Generally, PCBs constitute electronic components in insulating and conductive layers. Additionally, there are various PCB types like single-sided, multilayer, etc. Of the numerous types, our focus today is flex PCBs (FPCBs). Undeniably, flexible PCBs are the most expensive PCB types compared to other types. Which factors contribute to the highly flexible PCB cost?
Stick around to know more about FPCB manufacturing steps, advantages, applications, and types.
What is a flexible PCB?
FPCB (Flexible PCB) is a circuit board composed of a flexible plastic substrate like thin sheets of glass, polyimide, or polyester.
What’s more, FPCBs bend and twist easily, hence able to change their shape. However, be careful not to pick an extremely flexible PCB that can break down during twisting or folding.
Why are flexible PCBS more expensive than other PCB types?
Flexible PCB types
The most common types of Flex boards include;
- High-density Flexible PCBs; They have microvias and features like high electrical performance, better reliability, and improved usage of ICs. Additionally, they offer technical solutions related to construction, design, and layout.
- Rigid-Flex boards; Here, manufacturers use PTH technology to assemble the rigid circuit board. Then, they integrate flexible layers with rigid layers. Furthermore, the designers use both flexible and rigid layers to create small interconnect areas with low chances of failure.
- Multilayer PCB; The connection in multilayer FPCBs is through PTH or vias. Also, the PCB has ten layers of copper and is applicable in high-density connectors.
(Robotics soldering multilayer PCB)
- Double-sided FPCB; Its layers connect through (PTH) plated through holes or vias. The copper layers lie on both PCB sides and are easy to manufacture.
- Single-sided PCB; It has a conductive copper layer on one side and is recommendable for highly flexible circuit technology.
Materials used in FPCB
The flexible materials used in Flex PCB constitute adhesives and flex substrates.
- The substrate constituent is a Polyimide film (PI) that remains flexible on heating. Use an upgraded PI as the base material to overcome the low resistance against humidity.
- Since it’s hard to achieve a flexible adhesive, manufacturers use PIs that lack adhesives to embed copper layers.
- Then, a PCB manufacturer uses staffers to make areas hard rather than solder masks. They also replace solder masks with coverlay film created with PI.
The FPCB manufacturing process
The FPCB manufacturing process involves three steps that require a specific environment and raw materials, are complex, lengthy, and costly.
Step one: Building FPCB
- CAD design: First, use CAD software to prepare the design.
(Engineer using CAD system)
- Then, drill small-sized holes on a board before adding a small amount of excess material to serve PCB assembly.
- Thirdly, use a thin copper, then etch the material to compensate for line width losses.
- Next, perpendicularly hold the conductor to enable bending and folding and create routes.
- Lastly, create a ground plane to reduce the PCB's weight and improve flexibility.
Step two: Process of PCB fabrication
- Hole size – Despite small holes being hard to drill, they are ideal for FPCBs.
- Filleting helps increase flexibility by reducing stress and raising the area, and it links land termination points and joining pads.
- Using copper to make PTH and vias (conductive layers).
Step three: Testing/ Noting physical constraints
- Adhesive-backed films help overcoat the PCB.
- Secondly, screen printable liquid overcoats work on thick polymer films.
- Also, we have photo imaginable and film polymer for overcoating as it acts as a solder mask and avoids circuit traces. Additionally, it prevents overall PCB damages.
- Lastly, apply a flex circuit overlay (laminating the flex circuit design).
(soldering on PCB)
Advantages of flexible PCB
They are as follows;
- The capability of FPCB products is higher.
- Other than being durable, you can easily install them.
- You can use its subtype, single-sided FPCBs, for highly flexible applications because they’re compact and lightweight.
- You can arrange it in several stacked configurations.
- It surpasses other technologies like connectors, rigid PCBs, and wire harnesses.
- Lastly, you can shape, fold, bend, and twist it in various dimensions.
Flexible PCB cost Dependent factor
Many criteria determine the cost of FPCBs, and we have highlighted the major ones below;
- Physical Size; A large FPCB means a higher price, and its calculation is a cost per square inch (FPCB measurement).
- Circuit Construction; It depends on the materials used and the number of layers and pads. An additional layer is costly, and quality materials plus more pads also increase manufacturing costs.
- Volume; a greater volume results in a high cost.
- Layers; Added circuit layers augment assembly costs; thus, if you're comfortable with a single-sided FPCB, stick with it.
- Finishing; Almost always, a good finishing guarantees a long shelf life for FPCB. Therefore, it’ll be pricey.
- Number and size of holes; Since drilling small holes is tough, FPCB prices are higher. Not only that, but more holes equal more cost.
- Flex Board types; the type depends on layers which ultimately determines the price.
- Custom or unique specification; If you require added features on your FPCB, for instance, solder mask clearance, side plating, or contoured edges, you’ll pay extra.
How to reduce Flexible PCB cost?
Every manufacturer should have a flex PCB cost estimator list that helps lower FPCB cost.
- Keep flexible layers to a minimum; Usually, rigid laminates are more cost-effective than flexible laminates. You'll lower the cost by reducing the number of layers in the flexible circuitry.
- Keep overall layers to a minimum; If you reduce the number of layers, the number of plies of flow prepreg you’ll need will also be low. Thus, the cost decreases.
- Limit controlled impedance requirements; It might be tempting to incorporate all impedance values achievable. However, if you consider the design's cost-effectiveness, just test and model the values your flex circuit board needs.
- The copper thickness can be flexible and about 1/3 oz.
- Finally, buy FPCBs in large quantities to lower the overall cost.
Flexible PCB application
You will mostly find flexible circuit boards in the following industries;
- Medical industry – Exercise monitors, heart monitoring devices, hearing aid devices, etc.
- Automotive industry – Engine controls, anti-lock brakes, airbag systems, among others.
- Manufacturing industry – human-machine interface equipment, bar code equipment, etc.
- Electronics – Wristwatches, computer keyboards, flip cell phones, printer heads, calculators, etc.
(PCB of a computer keyboard)
- Others – Motion and light systems, LCD fabrication, tower lights, capacitors, satellites, and resistors.
- Other applications are;
- Flex-to-install/static applications (Inexpensive electrodeposited copper used), and
- Dynamic applications (Rolled annealed copper used)
As we end our post, we hope you've gained enough knowledge on flex circuit boards and why they are costly. Nonetheless, there’s still high demand for FPCBs because of their quality features.
For clarifications or inquiries, kindly reach out to us.