The product quality, electrical conductivity, welding stability and service life of copper foil flexible busbar largely depend on the pre‑processing procedures. As the critical upstream manufacturing step, pre‑processing performs refined treatment on electrolytic copper foil (0.05‑0.2 mm thickness). It eliminates raw‑material defects such as deformation, oil contamination, oxidation and burrs, laying a solid foundation for subsequent stacking, diffusion welding, brazing and surface plating. This effectively avoids common failures including virtual welding, delamination, local overheating, peeling‑off of plating and insulation damage. The standardized pre‑processing workflow is shown below:

1. Uncoiling, Slitting and Cutting

Electrolytic copper foil is supplied in rolls. It is uncoiled, slit and cut to specified lengths according to drawing requirements. Width and length tolerances are strictly controlled to prevent uneven dimensions. Cutting‑edge quality is monitored to avoid edge tearing, curling and deformation. Accurate cutting ensures neat stacking of copper foils. Poor dimensional accuracy will cause misaligned layers, excessive inter‑layer gaps, local overheating and unstable resistance under working current.

2. Leveling

Copper foil rolls contain intrinsic curling stress and are prone to warping and wavy deformation during transportation and storage. Cut foils pass through multi‑roll levelers to release internal stress and correct distortions. Well‑leveled foils can be closely stacked without bulges or gaps. This prevents welding voids and delamination, and improves the compactness and reliability of end‑joint welding.

3. Edge Deburring

Slitting produces micro‑burrs, copper chips and sharp edges. Unremoved burrs may pierce insulating sleeves and cause short‑circuit risks, as well as increase inter‑layer gaps and degrade welding performance. Common deburring methods include brush polishing, roller grinding and fine grinding wheel treatment. Smooth edges are achieved for better safety and further processing.

4. Precision Degreasing & Cleaning (Key Process)

Rolling oil, lubricants and fingerprints contaminate copper foil surfaces during production, slitting and handling. Oil residue is the primary cause of virtual welding and delamination. Dual‑stage cleaning is adopted: solvent degreasing with alcohol or special copper‑compatible degreaser, followed by high‑pressure pure‑water spray washing to remove contaminants completely for reliable diffusion welding and brazing.

5. Surface Oxide Removal

Copper readily forms cupric and cuprous oxide films in air. Oxide layers have poor conductivity and hinder inter‑layer atomic bonding, greatly reducing welding strength. Slight oxidation is removed by mechanical brushing; heavy oxidation is treated by mild acid pickling. Multi‑stage pure‑water rinsing is performed immediately afterwards to eliminate acid residue and prevent later‑stage corrosion, blackening and premature failure.

6. Pure‑Water Rinsing & Constant‑Temperature Drying

After pickling and washing, copper foils are thoroughly rinsed with pure water to remove residual chemicals and moisture. Low‑temperature constant‑temperature drying is applied to achieve full dehydration while avoiding re‑oxidation and discoloration caused by excessive heat. Dried foils shall be dust‑proof sealed and transferred to downstream processes without prolonged storage.

7. Pre‑stacking Inspection & Sorting

Dual manual‑and‑equipment inspection is carried out after pre‑processing. Foils with warpage, deep scratches, severe oxidation, notches or residual oil are rejected. Qualified copper foils are neatly stacked under dust‑proof conditions to guarantee qualified raw‑material input for stacking and welding, and improve overall yield.

Key Risk Control for Pre‑processing

1. Incomplete oil removal: virtual welding, delamination, high resistance and overheating.
2. Insufficient leveling: poor inter‑layer contact, welding voids and unstable mechanical performance.
3. Residual acid after rinsing: gradual copper corrosion and shortened service life.
4. Residual burrs: insulation piercing and potential short‑circuit hazards.
5. Inadequate drying or long‑time storage: re‑oxidation, impairing welding and plating quality.

Complete pre‑processing is essential for copper foil flexible busbar to achieve high conductivity, good flexibility, vibration resistance and long service life. It represents a key technical standard distinguishing high‑end products from low‑end alternatives, widely applied in energy‑storage systems, new‑energy vehicles, charging piles, high‑voltage switchgears and industrial power supplies.

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