Effects of rare earth element Ce on solderabilities of micron-powdered Sn-Ag-Cu solder

Several important properties of the micron-powdered Sn-Ag-Cu-Ce solder, including the spreadability, spreading ratio, wetting time, and melting point, were investigated for verifying the effects of rare earth element Ce on solderabilities of micron-powdered Sn-Ag-Cu solder. The solidus and the liquidus of the micron-powdered Sn-Ag-Cu-Ce solder are 193.6℃ and 218.4℃, respectively, about 28℃ and 3℃ lower than the melting point of the block Sn-Ag-Cu solder, which reminds the existence of the surface effect of the micron-powdered solder. By adding Ce into Sn-Ag-Cu alloy, its wetting time on pure copper can be obviously decreased. For the Sn-Ag-Cu-0.03%Ce, the soldering temperature is 250℃, and the wetting time on pure copper is close to 1s, with the soldering temperature approaching to 260℃, the wetting time is dropped to 0.8s, which is close to the wetting time, 0.68s, of Sn-Pb solder at 235℃.

电镀参数对电沉积Sn-Ag-Cu合金镀层的影响

采用自主研发的甲磺酸锡银铜电镀液在黄铜基体上制备了Sn-Ag-Cu合金镀层。通过扫描电子显微镜(SEM)及其自带的能谱仪(EDS)分析了电镀工艺参数对Sn-Ag-Cu合金镀层的成分、表面形貌以及镀层厚度产生的影响。结果表明,当电流密度为4 A/dm^(2)、温度为25℃及pH为5.5时,可获得结晶较细且致密,表面平整光亮且厚度均匀的Sn-Ag-Cu合金镀层。

Preventing formation of intermetallic compounds in ultrasonic-assisted Sn soldering of Mg/Al alloys through pre-plating a Ni coating layer on the Mg substrate

Magnesium and aluminum alloys are widely used in various industries because of their excellent properties,and their reliable connection may increase application of materials.Intermetallic compounds(IMCs)affect the joint performance of Mg/Al.In this study,AZ31 Mg alloy with/without a nickel(Ni)coating layer and 6061 Al alloy were joined by ultrasonic-assisted soldering with Sn-3.0Ag-0.5Cu(SAC)filler.The effects of the Ni coating layer on the microstructure and mechanical properties of Mg/Al joints were systematically investigated.The Ni coating layer had a significant effect on formation of the Mg_(2)Sn IMC and the mechanical properties of Mg/Al joints.The blocky Mg_(2)Sn IMC formed in the Mg/SAC/Al joints without a Ni coating layer.The content of the Mg_(2)Sn IMC increased with increasing soldering temperature,but the joint strength decreased.The joint without a Ni coating layer fractured at the blocky Mg_(2)Sn IMC in the solder,and the maximum shear strength was 32.2 MPa.By pre-plating Ni on the Mg substrate,formation of the blocky Mg_(2)Sn IMC was inhibited in the soldering temperature range 240–280℃and the joint strength increased.However,when the soldering temperature increased to 310℃,the blocky Mg_(2)Sn IMC precipitated again in the solder.Transmission electron microscopy showed that some nano-sized Mg_(2)Sn IMC and the(Cu,Ni)_(6)Sn_(5)phase formed in the Mg(Ni)/SAC/Al joint soldered at 280℃,indicating that the Ni coating layer could no longer prevent diffusion of Mg into the solder when the soldering temperature was higher than 280℃.The maximum shear strength of the Mg(Ni)/SAC/Al joint was 58.2 MPa for a soldering temperature of 280℃,which was 80.7%higher than that of the Mg/SAC/Al joint,and the joint was broken at the Mg(Ni)/SAC interface.Pre-plating Ni is a feasible way to inhibit formation of IMCs when joining dissimilar metals.

