Sawing Investigation for Thin Wafer Laminated with Die Attach Film

The drive for smaller size and thickness has created new package assembly process challenges. Stacked die packages are increasing in interest due to the resultant smaller package and increased functionality. The requirements for a stacked package is a thinner wafer that enables more die to be stacked in a package. The die are bonded using Die Attach Film (DAF) that is laminated on the back of a wafer prior to singulation. The singulation of DAF laminated wafers with wafer thickness <3 mils is challenging, especially for devices used in automotive applications. Part of the singulation challenge is that it involves two different hardness materials (Si and the DAF polymer). Previous studies have shown that for thin die, a step-cut saw process is better than single cut but backside chipping and residual DAF whiskers must be resolved. In this study, the saw singulation process was optimized through a series of wafer saw singulation experiments. The results showed that the depth of cut for both Z1 and Z2 is a key process parameter to improve the backside chipping and resolution of DAF residual/whisker formation. Singulated die were evaluated optically and by SEM to characterize the dicing performance, including chipping and cracking. With optimized parameters, the backside chipping can meet backside chipping requirements with no DAF residual material or whisker formation in a high volume production monitor. Packaged stacked die also passed all AEC Grade 1 requirements with no chipping related defect.