Interfacial Compounds Characteristic and Its Reliability Effects on SAC305 Microjoints in Flip Chip Assemblies

The (TiCr)N hard reactive films with 4 different Ti/Cr atomic ratios are prepared by using multi-arc ion plating. The Ti and Cr targets are used as cathodes in the co-deposition process. The high speed steel (HSS) specimens are adopted as substrate. The thermal shock cycle tests in air cooling (AC) way for the (TiCr)N films are carried out. The test temperatures are chosen as 600 °C and 700 °C, respectively. The changes of the surface compositions and morphology in the thermal shock cycle tests are investigated. The effects of Cr content in the (TiCr)N films, the temperature at which the thermal shock cycle tests are performed and the cycling times on the thermal shock resistance of the (TiCr)N films are discussed and analyzed in detail. The thermal shock behaviors of the (TiCr)N films show that the thermal shock cycling process of the (TiCr)N films consists of two stages, the steady-state oxidation stage with the increase of oxygen content at the early stage of thermal cycles, and, the instable oxidation stage with the oxidation aggravation and the occurrence of the surface cracks. The simple increase of Cr content in the (TiCr)N film does not improve the thermal shock resistance of the (TiCr)N films but easy to aggravate the surface oxidation process during the thermal shock cycles.

In this work, the intermetallic compound (IMC) evolution in Cu pad/SnAgCu solder interface and SnAgCu solder/Ni pad interface was investigated using thermal shock cycling experiments with 100-μm-pitch and 200-μm-pitch flip chip assemblies. The study mainly focused on the size effect of solder joints on the microstructure of IMC. The experiments showed that lower stand-off height of solder joint and higher thermo-mechanical stress played a greater role on the IMC microstructure evolution for the smaller size solder joint under thermal shock test. By comparing the IMC growth of 100-μm-pitch with that of 200-μm-pitch solder joints, it was found that on the chip side with Ni pad, the amount of (Ni, Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> reduced gradually with more cycles for both cases. However, after 1200 cycles, (Ni, Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> completely disappeared for the 100-μm-pitch case, while a thin layer of (Ni, Cu) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> still remained for the 200-μm-pitch flip-chip assembly. In addition, the growth rate of (Cu, Ni) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> Sn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> was faster for 100-μm pitch on both die and substrate sides, especially before 400 cycles. Finite-element analysis also showed that 100-μm-pitch solder joints experienced larger regions of higher stresses under thermal shock. The faster IMC growth rate for smaller joints could be explained through shorter diffusion path and higher thermo-mechanical stresses.

An investigation on the deterioration of physical and mechanical properties of granite after cyclic thermal shock

Based on the size effect on solidification behavior of lead-free solders, we propose a novel method to prepare solder joints with the metallurgical bonding between the undercooled liquid solder and Cu metallization under the temperature lower than the solder's melting point. The interfacial reaction and growth behavior of intermetallic compound (IMC) between the undercooled liquid Sn-3.0Ag-0.5Cu solder and Cu metallization have been investigated. The results show that for Sn-3.0Ag-0.5Cu solder as the undercooled melt or eutectic melt or normal melt in the joints, both of the interfacial IMC thickness and Cu 6 Sn 5 grain size increase with prolonging time. The depth of the groove between scallop-like grains in the interfacial IMC layer increases with increasing either the dwelling time or temperature. However, under different liquid solder dwelling conditions, the change tendency of interfacial IMC thickness is different, which is directly related to the dynamic equilibrium between the deposition and dissolution of the interfacial Cu-Sn phase. Furthermore, when the joints are mainly formed at the undercooling temperature, the excessive growth of interface IMC and the consumption of UBM can be reduced. The proposed method has the potential to be a new technique for preparing solder joints with thin interfacial IMC layer.