Sn-Ag-Cu钎料的制备与显微组织性能研究

Sn-Ag-Cu系低银钎料凭借其优良的工艺和力学性能被普遍认为是最有前途的含铅钎料替代品。为了研究低银钎料的制备及其显微组织特性,制备银的质量分数分别为0、0.3%、0.5%、1.0%的四组低银钎料。比较分析熔化温度与银的质量分数对低银钎料的熔化特性、显微组织、抗拉强度及润湿特性的影响。结果表明,添加少量的银可以降低锡铜钎料的熔化温度,使锡铜钎料的晶粒变得细小,晶粒排列得更加紧密。当钎料中银的质量分数为1.0%时,钎料的抗拉强度达到47.4 MPa,在紫铜基体上的铺展面积为39.9 mm2,润湿角为5.01°。

Effect of diode-laser parameters on shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder on Au/Ni/Cu pad

Soldering experiments with Sn-3.5Ag-0.5Cu lead-free solder on Au/Ni/Cu pad were carried out by means of diode-laser and IR reflow soldering methods respectively.The influence of different heating methods as well as output power of diode-laser on shear force of micro-joints was studied and the relationship between the shear force and microstructures of micro-joints was analyzed.The results indicate that the formation of intermetallic compound Ag3Sn is the key factor to affect the shear force and the fine eutectic network structures of micro-joints as well as the dispersion morphology of fine compound Ag3Sn,in which eutectic network band is responsible for the improvement of the shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder.With the increases of output power of diode-laser,the shear force and the microstructures change obviously.The eutectic network structures of micro-joints soldered with diode-laser soldering method are more homogeneous and the grains of Ag3Sn compounds are finer in the range of near optimal output power than those soldered with IR reflow soldering method,so the shear force is also higher than that using IR reflow soldering method.When the output power value of diode-laser is about 41.0 W,the shear force exhibits the highest value that is 70% higher than that using IR reflow soldering method.

Effects of bismuth on growth of intermetallic compounds in Sn-Ag-Cu Pb-free solder joints

The effects of Bi addition on the growth of intermetallic compound (IMC) formation in Sn-3.8Ag-0.7Cu solder joints were investigated. The test samples were prepared by conventional surface mounting technology. To investigate the element diffusion and the growth kinetics of intermetallics formation in solder joint, isothermal aging test was performed at temperatures of 100, 150, and 190℃, respectively. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe microstructure evolution of solder joint and to estimate the thickness and the grain size of the intermetallic layers. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffractometer (XRD). The results clearly show that adding about 1.0% Bi in Sn-Ag-Cu solder alloy system can refine the grain size of the IMC and inhibit the excessive IMC growth in solder joints, and therefore improve the reliability of the Pb-free solder joints. Through observation of the microstructural evolution of the solder joints, the mechanism of inhibition of IMC growth due to Bi addition was proposed.

Wetting behavior and interfacial characteristic of Sn-Ag-Cu solder alloy on Cu substrate

Wettability of molten Sn-Ag-Cu alloy on Cu substrate has been determined by sessile drop method, as well as its dependence on time and temperature. It was found that the evolution of contact angle at the alloy’s melting point experienced four different stages. Especially, the contact angle was unstable and fluctuant in stage II, and gradually decreased in stage III mainly due to a chemical reaction between Sn-Ag-Cu alloy and Cu substrate. The contact angle decreased with increasing temperature, but increased slightly at 629 K, for another chemical reaction occurred. Interfacial characteristic has been further investigated by examining the sample’s cross section. Intermetallic compounds of Cu6Sn5 and β-Sn phase were found at the interface of Sn-Ag-Cu/Cu.

Effect of cerium on microstructure and mechanical properties of Sn-Ag-Cu system lead-free solder alloys

The melting point, spreading property, mechanical properties and microstructures of Sn-3.0Ag-2.8Cu solder alloys added with micro-variable-Ce were studied by means of optical microscopy, scanning electron microscopy(SEM) and energy dispersive X-ray(EDX). The results indicate that the melting point of Sn-3.0Ag-2.8Cu solder is enhanced by Ce addition; a small amount of Ce will remarkably prolong the creep-rupture life of Sn-3.0Ag-2.8Cu solder joint at room temperature, especially when the content of Ce is 0.1%, the creep-rupture life will be 9 times or more than that of the solder joint without Ce addition; the elongation of Sn-3.0Ag-2.8Cu solder is also obviously improved even up to 15.7%. In sum, the optimum content of Ce is within 0.05%-0.1 %.

