FFC cable specification requires defining three dimensions together: total length, stiffener structure, and exposed contact size. A typical 0.5 mm pitch FFC may use 30–50 conductors, 4 mm exposed contacts, and a 0.2–0.3 mm stiffener thickness depending on connector design. Manufacturer specifications often control length tolerance within ±1 to ±5 mm according to cable size, while exposed contact tolerance is commonly around ±0.5–1 mm. A complete drawing should include pitch, pin count, contact direction, bend requirements, stiffener material, and measurement references to avoid connector mismatch.

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How to Specify FFC Cable Length, Stiffeners and Exposed Contacts

FFC cable drawings must define more than the overall cable size. The connector interface depends on the relationship between cable length, exposed conductor length, and stiffener thickness. A 0.5 mm pitch FFC with 40 circuits has a conductor span close to 19.5 mm before adding edge margins, while the exposed contact area may only be 4 mm long. A small dimension error at the connector end can affect insertion depth and electrical contact. Commercial FFC specifications commonly define pitch, exposed contact length, stiffener length, and cable length as separate controlled dimensions.

A production drawing should state the cable length reference point, because “150 mm FFC” can describe different measurements between suppliers.

The first item to define is how cable length is measured. Some manufacturers measure from the outer edge of the cable, while others use the distance between reinforced ends or between exposed contact areas. A 150 mm cable measured from stiffener edge to stiffener edge is not identical to one measured from conductor termination to conductor termination.

Common length definitions include:

FFC suppliers usually apply wider tolerances as length increases. A specification published for standard flat flexible cables lists examples such as ±2 mm for shorter cables and larger tolerances for cables above 300 mm.

Cable length also depends on installation routing. A design using a 100 mm straight connection may require additional length when the cable bends around a display frame, camera module, or PCB edge. The designer should include:

• connector insertion depth;
• minimum bending radius;
• movement allowance;
• assembly clearance.

A cable that is too short may pull on the connector during assembly. A cable that is too long may create unwanted folds or contact with nearby components.

For a 0.3 mm thick FFC, keeping the bend radius around several times the cable thickness helps reduce stress on copper conductors.

Bending requirements become more important in products with repeated movement. Some FFC catalogs specify bending performance using cycle testing, with examples reaching millions of bending cycles under controlled bend diameter conditions.

The next specification area is the stiffener. The stiffener is attached behind the exposed contacts to increase insertion strength and maintain a stable interface with the connector. Without reinforcement, the thin polymer film can deform during insertion into a ZIF or LIF connector.

Typical stiffener materials include:

Stiffener thickness must match the connector specification. A connector designed for a 0.3 mm mating thickness may not clamp correctly if the reinforcement changes the total thickness by several tenths of a millimeter.

A stiffener drawing should include material, thickness, length, width, adhesive area, and location relative to the contact edge.

The stiffener length is normally shorter than the total cable length and is placed near the insertion end. Commercial specifications show examples such as 3.3 mm stiffener length for 0.25 mm pitch products and around 8 mm for some 0.5 mm pitch shielded FFC products.

The exposed contact area requires the same level of detail. The exposed contacts are the copper fingers that enter the connector and carry electrical signals. Their length, orientation, and plating must match the connector design.

Important exposed contact parameters include:

Many standard FFC products use exposed contact lengths between approximately 2 mm and 5 mm depending on connector design. A 0.5 mm pitch specification may use 4 mm exposed contacts, while other designs use different values based on socket depth.

The contact orientation must also be included. FFC cables are commonly available with contacts on the same side at both ends or opposite sides at each end. Type A and Type B naming is often used for these configurations.

A cable with the correct pitch and pin count can still fail assembly if the contact side does not match the connector position.

A complete FFC specification should connect the cable geometry with the mating connector information. Engineers normally include:

• connector part number;
• pitch;
• circuit count;
• cable thickness;
• total length;
• exposed length;
• stiffener dimensions;
• contact direction.

For example:

Manufacturing drawings should also define inspection points. A supplier may check conductor pitch, cable width, exposed contact length, and end thickness separately because each dimension affects connector fit. Published specifications commonly control pitch around ±0.05 mm and conductor thickness around ±0.005 mm for standard designs.

A revision-controlled drawing with connector data reduces differences between prototype samples and mass production parts.

FFC applications in displays, printers, scanners, automotive modules, and industrial equipment often use similar structures but different mechanical limits. A display cable may prioritize thinness and flexibility, while an industrial module may require stronger reinforcement and higher temperature materials.

When preparing an FFC order, the minimum required information is:

A properly specified FFC cable allows the supplier to manufacture according to measurable dimensions rather than assumptions. Accurate length references, matched stiffener thickness, and correct exposed contact geometry provide consistent connector fitting across prototypes and production runs.