Effect of Soldering Temperature on Wetting and Optical Density of Dip Coated Sn and Sn-3.5Ag Solders

The effects of soldering temperature on wetting characteristics and optical density of dip coated Sn and Sn–3.5Ag solders on Cu substrate were investigated. The wettability of solders was assessed by the wetting balance tester. The temperature of the solder bath varied in the range of 250–300°C. With the increase in temperature, a slight decrease in the surface tension of solders was noticed. The wetting tests demonstrated an increased solderability of pure Sn with temperature compared to Sn-3.5Ag solder. The optimum solderability of each solder was obtained at 270°C. The optical density of both the solders was also found to be highest at 270°C. It is reported that wettability and optical density of a solder are related to each other and can be tailored by varying the soldering temperature.     

Lötbarkeitsuntersuchungen in der Dickschicht-Hybridmikroelektronik

Thick Film Hybrid Microelectronics – Aspects of Solderability The interconnection techniques for microelectric circuits requires a high level of reliability. Soft solder applications are widely used because of their economy. The quality of bonds made in this technology is determined by the solderability of the materials used. Starting with a definition of the solderability this paper describes a method to determine the solderability of thick film metallizations.     

Solderability of Electrodeposited Fe-Ni Alloys with Eutectic SnAgCu Solder

Solderabilities of electrodeposited Fe-Ni alloys with SnAgCu solder were examined by wetting balance measurements and compared to those of pure Ni and pure Fe platings. Excellent solderability was found on the Ni-52Fe plating as both the wetting force and kinetics approached or exceeded those on the pure Ni. However, upon further increase in Fe content to 75 at. pct, the solderability of the alloy was severely degraded even though it was still better than that of the pure Fe plating. X-ray photoelectron spectroscopy showed that such a strong dependence of solderability on Fe content is related to the much thinner, incomplete oxide coverage of Ni-rich plating surface.     

Properties and microstructure of Sn–0.7Cu–0.05Ni solder bearing rare earth element Pr

Effects of trace amount of rare earth element Pr on properties and microstructure of Sn–0.7Cu–0.05Ni solder were investigated in this paper. The solderability of Sn–Cu–Ni–xPr alloy and shear strengh of Sn–Cu–Ni–xPr soldered micro-joints were determined by means of the wetting balance method and shear test, respectively. Moreover, microstructure of solder alloys bearing Pr, as well as intermetallic compound (IMC) layer formed at solder/Cu interface after soldering were observed. It was concluded that the major benefits of rare earth element Pr on Sn–Cu–Ni lead-free solder are: improving solderability, refining microstructure, and depressing IMC (IMC) growth, which exhibited improved mechanical properties. It also revealed that (Cu,Ni)₆Sn₅ is the majority IMC phase at the interface of Sn–Cu–Ni–xPr/Cu solder joints. Ni added into the solder effectively suppressed the growth of Cu₃Sn and consequently also the total IMC layer thickness. Above all, the thickness and morphology of the interfacial (Cu,Ni)₆Sn₅ IMC were optimized due to alloying Pr. It can be inferred that Pr and Ni would play an important role in improving the reliability of Sn–Cu–Ni lead-free solder joints.     

Solderability of SnBi-nano Cu solder pastes and microstructure of the solder joints

The solderability of the Sn58Bi (SnBi)-nano Cu solder pastes and the microstructure of the solder joints were investigated. Experimental results indicated that the addition of the nano Cu particles in the SnBi solder paste shows limited effect on the solidus. The liquidus of the SnBi-3nano Cu solder paste was 1 °C higher than the SnBi solder paste. Solid Cu₆Sn₅ intermetallic particles formed in the SnBi-3nano Cu solder paste during the heating process. The Cu₆Sn₅ intermetallic particles decreased the mobility and wettability of the molten solder. Meanwhile, the Cu₆Sn₅ nano particles worked as nucleation sites for the formation of Bi grains and Sn–Bi eutectic phase during the cooling process and led to the grain refinement of the solder bulk. The SnBi-1nano Cu solder paste showed the smallest grain size in this research. Additionally, the SnBi-3nano Cu/Cu solder joint showed a eutectic microstructure of Sn–Bi system at the center of the solder bulk but a hypereutectic microstructure with polygon Bi grains near the margin in the solder bulk.     

