Microstructural Investigation of Solder Joint Failure in Heavy Duty Trucks

Abstract

The reliability of electronic control units (ECUs) used in heavy-duty vehicles is strongly influenced by the thermo-mechanical behaviour of Ball Grid Array (BGA) solder joints. This study investigates the microstructural evolution of SAC305 BGA solder joints subjected to accelerated environmental loading and compares laboratory-aged samples with a field-returned component. SAC305 solder joints were investigated after thermal shock testing for 1000 and 2000 cycles, vibration testing, combined thermal cycling and vibration, and field service. The samples were characterized using polarized optical microscopy (POM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and quantitative Image analysis. The investigation focused on Ag3Sn particle evolution and interfacial intermetallic compound (IMC) layers. The results showed measurable microstructural evolution, including changes in Ag3Sn particle morphology and distribution and variations in IMC thickness. The PCB-side IMC was generally thicker than the package-side IMC. No visible fatigue cracks or interfacial delamination were observed after 1000 or 2000 thermal cycles, indicating an early stage of solder degradation. The vibration and combined loading samples also exhibited microstructural changes, although the individual effects of thermal and mechanical loading could not be separated conclusively. Comparison with the field-returned component showed differences in Ag3Sn morphol ogy and IMC characteristics, demonstrating that laboratory thermal shock alone cannot fully reproduce the complexity of field ageing