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When Welding Copper Flexible Connections with Polymer Diffusion Welder, What Welding Defects Are Caused by Inadequate Surface Pretreatment of Workpieces?
Sep 27,2026
The polymer diffusion welder relies on high temperature and high pressure to make atoms at the interfaces of multiple copper foils mutually diffuse and form a firm bond. Copper flexible connections easily form oxide films and become contaminated with oil and dust impurities during processing and storage. If surface pretreatment before welding is inadequate, impurities remain at the interlayer interface, hinder atomic diffusion, and bring various welding defects.
I Interlayer Cold Joints and Local Non-Fusion
1.Oxide films on copper surfaces are not thoroughly cleaned, forming an isolation layer that hinders copper atom diffusion, producing point-like or sheet-like unfused zones.
2.Residual stamping oil and rust-preventive oil on workpiece surfaces form isolation gas films at high temperature, preventing effective metallurgical bonding between layers.
3.Dust and metal chips get sandwiched between copper foils, causing local poor fitting; even with pressure applied, diffusion welding cannot be completed.
II Interlayer Bubbles and Pore Defects
1.Residual oil and moisture vaporize under high-temperature conditions; gas is sealed inside the layers forming bubbles, reducing the conductive area, and causing abnormally elevated local temperature after current flows through the product.
2.Oxide films absorb moisture; when heated, released gas gathers to form bubble bands. Under force, the flexible connection easily tears apart and delaminates at the bubble positions.
III Interlayer Inclusions, Product Prone to Fracture and Poor Conduction
1.Solid impurities produced by cleaning and grinding remain between layers, forming inclusions and breaking the continuous bonding surface.
2.Bonding strength at inclusion positions is low; when the product is bent or subjected to vibration, it easily cracks and delaminates from the inclusion positions.
3.Impurities conduct poorly, increasing contact resistance.
IV Product Appearance Color Difference and Surface Blackening
1.Residual oil and oxide scale oxidize continuously at high temperature, causing the workpiece surface to turn black and dark.
2.Resistance rises in heavily oxidized zones, degrading contact performance at the terminal positions.
V Interface Micro-Cracks, Hidden Failure Risk
1.Interface impurities cause different diffusion-bonding degrees in various zones; stress distribution becomes unbalanced during cooling shrinkage, producing interface micro-cracks.
2.Micro-cracks cannot be identified by naked eye; they propagate continuously under repeated vibration and alternating hot-cold conditions, eventually causing delamination fracture.
VI Pretreatment Control Key Points
1.Strictly remove the oxide layer on copper foil surfaces to ensure interlayer cleanliness and avoid residual isolation layers.
2.Clean oil and fingerprints to prevent high-temperature vaporization producing pores and air pockets.
3.Control the storage time of cut semi-finished products and weld promptly to prevent secondary surface oxidation.
4.Perform exhaust and flattening during stacking to expel interlayer air and avoid air-sealed inner-layer cold joints.
5.Keep mold surfaces clean to prevent secondary contamination and uneven force application.
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