Effects of trace rare earth Nd addition on microstructure and properties of SnAgCu solder

Effects of rare earth Nd on solderability of the Sn3.8Ag0.7Cu alloy were studied by wetting balance method, and the mechanical properties (such as pull-force and shear-force) of the joints soldered with SnAgCu–XNd solders were determined using STR-1000 joint strength tester. Moreover, the microstructures of SnAgCu–XNd solders bearing different amount of Nd as well as the intermetallic compounds (IMCs) formed at solder/Cu interface during soldering have been investigated using optical microscopy, scanning electron microscopy and energy dispersive X-ray analysis, respectively. The results indicate that trace amount of Nd addition can remarkably improve the solderability and mechanical properties of SnAgCu solder. At the same time, it is found that rare earth Nd in SnAgCu solder could refine and improve microstructure of the solder, some bigger IMC plates in SnAgCu solder were replaced by fine granular IMCs. Moreover, the thickness of the intermetallic layer at the Cu/solder interface was reduced significantly. In summary, we suggest that the most suitable content of rare earth Nd is about 0.05 wt% and it will be inadvisable when the Nd exceeds 0.25 wt%.     

Effects of rare earth Ce on properties of Sn–9Zn lead-free solder

The influences of different Ce content on the properties of Sn–9Zn lead-free solder were investigated. The results indicate that Ce plays an important role not only in the structure and the solderability, but also in the interfacial structure of Sn–9Zn–xCe/Cu and mechanical property of soldered joint. Sn–9Zn–0.08Ce shows finer and more uniform microstructure than Sn–9Zn, and when the quantity of Ce is 0.5–1 wt%, some dark Sn–Ce compounds appear in the solder. With the addition of 0.08 wt% Ce, the solderability of solder is significantly improved because the surface tension of molten solder is decreased. Adding Ce makes the Cu5Zn8 IMCs formed at the interface of solder/Cu become much thicker than that of Sn–9Zn/Cu because much more content of Zn diffuse to the interface of solder/Cu to react with Cu. Results also indicate that adding 0.08 wt% Ce to the solder enhances mechanical property of soldered joint. When the Ce content is 0.1–0.5 wt%, some hard and brittle Cu–Zn IMCs appear in the bottom of dimples and the pull force of soldered joint decreases.     

Effects of Ga addition on microstructure and properties of Sn–0.5Ag–0.7Cu solder

The effects of rare element Ga on solderability, microstructure, and mechanical properties of Sn–0.5Ag–0.7Cu lead-free solder were investigated. The experimental results show that Ga plays a positive role in improving the wettability and the microstructure of the solder. When the content of Ga is at 0.5 wt%, the grain size of the solder is smaller and the shear force is enhanced greatly. It is also found that the thickness of the IMCs at the solder/Cu interface is reduced with proper addition of Ga. The increase of mechanical properties may be related to the refining of IMCs of the solder due to Ga addition.     

Effects of rare earth element Nd on the solderability and microstructure of Sn�CZn lead-free solder

Effects of trace amount addition of rare earth Nd on the properties of eutectic Sn?CZn solder were studied in this paper. Results indicate that adding trace rare earth element Nd could remarkably improve the solderability and mechanical properties of Sn?C9Zn solder joints. Especially when the content of Nd was 0.06 wt%, the wettability of the solder was improved significantly, and the shear force of Sn?C9Zn?C0.06Nd solder joint was enhanced by 19.6% as well as pull force increased by 26.6% compared to that of Sn?C9Zn solder joint,respectively. It is also found that addition of rare earth Nd could refine the microstructure of the solder and some NdSn₃ phase appeared in the solder matrix. Moreover, the IMCs thickness at the solder/Cu interface was reduced. NdSn₃ phase appeared at the interface with excessive addition of Nd, which is the key reason that deteriorates the mechanical properties of soldered joint.     

Investigation on properties of Ga to Sn–9Zn lead-free solder

The influences of different Ga content on the properties of Sn–9Zn lead-free solder were investigated. The results indicate that Ga plays an important role not only in the structure and melting behavior, but also in the solderability and mechanical property. Sn–9Zn–0.5Ga shows finer and more uniform microstructure than Sn–9Zn. With the addition of low-melting-point Ga, TL (liquidus temperature) and TS (solidus temperature) of the alloys decreases with increasing of Ga content while △T (liquidus temperature minus solidus temperature) increases. Ga can improve the oxidation resistance and reduce the surface tension of solder, so the solderability of Sn–9Zn–xGa lead-free solder is significantly improved. When the content of Ga is 0.5 wt.%, the pull force of soldered joint is 16.1 N, enhanced by 11% compared to that of Sn–9Zn, and the fracture micrographs show that the joint failed in a ductile manner. The addition of 3 wt.%Ga resulted in a brittle failure. The introduction of 0.5 wt.% Ga into Sn–9Zn alloy improves creep resistance of the solder.     

