Are you curious about materials used in rigid-flex PCB? What are the inner workings of the high-tech PCBs power advanced electronic devices? In this blog, we’ll unravel the secrets of Rigid-Flex PCBs and explore the fascinating world of materials used in rigid-flex PCB, which are advanced circuit boards. We will provide worthy insights here if you are eager to learn about this topic. The materials that make Rigid-Flex PCBs are game-changers in the electronics industry. Read on to find out more.
Explain Simply What a Rigid-Flex PCB is
Rigid-Flex PCBs offer a unique blend of flexibility and durability, making them ideal for complex applications with limited space. These innovative boards consist of both rigid and flexible sections that are seamlessly integrated, allowing for greater design flexibility and improved reliability.
The materials used in rigid-flex PCB contribute to the boards’ overall performance and functionality. From the substrate materials that provide strength and support to the coverlay materials that protect the delicate traces, we’ll explore the components that make Rigid-Flex PCBs remarkable.
So, if you’re ready to unlock the mysteries of Rigid-Flex PCBs and gain a comprehensive understanding of the materials used in these high-tech wonders, let’s dive in together.
Substrate Materials
Substrate Materials Used in Rigid-Flex PCBs
Here are some commonly used substrate materials that play a vital role in these advanced PCB designs:
FR4 (Flame Retardant 4)
FR4 is a widely used substrate material known for its excellent electrical insulation properties.
It offers good mechanical strength, making it suitable for various rigid-flex applications.
Different variations of FR4 exist, with varying thicknesses, impedance requirements, and layer configurations, allowing for versatility in design. Specifically:
Different variations of FR4 exist, with varying thicknesses, impedance requirements, and layer configurations, allowing for versatility in design.
Standard FR4
This is the most common type of FR4, with a thickness range of 0.2 mm (8 mil) to 1.6 mm (63 mil) or more.
Thin FR4
Designed for applications where space is limited. It typically has a thickness range of 0.1 mm (4 mil) to 0.2 mm (8 mil)
High-Tg FR4
Means high glass transition temperature), and it is used when elevated temperatures are expected during the PCB’s operation. It usually has a higher Tg value, such as 170°C or 180°C.
Low-Dk and Low-Df FR4
These variations are specifically engineered for applications that require low dielectric constant (Dk) and low dissipation factor (Df) to minimize signal loss and improve signal integrity.
Prepreg FR4
They’re fiberglass cloth impregnated with resin. They come in various thicknesses, such as 0.1 mm (4 mil), 0.2 mm (8 mils), and 0.3 mm (12 mil), and are used for building up the layers in multilayer PCBs.
Polyimide (PI)
It’s the most popular choice for flexible substrates in rigid-flex PCBs. PI can also be used as a coverlay in rigid-flex PCBs.
As a substrate, polyimide is a high-performance polymer with excellent thermal stability, mechanical strength, and chemical resistance. Polyimide substrates provide a solid foundation for the circuitry and components of the PCB.
The material offers good insulation properties and can withstand the temperatures and stresses encountered during PCB assembly and operation.
Liquid Crystal Polymer (LCP)
LCP is a specialized substrate that provides excellent electrical and mechanical properties for rigid-flex PCBs.
It offers high-temperature resistance, low moisture absorption, and exceptional dimensional stability.
LCP substrates are known for their compatibility with high-frequency and high-speed applications.
PTFE (Polytetrafluoroethylene)
Particularly great for applications that require high-frequency performance.
PTFE is a fluoropolymer known for its excellent electrical properties, including low dielectric constant and loss tangent.
It offers exceptional signal integrity, making it suitable for high-frequency applications such as RF and microwave circuits.
PTFE substrates are also known for their high thermal stability and resistance to moisture and chemicals.
Polyester (PET)
PET is a flexible and cost-effective material that offers good mechanical properties.
It is used as a substrate material in rigid-flex PCBs and finds its application as a coverlay material.
Pprovides insulation and protection for the circuitry.
Polyether Ether Ketone (PEEK)
PEEK exhibits excellent chemical resistance, high-temperature stability, and exceptional mechanical strength.
It offers outstanding dimensional stability.
These substrates can withstand harsh environments and provide reliable performance in applications such as aerospace, automotive, and medical devices.
Note that different variations can be available within each substrate material category in the market. The needs of your PCB design may change the precise type and grade of the material.
In the next section, we will delve into the essential coverlay materials used in rigid-flex PCBs, which play an urgent role in protecting the circuits and ensuring their functionality.
