无铅焊料的发展动态

本文综述了国外无铅焊料的研究开发动态，论述了无铅焊料应用的迫切性和必要性以及无铅焊料所具备的性能要求。     

无铅焊料的新发展

传统焊接技术使用锡铅焊料,对环境造成严重伤害。文章从环保角度出发,阐述了应用无铅焊料的必然性,并介绍了无铅焊料近几年的发展,指出现阶段无铅焊料离市场要求还有一定差距, 需进一步加强研究与开发。     

电子封装用无铅焊料的最新进展

随着WEEE/RoHS法令的颁布,电子封装行业对于无铅焊接提出了更高的要求.根据国际上对无铅焊料的最新研究进展提出了无铅焊料"三大候选"的概念.总结了目前无铅焊料尚存的三大主要弱点,并对国际上推荐使用的几种无铅焊料的优缺点进行了概述.     

Sn—Bi无铅焊料的研究

通过总结传统Sn-Pb焊料的特点和研制无铅焊料的条件,综述Sn-Bi无铅焊料低熔点等优点以及脆性大、易偏析的缺点,分析添加In,Ag,AI,Sb等微量合金元素对Sn-Bi无铅焊料微观组织及性能的影响,提出了此合金系焊料的抗蠕变性、导电性、润湿性、拉伸性能等尚待完善的性能及可采用合金化、开发新型焊剂等新方法使Sn-Bi焊料成为理想的无铅焊料,为无铅焊料的进一步研究提供一定的参考.     

助焊剂腐蚀失效案例分析

随着国内外环保要求的不断提高,电子产品正全速向低毒、低碳方向前进,由此也引发产品制造业向无铅、无卤方向快速发展。由于无铅焊料的焊接温度范围受到PCB和元器件耐温要求的限制,特别是无铅焊料本身的润湿性较锡铅焊料差,无铅焊接工艺的难度大大得提高,由此导致大量的焊接工艺缺陷。为了客服无铅工艺焊接能力较差的问题,人们纷纷开发了更加适合无铅焊接的焊接辅助材料,其中新型无铅助焊剂在提高无铅焊接能力上起到了很大的作用。     

基于Sn-Zn系列的无铅焊可靠性分析

铅和铅的化合物有害人身健康，破坏环境。本文介绍了无铅焊料研究开发的迫切性和开发新型无铅焊料应满足的要求。从抗氧化性和提高浸润性两方面对SnZn焊料的可靠性进行了分析说明。介绍了微合金化和N2对SnZn可靠性的影Ⅱ向，并作出了其基本回流温度曲线示意图。     

无铅合金与锡铅合金性能对比分析

随着人们对环境的日益重视,全球对电子组装焊料合金的无铅化和电子产品的质量要求也越来越高.介绍了无铅焊料合金的发展及技术应用情况,针对无铅焊料合金与锡铅焊料合金的物理性能、机械性能等指标进行对比,定性地分析在特殊环境下两种焊料合金形成的焊点差异.     

无铅焊料及其可靠性的研究进展

环保和微电子器件高度集成化的发展驱动了高性能无铅焊料的研究和开发。本文介绍了国内外对Sn-Ag,Sn-Zn,Sn-Bi,Sn-Sb和Sn-In系无铅焊料的发展现状及所取得的研究成果;列出了美国抗高温疲劳焊料研究计划筛选的七种抗热疲劳无铅焊料合金;对焊点的一般可靠性问题及无铅焊料引入的新的可靠性问题进行了归纳和讨论。     

低温无铅焊料

随着无铅焊料的发展,低温组装技术越来越多的需求对低温无铅焊料提出了诸多挑战。对国内外低温无铅焊料的发展情况进行了综述,详细介绍了四种不同的低温无铅焊料的研究现状,以及不同的领域应用的优缺点和解决方案,分析了未来实现低温安装的途径与开发方向。     

电子产品中的无铅焊料及其应用与发展

由于传统焊接技术使用的Sn-Pb焊料中的铅会对环境造成污染而被禁止使用,近年来无铅焊料成为了研究热点。文中介绍了运用于电子产品中的无铅焊料的发展背景、特点及要求。根据应用温度不同,无铅焊料可以分为低温、中温和高温无铅焊料。文章综述了它们各自的应用特点、场合及存在的问题和发展前景。     

