Flexible PCB Assembly

NextPCB Vocabulary

Definition: Flexible PCB Assembly/FPC Assembly is the process of mounting electronic components onto a flexible substrate, such as polyimide (PI), PEEK, or transparent conductive polyester films. Unlike traditional rigid FR-4 boards, flexible circuits can bend, fold, or wrap, enabling compact, lightweight designs in tight or irregular spaces.

Simply put: It is the process of soldering components onto bendable circuit boards—like slapping chips onto a plastic sheet that twists without breaking.

Flexible PCBs (FPCs) differ fundamentally from rigid PCBs in their “flexibility”. To assemble them effectively, manufacturers transform the FPC into a pseudo-rigid form, typically by mounting it onto a carrier or pallet.

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1. Key Advantages

• Ultra-thin & lightweight – Ideal for wearables, mobile devices, and medical equipment. (Polyimide for high heat resistance, Polyester for transparent OLED applications.)
• High reliability – Flexibility reduces mechanical strain on components while maintaining electrical performance.
• Space-saving – Supports unique shapes and tight-space integration, especially valuable in automotive dashboards and aerospace electronics.

2. Fixing and Positioning FPC on a Carrier

• Create a locating jig and carrier tailored to the FPC's hole pattern and thickness. The carrier often features matching positioning pins or slots.
• Assembly sequence:

- Mount carrier onto locating jig

- Insert the FPC onto carrier

- Overlay with a top plate or clamp for alignment

- Once fixed, lift the entire setup from the jig to proceed with solder paste printing, component placement, and reflow steps.

3. Choosing the Right Carrier Design

Optimize carrier choice based on production volume and FPC characteristics:

Magnetic carriers:

Incorporate high-temperature magnets and clamps to hold the FPC securely.

• Pros: consistent fixation, no adhesives.
• Cons: higher cost and tooling complexity.

Silicone-coated carriers:

Offer adhesion and easy release.

• Pros: reusable and gentle on FPC.
• Cons: limited surface design flexibility, reduced longevity.

Heat-resistant tape carriers:

Simple and affordable option.

• Pros: firm hold, no residue when chosen correctly.
• Cons: labor-intensive prep and potential damage during removal.

Recommend Reading: The most comprehensive introduction to FPC PCB design principles

Ideal carrier materials include aluminum, synthetic stone (engineering plastics), or silicone—chosen for lightweight, rapid heat dissipation, and minimal thermal deformation.

4. FPC Key Features

5. Typical Flexible PCB Assembly Workflow

Pre-Baking Treatment

FPCs tend to absorb moisture during storage or shipping. To prevent soldering defects like delamination or bubbling, manufacturers perform low-temperature baking (typically 80–125 °C for 4–8 hours, depending on board thickness). They conduct sampling to optimize bake time, and stack only ~10–20 panels for uniform drying.

Solder Paste Printing & Component Placement

• After fixing the FPC to the carrier, apply solder paste via a stencil. Uneven surfaces can cause issues like too much or too little paste. Adjust carrier design or tape placement to compensate.
• Component placement uses standard SMT pick-and-place equipment, yet requires calibration to account for slight gaps between the FPC and carrier. Nozzle pressure, height, and speed must be tuned carefully to avoid misplacement or damage.

Reflow Soldering

• Use a hot-air convection reflow oven to ensure uniform heat distribution.
• Apply gentle ramp-up and controlled cooling profiles to prevent thermal warping and ensure good solder joints.

Inspection & Separation

• Conduct optical inspection (AOI), X-ray, or manual checks to find soldering defects or component misalignments.
• When processing multiple FPCs on a panel, utilize punching or machining to separate individual units cleanly.

6. Use Cases & Trends

Flexible PCB assembly is widely used in consumer electronics, medical devices, IoT wearables, and automotive systems where miniaturization and movement tolerance are essential. Methods like tape-automated bonding (TAB) enable efficient chip-on-flex (COF) integration, offering high-speed, automated assembly for applications like mobile cameras and smart card modules.

• Phones: Vibrating motor links, folding displays
• Medical: Endoscope coils, glucose tracker bands
• EVs: Battery cell monitors (wraps around cylinders!)
• Next-Gen Trend: TAB-bonded chips-on-flex (COF) for 4K camera modules

7. Conclusion

• The heart of FPC assembly lies in designing a carrier that rigidizes the flexible substrate while minimizing deformation.
• Essential factors include: carrier material and structure, accurate positioning mechanisms, thorough drying, and precise thermal and printing controls.
• Effective carrier design and process control significantly boost assembly yield and maintain product integrity.

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About the Author

Sylvia Zhang

Sylvia joined NextPCB two years ago and has already become the go-to partner for clients who need more than just boards. By orchestrating supply-chain resources and refining every step from prototype to mass production, she has repeatedly delivered measurable cost savings and zero-defect launches. Consistency is her hallmark: every client, every order, receives the same uncompromising quality and responsive service.

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