Coverlay Materials
Essential Coverlay Materials Used in Rigid-flex PCB
Are the following:
Polyimide (PI) as a coverlay material
As mentioned previously, polyimide is a versatile material that can be used both as a substrate and a coverlay in rigid-flex PCBs. With its high-temperature resistance, it can withstand the soldering process during PCB assembly.
When used as a coverlay, PI provides a protective layer over the circuitry, offering insulation, moisture resistance, and shielding from contaminants. It acts as a barrier, safeguarding the flexible portions of the PCB from moisture, dust, and other contaminants, significantly enhancing the circuit’s overall reliability and longevity.
Liquid Photoimageable Solder Mask (LPSM)
This material is another important coverlay material used in rigid-flex PCBs. Here’s why it is essential:
- LPSM is a liquid-based material applied to the PCB and then exposed to UV light to selectively cure and define the desired pattern.
- It provides a protective layer that shields the circuitry from environmental factors and prevents solder bridges and short circuits during the soldering process.
- Offers excellent adhesion to various substrates.
Acrylic
Known for its versatility and ease of application. Here’s why acrylic is great as one of the materials used in rigid-flex PCB:
- Acrylic offers good electrical insulation properties and protection against moisture and contaminants.
- They can be easily applied to the flexible portions of the PCB
- Available in different thicknesses, allowing freedom in flexible PCB design
Epoxy-based coverlays
Epoxy-based coverlays are widely used in rigid-flex PCB due to excellent adhesion properties and durability.
- These coverlay materials used in rigid-flex PCB offer high-temperature resistance, making them suitable for the soldering process
- They provide excellent electrical insulation and mechanical strength
- Epoxy-based coverlays can withstand harsh environmental conditions and provide long-term protection against wetness
Thermoplastic Polyurethane (TPU)
Here are the specific reasons TPU is popular as one of the materials used in rigid-flex PCB:
- TPU offers excellent flexibility and elongation properties, allowing it to conform to the curved and flexible areas of the PCB without compromising its protective function.
- It provides good resistance to abrasion, impact, and chemicals,
- Maintains the required flexibility for the rigid-flex design.
Polyester (PET)
Various types of PET films are available in the market, including transparent PET, white PET, black PET, and metalized PET. Each type offers specific properties and characteristics. For instance:
- Transparent PET provides excellent clarity and visibility
- White PET offers better opacity and contrast.
- Black PET is commonly used for light-blocking applications
- Metalized PET provides enhanced shielding properties
Polyethylene Naphthalate (PEN)
It’s another popular coverlay material with different options available in the market. PEN films are available in various thicknesses, such as 25µm, 50µm, and 75µm. Additionally, PEN films may have different surface finishes, such as matte or glossy, offering flexibility in design and appearance.
Thermosetting materials
They come in different formulations, used as coverlays in rigid-flex PCBs, such as epoxy-based coverlays. These formulations may have varying characteristics and performance properties, varying due to the following:
- Glass transition temperatures (Tg)
- Dielectric constants
- Coefficients of thermal expansion (CTE)
Here’s a short video explaining the importance of these concepts:
UV-curable materials
The market offers a range of UV-curable materials for coverlays as materials used in rigid-flex PCB. These include UV-curable liquid coatings, adhesives, or solder masks. They can be found in different formulations, viscosities, and curing characteristics. UV-curable materials may also come in various colors, such as transparent, black, or white, providing options for different aesthetic and functional needs.
Adhesive materials used in rigid-flex PCB
These things play the role of bonding the layers of a rigid-flex PCB together. Let’s specify some common types of adhesive materials used:
Epoxy-based adhesives and modified epoxy adhesives
There are various types of epoxy-based adhesives available in the market, including:
Standard epoxy adhesives: These provide excellent bonding strength and chemical resistance.
Electrically conductive epoxy adhesives: They enable electrical connectivity between components while providing bonding.
Flexible epoxy adhesives: Offer enhanced flexibility to withstand bending and flexing in rigid-flex PCBs.
Low-temperature epoxy adhesives: They are suitable for heat-sensitive components and are designed to cure at lower temperatures.
Acrylic adhesives
Acrylic adhesives available for sale include:
Transparent acrylic adhesives: These provide excellent optical clarity and are commonly used for bonding display components.
High-strength acrylic adhesives: Results in superior bonding strength and resistance to environmental factors like moisture and temperature variations.
Flexible acrylic adhesives: These are designed to maintain bond integrity in applications requiring flexing or vibration resistance.
