连接器锡晶须形成机理及研究

针对锡晶须的形成原因,把机械地从外部到镀层表面形成的应力所产生的锡晶须定义为外部应力型,并主要叙述以连接器为主的外部应力型晶须;另一方面,把从基底材料的扩散和表面氧化等自然现象所产生的锡晶须定义为内部应力型晶须.推荐了锡晶须的测试方法,阐述了锡晶须的形成机理,并简要介绍了对锡晶须研究的现状及今后的研究课题.     

锡晶须问题的现状与课题

欧洲的RoHS和中国的RoHS都严禁使用有害物质铅及铅合金，电子领域元器件安装用的焊接材料Sn／Pb首当其冲。为了寻求替代产品，人们开发了不含Pb的Sn基焊料。然而不含Pb的Sn镀层易产生锡晶须，引起电子设备短路故障。为此，对锡晶须的研究又重新摆在电子工程师们面前。本文执应力学成因一说，以电子连接器的触点为叙述点，把却融．地从外部到镀层表面形成的应力所产生的锡晶须定义为外部应力型，并主要叙述以连接器为中心的外部应力型晶须；另一方面，把从基底材料的扩散和表面氧化等自然现象所产生的锡晶须定义为内部应力型晶须。文中推荐了锡晶须的测试方法，阐述了锡晶须的形成机理，并简要介绍了对锡晶须研究的现状及今后的研究课题。     

挠性电路板引脚嵌合部无铅镀层的锡须生长

以民用挠性印制电路板(FPC)引脚和连接器嵌合部无铅镀层为对象,通过研究引脚上的Ni/Sn无铅镀层的显微形貌和锡须尺寸,探讨了Ni/Sn无铅镀层的长期可靠性。结果表明,在25℃,RH为45%～55%的条件下,挠性印制电路板引脚和连接器嵌合部无铅镀层上生长的锡须呈现针状、柱状等多种不同的显微形貌,其中大部分是针状锡须,少量针状锡须的长度已超过了50μm临界值,很可能因锡须桥接引起电流泄漏和短路,对FPC互连可靠性产生威胁。抑制少量超长的针状晶须的生长,是防止风险的关键。     

锡晶须问题的现状与课题

针对锡晶须的形成原因,文章执应力学一说,以电子连接器的触点为叙述点,把机械地从外部到镀层表面形成的应力所产生的锡晶须定义为外部应力型,并主要叙述以连接器为中心的外部应力型晶须;另一方面,把从基底材料的扩散和表面氧化等自然现象所产生的锡晶须定义为内部应力型晶须。文中推荐了锡晶须的测试方法,阐述了锡晶须的形成机理,并简要介绍了对锡晶须研究的现状及今后的研究课题。     

外部应力型晶须抑制方法的研究

当电子工业中完全实现无铅化时,晶须问题成为新的悬念。关于Sn晶须的成长机理和抑制方法的研究已经遍及全世界。晶须发生和成长被认为是Sn镀层上的压缩应力引起的。晶须分为内部和外部应力型。文章通过压缩负荷试验研究了外部应力型晶须的抑制方法。这种方法是Sn表面镀层和Cu上的Ni基底镀层之间介入薄Au镀层。结果发现镀Sn以后不久就形成了金属间化合物AuSn4,Au镀层有效地减轻了Sn晶须的数量,缩短了Sn晶须的长度。     

引线可焊性组合镀层的研究

一、前言一般认为影响铜芯引线可焊性的因素主要有二个方面①是铜锡合金层(η相)的扩散生长,②是镀层表面氧化物的生成。为了提高元器件引线的可焊性,文献曾报道采用中间加阻挡层的组合镀层取得了良好的效果。本文研究了几种组合镀层对可焊性的影响。即在铜基底上电镀可作为阻挡层的中间镀层,然后镀覆光亮锡镀层。中间镀层分别采用暗镍、低pb—Sn(即含pb量<40％重量的pb—Sn合金)和高pb—Sn(即含pb>60％重量的pb—Sn合金)三种镀层。中间镀层厚度控制在3～4μm,光亮锡镀层7～6μm,总厚度控制在10μm左右。另外一组作对照的试验样品是在铜基体直接镀光亮锡(10μm左右),无中间阻挡镀层。每组样品都分     