无铅焊膏的设计与展望

分析了无铅焊膏的构成和技术要求。对无铅焊膏用焊粉及助焊剂配方设计的现状进行了讨论,焊粉的成分多为Sn、Ag和Cu,粒度越来越多地采用20μm;助焊剂多为改性松香、有机酸活化剂等。展望了无铅焊膏的研究与发展趋势。     

Isothermal aging effects on flex cracking of multilayer ceramic capacitors with standard and flexible terminations

Multilayer ceramic capacitors (MLCCs) are known to experience flex cracking when subjected to bending stresses. An experimental study was conducted to determine the susceptibility to flex cracking of flexible- and standard-termination surface mount MLCCs assembled with lead-free or tin–lead solders and aged at two different temperatures for 200 h. Experimental results showed that MLCCs mounted on printed circuit boards with lead-free solder are less susceptible to flex cracking compared with MLCCs mounted on boards with eutectic tin–lead solder. Two factors which make capacitors assembled with lead-free solder less susceptible to flex cracking were discussed: the lower tensile stresses inside the capacitor body which are a result of the differing elastic–plastic mechanical properties of the solder, and the higher residual compressive stresses after solder reflow assembly which are a result of the higher solidification temperature for the Sn3.0Ag0.5Cu lead-free solder. Flexible-termination MLCCs showed much more resistance to flex cracking in comparison to standard-termination MLCCs assembled with both lead-free and tin–lead solders. Aging at elevated temperatures had little effect on flex cracking susceptibility of MLCCs assembled with tin–lead solder. For MLCCs assembled with lead-free solder, aging at 150 °C increased the susceptibility to flex cracking in comparison with un-aged MLCCs.     

印制电路板铜面保护层对无铅焊点结构影响

采用扫描电镜与能谱测试,研究了两种不同印刷电路板铜面保护层,即有机保护层(Organic Solderability Preservatives,OSP)与浸银层(Immersion Ag,I—Ag),对无铅焊点结构的影响。结果显示,采用有机保护层的焊接界面金属间化合物层厚度明显超过了浸银层;在两种不同保护层中的焊点中,均出现薄片状或树枝状Ag3Sn金属间化合物,但在浸银层焊点中,薄片状Ag3sn主要在焊接界面层处非均匀形核长大,而有机保护层焊点中,薄片状Ag3Sn较少出现,代之以树枝状Ag3Sn近似均匀地分布在焊点中。断口分析显示,采用有机保护层的焊点中出现了较多的气孔,而且气孔主要出现在靠近铜面焊点中,这明显降低了焊点的强度。     

Hygrothermal Failures From Small Defects in Lead-Free Solder Reflowed Electronic Packages

Steam-driven delamination failure is a main failure mode in electronics packages during solder reflow. Steam pressures built up within interfaces in packages are sensitive functions of the reflow temperature. The switch to lead-free soldering will raise re-flow temperature by more than 20degC and double the equilibrium saturated steam pressure within defects in the package. The effects of saturated steam driven interfacial failure was analyzed using finite element in this study. Analyses revealed that packages which are thin and made using high thermal conductivity materials are at higher risk of failure than conventional packages made using standard materials. This suggests that electronics made with thick and inexpensive encapsulants are less prone to failure when switched to lead-free solder. Portable and mobile electronics which have low profiles and are made of high thermal conductive encapsulants are at higher risk when switched to lead-free solder reflow. Moreover, the study found that the critical temperature for failure is dependent on the defect size in the package. Reduction of initial defect size can reduce failures in high risk packages in lead-free solder reflow.     

无铅转化给波峰焊工艺所带来的问题研究

无铅焊料的应用使得波峰焊设备问题更加突出,其中主要的问题是设备的腐蚀及材料的寿命.无铅焊料和助焊剂的特性决定了无铅波峰焊设备在结构和材料选用上有很大不同.无铅钎料的成分配比不同于有铅钎料,因此在无铅钎焊时,其工艺流程、工艺参数也有所改变.从焊接温度、波峰高度、浸锡时间、冷却系统、传输系统等方面分析了无铅波峰焊的工艺要求...     