Pressure-sensitive adhesives (PSA)
Several types of PSA are out there, including:
Acrylic PSA: Known for their high tackiness and excellent bonding to various substrates.
Silicone PSA: They are suitable for high-temperature applications and give good temperature resistance and low outgassing properties.
Rubber-based PSA: These provide excellent initial adhesion and conformability.
Various Adhesives for Rigid-Flex PCBs
Thermal conductive adhesives
Obtainable options include:
Epoxy-based thermal conductive adhesives: They provide reliable bonding and effective heat transfer in rigid-flex PCBs
Silicone-based thermal conductive adhesives (see below)
Silicone adhesives
Are known for their excellent temperature resistance and flexibility. They are available in various formulations, including:
High-temperature silicone adhesives: Designed to withstand extreme temperatures, they are suitable for applications where heat dissipation is crucial.
Room-temperature vulcanizing (RTV) silicone adhesives: These adhesives cure at room temperature, providing good adhesion to a wide range of substrates.
Low-volatile silicone adhesives: Offering low outgassing properties, they are commonly used in electronic applications where minimal contamination is essential.
Cyanoacrylate
Also known as instant adhesives or superglues, cyanoacrylate adhesives bond rapidly through a chemical reaction with moisture. They come in different viscosities, such as:
General-purpose cyanoacrylate adhesives: Are excellent for joining a variety of materials, such as rubber, metal, and plastic.
Flexible cyanoacrylate adhesives: Designed to withstand bending and flexing, they are suitable for applications where joint movement is expected.
High-strength cyanoacrylate adhesives: Means superior bonding strength, they are used for applications requiring robust adhesion.
Polyurethane
Provide excellent bonding strength. Polyurethane is available in different types, such as:
Single-component polyurethane adhesives: These adhesives cure when exposed to moisture or specific environmental conditions
Two-component polyurethane adhesives: These adhesives require mixing two components to initiate the curing process
Flexible polyurethane adhesives: Designed to maintain adhesion and flexibility under dynamic conditions, they are suitable for movement or vibration applications.
Note that Polyurethane is a versatile material that can serve as both an adhesive and a coverlay material for rigid-flex PCBs. As a coverlay, it offers excellent mechanical strength, flexibility, and resistance to environmental factors.
That’s quite a list! The adhesive material used in rigid-flex PCB options we provide you with gives you the flexibility to select the most suitable one for your needs. Great, let’s move on to the next category, then.
Conductive materials
Conductive materials used in rigid-flex PCB
The materials below are chosen for their excellent electrical conductivity. They allow efficient transmission of signals and power within the circuit.
Copper
Due to its excellent electrical conductivity and cost-effectiveness, copper is widely used as a conductive material in rigid-flex PCB. Some common types of copper used in PCB manufacturing include:
Electrolytic Tough Pitch (ETP) Copper: This is the most common type of copper used in PCBs, known for its high purity and good conductivity. It is readily available from manufacturers such as Olin Brass, KME, and Aurubis.
Oxygen-Free Copper (OFC): OFC is a high-quality copper with a minimal oxygen content, ensuring better conductivity and corrosion resistance. Some well-known manufacturers of OFC include Wieland, Mitsubishi Materials, and Sam Dong.
Rolled Annealed (RA) Copper Foil: RA copper foil is commonly used for flexible circuits in rigid-flex PCBs. Companies like Mitsui Mining & Smelting, Doosan, and JX Nippon Mining & Metals manufacture it.
Silver
It is another highly conductive material used in rigid-flex PCBs. It offers excellent electrical conductivity and is suitable for high-frequency applications. Some common types of silver conductive materials used in rigid-flex PCB manufacturing include:
Silver Ink or Paste: These inks and pastes are used in printed electronics for conductive traces and pads. They are available from manufacturers such as Henkel, DuPont, and Heraeus.
Silver Plating: It’s a process that deposits a thin layer of silver onto the PCB surface, providing a conductive coating. It can be sourced from companies like MacDermid Alpha, Atotech, and Technic.
Gold
Valued for its superior conductivity, gold is also known for its corrosion resistance and strength. It is commonly used in connectors, pads, and contact points in rigid-flex PCBs. Some types of gold coatings used in PCB manufacturing include:
Electroless Nickel Immersion Gold (ENIG) for the gold plating process (we will discuss this under Surface Finish options below). Leading manufacturers of gold material for rigid-flex PCB include MacDermid Alpha, Atotech, and OMG Electronics.
Hard Gold Plating is commonly used in high-wear areas and can be obtained from companies like Tech-Etch, Entek, and KPW.
