含稀土La的Sn-Ag-Cu无铅钎料组织与性能研究

【作者】 周迎春；

【导师】 潘清林；

【作者基本信息】 中南大学 ， 材料物理与化学， 2008， 硕士

【摘要】 采用铸锭冶金法制备了La含量分别为0、0.05、0.1和0.4（质量分数,%）的四种Sn-3.0Ag-0.5Cu钎料合金,采用回流焊方法制备了四种钎料合金与铜的钎焊接头。测试了四种钎料合金的室温力学性能、熔化特性、电导率、润湿性能;采用金相显微镜（OM）和扫描电子显微镜（SEM）观察了四种钎料合金的显微组织、钎焊和时效状态下的钎焊界面及钎料内部显微组织。研究了La对Sn-3.0Ag-0.5Cu钎料合金力学性能、物理性能和显微组织的影响,以及La对Sn-3.0Ag-0.5Cu钎料与铜钎焊界面金属间化合物（IMC）形成与生长行为的影响;探讨了La在Sn-3.0Ag-0.5Cu钎料合金及Sn-3.0Ag-0.5Cu钎料与铜钎焊接头中的存在形式与作用机理。结果表明:（1）Sn-3.0Ag-0.5Cu钎料合金显微组织主要由β-Sn枝晶和共晶组织组成,共晶组织包含Sn-Ag、Sn-Cu二元共晶以及Sn-Ag-Cu三元共晶。微量La加深成分过冷,从而使显微组织细化,β-Sn枝晶分形加剧,高次枝晶发达。含0.4%La的钎料合金中形成了粗大的初生LaSn₃枝晶相。（2）在Sn-3.0Ag-0.5Cu钎料合金中添加0.05%La和0.1%La,能提高抗拉强度、屈服强度和延伸率。添加0.4%La时,抗拉强度和屈服强度仍得到提高,但延伸率下降较快。微量La提高力学性能来源于净化晶界和β-Sn枝晶分形,晶界滑动被削弱。LaSn₃枝晶相与基体界面结合力较弱而降低力学性能。（3）Sn-3.0Ag-0.5Cu钎料合金中添加微量La后,固相线温度和熔点随着La含量的增加逐渐轻微上升,熔化区间也逐渐轻微扩大;电导率随着La含量增加而轻微下降;β-Sn枝晶和共晶组织的显微硬度值随着La含量增加逐渐上升,但仍远低于初生LaSn₃脆性相的显微硬度值。（4）在Sn-3.0Ag-0.5Cu钎料合金中添加0.05%和0.1%La,能显著降低润湿角,提高合金的润湿性能。添加0.4%La后,润湿角因为LaSn₃相的氧化而急剧增加,润湿性能变差。（5）四种Sn-3.0Ag-0.5Cu钎料合金与铜于260℃钎焊5min后在界面上形成了扇贝形的Cu₆Sn₅化合物层,其厚度和直径均随La含量的增加而减小,但添加0.4%La的钎料合金因LaSn₃相强烈吸氧在界面上形成了球形的孔洞。（6）四种Sn-3.0Ag-0.5Cu钎料合金与铜的钎焊界面在150℃下时效100h后在铜基板和Cu₆Sn₅化合物层之间析出连续且薄平的Cu₃Sn化合物层,在Cu₆Sn₅化合物层中镶嵌有Ag₃Sn颗粒。界面IMC的总厚度随时效时间的增加而增厚,且在相同的时效条件下随La含量的增加而减小。过程IMC生长动力学的时间系数随着La含量的增加逐渐增大,即La的增加使钎料与铜界面IMC在时效过程中的生长机制从晶界扩散向体扩散转变。（7）含La的Sn-3.0Ag-0.5Cu钎料合金与铜钎焊后,Ag原子仍存在于网络共晶组织中,但钎焊时铜基板中的Cu原子向钎料内部的溶解形成了中空和实心两种六方棱Cu₆Sn₅化合物。时效100h后Ag₃Sn粒子沿共晶网络析出,随时效时间的延长逐渐粗化。添加0.4%La的Sn-3.0Ag-0.5Cu钎料合金中铸态形成的LaSn₃相在钎焊和时效后仍保持粗大的枝晶形状。更多还原

【Abstract】 Sn-3.0Ag-0.5Cu solder alloys with 0,0.05,0.1 and 0.4（wt.%）La additions were prepared by ingot metallurgy processing.Four solder joints with different La content were prepared by reflow process.The mechanical properties,melting behaviors, electrical conductivities,wetting behaviors of Sn-3.0Ag-0.4Cu solder alloys with different La content were investigated.Optical microscopy（OM）and scanning electron microscopy（SEM）were utilized to observe the microstructures of four solder alloys,solder joints and inside the solders after soldering and aging.The effects of La on mechanical properties,physical properties,and microstructures of Sn-3.0Ag-0.5Cu solder alloy were investigated,as well as the effects of La on the formation and growth behaviors of IMC of Sn-3.0Ag-0.5Cu solder joints.The existing form and alloying mechanism of La in Sn-3.0Ag0.5Cu and solder joints were discussed.The conclusions can be summarized as follows:（1）The microstructure of Sn-3.0Ag-0.5Cu solder alloy consists of brightβ-Sn grains surrounded by eutectic networks.The addition of La can refine the microstructure of Sn-3.0Ag-0.5Cu solder alloy by deepening constitutional supercooling.Adding 0.4%La to Sn-3.0Ag-0.4Cu solder alloy can form coarse and primary LaSn₃ dendrite phases.（2）The ultimate tensile strength,yield strength,and elongation of Sn-3.0Ag-0.5Cu have been improved by adding 0.05%and 0.1%La.Adding 0.4%will decrease the elongation.The additions of La improve mechanical properties by reducing the impurities.0.4%La decreases the mechanical property due to the weak combination between LaSn₃ phases andβ-Sn.（3）The Vickers microhardnesses ofβ-Sn and eutectic area are both enhanced with the addition of La and the microhardness of LaSn₃ is much larger than those ofβ-Sn and eutectic area.The solidus temperature,melting temperature and melting range are enhanced slightly with increasing the La addition.The electrical conductivities of Sn-3.0Ag-0.5Cu solder alloys are decreased slightly as increasing the La content.（4）Adding 0.05%and 0.1%La to Sn-3.0Ag-0.5Cu solder alloy can obviously improve the wetting behavior by decreasing the wetting angle,while adding 0.4%La will deteriorate the wetting behavior due to the oxidation of LaSn₃ phases.（5）A scallop Cu₆Sn₅ layer is formed at the interface when the four solder alloys soldered with copper substrate at 260℃for 5min.The thickness and diameter of Cu₆Sn₅ IMC decrease as increasing the La content.There are some voids at the interface of solder alloy with 0.4%La/copper due to the existing of LaSn₃ phases.（6）A continuous planar Cu₃Sn layer is formed between Cu₆Sn₅ layer and copper substrate when aging at 150℃for 100h,while Some Ag₃Sn particles are embedded in the Cu₆Sn₅ layer.The total IMC thickness increases with aging time,and decreases as increasing La content under the same aging condition.Increasing the La content alter the growth mechanism of IMC from grain-boundary diffusion to bulk diffusion.（7）Ag elements exist in eutectic structures after soldering,and solid stick and hollow stick Cu₆Sn₅ IMC have formed in the solder alloys.Ag₃Sn particles are precipitated along the eutectic bonds after aging,and coarsen as increasing the aging time.The LaSn₃ phases formed during casting in Sn-3.0Ag-0.5Cu solder with 0.4% La keep the coarse dendrite shape during soldering and aging process.更多还原