Mechanical properties of QFP micro-joints soldered with lead-free solders using diode laser soldering technology

Soldering experiments of quad flat package(QFP) devices were carried out by means of diode laser soldering system with Sn-Ag-Cu and Sn-Cu-Ni lead-free solders, and competitive experiments were also carried out not only with Sn-Pb eutectic solders but also with infrared reflow soldering method. The results indicate that under the conditions of laser continuous scanning mode as well as the fixed laser soldering time, an optimal power exists, while the optimal mechanical properties of QFP micro-joints are gained. Mechanical properties of QFP micro-joints soldered with laser soldering system are better than those of QFP micro-joints soldered with IR reflow soldering method. Fracture morphologies of QFP micro-joints soldered with laser soldering system exhibit the characteristic of tough fracture, and homogeneous and fine dimples appear under the optimal laser output power.

Effects of Ag contents in Sn-xAg lead-free solders on microstructure,corrosion behavior and interfacial reaction with Cu substrate

The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders,and on the formation of intermetallic layer of the solders with Cu substrate were investigated.The Ag contents(x)were 0,3.0,3.5,4.0,and5.0 wt.%.The Ag content played a role in the morphology of Ag3 Sn phase in the solders.The microstructure analysis showed that theβ-Sn phase was surrounded by eutectic networks in the 3.0 Ag and 3.5 Ag solders and large plate-like Ag3 Sn formed in the 4.0 Ag and5.0 Ag solders.Nonetheless,the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test.After soldering,only a single layer of a Cu6 Sn5 intermetallic compound formed at the Sn-xAg/Cu interface.By comparison,the Cu6 Sn5 intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder.The fine Ag3 Sn particles in the eutectic networks precipitating in the 3.0 Ag and 3.5 Ag solders effectively hindered the growth of Cu6 Sn5 grains compared to large plate-like Ag3 Sn in the 4.0 and 5.0Ag solders.

Effects of phosphorus addition on the properties of Sn-9Zn lead-free solder alloy

This article explores tile effects of phosphorus addition on the wettability between Sn-9Zn solder alloy and Cu substrates, the oxidation behavior and the corrosion behavior of Sn-9Zn solder alloy. Spreading test was used to characterize the wettability of Sn-9Zn-xP solder alloys to Cu substrates. The oxidation and corrosion behaviors of Sn- 9Zn-xP solder alloys were determined by means of weight gaining, and secondary ion mass spectrometry was used to analyze the oxygen content. The role and mechanism of P in the solder alloys were also discussed. It is found that the addition of P can significantly improve the wettability of the solder alloys. Incorporating P into Sn-9Zn solder alloy obviously decreases the oxygen content and enhances the oxidation and corrosion resistance. Microstructure observations show that an appropriate amount of P can greatly refine coarse rod-like Zn-rich phases in Sn-gZn solder alloy.

Formation of Bulk Intermetallic Compound AgaSn in Slowly-Cooled Lead-Free Sn-4.0 wt pct Ag Solders

Sn-Ag alloy system has been regarded as one of the most promising lead-free solder to substitute conventional Sn- Pb eutectic solder. But the formation of bulk Ag3Sn intermetallic compounds （IMCs） during reflow and post heat treatment significantly influences the performance of the solder joints. With an effort to clarify its microstructural evolution as a function of slow cooling rates, the fraction of bulk IMCs within the slowly solidified Sn-4.0 wt pct Ag solder was investigated by standard metallographic and compared with that detected by thermal analysis. It was found that the bulk IMCs fraction determined by thermal analysis corresponds quite well with the microstructure observation results. In accordance with the conventional solidification theory, the lower the applied cooling rate, the fewer the amount of bulk Ag3Sn IMCs formed in Sn-4.0 wt pct Ag alloy. In addition, Vickers hardness measurement results indicated that the relative coarse eutectic Ag3Sn IMCs distributing in the lamellar eutectic structure favored the improvement of the mechanical performance.

