金属间化合物对AZ31B镁/6061铝异种金属激光焊接性的影响

对AZ31B镁合金和6061铝合金进行了异种金属激光搭接焊接,并着重分析了焊缝中金属间化合物对焊接性的影响.研究表明,中心搭接接头易在铝板内的焊缝近缝区和镁、铝板界面的焊缝部位出现凝固裂纹.边缘搭接接头中不同Mg-Al系金属间化合物在焊缝中弥散分布,并非以简单的金属间化合物层的形式存在.随镁元素在焊缝中浓度梯度的变化,焊缝各局部区域形成的Mg-Al系金属间化合物类型亦因之不同.在本试验条件下,采用适当的激光加工参数可以得到无裂纹的镁/铝异种金属搭接焊缝.但由于焊缝中Mg-Al系金属间化合物不可避免,焊缝脆化现象依然存在.多种金属间化合物分布的焊缝近缝区是焊接接头的薄弱部位.     

Effect of thermal cycling on the growth of intermetallic compounds at the Sn-Zn-Bi-In-P lead-free solder/Cu interface

The low-temperature Sn-9Zn-1.5Bi-0.5In-0.01P lead-free solder alloy is used to investigate the intermetallic compounds (IMCs) formed between solder and Cu substrates during thermal cycling. Metallographic observation, scanning electron microscopy, transmission electron microscopy, and electron diffraction analysis are used to study the IMCs. The γ-Cu₅Zn₈ IMC is found at the Sn-9Zn-1.5Bi-0.5In-0.01P/Cu interface. The IMC grows slowly during thermal cycling. The fatigue life of the Sn-9Zn-1.5Bi-0.5In-0.01P solder joint is longer than that of Pb-Sn eutectic solder joint because the IMC thickness of the latter is much greater than that of the former. Thermodynamic and diffusivity calculations can explain the formation of γ-Cu₅Zn₈ instead of Cu-Sn IMCs. The growth of IMC layer is caused by the diffusion of Cu and Zn elements. The diffusion coefficient of Zn in the Cu₅Zn₈ layer is determined to be 1.10×10⁻¹² cm²/sec. A Zn-rich layer is found at the interface, which can prevent the formation of the more brittle Cu-Sn IMCs, slow down the growth of the IMC layer, and consequently enhance the fatigue life of the solder joint.     

Investigation of the Phase Equilibria of Sn-Cu-Au Ternary and Ag-Sn-Cu-Au Quaternary Systems and Interfacial Reactions in Sn-Cu/Au Couples

The phase equilibria of the Sn-Cu-Au ternary, Ag-Sn-Cu-Au quaternary systems and interfacial reactions between Sn-Cu alloys and Au were experimentally investigated at specific temperatures in this study. The experimental results indicated that there existed three ternary intermetallic compounds (IMCs) and a complete solid solubility between AuSn and Cu₆Sn₅ phases in the Sn-Cu-Au ternary system at 200°C. No quaternary IMC was found in the isoplethal section of the Ag-Sn-Cu-Au quaternary system. Three IMCs, AuSn, AuSn₂, and AuSn₄, were found in all couples. The same three IMCs and (Au,Cu)Sn/(Cu,Au)₆Sn₅ phases were found in all Sn-Cu/Au couples. The thickness of these reaction layers increased with increasing temperature and time. The mechanism of IMC growth can be described by using the parabolic law. In addition, when the reaction time was extended and the Cu content of the alloy was increased, the AuSn₄ phase disappeared gradually. The (Au, Cu)Sn and (Cu_,Au)₆Sn₅ layers played roles as diffusion barriers against Sn in Sn-Cu/Au reaction couple systems.     

Hillock and Whisker Growth on Sn and SnCu Electrodeposits on a Substrate Not Forming Interfacial Intermetallic Compounds

Intermetallic compound (IMC) formation at the interface between the tin (Sn) plating and the copper (Cu) substrate of electronic components has been thought to produce compressive stress in Sn electrodeposits and cause the growth of Sn whiskers. To determine if interfacial IMC is a requirement for whisker growth, bright Sn and a Sn-Cu alloy were electroplated on a tungsten (W) substrate that does not form interfacial IMC with the Sn or Cu. At room temperature, conical Sn hillocks grew on the pure Sn deposits and Sn whiskers grew from the Sn-Cu alloy electrodeposits. These results demonstrate that interfacial IMC is not required for initial whisker growth.     

