Electromigration Critical Product to Measure Effect of Underfill Material in Suppressing Bi Segregation in Sn-58Bi Solder
Electromigration Critical Product to Measure Effect of Underfill Material in Suppressing Bi Segregation in Sn-58Bi Solder
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DOI：
10.1007/s11664-017-5507-8
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发表时间：
2017-04
影响因子：
2.1
通讯作者：
Xu Zhao;S. Takaya;M. Muraoka
中科院分区：
文献类型：
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作者：
Xu Zhao;S. Takaya;M. Muraoka
最近，我们检测到Sn-58Bi（SB）焊料的长度相关的电迁移（EM）行为，并揭示存在的Bi回流，这阻碍了EM诱导的Bi偏析，并依赖于焊料长度。回流的原因归因于SB焊料上形成的氧化层。目前，在倒装芯片封装中，通常使用UF材料作为芯片和基板之间的填充物，以包围焊料凸点。在这项研究中，我们定量研究了UF材料作为钝化层对SB焊带中EM的影响。同时对50 μ m、100 μ m和150 μ m长的SB焊带进行了电磁测试。一些样品涂覆有商业热固性环氧树脂UF材料，其充当Cu-SB-Cu互连上的钝化层。SB焊料的关键产品值估计为38 A/cm至43 A/cm（353 K至373 K，无UF涂层）和59 A/cm（373 K，有UF涂层）。UF材料作为钝化层抑制了电磁感应引起的Bi偏析，并将阈值电流密度提高了37%至55%。然而，在非常高的电流密度下，这种影响变得非常轻微。此外，Bi原子可以通过Sn相扩散到阳极侧，因此向Sn相中添加微量元素以形成障碍物，例如金属间化合物，可以延缓SB焊料中的Bi偏析。
Recently, we detected length-dependent electromigration (EM) behavior in Sn-58Bi (SB) solder and revealed the existence of Bi back-flow, which retards EM-induced Bi segregation and is dependent on solder length. The cause of the back-flow is attributed to an oxide layer formed on the SB solder. At present, underfill (UF) material is commonly used in flip-chip packaging as filler between chip and substrate to surround solder bumps. In this study, we quantitatively investigated the effect of UF material as a passivation layer on EM in SB solder strips. EM tests on SB solder strips with length of 50μm, 100μm, and 150μm were conducted simultaneously. Some samples were coated with commercial thermosetting epoxy UF material, which acted as a passivation layer on the Cu–SB–Cu interconnections. The value of the critical product for SB solder was estimated to be 38 A/cm to 43 A/cm at 353 K to 373 K without UF coating and 59 A/cm at 373 K with UF coating. The UF material acting as a passivation layer suppressed EM-induced Bi segregation and increased the threshold current density by 37% to 55%. However, at very high current density, this effect became very slight. In addition, Bi atoms can diffuse to the anode side through the Sn phase, hence addition of microelements to the Sn phase to form obstacles, such as intermetallic compounds, may retard Bi segregation in SB solder.