Flex Cables: The Unsung Heroes of Electronic Flexibility

Flex cables, also known as flexible printed circuits (FPCs), are an essential component in modern electronics that enable compact and flexible connections between PCBs and displays/components. Though often overlooked, flex cables are vital for electronic flexibility and durability across industrial, medical, automotive and consumer devices.

What Are Flexible Cables and How Do They Work?

A flex cable consists of thin, flexible copper traces laminated onto a thin polyimide film. The traces are photolithographically printed onto the film in the same process used to produce traditional rigid PCBs.

The flexible nature of the thin plastic substrate allows the cable flex to bend and twist repeatedly without damage to the copper traces. This makes them ideal for applications where connections need to endure frequent flexing motions like hinges, sliding mechanisms and folding devices.

Flex cables use many of the same connector types as traditional round wire cabling but in compact surface-mount packages including FFC/FPC, FFV, and FFC/FPC mezzanine connectors. These low-profile connections allow flex cables to interface between PCBs and displays/components in tight spaces.

Flexible cables are commonly used for:

• Connecting PCBs to flat panel displays (LCD, OLED)
• Interconnections between PCBs in folding devices
• Part wiring in consumer devices
• Critical cabling in automotive systems
• Medical devices like endoscopes

The Evolution of Flex Cables

The need for flex cables arose with the miniaturization of electronic devices. As devices became smaller and more compact, there was a pressing need for a wiring solution that could fit into tight spaces without compromising on functionality. Enter flex cables, which could be folded, twisted, and even rolled up, making them perfect for

Benefits of Cable Flex

There are several key benefits that make flexible cables well suited for electronics:

Compact Size – The thin, flat form factor allows flex cables to fit into tight spaces where bulky round cables won’t work. This enables smaller product designs.

Flexibility – The ability to twist and bend repeatedly without breakage allows dynamic connections and moving joints. Flex cables are made for frequent motion.

Durability – Carefully engineered materials like polyimide withstand wear and tear better than round wiring. Flex cables last despite frequent bending.

Lighter Weight – The lack of shielding and thin traces means flex cables weigh a fraction of comparable round cables. This lightness aids portability.

Easier Assembly – Surface mount connectors integrate easily onto PCBs and components without soldering or screw terminals needed. Automated production is simpler.

Lower Cost – Printed circuits cut the need for manual assembly and shielding required in round cables. Flex cables can lower costs.

For applications requiring electrical connections that move and bend repeatedly, flex cables offer the ideal combination of flexibility, durability, and compact size.

Types of Flex Cables

There are several varieties of flex cables to suit different mechanical and electrical needs:

Single Sided Flex Circuits

• Copper traces on only one side of the substrate
• Suitable for simple low-density connections
• Often used for dynamic displays and basic internal wiring

Double Sided Flex Circuits

• Traces etched on both sides of the substrate
• Allows for higher trace densities
• Enables more complex wiring in tight spaces
• Used in advanced displays, printers, disk drives

Multilayer Flex Circuits

• Multiple trace layers laminated together
• Highest trace densities for complex applications
• Allows crossing signals on inner layers
• Used in medical, telecom, automotive, aerospace systems

Rigid-Flex Circuits

• Combines rigid PCB sections with flexible cables
• Allows flexible joints on primarily rigid PCBs
• Simplifies design of integrated flexible/rigid electronics
• Used in cell phones, laptops, military radios, etc.

Shielded Flex Cables

• Flex layer is sandwiched between ground planes
• Protects signals from EMI/RFI interference
• Often used in medical, automotive, and data devices

High Speed Flex Cables

• Engineered for fast data transmission
• Controlled impedances to match system characteristics
• Used in high-frequency applications like USB 3.0, HDMI

Design Considerations for Flex Cables

Successfully implementing flex cables requires following clever design practices tailored to their unique properties:

• Allow slack Avoid pulling flex cables tight to prevent tearing or distorting joints. Leave slack for free movement.
• Consider fatigue life Don’t exceed bend radius limits which cause metal/plastic fatigue over repeated flexing.
• Mind orientation Position cables flex so bending occurs in the intended directions during motion. Watch twist and peel stresses.
• Spread dynamic areas Distribute flexing over larger cable flex segments to reduce mechanical stresses. Avoid short/sharp bends.
• Reinforce terminals Anchor the flex cable ends to rigid structures to avoid ripping. Allow some flex relief.
• Protect tracing Shield thin copper traces from nicks and cuts, especially at edges and joints. Consider protective coatings.
• Manage layer stacks Ensure the order/alignment of multilayer flex cables allows all traces to safely cross within the laminated layers.

