远程操作矿用双速调度绞车的设计（含CAD图纸源文件）
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本 科 生 毕 业 设 计姓 名： 学 号： 学 院： 专 业： 机械制造及其自动化 设计题目： 远程操作矿用双速调度绞车的设计专 题： 指导教师： 职 称： 年 月 设计任务书专业年级 学号 学生姓名 任 务 下 达 日 期 ： 毕业设计日期： 毕业设计题目:远程操作矿用双速调度绞车的设计毕业设计专题题目：毕业设计主要内容和要求：矿用调度绞车是司机须站在滚筒前用双手操作刹车手柄，这种操作方式非常不安全，断绳经常打伤司机，过载时钢丝绳连带绞车及其底座一同拉起。本课题设计的绞车通过液压离合器和多级定轴齿轮传动实现变速切换，高速时提升速度快；低速时，提升力矩大，液压制动器制动滚筒。通过控制电机、液压离合器、液压制动器实现远程操作。本课题涉及机械、液压、控制系统的设计，可较好锻炼学生机械、液压、控制的综合设计能力，培养学生具有开发和设计机电产品的能力。指导教师签字：郑 重 声 明本人所呈交的毕业设计，是在导师的指导下，独立进行研究所取得的成果。所有数据、图片资料真实可靠。尽我所知，除文中已经注明引用的内容外，本毕业设计的研究成果不包含他人享有著作权的内容。对本论文所涉及的研究工作做出贡献的其他个人和集体，均已在文中以明确的方式标明。本论文属于原创。本毕业设计的知识产权归属于培养单位。本人签名： 日期： 毕业设计指导教师评阅书指导教师评语（基础理论及基本技能的掌握；独立解决实际问题的能力；研究内容的理论依据和技术方法；取得的主要成果及创新点；工作态度及工作量；总体评价及建议成绩；存在问题；是否同意答辩等）：成 绩： 指导教师签字：年 月 日毕业设计评阅教师评阅书评阅教师评语（选题的意义；基础理论及基本技能的掌握；综合运用所学知识解决实际问题的能力；工作量的大小；取得的主要成果及创新点；写作的规范程度；总体评价及建议成绩；存在问题；是否同意答辩等）：成 绩： 评阅教师签字：年 月 日毕业设计答辩及综合成绩答 辩 情 况回 答 问 题提 出 问 题 正 确基 本正 确有 一般 性错 误有 原则 性错 误没 有回 答答辩委员会评语及建议成绩：答辩委员会主任签字： 年 月 日学院领导小组综合评定成绩：学院领导小组负责人： 年 月 日英文翻译Effect of Zn on properties and microstructure of SnAgCu alloyLiang ZhangJi-guang HanCheng-wen HeYong-huan GuoAbstractThe microstructures, wettabilities and mechanical propertiesofSnAgCu-xZn(x = 0,0.5,0.8,1.0,1.2,2.0, 2.5, 3.0) solders were investigated, respectively. The results indicated clearly that adding pretty small amount of Zn element could evidently improvethewettability,mechanicalpropertiesandrefinethemicrostructure of SnAgCu lead-free solder. However, thereexisted an effective range for the Zn addition, the best Zncontent was found to be 0.8 % in the current study. Moreover, the presence of Zn in the solders plays a major rolein inhibiting the growth of CuSn intermetallic layer in the solder/Cu interface. Based on thermal-cycling tests, it is demonstrated that the addition of Zn can enhance the thermal-fatigue properties of SnAgCu solder joints.1 IntroductionSnPb solders have been used extensively in microelectronic applications to form electrical interconnections between packaging levels, to facilitate heat dissipation form active devices, to provide mechanical/physical support, and to serve as a solderable surface finish layer of printed circuit boards (PCBs) and lead frames 1, 2. In recent years, the pollution of environment from Pb and Pb containing materials in microelectronic devices attracts more and more attentions in academia and industry 3. Under the pressure of legislation (WEEE/RoHS) and trade competitions, large quantities of work have been carried out for the substitutes of traditional SnPb solders. Among various lead free solder, SnAgCu lead-free solder alloy has been proposed as an alternative to replace Pb-containing solders because of its relatively low melting temperature compared with the SnAg binary eutectic alloy, and better solderability and mechanical properties compared with the SnCu binary eutectic alloy 46. Furthermore, under the drives of increasingly finer pitch of devices and severe service conditions, novel lead-free solders with better properties are needed sometimes. In order to further enhance the properties of SnAgCu solders, a small amount of alloying elements were selected by lots of researchers as alloys addition into these alloys 710. Zn is one of the elements can enhances the mechanical properties, lows the melting temperature and improves the microstructures of SnAgCu based lead free solders. Kang et al. 11 found that the minor Zn addition was shown to reduce the amount of undercooling during solidification and thereby suppress the formation of large Ag3Sn plates. Moreover, it has been verified by Lin 12 that tin whiskers can be prevented by the addition of 0.2 wt.