Flexible Flat Cables: Having it your way

Need a super flexible flat cable? Need a 36AWG ribbon cable with 21 conductors all in pink? No problem.

Off the shelf flat cables are often available in limited sizes and flexibility which creates problems for designers who need more robust or flexible flat cables. Off the shelf flat cables are normally made of PVC and the conductor stranding is 7 or 19 strand. For applications requiring high flex cables, resistance to chemicals or flexibility off the shelf cables may fail to meet your expectations. Off the shelf cables do not give options for:

• Flexibility and hi-flex applications
• Odd number of conductors
• Uncommon sizes
• Unusual configurations
• Custom colors
  
  

Flexible flat cables are ideal for hand held devices, automation and robotic applications. Engineers and product designers do have options by working with custom wire and cable manufactures to design exactly what they need. Custom wire and cable manufacturers can offer a variety of sizes, configurations and flexible flat cable options. There are two basic types of flat cables:

Ribbon cables - Ribbon cables are multiple conductors connected in a parallel configuration where the conductor spacing is controlled. Silicone ribbon cables are a popular choice for applications where an ultra flexible ribbon cable is needed. Using silicone along with high strand count conductors and/or alloys for added strength and resistance to fatigue for hi flex applications will add to a ribbon cable's flexibility other flexible material are TPE, Polyurethane, and even PVC (Calmont's Superflex PVC).

Top 3 Choices for Ultra Flexible Wire or Cable

Flexible wire in terms of how limp it is starts with the wire design options. The choices you make can greatly impact how flexible the wire or cable will be. The right choices can make the difference between flexible wire and a super flexible wire. Designing a flexible wire or flexible cable begins with the design. We start at the core, conductor stranding and construction.

1. Conductor stranding: Conductors are made up of fine strands of wire assembled together into several configurations. The more strands in the construction, the more flexible and resistant to repetitive flexing the conductor will be. Conductor stranding options range from a solid strand (one strand) to over a thousand strands depending on the wire gauge. The construction of conductor stranding is important as well. Stranded conductors can be manufactured in a variety of configurations, the most common being concentric (true concentric, equilay concentric, unidirectional concentric, and unilay concentric), bunched and rope.

Conductor stranding with rope construction makes for a more flexible wire. This construction has the advantage of increasing flexibility by using a larger number of finer strands while maintaining a tighter diameter tolerance than a simple bunched construction. Ropes are more evident in the larger AWG sizes, such as 8 AWG and larger, but there are also many applications that require the flexibility of rope constructions in the smaller gauges. Constructions vary and can contain hundreds or thousands of strands. To achieve the most flexible wire design, be sure to use the higher stranded conductors. For flexible wire with repetitive flexing applications, consider using an alloy for fatigue resistance.

2. Insulation: Flexible wire and cable requires a flexible insulation material. There are many choices for insulating materials. The most flexible wire insulation is silicone, together with the right conductor stranding can be as limp as a wet noodle. While silicone is the most flexible wire insulator, it does have poor abrasion resistance. Choosing the right material will depend on your application and use, consult your wire and cable manufacturer to determine which material will work best for your application. Flexible insulation and jacket materials include TPE/TPR, polyurethane and even PVC, Calmont's Superflex® uses a special PVC formula for increased flexibility. When choosing an insulation or jacket material, consider your requirements. Is your application requiring sterilization? Is abrasion resistance required? Temperature, chemical contact and bio-compatibility are other requirements to consider. Calmont's insulation and jacket material chart is a helpful tool.

3. Cable construction: Cable construction is another component for super flexible cables. Cable lay length and shielding can increase the cable's flexibility. The cable lay is how the conductors are cabled together, the wires can run parallel or be twisted around each other. The length between each twist can be adjusted for maximum cable flexibility. Shield options include spiral, braid and Mylar or foil wrap. The application is important when considering shield types. For flexible cables which undergo repetitive flexing, spiral and foil type shield are not good options as the shield coverage will be compromised over time.

If you want a more flexible cable design, contact Calmont Wire & Cable to learn more about material choices.

Conductor Stranding: Poor designs lead to breakage.

Conductor stranding is an important component for applications with hi flex cycles or vibration. The higher the conductor stranding the better the resistance to stress caused by flexing. Custom cables with high strand count conductors are the best choice for these types of applications. Higher conductor stranding also makes for an ultra flexible wire when using the right insulation. Discussing the flex requirements with your wire and cable manufacturer is critical to choosing the right cable construction.

Are there circumstances when conductor stranding doesn't help with wire breakage and loss of conductivity? Yes! Recently, I was asked what type of wire I would recommend for an application that required the wire to be soldered onto a PCB. This person was repairing PCBs experiencing conductor breakage at the solder point due to vibration and he thought the wire was to blame. This is a common problem when the wire is soldered onto PC boards especially now with the use of lead free solders.  Applications such as aerospace that are subject to vibration and movement of the wire can cause stress at the solder point.  The problem has nothing to do with conductor stranding or flexibility of a wire, while it is true that high strand conductors and the use of alloy materials adds strength to the conductors. The reason for this has nothing to do with the conductor stranding or how flexible a wire is, but the termination. Termination with connectors is recommended to solve this problem. Cable assembly and contract manufacturers understand this problem and are using edge cards and other types of connectors for termination with newer PCB applications. The problem is more prevalent among legacy boards that are being repaired where retrofitting connectors is usually not an option. Often times a strain relief cannot be installed due to the nature of the application. The solution to repair this type of problem with the old boards may be as simple as using an epoxy to secure the wire to the board to prevent stress at the termination point.

