IMC生长对无铅焊球可靠性的影响

通过模拟及实验研究了IMC层及其生长对无铅焊点可靠性的影响.采用回流焊将无铅焊球(Sn3.5Ag0.7Cu)焊接到PCB板的铜焊盘上,通过-55～125℃的热循环实验,获得了IMC厚度经不同热循环次数后的生长规律.采用有限元法模拟了热循环过程中IMC厚度生长对无铅BGA焊点中应力变化的影响,并由能量疲劳模型预测了无铅焊点寿命.计算结果显示,考虑IMC层生长所预测的焊点热疲劳寿命比不考虑IMC层生长时缩短约30%.     

电子封装与组装焊点界面反应及微观组织研究进展

软钎焊焊点界面反应是连接金属的最古老的冶金工艺过程。随着倒装芯片(FC)、球栅阵列(BGA)和芯片级封装(CSP)等面封装技术的兴起,近年来Sn基钎料被广泛应用于微电子制造,包括芯片和基板之间的封装互连以及基板与印制电路板之间的组装互连。这就需要系统地研究Sn基钎料焊点界面反应及微观组织。从形态学、热力学和动力学的角度回顾总结了SnPb共晶钎料、高Pb钎料和无Pb钎料与Cu、Ni、Au/Ni/Cu、PdAg焊盘之间的界面反应。     

波峰焊及再流焊无铅焊点组织演变规律的研究

以电子封装线上的波峰焊无铅焊点Sn-0.7Cu/Cu、回流焊无铅焊点Sn-3Ag-0.5Cu/Cu为对象,研究了150 ℃时效过程中无铅焊点处金属间化合物(IMC)、焊料合金组织的演化规律及界面处金属间化合物生长的动力学.试验结果表明:两种无铅焊点处IMC层的厚度随着时效时间的延长而增加,IMC层的生长基本上符合抛物线规律,因此IMC层的长大受元素扩散控制;且两种无铅焊点处IMC层的生长速率常数相近,但Sn-0.7Cu焊料中Sn的晶粒尺寸较Sn-3Ag-0.5Cu中的大;长期时效后,在试样的IMC层内发现有孔洞产生.     

航天电子微焊点液-固界面反应过程中的尺寸效应与工艺优化

针对微型化趋势下焊球的尺寸效应问题,研究了航天电子微焊点互连工艺过程中液-固界面反应与微观组织的影响规律,并对互连工艺进行了优化.具体研究了不同直径(200、400μm)的Sn-3.0Ag-0.5Cu和Sn-37Pb焊球分别在球栅阵列(BGA)器件侧金属化层(电镀Ni/Au)上进行单侧植球回流焊后的尺寸效应现象.研究结果表明:Sn-37Pb焊点界面处生成针状或短棒状的Ni₃Sn₄类型的金属间化合物(IMC)晶粒;Sn-3.0Ag-0.5Cu焊点界面处生成不规则的块状(Cu,Ni)₆Sn₅晶粒.两种类型的焊点在液-固界面反应过程中均表现出明显的尺寸效应现象,即焊球尺寸越小,界面生成的IMC晶粒直径越大,IMC层越厚.基于建立的浓度梯度控制(CGC)界面反应理论模型,揭示了界面反应尺寸效应产生的原因与界面反应进程中界面溶质原子的浓度梯度相关,较小尺寸焊点界面处的溶质原子浓度梯度较小,溶质原子扩散通量较低,形成的界面IMC晶粒较大.基于CGC界面反应理论模型,对200μm直径Sn-3.0Ag-0.5Cu焊...     

有铅焊料与无铅BGA混合焊点显微组织性能研究

随着近年来电子产品无铅化的发展,越来越多的有铅器件被无铅器件替代,其中SnAgCu合金成为BGA器件锡球的主要成分.然而在无铅焊点的可靠性未被认可之前的过渡时期,有铅焊膏和无铅器件混合焊接的情况就不可避免,尤其是在高可靠电子产品领域.因此混合焊接工艺和焊点的性能成为高可靠性电子产品组装和焊点寿命分析中的研究重点.总结了近年来对有铅焊料和无铅BGA混合焊接的一些相关研究,主要涉及混合焊接温度、混合焊点的显微组织、界面处金属间化合物、焊点力学性能、可靠性以及焊点失效机制等方面.     

