BGA结构Sn-3.0Ag-0.5Cu/Cu焊点低温回流时界面反应和IMC生长行为

THE INTERFACIAL REACTION AND INTERMETALLIC COMPOUND GROWTH BEHAVIOR OF BGA STRUCTURE Sn-3.0Ag-0.5Cu/Cu SOLDER JOINT AT LOW REFLOW TEMPERATURES

采用差示扫描量热法将焊点的熔化行为表征与焊点回流焊工艺相结合,研究了球栅阵列(BGA)结构单界面Sn-3.0Ag-0.5Cu/Cu微焊点在钎料熔化温度附近等温时效形成局部熔化焊点时的界面反应及界面金属间化合物(IMC)的生长行为.结果表明,在钎料熔点217℃时效时,焊点中钎料基体仅发生界面局部熔化;而在稍高于熔点的218℃时效时,焊点钎料基体中全部共晶相和部分-Sn相发生熔化,且Cu基底层的消耗量显著增大,绝大部分Cu基底直接溶蚀进入钎料基体并导致界面IMC净生长厚度相对217℃时效时减小;等温时效温度升高至230℃时,焊点中钎料基体全部熔化,界面IMC厚度达到最大值.界面IMC的生长动力学研究结果表明,界面Cu_6Sn_5和Cu_3Sn层的生长分别受晶界扩散和体积扩散控制,但界面IMC层的晶界凹槽、晶粒粗化和溶蚀等因素对其生长行为也有明显影响.

In recent years, the electronic packaging technologies have become more diversified and sophisticated, and among these technologies the interracial metallurgical reaction between the solder and metallic substrate is significantly different from each other. However, in contrast to plenty of studies about the microstructure evolution in solder joints prepared by the conventional soldering processes, such as wave soldering and reflow soldering in surface mount technology （SMT）, relatively little is known about the solder＇s melting feature, interracial mass transition and metallurgical reaction as well as dissolution behavior of the under bump metallization （UBM） in the micro-scale solder joints manufactured by using the novel soldering technologies, for example, the local melting reflow process. In this study, the differential scanning calorimetry （DSC） experimental approach was employed to simulate the local melting reflow soldering process, and the melting behavior of ball grid array （BGA） structure Sn-3.0Ag-0.5Cu/Cu joints, the interracial reaction and intermetallic compound （IMC） growth behavior of the joints during tile liquid isothermalaging at the temperatures near or above the solder＇s melting point were studied systematically. Results showed that only a part of the solder matrix adjacent to the interface of the joints melted during the liquid isothermal aging at the solder＇s melting point of 217 ℃. Then, a slight increase of the aging temperature from 217 ℃ up to 218 ℃ has a significant influence on the melting status of the solder matrix and the Cu substrate consumption during isothermal aging process, that is, all the eutectic phases and partial β-Sn phase in the solder matrix melted, and the proportion of the Cu substrate dissolved into the Sn matrix in the total consumption of Cu substrate also increased greatly. However, the thickness of the interfacial Cu6Sn5 layer and total Cu-Sn IMC layer had a slight decrease due to the fact that Cu substrate rapidly dissolved into the solder matrix and resulted in less supply of Cu in the growth of interfacial IMC layers. When the aging temperature was increased to 230 ℃, the content of Cu in the solder matrix nearly reached saturation, and the thickness of interracial Cu-Sn IMC layers also reached the highest value. The results of interfacial IMCs growth kinetics show that the growth of the interfacial Cu6Sn5 and Cu3Sn is mainly controlled by grain boundary diffusion and bulk diffusion, respectively; and the grain boundary grooving and grain coarsening can also influence the growth kinetics of the interfacial Cu-Sn IMCs.