# Silver Sintering for Silicon Carbide Die Attach: Process Optimization and Structural Modeling
## 4 Conclusions  
The presented activity has proposed an experimental methodology for the optimization of the pressure of the silver sintering die attach process. The assessment was based on a liquid-to-liquid thermal shock (TS) test and on dedicated physical analyses (SEM, SAM and electric measurements) aiming to check and monitor sintering layer degradation during the reliability stress. Considering that the effect of three different pressure values has been analyzed, the porosity fraction has been identified as the main representative physical parameter. The employed investigation has highlighted that the maximum pressure value \(p_{3}\) leads to the best reliability performances. In the framework of process characterization, two non-destructive techniques (SAM and electric measurements) were proposed that can analyze how delamination evolves with TS. Moreover, a dedicated uniaxial tensile test was employed to characterize the stress-strain behavior of almost-bulk (free of voids) silver sintering samples at different temperatures ranging from \(-65\) to \(200\,^{\circ}\)C. This experimental characterization acted as a starting point to simulate the mechanical behavior of a silver sintering joint--with a defined percentage of void and without the need of dedicated uniaxial tests for a specific void ratio--via finite element analysis (FEA).  
The mentioned capability to simulate the elasto-plastic behavior as a function of void percentage in sintering layer is needed to perform the FEA simulation of material degradation due to a reliability stress such as TS. Porosity is a parameter that can be quantified; therefore. the proposed simulation method allows to account for the real silver sintering properties. It is of paramount interest that the virtual characterization of sintering material considers the same average of a void fraction but a different or irregular silver pattern. Since it is expected that elastic properties mainly depend on porosity average, this investigation may highlight different plastic behaviors. A further development of the presented activity will be the virtual simulation of the degradation during thermal shock.  
The implementation of a multiscale modeling approach, such as the \"global-local\" model, can support this specific purpose. Such a technique allows the calculation of deformation by a \"global\" model that represents the entire package, meanwhile, stress on the sintering layer is computed by a \"local\" model that takes \"global\" deformation as input. Once the model is calibrated step by step with physical evidence such as the presented SAM and electric measurements, the creation of a finite element model permits to reduce the time needed for future assessment and to make very accurate analyses in terms of geometry and time resolution. Moreover, interface analysis can be enriched by the characterization of sintering adhesion properties and relevant fracture mode-mixity, which can be achieved by performing a set of experiments on dedicated specimens and applying an advanced theoretical model such as the cohesive zone model (CZM) [23].  
Conceptualization, G.S.; data curation, M.C.; investigation, A.S.; methodology, M.C.; supervision, S.M.O. and G.S.; validation, M.C.; writing--original draft, A.S. All authors have read and agreed to the published version of the manuscript.  
This paper belongs to a research path funded by Regione Sicilia (Azione 1.2.1_03 del PO FESR SICILIA 2014-2020 - Progetto PON03 PE_00206_1 AMELIE \"Advanced framework for Manufacturing Engineering and product Lifecycle Enhancement.\" CUP G76I20000060007).  
Not applicable.  
The authors declare no conflict of interest.