Aluminum
This material is a lightweight and cost-effective conductive material used in rigid-flex PCBs, especially for heat dissipation purposes. One type of aluminum PCB is well-known in rigid-flex PCB production. It is Aluminum Core PCB. These PCBs have an aluminum core, providing superior thermal conductivity. Manufacturers such as Bergquist, Ventec, and Arlon offer aluminum-based PCB materials.
Carbon
The carbon-based conductive materials used in rigid-flex PCB are for specific applications that require low resistance, electromagnetic shielding, or antistatic properties. Carbon Ink and Carbon Paste are the most common carbon-based materials used in rigid-flex PCB. Printed electronics use These for conductive traces, grounding, and shielding. They can be sourced from DuPont, Henkel, and MG Chemicals.
Again, as we have said before, it’s recommended to consult with reputable PCB material suppliers or manufacturers to explore the options that best suit your project. Meanwhile, let’s answer an essential question: why do we need these materials used in rigid-flex PCB? What makes them so special?
Benefits vs. Drawbacks of Using the Right Materials for Rigid-Flex PCB Projects
Using the right materials in rigid-flex PCBs is crucial for ensuring their optimal performance and reliability. Neglecting the selection of appropriate materials can have significant repercussions on the functionality and longevity of the PCB design. Here’s why these specific materials are essential:
The right substrate materials
Imagine you’re designing a high-speed communication device, a 5G base station module, and you choose a low-grade substrate material with poor signal integrity. As a result, the device experiences significant signal degradation, leading to data loss, corrupted transmissions, and unreliable communication.
Correct coverlay
Let’s say you neglect to use a suitable coverlay material with adequate protection against environmental factors such as moisture and dust in a flexible section of a rigid-flex PCB. Result: Over time, the exposed flexible traces become vulnerable to moisture absorption and contamination, leading to corrosion, short circuits, and even complete failure of the PCB. The device may malfunction or stop functioning altogether, rendering it inoperable.
Superb adhesive materials
For instance, you opt for a subpar adhesive material during the lamination process of a rigid-flex PCB. Result: Over time, the weak adhesive bond deteriorates, causing delamination and electrical failures. The device becomes unreliable, and certain components may cease to function.
Conductive materials that solve the issue
Suppose you cut corners and use a lower-quality conductive material in an electric vehicle (EV) battery management system; it’s a power-intensive application. The inadequate conductivity of the material causes excessive resistance, leading to heating issues and thermal problems. The EV will get overheated, causing performance degradation or long-term damage.
Surface finish materials for perfection
Consider a situation where you neglect to apply a suitable surface finish to protect the copper traces on the PCB. Result: Without proper protection, the exposed copper is prone to oxidation, leading to poor solderability and increased susceptibility to corrosion. This can result in intermittent connections, malfunctioning components, and premature device failure.
As you’ve learned about the significance of using the right materials in rigid-flex PCBs to ensure optimal performance and avoid potential issues, you might be eager to discover a reliable solution for sourcing these reputable materials. Our upcoming section has just the answer you’ve been looking for. We understand your need for convenience and quality, so we’re excited to introduce you to MV Flex Circuit.
Reputable Manufacturer for Rigid-Flex PCB
Where to Get Reputable Materials Used in Rigid-Flex PCB?
Are you looking for materials for your rigid-flex PCB projects? Finding a trustworthy supplier is crucial. It would help if you had a partner who understands your unique requirements, values quality, and offers a wide range of genuine materials. Look no further than MV Flex Circuit, your trusted source for high-quality rigid-flex PCB materials.
MV Flex Circuit: Your Trusted Source for Genuine and High-Quality Rigid-Flex PCB Materials
At MV Flex Circuit, we pride ourselves on being a leading provider of top-notch materials specifically designed for rigid-flex PCB applications. We understand materials’ key role in your PCBs’ performance, reliability, and longevity. We are dedicated to providing top-notch Flex and Rigid-Flex goods that precisely fit your needs.
When you choose us as your Rigid-Flex PCB as your supplier, you can expect nothing less than excellence. We’ve got you covered from substrate materials to coverlays, adhesive materials to conductive materials, and surface finish materials.
As a respected international PCB maker, we have established strong partnerships with reputable manufacturers who share our commitment to excellence. Our materials undergo rigorous testing and quality control processes to ensure they meet the highest industry standards.
MV Flex Circuit is the name you can count on. To discover more Rigid-Flex and Flex PCB possibilities, contact us now!