Following best practices during mechanical and electrical design helps avoid field issues and extend flex cable lifetimes. Careful engineering prevents flex fatigue.

Flex Circuit Materials and Construction

Flex cables achieve their flexibility through careful material choice and construction:

Polyimide Substrate

The base material is typically polyimide plastic film chosen for its durability, electrical insulation, and high temperature tolerance. Polyimide provides the thin, flexible backbone onto which traces are etched.

Copper Traces

Copper offers the best balance of cost and conductivity for flex circuit traces. It can be etched very thin (down to 8 microns) without losing low resistivity. Durability is enhanced by selecting high purity copper.

Polyimide Coverlay

To protect the copper traces from environmental damage, an insulating polyimide coverlay is laminated over the tracings. Openings in the coverlay allow for selective connections.

Adhesives

Flex layers are bonded using acrylic, epoxy or polyimide adhesives that remain stable over the operating temperature range. They bond reliably without cracking under flexing.

By optimizing each layer in the laminated structure, flex cables achieve maximum flexibility while retaining reliable electrical connectivity. Every aspect of their construction focuses on dynamic mechanical performance.

Popular Connectors for Flex Cables

There are a variety of compact connectors designed to terminate flex cables and integrate them with PCBs:

FFC/FPC Connectors

• Low-profile, flexible connection to PCB
• Cable flex slides into/aligns in connector
• Locking tabs or hinges secure cable flex
• Common in consumer electronics

FFV Connectors

• Vertical version of FFC/FPC
• Cable flex inserts vertically into socket
• Takes less space than horizontal style
• Often found in folding devices

FPC Mezzanine Connectors

• Stacked dual row connector for multilayers
• Cable flex folds around connector
• Mates flex cable and rigid PCB
• Used where vertical space is limited

Board-to-Board Connectors

• Allows direct connection between parallel PCBs
• Flex cable acts as flexible jumper
• No cable-to-board termination needed
• Used to link rigid PCB sections

Crimp/Solder Terminals

• Flex cables can terminate in crimped pins
• Allows integrating into standard wiring with proper strain relief
• Solderable flex cable ends also an option

Connector choice depends on cable orientation, space constraints, and termination method. Modern flex connectors supply compact, reliable interfaces between cables flex and PCBs.

 Flex Cable Terminations Must Consider Strain Relief and Strength

Properly ending flex cables is critical for a robust mechanical connection. The flexible section must transition securely into anchored rigid sections to prevent stresses which can tear copper traces.

Strain relief Generous slack should be allowed near terminations to prevent pull forces from being transmitted down the cable flex length as it moves. The flexible portion should float freely.

Reinforcement Terminating pads/pins should be oversized and anchored with added stiffening structure. This distributes forces over larger areas and provides mechanical support.

Adhesive backing High-bond adhesives applied to areas around terminations further reinforce connections. This reduces stress concentrations at joints.

Abrasion protection Heat shrink tubing or other shielding placed around termination regions of the flex cable protects against wear.

By following good strain relief and termination practices, flex cables can survive millions of duty cycles even in demanding mechanical environments. Proper installation prevents undue stress where the flexible transitions to rigid anchoring points.

Type FCC Cables

 Type FCC cables are a variety of flexible printed circuit often used for internal connections between PCBs. The acronym FCC stands for “flat flexible cable” describing their thin, bendable structure. Type FCC cables consist of unshielded, uncovered copper traces bonded to a flexible plastic base layer. The simple design makes them one of the most cost-effective solutions for dynamic flexible interconnects.

 Type FCC cables come in single-sided and double-sided configurations to suit different trace density requirements. They can integrate with PCBs using compact surface-mount connectors like FFC/FPC types. Their uncomplicated construction also allows for economical reel-to-reel manufacturing. When high-frequency performance is not required, type FCC cables offer an affordable flexible wiring option.

 Flat Cable Assemblies

 Flat cable assemblies take flexible printed circuit cables and incorporate connectors and other components to produce a complete interconnected system. The flat cable itself becomes just one part of a pre-configured wiring assembly optimized for the application.

 Flat cable assemblies are commonly used in automation systems, appliances, vehicles, and consumer electronics. They allow engineers to integrate a full flexible wiring system without needing to individually source cables, connectors, terminations, etc. The assembly provider configures all required parts together into a purpose-built solution.

 Benefits of utilizing flat cable assemblies include faster production by eliminating assembly steps, fully verified performance, and consistency across manufactured products. With expertise in flex circuit integration, assembly providers can potentially optimize designs beyond what individual engineers may conceive.

 What is FFC Cable?

FFC cable stands for flexible flat cables, one of the most common types of flex circuit. An FFC cable consists of thin copper traces laminated onto a flexible plastic film substrate. What makes FFC cable unique is that it’s unshielded, unlike many other varieties of flex circuits.

