Thermomechanical fatigue behavior of Sn-Ag solder joints

Microstructural studies of thermomechanically fatigued actual electronic components consisting of metallized alumina substrate and tinned copper lead, soldered with Sn-Ag or 95.5Ag/4Ag/0.5Cu solder were carried out with an optical microscope and environmental scanning electron microscope (ESEM). Damage characterization was made on samples that underwent 250 and 1000 thermal shock cycles between −40°C and 125°C, with a 20 min hold time at each extreme. Surface roughening and grain boundary cracking were evident even in samples thermally cycled for 250 times. The cracks were found to originate on the free surface of the solder joint. With increased thermal cycles these cracks grew by grain boundary decohesion. The crack that will affect the integrity of the solder joint was found to originate from the free surface of the solder very near the alumina substrate and progress towards and continue along the solder region adjacent to the Ag₃Sn intermetallic layer formed with the metallized alumina substrate. Re-examination of these thermally fatigued samples that were stored at room temperature after ten months revealed the effects of significant residual stress due to such thermal cycles. Such observations include enhanced surface relief effects delineating the grain boundaries and crack growth in regions inside the joint.     

醇胺对免清洗焊芯用助焊剂性能的影响

通过添加醇胺制备免清洗焊芯用助焊剂,研究了两种醇胺及其复配对助焊剂性能的影响。结果表明:添加适当的醇胺有利于降低助焊剂体系酸值,提高焊接性能,减少对线路板的腐蚀,提高焊接可靠性。使用任意一种醇胺,质量分数在1.0%~1.5%时,助焊剂的焊接性能较好,但酸值不能满足免清洗助焊剂的要求。两种醇胺进行复配,质量分数均为1.0%~1.5%时,助焊剂的综合性能优良,用无铅焊锡丝SnAg3.0Cu0.5测定其焊接性能,扩展率为79%,酸值148 mgKOH/g,铜板腐蚀、绝缘电阻、电迁移等可靠性指标较好。     

Morphology of intermetallic compounds formed between lead-free Sn-Zn based solders and Cu substrates

The morphologies of intermetallic compounds formed between Sn-Zn based solders and Cu substrates were investigated in this study. The investigated solders were Sn-9Zn, Sn-8.55Zn-0.45Al, and Sn-8.55Zn-0.45Al-0.5Ag. The experimental results indicated that the Sn-9Zn solder formed Cu₅Zn₈ and CuZn₅ compounds on the Cu substrate, while the Al-containing solders formed the Al_4.2Cu_3.2Zn_0.7 compound. The addition of Ag to the Sn-8.55Zn-0.45Al solder resulted in the formation of the AgZn₃ compound at the interface between the Al_4.2Cu_3.2Zn_0.7 compound and the solder. Furthermore, it was found that the cooling rate of the specimen after soldering had an effect on the quantity of AgZn₃ compound formed at the interface. The AgZn₃ compound formed with an air-cooling condition exhibited a rougher surface and larger size than with a water-quenched condition. It was believed that the formation of the AgZn₃ compound at the interface occurs through heterogenous nucleation during solidification.     

Suppressing Growth of the Cu<Subscript>5</Subscript>Zn<Subscript>8</Subscript> Intermetallic Layer in Sn-Zn-Ag-Al-Ga/Cu Solder Joints

Cu₅Zn₈ normally forms between Sn-Zn solder and Cu metallization. In this study, the growth of the intermetallic compound (IMC) layer is slowed by increasing the silver content in the Sn-8.5Zn-Ag-Al-Ga/Cu system. Experimental results showed that the total thickness of the IMC layers formed with 1.5 wt.% silver content was about half that without silver. The reduction might be due to the formation of the intermetallic compound (Ag,Cu)-Zn at the interface in addition to silver.     

Encapsulation of lead-free Sn/Zn/Bi solder alloy particles by coating with wax powder for improving oxidation resistance

An encapsulation treatment of lead-free Sn/Zn/Bi solder powder was investigated for improving the oxidation resistance. Sn-8mass%Zn-3mass%Bi alloy particles were coated with a wax (12-hydroxystearic acid) powder by means of a dry mechanical treatment method using a ball mill. In order to determine the optimum operating conditions of the ball mill in the wax-coating treatments, the compressive energy required for deforming a single Sn/Zn/Bi alloy particle was measured with an unconfined compression tester and the mechanical energy applied to the alloy particles in the ball mill was estimated using the results of the compression test. The optimum operating conditions were determined based on both the applied energy and the flowability of solder pastes, and the wax-coated alloy particles maintaining the spherical shape were obtained under the conditions. The wettability test and the solder balling test for the solder pastes containing the wax-coated alloy particles stored at room temperature in air were carried out to evaluate the oxidation resistance performance. The wax-coated alloy particles had an excellent wettability compared with the original alloy particles, and the oxidation resistance of the Sn/Zn/Bi solder powder was improved by the encapsulation treatment.     

