Fatigue fracture of SnAgCu solder joints by microstructural modeling

Abstract

The ongoing miniaturization trend in the microelectronic industry enforces component sizes to approach the micron, or even the nano scale. At these scales, the underlying microstructural sizes and the geometrical dimensions are comparable. The increasing influence of microscopic entities on the overall mechanical properties makes conventional continuum material models more and more questionable. In this study, the thermomechanical reliability of lead-free BGA solder balls is investigated by microstructural modeling. Microstructural input is provided by orientation imaging microscopy (OIM), converted into a finite element framework. Blowholes in BGA solder balls are examined by optical microscopy and a statistical analysis on their size, position and frequency is conducted. Combining the microstructural data with the appropriate material models, three dimensional local models are created. The fatigue life of the package is determined through a critical solder ball. The thermomechanical reliability of the local models are predicted using cohesive zone based fatigue damage models. The simulation results are validated by statistical analyses provided by the industry.

Impact of laminate cracks under solder pads on the fatigue lives of ball grid array solder joints

“…In this case, the orientation of a tin grain in a single-grained SAC solder joint will have a large impact on the resulting stresses. At ambient conditions, the CTE along the a-and b-axes in a tin grain (about 15 ppm/°C) is at the same level as the CTE of copper (16-17 ppm/°C [11,15,29]) and of the PCB and BGA laminates in the x-and y-directions (about 12-18 ppm/°C [14,15,30]). Therefore, if the tin grain is oriented with the a-and b-axes parallel to the board surface, the stresses at the interfaces will be low.…”

“…Thus, the number of tin grains and the orientation of the grains in a SAC solder joint will have a large impact on the resulting stress levels. Several studies have shown that the orientation of the tin grains has a nearly random distribution [7,8,15]. This means that there may be a large difference in stress levels even for two neighbouring solder joints.…”

Development of a Cohesive Zone Model for Fatigue Crack Growth

“…Abdul-Baqi et al [21] described the process of fatigue damage of shoulder bumps using this approach. Moreover, this approach was applied to simulate interfacial fatigue damage [22] and fatigue damage of shoulder joints incorporating with microstructures [23,24].…”

Effects of bulk Cu6Sn5 intermetallic compounds on the properties of Sn‐Ag‐Cu‐Ce soldered joints

“…After July 1, 2006, when the RoHS directive came into effect electronics products sold in Europe must not contain lead (Xia and Xie, 2008;Zhang et al, 2008b). Among the lead-free solder alloys, the Sn-Ag-Cu solder system, which has better thermo-mechanical properties compared to those of Sn-Pb solder, is regarded as one of the promising candidates for use in electronic assembly, moreover, the Sn-Ag-Cu solder alloys can wet and form good quality joints with Cu substrates (Hao et al, 2008;Erinc et al, 2008;Gao et al, 2008). In addition, under the drivers of increasingly finer pitch and severe service conditions, novel lead-free solders with better creep and thermal fatigue performances are sometimes needed (Shi et al, 2008).…”