Study on thermal shock behavior of YSZ abradable sealing coating prepared by mixed solution precursor plasma spraying

Marble is a common rock used in many buildings for structural or ornamental purposes and is widely distributed in underground engineering projects. The rocks are exposed to high temperatures when a tunnel fire occurs, and they will be rapidly cooled during the rescue process, which has a great impact on the rock performance and the underground engineering stability. Therefore, the role of cyclic thermal shocks on the physical and mechanical properties of marble specimens was systematically investigated. Different cyclic thermal shock treatments (T = 25, 200, 400, 600, 800 °C; N = 1, 3, 5, 7, 9) were applied to marble specimens and the changes in mass, volume, density and P-wave velocity were recorded in turn. Then, the thermal conductivity, optical microscopy and uniaxial compression tests were carried out. The results showed that both the cyclic thermal shock numbers (N) and the temperature level (T) weaken the rock properties. When the temperature of a thermal shock exceeds 600 °C, the mass loss coefficient and porosity of the marble will increase significantly. The most noticeable change in P-wave velocity occurs between 200 and 400 °C, with a 52.98% attenuation. After three thermal shocks, the cyclic thermal shock numbers have little influence on the uniaxial compressive strength and Young’s modulus of marble specimens. Shear failure is the principal failure mode in marble specimens that have experienced severe thermal damage (high N or T). The optical microscopic pictures are beneficial for illustrating the thermal cracking mechanism of marble specimens after cyclic thermal shocks.

A solid-state reaction between the Sn–Ag–Cu solder and Ni metallization resulted in the formation of interfacial bilayer Cu6Sn5-based intermetallic compounds (IMCs) in a solder joint incorporating Au/Pd metallization. The layer near the Ni metallization was identified as (Cu,Ni,Au)6Sn5 containing 20.3 at.% of Ni and 1.7 at.% of Au, and the layer near the solder matrix was identified as (Cu,Au,Ni,Pd)6Sn5 containing 5.7 at.% of Au, 1.2 at.% of Ni, and 1.0 at.% of Pd. The electron diffraction analysis with high resolution transmission electron microscopy further characterized the interfacial bilayer IMCs as having the same hexagonal crystal structure with different crystal orientations. The kinetics study revealed that the (Cu,Ni,Au)6Sn5 in the interfacial bilayer reaction products was formed during the initial reflow process, while the (Cu,Au,Ni,Pd)6Sn5 layer was formed during subsequent solid-state aging. Predominant growth of the (Cu,Au,Ni,Pd)6Sn5 layer was observed during solid-state aging. In contrast, the growth of the initially formed (Cu,Ni,Au)6Sn5 layer was suppressed. The growth of the (Cu,Au,Ni,Pd)6Sn5 layer was governed by the dissolution of the (Au,Pd)Sn4 IMC that occurred during solid-state aging. The complete dissolution of (Au,Pd)Sn4 resulted in a reactant-limited chemical reaction from the conversion of (Au,Pd)Sn4 to (Cu,Au,Ni,Pd)6Sn5. The development of the interfacial bilayer IMCs in the solder joint incorporating Au/Pd metallization suppressed excessive IMC growth and unfavorable phase transformation during long-term solid-state aging. The detailed mechanism of the formation of the interfacial bilayer Cu6Sn5-based IMCs was investigated in this paper.

Thermal shock behavior of EB-PVD thermal barrier coatings

A comparative study of solid/solid interfacial reactions of electroless Ni-P (15 at.% P) with lead-free solders, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, and pure Sn, was carried out by performing thermal aging at 150°C up to 1000 h. For pure Sn and Sn-3.5Ag solder, three distinctive layers, Ni3Sn4, SnNiP, and Ni3P, were observed in between the solder and electroless Ni-P; while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders, two distinctive layers, (CuNi)6Sn5 and Ni3P, were observed. The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated, as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers. With increasing aging time, the coarsening of interfacial Ni3Sn4 IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)6Sn5 IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders. Furthermore, the Ni content in interfacial (CuNi)6Sn5 phase slightly increased during aging. A small addition of Cu (0.7 wt.%) resulted in differences in the type, morphology, and growth kinetics of interfacial IMCs. By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers, the role of initial Cu and Ag in lead-free solders is better understood.

