# Comparison of Tensile and Fatigue Properties of Copper Thin Film Depending on Process Method
## 4 Conclusions  
This study investigated the effect of fabrication on the tensile and fatigue properties of copper thin film, which is widely used in FPCB. Some conclusions are drawn:  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **S-N Curves** & **S-N Curves Modified by** \\  & & **Goodman Method** \\ \hline Rolled Copper R = 0.1 & \(S_{a}=513(2N_{f})^{-0.1113}\) & \(S_{alt}=2055(2N_{f})^{-0.1836}\) \\ Electrodeposited copper R = 0.1 & \(S_{a}=277(2N_{f})^{-0.0759}\) & \(S_{alt}=776(2N_{f})^{-0.1225}\) \\ Type A \(S_{m}=0.5S_{TS}\) & \(S_{a}=431(2N_{f})^{-0.0834}\) & \(S_{alt}=910(2N_{f})^{-0.0895}\) \\ Type B \(S_{m}=0.5S_{TS}\) & \(S_{a}=872(2N_{f})^{-0.1507}\) & \(S_{alt}=1191(2N_{f})^{-0.1091}\) \\ Type C \(S_{m}=0.5S_{TS}\) & \(S_{a}=519(2N_{f})^{-0.0923}\) & \(S_{alt}=1743(2N_{f})^{-0.1507}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of stress-life equation according to the process using Goodman method.  
Figure 11: P-S-N curve from fatigue test for Cu thin films depending on process method.  
(1) The tensile test results show that the copper thin films by the rolling process are more brittle than by the electrodeposition process. Elastic moduli show little difference between the two types but are all lower than the bulk material and even previous study for three types. In addition, there is difference among the two types that the 0.2% offset yield strength and the ultimate tensile strength of the rolled copper thin film are higher than the electrodeposited copper thin film but the both copper thin film are higher than the bulk material.  
(2) The fatigue test results show that the copper thin films by the rolling process are better than by the electrodeposition process in fatigue life in all region. From the experimental results, the mechanical characteristics of the thin film are influenced by the manufacturing method even if they are the same material, and it is important to directly obtain the mechanical properties to secure the reliability of an electric product.  
From the results of this study, in order to secure the reliability of electronic products using FPCB, it is found that it is appropriate to use a rolled copper thin film. However, there is a great difference between the mechanical characteristics depending on the direction of the rolling in the rolled thin film, so care must be taken when using it.  
Conceptualization, J.-H.P.; methodology, J.-H.P.; software, D.-J.K.; validation, [PERSON]-H.P. and D.-J.K.; formal analysis, H.-G.M. and [PERSON]-H.P.; investigation, H.-G.M.; resources, [PERSON]-H.P. and H.-G.M.; data curation, H.[PERSON]; writing--original draft preparation, [PERSON] and [PERSON]; writing--review and editing, [PERSON], [PERSON] and [PERSON]; visualization, [PERSON]; supervision, [PERSON] and [PERSON]; project administration, [PERSON]; funding acquisition, [PERSON], This paper was prepared the contributions of all authors. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the KETEP (Korea Institute of Energy Technology Evaluation and Planning) and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT No. 20153010024470, NRF-2019R1H1A2101531). The authors declare no conflict of interest.