Study of die bond on roughened NiPdAu-Ag pre-plated frame with anti-EBO

This paper studies the challenges and behavior of epoxy material between the silicon (Si) material and roughened Ni/Pd/Au-Ag alloy-plated Copper (Cu) leadframe (known as μPPF) with anti-epoxy bleed-out (EBO) during die bond process. Die bond on die attach paddle (DAP) of roughened μPPF using Silver (Ag)-based epoxy has been a challenge for its manufacturability in terms of maintaining the target epoxy fillet height for a 300 μm Si chip thickness. The study on the roughened μPPF utilizing die bond parameters for Ag-based epoxy on standard Ag-plated DAP Cu leadframe yielded fillet height greater than the maximum target limit of 75% of die thickness and reaching as high as 100% fillet height. This occurrence leads to risks of epoxy component creeping onto the chip surface which is detrimental on reliability (delamination on die top) and can cause manufacturing yield loss due to die contamination and non-stick on pad (NSOP) during wire bonding. The processability of the epoxy on the surface of the roughened μPPF leadframe needs to be established due to this significant difference in fillet height result when compared to the Ag-plated Cu leadframe which has a major impact in the quality of the chip assembly. The development of the die bond process for the roughened μPPF is separated into two assessments, namely epoxy dispense scale assessment and die bond parameter design of experiment (DoE). The epoxy dispense scale assessment studies the optimum epoxy glue coverage with respect to chip area that will ensure a consistent epoxy volume underneath the Si chip (bond line thickness or BLT) and achieving a linear epoxy fillet height formation along the sidewall of the Si chip. Once the optimum dispense scale is established via DoE, the critical die bond parameters identify a parameter window where a controlled fillet height is observed without any impact on the functionality test response of the epoxy. The study shows that a high epoxy dispense scale and optimum die bond parameter, namely, component over travel distance and dispensing height are required to achieve an optimum epoxy fillet height control along the side wall of the Si chip.