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

An orthogonal method was used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solders by wetting balance method. The results show that the optimal loading of Ga, Al, Ag, and Ce was 0.2 wt.%, 0.002 wt.%, 0.25 wt.%, and 0.15 wt.%, respectively. Intermetallic compounds （IMCs） formed at the interface between Sn-9Zn-0.2Ga-0.002Al-0.25Ag- 0.15Ce solder and Cu substrate were investigated by scanning electron microscope （SEM） and energy dispersive spectroscopy （EDS） analysis. The SEM images illustrate that the IMCs can be divided into two portions from the substrate side to the solder side： a planar CusZns layer and an additional continuous scallop-like AgZn3 layer. The EDS analysis also shows that Ga segregates in the solder abutting upon the interface. X-ray photoelectron spectroscopy （XPS） and Auger electron spectroscopy （AES） of the surface components of Sn-9Zn-0.2Ga-0.002Al- 0.25Ag-0.15Ce solder indicate that Al aggregates at the surface in the form of Al203 protective fdm, which prevents the further oxidation of the solder surface. On the other hand, Ce aggregates at the subsurface, which may reduce the surface tension of the solder and improve the wettability in consequence.

Influence of Cu content on microstructure,grain orientation and mechanical properties of Sn-xCu lead-free solders

The effect of Cu content on the microstructure,grain orientation and mechanical properties of Sn-xCu(x=0-4.0 wt.%)lead-free solder was studied.Results showed that added Cu induced the formation of intermetallic phases.Only theη-Cu;Sn;andε-Cu;Sn phases were present in theβ-Sn matrix.For all contents,the strongly preferred orientation of theβ-Sn phase was formed on the{001}plane.In Sn doped with 1.0 wt.%Cu,theη-Cu;Sn;phase exhibited the preferred orientation of{0001}plane,whereas doping with 3.0 or 4.0 wt.%Cu transformed the preferred orientation to the{010}plane.In addition,only the{0001}and{■}planes were present in theε-Cu;Sn phase.The high Cu contents contributed to an increased number of low-angle boundaries,high residual strain,tensile strength and microhardness.

Effect of diode-laser parameters on shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder on Au/Ni/Cu pad

Soldering experiments with Sn-3.5Ag-0.5Cu lead-free solder on Au/Ni/Cu pad were carried out by means of diode-laser and IR reflow soldering methods respectively.The influence of different heating methods as well as output power of diode-laser on shear force of micro-joints was studied and the relationship between the shear force and microstructures of micro-joints was analyzed.The results indicate that the formation of intermetallic compound Ag3Sn is the key factor to affect the shear force and the fine eutectic network structures of micro-joints as well as the dispersion morphology of fine compound Ag3Sn,in which eutectic network band is responsible for the improvement of the shear force of micro-joints soldered with Sn-Ag-Cu lead-free solder.With the increases of output power of diode-laser,the shear force and the microstructures change obviously.The eutectic network structures of micro-joints soldered with diode-laser soldering method are more homogeneous and the grains of Ag3Sn compounds are finer in the range of near optimal output power than those soldered with IR reflow soldering method,so the shear force is also higher than that using IR reflow soldering method.When the output power value of diode-laser is about 41.0 W,the shear force exhibits the highest value that is 70% higher than that using IR reflow soldering method.

Property alterations of Sn-0.6Cu-0.05Ni-Ge lead-free solder by Ag, Bi, In and Sb addition

The Sn-Cu-Ni-Ge solder is a strong challenger to the Sn-Ag-Cu（SAC） solders as a replacement for the Sn-Pb eutectic solder. This research investigated the effects of addition of Ag, Bi, In, and Sb on the physical properties of the Sn-0.6 Cu-0.05 Ni-Ge（SCNG） lead-free solder and the interfacial reaction with the Cu substrate. The melting behavior, microstructure, tensile strength, and wettability of the SCNG-x（x=Ag, Bi, In, Sb） solders were examined. The findings revealed that the introduction of Ag, Bi, In, and Sb minimally altered the solidus temperature, liquidus temperature, and tensile strength of the solder. However, the cooling behavior and solidified microstructure of the solder were affected by the concentration of the alloying elements. The wettability of the SCNG solder was improved with the doping of the alloying elements except Sb. The thickness of intermetallic layer was increased by the addition of the alloying elements and was related to the cooling behavior of the solder. The morphology of intermetallic layer between the SCNG-x solders and the Cu substrate was different from that of the typical SAC solders. In conclusion, alloying the SCNG solder with Ag, Bi, In or Sb is able to improve particular properties of the solder.

