?

A printed circuit board (PCB) is a basic building block on which electronic circuit is made to carry out desired task. It has a board like structure and commonly found in green color in electronic devices.

It provides mechanical strength and a platform for making electrical connection to the electronics component for the flow of current. Basic electronic circuit consist of single layer, while complex circuit has multiple layers depending upon the device functions.

What are the types of PCB?

All the manufactured PCB in the world consist of approximately 90% of rigid PCB. It is commonly used in our daily life consumer devices. They provide mechanical strength to the circuit and hence they cannot bend.

On the other hand where flexibility is required in the device then flex PCB are used. The flex PCB is the second type of PCB which consist of 10% of the total manufactured PCB in the world. The flex PCB design has the property of flexibility which makes them ideal for making display in electronic devices.

There is also a third type of PCB called rigid-flex PCB which consist of both rigid and flex part in it. Flex part makes the connection of the PCB and electronic components are soldered on the rigid board. The flex part is not permanently solder with rigid part, instead it used connectors for connecting to each other.

What is the feature of flex PCB?

Flex printed circuit board is highly flexible and has the properties of high wiring density, light weight, thin thickness and good bending property.

It has configured lines which save the connection time.
It reduce volume of the product and makes it convenient to carry.
It also reduces the weight of the product.
It also improve the softness of the PCB and reduces space of the product.

What are the advantages of flex PCB?

The flexibility of the flex PCB design makes a good option for devices which requires movement in their operation. The flexible substrate makes the electrical contact intact and does not beak the flow of the current. Due to this property it has number of advantages:

Its ability to freely bend and wound allows it to expand to space layout requirement.
It highly reduced weight, high density and miniaturized makes it ideal for communication devices, military equipment and aerospace technology.
It has high heat dissipation, easy assembly and good solder ability reduces the overall cost.

How to make a PCB design？

A printed circuit board(PCB) is flat board which consist of insulating surfaces. These insulating surfaces consist of conducting material for electrical connection of the electronic components. Since PCB board is building block for any electronic circuit, its designing is crucial for getting the desired output. PCB designing is an important role which includes following steps:

Before designing a PCB design it is important to consider maximum current, voltages, capacitance, shielding and component location.
Creating a schematic which show basic layout for the electronic components to be used.
Schematic designing software like altium, KiCAD, eaglePCB, etc make designing and editing lot easier and faster.
The design must fulfill IPC standard and acceptability criteria to meet industry and consumer standards.
Placement of components is checked because some component are sensitive to electrical noise and magnetic field.
After drilling the holes traces are routed to connect the components.
Identifiers, labels and markings are put on the PCB for references to the designer.

What are the considerations in the flex PCB design?

Since flex PCB design is different from rigid PCB certain things must be kept in mind before designing a flex PCB design. For flex PCB design it is necessary to keep electronic component away from bending areas.

Also the pads and vias should not be on the bending area. The hole shape is teardrop to increase its ruggedness. The traces are routed perpendicular to bend line to increase durability. Sharp angles and corners are avoided to increase lifespan of a flex PCB.

What material is used in flex PCB?

The most common rigid type PCB is made from fiberglass or metal base on the other flexible polymer is used to build flex PCB design. The flexible polymer consist of polyimide subtrate which does not get soften when heat is applied after thermosetting.

It also uses special adhesive material for attaching its layers.But manufacturers now use adhesiveless polyimide that attaches to copper without adhesive to increase its reliability. This material helps manufacturer to make thinner flex PCB design which has lower breakage.

How to manufacture the Flex PCB according to flex PCB design?

The manufacturing process of flex PCB design is different from rigid PCB. For manufacturing a flex PCB, its step-by-step process is followed:

The primary material use for flex PCB is polyimide which is expensive compare to FR4 material.Nesting technique is use to keep circuit close to each other.
Slight amount of extra material is use know as service loop which services circuit assembly.
Thinnest copper is use for greatest flexibility known as sizing conductor.
Etching is use to compensate any isotropic losses.
Routing is done perpendicular to bend line to improve bending and reducing stress.
Ground planes are added to the PCB to reduce weight and improve flexibility of the circuit.
The flex PCB design uses standard conductor width of 375 micrometer.
Size of the holes on the flex PCB design can be as small as 25 micrometer.
Manufacturers use copper to make through hole and vias.
Adhesive backed films are used for dynamic flex circuit.
Photo imaginable liquid and film polymer act as a solder mask and prevent solder from circuiting traces. It also prevent circuit from external electrification.

Conclusion

Since the dawn of electronics, the life of human being have become more and more dependent on these electronic devices. With advancement of technology, the property of bending and folding in electronic device rise.

Thus, flex printed circuit board(PCB) were manufactured for solving the problems of manufacturer and enabling them to design and make devices according to the requirement of the people. The application of flex PCB is unique which cannot be taken away from it. Its ability of bending has enabled manufacturers to make foldable display and lightweight handheld devices for both consumer and industrial use.