Flexible circuit materials are important for your board’s durability and reliability.
Surprisingly, some materials have better electrical properties than others, whereas some have excellent flexibility.
Moreover, you’ll find some materials are more durable than others.
On the brighter side, most materials suit certain applications that optimize their features and characteristics.
For example, you don’t have to go with a material with high tolerance to heat if you’re using your PCB in low heat set-ups.
In today’s piece, we are looking at flexible circuit board materials and what you should consider.
Table of Contents
- Primary Flexible Circuit Board Materials
- Why Polyimide PCB Materials Offer The Best Flexible Design Option
- Considerations While Choosing The Right Flexible PCB Material
- Benefits of Using a Flexible PCB
- Final Remarks
Primary Flexible Circuit Board Materials
The primary flexible circuit board materials include:
Flame Retardant Type-4 (FR-4)
FR-4 is a popular board PCB material made of epoxy laminates and woven glass.
Manufacturers use it to fabricate generic circuit boards for medium-speed applications.
However, the material is susceptible to heat and fluctuating voltages in high-speed circuit board applications.
Polyimide is a popular circuit board material because of its excellent thermal and mechanical properties.
Therefore, it can withstand high temperatures and is resistant to chemical exposure.
Consequently, you can employ them in harsh conditions, which is rare with rigid PCBs.
Polyester is a low-cost material with excellent mechanical properties.
However, this material doesn’t have the heat-resistant properties of the polyimide material above.
Nevertheless, this material is still a good alternative for systems that don’t generate high temperatures.
(A rigid PCB)
Polytetrafluoroethylene, or PTFE, has excellent electrical properties making it an ideal choice for flexible circuit boards. Moreover, it is gaining popularity as an alternative to the FR-4 in 5G wireless communication systems.
Manufacturers use epoxy as a thermal setting resin or adhesive in flexible printed circuit board applications. Generally, they use it to coat circuit boards against moisture and chemicals.
Remember, there’s no fit-for-all material when designing and manufacturing flexible printed circuit boards.
However, some factors determine the material selection, including the manufacturing capability and cost.
Also, you’ll find some materials expensive when you produce in mass while others are cheaper.
Why Polyimide PCB Materials Offer The Best Flexible Design Option
(Holding a flexible circuit board)
Polyimide is a popular material for manufacturing flexible PCBs. Here are the reasons that boost its popularity:
Flexibility: These highly flexible materials allow bending to different shapes without breaking.
Therefore, they are the best options for use in tight spaces and compact electronics.
High-temperature resistance: Surprisingly, these materials are heat-resistant.
Therefore, you can employ them in applications that need heat-resistant materials.
Chemical resistance: Besides being heat and temperature resistant, these materials are also chemical-resistant.
The materials resist solvents and acids that they may come across after installation.
Consequently, it is ideal for use in applications where the board may interact with harsh chemicals.
Low water absorption: Polyimide PCB materials have low water absorption.
In other words, they are waterproof, which helps prevent damage to the board from moisture exposure.
Considerations While Choosing The Right Flexible PCB Material
It would help to consider a material’s electrical properties before manufacturing your PCb.
The dielectric constant will show the amount of electrical energy the circuit board will have.
Furthermore, use a material with low dielectric constants as insulators and covers for the copper traces.
Also, ensure that the material retains its dielectric constant throughout its lifetime.
(A circuit board IC burns)
Flexible PCBs generate heat as current passes through the conducting paths.
The heat results in thermal stress, which may cause the materials and components to disintegrate faster.
Moreover, the heat can result in expansion, causing cracks and, eventually, circuit board failure.
Chemical and Mechanical Properties
The kind of environment for using a circuit board will be crucial when assessing its chemical resistance.
You want a material with excellent chemical resistance and minimal moisture absorption.
Additionally, engineers should seek materials with flame-retardant characteristics, meaning they won’t burn for long during combustion.
Also, choose a material with sufficient flexural strength to maintain the physical load.
Moreover, it should retain its flexibility and bent angle over the lifespan of the circuit board.
Even when the frequencies rise, signal performance should remain consistent with low signal loss. The materials should have a low dissipation factor (DF) for this benefit.
Benefits of Using a Flexible PCB
(Inspecting a flexible PCB at a quality check station )
Optimizing the space available in modern-day devices calls for using flexible PCBs. They are getting increasingly popular due to several benefits, including:
Saving Space: You can twist and roll flexible PCbs without risking that you may damage them. Consequently, manufacturers design them to fit into tight spaces, which the rigid PCBs would not.
Additionally, they can follow complex three-dimensional (3D) shapes making them ideal for portable devices like wearables.
Lightweight: If you’re designing a system and weight is an important consideration, use flexible PCBs. They are lighter in weight than rigid PCBs while still being equally reliable.
Durability: Flex PCBs last longer than rigid PCBs due to their flexibility. Moreover, they are less likely to break under shock and vibrations.
Better Reliability: Flexible PCBs offer better signal integrity and impedance control than rigid PCBs. As a result, they are more reliable, especially for long-term use.
Easy to install: You can bend, twist, and fold a flexible PCB to fit into various configurations. Therefore, they are easier to install and integrate into electronic products.
Environmental Resistance: Flexible PCBs can withstand extreme weather conditions that the rigid PCBs may struggle against.
For instance, they are more tolerant of moisture, chemicals, and extreme temperature.
Are flexible PCB materials affordable?
Generally, flexible PCB materials cost more than those we use to manufacture traditional rigid PCBs.
However, the cost may vary depending on factors that include design complexity and volume of production.
But that’s not to mean that they are not affordable.
Special flex PCB materials like coverlays, conductive inks, and adhesives may be affordable.
Moreover, the cost of these materials keeps getting cheaper as their production process improves.
Additionally, the benefits of using flex PCBs may outweigh their initial costs in the long run.
Is it possible to make a rigid-flex PCB?
Yes, you can make a printed circuit board that bends the characteristics of both flexible and rigid PCBs.
Typically, the boards combine multiple layers of flexible PCBs with one or more rigid PCBs through a lamination process.
Thus, the flexible sections twist to fit a certain shape, while the rigid parts provide additional support and stability.
Does material Affect flexible PCB performance?
Yes, the type of material you will use can affect the performance of your flexible PCB.
In other words, your choice of materials affects the board’s flexibility, durability, thermal stability, and electrical performance.
For instance, most flexible PCBs use polyimide for its excellent chemical resistance, thermal stability, and flexibility.
If you use any other material that downgrades the board, you risk lowering its performance.
Flexible circuit boards are reliable due to their strict material and manufacturing processes.
They require great attention to detail to ensure everything is in order during manufacturing.
For instance, you’ll need to apply coverlay to its surface to protect the circuit traces from damage and to provide additional insulation.
Applying a lower-quality coverlay can significantly impact the flexible circuit board performance.