Enhanced Processability and Thermal Fatigue Reliability With Low Melting Point SnBi Solder Alloy LMPA-Q

SnBi based solder alloys become an interesting alternative for standard SnAgCu as they can be used to solder components at much lower temperature. The typically 50°C lower solder reflow temperature is less damaging for PCB and components, and also prevents hot tear and head-in-pillow failures for large fine pitch BGA components. A reasonable concern for these low-melting temperature solders is the thermal cycling reliability performance, in particular for harsh conditions such as automotive products. In this work, thermal cycling testing and failure analysis have been performed on 9 × 9 mm size QFN components and large chip components (2010 and 2512) which are typically sensitive to thermal fatigue. The results are benchmarked to standard SAC alloy. Also the process advantages from the low temperature solder alloys are depicted in this paper. Finally, the effect of Pb contamination on this SnBi based solder is investigated.

Development and application of load profiles for thermal qualification testing of receptacle automotive connectors

Receptacle contacts often are a weak spot of the reliability in electronic systems. During the application phase of the lifecycle, especially in the automotive wiring harness, connectors experience severe loads such as temperature changes. During qualification testing, accelerated tests simulate these thermal stresses. Yet, only the damage mechanisms relevant for service life must be triggered. However, the increasing complexity of electronic components and wiring harnesses demands a continuous adaptation of test strategies. Therefore, this study develops and applies application-oriented load profiles for thermal qualification testing of connectors. Experiments include load profiles inspired by seasonal changes and daily car usage. The tests are carried out on a relative movement test bench as well as in a thermal cycling testing chamber. Contact resistance progression curves, the surface roughness of the contacts, and the area of the stressed contact zones assist in evaluating the effectiveness of the load profiles. All contacts tested during relative movement experiments show no change in contact resistance. The thermal cycling load profile however results in a significant rise in contact resistance. Additionally, the roughness values show varying damages on the contacts due to the different load profiles.

Hot-Corrosion Behavior of Modified YSZ Thermal Barrier Coating

A modified YSZ thermal barrier coating (TBC) was prepared by simultaneously depositing two components, NiCrAlY and YSZ, on nicked-based superalloy DZ125 via atmospheric plasma spraying. In this study, the sodium salt was deposited on substrate surface at the deposition rate of 3 mg/cm-2. After being heated at 950 °C for 50min, the specimens were cooled to ambient temperature within 10 min. The specimens were recoated after each 10 cycles. Subsequently, the corrosion products were analyzed via X-Ray diffraction and SEM. The results indicated that deterioration of traditional YSZ coating mainly resulted from the fluxing of thermal grown oxides (TGO). Conversely, abnormal growth of TGO and enrichment of molten salt around segmentation crack were not observed in the modified YSZ thermal barrier coating. Moreover, the modified YSZ-TBC exhibited higher thermal resistance than traditional YSZ-TBC in the thermal cycling testing.

Shear Toughness Evaluation of Solder Joints for the Reliability Tests

The effects of isothermal aging and the thermal cycling loading on the shear toughness of different solder materials and ball sizes have been explored. The difference between shear toughness values of traditional Sn/37Pb eutectic solder ball joints and the lead free Sn/3.0Ag/0.5Cu solders are chosen for discussion. The experiment measurements under the ball shear test (BST) have been compared and studied for both solder joints. The fracture behaviors of the solder joints under the high temperature aging and thermal cycling testing are examined by scanning electron microscope (SEM). The variation of shear toughness of different ball joints reveals that the high temperature aging and thermal cyclic loading reduce the shear toughness significantly. The measured shear toughness values indicate that the Sn/3.0Ag/0.5Cu solder joints have better ductility for the joints undergoing the high temperature aging and the thermal cycle loadings. Based on the measured results, the better reliability for the Sn/3.0Ag/0.5Cu ball joints is expected, due to the aging and cycling load testing.