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68 SMT007 MAGAZINE I JULY 2019 significantly altering the "as-received" condi- tion (Figure 18). Manufacturability: QFN Voids One surprising result was how well the lower-temperature paste materials performed under the QFN/BTC component. While void- ing in our control SAC305 paste materials aver- aged 9.9%, the lower-temperature materials averaged between 1.8% for Paste C, 5.9% for Paste B, and 8.4% for Paste D. These results are shown in Figures 19–22. Reliability: Four-point Monotonic Bend Test We followed JEDEC 9702 recommended pro- cedures to perform four-point monotonic bend testing on four boards of each paste type. We mounted a single 35x35 daisy-chained BGA to each four-layer test board with a thickness of 62 mils (1.6 mm). The strain rates were driven Figure 16: Cold slump test sample. Figure 18: A typical X-ray inspection result of the 35x35 BGA with SAC305 balls. Figure 17: Description of both the hot and cold slump test.