EVOLUTION OF MICROSTRUCTURE OF Sn-Ag-Cu LEAD-FREE FLIP CHIP SOLDER JOINTS DURING AGING PROCESS

Flip chip bonding has become a primary technology that has found application in the chip interconnection process in the electronic manufacturing industry in recent years. The solder joints of the flip chip bonding are small and consist of complicated microstructures such as Sn solution, eutectic mixture, and intermetallic compounds （IMCs）, whose mechanical performance is quite different from the original solder bulk. The evolution of microstructure of the flip chip solder joints under thermal aging was analyzed. The results show that with an increase in aging time, coarsening of solder bulk matrix and AuSn4 IMCs occurred within the solder. The IMCs that are formed at the bottom side of the flip chip bond were different from those on the top side during the aging process. （Cu, Ni, Au）0Sn5 were formed at the interfaces of both sides, and large complicated （Au,Ni, Cu）Sn4 IMCs appeared for some time near the bottom interface after aging, but they disappeared again and thus （Cu,Ni, Au ）0Sn5 IMC thickness increased considerably. The influence of reflow times during the flip chip bonding （as-bonded condition） on the characteristics of interfacial IMCs was weakened when subjected to the aging process.

Microstructures and properties of Sn-Ag-Cu lead-free solder alloys containing La

Trace amounts of La were utilized to improve the melting behaviors,microstructures,tensile properties and microhardness of Sn-3.0Ag-0.5Cu lead-free solder alloy. La has little effect on the melting behavior of Sn-3.0Ag-0.5Cu alloy according to the differential thermal analysis(DTA) tests. The X-ray diffraction(XRD) patterns show that β-Sn,Ag3Sn and Cu6Sn5 coexist in the as-cast solder alloys and LaSn3 phases emerge when adding 0.4% La. The microstructures modified by La are more uniform and much finer than that of baseline alloy,and the coarse LaSn3 particles with complex dendrites are observed by optical microscopy(OM) and scanning electron microscopy(SEM) when the addition of La is up to 0.4%. The composition of the LaSn3 phases is identified by energy-dispersive spectroscopy(EDS). There are considerable improvements in mechanical properties with 0.05% and 0.1% addition,but degenerations by adding 0.4%La. The Vickers microhardness of β-Sn and eutectic area are both enhanced with the addition of La and the microhardness of LaSn3 is much larger than those of β-Sn and eutectic area.

A review of soldering by localized heating

In recent years,the rapid development of the new energy industry has driven continuous upgrading of high-density and high-power devices.In the packaging and assembly process,the problem of differentiation of the thermal needs of different modules has become increasingly prominent,especially for small-size solder joints with high heat dissipation in high-power devices.Localized soldering is con-sidered a suitable choice to selectively heat the desired target while not affecting other heat-sensitive chips.This paper reviews several local-ized soldering processes,focusing on the size of solder joints,soldering materials,and current state of the technique.Each localized solder-ing process was discovered to have unique characteristics.The requirements for small-size solder joints are met by laser soldering,microres-istance soldering,and self-propagating soldering;however,laser soldering has difficulty meeting the requirements for large heat dissipation,microresistance soldering requires the application of pressure to joints,and self-propagating soldering requires ignition materials.However,for small-size solder junctions,selective wave soldering,microwave soldering,and ultrasonic soldering are not appropriate.Because the magnetic field can be focused on a tiny area and the output energy of induction heating is large,induction soldering can be employed as a significant trend in future research.

