Optimization of Saw Street Configuration to Save Saw Blade in Assembling QFN Packages

Saw singulation is an indispensable process to sever the Mold Array Package (MAP) strips into individual units in assembling Quad Flat No-lead (QFN) packages. Mechanical saw, cutting the MAP strip along saw streets using dicing blade, is a mainstream mode in the saw singulation process. Accordingly, the dicing blade, a continuously consumed part, takes a significant portion of the assembly cost. The saw blade consumption is generally determined by saw blade type, MAP strip structure and process parameter. In this study, the effects of MAP strip structure, specifically, the saw street configuration in lead frame, on the saw blade saving have been experimentally investigated. The saw street configuration was first investigated by comparing the wear amount of saw blade for cutting discrete and continuous saw streets of equal length and same configuration in 3×3 mm, 6×6 mm and 9×9 mm QFN packages. It is found that (i) the wear amount of the discrete saw streets may be significantly less than its counterpart of the continuous saw streets and (ii) the saw blade saving in the discrete saw streets goes more as the package size goes smaller. The saw blade saving is attributed to the additional saw process improvement contributed by the discrete saw streets. The saw street configuration was also investigated by comparing the wear amount of saw blade for cutting saw streets of 5 mil and 8 mil lead frames in the 6×6 mm QFN package. It is proved that less metal amount in the saw street consumes less saw blade. The merit of the discrete saw street and metal amount reduction in saw street were then implemented in the revised lead frame of the 6×6 mm package, and the saw blade consumption per MAP strip dropped to 15.8 μm in revised lead frame from 113.0 μm in original lead frame in statistical sense.