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The objective of this article is to investigate the thermal-fatigue properties of a commercially available lead-free solder alloy (SnBiAgCu) under the use of different types of potting compounds. Solder alloys with lower silver content are expected to substitute the conventional solder alloys SAC305 (Sn-3.0Ag-0.5Cu). First, the tensile behavior and creep behavior of the SnBiAgCu solder alloys were studied at three temperatures (25℃, 75℃, 125℃). Results show that this type of solder alloys presented higher tensile strength and creep deformation endurance than conventional SAC305 solder alloys. Second, a dynamic mechanical analysis was performed to get the storage modulus and glass transition temperature of three types of potting compounds, which were used in the thermal-fatigue simulation. Third, the experimentally determined material data was used for the averaged strain energy density increment calculated by the finite element method. This simulation approach was selected as damage metrics to evaluate solder interconnect reliability under different combinations of materials. It is found that the application of potting compounds will increase strain energy density significantly when compared with the strain energy density calculated without potting compound, which means that potting compounds will deteriorate the thermal-fatigue reliability of solder interconnects. These accurate data-driven simulation models can in the future form the basis for compact digital twins for predicting useful remaining lifetime.

SnBiAgCu solder alloy is an attractive soldering material for temperature-sensitive electronic devices due to its excellent creep properties. This study firstly reports the creep properties of SnBiAgCu solder alloy under different temperatures. Results show that the addition of Bi resulted in better creep resistance compared with that of commercial SAC305 (Sn-3.0Ag-0.5Cu). Secondly, dynamic mechanical analyses were performed to get the storage modulus and glass transition temperature of potting compounds. Finally, a finite element modeling based analysis were used to figure out the different failure mechanism due to the presence of potting materials. The accurate simulation data offers an optimization reference for the selection of solder and potting materials.

The application of microporous sintered copper (Cu) as a bonding material to replace conventional die-attach materials in power electronic devices has attracted considerable interest. Many previous studies have focused on the effect of processing parameters (temperature, time, pressure) on the microstructure evolution of sintered Cu. However, there are only a few studies with regard to the mechanical properties of sintered Cu. As the die-attach layer undergoes thermal and mechanical stress durin g its application, it is essential to investigate the micro-scale mechanical properties of sintered Cu. Fracture toughness is a measure of the resistance of a material to crack propagation under predominantly linear-elastic conditions, which is an essential para meter for predictin g fracture failure. As cracks and defects are difficult to avoid during fabrication and application processing for sintered Cu, which will defin itely cause a sign ificant effect on micromechanical properties. Thus, it is essential to reveal the effect of microstructure on fracture toughess of sintered Cu nanoparticles.

The trend to 3D and heterogeneous integration enable driving multi-functional blocks in one package. Flip-chip integration is currently playing an important role and is based on solder joints. To overcome the limitations of solder joints, allcopper interconnects have been investigated to meet electrical, thermal, and reliability demands in 3D integration. The underfill process is widely applied in flip-chip encapsulation technology. We propose a novel wafer-scale all-Cu interconnect method combining epoxy-based photo-patternable polymer as self-aligned underfill layer with the patterned copper nanoparticles interconnects. The resulting test wafers were able to pattern 20 μm pitch copper nanoparticle-paste interconnects on both substrates with and without photoimageable polymer. The Cu paste was applied to form the interconnects and was sintered after bonding process. Free-standing nanocopper is sintered to obtain mechanical properties with a Young's modulus of 112 GPa. All-Cu interconnects with diameter of 50 μm and 100 μm were measured to achieve the specific contact resistance, ranging from 1.4 × 10 −5 Ω•cm 2 to 1.0 × 10 −5 Ω•cm 2 at different sintering temperature when epoxy-based underfill existing. And its resistivity was 4.54 × 10 −4 Ω•cm, compared to 5.86 × 10 −4 Ω•cm for the all-Cu interconnects without underfill.