What is a flexible PCB substrate, and what does it do? Or rather, what materials can you use for a flexible PCB substrate?
All these questions and others are being asked online, and we suspect you’re also here for answers. If so, you just came to the right place.
Generally, a flexible PCB substrate is a thin material that acts as the base layer for a PCB. It is made of polymers like polyethylene terephthalate and polyimides.
Most manufacturers shift from rigid to flexible substrates because they can bend to fit tight places.
Moreover, they have excellent characteristics like heat and stress resistance.
Therefore, they’re the perfect solution for designing compact devices and electronics for harsh conditions.
This article discusses flexible PCB substrates, including material types, uses, benefits, and characteristics.
Table of Contents
- What Is Flexible PCB Substrate Material?
- Flexible PCB Substrate Material Types
- Choosing The Best Flexible PCB Substrate Materials
- Flexible PCB Substrate Uses
- Benefits of Flexible Substrates
- FAQ
- Conclusion
What Is Flexible PCB Substrate Material?
(Human holding an orange flex PCB)
Flexible PCB substrate materials are the main materials used to form a circuit board. They mainly form the base, where we attach other board layers.
Also, the materials allow minimum electricity flow in the circuit and normally have epoxy resin reinforcement.
One characteristic of this material is that they’re thin and highly flexible. Therefore, they form the basis for flex PCB ductility.
Flexible PCB Substrate Material Types
(A clear electronic flex PCB membrane)
We have different flex PCB substrate materials with unique properties. Check them out below:
FR-4
This laminate material is impregnated using flame-resistant resin and reinforced with glass fabric.
Additionally, it’s versatile and comes from prepreg sheets.
Also, they offer the best features regarding ease of drilling and metallization.
Surprisingly, these materials feature excellent mechanical, thermal, and electrical features.
Therefore, they have a glass transition temperature of 135 degrees Celsius.
Furthermore, they have a high strength-to-weight ratio making them ideal for high-density applications.
Finally, their high dielectric loss is perfect in high-speed digital electronics.
PTFE
Polytetrafluoroethylene is among the most efficient substrates with key applications in microwave and high-power PCBs.
Additionally, the substrates have excellent dielectric strength and thermal conductivity.
Surprisingly, it maintains a high flexural strength when temperatures are very low.
These substrates are highly versatile and find application in the defense and aerospace industries.
Besides having a melting point of 327 degrees Celsius, the substrate material is thermally stable and chemically inert.
Finally, the material is environmentally friendly and repels water and oil.
Polyimide
Although these materials are more costly than FR-4, they boast a higher temperature performance.
Also, they’ll still offer higher performance in harsh conditions like vibrations and high temperatures.
Moreover, the lower expansion characteristics make them perfect for creating multiple-layer boards.
Furthermore, since the materials are chemical resistant, the resulting circuit board can function effectively in corrosive environments.
Surprisingly, the materials have high-level flexibility and excellent thermal stability.
Therefore, manufacturers prefer them for designing rigid-flex boards.
CEM
The composite epoxy materials offer the cheapest replacement for FR-4 materials.
We have different CEM materials, including the CEM 1, perfect for developing single-sided PCBs.
Additionally, CEM 1 has a glass temperature of about 122 degrees.
Alumina
Finally, on our list is this ceramic-based substrate that finds significant application in designing high-frequency electronics.
Moreover, the substrate has high thermal conductivity and is very cost-effective.
Since it can transmit heat from important components, you’ll find them more in high-power PCBs.
Choosing The Best Flexible PCB Substrate Materials
The industry has many flexible PCB substrates varying in thickness and strength.
Therefore, many designers find it difficult to select a suitable option.
Luckily, we have highlighted the properties for you to consider below:
- Mechanical properties: First, you must consider the flexural and peel strength. The peel strength involves the strength between the dielectric and copper material. On the other hand, flexural strength represents the ability of the substrate to handle mechanical stress without damage.
- Electrical properties: The electrical strength and dissipation factors are the most important. Furthermore, it would be best to consider the substrate dielectric constant, which determines impedance considerations and signal integrity. Finally, consider the substrate volume and surface resistivity.