Having the right strain relief is important especially with handheld devices. The lack of or using the wrong type of strain relief can actually cause a stress point and product failure. Strain reliefs can vary in sizes and materials, consult your cable assembly house or contract manufacturer for guidance. I had a customer experiencing conductor breakage on his handheld tool and sent us a sample for analysis. Though his design used high strand count conductor strands, we found the conductor stranding to be damaged at the strain relief, it was discovered the strain relief design had been changed to a spring which caused added strain to the conductors. He changed his design and the returns on his product ceased.

The moral to the story is that though high stranded conductors do resist the stresses of flexing, the cause of the problem may not be in the cable design. Take the time to consult your cable manufacturer and the contract manufacturer for the best material options for your device.

Wire and Cable manufacturers: What’s the difference?

Wire and cable manufacturers are not all the same, many have their specialties or niche. Depending on your needs, finding the right wire and cable manufacturer can be difficult. If the wire and cable you need is not easily found through distribution, chances are you will need to find a manufacturer to design and manufacture it. Wire and cable manufacturers can be categorized as follows:

• Commodity - This includes Mil-Spec, industrial, wire and cable. Their products are easily purchased through distribution. Commodity wire and cable manufacturers usually have their manufacturing lines dedicated to the products they produce regularly so when ordering a custom wire or cable from these types of manufacturers usually results in long lead times and high minimum orders. Why? They have to place the custom wire or cable order into their production schedule, set up the equipment, and stop production of their normal product on that line.

• Custom - Custom wire and cable is made to order to your specification. Custom wire and cable manufacturers are basically job shops, they set up the production lines and schedules based on their orders and this is figured into their cost. This is why you can order custom wire and cable in smaller quantities and shorter lead times than from a commodity wire manufacturer. Ordering commodity cables from a custom wire manufacturer can be costly due to the sheer volume commodity manufacturers produce these products. What makes a cable custom can be a simple as a unique color or more flexible design of a commodity cable to complicated composite cable designs.
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• Specialty - Specialty wire and cable can include extremely small gauges such as 50AWG or smaller, unusual or molded shapes, or unique materials. These custom cable manufacturers do fall into the custom category but are known for their specialties throughout the industry. Many custom wire and cable manufacturers have a specialty product or a niche market.

Working with custom wire and cable manufacturers is easy, whether you have a design, need a design or are not sure what you need. Most custom wire and cable design engineers can assist you in choosing the right materials and construction to meet your requirements. Finding the right manufacture is not difficult by using Google or Global Spec you can do keyword search or ask other industry professionals. It's a small industry.

Reverse Engineering: Why you need it and when.

Do you need a wire or cable and have no idea what it is? You are not alone, it happens more times than not especially for equipment repairs, obsolete parts, and failure analysis. When do you need to have a cable reversed engineered? You may like a particular cable's performance or you have a piece of cable that you or your customer may want more of but don't know what it is or who manufactured it. Then reverse engineering is the answer. Who performs this service? Most custom wire and cable manufacturers can assist you.

Reverse engineering wire or cable is commonly performed to determine:

• Conductor stranding and material.
• Cable construction
• Insulation and jacket materials

Custom wire and cable manufacturers routinely reverse engineer wire and cable to identify the materials used and the cable construction. It is best to provide a sample between 1 to 2 feet if possible and keep in mind it will be dissected in the process.

Outer jacket
Reverse engineering wire and cable begins with measuring the outside diameter (OD) of the wire or cable. The longer the piece the better it is to obtain the nominal OD. The outer jacket is carefully removed to expose the core. Normally, cross sections are taken of the outer jacket to measure wall thickness. Jacket material is tested to identify the type of material used.

Braid, shield or tape
If there is a braid or shield the construction will be examined. The pitch, number of ends, material and coverage can be determined at this point. If there is a tape wrap present, the overlap, type of material and size will be examined.

Core construction
The next step is to examine the cabling construction. Once the shield and/or tape is removed the following can be determined: Cable lay or twists per inch, filler material used, the use of strength members, number of conductors and conductor color code.

Conductors
The conductor material, plating used (if any), gauge and conductor strand count and construction are checked. A cross section of the conductor will identify the wall thickness of the insulation and OD. At this point the insulation material will be identified.

Insulation and jacket materials
There are several ways to identify the materials used for insulation and jackets. The obvious is the look and feel of the insulation or cable jacket. Computer analysis and burn testing are also used. Plastics and rubber each have distinct characteristics when placed on a flame. Experienced engineers can determine the type of insulation material by whether it burns, melts, or self extinguishes. The odors produced when burned also are distinct to each type of material. Burn testing should only be done by experienced individuals in a controlled environment, gases can be toxic as well as the risk of fire is present.

Failure analysis
Failure analysis is another reason for reverse engineering wire and cable. When a cable fails, determining the cause can many times be done with reverse engineering to pinpoint the problem. Common problems with handheld devices with poor strain relief is damage to conductors or conductor stranding due to excessive bending. Shielding materials can over time damage conductor insulation. Dissecting the cable at the problem area can expose the problem. Custom wire and cable manufacturers can make material suggestions such as the use of higher conductor stranding or alloys, insulation materials or cable construction design alterations based on the findings of reverse engineering.