Effects of rapid solidification on the microstructure and microhardness of a lead-free Sn-3.5Ag solder

A lead-free Sn-3.5Ag solder was prepared by rapid solidification technology. The high solidification rate, obtained by rapid cooling, promotes nucleation, and suppresses the growth of Ag3Sn intermetallic compounds （IMCs） in Ag-rich zone, yielding fine Ag3Sn nanoparticulates with spherical morphology in the matrix of the solder. The large amount of tough homogeneously-dispersed IMCs helps to improve the surface area per unit volume and obstructs the dislocation lines passing through the solder, which fits with the dispersion-strengthening theory. Hence, the rapidly-solidified Sn-3.5Ag solder exhibits a higher rnicrohardness when compared with a slowly-solidified Sn-3.5Ag solder.

Effect of indium addition on the microstructural formation and soldered interfaces of Sn-2.5Bi-1Zn-0.3Ag lead-free solder

The microstructural formation and properties of Sn-2.5Bi-xln-lZn-0.3Ag （in wt%） alloys and the evolution of soldered interfaces on a Cu substrate were investigated. Apart from the relatively low melting point （about 195C）, which is close to that of conventional eutectic Sn-Pb solder, the investigated solder presents superior wettability, solderability, and ductility. The refined equiaxial grains enhance the me- chanical properties, and the embedded bulk intermetallic compounds （IMCs） （Cu6Sn5 and CusZns） and granular Bi particles improve the joint reliability. The addition of In reduces the solubility of Zn in the 13-Sn matrix and strongly influences the separation and growth behaviors of the IMCs. The soldered interface of Sn-2.5Bi-xln-lZn-0.3Ag/Cu consists of Cu-Zn and Cu-Sn IMC layers.

EVOLUTION OF MICROSTRUCTURE OF Sn-Ag-Cu LEAD-FREE FLIP CHIP SOLDER JOINTS DURING AGING PROCESS

Flip chip bonding has become a primary technology that has found application in the chip interconnection process in the electronic manufacturing industry in recent years. The solder joints of the flip chip bonding are small and consist of complicated microstructures such as Sn solution, eutectic mixture, and intermetallic compounds （IMCs）, whose mechanical performance is quite different from the original solder bulk. The evolution of microstructure of the flip chip solder joints under thermal aging was analyzed. The results show that with an increase in aging time, coarsening of solder bulk matrix and AuSn4 IMCs occurred within the solder. The IMCs that are formed at the bottom side of the flip chip bond were different from those on the top side during the aging process. （Cu, Ni, Au）0Sn5 were formed at the interfaces of both sides, and large complicated （Au,Ni, Cu）Sn4 IMCs appeared for some time near the bottom interface after aging, but they disappeared again and thus （Cu,Ni, Au ）0Sn5 IMC thickness increased considerably. The influence of reflow times during the flip chip bonding （as-bonded condition） on the characteristics of interfacial IMCs was weakened when subjected to the aging process.

Interfacial intermetallic compound growth and shear strength of low-silver SnAgCuBiNi/Cu lead-free solder joints

The growth rule of the interfacial intermetallic compound （IMC） and the degradation of shear strength of Sn-0.SAg-0.5Cu-2.0Bi-0.05Ni （SACBN）/Cu solder joints were investigated in comparison with Sn-3.0Ag-0.5Cu （SAC305）/ Cu solder joints aging at 373, 403, and 438 K. The results show that （Cul-x,Nix）6Sn5 phase forms between the SACBN solder and Cu substrate during soldering. The interracial IMC thickens constantly with the aging time increasing, and the higher the aging temperature, the faster the IMC layer grows. Compared with the SAC305/Cu couple, the SACBN/Cu couple exhibits a lower layer growth coefficient. The activation energies of IMC growth for SACBN/Cu and SAC305/Cu couples are 111.70 and 82.35 kJ/mol, respectively. In general, the shear strength of aged solder joints declines continuously. However, SACBN/Cu solder joints exhibit a better shear strength than SAC305/Cu solder joints.

Nano ZrO_(2) Particulate-reinforced Lead-Free Solder Composite

A lead-free solder composite was prepared by adding ZrO2 nanopowders in eutectic Sn-Ag alloy. Microstrucrural features and microhardness properties of those solders with different ZrO2 nanopowder fraction were examined. Results indicate that the addition of ZrO2 nanopowders reduced the size of β-Sn grains and restrained the formation of bulk Ag3Sn intermetallic compounds （IMCs） due to the adsorption effect of the ZrO2 particles. The Vicker＇s hardness of the obtained lead-free solder composites fits well with the HalI-Petch relationship. The refinement of β-Sn grains favors to improve the microhardness of composite solders.

