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Flexible and Flex-Rigid Printed Circuit Board Applications
Jun 27, 2018

Are you considering the use of flexible or flex-rigid PCBs in an upcoming device, product or prototype? Every device and every build begins with the core component: PCBs, or printed circuit boards. The type of PCB you choose depends on your application.


There are two major types of circuitry and boards used in industrial and large-scale manufacturing: flexible PCBs and flex-rigid PCBs. Both types differ from traditional, rigid PCBs. As you'd expect, these board types are designed using a combination of flexible and rigid materials and technologies. Flexible circuit boards are rolled with copper and similar materials, and the main goal is to provide sufficient flexibility and bending resistance. Flex-rigid PCBs, on the other hand, are built using a combination of the two technologies and have both flexible and rigid areas.

Flexible Printed Circuit Boards

Flexible printed circuit boards are considered "flexible" for multiple reasons, but the most obvious one is that their circuitry can be designed to match up with the electronic device or core product. Manufacturers are not forced to create a product or casing around the board itself. Instead, they can adapt the board to fit an existing design. This is beneficial when creating components or hardware that feature orthodox designs. For instance, if you are concerned with the total weight, portability and durability of a particular device, conventional boards may be out of the question.


Flexible boards must sometimes be adapted to a product's limitations. For example, the board size may need to be decreased, and circuits may need to be moved or redesigned to match up with case specifications and dimensions. All circuitry is laid out in a distinct pattern — including components — and then highlighted by a malleable base material, such as copper. Traditional printed circuit boards are also rolled this way, except the materials used are much heavier and more rigid.


Flexible PCB Pros and Cons:
• Reliability: Excellent due to removal of mechanical connectors;
• Cost: Higher cost than rigid or flex-rigid;
• Temperature Resistance: Fair;
• Completely flexible and pliable;
• Can accommodate any design;
• Better for rapid movement and high-stress conditions;

Flex-Rigid Printed Circuit Boards

Flex-rigid PCBs derive their name from the fact that they use a combination of flexible and rigid circuitry areas. Like most printed circuit boards, flex-rigid boards have multiple layers but generally have more than conventional designs.


These additional conductive layers are outlined with rigid or flexible insulation depending on the product needs. Outer layers on a board — no matter how many there are — often contain exposed pads or covers for safety. Conductors are deployed for the primary rigid layer, while flexible plated through-holes are used for any additional layers both flexible and rigid.


Some projects call for using traditional rigid technologies and designs. Others have limitations that prevent manufacturers from using these larger, less flexible boards. For instance, mobile and portable devices would suffer if designed with standard boards. There are just too many moving parts and components that would perform poorly when subjected to certain conditions. Mobile devices need to be portable, lightweight and able to tolerate conditions like heat, cold and, at times, moisture.


Flex-Rigid PCB Pros and Cons:
• Reliability: Excellent due to reduced need for solder joints;
• Cost: Lower cost compared to flexible boards;
• Temperature Resistance: Excellent;
• Ideal for moderate to slightly higher than normal movement and stress;
• More flexible and pliable than conventional boards;
• Long-term reliability thanks to fewer interconnects and components;
• Requires minimal maintenance;


Flexible and flex-rigid PCBs unique capabilities make them well suited for different applications. Consider the features your design requires when deciding between flexible, flex-rigid and rigid boards.

Flexible PCB Applications

Flexible circuits and their board types are often used when reliability and maximum adaptability are needed. If a circuit needs to be bent during package assembly, flexible design is required. They are also ideal when flexing and warping cannot be avoided. Flexible PCBs have come a long way in recent years, allowing them to be used in much more compact and limiting situations. This has also increased the demand for flexible circuit boards to unprecedented levels. Both flexible and flex-rigid boards are expected to see huge growth over the annual periods between 2017 and 2027.