氮气保护在无铅化电子组装中的应用

无铅钎料的高熔点、差润湿性给SMT传统的焊接工艺带来了很大冲击,并且对焊点质量也产生了很大的影响。为了防止氧化,改善钎料与焊盘、元件引脚之间的润湿性,提高产品合格率,目前在电子纽装中普遍采用氮气保护。针对几种常用无铅钎料进行了氮气气氛中润湿性和焊点组织的分析,并初步研究了氮气保护对焊点质量和氧化渣的影响。结果表明：氮气保护可以改善无铅钎料润湿性,细化焊点组织,减少氧化渣量,而且对焊点外观和成品率也有一定的影响。     

Lead-free chip scale packages: assembly and drop test reliability

Three underfill options compatible with lead-free assembly have been evaluated: capillary underfill, fluxing underfill, and corner bond underfill. Chip scale packages (CSPs) with eutectic Sn/Pb solder were used for control samples. Without underfill, lead-free and Sn/Pb eutectic drop test results were comparable. Capillary flow underfills, dispensed and cured after reflow, are commonly used in CSP assembly with eutectic Sn/Pb solder. With capillary flow underfill, the drop test results were significantly better with lead-free solder assembly than with Sn/Pb eutectic. Fluxing underfill is dispensed at the CSP site prior to CSP placement. No solder paste is printed at the site. The CSP is placed and reflowed in a standard reflow cycle. A new fluxing underfill developed for compatibility with the higher lead-free solder reflow profiles was investigated. The fluxing underfill with lead-free solder yielded the best drop test results. Corner bond underfill is dispensed as four dots corresponding to the four corners of the CSP after solder paste print, but before CSP placement. The corner bond material cures during the reflow cycle. It is a simpler process compared to capillary or fluxing underfill. The drop test results with corner bond were intermediate between no underfill and capillary underfill and similar for both lead-free and Sn/Pb eutectic solder assembly. The effect of aging on the drop test results with lead-free solder and either no underfill or corner bond underfill was studied. Tin/lead solder with no underfill was used for control. This test was to simulate drop performance after the product has been placed in service for some period of time. There was degradation in the drop test results in all cases after 100 and 250 h of storage at 125/spl deg/C prior to the drop test. The worst degradation occurred with the lead-free solder with no underfill.     

BGA混合焊点热循环负载下的可靠性研究

焊料从有铅向无铅转换中,不可避免会遇到二者混合使用的情况,有必要对生成的混合焊点进行可靠性研究。通过对不同工艺参数下形成的混合焊点和无铅焊点进行了外观检测、X射线检测和温度循环测试。结果显示,只要工艺参数控制得当,混合焊点是可行的。在焊球合金、焊料合金、峰值温度、液相线以上时间和焊接环境五个关键因素中,前四项对焊点可靠性比较重要,焊接环境对焊点可靠性的影响不很显著。     

Effects of thermomechanical cycling on lead and lead-free (SnPb and SnAgCu) surface mount solder joints

Accelerated reliability tests have been performed on leadless and leaded lead-free and lead containing SMT component assemblies. Results so far have shown that lead-free reflow soldering is a viable alternative for conventional lead based reflow soldering. The selected ternary eutectic solder alloy SnAg3.8Cu0.7 requires higher processing temperatures which could restrict the use of certain board and component types, but other than that no major modifications seem necessary. Although better SnAg3.8Cu0.7 bulk mechanical properties were obtained compared to the near eutectic lead bearing bulk solder properties, reflowed solder joints did not reflect this difference. In general, quite similar reliability results were obtained as found for the lead based solders. Dependent on board and component metallisations and use environment, the reliability of the lead-free solders could perform better or worse than the lead based solders. Temperature dependent aspects such as solderability and mechanical behaviour of the lead-free assemblies could play a role in this. Although microstructural differences can be seen between the lead-free and lead bearing solder joints, similar joint failure mechanisms occur. Resistor solder joint cracks propagate from underneath the component through either transgranular (lead-free) grains or along intergranular (lead) grain boundaries between lead-rich and tin-rich areas and into coarsened regions near the component terminations. Gullwing lead cracks were seen propagating from the heel fillet along the lead/solder interfacial intermetallic mostly (some cracks started in the heel fillet and propagated through the solder body dispersed with coarsened spherical Ag₃Sn intermetallic particles). Package design and leadframe material seem to play a more important role in the fatigue mechanism than the change in microstructure of the solder joint.