The Development Status On Advanced Packaging Copper Pillar Bump Interconnection Technology and Reliability
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摘要:
随着电子元器件朝着轻量化发展,铜柱凸点因其独特的结构而具有更小的尺寸和更高的互连密度,提供了一种高性能、高可靠性的倒装芯片互连方案. 本文对比了传统C4凸点与铜柱凸点的差异,总结出铜柱凸点在结构与性能上的优势和目前存在的一些问题. 讨论了电镀制备铜柱凸点的工艺流程,详细叙述了镀液成分和电镀参数对铜柱凸点质量的影响. 分析了铜柱凸点在热循环和电迁移可靠性方面的表现,包括热老化、热循环、电迁移等试验对铜柱凸点的影响. 最后对铜柱凸点未来发展方向进行了总结和展望.
Abstract:With the rapid development of the lightweight electronic components, copper pillar bump (CPB) provides a high-performance, high-reliability flip-chip interconnect solution with its unique structure, smaller size and higher connection density. In this paper, the differences between conventional C4 bumps and CPB are compared, and the advantages of CPB in terms of structure and performance are summarized, while the challenges faced by CPB are presented. The process flow of the electroplating method is discussed, and the effects of the plating solution composition and plating parameters on the quality of CPB are reviewed. This paper summarizes the performance of CPB in terms of thermal-cycle and electromigration reliability, including the effects of thermal aging, thermal cycling, and electromigration tests on CPB. Finally, the future development direction of CPB is summarized and prospected.
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Keywords:
- Copper pillar bump /
- electrodeposition /
- reliability /
- advanced joining
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图 3 不同电流密度下凸点形貌对比[34]
Figure 3. Comparison of bump morphology at different current densities.
图 5 不同形状铜柱凸点对应力分布影响[44]
Figure 5. The influence of different CPB types on stress characteristics. (a) plate type; (b) pin type; (c) conical frustum type; (d) skirt type; (e) zigzag type; (f) equivalent stress characteristics
图 6 底部填充对于铜柱凸点影响[55]
Figure 6. The influence of underfill on CPB (a) without underfill; (b) with underfill
图 7 不同凸点的电迁移性能比较 (145°C,700mA)[67]
Figure 7. Comparison of different bumps EM performance.
图 8 铜柱凸点的断裂模式 (197°C , 29. 8 kA cm−2) [69]
Figure 8. SEM images of the CPB with a current density of 29. 8 kA cm−2 at 197 °C. (a)500h; (b) 870h
图 9 不同形状凸点的电迁移微观图像[68]
Figure 9. SEM images of different shapes under electromigration test. (a) hourglass-shaped; (b) cylinder-shaped, (c) barrel-shaped
图 10 铜柱凸点在电流作用下的微观结构(197°C , 29. 8 kA cm−2 ,600 h) [76]
Figure 10. Microstructure of CPB after current stressing at 1. 5 × 104 A/cm2 at 125 °C for 600 h. (a) SEM image; (b) EBSD image
表 1 C4凸点和CPB的比较
Table 1 Comparison between C4 bump and CPB
性能对比 C4凸点 铜柱凸点 电阻率(μΩ m) 0.12-0.14 0.0172 热导率(μΩ m) 55-60 400 屈服强度 低 高 凸点节距(μm) 50-200 20-150 凸点高度(μm) 50-70 30-80 制备难度 容易 复杂 结构设计 固定 灵活 I/O密度 低 高 自对准效应 强 弱 表 2 电镀CPB方法对比
Table 2 Comparison of electroplating CPB methods
基础镀液 Cl- 抑制剂 加速剂 整平剂 电流密度 特点 参考文献 0.40 mol/L CuSO4
1.80 mol/L H2SO460 ppm 20mg/L EO/PO 0.7mg/L
SPS-- 18∼20 mA/cm2 通过提高Cl-浓度,加快了铜离子的还原反应,形成了致密的铜结构 [26] 0.26 M CuSO4
2 M H2SO41.13 mM 0. 02mM
PEG0.01 mM
SPS-- 20 mA/cm2 同时使用PEG和SPS可以很好降低沉积铜的间隙 [27] 0.6MCuSO4·5H2O
1.2 M H2SO460 ppm 600ppm
PEG9 ppm
SPS-- 5 A/dm2 该浓度下PEG和SPS可以获得具有细小晶粒的铜层且铜柱光洁性好 [28] 0.88MCuSO4·5H2O
0.54 M H2SO450 ppm 200ppm
PEG-branch1 ppm
SPS-- 30 mA/cm2 PEG-Branch具有较强的抑制能力,使得铜柱表面呈现平整度较高的外凸型 [29] 200 g/L CuSO4⋅5H2O
50 g/L H2SO460 ppm 200ppm
PEG5 ppm
SPSmST 2 A/dm2 PEG-mST-SPS体系所需的电镀效率高于PEG-JGB-SPS体系 [30] 140 g/L H2SO4
120 g/L CuSO4⋅5H2O50 mg/L 100ppm
PEG8 ppm
SPSKunyuan
Chemical3∼7 A/dm2 整平剂沉积速率快,同时,在大电流密度下,铜柱表面平整度最好 [31] 表 3 不同表面处理后CPB热循环可靠性分析
Table 3 the influence of different surface finishes on the thermal reliability of CPB
表面处理
方法温度循环
试验高温蒸煮
试验高温储存
试验温度冲击
试验ENIG 失效 较差 失效 良好 Sn 良好 良好 优秀 非常优秀 Sn/Ag 较差 良好 失效 较差 OSP 良好 非常优秀 失效 非常优秀 -
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