**4.7 Bondline vs. environment condition**

**4.5 Better design vs. design complexity**

*Advanced Functional Materials*

**4.6 Air pockets on the bondline**

*Gap and design complexity between tape and adhesive.*

**Figure 15.**

**Figure 16.** *Air pocket for tape.*

**302**

Tape solution has a certain thickness (1 mm) of tape and once it is pressed, it becomes to 0.8 mm thickness. When adopting the glass plate bonding design, its own tape thickness puts some limitations on the freedom of design and causes additional unnecessary and complicated design and assembly process due to its design. For instance, 0.8 mm of gap between glass pate and body frame is clearly and easily visible to the eyes of consumers as the application of glass bonding is always external and it affects the image of their product on consumer's preference and expectation on high-end image appliances. Manufacturers who used a tape solution have adopted additional side frame to cover the gap and not to let consumers realize that there was a gap clearly visible, or designed a special threshold on the outer end of body frame so that the gap is not visible outside from the eyes of consumer as shown in **Figure 15**; ultimately, it has caused more cost, more process complexity, and more manpower as well as poor high-end image as it is clearly and vividly different if they compare the image of refrigerator between the one that has a side cover on the glass (with tape solution) and the one that has no side cover, just

Tape solution has an inheritable structural limitation to achieve a complete contact to substrate as it is a solid form, and taping/pressing is also done manually. **Figures 16** and **17** show an actual application with tape for refrigerator; as shown in figures, many area of tape has detached area causing a low bonding strength and durability, and especially in the high-temperature, high-humidity aging condition, the bonding reliability decreases as the detached area is expanding due to temperature increase and moisture ingress over time. In general, the air pockets in the tape solution on the bondline are quite substantial such as 40–50% in some worst cases as the substrate surface is not always flat. On the other hand, the adhesive solution can prevent such air pocket possibilities as it is a liquid and it flows and fills all the

bonding of glass plate to body frame (with adhesive solution).

Tape solution when subjected to various environment conditions increases its thickness by expanding, due to high temperature and moisture ingress; it increases to 1 mm in some cases. The adhesive solution maintains quite consistently in terms of its thickness before and after various environment conditions. In case of hightemperature condition (80°C for 7 days), the delta is average 0.04 mm which is very minimal as shown in **Tables 1–3**. In case of thermal cycle condition (50°C, 95% RH for 8 h to 5°C, 95%RH for 8 h as 1 cycle for 1000 h), the delta is 0.01 mm. In case of bigger range of thermal cycle, (60°C, 95%RH for 16 h to 30°C for 4 h as 1 cycle for 1000 h), the delta is 0.05 mm. The above test results confirm the reliability and excellent environmental resistance of adhesive solution in achieving a durability and ultimately a better quality of appliances.

**Figures 18** and **19** explain the gap generated between adhesive solution and tape solution. For adhesive solution, as shown in **Figure 18**, it is very narrow for a coin to penetrate, while for tape solution, as shown in **Figure 19**, there is a gap that is big enough for coin to penetrate.

**Figure 17.** *No air pocket for adhesive.*


**Table 1.** *High temperature.*
