Protected WLCSP collision test via bowl feeder

Recently, the usage of WLCSP (Wafer Level Chip Scale Package) is becoming more widespread, because of WLCSP with virtues in terms of light, thin, short and small aspects [1]. However, it is well known that WLCSP is more critical compared to QFP, QFN and BGA products, regarding die chipping and crack issue, shown in Figure 1a & 1b. Since there is no molding compound to protect the chip, chip will be easily damaged by mechanical force. Especially, during SMT (Surface Mount Technology) process, operators may use the tweezer to pick up devices and cause die chip out phenomenon. Therefore, the purpose of this paper is to study pWLCSP (protected WLCSP), see Figure 2, sample with different molding compound thickness and put into bowl feeder for collision test. For bowl feeder trial run, shown in Figure 3, we will put the dedicated samples with different side wall thickness in terms of 10um, 30um and 90um into the bowl feeder, let samples collide each other, then to check protection ability. In addition, pure Silicon die (WLCSP, no protection) and embedded device will be added into overall DOE (Design of Experiment) plan, we also would like to compare pure Silicon die and embedded samples collision test performance. In summary, it was revealed that thicker side wall thickness pWLCSP sample will be good in bowl feeder trial run, 90um side wall protection thickness and embedded sample are the best as well as we did not find chip out issue after whole experiment. The other key is to control time which sample collision in bowl (within 15min which base on the experiment result), particularly for thin side wall thickness samples.