热效应作用下SnAgCu基钎焊接头界面化合物生长机制

Growth Mechanism of Interfacial compounds in SnAgCu-Based Lead-Free Solder under Thermal Effect

通过用扫描电镜(SEM)观察经恒温时效和热循环后Sn4.7Ag1.7Cu/Cu钎焊接头的组织,结合能谱(EDS)分析,研究接头在恒温时效和热循环过程中组织变化,结合热力学和扩散理论,建立金属间化合物生长物理模型,探究接头中金属间化合物形成机制。研究结果表明,再流焊后Sn4.7Ag1.7Cu/Cu界面优先生成焓变较高的Cu6Sn5化合物,并以吉布斯自由能较低的笋状分布;随着恒温时效的进行,接头中Cu原子由铜母材向钎料中扩散,Cu6Sn5化合物逐渐长大延伸,并趋于平直,Cu3Sn化合物逐渐形成并生长;热循环条件下,热效应作用有利于Ag3Sn颗粒的粗化和快速生长,但是界面近域反常长大的Ag3Sn颗粒反过来又阻止了Cu6Sn5化合物的增长,使得局部的Cu6Sn5化合物到热循环后还保持着笋状形态,易在笋状根部的凹槽处产生应力集中而出现微裂纹并逐渐扩展,不利于焊点的可靠性。

The microstructure of Sn4.7 Ag1.7 Cu/Cu brazed joint after constant temperature aging and thermal cycle was observed by scanning electron microscope(SEM).Combined with energy spectrum(EDS)analysis,the microstructure changes of the joint during constant temperature aging and thermal cycle were studied,combined with thermodynamics and diffusion theory.The growth physical model of intermetallic compounds was established to explore the formation mechanism of intermetallic compounds in joints.The results showed that the Cu6Sn5 compounds with higher enthalpy were formed at the Sn4.7 Ag1.7 Cu/Cu interface after reflow welding,and the generated compounds with lower free energy were distributed in the form of bamboo shoots.With the progress of constant temperature aging,the Cu atoms in the joints changed from copper base metal to solder.In the middle diffusion,Cu6Sn5 compounds gradually grew and extended,and tended to be straight,Cu3Sn compounds gradually formed and grew.Under the condition of thermal cycle,the thermal effect was beneficial to the coarsening and rapid growth of Ag3Sn particles,but the abnormal growth of Ag3Sn particles near the interface in turn prevented the growth of Cu6Sn5 compounds.So that the local Cu6 Sn5 compounds still maintained the shape of bamboo shoots after thermal cycle,and it was easy to produce stress concentration and microcracks at the grooves of the root of bamboo shoots and gradually expanded,which was not conducive to the reliability of solder joints.