Interfacial reaction study on a solder joint with Sn-4Ag-0.5Cu solder ball and Sn-7Zn-Al (30 ppm) solder paste in a lead-free wafer level chip scale package |
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Authors: | Huann-Wu Chiang Jun-Yuan Chen Jeffrey C. B. Lee S. M. Li |
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Affiliation: | (1) Department of Materials Science and Engineering, I-SHOU University, 84008 Kaohsiung, Taiwan;(2) Engineering Center, Advanced Semiconductor Engineering, Inc., 84008 Kaohsiung, Taiwan |
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Abstract: | The interfacial reactions of solder joints between the Sn-4Ag-0.5Cu solder ball and the Sn-7Zn-Al (30 ppm) presoldered paste were investigated in a wafer level chip scale package (WLCSP). After appropriate surface mount technology (SMT) reflow process on the printed circuit board (PCB) with organic solderability preservative (Cu/OSP) and Cu/Ni/Au surface finish, samples were subjected to 150°C high-temperature storage (HTS), 1,000 h aging. Sequentially, the cross-sectional analysis is scrutinized using a scanning electron microscope (SEM)/energy-dispersive spectrometer (EDS) and energy probe microanalysis (EPMA) to observe the metallurgical evolution in the interface and solder buck itself. It was found that Zn-enriched intermetallic compounds (IMCs) without Sn were formed and migrated from the presolder paste region into the solder after reflow and 150°C HTS test. |
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Keywords: | Interfacial reaction lead-free solder intermetallic compound (IMC) Sn-Zn-Al solder paste wafer level chip scale package (WLCSP) |
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