Interfacial reaction behavior and mechanical properties of 5A06 Al alloy soldered with Sn-1Ti-xGa solders at a low temperature

Active soldering of 5A06 Al alloy was performed at 300 ℃ by using Sn-1Ti and Sn-1Ti-0.3Ga active solders, respectively. Theeffects of soldering time on the microstructure and mechanical properties of the joints were investigated. The results showed that the Sn-1Tisolder broke the oxide film on the surface of the Al substrate and induced intergranular diffusion in the Al substrate. When Ga was added tothe solder, severe dissolution pits appeared in the Al substrate due to the action of Sn-1Ti-0.3Ga solder, and many Al particles were flakedfrom the matrix into the solder seam. Under thermal stress and the Ti adsorption effect, the oxide film cracked. With increasing solderingtime, the shear strength of 5A06 Al alloy joints soldered with Sn-1Ti and Sn-1Ti-0.3Ga active solders increased. When soldered for 90 min,the joint soldered with Sn-1Ti-0.3Ga solder had a higher shear strength of 22.12 MPa when compared to Sn-1Ti solder.

Research Progress on the Solder Joint Reliability of Electronics Using in Deep Space Exploration

The spacecraft for deep space exploration missions will face extreme environments,including cryogenic temperature,intense radiation,wide-range temperature variations and even the combination of conditions mentioned above.Harsh environments will lead to solder joints degradation or even failure,resulting in damage to onboard electronics.The research activities on high reliability solder joints using in extreme environments can not only reduce the use of onboard protection devices,but effectively improve the overall reliability of spacecraft,which is of great significance to the aviation industry.In this paper,we review the reliability research on SnPb solder alloys,Sn-based lead-free solder alloys and In-based solder alloys in extreme environments,and try to provide some suggestions for the follow-up studies,which focus on solder joint reliability under extreme environments.

Effect of Strain Rate on Tensile Behavior of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} Lead-Free Solder Alloys

The tensile properties of Sn-9Zn-xAg-ySb;{(x, y) = (0.2, 0.6), (0.2, 0.8), (0.6, 0.2), (0.8, 0.2)} lead-free solders were investigated. All the test samples were annealed at 150°C for 1 hour. The tests are carried out at room temperature at the strain rate of 4.17 × 10-3 s-1, 20.85 × 10-3 s-1, and 208.5 × 10-3 s-1. It is seen that the tensile strength increases and the ductility decrease with increasing the strain rate over the investigated range. From the strain rate change test results, the strain sensitivity values are found in the range of 0.0831 to 0.1455 due to the addition of different alloying elements.

大尺寸AlN活性金属焊接覆铜基板的界面结合机理

基于190 mm×139 mm×0.635 mm的大尺寸AlN表面活性金属钎焊(AMB)覆铜板工艺制程,开展其界面显微组织、物相组成等的研究,确定钎焊界面结合机理,为制备大尺寸、低气孔、高剥离强度AlN-AMB覆铜板提供支持。结果表明,在大尺寸AlN-AMB覆铜板钎焊过程中,Ag-Cu-Ti合金钎料中的Ag-Cu合金与Cu箔扩散溶合,形成强的冶金结合界面。同时,钎料中的活性Ti原子向AlN基板表面扩散,并与其反应,生成厚度为0.5~1μm的TiN反应层,形成强的反应结合界面。此外,钎料熔体难以填充基板的AlN晶界和凹坑,其中的Ti原子也不与Y-Al-O第二相颗粒反应,导致AlN基板表面TiN反应层不连续分布,形成气孔,降低大尺寸AlN-AMB覆铜板的界面结合强度及可靠性。

SnAgCu/SnBi混装焊点的热循环可靠性研究

Sn-Bi和Sn-Ag-Cu混装焊点是利用低熔点的Sn-58Bi锡膏将高熔点的Sn-3.0Ag-0.5Cu(SAC305)的小球回流焊接在印制电路板(PCB)上,从而实现高温芯片的低温焊接工艺.文中研究了SnAgCu/SnBi混装焊点在热循环条件下的可靠性并通过有限元模拟揭示了混装焊点热循环可靠性的应变演变行为.热循环试验发现混装焊点的寿命要优于SAC305无铅焊点.有限元计算表明,结构混装焊点内SnBi钎料层的添加能够减小最大非弹性应变范围,从而提升混装焊点的热循环可靠性.