Some things to consider before selecting flexible printed circuit boards include:
• Total needed: Flexible PCBs are often best when 20 or more conductors are necessary;
• Amount of available space: They work well when space is limited;
• Weight: If you need lightweight boards, go with flexible PCBs;
• Manufacturing ability: Flexible PCBs are generally best in situations where assembly and manufacturing labor must be limited;


Questions you might want to ask yourself when looking at flexible PCBs include
• How important is reliability?
• Are shielding and impedance control methods required?
• Do the board circuits need to be dynamic and flexible?

Flexible PCBs In Computer Electronics


Many computer components rely on flexible circuit boards for operation. The components in hard drives, for example, need to be flexible to keep up with the high speeds at which they write data as well as relatively small and thin. If operating for extended periods of time, hard drives can also get hot, meaning the board must be able to withstand high temperatures. The boards in hard drives are often credited with enabling to last as long as they do.


These issues aren't exclusive to hard drives. Computer electronics today tend to be small and thin and can sometimes reach high temperatures. You can find flexible circuit boards in many other consumer electronics applications as well including televisions, gaming systems, printers and microwaves.


Flexible PCBs in Automotive Electronics


When it comes to modern automobiles, the majority of their electronic hardware uses flexible printed circuit boards. This includes EMUs (engine management units or computers), anti-lock braking systems, air bag controllers, instrument panels and dash systems and much more.


Flexible boards can be designed to fit into smaller spaces and spaces with an irregular shape, which provides more flexibility to engineers. Circuits can also be synced up with other electronics without the need for bulky cable ties or connectors. In many vehicles, weight is also a concern. Even the smallest of add-ons can make a difference. Flexible boards are relatively lightweight and smaller than conventional parts.


The electronic components in cars also need to be able to withstand extreme conditions. They'll be exposed to extreme heat and cold when people leave their cars outside and experience intense vibration during driving.


Flexible PCBs In Smartphones


Smartphones are perfect candidates for flexible circuit boards. They are handheld, so they need to remain small, lightweight and portable. A single, thin-layer board is needed to connect and sync up all core components.


Conventional circuit boards cannot be adapted to fit inside these small spaces. Since mobile devices are taken everywhere, the hardware inside must withstand changing temperatures and environments too. Neither of these scenarios is conducive to regular circuit boards.


Smartphone manufacturers have also begun designing phones with flexible screens, even ones that are malleable enough to bend and roll up. This clearly requires the use of a flexible printed circuit board. Smartphones are now often designed with water-resistant and waterproof repelling cases designed to allow the phone to work while and after it's in contact with a liquid. Flexible boards provide the reliability that's necessary for this feature.


Flexible PCBs in the Medical Field


Flex PCBs are crucial for pharmaceutical and medical applications, especially when those circuits must survive extreme conditions inside human body.


A swallowable pill camera called PillCam makes use of super-fine flex circuitry, which must be non-toxic and durable. Patients swallow the pill, and it allows doctors and medical professionals to get an accurate view of body issues or ailments from inside the body. The pill needs to be extraordinarily small and must be able to adapt and flex as it moves through a patient's body.


Researchers have also developed a process for printing circuitry onto a flexible, organic material that can be implanted in the body to create more realistic prosthetic limbs. This new material is even more flexible than typical flexible PCBs, allowing it to move naturally without becoming damaged.


Flex-Rigid PCB Applications

Flex-rigid boards are similar to flexible boards with one major exception: They have rigid layers. They require added materials compared to purely flexible or conventional boards, but the rigid layers also make them more reliable.


When looking at Flex-rigid PCBs, you'll want to consider the same factors as flexible boards, with these exceptions
• Do you have added reliability to make up for?
• Are costs and expensive designs less of a concern?
• Are extreme temperatures and conditions a factor?
• Do you need smaller, shapeable boards yet rigid benefits?

For quite some time, flex-rigid PCB were primarily used in the military and in aerospace industries. More recently, though, flex-rigid PCB industries have adapted board designs and circuitry for use in consumer products. Additionally, flex-rigid PCBs may be what you need when motion is necessary, yet durability is also a factor. Here are some of the most common applications for these PCBs.