 The lack of shielding minimizes weight and thickness, making FFC cables perfect for tight, lightweight applications like camera modules and folding displays. The simplest versions are single-sided, with conductors on only one face of the cable. Higher density versions stack multiple layers to allow crossing of traces internally.

 FFC cables integrate with PCBs using specialized low-profile connectors like FPC and FFC/FPC types. These provide a reliable mechanical and electrical connection able to withstand repeated dynamic flexing. When designed properly, FFC cables can survive millions of flex cycles even in demanding uses. Their simplicity and durability make FFC cables a cost-effective choice for dynamic flexible interconnections.

Key Applications of Flex Circuits

Flex cables’ compact size and dynamic durability make them well suited for:

Consumer Electronics

In the realm of home appliances, the integration of digital displays has transformed the user experience. From smart refrigerators that notify you when you’re out of milk to washing machines that can be controlled via smartphone apps, the role of flex cables is paramount. These cables facilitate the connection between the main control unit and the display, ensuring real-time data transmission. Their flexibility is especially beneficial in appliances with curved or unconventional designs, allowing manufacturers to place displays in ergonomic positions for the user without being constrained by rigid wiring.

• Cell phones
• Laptops
• Cameras
• Flat screen TVs

Automotive Use

• ABS/steering systems
• Transmission sensors
• Engine wiring harnesses
• Door mechanisms

Medical Equipment

The medical field has seen rapid advancements in technology, with devices becoming more sophisticated and patient-friendly. Flex cables are at the heart of many medical devices, especially those that require mobility and precision. For instance, in advanced imaging systems like MRIs and CT scanners, flex cables connect the display monitors to the main units, ensuring high-resolution imaging. In endoscopic procedures, these cables play a dual role: transmitting data from the camera to the display and ensuring the device remains flexible enough to navigate the human body.

• Hearing aids
• Endoscopes
• Surgical devices
• Patient monitors

Home Appliances

In the realm of home appliances, the integration of digital displays has transformed the user experience. From smart refrigerators that notify you when you’re out of milk to washing machines that can be controlled via smartphone apps, the role of flex cables is paramount. These cables facilitate the connection between the main control unit and the display, ensuring real-time data transmission. Their flexibility is especially beneficial in appliances with curved or unconventional designs, allowing manufacturers to place displays in ergonomic positions for the user without being constrained by rigid wiring.

• Vacuums
• Washers
• HVAC systems
• Small kitchen appliances

Industrial Devices

The industrial sector, known for its robust and heavy-duty machinery, has not been left behind in the digital revolution. Modern industrial machines come equipped with intricate touch-screen panels and digital readouts that provide operators with precise data. Flex cables in these devices ensure that displays can withstand the vibrations, temperature fluctuations, and other harsh conditions typical in industrial environments. Their durability and reliability make them the preferred choice for connecting displays in equipment ranging from CNC machines to industrial robots.

• 3D printers
• Robots
• Control panels
• Conveyor systems

Any application where connections undergo repeated motion and flexing is a candidate for flex cables. Their flexibility enables simpler mechanical designs.

Here’s a table outlining the most important parameters and their typical values for flex cables across different contexts:

Please note that the values provided are typical and can vary based on the specific requirements and customizations of the device or application. Manufacturers might choose different materials or specifications based on the unique needs of their products.

Riverdi Product Catalog

Riverdi offers a diverse range of products tailored to suit various projects. Their offerings include:

• uxTouch Displays: These are advanced touch screen options that provide an enhanced user experience.
• Capacitive Touch Screens: Known for their sensitivity and multi-touch capabilities.
• Resistive Touch Screens: These screens determine the touch position by measuring resistance and are pressure-sensitive.
• Screen Sizes: Riverdi offers a variety of screen sizes ranging from 3.5” to 10.1”.
• Graphics Controllers: Multiple options are available to cater to different graphical requirements.

Specific Product Categories:

• STM32 Embedded Displays: These are displays integrated with STM32 microcontrollers.
• RGB, LVDS, MIPI DSI LCD Displays: Different types of LCD displays catering to various connectivity and display quality needs.
• EVE Intelligent Displays: Advanced displays with integrated graphical processing capabilities.
• HDMI Displays: Displays that support HDMI connectivity for high-definition output.
• E-Paper Modules: Electronic paper displays that mimic the appearance of ordinary ink on paper.
• Evaluation Boards: Boards designed to test and evaluate the functionality of Riverdi’s products.
• Accessories: Additional components and tools to complement Riverdi’s main products.

Customization Options: Riverdi also offers customization options to ensure that products fit specific design, feature, and functionality requirements. They emphasize the use of high-quality materials and components.

