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Welding Process for Copper‑Foil Flexible Connectors with Nickel Tabs

Aug 18,2026

Copper‑foil flexible connectors assembled with nickel tabs are widely‑used conductive components in new‑energy batteries, energy‑storage modules and integrated bus‑bars. Copper foil offers good flexibility and stable conductivity. Nickel tabs feature high hardness, oxidation resistance and corrosion resistance, reinforcing terminals for long‑term vibration and thermal‑cycling service.

Copper‑nickel are dissimilar metals. Conventional welding leads to cold joints, delamination, unstable resistance, terminal overheating and peeling fracture. Polymer diffusion welding achieves solid‑state atomic bonding without filler metal. It yields flat non‑deformed welds, stable conductivity, good vibration‑resistance and high‑temperature tolerance, ideal for copper‑to‑nickel laminating welding.

I Core Difficulties of Copper‑Nickel Welding

1.Copper is soft with high thermal conductivity while nickel is hard with low thermal conductivity. Discrepant heating, deformation and diffusion rates easily produce pseudo‑welds with incomplete fusion on one side.

2.Dense oxide layers readily form on nickel‑tab surfaces, acting as barrier interlayers and triggering hidden cold joints and resistance fluctuation.

3.Multi‑stacked thin copper foils trap inter‑layer air, resulting in internal voids, delamination loosening and overheating under energization.

4.Weld joints from traditional processes lack ductility and tend to crack and detach.

II Advantages of Polymer Diffusion Welding

1.Under constant temperature and pressure, copper and nickel atoms inter‑penetrate and fuse into integrated joints, delivering high bonding strength and anti‑detachment performance.

2.Constant‑temperature‑pressure plastic bonding thoroughly eliminates surface oxide films and avoids barrier‑layer‑induced cold joints.

3.Mild heat input and uniform pressure prevent nickel‑tab warping and copper‑foil crushing; no post‑weld finishing required.

4.Compact weld interfaces free of pores or inclusions yield stable contact resistance and resist overheating under high‑current operation.

III Welding Procedure

1.Pre‑weld Cleaning: Remove oil, fingerprints, dust and black oxide spots from copper‑foil and nickel‑tab surfaces to eliminate impurity barriers against atomic diffusion and partial cold joints.

2.Stack Preparation & Fixture Positioning: Arrange multi‑layer copper foils neatly with clean cuts, no misalignment, loose strands or warped edges. Center nickel tabs over copper‑foil terminals and fix with dedicated tooling. Ensure flat lay‑up free of offset, suspension or wrinkles for even pressure distribution.

3.Low‑Pressure Pre‑Compression for Air Exhaust: Slowly compress stacked laminates to expel inter‑layer air step‑by‑step and close micro‑gaps. Avoid abrupt high‑pressure squeezing which traps air and creates internal voids and delamination.

4.Constant‑Temperature Diffusion Fusion: Adopt stable constant‑temperature holding instead of instantaneous thermal shocks. Sufficient soaking activates copper‑nickel atoms for thorough interfacial inter‑diffusion to realize monolithic compact bonding and eliminate superficial‑only pseudo‑welds.

5.Pressure‑Held Slow Cooling & Setting: Do NOT release pressure immediately after welding. Copper and nickel feature different shrinkage rates; fast pressure‑release generates residual stress, micro‑cracks and hidden delamination. Keep pressure applied during slow cooling to release welding stress, lock the monolithic structure and obtain flat non‑rebounding finished parts.

IV Core Parameter Tuning Rules

1.Temperature: Keep moderate stable temperature. Excessively high temperature blackens nickel tabs and embrittles copper foil; too‑low temperature cannot remove oxide films and causes weak bonding.

2.Pressure: Maintain soft steady pressure throughout. Excessive pressure crushes copper foil, hardens terminals and makes them fracture upon bending; insufficient pressure leaves gaps and pores with high resistance.

3.Soaking‑Time: Guarantee adequate constant‑temperature diffusion duration. Copper‑nickel atomic diffusion proceeds slowly; insufficient soaking brings incomplete inner‑layer bonding.

V Graphite‑Mold Operation & Maintenance

Mold surfaces must be flat and smooth, scratch‑free, carbon‑deposit‑free and free of bumps, to prevent workpiece indentation and partial cold joints. Clean mold surfaces before each production run. Periodically calibrate mold parallelism for uniform pressure. Stabilize mold temperature to prevent batch‑to‑batch quality fluctuation caused by large thermal swings.

VI Common Defects

1.Nickel‑tab peeling, delamination, low tensile strength: Incomplete oxide removal, insufficient soaking‑temperature or diffusion‑time, interfacial impurities.

2.Hardened terminals, easy fracture in bending, loss of flexibility: Over‑high temperature, prolonged high‑temperature soaking, excessive pressure inducing copper embrittlement.

3.Internal voids & multi‑layer copper‑foil delamination: Disordered stacking of copper foils, insufficient pre‑compression, fast temperature‑rise trapping air.

4.High resistance & severe heating under current: Incomplete interfacial diffusion, residual micro‑pores, oxide‑containing impurity interlayers.

5.Unstable batch quality: Mold heat accumulation, dirty mold surfaces, positioning offset, parameters mismatched for hot‑cold working conditions.