- Thermal properties: Also, you must focus on thermal factors like thermal conductivity and CTE (coefficient of thermal expansion). CTE represents how much a material expands when exposed to heat, while thermal conductivity represents the heat transfer rate.
- Chemical properties: Finally, consider chemical properties like moisture absorption, which represents the ability of a substrate to resist moisture.
Flexible PCB Substrate Uses
(Different sizes of smart cameras with flexible PCBs)
Flexible PCB substrates find common use in the medical and industrial sectors for various technologies and applications.
Surprisingly, the material is highly durable and preferred for smaller devices.
Also, they’re common in electronics used in intense working conditions where things like high heat generation and vibrations always come into play.
But suppose we were to point out major use cases.
In that case, they include the following:
- Automobile features for smart cars
- Electronic and computing devices, including tablets, digital cameras, and smartphones
- Devices that generate high temperatures, like microwaves
- Industrial application for high-stress machines that line conveyor belts
- LED lighting systems
- Medical devices like electronic implants and surgical tools
- High power electronics
Benefits of Flexible Substrates
(A flex PCB and small electronic component)
These substrates present many benefits to their users and manufacturers.
It’s not by accident that manufacturers are slowly replacing rigid boards in their designs.
For example, while rigid board substrates are difficult to handle, flex substrates are easy to install, repair, handle, and uninstall.
We’ll summarize the benefits of flexible PCB substrates below:
Reduced Space and Weight
Generally, flexible PCB substrates have less weight and size.
Therefore, you’ll find them easier to slot into different electronic devices.
You can install them into any of the smallest electronic devices imaginable.
Surprisingly, they reduce the PCB weight by almost 90% and space by about 50%.
There are no better substrates for designing electronics in the air or space than flexible substrates.
Easier Service and Installation
Since you can flex and bend flexible substrate and PCB to fit into devices, they’re easy to install.
Surprisingly, the ease of installation trickles down to reduced manufacturing costs.
Moreover, you’ll find repairing and replacing a flexible PCB easy when something goes wrong.
Increased Reliability
The whole flexible circuit board setup doesn’t require interface connections.
Therefore, you won’t have to consider contact crimps, connectors, or solder joints. And thanks to this, there are limited cases of failure.
Furthermore, these circuit boards are built with the strength to withstand heat, shock, and vibration impacts.
Consequently, they’re more reliable and are preferable for use in high-impact devices for medical and military use.
Better Aesthetics
Most flexible circuit boards have a transparent and sleek appearance giving them easier identification and better aesthetics.
Older systems were mainly designed with many wire connections making critical parts difficult to identify.
Therefore, the normal user finds the sleek appearance less intimidating.
Reduced Assembly Costs
To begin with, flex PCBs are thin and lightweight, thus using fewer materials. Also, the circuit boards eliminate the need for connectors and wires.
Therefore, they’re less costly to design and fabricate. Luckily, the same applies to repairing these circuit boards in case of damage.
FAQ
How do you use a flexible PCB substrate?
You can use a flexible PCB substrate to create a single-layer, double-layer, or multilayer circuit board.
With a single-layer PCB, you’ll have one substrate on one side and a single conductive layer on the other.
You have a substrate sandwiched between two conductive layers for the double-layer PCB.
However, the multilayer PCB combines several single and double-layer PCBs; it has several substrate layers.
Interestingly, we use adhesives to bond a substrate to a conductive layer.
What are flexible PCB materials?
Generally, a flexible PCB is made up of multiple materials.
Check them out below:
- A substrate material including FR-4, polyimide, alumina, CEM, or PTFE
- A conductive layer including copper, gold, or silver
- Stiffeners to strengthen the layer
- Adhesives to bond layers
- Surface finish material
Conclusion
We hope now you understand everything important about flexible PCB substrate.
Without them, it would be impossible to have a flexible PCB since it acts as the base material.
As mentioned, the main PCB material types include FR-4, polyimide, alumina, CEM, and PTFE. Each material has unique features that make it perfect in certain use cases.
You can use these substrates in any application that requires durability and high performance in harsh conditions.
Moreover, flexible substrates offer better aesthetics, increased reliability, and easier installation.
Finally, count on them if you want to reduce assembly costs.