BGA锡球再置可靠性

已有很多关于混合合金焊点的可靠性的文章发表,主要重点放在BGA器件上。乍看起来,这些BGA器件上的混合合金焊点看来有可以接受的焊点强度及可靠性,但工序要求对回流焊工艺和温度曲线有更大的控制。因此,很多制造商以含铅锡球工艺对无铅BGA进行锡球再置,并未更改工序即加工组件。论述了有关经再置锡球的器件的可靠性问题,特别是器件焊盘铜溶解及额外热循环对芯片/封装的影响。     

BGA表面贴装技术及过程控制

SMT(表面贴装技术)与SMD(表面贴装器件)不断发展更新,BGA顺应时代潮流成为高频化、高I/O数及小型化封装的最佳选择.但是BGA焊接后焊点质量的保证及其返修却是令生产者头疼的问题.简要介绍BGA器件、BGA器件发展现状和应用情况,重点论述BGA生产中应用的检测方法和返修工艺.     

SAC105掺Ni焊球对焊接点强度与可靠性的影响

在内存封装领域,球栅阵列封装(BGA)由于具有高密度和低成本的特点而被广泛采用.在实际的使用过程中,由于遭受外界各种形式的机械负载和冲击造成器件失效,为了改善焊点的强度和可靠性,以SAC105(Sn985AgCu0.5)无铅焊球为参照制备出SAC105 Ni005焊球.为了研究两种焊球焊接点的可靠性与强度,采用焊球的快速剪切测试以及BGA器件的剪切测试方法来检测焊点强度,同时采用威布尔分析方法对两种焊球的热循环测试(TCT)结果进行分析.研究表明,SAC105 Ni0.05焊球比SAC 105焊球具有更长的温度循环可靠性预期寿命、更强的焊接点强度以及更低的脆性断裂的概率.     

ESPI在板级BGA封装器件焊球失效检测中的应用

球栅阵列封装(BGA)综合性能好,广泛应用于表面贴装.采用电子散斑干涉(ESPI)离面位移光路,在简单机械加栽情况下,对板级组装BGA器件的离面位移进行测量,比较了完好BGA、焊球分层BGA与焊球脱落BGA器件的测量结果.发现焊球有缺陷样品的条纹形状与完好样品相比有明显的差别,ESPI条纹在失效焊点附近发生突变.通过计算ESPI的位移测量值后,可判断BGA焊点的失效位置.结合有限元(FEM)模拟,对位移异常的BGA焊点进行分析.通过将计算结果与ESPI的位移测量值比较,可判断BGA焊点的失效模式.     

无铅BGA封装可靠性的力学试验与分析

着重研究了机械冲击和应力对无铅BGA封装焊点可靠性的影响,介绍了BGA封装的可靠性力学试验(跌落、弯曲试验)及其分析方法.通过对力学试验中失效焊点的分析以及借助ANSYS模拟工具,找出引起失效的根本原因,为开发性能更好、高可靠性的无铅材料、改进无铅工艺提供依据.     

BGA组装技术与工艺

从BGA的封装形式、PCB的设计、焊膏印刷、贴片、回流焊接工艺等方面分析了BGA组装过程中应注意的问题及其预防措施。以常用的PBGA和CBGA为例,分析了两种不同封装形式BGA的结构特点和组装过程中应注意的问题,以焊膏Sn63Pb37、Sn62Pb36Ag2和Sn96.5Ag3.0Cu0.5为例,分析了传统的SnPb组装工艺和无铅组装工艺的特点,以提高BGA组装的质量。     