Solderability, IMC evolution, and shear behavior of low-Ag Sn0.7Ag0.5Cu-BiNi/Cu solder joint

The solderability, intermetallic compounds (IMC) evolution, and shear behavior of the low-Ag Sn0.7Ag0.5Cu-3.5Bi-0.05Ni (SAC0705-BiNi)/Cu solder joint was investigated by comparing with Sn0.7Ag0.5Cu (SAC0705)/Cu and Sn3.0Ag0.5Cu (SAC305)/Cu solder joints. Experimental results demonstrated that the melting temperature of Sn0.7Ag0.5Cu-BiNi solder alloy was lower than that of SAC0705 and SAC305 solder. But the melting range of Sn0.7Ag0.5Cu-BiNi was wider. Compared with the other two kinds of alloys, SAC0705-BiNi showed the best wettability. SAC0705/Cu, SAC0705-BiNi/Cu, and SAC305 solder joints appeared similar IMC morphologies and grain size at the beginning of soldering, but evolved to different appearance as the soldering process proceeded. The growth rate of the IMC grains in SAC0705-BiNi/Cu solder joint was the lowest because of the refinement of Ni. SAC0705-BiNi/Cu solder joint showed the highest shear strength before and after being aged, mainly due to the enhancement of solid solution strengthening and dispersion strengthening of Bi and Ni in the bulk solder, as well as the refinement of Ni at the soldering interface.     

Die Benetzungswaage,ein neues Hilfsmittel bei der Prüfung von Weichlötflußmitteln

The “Wettingbalance”, a new aid for testing softsoldering fluxes . A new method for the determination of behaviour of materials related to soft solderability, evaluates the forces acting on immersed samples, which are significant for the achieved wetting quality. The influence of various factors such as condition of the samplesurface, flux and solder are sensitively registered and allow their objectiv assessment. Sofar the wettingcurves are mostly interpreted from a qualitative point of view. The presented method, taking the comparative testing of fluxes as an example, describes the quantitative evaluation of the wetting behaviour. In the beginning a summary of the physical background of the process as well as few remarks relatet to the experimental procedure are given.     

Sn62Pb36Ag2焊料的微结构粗化

在焊料的浸镀及表面贴装过程中,发现Ｓｎ６２Ｐｂ３６Ａｇ２焊料的微结构粗化,并且可焊性很差。金相研究发现：Ｓｎ６２Ｐｂ３６Ａｇ２合金焊料在熔体状态保温较长时间以及冷却速率较慢,均会促进焊料的微结构粗化。其机理为焊料中生成较多的Ａｇ３Ｓｎ和Ｃｕ６Ｓｎ５等金属间化合物,消耗了合金焊料中的部分锡,使焊料组成偏离共晶点,从而最终导致富铅相偏析。组成偏离及微结构粗化致使焊料在铜上的润湿性降低,并影响焊料的可焊     

Effects of Ga,Al, Ag,and Ce multi-additions on the properties of Sn–9Zn lead-free solder

Wetting balance method is used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the solderability of Sn–9Zn lead-free solders, results show that the optimal addition amounts of Ga, Al, Ag, and Ce is 0.2, 0.002, 0.25, and 0.15 wt% respectively. The surface property of Sn–9Zn–0.2Ga–0.002Al–0.25Ag–0.15Ce solder is studied by X-ray photoelectron spectroscopy and auger electron spectroscopy analysis; results indicate that Al aggregates on the surface as a compact aluminum oxide film which prevents the further oxidation. The aggregation of Ce on the subsurface can reduce the surface tension of solder, and improve the solderability accordingly. Meanwhile, SEM and XRD analysis indicate that Cu₅Zn₈ and AgZn₃ intermetallic compounds form at the interface between Sn–9Zn–0.2Ga–0.002Al–0.25Ag–0.15Ce solder and Cu substrate, while AuZn₃ and AuAgZn₂ form at the interface between solder and Cu/Ni/Au substrate. Moreover, results also indicate that the mechanical property of soldered joints is improved duo to the dispersion strengthening effects of AgZn₃ in Sn–9Zn–0.2Ga–0.002Al–0.25Ag–0.15Ce solder.     

Effects of Dy substitution for Sn on the solderability and mechanical property of the standard near eutectic Sn–Ag–Cu alloy

In this study, the solderability of Sn–3.5Ag–0.5Cu–xDy solders were investigated and the shear strength properties of joints with Cu substrate were investigated. The results indicated that a small amount Dy addition can improve the solderability, and the optimal amount of Dy was 0.025 wt%. The maximum shear strength can be found with 0.025 wt% Dy addition, improved by 74%. With the observation of the fracture morphology, it was found that a small amount Dy can improve the ductility of the solder joints; but excessive amount of Dy would deteriorate the shear strength and form large dimples on the fracture surface.     

