# Prediction of Curing Time/Shear Strength of Non-Conductive Adhesives Using a Neural Network Model
## 3 Results
### Verification of Curing Time and Shear Strength Using Third-Party Experimental Data  
To verify the accuracy of the trained ANN models, the predicted curing time and the shear strength of NCA were compared with third-party experimental data. NCA formulation with 100 phr and 50 phr of DGEBA as the resin, 80 phr of MHHPA as the hardener, 15 phr of 2 MZ as the catalyst, and 0.55 phr of coupling agent was selected to verify the curing time of NCA from [PERSON] et al. 's study [4] and [PERSON] et al. 's study [20]. In order to verify the shear strength, NCA formulation, which is 50 phr of DGEBA, 80 phr of MHHPA, 20 phr of HX-3941, and 0.55 phr of coupling agent was selected from [PERSON] et al. [29]'s study. The predicted curing times from the trained ANN model were 3.9 s with 100 phr of the resin and 4.4 s with 50 phr of the resin, and the curing times from the reference [4,20] were 4.6 s and 4.0 s, respectively. The difference between the predicted and measured data were 0.7 s and 0.4 s, which can be accepted by using an adequate margin in the process design. The predicted shear strength was 37.96 MPa, and the experimental shear strength for verification was 32.30 MPa [29]. The difference is relatively critical because the shear strength requirement of epoxy resin adhesive is 34.33 MPa [30,31]. The comparison is summarized in Table 3.  
Figure 5: Correlation analysis for regression models for shear strength of NCA **(a)** training, **(b)** validation, and **(c)** all. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Curing Time (s)** & \multicolumn{2}{c}{**Shear Strength**} \\  & & **(MPa)** \\ \hline Reference & [20] & [4] & [25] \\ Predicted data & 3.9 & 4.4 & 37.96 \\ Experimental data & 4.6 & 4.0 & 32.30 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Predicted and verified data of curing time and shear strength. Case Study 1: Prediction of Curing Time and Shear Strength of NCA Based on Resin, Hardener, and Catalyst Contents  
The effects of input parameters on curing time and shear strength were investigated by the ANN models. In the estimation, curing time and shear strength were predicted by varying two input variables, while other variables were fixed. Figure 6 shows the estimation of curing time according to the contents of resin and catalyst. DGEBA was considered as the resin, while HX- 3941 and 2 MZ were selected as the catalyst, respectively in Figure 6,b. The hardener and the coupling agent were 80 phr of MHHPA and 0.55 phr of A-174, respectively. The curing times of NCA with HX-3941 and 2 MZ catalyst were decreased from 8.19 s to 2.19 s and from 7.2 s to 3.9 s as the contents of resins and catalysts were increased. The increase in the content of the catalyst increases the number of reactors and the catalyst concentration [4; 9; 20], which resulted in a decreased curing time. Figure 7 shows the estimation of shear strength according to the contents of resin and catalyst. DGEBA and HX-3941 were considered as the resin and the catalyst, respectively. The coupling agent was 0.55 phr of A-174, and 80 phr of MHHPA hardener was added (Figure 7) or not (Figure 7). The shear strengths with and without the hardener were predicted from 29.73 MPa to 45.52 MPa and from 13.97 MPa to 34.87 MPa, respectively. By increasing the catalyst content, the shear strength increased due to an increase in the number of reactors and the catalyst concentration. The predicted shear strength of NCA with the hardener showed 30.5-187% higher than that of NCA without the hardener. The role of the hardener is to cure the epoxy resin. The hardener causes a reaction with the epoxy groups, and the reaction creates a cross-linked polymer and prompts a strong chemical bonding mechanism [4; 9; 20; 32]. Shear strength of 34.33 MPa or higher is recommended for commercial NCA with epoxy resin [30; 31]. The predicted shear strengths of NCAs with the hardener were over 34.33 MPa when the resin content was more than 50 phr, and the catalyst content was more than 20 phr.