In-depth characterization of die attach adhesive for low-k automotive device application

Despite the introduction of newer die attach adhesive material such as die attach films, conventional die attach epoxy remains to be the most important material for die attach process in semiconductor packaging. In response to the demand for high bonding strength and thermal dissipation while maintaining good manufacturability, the requirements on the behavior and characteristics of the epoxy are becoming increasingly more critical. To meet the stringent requirements of automotive application, delamination remains an integral part of die attach reliability issue. The consistencies of epoxy dispensing and resultant epoxy coverage are important criteria in epoxy selection, and both of these responses critically affect delamination performance. In particular for low-k devices, both of these responses are extremely crucial to ensure that the devices do not encounter die inner layer dielectric (ILD) delamination issues. Die shear tests and scanning acoustic micrograph inspection after MSL pre-conditioning are also important tests that require in-depth study for package delamination performance. This paper specifically discusses on detailed characterization to establish robust die attach process by evaluating various responses on die attach epoxy with various values of epoxy viscosity. The die attach epoxy behavior is studied through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). In terms of die attach process, focus is provided on the various output responses which are critical to the process consistency and manufacturability. Furthermore, a study on the impact towards wire bond process is also presented, where emphasis is mainly placed on the 2nd bond performance, due to varying degree of epoxy out-gassing. In addition, the results from various reliability tests towards meeting the automotive reliability requirements are also presented.