The combined effects of ultrasonic wave and electric field on the microstructure and properties of Sn2.5Ag0.7Cu0.1RE/Cu soldered joints

The effect of ultrasonic wave (USW) and electric field (E) on the solderability of Sn2.5Ag0.7Cu0.1RE/Cu was investigated. Compared with the sample soldered conventionally, the solder joint obtained with USW and E assisted resulted in significant changes in the microstructure. The thickness and roughness of the interfacial Cu₆Sn₅ intermetallic compound (IMC) layer decreased by 39 and 56 %, respectively. The shear strength of the solder joint increased by 68 %, and the fracture mechanism of the solder joint transformed from brittle fracture occurred in the interfacial IMC layer to ductile fracture occurred in the solder alloy. The results reveal that reliable soldering of Sn2.5Ag0.7Cu0.1RE/Cu can be achieved with USW and E assisted, despite of low-halogen flux.     

多次重熔过程中La2O3对Sn-58Bi钎料组织及性能的影响

为提高Sn-58Bi钎料的钎焊性,采用机械混合法制备了不同La2O3含量的Sn-58Bi低温无铅复合钎料.借助SEM、EDS和DSC等分析手段研究了La2O3对Sn-58Bi钎料显微组织、熔化特性以及力学性能的影响,并考察了多次重熔过程中Sn-58Bi-x La2O3/Cu界面IMC层组织演变.研究结果表明:La2O3的加入可以抑制大块富Bi相的偏析生成,但对钎料熔点的影响不大;在多次重熔过程中,同一种钎料的界面IMC层晶粒粒径随重熔次数的增加而增大,但La2O3的加入能有效阻碍界面IMC层晶粒粗化;加入不同含量La2O3后,复合钎料的硬度和模量都有一定程度的提高,其抵抗局部变形、开裂的能力提高,从而提高无铅钎料焊点在实际封装过程中的可靠性.     

某型非标准波导管钎焊接头裂纹分析

针对某型非标准波导管使用中发现90°波导弯头钎焊接头处存在裂纹的问题,运用X光检测和扫描电镜分析等手段,对裂纹产生的原因进行了分析。结果表明:在波导管加工过程中,线切割后的焊接面形成一层氧化膜,由于钎焊前清洗不彻底,在焊接时焊料无法粘结,造成钎料未钎满;另波导管在焊接时定位不准,偏向一边,造成单边间隙过小,焊料不能充分流入,使得波导管在焊接过程中焊料未能充分渗透、填满。根据故障原因,采取了相应的改进措施,使钎焊接头裂纹问题得到了解决。     

Implementation of the pin-in-paste process in a contract manufacturing environment

The pin-in-paste process was developed and validated for a contract manufacturing PCB assembly environment. A systematic approach was used to implement this process in a production environment. The sequence used for process development included solder paste volume calculations for through hole components (THCs), stencil aperture design for the pin-in-paste application, solder paste deposition through stencil printing, reflow profile development, inspection, and testing. A series of experiments were conducted to identify the 'process window' associated with each process step. The required volume of solder paste was computed using a set of empirical equations. The stencil printing process was 'optimized' using a 'design of experiments' based approach. Response surfaces were plotted and used to identify the 'optimal' print parameters. Thermal profiles were developed for reflow soldering the THCs in conjunction with the surface mount components (SMCs) in a single reflow pass. The assemblies were built using the 'optimized' process parameters. The assemblies were then inspected under an X-ray system to check for solder voiding. Electrical testing was then done to check for solder shorts and open connections. The shape of the solder joints was similar to a wave soldered joint, voiding was minimal, and there was no instance of solder shorts or an open connection. The solder joints were then cross-sectioned as a part of destructive testing. The cross sections showed the formation of good positive fillets (both top and bottom fillet), the solder paste had filled the plated through hole (PTH) completely, and voiding was minimal.     

Shear performance of microscale ball grid array structure Sn–3.0Ag–0.5Cu solder joints with different surface finish combinations under electro-thermo-mechanical coupled loads

The shear performance and fracture behavior of microscale ball grid array structure Sn–3.0Ag–0.5Cu solder joints with different substrate surface finishes (Cu with organic solderability preservatives and electroless Ni/immersion Au) combinations under electro-thermo-mechanical (ETM) coupled loads with increasing current density (from 1.0?×?10³ to 6.0?×?10³ A/cm²) were systematically investigated by experimental characterization, theoretical analysis, and finite element simulation. The results reveal that the shear strength varies slightly with different surface finish combinations, initially increasing and then decreasing as the current density is increased. Moreover, the increase in current density shifts the fracture location from the solder matrix to the interface between solder and intermetallic compound (IMC) layer, resulting in a ductile-to-brittle transition. The interfacial fracture is triggered by electric current crowding at the groove of the IMC layer and driven by the mismatch strain at the solder/IMC layer interface.