Flexible PCB Manufacturing Process: How to Fabricate FPC

A flexible PCB (FPC) is a bendy circuit board made from polyimide (PI) or polyester (PET). It’s light and thin, perfect for folding or bending. FPCs come in single-sided, double-sided, and colors like yellow, black, white, or clear. They’re great for things like wearable gadgets, medical tools, and small electronics. Making them takes careful steps with machines to ensure they work well. Here’s a clear look at each step with all the important details.

Step 1. Fabricating Flexible PCB Laminates

The process starts by getting materials for the FPC design and order. Workers use rolled annealed copper (RA) or electrolytic copper foil (ED), plus polyimide (PI) film and glue (usually acrylic or epoxy). On the copper line, machines press the foil to a thin layer, about 12-70 µm thick. This keeps circuits steady. At the same time, the PI film, 25-125 µm thick, gets coated with glue using smooth rollers. Then, it’s pressed at hot temperatures (150–200°C) and strong pressure (100–300 PSI). This makes the coverlay, which guards circuits and keeps the board bendy.

Step 2. Cut Laminates for FPC Fabrication

The PI coverlay, already glued, is cut to exact sizes with CNC machines to match the FPC design. The copper foil is also trimmed to fit the coverlay. These cut pieces get joined in a first pressing step at warm temperatures (120–150°C). This makes sure they stick well without losing bendiness. Now, they’re ready for drilling and making circuits.

Step 3. Drilling

Lasers drill tiny Plated Through Holes (PTH) in the copper layers. These holes can be as small as 50 µm for packed designs. CO2 or UV lasers make clean, exact holes without hurting the PI base. These PTH holes connect circuit layers in multilayer FPCs. Before plating, plasma cleaning removes dirt to help copper stick better.

Step 4. VCP Electroplating

Vertical Continuous Plating (VCP) adds copper to PTH hole walls, making them 15–25 µm thick. A moving conveyor dips the layers in copper sulfate baths. Careful current control ensures even copper layers. This makes vias strong, lowers resistance, and boosts signal quality for high-speed uses.

Step 5. Circuit Transfer (Exposure)

A UV-sensitive dry film is put on the copper with hot rollers for even coverage. A phototool film with the circuit pattern is lined up using markers. It’s exposed to UV light (350–400 nm) for 10–30 seconds. This hardens the film where circuits will be, protecting them during etching. High-tech systems make tiny 25 µm lines for detailed designs.

Step 6. Etching

Etching uses a sodium hydroxide (NaOH) or ammonium persulfate mix to remove extra copper. Only the protected circuit pattern stays. The etching machine works in steps: it removes copper, then rinses to clear chemicals. Next, a 2–5% NaOH solution at 50°C strips the film. This leaves clean copper traces with little damage for precise circuits.

Step 7. Drilling Positioning Holes

Three or four small holes (1–2 mm wide) are drilled across the FPC panel’s corners. High-speed drills or lasers make them. These holes keep things lined up for testing and shaping. Exact drilling avoids mistakes that could ruin boards. Automated optical inspection (AOI) checks hole placement within ±10 µm.

Step 8. Electrical Test

Each circuit layer gets tested with a special jig. Pogo pins touch test pads to send a low-voltage signal (5–12V). This checks for good connections, insulation, and no shorts. Machines log results to ensure circuits work 99.5% of the time before moving on.

Step 9. Cleaning and Scrubbing

The cleaning line uses pure water and gentle soaps to wash away oxides, leftover NaOH, and water. Soft polymer brushes scrub to make surfaces shiny, helping with soldering and looks. Ultrasonic cleaning clears tiny holes, ensuring no dirt affects later steps like lamination or finishing.

Step 10. FPC Layers Alignment and Lamination

For multilayer FPCs, PI, glue, and copper layers are lined up carefully using pins and cameras. A hydraulic press bonds them at 180–220°C and 200–400 PSI. This makes strong layers without gaps. Vacuum pressing keeps air out, making boards reliable for bendy uses like foldable screens.

Step 11. Printing Silkscreen

Silkscreen printing puts epoxy ink on boards to mark part names, logos, and direction signs. A stencil printer does this. UV-cured inks stay strong when the board bends. Machines place marks within ±50 µm, meeting IPC-A-600 rules for clear labels to help with assembly and testing.

Step 12. Baking Flexible PCBs

Boards bake at 120–150°C for 30–60 minutes in a hot oven. This dries the ink and removes water. It keeps layers from splitting during finishing. Slow heating and cooling prevent stress, keeping the PI base bendy and steady.

Step 13. Surface Finish

Finishes like Electroless Nickel Immersion Gold (ENIG) or immersion tin go on exposed copper pads. ENIG adds 3–5 µm nickel and 0.05–0.1 µm gold for good soldering and rust protection. The process includes cleaning, light etching, and dipping in chemical baths. It follows RoHS rules and fits specific job needs.

Step 14. Finished FPC Electrical Test

A final test checks the whole FPC for shorts, opens, and steady signals. Flying probe testers do this. Tests adjust for high-speed or high-voltage jobs to ensure no defects before shipping.

Step 15. Forming Flexible PCBs

Profiling cuts single FPCs from big panels. Precision dies make straight edges, or steel-rule dies shape tricky designs. Lasers cut complex shapes with ±50 µm accuracy. This gives clean edges without rough bits, perfect for fitting into small cases or connectors.

Step 16. Visual Inspection

Workers check boards under 10x magnifying glasses for scratches, dirt, or solder mask flaws. Automated Optical Inspection (AOI) scans for surface issues, meeting IPC-6013 standards. They also count boards to match production records, avoiding shortages or extras.

Step 17. Sampling Testing

A random 6–10% of boards get tough tests. These include bending up to 10,000 times for moving FPCs, cold-to-hot shock tests (-40°C to 125°C), and soldering checks. If problems show up, the whole batch gets rechecked to keep defects below 0.1% for trusty boards.

Step 18. Packaging and Warehousing Before Delivery

FPCs go into anti-static bags or vacuum-sealed trays based on client needs. Desiccant packs keep moisture out. Boards stay in a cool, controlled warehouse (20–25°C, 40–60% humidity). They ship via partners like FedEx, UPS, or DHL with tracking for fast, safe delivery.

Why Choose PCBAStore for One-Stop Flexible PCB Fabrication

PCBAStore has over 16 years of skill in making flexible PCBs. They offer full help from design to final assembly. Certified with ISO9001, IATF16949, UL, RoHS, REACH, and IPC standards, they make high-quality, budget-friendly FPCs. Their services include quick quotes, helpful engineering support, and easy blending into your product process. This makes them perfect for both test runs and big production.Simply visit our website or email us at svc@pcbastore.com for personalized support on your next project