% Zn into Sn3Ag0.5Cu0.5Ce solder, as excess Zn addition causes poor oxidation resistance and inferior bonding strength. And Song 13 found that after the Zn addition into Sn1Ag0.5Cu solders, the Cu6Sn5and Ag3Sn phases were gradually replaced by the Cu5Zn8, Ag5Zn8 and Ag3Zn phases and the amount of them were increased with increasing Zn content, and the tensile tests showed that while the elongation of the alloy decreased with increasing Zn content, the strength was increased by Zn additions for Zn content1 wt.%, but decreased at Zn content of 2 wt.%. Therefore, in this paper, minute amounts of Zn was added to SnAgCu solders to examine the effect of different of Zn on wetting, tensile force, shear force, microstructure and interfacial layer of SnAgCu solder, and to optimize the quantity of Zn in the SnAgCu alloy.2 Experimental procedure2.1 Alloy design and preparation The pure Sn, Zn, SnCu alloy (415) and SnAg alloy (480) were used as raw materials. In this work, SnAgCu solders bearing different contents of Zn were chosen to compare with original SnAgCu. Series of investigated solder alloys are listed in Table 1. The raw materials of Sn, Zn, SnCu alloy, SnAg alloy were melted in a ceramic crucible, and melted at 550 1 for 40 min. To homogenize the solder alloy, mechanical stirring was performed every 10 min using a glass rod. During the melting, KCl : LiCl (1.3:1), were used over the surface of liquid solder to prevent oxidation. The molten alloys were chill cast ingots in a ceramics mold. Then they were solidified by nominally air-cooling. All solder specimens were heat treated at 125 for an hour to stabilize the microstructure of the SnAgCu-xZn solder alloys. Table 1 Series of investigated solder alloys2.2 Wetting testingSolderability that is dependent upon the wettability of two surfaces being joined is crucial to the efficiency of manu facturing and the reliability of electronic devices 14. The wettingiscrucialforsoldering,asitplaysanessentialrolein ensuring good bonding between the lead free solder and substrate. Wettability between the solder and substrate is an important issue in reliability of electronic packaging 15. The driving force of wetting on substrates is mainly the interfacial energy that results from the imbalance of the surface and interface energies 16.Youngs equation gives thebalance of surface and interfacial tensions at equilibrium: =gs+ coslsglwhere the surface tension of the solid/gas interface, the interfacial tension of the gs lssolid/liquid, the surface tension of the gas/liquid interface, and is the equilibrium contact langle. Figure 1 shows a schematic drawing of the measured angle () of the SnAgCu-xZn solders on copper substrate.Fig. 1 Schematic drawing of wetting properties of SnAgCu-xZnSolder2.3 Mechanical properties testingFor the present work, the QFP devices were selected as test carrier, which were soldered with two sorts of lead-free solders, SnAgCu/SnAgCuZn, respectively. The experimental samples are QFP100 devices (as shown in Fig. 2) with the lead-free solder paste on PCBs. The package meets the EIAJ (Electronic Industry Association of Japan) package specification, the dimensions of this QFP256 device are 28 mm 9 28 mm 9 1.4 mm and the body is made of plastic. The packages were dried for 24 h at 125 ?C prior to reflow soldering. Reflow was done at a peak temperature of 245 ?C as was determined on the boards. The soldering of the samples was conducted in an industrial reflow oven with seven heating zones and one cooling zone. The samples with defect-free soldered joints tested by X-ray should be selected before experiments for the accuracy of results. Pull test was adopted to evaluate the tensile strength of the two solders by STR-1000 microjoints strength tester. During the pull test of the lead, the angle between the hook and the PCB was 45?, as shown in Fig. 3. Total number of leads pull tested was 40 for each soldering condition (Figs. 4, 5). 