Mechanical and Electrical Properties of Some Sn-Zn Based Lead-Free Quinary Alloys

Although there are many lead-free soldering alloys on the market, none of them have ideal qualities. The researchers are combining binary alloys with a variety of additional materials to create the soldering alloys’ features. The eutectic Sn-9Zn alloy is among them. This paper investigated the mechanical and electrical properties of Sn-9Zn-x (Ag, Cu, Sb);{x = 0.2, 0.4, and 0.6} lead-free solder alloys. The mechanical properties such as elastic modulus, ultimate tensile strength (UTS), yield strength (YS), and ductility were examined at the strain rates in a range from 4.17 10−3 s−1 to 208.5 10−3 s−1 at room temperature. It is found that increasing the content of the alloying elements and strain rate increases the elastic modulus, ultimate tensile strength, and yield strength while the ductility decreases. The electrical conductivity of the alloys is found to be a little smaller than that of the Sn-9Zn eutectic alloy.

Preventing formation of intermetallic compounds in ultrasonic-assisted Sn soldering of Mg/Al alloys through pre-plating a Ni coating layer on the Mg substrate

Magnesium and aluminum alloys are widely used in various industries because of their excellent properties,and their reliable connection may increase application of materials.Intermetallic compounds(IMCs)affect the joint performance of Mg/Al.In this study,AZ31 Mg alloy with/without a nickel(Ni)coating layer and 6061 Al alloy were joined by ultrasonic-assisted soldering with Sn-3.0Ag-0.5Cu(SAC)filler.The effects of the Ni coating layer on the microstructure and mechanical properties of Mg/Al joints were systematically investigated.The Ni coating layer had a significant effect on formation of the Mg_(2)Sn IMC and the mechanical properties of Mg/Al joints.The blocky Mg_(2)Sn IMC formed in the Mg/SAC/Al joints without a Ni coating layer.The content of the Mg_(2)Sn IMC increased with increasing soldering temperature,but the joint strength decreased.The joint without a Ni coating layer fractured at the blocky Mg_(2)Sn IMC in the solder,and the maximum shear strength was 32.2 MPa.By pre-plating Ni on the Mg substrate,formation of the blocky Mg_(2)Sn IMC was inhibited in the soldering temperature range 240–280℃and the joint strength increased.However,when the soldering temperature increased to 310℃,the blocky Mg_(2)Sn IMC precipitated again in the solder.Transmission electron microscopy showed that some nano-sized Mg_(2)Sn IMC and the(Cu,Ni)_(6)Sn_(5)phase formed in the Mg(Ni)/SAC/Al joint soldered at 280℃,indicating that the Ni coating layer could no longer prevent diffusion of Mg into the solder when the soldering temperature was higher than 280℃.The maximum shear strength of the Mg(Ni)/SAC/Al joint was 58.2 MPa for a soldering temperature of 280℃,which was 80.7%higher than that of the Mg/SAC/Al joint,and the joint was broken at the Mg(Ni)/SAC interface.Pre-plating Ni is a feasible way to inhibit formation of IMCs when joining dissimilar metals.

Ligand modulation of active center to promote lead-free Cs_(2)AgInCl_(6)photocatalytic CO_(2)reduction

Metal halide perovskites(MHP)are potential candidates for the photocatalytic reduction of CO_(2)due to their long photogenerated carrier lifetime and charge diffusion length.However,the conventional long-chain ligand impedes the adsorption and activation of CO_(2)molecules in practical applications.Here,a ligand modulation technology is employed to enhance the photocatalytic CO_(2)reduction activity of lead-free Cs_(2)AgInCl_(6)microcrystals(MCs).The Cs_(2)AgInCl_(6)MCs passivated by Oleic acid(OLA)and Octanoic acid(OCA)are used for photocatalytic CO_(2)reduction.The results show that the surface defects and electronic properties of Cs_(2)AgInCl_(6)MCs can be adjusted through ligand modulation.Compared with the OLA-Cs_(2)AgInCl_(6),the OCA-Cs_(2)AgInCl_(6)catalyst demonstrated a significant improvement in the catalytic yield of CO and CH_(4).The CO and CH_(4)catalytic yields of OCA-Cs_(2)AgInCl_(6)reached 171.88 and34.15μmol g^(-1)h^(-1)which were 2.03 and 12.98 times higher than those of OLA-Cs_(2)AgInCl_(6),and the total electron consumption rate of OCA-Cs_(2)AgInCl_(6)was 615.2μmol g^(-1)h^(-1)which was 3.25 times higher than that of OLA-Cs_(2)AgInCl_(6).Furthermore,in situ diffuse reflectance infrared Fourier transform spectra revealed the enhancement of photocatalytic activity in Cs_(2)AgInCl_(6)MCs induced by ligand modulation.This study illustrates the potential of lead-free Cs_(2)AgInCl_(6)MCs for efficient photocatalytic CO_(2)reduction and provides a ligand modulation strategy for the active promotion of MHP photocatalysts.