Third-Party Development Tools: Riverdi supports a range of third-party tools to facilitate the development of applications using their products. Examples include the EVE Screen Designer from Bridgetech and the Riverdi click from MikroElektronika.

For a more detailed look into each product and its specifications, you can visit the Riverdi Product Catalog.

Designing and Sourcing Custom Flex Cables

Specialized flex circuit companies offer custom cable flex design, prototyping and production services catered to unique applications.

Collaborating with an expert provider, engineers can take a product from concept through validation using:

• Design consultation Experts help perfect flex cable routings, terminations, and materials for reliability.
• Prototyping Low volume first builds validate performance prior to full production.
• Materials analysis Testing determines the best materials and constructions to withstand application stresses.
• Quality assurance Flex cables are inspected throughout manufacturing to meet standards like IPC-6013.
• Volume production Once validated, quick ramp-up to cost-effective high-volume manufacturing.
•  Supply chain management Production scheduling, inventory management, and shipment to optimize workflow.

By using the expertise of a flex circuit specialist, builders of flex cable-enabled products can focus on core competencies while leaving cable engineering to the experts. This allows faster time-to-market.

The Future of Flex Circuits is Bright

Demand for flexible cabling is poised for strong continued growth as electronics become more compact, portable, and feature rich. Market researchers forecast the global flex circuit market to reach nearly $28 billion USD by 2026.

Driving forces behind increasing flex cable adoption:

• Wearables Flex cables enable smart watches, fitness trackers, and body monitors requiring dynamic connections.
• Internet of Things Interconnected smart home and industrial devices rely on flex cables for reliability in motion and vibration.
• Electric vehicles Lightweight flex cabling suits demanding automotive environments while meeting weight goals.
• Medical devices Healthcare innovations like robotic surgery and implanted sensors would not be possible without durable flex circuitry inside.
• Defense electronics Rugged flexible connections protect mission-critical systems under harsh environmental conditions.

Thanks to their unique combination of small size, durability, and dynamic flexibility, expect to see flex cables enabling more exciting new electronic products than ever.

Conclusion

Though they often go unnoticed by end-users, flexible printed circuit cables flex are mission-critical components enabling the compact flexible design of modern electronics. Combining conductive traces and insulating polymers into dynamic cabling, flex cables can survive millions of tight bends and twists where rigid alternatives would quickly fail. As electronics advance toward more portable and feature-rich designs, expect flex cables to take on an even more essential role behind the scenes. By learning to integrate flex cables into products effectively, engineers can take advantage of their compact connectivity to build the dynamic electronics of the future.

Frequently Asked Questions (FAQ) on Flex Cables in Home Appliances & Industrial Devices

Q1: Why is it important to consider the operating environment when choosing flex cables?

A: Different environments pose unique challenges. Home appliances might face humidity, while industrial devices can be exposed to extreme temperatures, chemicals, and vibrations. The flex cable should be chosen based on these conditions to ensure longevity and functionality.

Q2: How do I ensure the durability of flex cables in my design?

A: Opt for high-quality cables that match the wear and tear expected in the device’s setting. Industrial devices, in particular, require cables with enhanced durability due to their harsh operating conditions.

Q3: What should I consider regarding space constraints and flex cables?

A: Flex cables are adaptable and can be routed in tight spaces. Ensure your design leverages this adaptability, especially in compact home appliances or complex industrial layouts.

Q4: Why is shielding important for flex cables?

A: Shielding prevents electromagnetic interference (EMI), ensuring clear data transmission and preventing device malfunctions, especially crucial in industrial settings and smart home appliances.

Q5: How can I design for easy maintenance and replacement of flex cables?

A: Ensure that the device allows for straightforward flex cable replacement without the need to dismantle the entire appliance or machine.

Q6: How do I future-proof my design with flex cables?

A: Choose cables that can accommodate potential future upgrades, ensuring that newer components can be integrated without a complete device redesign.

Q7: Why is real-world testing important for flex cables?

A: Testing under conditions that mimic actual usage helps identify potential issues before mass production, ensuring reliability.

Q8: How can collaborating with flex cable suppliers benefit my design?

A: Reputable suppliers can provide insights, customization options, and recommendations based on their expertise, ensuring optimal cable choice and integration.

Q9: What is the significance of the bending radius in flex cables?

A: The bending radius indicates how much the cable can be bent without damage. Respecting this limit in your design ensures the cable’s longevity.

Q10: How can I stay updated with the latest advancements in flex cable technology?

A: Regularly engage with industry publications, attend seminars, and collaborate with suppliers to keep abreast of the latest innovations and best practices in flex cable technology.