Comparison between die attach film (DAF) and film over wire (FOW) on stack-die CSP application

Due to the strong requirement of the miniaturization of micro electronic products, the development of IC package has been pushed toward to a smaller, thinner, lighter and higher density package structures. For the purpose of mass production, the designs of stack die-attached process should be simplified and wire-penetrated. In this paper, the characteristics of the Die Attach Film (DAF) and Film over Wire (FOW) as well as the following process to stack dies were defined. The cure kinetics and thermal resistances of the DAF and FOW materials were analyzed by Differential Scanning Calorimetry (DSC) and Thermo gravimetric Analysis (TGA). The geometry and distribution of filler of attached materials were analyzed by were examined by Scanning Electronic Microscopy (SEM) and Optical Microscope (OM). The thermo-deformation and pressure-induced flow behaviors of the attached materials were evaluated by the dynamic mode in rheology test. The results revealed that the FOW materials exhibit optimum and wider lowest-viscosity working window than DAF that obviously would contribute enough time to flow over the wires and easily to control bond line thickness, that can enhance the quality of Stack-die CSP. Besides, the geometry influences of filler were fully discussed in this paper.