国外工艺文献导读

20060201表面氧化与锡须晶生长—W John Wolf-gong.Circuits Assembly,2005,16(12):24~27(英文)纯锡涂层可产生“晶须”,晶须是锡的小针状突出的生成物。这些晶须导电,因此可在电子产品中造成短路。在本研究中,我们发现锡镀层的氧化加快了晶须的形成。这可能同表面应力状况的变     

无铅纯锡电镀中的若干问题

由于纯锡镀层具有许多优良的性质,如可焊性、延展性、导电性和耐蚀性等,因而纯锡已成为电子工业中无铅电镀的首选.但纯锡电镀中存在着许多问题,如锡晶须、镀层变色及镀液混浊等.这些问题对工业电子电镀过程来说是非常重要的,但目前对它们的了解还不多.通过对这些问题进行较深入的研究,找到了镀层变色及镀液混浊的影响因素,给出了三种解决变色问题的方法:电镀添加剂、后处理及Ni(P)阻挡层.开发了一种新的镀锡抗氧化剂.     

锡合金镀层的晶须抑制效果及其机理

概述了无铅锡合金镀层的概要,锡合金镀层的晶须评价试验,以及Sn-Pb合金镀层和无铅合金镀层的晶须抑制机理。     

锡晶须及其抑制技术

晶须特别是锡须问题已成为印制板无铅焊接质量可靠性的核心问题之一.从研究外应力型、内应力型以及焊接过程中热循环等产生晶须的主要因素出发,分析了不同条件下晶须的产生机理,并给出了如何有效抑制晶须产生的措施.最后扼要指出了晶须研究的今后研究方向.     

锡涂覆层—SERA锡评价提供了对锡性能的深入理解

热风焊料整平(HASL)的技术、经济和环境因素迫使人们寻找其取代物。这些因素中包括新的元件如BGA、GOB和倒装芯片等的安装对PCB要求有更平整的连接盘,同时铅的特性也威胁着人类的健康。取代物的研究朝着两个方     

退锡废水中锡的分离实验研究

文章以碱中和退锡废水所得锡泥为原料,研究了碱浸法分离锡泥中的锡,在煮沸转化液固比为2,氢氧化钠与锡摩尔比为7～8,微沸(100℃～110℃)时间为2h,水洗液固比为5时,锡的分离率可以达到98%以上。     

减少锡须

组建iNEMI锡须用户研究小组的目的就是为了把锡须引起的故障风险减至最小程度。本文回顾了该小组的推荐意见，它反映了现在可以获得的有关锡须形成和控制的最新资料．包括常用的无铅处理涂层的信息及其帮助减少锡须的效果。[编者按]     

浅谈电镀锡线状渗镀——记马达板线状渗镀处理

文章简要介绍我公司TRAL马达板纯锡电镀生产过程中“线状渗镀”异常,为后续同类问题的控制提供借鉴。     

Tin whiskering risk factors

Whiskers are elongated single crystals of pure tin that have been reported to grow to more than 10 mm (250 mils) in length (though they are more typically 1 mm or less) and from 0.3 to 10 /spl mu/m. in diameter typical 1-3 /spl mu/m). Whiskers grow spontaneously without an applied electric field or moisture (unlike dendrites) and independent of atmospheric pressure (they grow in vacuum). Whiskers may be straight, kinked, hooked, or forked and some are reported to be hollow. Their outer surfaces are usually striated. Whiskers can grow in nonfilament types which are sometimes called lumps or flowers. Whisker growth may begin soon after plating. However, initiation of growth may also take years. The unpredictable nature of whisker incubation and subsequent growth is of particular concern to systems requiring long term, reliable operation.     