银含量对随机振动条件下无铅焊点可靠性的影响

为了探究银含量对无铅焊点在随机振动条件下的可靠性的影响,对Sn-3.0Ag-0.5Cu、Sn-1.0Ag-0.5Cu和Sn-0.3Ag-0.7Cu三种不同Ag含量材料的焊点做窄带范围内的随机振动疲劳实验,并对失效焊点进行分析。结果表明:三种材料焊点的失效位置基本都在靠近PCB侧,最外围焊点最容易失效,失效模式均为脆性断裂,并且随着Ag含量的降低,金属间化合物的厚度逐渐减小,焊点的疲劳寿命逐渐延长。     

Comparative study of interfacial reactions of Sn-Ag-Cu and Sn-Ag solders on Cu pads during reflow soldering

The interfacial reaction in soldering is a crucial subject for the solder-joint integrity and reliability in electronic packaging technology. However, electronic industries are moving toward lead-free alloys because of environmental concerns. This drive has highlighted the fact that the industry has not yet arrived at a decision for lead-free solders. Among the lead-free alloys, Sn-3.5Ag and Sn-3.5Ag-0.5Cu are the two potential candidates. Here, detailed microstructural studies were carried out to compare the interfacial reaction of Sn-3.5Ag and Sn-3.5Ag-0.5Cu solder with a ball grid array (BGA) Cu substrate for different reflow times. The Cu dissolution from the substrate was observed for different soldering temperatures ranging from 230°C to 250°C, and the dissolution was found to increase with time and temperature. Dissolution of Cu in the Sn-3.5Ag solder is so fast that, at 240°C, 12 μm of the Cu substrate is fully consumed within 5 min. Much less dissolution is observed for the Sn-3.5Ag-0.5Cu solder. In respect to such high dissolution, there is no significant difference observed in the intermetallic compound (IMC) thickness at the interface for both solder alloys. A simplistic theoretical approach is carried out to find out the amount of Cu₆Sn₅ IMCs in the bulk of the solder by the measurement of the Cu consumption from the substrate and the thickness of the IMCs that form on the interface.     

电迁移对Sn3.0Ag0.5Cu无铅焊点剪切强度的影响

通过热风回流焊制备了Cu/Sn3.0Ag0.5Cu/Cu对接互连焊点,测试了未通电及6.5 A直流电下通电36 h和48 h后焊点的剪切强度.结果表明,电迁移显著地降低了焊点的剪切强度,电迁移36 h使剪切抗力降低约30%,电迁移48 h降低约50%.SEM观察断口和界面形貌表明,界面金属间化合物增厚使断裂由韧性向脆性...     

Eddy Current Induced Heating for the Solder Reflow of Area Array Packages

This paper presents a feasibility study of using eddy current induced heating for the solder reflow of area array packages. With a high frequency electromagnetic field, Sn 3.5% Ag lead-free solder balls were heated to melt and wet the solder pads on an organic substrate. The experimental results showed that such a solder reflow process could be implemented effectively in a wide processing window. With an infrared temperature sensor, it was found that the temperature difference between the solder balls and the FR4 board might reach 80 , indicating a rather localized heating mechanism. In addition, the heating and cooling rates during the soldering were found very high. This is another feature of the induction heating reflow process. It was also found that the generated temperature in the solder balls would depend on the size of the solder balls. This characteristic may be used to perform selective soldering of flip chip BGA packages. Furthermore, the developed soldering process was applied to the board level reflow of actual components. The result verified that the induction heating reflow is a feasible soldering process in actual applications.     

Failure Morphology after the Drop Impact Test of the Ball Grid Array Package with Lead-Free Sn-3.8Ag-0.7Cu on Cu and Ni Under-Bump Metallurgies

High strain-rate drop impact tests were performed on ball grid array (BGA) packages with lead-free Sn-3.8Ag-0.7Cu solder (in wt.%). Plated Ni and Cu under-bump metallurgies (UBMs) were used on the device side, and their drop test performances were compared. Failure occurred at the device side, exhibiting brittle interfacial fracture. For Ni UBM, failure occurred along the Ni/(Cu,Ni)₆Sn₅ interface, while the Cu UBM case showed failure along the interface between two intermetallics, Cu₆Sn₅/Cu₃Sn. However, the damage across the package varied. For Cu UBM, only a few solder balls failed at the device edge, whereas on Ni UBM, many more solder bumps failed. The difference in the failure behavior is due to the adhesion of the UBM and intermetallics rather than the intermetallic thickness. The better adhesion of Cu UBM is due to a more active soldering reaction than Ni, leading to stronger chemical bonding between intermetallics and UBM. In our reflow condition, the soldering reaction rate was about 4 times faster on Cu UBM than on Ni UBM.     

