# Influence of Thin Fluorine Resin Film on DUV LED Packaging Devices
## 3 Results and Discussion
As shown in Figure 5a, when the curing time was 2 h, the light output power improved gradually from 4.95 mW to 5.86 mW with the increasing dripping applications, which had a rise of 18.41%. After curing for 24 h, the trend of the curve changed. The light output power improved from 4.95 mW to 5.44 mW when dripping two times, which had a rise of 9.87%;  
Figure 4: (**a–d**) Cross-sectional SEM image of fluorine-resin-packaged devices with different numbers of drip coatings, crack is shown by the red arrows. (**e**) Thickness of the fluorine resin. Figure 3: Top view of fluorine-resin-packaged device (**a**) before curing and (**b**) after curing. Device after heating to (c)170 \({}^{\circ}\)C, (**d**) 180 \({}^{\circ}\)C, (**e**) 190 \({}^{\circ}\)C, (**f**) 200 \({}^{\circ}\)C, (**g**) 210 \({}^{\circ}\)C and (**h**) 240 \({}^{\circ}\)C for 3 min. however, when the dripping was performed more than two times, the light output power was reduced to \(\sim\)5 mW, which was almost unchanged compared with the initial value. Compared with the result of cross-sectional SEM, the reason may be that when the number of drip coatings was lower, the fluorine resin film was too thin to cover the whole surface of the chip. With the increase in drip coatings, the thickness of the film also increased, which formed an overall coverage of the chip and promoted more light to be emitted. However, due to the presence of the crack appearing during the curing process, as shown in the cross-sectional SEM image, the surface of the chip in the crack region was still in contact with the air, and as DUV light needs to pass through the air in the crack and then through the reflection and absorption of the fluororesin layer to emit out, the light output power of the packaging device after complete curing reduced compared with the device when curing for just 2 h was not sufficient. When the drip coating was applied more than two times, the crack became too large, and light output power had no clear increase after complete curing, although it increased obviously after 2 h of curing. The result also revealed that if the crack can be controlled, a larger enhancement of light output power can be received. Table 1 shows the result of light output power enhancement and cost, which are compared with a previous study. Although the enhancement in this work is still lower than 50% [15], the cost is only \(\sim\)10%. This may be more suitable for industrial production applications. Figure 5b shows the electroluminescence (EL) spectra of the fluorine-resin-packaged device. The peak wavelength was \(\sim\)275 nm, and there was no obvious shift in wavelength \begin{table}
\begin{tabular}{c c c c c}  & **Packaging Form** & **Enhancement of Light Output** & **Consumption of Fluorine Resin (g/pcs)** & **Cost of Fluorine Resin (USD/pcs)** \\ This study & Thin film & \(\sim\)10\% & 0.00064 & 0.0277 \\ Previous study & Hemisphere & \(\sim\)50\% & 0.00470 & 0.2036 \\ \end{tabular}
\end{table} 
Table 1: Light output power enhancement and cost of fluorine resin in different studies. Figure 5: (**a**) Light output power of fluorine-resin-packaged device, (**b**) electroluminescence (EL) spectra of fluorine-resin-packaged device after curing for 24 h, (**c**) voltage of fluorine-resin-packaged device and (**d**) light output power decay for fluorine-resin-packaged device after curing for 24 h. All measurements were performed at 40 mA. in the EL spectra after fluorine resin was used for packaging. Figure 5c shows the voltage of the fluorine-resin-packaged device, the voltage was around 6 V, and no significant change was observed. The results indicated that fluorine resin only affected the light output power of the device, and there was no effect on the wavelength and the voltage. Preliminary reliability tests on fluorine-resin-packaged devices are shown in Figure 5d. After aging for 1000 h, the devices were stable under a direct current (DC) mode operation current of 40 mA, and no degradation was observed.