2.4 Microstructure observationSnAgCu-xZn solders were mechanical polished with 1 lm diamond paste. The etching solution contained 93 % methanol, 5 % nitric acid, and 2 % hydrochloric acid. The microstructure do these solders were examined by optical microscopy (OM) and scanning electron microscopy (SEM) with a voltage of 20 keV. And the SEM equipped with energy dispersive spectrometry (EDS) was utilized to analyze the spatial distribution of chemical species for identification of intermetallics at the interface.Fig. 2 QFP100 device Fig. 3 Tensile tests of quad flat packageFig. 4 RC104 Fig. 5 Shear tests of RC2.5 Thermal cycles testingIn order to assess a long term reliability of soldered joints, the most important criterion is the failure by thermal fatigue. This is observed as the result of the thermal expansionof each component caused by the heating up and coolingdown of the PCB and package materials or by the temperature change of the circumstance. As a result, the thermal stress is concentrated on the micro-jointing interface continuously and the solder joint will cause the thermal fatigue fracture. Experimentally, the thermal-fatiguetesting of SnAgCu-xZn solder joints is determined bycycling the assembled device between two fixed temperatures. According to MIL-STD-883 specification, temperature loading was selected to be imposed on the QFP/RCassembly. The temperature ranges from 218 to 398 K, dwell time at all peak temperature is 15 min, the rate ofdescend and ascend temperature are 12 K/min.3 Results and discussion3.1 WettabilitySnAgCu solder wettability results revealed that with theaddition of Zn as reinforcement, wettability improved asshown graphically in Fig. 6. The wetting angles of thesesolders are shown calculated respectively. The wettingresults of the SnAgCu-xZn solders measured with respect to the contact angles revealed that addition of Zn in solder enhanced the wetting behavior. It is no doubt that Sn3.8Ag0.7Cu0.8Zn solder got the smallest angle and wetting angle of Sn3.8Ag0.7Cu3Zn solder is the biggest. For the SnAgCu-xZn systems, it is observed that the optimal wettability was obtained with the addition of 0.8 % Zn. More, Kamal 17 found that the wetting property of Sn3.5Ag solder can be improved with the addition of 1.5 % Zn. However, the wettability decreases significantly when Zn content increases up to 3 %. Due to the Zn is very prone to oxidation 18, 19, the formation of oxide residue during soldering may lessen the wettability of the SnAgCu solder. With the increase of Zn content, the disadvantage of the oxide residue may exceed the favorable aspect of Zn.3.2 Tensile strengthThe tested average value of tensile force was conducted. Figure 7 shows the pull strength data of the QFP solder joints, the tensile force of SnAgCuZn solder joints is found to be evidently stronger than that of SnAgCu soldered joints, which means that adding a small amount of Zn can significantly increase the tensile strength of the SnAgCu soldered joints. The tensile force varied from 13.46 N to 14.81 N and increasedwith increased Zn content, approaching a maximum vale with 0.8 % Zn addition, when the Zn exceeds 0.8 %, the tensile force decreases evidently, and it is found that the tensile force of SnAgCu solder joints gives an 10 % increase with the addition of 0.8 % Zn. Furthermore, it is noticed that the variation of the shear force of SnAgCu solder joint with different content of Zn is similar to that of the tensile force result as shown in Fig. 8, the shear force of SnAgCu-xZn gradually increases with the increase of Zn content, reach a peak value when the content of Zn is 0.8 %, and then decreases dramatically with further in crease of Zn content. The reasonable explanation for this is that the Zn element has stronger affinity for oxygen than most metals, and an excessive amount of Zn element addition will form superfluous Zn-oxides, which will degrade the integrity and mechanical properties of the SnAgCu-xZn solder joints. Moreover, Song 13 reported that the strength of Sn1Ag0.5Cu solder was increased by Zn additions for Zn content1 %, but decreased at Zn content of 2 %.Fig. 6 Contact angle of SnAgCu-xZn systemsFig. 