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What Welding Defects Tend to Occur in Copper Flexible Connections Produced by Polymer Diffusion Welders after Oxide‑Film Formation on Copper Foils?

Aug 27,2026

During mass production of new‑energy copper‑foil flexible connections, blackening and oxide‑film accumulation on copper‑foil surfaces are invisible adverse sources which are most easily overlooked yet exert great influence.

Polymer diffusion welding realizes solid‑state metallurgical bonding via atomic inter‑diffusion and requires high cleanness of welding surfaces. Hard and high‑temperature‑resistant copper‑foil oxide films directly block metal bonding and trigger various welding defects. Moreover, welding defects caused by oxidation cannot be eliminated merely by adjusting welding parameters.

I Core Causes of Welding Defects Induced by Copper‑Foil Oxide Films

1.Oxide films possess no metallic activity and cannot participate in atomic inter‑diffusion bonding. They form permanent isolating interlayers between copper‑foil layers and bring about pseudo‑welds and delamination‑type cold joints.

2.Oxide films are hard and brittle while pure‑copper material is soft. Uneven force bearing under welding pressure readily generates micro‑cracks and gaps at interfaces.

3.Oxide films resist high temperature. Conventional temperature‑pressure settings for diffusion welding cannot melt or break oxide films, leaving impurities on welding interfaces.

4.Oxide interlayers reduce effective conductive area, resulting in over‑heating under current and unstable resistance, with hidden electrical‑safety risks.

II Common Welding Defects Caused by Copper‑Foil Oxidation

1.Hidden inter‑layer delamination, peel‑off by hand‑tearing

2.Cold joints, unstable tensile strength

3.High internal resistance, severe heating under current

4.Terminal bulges, internal voids

5.Brittle‑hard terminals, easy cracking upon bending

6.Blackened end faces, poor appearance color difference

7.Unstable batch‑wise quality

III Solutions for Oxidation‑Induced Defects

1.Strict incoming‑material quality control

Store copper foils in sealed and dry conditions with dust‑proof and moisture‑proof measures. Isolate and scrap copper foils with yellowed, blackened or severe oxidation; forbid feeding them into production. Prohibit mixed‑batch production of copper foils with varying oxidation degrees.

2.Standardize pre‑weld cleaning procedures

Clean copper‑foil welding surfaces before mass production to remove oil stains, dust and surface oxides. Gently wipe or lightly abrade slightly‑oxidized areas to expose bright pure‑copper base material. Scrap heavily‑oxidized foils directly; do not force them into production.

3.Shorten semi‑finished‑product turnover time

Send cut and sorted copper foils for welding as soon as possible to avoid secondary oxidation from long‑time air exposure. Seal and store unused semi‑finished products timely to isolate moisture and air.

4.Standardize operating procedures

Forbid bare‑hand contact with copper‑foil welding zones to prevent sweat and stain residues. Flatten and align foils layer‑by‑layer during stacking to expel inter‑layer gaps and secure tight fitting of welding surfaces.