PCB中耐高温有机可焊保护剂成膜机理及性能研究

印制电路板铜焊盘表面生成耐高温有机可焊保护剂(HT-OSP)膜是克服无铅高温回流焊工艺并获得良好焊点的关键。选用2-[(2,4-二氯苯基)甲基]-1H-苯并咪唑(C_(14)H_(10)Cl_2N_2)作为成膜剂,在铜层表面生成了HT-OSP膜。理论计算结合对比实验,研究C_(14)H_(10)Cl_2N_2分子与Cu原子反应生成HT-OSP膜机理。基于量子化学密度泛函理论,模拟C_(14)H_(10)Cl_2N_2分子与Cu~+之间的络合反应;利用红外光谱对HT-OSP膜中的特征官能团进行表征;借助X射线光电子能谱测试HT-OSP膜中Cu元素的化合价;设计对比实验分析Cu~(2+)对生成HT-OSP膜的影响。结果表明:HT-OSP膜生成机理是C_(14)H_(10)Cl_2N_2分子与Cu原子发生反应生成HT-OSP膜并沉积在铜层表面,Cu~(2+)通过络合反应促进HT-OSP膜生长。另外,HT-OSP膜的分解温度高达531℃,HT-OSP膜保护的铜层放置在自然环境中180天没有被氧化,证明HT-OSP膜具有优异的耐热性和抗氧化性。

基于度量学习的电路焊点缺陷检测方法

针对目前电路焊点缺陷检测方法效率低、准确度差、焊点图像样本量小的问题,提出了一种基于度量学习的快速识别焊点缺陷的方法.首先利用工业相机搭配远心镜头获取焊点图像.通过挖掘焊点图像特征,设计交点检测法来分割焊接单元图像,制作焊点缺陷数据集.在此基础上,设计焊点图像全局特征与局部表征提取方法来对焊点的两类特征进行融合,并对注意力机制进行改进,加入到全局特征提取模块中.对焊点缺陷的检测实验结果表明该方法最终实现了准确率达到98.4%,满足焊点缺陷检测的实际生产要求.

基于双目结构光的三维立体电路板焊点定位

三维立体电路将传统二维集成电路拓展至三维,在提高了电路板形状设计柔性的同时,也提升了电路板上元器件焊点定位的复杂度.为了降低三维立体电路加工过程中的人力成本,提高加工效率,设计了一种用于焊接机床对三维立体电路板焊点定位的双目结构光系统,并针对双目结构光系统在与焊接机床结合应用过程中存在的坐标转换、焊点识别困难等问题,从硬件与算法层面提出了解决方案.在软硬件的配合下,可以简单快速地完成双目结构光系统与焊接机床之间的坐标转换,并对电路板焊点完成定位与坐标计算,代替了人工对三维立体电路板焊点测量定位的复杂流程.实验表明,提出的方案具有较高的精度,能够满足机床焊接元器件过程中对焊点的定位需求.

Sn-Cu、Sn-Ag-Cu系无铅钎料的钎焊特性研究

制备了Sn-0.7Cu、Sn-3.5Ag-0.6Cu钎料,用润湿平衡法测量了钎料对铜的润湿曲线,研究了温度、钎剂活性、钎焊时间对润湿行为的影响,并与Sn-37Pb钎料进行了比较。结果表明:升高温度能显著改善无铅钎料对铜的钎焊性。当温度<270℃时,Sn-0.7Cu的钎焊性明显低于Sn-3.5Ag-0.6Cu钎料;而当温度≥270℃时,两种钎料对铜都会显示较好的润湿性,而Sn-0.7Cu略优于Sn-3.5Ag-0.6Cu钎料。提高钎剂活性能显著增强钎料对铜的润湿性,其卤素离子的最佳质量分数均为0.4%左右。随着浸渍时间的延长,熔融钎料与铜的界面间产生失润现象。无铅钎料的熔点和表面张力较高,是钎焊性较差的根本原因。