0.5mm间距CSP/BGA器件无铅焊接工艺技术研究

芯片级封装器件因其小尺寸、低阻抗、低噪声等优点广泛应用于电子信息系统中.从器件封装、印制板焊盘设计、焊膏印刷、贴装以及回流焊接等方面探讨了0.5 mm间距CSP/BGA器件无铅焊接工艺技术.     

有铅焊料焊接无铅BGA回流参数探索

航天电子产品尚未允许采用无铅焊接,而航天电子产品中采用的进口元器件多为无铅器件,因此需要对有铅焊料焊接无铅元器件进行研究。通过对无铅焊球和有铅焊料的焊接特性分析,设计数种回流参数,进行回流焊接试验,并对试验结果进行焊接分析,得出回流峰值温度为228℃~232℃,液相线(217℃)以上时间为50s~60s的回流曲线能较好完成有铅焊料对无铅BGA的焊接。     

Study of interfacial reactions between Sn3.5Ag0.5Cu composite alloys and Cu substrate

For development of a lead-free composite solder for advance electrical components, lead-free Sn3.5Ag0.5Cu solder was produced by mechanically mixing 0.5 wt.% TiO₂ nanopowder with Sn3.5Ag0.5Cu solder. The morphology and growth kinetics of the intermetallic compounds that formed during the soldering reactions between Sn3.5Ag0.5Cu solder with intermixed TiO₂ nanopowder and Cu substrates at various temperatures ranging from 250 to 325 °C were investigated. A scanning electron microscope (SEM) was used to quantify the interfacial microstructure at each processing condition. The thickness of interfacial intermetallic layers was quantitatively evaluated from SEM micrographs using imaging software. Experimental results show that a discontinuous layer of scallop-shaped Cu-Sn intermetallic compounds formed during the soldering. Kinetics analysis shows that the growth of such interfacial Cu-Sn intermetallic compounds is diffusion controlled with an activation energy of 67.72 kJ/mol.     

Intermetallic reactions in Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder BGA packages with Au/Ni surface finishes

The intermetallic compounds (IMCs) formed during the reflow and aging of Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder BGA packages with Au/Ni surface finishes were investigated. After reflow, the thickness of (Cu, Ni, Au)₆Sn₅ interfacial IMCs in Sn3Ag0.5Cu0.06Ni0.01Ge was similar to that in the Sn3Ag0.5Cu specimen. The interiors of the solder balls in both packages contained Ag₃Sn precipitates and brick-shaped AuSn₄ IMCs. After aging at 150°C, the growth thickness of the interfacial (Ni, Cu, Au)₃Sn₄ intermetallic layers and the consumption of the Ni surface-finished layer on Cu the pads in Sn3Ag0.5Cu0.06Ni0.01Ge solder joints were both slightly less than those in Sn3Ag0.5Cu. In addition, a coarsening phenomenon for AuSn₄ IMCs could be observed in the solder matrix of Sn3Ag0.5Cu, yet this phenomenon did not occur in the case of Sn3Ag0.5Cu0.06Ni0.01Ge. Ball shear tests revealed that the reflowed Sn3Ag0.5Cu0.06Ni0.01Ge packages possessed bonding strengths similar to those of the Sn3Ag0.5Cu. However, aging treatment caused the ball shear strength in the Sn3Ag0.5Cu packages to degrade more than that in the Sn3Ag0.5Cu0.06Ni0.01Ge packages.