Dicing die attach films for high volume stacked die application

The usage of die attach film (DAF) is rapidly growing propelled by stacked die and 3 dimensional packaging. The die attach film is integral in facilitating the growth of wafer level packaging and stacked die packaging. Currently stacked layers of 7 and more dies are possible using DAF. The adhesive on these tapes have the double function of providing adhesion for the wafer during dicing and also providing the adhesive for die attach to substrate. The die attach film (DAF) applied to the backside of wafers prior to saw offers a breakthrough in die attach technology by eliminating the epoxy dispense process step in the assembly line. DAF has many advantages including no die tilt, no voids, consistent bond-line, no bleed-out, and no fillet which improves the real estate on the substrate. Dispensing adhesive paste on top of another die can be problematic especially for highly thinned dies. Yet very little information has been published on DAF by the manufacturers and by the users. This paper reveals some of the advantages and shortcomings of integrating DAF into the assembly process. Adhesion of die with DAF to various substrate materials is compared. Dies thinned to thicknesses of 75 and 50 micrometers mounted with DAF are found to show improvement in stackability and die shear strength over paste adhesives. Die shear strength and wirebondability of the very thin stacked die with 0.635mm of overhang is evaluated. Also the effect of the backside roughness by backgrind, chemical mechanical polish and dry polish methods on shear strength is compared. It was found that the most important factor for stacked die strength is sidewall chipping. For high volume stacked die assembly, dicing parameters are critical to minimal sidewall chipping and minimal DAF whiskering.