| The high-density three-dimensional package integration required in 3D-IC will increase the current density in the package interconnect solder joints.At this stage,the average current density is usually as high as 104A/cm2,and with the improvement of integration,the limiting current density has reached as high as 106A/cm2,such a high-density current will induce electromigration failure of tiny solder joints.With the increase of integration,the Sn content in the middle of the weld is gradually reduced,which will increase the influence of the size effect.The middle of the weld may also completely react to the transition to the direction of generating all-intermetallic compounds.At this time,control the Sn orientation to suppress electricity.The method of migration will no longer be applicable.At the same time,such a high current density will lead to extremely large Joule heating,and the temperature of the solder joint will reach 200?.Among them,for the intermetallic compound Cu6Sn5which plays a role in metallurgical bonding,it will undergo a phase change near 186-189?.The resulting volume change will cause the solder joint to crack and fail.Although the electromigration suppression effect of all-intermetallic compound solder joints is significantly greater than that of traditional Sn-based micro-interconnect solder joints,its solder joint failure mechanism under high current and extremely high temperature conditions still needs further study.Through the research of the focused plasma beam processing(FIB)process and mechanism,the processing flow was designed and perfected,and the complete Cu/Ni-Sn-Ni/Cu interface structure was separated,which were prepared for isothermal aging and electric field conditions.Samples used for in-situ observation under TEM conditions.In order to adapt to the size of the chip channel,the cutting size of FIB samples for in-situ observation under electric field needs to be adjusted.Choose a region with a length of 35?m for in-situ observation of samples by electromigration FIB processing.It is clear that C-shaped etching has more advantages than"well"-shaped etching.It can quickly observe whether the internal structure of the weld area meets the requirements and reduce the stress impact on the observation area,which can effectively protect the observation area.The in-situ observation and evolution analysis of the tiny Sn/ENIG solder joints under isothermal aging were studied.The micro solder joints were characterized before heating,and the composition of the intermetallic compounds in the welds was analyzed.In-situ observations under TEM conditions were carried out during the heating and heat preservation process,and the evolution of the weld structure composition was analyzed.The changes of solder joint morphology and the distribution of intermetallic compounds after the end of isothermal aging are studied,and related models are proposed.It is verified that the phase transition of?and?'occurs in Cu6Sn5 near the phase transition point during the heating and cooling process.The in-situ observation and evolution analysis of electromigration were carried out on the all-metallic compound solder joints of tiny Sn/ENIG.A stepped current gradient is set up to analyze the behavior and failure modes of the samples under normal service and extreme aging conditions.At the same time,grooves are designed and processed in the weld to be divided into a heat-affected zone and an electrothermal composite-affected zone.Before energizing,the tiny solder joints were characterized,and the composition of the intermetallic compound in the weld was analyzed.During the electrification process,the electromigration evolution law of the small Sn/ENIG all-metallic compound solder joint under high current density was studied,and the expected thermoelectric separation phenomenon was obtained.The law of material migration under the condition of electromigration of tiny solder joints is analyzed,and the failure mode of tiny solder joints under high-density current is summarized. |
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