Joule Heating Enhanced Electromigration Failure in Redistribution Layer in 2.5D IC
Joule Heating Enhanced Electromigration Failure in Redistribution Layer in 2.5D IC
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焦耳热增强了 2.5D IC 中重新分布层的电迁移失效
DOI：
10.1109/ectc.2016.212
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发表时间：
2016
期刊：
影响因子：
--
通讯作者：
K. Tu
中科院分区：
文献类型：
--
作者：
Yingxia Liu;Menglu Li;Mengjie Jiang;Dong Wook Kim;Sam Gu;K. Tu
在2.5D集成电路的系统级电迁移测试中，发现焦耳加热增强的电迁移失效发生在中间层的重分布层。在我们的测试样品中，有两个再分配层（RDL），每两个层级的焊点之间，所以有三个层级的焊点。首先，微凸点连接顶部的硅芯片和中间的中间芯片。其次，倒装芯片焊料连接中间层和底部的聚合物衬底。第三，BGA焊料球背面的基板作为I/O连接到外面。在我们的系统级电迁移测试中，一个BGA球作为阴极，允许电子流过通径孔、倒装芯片焊点、TSV和微凸点电路，然后以相反的方向返回到另一个BGA球作为阳极。在电迁移试验中，倒装焊点与微凸点之间的RDL是一个薄弱环节，容易发生烧坏。故障随电阻突然增大而随时间变化。初步模拟结果表明，由于散热不良，焦耳热量会积累，导致温度升高。温度的升高对RDL内的电迁移有正反馈作用，引起热跑失。
In system level electromigration test of 2.5D IC, Joule heating enhanced electromigration failure has been found to occur in redistribution layer in the interposer. In our test samples, there are two redistribution layers (RDL), each between every two levels of solder joints, so there are three levels of solder joints. First, the microbumps connect a Si chip on top and an interposer chip in the middle. Second, the flip chip solders connect the interposer and a polymer substrate on the bottom. Third, the BGA solder balls on the back of the substrate as I/O connections to the outside. In our system level electromigration tests, a BGA ball served as the cathode and allowed electrons to flow through the circuit of path-through-holes, flip chip solder joint, TSV, and microbumps, and then to return in the opposite direction to another BGA ball as the anode. We found that the RDL between the flip chip solder joints and micro-bumps is the weak-link and failed easily by burn-out in electromigration tests. The failure is time-dependent with sudden resistance increase. Preliminary simulation results show that because of poor heat dissipation, Joule heating will accumulate, leading to temperature increase. The increased temperature has a positive feedback to enhance electromigration in the RDL and caused the thermal run-away failure.