Ze Zhu

Reliability analysis of smartwatch

The reliability of electronics products has become a serious problem due to the increasingly harsh environmental conditions when the products are in use. Due to demand on greater performance and higher integration in microelectronic devices, the electronics industry has been seeking suitable components, packaging and cooling techniques to achieve low-cost and high-reliability. This paper presents the experimental verifications to analyze the effect of temperature and humidity on the electronic circuit as well as evaluating the device reliability, using Xiaomi Band 2 as a real case. It is found that 125°C has been a critical temperature for the smart watch, above which the sealed plastic case ruptured easily. However, 150°C has been found to be the temperature to burst the battery. Cold storage test with a temperature of − 70°C shows that low-temperature will only cause the smartwatch to hibernate, even for up to 400 hours, after which the device will be restored to work under a room temperature. Humidity has been found to be a crucial factor in damaging the device, which changes the rubber ring and plastic case into brittle and corrodes the interconnects on printed circuit board. Further investigation into the microstructure evolution of interconnects has found that the highly accelerated stress test has caused serious cracks in solder joints and electronic components, such as, resistors and capacitors. In short, the smartwatch can work under harsher environment than the designated environmental conditions in the product manual.

Enhanced electromigration (EM) reliability of Sn58Bi solder due to the incorporation of ZrO 2 nanoparticles

The electromigration (EM) performance of pristine and ZrO₂ doped Sn58Bi solder was studied using line-type structure, in order to reduce current crowding at the solder/pad interface. Cu/solder/Cu interconnects were applied with a direct current of 2.5 A, which generated a current density of 7.96×10³ A/cm², and stored in an oven at a temperature of 70 °C. After 300 hours current stressing, samples were taken out to make metallographic specimens and cross-sectioned to observe the microstructure evolution. It was found that Cu₆Sn₅ intermetallic compounds (IMCs) layer at both the anode and the cathode grew thicker for both pristine and ZrO₂ doped Sn58Bi solders. The interfacial IMCs growth rate was found to lower down in ZrO₂ doped Sn58Bi solder. The Bi grains in the matrix were also found to be refined as the average size was decreased from 15.14 μm² to 10.31 μm². The EM rate was decreased by 21.5% as the Bi rich layers accumulated at the anode due to current stressing were measured to be 4.65 μm and 5.92 μm for pristine and modified Sn58Bi solder, respectively. The enhanced EM reliability of ZrO₂ doped Sn58Bi solder was due to the disordered orientations caused by finer microstructure, which scattered the migration of Bi atoms towards the anode more frequently. This study suggests that doping ZrO₂ nanoparticles into Sn58Bi solder is an effective method to improve the EM reliability.

Investigation in microstructure and mechanical properties of Ni-coated multi-wall carbon nanotubes doped Sn3.0Ag0.5Cu solder alloys

Reinforcement materials such as carbon nanotubes (CNTs), have been demonstrated to be beneficial in improving composite-solder reliability through their super electrical, mechanical and thermal properties. However, interfacial interaction weakness still exists between CNTs and solder alloys. In this study, we managed to incorporate nickel-coated multi-walled carbon nanotubes (Ni-CNTs) into Sn3.0Ag0.5Cu solder matrix with various weight percentages of 0.01 wt%, 0.05 wt%, and 0.1 wt%. Microstructures, intermetallic compound (IMC) layers, mechanical properties including micro-hardness and shear testing, have been implemented to investigate the solderability of composite solders with the utilization of scanning electron microscope and energy dispersive X-ray spectrometer analysis. In comparison with Ni-CNT doping method, CNT doping is easily getting saturated and hereafter arduously to be incorporated due to their physical and chemical limitations. With 0.05 wt% doping Ni-CNTs, fine Ag3Sn strips and scallop-shaped (Cu, Ni)6Sn5 IMC layer are formed at the solder-subtract interface, resulting in the maximum improvement of 24.3% and 14.9% in hardness and shear strength, respectively. The existence of micro dopants in the composite solder act as impurity centers and can effectively retard the diffusion of atoms. The increase in strengthening effects in solder joints can be attributed to the combination of (a) impeding effects of uniformly distributed second-phase particles and (b) the consumption of Ni by intermetallic reactions.

Effects of ZrO 2 nanoparticles on the mechanical properties of Sn 42 Bi 58 solder joint

Lead-free solder has been used to replace toxic lead-containing solder. Sn42Bi58 solder has attracted a lot of attention for its low-cost, low melting temperature. Nanoparticles, such as metallic, nonmetallic and oxidant, have been doped into solders to improve their performance. In this study, we investigated the effect of ZrO2 nanoparticles on the mechanical properties of Sn42Bi58 solder joints. Firstly, solder balls were made from solder paste by stencil printing and reflow. Next, solder balls were reflowed to form solder joints on Cu pad metalized with Au/Ni layers. Then, solder joints were put into an isothermal aging oven for different aging time. Shear tests were performed to investigate the shear strength of both solder joints subjected to aging time. Scanning electron microscope (SEM) was employed to study microstructure evolution in solder matrix. The results showed that the shear strength of Sn42Bi58 solder joints was reinforced with the incorporation of ZrO2 nanoparticles. The growth of intermetallic compounds (IMCs) in ZrO2 doped solder joints was observed to be impeded.