Effect of Interpass Annealing on the Microstructure, Nanoindentation Hardness, and Electrical Conductivity of 20-μm Cold-Rolled Copper Foils

Document Type : Research Paper

Authors

1 Department of Materials Engineering, Tarbiat Modares University, Tehran, Iran

2 Department of Advanced Materials and Renewable Energy, Iranian Research Organization for Science and Technology, Tehran, Iran

Abstract

Copper foils play essential roles in electronic technologies, including lithium-ion batteries, printed circuit boards, and electrical interconnects, where microstructure, hardness, and electrical conductivity critically determine performance. Achieving the optimal combination of these properties is therefore central to producing high-quality foils. In this work, 20-μm-thick copper foil was fabricated from tough pitch copper (TPC) through cold rolling, and interpass annealing was applied to tailor and improve these key characteristics.
The material was first rolled from 100 µm to 30 µm, followed by interpass annealing for all samples except A0. Rolling was continued to achieve a final thickness of 20 µm. Annealing treatments were performed at 150, 200, 250, and 300 °C for 10, 15, 20, and 30 minutes. Microstructure, hardness, and electrical conductivity were characterized using optical microscopy, nanoindentation, and four-point probe measurements.
The as-rolled sample (A0) showed elongated, highly deformed grains (17.64 µm), elevated hardness (124.09 HV), and the lowest conductivity (84.39% IACS). Significant improvements were observed in samples B4 and C1, where recrystallization produced refined grains (4.01 µm in B4 and 3.47 µm in C1), reduced hardness (64.56 HV and 55.36 HV, respectively), and enhanced conductivity (88.99% and 89.76% IACS, respectively). Continued annealing led to grain growth, with D4 exhibiting the highest conductivity (96.29% IACS).
Overall, the influence of interpass annealing was evaluated across all processing conditions, and the results indicated that the routes used for samples B4 and C1 were optimal for producing 20-µm copper foil suitable for electronic applications. Depending on available equipment, either route can be selected for industrial production.

Keywords

References

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Iranian Journal of Materials Forming
Volume 13, Issue 4
October 2026
Pages 4-14

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