Flex-Rigid PCBs In Medical Wearables


Wearable devices have exploded in recent years due to the popularity of fitness trackers and smartwatches. Other wearables include smart clothes, rings and jewelry and medical devices. In the medical field, it's extremely important that doctors remain informed about their patients at all times. This could entail monitoring heart rates, breathing patterns and more. Modern wearables allow medical professionals to stay better informed about patients' health even when they're beyond the reach of doctor's office or hospital.


Many of these wearables use flex-rigid boards. A combination of flexible and stiff components is used because the devices need to be small and lightweight, yet it's vital they operate reliability under the stress of everyday activity. The added rigid layers provide the necessary dependability that keeps these electronics going even in demanding situations.


Industrial Applications of Flex-Rigid PCBs


Flex-rigid PCBs help industrial equipment to operat under consistently stressful conditions and allows for more flexibility in machinery design. They're used in radio frequency communication technology, power distribution control circuits and many other types of equipment across industrial sector.


Flex-rigid board design allows sensors to be much smaller and thinner than they could be with rigid boards. This opens up new opportunities in the industrial space for how these sensors can be used. For instance, the ideal location for these sensors could be a small or irregularly-shaped space that they couldn't fit in without the use of a more flexible or smaller component.


Power distribution control circuits have been manufactured and maintained in operation for years, but many face problems with circuit failures. This is because frequent movement and other conditions put added stress on the components.


A flex-rigid board deployment is often used to remedy these issues by providing added reliability and durability to the control circuit. The flex-rigid design allows the machines in which it's used to remain operational for longer.


Traditional rigid boards can limit the use of such machinery and hold back the component's potential. Flexible design enables manufacturers to come up with more innovative solutions for equipment performance.

Flexible and Flex-Rigid PCBs in eCommerce

The benefits that flexible and flex-rigid printed circuit boards offer are ideal in many industries. With the state of modern technology and the growing need for more portable, lightweight and versatile electronics, flexible boards are a viable solution.


In the online retail business, for instance, shipping and fulfillment warehouses use modern electronics to scan, track and report on the shipping process. A package or product must be located and selected, marked for shipment, reported as shipped and then sent through the proper procedure to reach the customer who bought it.


All of this is usually tracked and reported using a portable PDA-like device that needs to be small and portable so that workers can use them comfortable on the warehouse floor. They also need to be able to survive the sometimes-harsh conditions of a busy warehouse. This makes flexible and flex-rigid PCBs ideal for these devices.

Why Choose Flexible or Flex-Rigid PCBs?

Electronic components are becoming increasingly compact. The need to be flexible and versatile is growing. Flexible and flex-rigid PCBs aren't ideal in every situation, but professionals recommend using them in the following situations:
• Motion and mobility are a requirement;
• Flexibility and warping of the board and circuits are major concerns;
• Tight spaces, sharp angles and unorthodox form factors are unavoidable;
• Weight and portability are a major factor such as in mobile devices and handhelds;
• Repair work or maintenance is simply not possible on a regular basis;
• The device, product or board will be subjected to extreme conditions and temperatures;


In some industries, especially in industrial or commercial applications, equipment needs to endure frequent movement, rapid pressure and extreme conditions. Rigid boards are just not reliable in these circumstances over extended periods of time. That's where flexible circuitry fits the mold, so to speak. They are capable of withstanding more extreme conditions, more rapid movement, high pressure and even warping. This is crucial, because when machinery and components are moving at rapid speeds, a certain amount of flexibility and warping is to be expected.


Sometimes boards and their circuitry must be designed to strict dimensions to match a product or its casing. Under these conditions, you cannot approach just any manufacturer to order the boards in the hopes that everything will be compatible. You must rely on a proprietary board manufacturer that is capable of delivering circuitry and products that suit your unique needs.

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