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Key Points for Nickel‑Plating on Both Sides of Large‑Size Copper‑Foil Flexible Connections with Polymer Diffusion‑Welder
Sep 08,2026
Polymer diffusion‑welding of large‑size multi‑layer copper‑foil flexible connections is widely applied in new‑energy energy‑storage, power‑battery and high‑voltage electrical‑equipment industries. By performing nickel plating on upper and lower surfaces of copper‑foil before diffusion‑welding, oxidation‑resistance, corrosion‑resistance and welding‑resistance can be improved. Products obtain more stable electric conductivity and fit subsequent assembly.
Copper and nickel are dissimilar metals with large material‑property differences. Besides, workpieces have large surfaces. Common defects in production include nickel‑layer peeling, blistering, inter‑layer hollowing, blackened nickel surface, cold joints at edges, surface collapse and brittle fracture at terminals.
I Core Process Difficulties of Large‑Size Nickel‑Plated Diffusion‑Welding
1.Great difficulty in dissimilar‑metal diffusion: Nickel features high hardness and low thermal‑expansion coefficient; copper shows large softening‑expansion amplitude. Uneven internal stress occurs in high‑temperature welding. Peeling, edge warping and inter‑layer delamination easily appear after cooling.
2.Difficult exhaust for large‑area surfaces: Numerous fitting gaps on large surfaces. Inter‑layer air and impurities cannot be fully exhausted. Continuous hollow and cold‑joint zones tend to form after welding.
3.Low heat‑resistance tolerance of nickel‑layer: Excess temperature causes oxidation‑blackening, hardening and embrittlement of nickel‑layer; insufficient temperature leads to inadequate copper‑nickel diffusion, low bonding strength and easy peeling.
4.Uneven stress and heat distribution over full surface: Slight unevenness of molds for large‑size workpieces or pressure deviation will bring middle‑part collapse, edge cold joints and local peeling.
II Pre‑Welding Surface Treatment and Stacking Key Points
1.Cleaning and de‑oxidation: Bonding surfaces of copper‑foil and nickel strips must be degreased, dedusted and de‑oxidized to achieve pure‑metal contact. Oil stains, dust and fingerprints will vaporize at high temperature to form pore interlayers, resulting in delamination‑peeling and blackened nickel surfaces.
2.Aligned stacking: Align four edges of multi‑layer copper‑foil with upper and lower nickel strips and center them for fitting. Dislocation leads to uneven stress and incomplete diffusion, and finished‑products tend to crack and warp.
3.Pre‑leveling and pre‑compression: Cut materials have slight warping. Pre‑level and pre‑compress before welding to eliminate local suspension and micro‑gaps, preventing massive defects amplified by high‑temperature welding.
III Core Control Points for Welding Temperature‑Pressure Time‑Sequence
1.Pressure control: Excessive pressure will crush copper‑foil, crack nickel‑layer and harden terminals, losing flexibility and causing fracture upon bending. Insufficient pressure cannot compress gaps thoroughly, resulting in insufficient diffusion, edge cold joints and poor bonding strength.
2.Temperature control: Excess temperature blackens and hardens nickel‑layer and causes brittle fracture of terminals. Insufficient temperature leads to inadequate copper‑nickel diffusion, loose bonding, unstable resistance and heat generation.
3.Time‑sequence control: Extend pre‑pressing time to fully exhaust inter‑layer air and compress micro‑gaps, fundamentally solving hollowing and delamination problems.
IV Notes for Mold & Tooling Usage
1.Keep molds flat and clean
2.Calibrate mold parallelism periodically
3.Standardize tooling positioning
V Defect Causes and Improvement Countermeasures
1.Nickel‑layer peeling & local delamination
Countermeasures: Strengthen pre‑welding cleaning; extend pre‑pressing exhaust time; implement strict slow cooling under pressure; lower peak welding pressure.
2.Blackened & heavily‑oxidized nickel surface
Countermeasures: Reduce constant‑temperature value; cut redundant heat‑holding duration; clean and polish mold surfaces.
3.Surface hollowing & continuous cold‑joint zones
Countermeasures: Level stacked materials; extend pre‑pressing time; calibrate mold parallelism.
4.Surface collapse & uneven thickness
Countermeasures: Adopt low‑pressure gradient pressure‑stabilizing process for soft compressing without squeezing base material.
5.Hardened terminals & fracture upon bending
Countermeasures: Strictly control temperature and pressure; shorten high‑temperature holding duration.
Wuxi Haifei Intelligent Equipment Co., Ltd. https://www.haifeiwelder.com/
Wuxi Haifei Intelligent Equipment Co., Ltd. has been focusing on the R&D and production of diffusion‑welding equipment for 17 years. The company has passed ISO9001 Quality Management System Certification, China Compulsory Certification (3C) and CE Certification. It is a National High‑tech Enterprise, a Specialized, Refined, Differential and Innovative Enterprise of Jiangsu Province, a Specialized, Refined, Differential and Innovative Enterprise of Wuxi, and a Gazelle Enterprise in the Southern Jiangsu National Self‑Dependent Innovation Demonstration Zone.
Should you be interested in our diffusion‑welding equipment, please contact us: 400‑0510‑750.
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Wuxi HAIFEI Intelligent Equipment Co., Ltd.
Wuxi HAIFEI Welding Equipment Co., Ltd.
Add: 28 Shuiyun Road, Yuecheng, Jiangyin, Jiangsu Province, China. (Postal Code: 214404)
Mobile: +86 18915302352
Email: wushijie@jshaifei.com