Development of UV Curable Wafer Back Side Protection-Film for Wafer Level Chip Size Package

Mobile communications packages are expected to become increasingly functional, thinner, and lighter. One of these package designs, WLCSP (Wafer Level Chip Size Package), is an excellent small, thin, and light weight package with electrical connections. However, the miniaturized WLCSPs are thin and brittle, so there is risk of damage during processing. Wafer back side protection-film (BPF) is used to mitigate handling damage, chipping during dicing, and increased package strength. Since the BPF requires a thermosetting process for several hours at $100 ^{\circ}\mathrm{C}$ or higher like other resin sealants, there are some issues, such as reduction of productivity, thermal damage to the package, warpage of the wafer, and the like. In this paper we describe a new process using an UV curable BPF that eliminates the heat curing process and still provides the advantages of the UV curing process. As a result, we have developed UV curable BPF and applied it to this new process, confirming that productivity is improved and thermal damage to the package is reduced. This process is expected to increase productivity, improve package reliability, and enable new devices that would otherwise be difficult to manufacture due to their sensitivity to thermal damage.