Effect of rare earth element addition on the microstructure of Sn-Ag-Cu solder joint

The effects of minimal rare earth (RE) element additions on the microstructure of Sn-Ag-Cu solder joint, especially the intermetallic compounds (IMCs), were investigated. The range of RE content in Sn-Ag-Cu alloys varied from 0 wt.% to 0.25 wt.%. Experimental results showed that IMCs could be dramatically repressed with the appropriate addition of RE, resulting in a fine microstructure. However, there existed an effective range for the RE addition. The best RE content was found to be 0.1 wt.% in the current study. In addition to the typical morphology of Ag₃Sn and Cu₆Sn₅ IMCs, other types of IMCs that have irregular morphology and uncertain constituents were also observed. The IMCs with large plate shape mainly contained Ag and Sn, but the content of Ag was much lower than that of Ag₃Sn. The cross sections of Cu₆Sn₅ IMCs whiskers showed various morphologies. Furthermore, some eutectic-like structures, including lamellar-, rod-, and needle-like phases, were observed. The morphology of eutectic-like structure was related to the RE content in solder alloys. When the content of RE is 0.1 wt.%, the needle-like phase was dominant, while the lamellar structure prevailed when the RE content was 0.05 wt.% or 0.25 wt.%. It is suggested that the morphology change of the eutectic-like structure directly affects the creep properties of the solder joint.     

Ag和RE对SnAgCuRE无铅钎料拉伸性能的影响

利用正交试验法,对SnAgCuRE系钎料合金的拉伸性能进行了检验。结果表明:SnAgCuRE系钎料合金的拉伸性能与Ag和RE的添加量密切相关,即拉伸强度会随Ag含量增大而提高;延伸率受RE影响最大,并在w(RE)为0.1%时延伸率和拉伸强度都达到最佳。当w(RE)达到0.5%时,会导致延伸率的下降。     

阻焊塞孔工艺改善

通过改良阻焊塞孔工具、规范网印塞孔操作、修改后固化参数,改善公司阻焊塞孔质量不稳定的问题。     

电子封装微焊点中的柯肯达尔孔洞问题

简述目前在微焊点内部产生的六种孔洞缺陷。微焊点中的孔洞会导致焊点强度快速下降,一直危害着电子产品的可靠性,软钎料／Cu基盘界面在高温时效老化后会出现了大量的柯肯达尔孔洞,柯肯达尔孔洞的存在将会对应用于高温环境和高应力的封装焊点可靠性产生不好的影响。结合目前的研究状况分析了时效老化时Kirkendall（柯肯达尔）孔洞的形成机理和Kirkendall孔洞对焊点可靠性的影响,重点研究了焊盘材料、材质、焊料掺杂元素和UBM预处理等因素影响柯肯达尔孔洞形成的机理。     

Effervescent-assisted dispersive liquid–liquid microextraction based on the solidification of floating organic droplets for the determination of fungicides in vinegar and juice

ABSTRACT

A method of effervescent-assisted dispersive liquid–liquid microextraction based on the solidification of a floating organic droplet is reported. This approach was used to measure the fungicides myclobutanil, tebuconazole and epoxiconazole in vinegar and juice. Acidic vinegar and juice reacted with the carbonate to produce effervescence in situ, which then promoted contact of the sample with the extraction solvent. The 1-dodecanol extraction solvent helped solidify the floating organic droplets and could be fully dispersed by effervescence. The extraction solvent, salt, carbonate, and extraction time were optimised. The optimal conditions were 200 μL of 1-dodecanol, 100 mg of sodium chloride, 50 mg of sodium bicarbonate, and 30 s of extraction time. The proposed method has good linearity between 10 and 1000 ng mL^?1. Recoveries were between 70.4% and 103.1% in different vinegar and juice samples. This method was successfully used to measure fungicides in vinegar and juice. This system is simple, fast and environmentally friendly.