Tin whisker test standardization

A National Electronics Manufacturing Initiative (NEMI) Committee, Whisker Test Method Standardization, was formed in 2001 to evaluate and identify environmental test conditions that are useful in predicting the propensity for tin whisker growth. The objective of the committee is to develop standardized whisker testing methods to provide to the electronics industry for characterizing and qualifying tin-based finishes. The team completed two evaluation phases and has identified three test methods effective in inducing whisker growth, two isothermal storage methods and one temperature cycle method. A Phase 3 evaluation was initiated in mid 2003 to confirm the consistency of these testing methods, determine effectiveness for different Sn-based finishes, and possibly define test end points by determining the longest duration for whisker growth saturation for different Sn-based finishes. Results thus far confirm that temperature cycling and 60C/93 RH isothermal storage are effective in producing whiskers. An additional evaluation, Phase 4, has been initiated to look at the effect of electrical bias on accelerating whisker growth. A Phase 5 Evaluation is in the design stage. The objectives of the Phase 5 Evaluation are still being discussed. A brief review of the Phase 1 and 2 Evaluations results which led to NEMI's test method recommendations will be provided. In addition, the latest results for the Phase 3 Evaluation and status of the Phase 4 and 5 Evaluations will also be shared.     

Effect of Pulse-Plated Nickel Barriers on Tin Whisker Growth for Pure Tin Solder Joints

We investigate the influence of pulse-plated Ni barriers, compared to direct current (DC)-plated Ni barriers, on the growth of Sn whiskers in laminated Cu/Ni/Sn samples. The results indicate that the pulse-plated Ni barriers exhibit much better resistance to Sn whisker growth than the DC-plated Ni barriers, i.e., when exposed to ambient of 60°C and 93% relative humidity (RH) for 40 days only a few small hillocks were observed as opposed to the long whiskers and large nodules of Sn for the DC-plated Ni barriers. The underlying mechanisms are addressed based on the texture characteristics of the plated Ni and Sn layers and the formation of intermetallic compounds.     

锡涂覆层将起支柱作用

在多重再流焊循环中,一种新奇的浸渍锡将掘起。 1 引言 由于热风焊料整平(HASL)表面涂覆具有好的可焊性和连接点的可靠性而得到了广泛的应用。但是由于元件的进步要求有     

Tin telluride based thermoelectrical alloys

The effect on the Hall hole concentration and the thermoelectric coefficient of various elemental impurities in SnTe containing excess Te and in some solid solutions based on it is investigated in the temperature interval 300–900 K. The variation of the kinetic parameters is treated on the basis of the concept of resonance states bound to cation vacancies and to the impurities determining the hole concentration. The low values of the thermoelectric coefficient in SnTe is explained by selectivity of scattering of charge carriers with more probable transition of the holes to the resonance states and vice versa. In isomorphic solid solutions based on SnTe, because of a shift in the energy position of the resonance states relative to the band edges and the Fermi level, it is possible to alter the nature of the resonance scattering and raise the thermoelectric coefficient to values which are optimal from the standpoint of obtaining maximum thermoelectric efficiency. In solid solutions of chalcogenides of group-IV elements with SnTe content about 40 mol% of the dimensionless parameter of thermoelectric efficiency ZT=1 at temperatures above 700 K. Fiz. Tekh. Poluprovodn. 32, 268–271 (March 1998)     

Tin Whisker Test Method Development

The International Electronics Manufacturing Initiative (iNEMI) proposed a set of tests that were subsequently standardized by the Joint Electron Device Engineering Council (JEDEC) Solid State Technology Association as JESD22A121. However, further optimization was needed to validate and verify proposed iNEMI tests to determine whether these test methods could differentiate between component surface finishes, to investigate the connection between short-term and long-term tests, and to determine optimal inspection intervals and test durations. In the current work, 15 surface finishes were evaluated using iNEMI's three proposed environmental test conditions. These finishes were evaluated for whisker presence and length using a scanning electron microscope (SEM) every 1000 h or 500 accelerated thermal cycles for a total of at least 9000 h of isothermal testing or 3000 accelerated thermal cycles. Test results showed that thermal cycling and high-temperature/humidity testing could grow whiskers for all Pb-free Sn-based finishes, while only a few finishes exhibited whiskers after 10 000 h in an air-conditioned office environment. The results described in this paper were used to change the JEDEC tin whisker test method from the original iNEMI proposal by decreasing the humidity of the high-temperature humidity test, controlling the ambient test condition to 30 degC and 60% relative humidity (RH), and increasing the number of leads per sample and number of samples (sample size) for inspection