金、铜丝球键合焊点的可靠性对比研究

金丝球焊是电子工业中应用最广泛的引线键合技术,但随着高密度封装的发展,铜丝球焊日益引起人们的关注。采用热压超声键合的方法,分别实现Au引线和Cu引线键合到Al-1%Si-0.5%Cu金属化焊盘。对焊点进行200℃老化实验的结果表明:铜丝球焊焊点的金属间化合物生长速率比金丝球焊焊点慢的多;铜丝球焊焊点具有比金丝球焊焊点更稳定的剪切断裂载荷,并且在一定的老化时间内铜丝球焊焊点表现出更好的力学性能;铜丝球焊焊点和金丝球焊焊点在老化后的失效模式不同。     

Influence of interfacial reaction layer on reliability of chip-scale package joint from using Sn-37Pb and Sn-8Zn-3Bi solder

The microstructure of Sn-37Pb and Sn-8Zn-3Bi solders and the full strength of these solders with an Au/Ni/Cu pad under isothermal aging conditions were investigated. The full strengths tended to decrease as the aging temperature and time increased, regardless of the properties of the solders. The Sn-8Zn-3Bi had higher full strength than Sn-37Pb. In the Sn-37Pb solder, Ni₃Sn₄ compounds and irregular-shaped Pb-rich phase were embedded in a β-Sn matrix. The Ni₃Sn₄ compounds were observed at the interface between the solder and pad. The microstructure of the as-reflowed Sn-8Zn-3Bi solder mainly consists of the β-Sn matrix scattered with Zn-rich phase. Zinc first reacted with Au and then was transformed to the AuZn compound. With aging, Ni₅Zn₂₁ compounds were formed at the Ni layer. Finally, a Ni₅Zn₂₁ phase, divided into three layers, was formed with column-shaped grains, and the thicknesses of the layers were changed.     

发动机用PCB的失效分析研究

PCB广泛用于集成电路生产业的各个方面,汽车发动机用PCB要求较高的可靠性。面对热循环失效的汽车动力系统的构件,不要急于取下所有元件,应先对失效点表面进行外观检查和EDX分析,再进行带元件的切片分析和SEM分析,确认各个点的IMC是否正常,以找出真正的失效原因。     

Effect of multiple reflows on interfacial reaction and shear strength of Sn-Ag electroplated solder bumps for flip chip package

The effect of displacement rate and intermetallic compound (IMC) growth on the shear strength of electroplated Sn-2.5Ag (in wt.%) flip chip solder with Cu under-bump metallization (UBM) were investigated after multiple reflows. Cu₆Sn₅ IMC was formed at the interface after one reflow. After five reflows, two different IMC layers, consisting of a scallop-shaped Cu₆Sn₅ phase and a planar Cu₃Sn phase, and their thicknesses increased with increasing reflow number up to 10. The shear strengths peaked after four reflows, and then decreased with increasing reflow number. Increasing displacement rate increased the shear force. The tendency toward brittle fracture characteristics was intensified with increasing displacement rate and reflow number.     

Microstructure and shear strength of Sn37Pb/Cu solder joints subjected to isothermal aging

The effects of isothermal aging on the microstructure and shear strength of Sn37Pb/Cu solder joints were investigated. Single-lap shear solder joints of eutectic Sn37Pb solder were aged for 1–10 days at 120 °C and 170 °C, respectively, and then loaded to failure in shear with a constant loading speed of 5 × 10⁻³ mm/s. The growth of the interfacial Cu–Sn intermetallic compounds (IMC) layer (Cu₆Sn₅ + Cu₃Sn) of Sn37Pb/Cu solder joints subjected to isothermal aging exhibited a linear function of the square root of aging time, indicating that the formation of Cu–Sn IMC was mainly controlled by the diffusion mechanism. And the diffusion coefficient (D) values of IMC layer were 1.07 × 10⁻¹⁷ and 3.72 × 10⁻¹⁷ m²/s for aged solder joints at 120 °C and 170 °C, respectively. Shear tests results revealed that as-reflowed solder joint had better shear strength than the aged solder joints and the shear strength of all aged solder joints decreased with increasing aging time. The presence of elongated dimple-like structures on the fracture surfaces of these as-reflowed or aged for short time solder joints were indicative of a ductile failure mode. As aging time further increased, the solder joints fractured in the mixed solder/IMC mode at the solder/IMC interface.     

Copper wire interconnect reliability evaluation using in-situ High Temperature Storage Life (HTSL) tests

This paper describes the use of in-situ High Temperature Storage Life (HTSL) tests based on a four point resistance method to evaluate Cu wire interconnect reliability. Although the same set up was used in the past to monitor Au–Al ball bond degradation, a different approach was needed for this system. Using conventional statistical methods of failure probability distributions and a fixed failure criterion were found to be unsuitable in this case. Besides this, tests usually take very long until a sufficient percentage of the population have failed according to that criterion. A simple physical model was used to electrically quantify ball bond degradation due to the prevailing failure mechanism in a substantially smaller amount of test time. The method enabled the determination of activation energies for a number of moulding compounds and is extremely useful for a fast screening of such materials regarding their suitability for Cu wire.