# Effect of Different Bonding Materials on Flip-Chip LED Filament Properties
## 3 Results and Discussion
### Photoelectric Properties of the FC-LED Filaments after Aging  
The steady-state voltage of the two types of FC-LED filaments are presented in Figure 8. As shien in Figure 8, at high-temperature and high-humidity (85 \({}^{\circ}\)C/85% RH ) aging conditions, the steady-state voltage of the Sn90 Sb10 filaments decreased before aging for 100 h and then increased. Moreover, after aging for 300 h, the steady-state voltage of the SAC0307 filaments was decreased by 0.23%, and that of the Sn90 Sb10 filament was decreased by 0.34% compared to the initial values. During aging of the filament, in the initial stage of aging, the test environment was at room temperature. When changing the high temperature and high humidity of the aging environment to normal temperature, an effect equivalent to the annealing effect was observed, and the defects in the solder layer were repaired to a certain extent. On the whole, the resistance of the filaments was reduced, and the steady-state voltage  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**NUMBER** & **1** & **2** & **3** & **4** & **5** & **AVG** \\ \hline
**Junction Temperature of SAC0307 Filament (\({}^{\circ}\)C)** & 122.16 & 123.85 & 124.22 & 124.09 & 125.18 & 123.9 \\
**Junction Temperature of SN90 SB10 Filament (\({}^{\circ}\)C)** & 116.76 & 117.3 & 116.93 & 117.27 & 117.34 & 117.12 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Junction temperature of the two types of FC-LED filaments.  
Figure 7: Blue light luminous flux of the two types of FC-LED filaments.  
decreased. However, as the aging time increased, the higher temperature destroyed the surface of the flip chip, causing the ohmic contact between the chip and the electrode to degrade. The internal delamination of the flip chip and the solder layer intensified, which caused increased resistance and poor heat conductivity. The steady-state voltage of the filaments rose, and the overall stability of the filaments was reduced, but the deterioration of the material properties inside the chip caused the blue light luminous flux to decrease [34; 35].  
The blue light luminous fluxed of the two types of filaments are presented in Figure 9. It can be observed that the blue light luminous flux of both the Sn90 Sb10 and the SAC0307 filaments decreased after aging for 300 h. Compared to the initial values, the blue light luminous flux of the Sn90 Sb10 filaments was decreased by 7.82%, and that of the SAC0307 filament was decreased by 9.27%. The factors which accelerates FC-LED filaments' aging were high temperature and high humidity. The aging mechanism of the two types of filaments consisted in the acceleration of chemical reactions at high temperatures and in the diffusion of moisture in the FC-LED filament caused by high humidity, which accelerated the aging of the filaments. In addition, aging can change the material performance, cause corrosion and failure of the chip, and decrease the blue light luminous flux of the filament. In conclusion, the Sn90 Sb10 filaments performed better in maintaining the blue light luminous flux; therefore, high temperature and high humidity had a greater influence on the SAC0307-welded filaments than on the Sn90 Sb10-welded ones [36; 37].  
Figure 8: Steady-state voltage after high-temperature and high-humidity aging.  
Figure 9: Blue light luminous flux after high-temperature and high-humidity aging.