The Growth Behavior Of IMC During Heat Preservation Stage At Sn-base Solder/Cu Interface

During the process of electronic packaging,the soldering of Sn-base solder is the critical interconnection technology and IMCs?Intermetallic Compound?that formed at interface during the soldring is the main factor to ensure the high reliability of solder joints.In the classical IMC growth model,resrarchers considered the soldering as a continue process and concluded the IMC has the same behavior.However,classical IMC growth model has some differences with the experiment results and can not explain some results.Some studied have showed that IMC has different behaviours in the heat preservation stage and cooling stage recently which is different with classical IMC growth model.In order to understand the mechanism of interfacial reaction deeply,this study has divide the whole process into heat preservation stage and cooling stage.The IMC grow in heat preservation stage is the basis of the cooling stage.So this study discuss the growth behavior of IMC in heat preservation stage.Studies have shown that IMC in different stage of whole soldering has different growth behavior and morphology change mechanism,thus dividing soldering into different parts is beneficial to understand the mechanism of interfacial reaction deeply.Generally,the whole soldering process can be divide into heat preservation stage and cooling stage.Sn?Sn-0.5Cu?Sn-0.7Cu solder ball and Cu substrate was soldered at three different temperature?250 °C?275 °C?300 °C?and different soldering time?10 s?30 s?60 s?90 s?120 s?respectively at first in this study,then used high pressure air to blow off the residual liquid solder obtaining the morphology of IMC in the heat preservation stage.This study mainly analyzed and discussed the morphology and dynamic mechanism of IMC of Sn-xCu/Cu solder joints during heat preservation stage,and studied the effect of the content of Cu of solder on the interfacial reaction;Besides,this study also discussed soldering interfacial reaction of solder with Ag.Sn-1.0Ag?Sn-3.0Ag solder ball was selected to discuss the the effect of Ag on the interfacial rection and the growth behavior of Cu₆Sn₅ and Ag3 Sn.The conclusions from the study can be summarized as follows:?1?During the heat preservation stage,the Cu₆Sn₅ grains at Sn/Cu and Sn-0.7Cu/Cu interface was scallop type all the time,while the grains at Sn-0.5Cu/Cu interface was scallop type first then changed to flat,become more and more flat.?2?The growth behavior of IMC at Sn-xCu/Cu interface during the heat preservation stage was followed n=1/3 law,showing the growth behaviour of IMC was controlled by grain boundary.?3?With the increase of soldering time,Ag3 Sn formed at Sn-1.0Ag/Cu,Sn-3.0Ag/Cu interface was granular type and size was rather small while the number increase gradually.The soldering temperature has no obvious effect on the growth of Ag3Sn;The Cu₆Sn₅ grain was from scallop to flat type and the size increase with the increase of soldering time.?4?Ag3Sn located on the different sites of Cu₆Sn₅ grains.At the begaining of the soldering,Ag3 Sn was located at the gap of the bottom of Cu₆Sn₅ grains.With the increase of the soldering time,Ag3 Sn was dispersed on the face of Cu₆Sn₅ grains even embedded into Cu₆Sn₅ grains.?5?The growth behavior of IMC at Sn-xAg/Cu interface during the heat preservation stage was followed the n=1/3 law,showing the growth of IMC was controlled by grain boundary.After calculating,the value of Q was obtained as following: Sn-1.0Ag was 27.7 kJ/mol;Sn-3.0Ag was 29.09 kJ/mol,both bigger than Sn/Cu;The thickness of IMC at Sn-1.0Ag/Cu?Sn-3.0Ag/Cu interface was smaller than Sn/Cu,showing the addition of Ag in the solder hind the growth of IMC.