Die cracking and reliable die design for flip-chip assemblies

Abstract

Die cracking during underfill cure or thermal cycling is a cause for concern in flip-chip assemblies. In this work, an integrated process-reliability modeling methodology has been developed to determine the stresses at the backside of the die during underfill cure and subsequent thermal cycling. The predicted die stresses have been compared with experimental data, and excellent agreement is seen between the theoretical predictions and the experimental data. The modeling methodology has been used to understand the effect of material and geometry parameters such as substrate thickness, die thickness, standoff height, interconnect pitch, underfill modulus and coefficient of thermal expansion (CTE), and solder mask CTE on die stresses and thus die cracking. Based on underfill-cure and thermal cycling models for specific cases, the critical flaw size to induce catastrophic die cracking has been calculated using linear-elastic fracture mechanics. Design recommendations, including die thinning and polishing, have been made to reduce the tensile stresses on the backside of the die and thus die cracking.

Study on thermomechanical reliability of a tunable light modulator

“…The maximum tensile stress, 47 MPa, occurs at the area adjacent to the inner boundary of the adhesive layer. Though this tensile stress is much lower than the strength of perfect silicon crystal, cracking might occur if a significant flaw exists at this highly stressed location [8]. However, a flaw in this region is not very likely.…”

“…For brittle materials, the most widely used criterion to predict failure is the maximum principal stress in the body. When the maximum principal stress reaches a critical value, failure is assumed to occur [8]. Fig.…”

Lifetime modelling for microsystems integration: from nano to systems

“…Critical crack tip parameters are tabulated for Si in literature [e.g. (Michaelides and Sitaraman 1999)], but much of the load carrying capability of the die depends on the presence and initial length of micro-cracks due to dicing (Zhao et al 2008). …”

Thermo-fatigue life evaluation of SnAgCu solder joints in flip chip assemblies

“…Several literatures also addressed the thermo-mechanical coupling response of slip chip devices. In such analysis, the stresses in a flip chip assembly were calculated [27][28][29][30], the interfacial fracture behavior of a flip chip package was investigated [1,31], the FEA parametric studies were also performed [32].…”