【作者】 何明敏；

【导师】 吴丰顺；

【作者基本信息】 华中科技大学 ， 材料加工工程， 2007， 硕士

【摘要】 无铅化和微型化是电子封装的两大发展趋势。在微型化的驱动下,传统球栅阵列封装技术(BGA:Ball Grid Array)中互连焊点的节距、焊盘尺寸以及焊点体积都将大大降低。焊点几何特征是微型化封装设计的重要部分,包括焊料体积、上/下接触角(θ)、焊点高度(SOH:Stand-off Height)和外形轮廓等,其中焊点互连高度是最为重要的设计参数之一。互连界面适量厚度金属间化合物(IMC:Intermetallic Compound)是焊接良好的标志,但由于IMC的本征脆性,过厚的IMC将导致焊点机械性能的降低。微型焊点互连高度的变化将对焊点微观组织有极大影响,对互连界面IMC形貌、成分及厚度有至关重要的作用,并且界面处IMC占焊点体积比例将随互连高度变化而变化,这将对互连可靠性造成直接影响。本文通过自行设计一套精确控制焊点互连高度的装置,获得不同互连高度的Cu/Ni/Au/焊料/Au/Ni/Cu结构焊点,选取Sn3.5Ag0.5Cu和Sn3.5Ag焊料作为对比分析,研究互连高度变化过程中界面IMC形貌、厚度及其占焊点比例的变化以及这些变化对焊点抗剪切和冲击性能的影响;采取Cu/Ni/Au/Sn3.5Ag/Cu结构,具有针对性的对界面IMC厚度进行研究。结果表明,伴随焊点互连高度降低,界面IMC厚度增加,占焊点体积比例增加,焊点抗剪切和冲击性能下降。另外,由于微型焊点互连高度降低,将增大焊点两侧焊盘镀层金属交互扩散作用的发生。两侧镀层金属元素将通过焊料扩散到对方,并在对方一侧形成IMC。因此,本课题采用Cu/Ni/Au/Sn3.5Ag/Cu结构,对不同互连高度焊点两侧镀层金属交互扩散作用进行了相应研究。研究表明,焊点两侧镀层金属元素存在交互扩散作用,并且随互连高度的降低呈增加趋势。更多还原

【Abstract】 Lead-free and miniaturization are the trends of electronic packaging. Under these trends, the patch, pad size and the volume of the solder joint will reduce greatly in the traditional BGA (Ball Grid Array) technology. The solder geometry that includes solder volume, lower/upper contact angles (θ), stand-off height (SOH) and solder joint profile is the key to the design of miniature electronic packaging, and the stand-off height of solder joint is one of the most important factor.The proper thickness of interfacial IMCs (Intermetallic Compound) layer in solder joint is the symbol of good connection, but due to IMCs intrinsic brittleness, thicker interfacial IMCs layer will degrade the reliability. The change of the SOH will affect the solder joint’s microstructure heavily, such as the morphology, the component and the thickness of the interfacial IMC, and then the reliability will be challenged by those changes.In this paper, a new a clamp apparatus was designed by the author to control the solder joint’s SOH exactly. The Cu/Ni/Au/solder/Au/Ni/Cu systems were used to study the effect of SOH changes on the morphology, thickness and the proportion of interfacial IMCs layer, then the shear test and impact test were applied, and the effect of the SOH changes on the reliability of miniature solder joint was analyzed too. The results showed that the thickness and the proportion of interfacial IMCs layer increased with the reduction of SOH, as well as the miniature solder joint’s mechanical behavior.In additional, the chance of metal elements interaction between UBM (Under Bump Metallization) and pad in miniature solder joint will increase with the reduction of SOH. The metal elements both at the UBM and the pad may diffuse to the opposite side and form complex IMCs. The Cu/Ni/Au/Sn3.5Ag/Cu system was used in this paper to study the interaction in miniature solder joint with the reduction of SOH. The result showed there existed the interaction between UBM and pad in miniature solder joint, and the degree increased with the reduction of SOH.更多还原