Effect of a Trace of Bi and Ni on the Microstructure and Wetting Properties of Sn-Zn-Cu Lead-Free Solder

The microstructure and melting behavior of Sn-9Zn-2Cu （SZC） lead-free solder with 3 wt pct Bi and various amount of Ni additions were studied. The wetting properties and the interracial reaction of Sn-Zn-Cu with Cu substrate were also examined. The results indicated that the addition of 3 wt pct Bi could decrease the melting point of the solder and Ni would refine the microstructure and the rod-shape Cu5Zn8 phase changed into square-shape （Cu, Ni）5Zn8 phase. The addition of Bi, Ni greatly improved the wettability of SZC solder. In addition, the interracial phase of the solders/Cu joint was typical planar Cu5Zn8 in SZC-3Bi-INi alloy.

Solderability and intermetallic compounds formation of Sn-9Zn-xAg lead-free solders wetted on Cu substrate

The eutectic Sn-9Zn alloy was doped with Ag （0 wt.%-1 wt.%） to form Sn-9Zn-xAg lead-free solder alloys. The effect of the addition of Ag on the microstructure and solderability of this alloy was investigated and intermetallic compounds （IMCs） formed at the solder/Cu interface were also examined in this study. The results show that, due to the addition of Ag, the microstructure of the solder changes. When the quantity of Ag is lower than 0.3 wt.%, the needle-like Zn-rich phase decreases gradually. However, when the quantity of Ag is 0.5 wt.%-1 wt.%, Ag-Zn intermetallic compounds appear in the solder. In particular, adding 0.3 wt.% Ag improves the wetting behavior due to the better oxidation resistance of the Sn-9Zn solder. The addition of an excessive amount of Ag will deteriorate the wetting property because the gluti- nosity and fluidity of Sn-9Zn-（0.5, 1）Ag solder decrease. The results also indicate that the addition of Ag to the Sn-Zn solder leads to the precipitation of ε-AgZn3 from the liquid solder on preformed interracial intermetallics （CusZn8）. The peripheral AgZn3, nodular on the Cu5Zn8 IMCs layer, is likely to be generated by a peritectic reaction L ＋ γ-Ag5Zns→AgZn3 and the following crystallization of AgZn3.

Wettability of Sn-Zn-Bi Based Lead-Free Solder with Rare Earths

Effect of different contents of La and Ga on the wettability and the mierostrueture of interface of Sn-8.9Zn- 2.7Bi trinary alloys was studied. The results show that different contents of La and Ga have significant effect on the wettability of Sn-Zn-Bi based lead-free solder under the condition of both atmosphere and nitrogen. By adding suitable amount of Ga, Cu and La to Sn-Zn-Bi solder, a new lead-free solder Sn-8.9Zn-2.7Bi- 1.0Ga-0.5Cu-0.2La with better wettability was prepared, which has a wetting angle of 25.1° to Cu.

Effects of cooling rates on microstructure and microhardness of lead-free Sn-3.5%Ag solders

The microstructure and microhardness of Sn-3.5%Ag solders were explored in the cooling rate ranging from 0.08 to 104 K/s. Under rapid cooling condition, the strong kinetic undercooling effect leads to the actual solidification process starting at the temperature lower than the equilibrium eutectic point, and the actual metastable eutectic point shifts to the higher Ag concentration. Hence, the higher the applied cooling rate is, the more the volume fraction of primary β-Sn crystal forms. At the same time, the separation of primary β-Sn crystal favors restraining the formation of bulk Ag3Sn intermetallic compounds (IMCs) in solder due to the mismatch crystalline orientation relationship, those Ag3Sn phase separating through the eutectic reaction could hardly cling to the primary β-Sn crystal and grow up. Additionally, the Vickers hardness test shows that fine β-Sn and spherical Ag3Sn phase in the rapidly solidified alloy strongly improves the microhardness of the Sn-3.5%Ag solder.