At present, Sn-3.0Ag-0.5Cu (SAC305) solder is one of the commonly used lead-free solders, and copper-clad laminate is the commonly used PCB substrate. SAC solder and copper substrate mainly generate two intermetallic compounds (IMCs) of Cu6Sn5 and Cu3Sn during the soldering process. Based on the first principles, this paper analyzes the formation difficulty of the two kinds of IMCs generated in the soldering, and the failure mechanism of the Sn/IMC and IMC/Cu interfaces. Firstly, based on the density functional theory (DFT), the “CASTEP” module in Material Studio (MS) is used to analyze the formation difficulty of the two IMCs from the point of the density of states, population analysis, and energy. The results show that Cu6Sn5 is easier to generate, which also explains the reason for the first generation of Cu6Sn5 in the initial stage of soldering. Then, Sn / IMC and IMC / Cu interfaces were established in MS, and the reason why solder joint failure mainly occurred at the Sn / IMC interface was explained by energy analysis.

To investigate the effect of cyclic thermal shock and mechanical loading on the fracture behavior of magnesia refractories showing different brittleness, the as‐received and cyclic thermally shocked specimens are subjected to monotonic and cyclic wedge splitting test. The whole duration of test is monitored by digital image correlation and acoustic emission. Both thermal and mechanical fatigue resistance increase with the reduction of brittleness. Repetitive thermal shock results in pronounced reduction of strength. However, the specific fracture energy and nonlinearity increase after exposure to thermal shock due to the expanded micro‐crack network inducing the development of a significant fracture process zone. Periodic loading mainly leads to the decrease of strain bearing capacity, as the fatigue loads favor the extension of crack tip instead of fracture process zone expansion. The combined application of periodic thermal shock and mechanical loads gives a new insight into the progressive damage behavior of refractory under critical conditions.

Cylindrical specimens of Al-20%Si alloys containing primary silicon crystals of different sizes were prepared and their thermal shock behavior was examined. The specimens were quenched into iced water after heated at 550°C for 20 min., and this was repeated. After thermal shock cycles, macroscopic and microscopic examinations were made and the resistance to thermal shock was discussed in relation to the size of primary silicon crystals.1) No crack was observed on the surface of the specimens with refined primary silicon crystals after subjected to the thermal shocks for 400 times. However, some cracks were detected in the central part after about 100 cycles.2) Cracks initiated at the interface between primary silicon and α-aluminum and propagated into the silicon crystal.3) Thermal shock cycles resulted in the deformation of the specimens, but it was confirmed that the resistance to deformation was higher in the specimens with refined primary silicon crystals.4) With an increase in thermal shock cycles, needle-like eutectic silicon changed its shape to spheres, but little change was observed for primary silicon crystals.

Dynamic splitting tensile behaviors of red-sandstone subjected to repeated thermal shocks: Deterioration and micro-mechanism

The isogeometric analysis (IGA) method was extended for the solution of the coupled thermoelastodynamic equations. The dimensionless formulation was accepted in discretization of the uncoupled and coupled thermoelasticity equations and the Generalized Newmark method was used in the time integration procedure. First, the performance of the proposed method was verified against a two-dimensional benchmark example subjected to constant thermal shock with available exact analytical solutions. Then a two-dimensional half-space benchmark example under thermal shock was solved. Finally, cyclic thermal shock (CTS) loading was applied on the half-space problem. The results dedicated that IGA can be used as a suitable approach in the analysis of the general thermomechanical problems.

NiCoCrAlY coatings strengthened by different content of nano-Al2O3p, using crosscurrent CO2 laser, were prepared on Ni-based superalloy substrates, and thermal shock behaviors of these coatings were investigated by cycling between 1050°C and room temperature (forced water quenching).The results show that the thermal shock resistances of nano-Al2O3p-added coatings are definitely better than that without adding nano-Al2O3p. Among the nano-Al2O3p-added coatings, the coating added with 0.5wt% nano-Al2O3p performs best. After 10 thermal shock cycles, the spalled and spalling area in the oxide scale of the no-nano-Al2O3p coating reaches up to 27.7%, and the main failure form of the oxide scale is an expanding unit-spalling type in thermal shock cycles. While the area in the oxide scale of nano-Al2O3p-added coatings is only 10%~60% to the no-nano-Al2O3p one, and the failure of these oxide scales is mainly in the form of unit-spalling type. After 100 thermal shock cycles, many cracks turn up in the cross-section of the no-nano-Al2O3p coating, including propagating crack and internal crack. While no internal crack appeared in nano-Al2O3p-added coatings, and the propagating cracks are smaller than no-nano-Al2O3p one.