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The Effect of Board Design on the Drop Shock Performance of Lead-Free Solder Alloys
Analysis Lab |
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Authored By:Saddam Daradkeh, Elizabeth Gainey, Mohamed El Amine Belhadi, Abdallah Alakayleh, Menghong Wang, John Evans, Sa’d Hamasha Auburn University AL, USA Michael Osterman University of Maryland John Blendell Purdue University SummaryTin-Silver-Copper (SAC) solders are widely recognized as superior alternatives to traditional tin-lead solders in microelectronics packaging due to their good mechanical properties. The frequent occurrence of drop events in portable electronic devices necessitates the assurance of board-level drop shock reliability to maintain optimal device performance and extend electronic device lifespan. This paper aimed to investigate the impacts of printed circuit board (PCB) design, including the PCB thickness and solder mask opening, on the fatigue performance of lead-free solders. Each test vehicle includes one of two component types: CABGA192 and MLF32, assembled using SnAgCu solder paste with an Organic Solderability Preservative (OSP) surface finish. Drop tests were performed at two acceleration levels—1500G and 3000G with a pulse width of 0.5 seconds. A predictive model for drop life was developed for each test condition across various energy levels. The results indicate that thicker PCBs typically demonstrate higher drop shock reliability due to their increased mechanical strength. Additionally, solder mask define opening (SMD) boards have shown much better reliability than Non-solder mask define (NSMD) boards, regardless of board thickness or component type. A detailed failure analysis was also conducted to identify the failure modes. ConclusionsTo sum up, SnAgCu305 alloy, applied with an OSP surface finish, was tested under two different board thicknesses (1 mm and 2.3 mm) and two mask define states (SMD and NSMD). The test was conducted in accordance with JEDEC standards (JESD22-B111A) to evaluate the effect of board design on the drop shock performance. The study focused on two key areas: drop shock reliability and failure analysis. In this study, Weibull analysis and microscopy images were used to assess the characteristic life and failure modes, respectively. The outcomes of the Weibull analysis indicate that SMD boards are more reliable than NSMD across all board thicknesses and component designs. Notably, SMD boards show a more consistent failure mode for both CABGA and MLF components. Moreover, thick boards are more reliable than thin boards for both component types and solder mask designs, and they offer better resistance to failure under shock stresses. One essential outcome was the more uniform crack propagation in SMD components compared to NSMD components, regardless of the board thickness. For instance, the cracks propagated along the IMC layer in BGA components with SMD design. In contrast, in NSMD boards, the failure occurred at different locations, including bulk solder, IMC, and even the traces. Trace cracking was particularly evident in NSMD boards, whereas SMD boards exhibited no trace-related failures. The finding highlighted that the overall reliability of SMD boards was notably higher, as they showed more stable failure modes without trace issues, making them more suitable for applications requiring high durability and performance. These findings emphasize the importance of board design, particularly the presence of solder masks, in enhancing the performance of solder joints under drop shock conditions. Initially Published in the SMTA Proceedings |
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