铜引线键合中芯片焊盘裂纹成因及消除研究

Crack Formation and Elimination Method on Bond Pad in Cu Wire Bonding

由于铜线硬度大和0.18μm技术芯片的结构复杂,在电子封装铜引线键合的大批量生产中,铜引线键合后芯片的焊盘上容易出现裂纹,造成了严重的质量缺陷。基于0.18μm技术芯片,利用ASM引线键合机型,研究了焊盘上产生的裂纹典型形貌和消除方法。首先分析现有铜引线键合参数下的裂纹形貌作为对比基准,然后通过全因子实验设计(DOE)分析产生裂纹的主要参数,再通过微调不同的参数来降低裂纹数量以及最后消除裂纹。实验中收集的数据类型有引线键合后铜球直径的大小、拉球值、推球值、金属间化合物的覆盖率及裂纹数量等。实验结果表明:1)在铜引线键合过程中存在塑性形变,大的塑性形变能够促进裂纹的形成;2)影响裂纹产生的主要参数为铜引线键合中的超声波输出各阶段键合功率,包括待机功率、预键合功率、键合功率;3)在初始键合接触阶段,设置较大的搜索速度、接触阈值和初始键合压力都有利于裂纹的消除;4)在铜引线键合的预键合阶段,相关的摩擦运动参数,如预键合功率、预键合摩擦运动的周期数及幅度等参数设置过大,不利于裂纹的消除,反而使裂纹数量迅速增长。通过实验研究得出了消除电子封装铜引线键合中的0.18μm技术芯片焊盘上裂纹的途径,可为相关芯片的铜引线键合技术及产品生产提供参考。

In electronic packaging, due to the high hardness of Cu copper wire and the complex structure of 0.18 μm technology chip, one of the serious quality defects is cracks that sometimes can be found on the dielectric insulation layer of chip after Cu wire bonding. Based on the 0.18 μm technology chip, the crack formation and elimination method under different Cu wire bonding parameters were studied experimentally on ASM wire bonding machine.The crack morphology under the existing Cu wire bonding parameters was analyzed and used as a reference for comparison. Then, the main parameters causing the crack were obtained through the design of experiment(DOE). Finally, the way to eliminate the crack was studied by means of fine-tuning different parameters successively. Collecting data type included the Cu ball diameter, wire pullstrength, ball shear strength, intermetallic compound coverage and crack number, etc. The results show that: 1) large plastic deformation promotes the formation of cracks;2) ultrasonic output power is the main influencing parameter of crack generation, including parameters of standby power, pre-base power, base power;3) at the Cu wire bonding contact stage, when the search speed, threshold and initial force are large, they are conducive to crack elimination;4) at the pre-bonding with Cu wire stage, the setting of parameters such as pre-base scrub power, pre-base scrub cycle, and pre-base scrub amplitude should not be too large, which is not conducive to the elimination of cracks, but promotes the rapid growth of the number of cracks. Therefore, the way to eliminate the crack of 0.18 μm technology chip in Cu wire bonding is obtained through experimental research, which can provide reference for correlated Cu wire bonding technology and product production.