7 Effect of Zn on the tensile force of SnAgCu solder jointsFig. 8 Effect of Zn on the shear force of SnAgCu solder joints3.3 MicrostructureThe microstructures of SnAgCu and SnAgCuZn solders are shown in Fig. 9. For SnAgCu ternary alloy in Fig. 9a, the SnAgCu solder shows typical microstructure of ternary alloy system consisting of primary-Sn grains, eutectic structure particles and intermetallic compounds (IMCs). The similar structure is also found in the case of SnAgCuZn, while the individual phase is obviously refined. And some dispersed particles appeared and were mainly located at the boundary between the refined b-Sn phase and the eutectic lamella. Such particles had been identified as CuZn IMC precipitates by EDX detection. With the addition of 0.8 % Zn into SnAgCu solder, the dendrite structures of b-Sn pahse break into granular shapes. The finer microstructure, especially the appearance of dispersed CuZn IMC precipitates, is expected to improve the mechanical properties of SnAgCu solder alloy. Some useful results are summarized by Luo 20, 1 %Zn not only reduced the supercooling of b-Sn, but also promoted the formation of c-(Cu, Ag)5Zn8, and the c phase played a role in accommodating additional Ag atoms, which is beneficial to inhibit Ag3Sn plates. However, McCormack 21 found that 1 %Zn addition suppressed the formation of b-Sn dendrites and yielded a uniform dispersion of Ag3Sn precipitates throughout the microstructure of Sn3.5Ag solder. The addition of Zn was found to suppress the formation of b-Sn dendrites and yields a uniform dispersion of the Ag3Sn IMC within the Sn-rich mixture producing a network-like microstructure 22. During soldering, the solder alloy melts and then reacts with Cu substrates to form IMCs at the joint interface, which forming a thin IMC layer, by the reaction between solder joint and substrate, it is desirable to achieve a good metallurgical bond, however, excessive IMC growth may have a deleterious effect 5, 2326. The cross sections at the solder/Cu interface of as-reflowed SnAgCu and SnAgCuZn solders after reflowing process are shown in Fig. 10. It can be seen that each solder joint consists of three colonies: Cu substrate, IMC layer and solder matrix. Cu6Sn5was scallop-like after reflow and Cu3Sn was not noticeable between Cu pad and Cu6Sn5scallops on either side. By comparing Fig. 10a, b, the IMC layer thickness of the SnAgCuZn solder is found to be thinner than that of the original SnAgCu solder, which indicates that the growth of CuSn IMCs in liquid/solid state reaction is inhibited with the addition of 0.8 %Zn. Inhabitation of IMC layer growth may attributed to an accumulation of Zn atoms at the interface, as detected in Fig. 11, the significantly depressed growth of IMC layer can be attributed to the effect of Zn addition in SnAgCu solder on the migration of Sn atoms toward the solder/IMC layer. Moreover, Wang 27 found that the IMC growth was remarkably depressed by the 0.2 % Zn addition in the SnAgCu solder matrix, this effect tended to be more prominent at higher aging temperatures, and thermodynamic analysis also showed the reduced driving force for Cu6Sn5IMC with addition of Zn in the solder. Cho 28 reported that the growth of IMCs (Cu6Sn5 and Cu3Sn) in Zn-added solders(SnCuZn and SnAgCuZn) was slower than those without Zn additions, and the growth of the Cu3Sn phase during thermal aging, in particular, was drastically reduced in the Zn-added solders on Cu substrates, and the minor addition of Zn to SnAgCu was very effective for reducing the IMC growth on Cu pads for multiple reflow cycles, while the effect was not significant for Au/Ni(P). For Sn-3.5Ag-xZn/Ni(P)solders, it is demonstrated that Zn suppressed the formation of solder joint IMCS: Ni3P, Ni3SnP, Ni3Sn4, and thereby enhanced the drop reliability 29. Therefore, the addition of Zn into SnAgCu solders, the CuSn interface reaction can be retarded obviously.3.4 Thermal-fatigue propertiesSolder joints in electronic devices undergo low cycle fatigue damage due to the mismatch of the coefficient of thermal expansion of connecting parts during temperature variation of connections 30. According to the study of Guo and Wang 31, the main cause for failure of electronic packaging is temperature fatigue (55 % comes from the US Air Force Avionics Integrity Program). Therefore, in this part, the effect of thermal cycling loading on the thermal fatigue of SnAgCu/SnAgCuZn solder joints is investigated. Figures 12 and 13 shows the thermal-fatigue property of both solder joints. It is seen that the mechanical properties (tensile force and shear force) of the solder joints decreases with the increase of thermal cycles. The SnAgCuZn solders have higher mechanical properties by comparison to SnAgCu solder. From the results mentioned above, it is briefly concluded that a certain addition of Zn can efficiently enhance the mechanical properties and thermal-fatigue properties.Fig. 9 Optical micrographs of a Sn3.8Ag0.7Cu, b Sn3.8Ag0.7Cu0.8ZnFig. 10 SEM micrographs of as-soldered cross sections a Sn3.8Ag0.7Cu, b Sn3.8Ag0.7Cu0.8ZnFig. 11 TEM micrograph and EDX of SnAgCuZn/Cu interfaceFig. 12 Tensile force of the QFP leads after thermal cyclingFig. 13 Shear force of the RC after thermal cycling4 ConclusionThis paper has investigated the effect of Zn on the wettability, mechanical properties, microstructures and interface layer in SnAgCu lead-free solder. The results can be concluded as follows:(1) With the addition of Zn, the wetting properties andthe tensile force and shear force of SnAgCu solder joints were greatly improved significantly, and the best Zn content was 0.8 %.(2) The 0.8 %Zn can refines the b-Sn grains and the intermetallic particles in the b-Sn matrix throughout the microstructures of SnAgCu solders, and the thickness of the IMC layer decreased significantly, and the morphology of the IMCs changes obviously.(3) When the amount of Zn is 0.8 % in SnAgCu lead-free solder joints, the thermal-fatigue properties of SnAgCu solder joints can be enhanced in the electronicdevices.Acknowledgments :The authors greatly appreciate the financial supported by the Jiangsu University of Science and Technology: Provincial Key Lab of Advanced Welding Technology Foundation (JSAWS-11-03) and the Xuzhou Normal University Foundation (11XLR16). References1. S.K. Kang, P.A. Lauro, D.Y. Shih, D.W. Henderson, K.J. Puttlitz, Microstructure and mechanical properties of lead-free solders and solder joints used in microelectronic applicationsJ. IBM J. Res. Dev. 49(45), 607620 (2005) 2. J.X. Wang, Z.M. Lai, S.B. Xue, Thermal cycling reliability of SnCuNi(Ce) jointsJ. Transactions of the China Weld Inst 31(2), 3640 (2010)3. G.D. Li, Y.W. Shi, Z.D. Xia, Y.P. Lei, F. Guo, Y.Y. Li, Effect of rare earth addition on shear strength of SnAgCu lead-free solder jointsJ. J. Mater. Sci.: Mater. Electron. 20(2), 186192 (2009)4. W.X. Deng, Y.W. Shi, Y.P. Lei, Z.D. Xia,
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